U.S. patent application number 09/753682 was filed with the patent office on 2001-09-20 for catalyst for treating waste water, method for preparing the same and process for treating waste water.
Invention is credited to Hashimoto, Takaaki, Ishii, Tohru, Miyazaki, Kuninori, Shiota, Yusuke.
Application Number | 20010022290 09/753682 |
Document ID | / |
Family ID | 27480920 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022290 |
Kind Code |
A1 |
Shiota, Yusuke ; et
al. |
September 20, 2001 |
Catalyst for treating waste water, method for preparing the same
and process for treating waste water
Abstract
This invention discloses a method for oxidizing and/or
decomposing organic and/or inorganic oxidizable substances in waste
water by wet oxidation with a use of a catalyst, wherein the
oxidizable substances are oxidized and/or decomposed with an oxygen
containing gas in the presence of the catalyst under pressure such
that said waste water retains the liquid phase thereof at
temperature of 50 to less than 170.degree. C.; the catalyst
contains activated carbon; and controlling an oxygen concentration
in an exhaust gas in the range from 0 to 5 vol %. The present
inventive method is capable of treating waste water efficiently for
a long period in a stable manner at the reduced temperatures and as
compared with the substantially higher temperatures and pressures
used in many of the prior art method.
Inventors: |
Shiota, Yusuke; (Himeji-shi,
JP) ; Miyazaki, Kuninori; (Himeji-shi, JP) ;
Hashimoto, Takaaki; (Himeji-shi, JP) ; Ishii,
Tohru; (Hyogo-ken, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27480920 |
Appl. No.: |
09/753682 |
Filed: |
January 4, 2001 |
Current U.S.
Class: |
210/749 ;
210/739; 210/762; 210/763 |
Current CPC
Class: |
B01J 21/18 20130101;
B01J 23/89 20130101; B01J 23/63 20130101; B01J 23/6562 20130101;
B01J 23/8906 20130101; B01J 23/54 20130101; B01J 23/6447 20130101;
B01J 23/40 20130101; C02F 1/725 20130101; B01J 37/0205 20130101;
B01J 23/626 20130101; C02F 11/08 20130101 |
Class at
Publication: |
210/749 ;
210/739; 210/762; 210/763 |
International
Class: |
C02F 001/72 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2000 |
JP |
2000-5198 |
Apr 4, 2000 |
JP |
2000-102629 |
Apr 14, 2000 |
JP |
2000-114130 |
Apr 14, 2000 |
JP |
2000-114131 |
Claims
What is claimed is:
1. A catalyst for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in waste water by wet oxidation
with a use of a catalyst, comprising: (i) activated carbon, (ii)
first component wherein the first component is at least one
selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Fe, Co,
Mn, Al, Si, Ga, Ge, Sc, Y, La, Ce, Pr, Mg, Ca, Sr, Ba, In, Sn, Sb
and Bi; and (iii) second component wherein the second component is
at least one selected from the group consisting of Pt, Pd, Rh, Ru,
Ir and Au.
2. The catalyst according to claim 1, wherein a decrease value in a
specific pore volume having 0.1 to 10 .mu.m pore diameter after the
first component is deposited on the activated carbon is in the
range from 0.01 to 0.5 ml/g compared with a specific pore volume
thereof before the first component is deposited.
3. The catalyst according to claim 1, wherein a decrease value of a
specific surface area after the first component is deposited on the
activated carbon is in the range from 50 to 800 m.sup.2/g compared
with a specific surface area thereof before the first component is
deposited.
4. A method of preparing a catalyst for oxidizing and/or
decomposing organic and/or inorganic oxidizable substances in waste
water by wet oxidation with a use of a catalyst, comprising the
steps of: 1) depositing first component on an activated carbon
wherein the first component is at least one selected from the group
consisting of Ti, Zr, Hf, Nb, Ta, Fe, Co, Mn, Al, Si, Ga, Ge, Sc,
Y, La, Ce, Pr, Mg, Ca, Sr, Ba, In, Sn, Sb and Bi; and 2) depositing
second component on the activated carbon wherein the second
component is at least one selected from the group consisting of Pt,
Pd, Rh, Ru, Ir and Au.
5. A method for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in waste water by wet oxidation
with a use of a catalyst, wherein the oxidizable substances are
oxidized and/or decomposed with an oxygen containing gas in the
presence of the catalyst under pressure such that said waste water
retains the liquid phase thereof at temperature of 50 to less than
170.degree. C. and the catalyst contains activated carbon; and an
oxygen concentration in an exhaust gas is controlled in the range
of 0 to 5 vol %.
6. The method according to claim 5, wherein the catalyst further
contains at least one selected from the group consisting of Pt, Pd,
Rh, Ru, Ir and Au.
7. The method according to claim 5, wherein the catalyst further
contains at least one selected from the group consisting of Ti, Zr,
Hf, Nb, Ta, Fe, Co, Mn, Al, Si, Ga, Ge, Sc, Y, La, Ce, Pr, Mg, Ca,
Sr, Ba, In, Sn, Sb and Bi.
8. The method according to claim 7, wherein a decrease value of a
specific pore volume having 0.1 to 10 .mu.m pore diameter after at
least one element selected from the group in claim 7 is deposited
on the activated carbon is in the range from 0.01 to 0.5 ml/g
compared with a specific pore volume thereof before the element is
deposited.
9. The method according to claim 7, wherein a decrease value of a
specific surface area after at least one element selected from the
group in claim 7 is deposited on the activated carbon is in the
range from 50 to 800 m.sup.2/g compared with a specific surface
area thereof before the element is deposited.
10. The method according to claim 5, wherein a supply amount of the
oxygen containing gas is controlled to obtain [oxygen amount in the
oxygen containing gas supplied]/[oxygen demand of the waste water
at maximum waste water treatment efficiency]=in the range from 0.8
to 1.3.
11. The method according to claim 5, wherein the oxygen containing
gas and the waste water descend concurrently at the catalyst.
12. The method according to claim 5, wherein the oxygen containing
gas is supplied from at least two location by dividing the total
amount of the oxygen containing gas.
13. A method for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in waste water by wet oxidation
with a use of a catalyst, wherein the oxidizable substances are
oxidized and/or decomposed with an oxygen containing gas in the
presence of a catalyst under pressure such that said waste water
retains the liquid phase thereof at temperature of 50 to less than
170.degree. C. and the catalyst contains activated carbon; and
supplying a catalyst protection liquid which contains easily
decomposable substances at the time of temperature rising when
starting up a operation of the wet oxidation and/or at the time of
temperature lowering when suspending the operation.
14. The method according to claim 13, wherein a supply amount of
the catalyst protection liquid is controlled so as to the easily
decomposable substances in the protection liquid is remained in a
liquid passed through the catalyst.
15. The method according to claim 13, wherein a temperature during
the catalyst protection liquid is supplied is lower than a
temperature during the waste water is treated.
16. The method according to claim 13, wherein an oxygen
concentration in an exhaust gas is controlled in the range from 0
to 5 vol % at the time of temperature rising when starting up a
operation of the wet oxidation and/or at the time of temperature
lowering when suspending the operation.
17. The method according to claim 13, wherein a supply amount of an
oxygen containing gas or an oxygen uncontaining gas is controlled
to obtain [oxygen amount in the gas supplied]/[oxygen demand in the
protection liquid at maximum catalyst protecting efficiency]=in the
range from 0 to 1.3 at the time when supplying the catalyst
protection liquid to the catalyst.
18. A method for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in waste water by wet oxidation
with a use of a catalyst, wherein the oxidizable substances are
oxidized and/or decomposed with an oxygen containing gas in the
presence of a catalyst under pressure such that said waste water
retains the liquid phase thereof at temperature of 50 to less than
170.degree. C.; the catalyst contains activated carbon; and
supplying a catalyst recovering liquid which contains easily
decomposable substances to the catalyst under temperatures in the
range from 55.degree. C. to less than 200.degree. C.
19. The method according to claim 18, wherein a supply amount of
the catalyst recovering liquid is controlled so as to the easily
decomposable substances in the recovering liquid is remained in a
liquid passed through the catalyst.
20. The method according to claim 18, wherein a supply amount of an
oxygen containing gas or an oxygen uncontaining gas is controlled
to obtain [oxygen amount in the gas supplied]/[oxygen demand in the
recovering liquid at maximum catalyst recovering efficiency]=in the
range from 0 to 1.3 at the time when supplying the catalyst
recovering liquid to the catalyst.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a process for treating waste water
containing organic and/or inorganic oxidizable substances by wet
oxidation with a use of a catalyst performed in the presence of an
oxygen-containing gas, and more particularly pertains to a process
for treating waste water efficiently for a long period in a stable
manner by using a solid catalyst containing activated carbon and by
regulating the oxygen concentration in an exhaust gas.
[0003] This invention further relates to a process for suppressing
deterioration of the catalytic activity of the solid catalyst at
the time of temperature rising when starting up a operation of the
wet oxidation and/or at the time of temperature lowering when
suspending the operation by protecting the catalyst according to
needs, or to a process for efficiently recovering the degraded
catalytic activity of the solid catalyst containing activated
carbon according to needs.
[0004] 2. Description of the Related Art
[0005] Heretofore, there have been known, for example, biological
treatment and wet oxidation treatment, as means for purifying waste
water containing organic or inorganic oxidizable substances.
Biological treatment has a disadvantage in consuming a long time to
decompose the oxidizable substances in the waste water. Further,
this treatment is limited to treat waste water of a low
concentration. In the case where the waste water is of high
concentration, it is required for diluting the waste water to a
proper concentration. The method demands a large space for the
installation of facilities for diluting waste water. Further,
microorganisms that are used in the biological treatment are
susceptible to change of the environment such as temperature. These
factors make it difficult to stably operate the waste water
treatment for a long time.
[0006] Wet oxidation is a process for treating waste water in the
presence of oxygen at a high temperature under high pressure to
oxidize and/or decompose oxidizable substances in the waste water.
As an example of this process, there has been proposed a wet
oxidation using a solid catalyst (herein after may be referred to
as "catalytic wet oxidation") as a means for speeding up the
reaction rate and loosening the requirements for reaction (reaction
condition). In the catalytic wet oxidation, a catalyst using an
oxide, and a catalyst using combination of such an oxide and a
precious metal element are employed.
[0007] In the aforementioned wet oxidation process, it has been
required to treat waste water at a temperature of 170.degree. C. or
more in order to oxidize and/or decompose various oxidizable
substances in the waste water. It is often the case that a pressure
as large as 1 MPa (Gauge) or more is required. For example,
Japanese Unexamined Patent Publication No. 11-347574 proposes a
technique in which a catalyst comprising platinum supported on
titania is used and acetic acid is subjected to wet oxidation at
170.degree. C. This technique still requires a treating condition
of setting the temperature at a relatively high degree. Therefore,
there has been a demand for developing a technique of treating
waste water at a low temperature and low pressure and with a high
treating performance.
[0008] In view of the above problems residing in the prior art, the
inventors of this invention has been developing a new catalyst and
researching a new waste water treating process. As a result of
trials and errors, the inventors found that a solid catalyst
containing activated carbon exhibits significantly high catalytic
activity to organic and/or inorganic oxidizable substances under a
temperature lower than 170.degree. C. and a low pressure. Such a
low temperature and low pressure condition contributes to loosening
the requirements for reaction.
[0009] In the case where a solid type catalyst containing activated
carbon is used, there has to be considered various problems as
follows. Activated carbon is liable to be brought into combustion
under the conventional wet oxidation. Therefore, it has been
impossible to utilize activated carbon as a catalytic component for
wet oxidation. Specifically, in the case where a catalyst
containing activated carbon is employed, it is often the case that
the catalyst does not have heat resistance of resisting a high
temperature such as 170.degree. C. or more. Even if the catalyst
exhibits a high catalytic activity at an initial stage of reaction,
the catalytic activity deteriorates rapidly within 100 hours or
less. Therefore, utilization of the catalyst containing activated
carbon has been practically impossible.
[0010] On the other hand, in the case where there is not provided
sufficient measures for protecting the catalyst during its use even
at a low temperature such as 170.degree. C. or less, the activated
carbon itself is subjected to combustion due to existence of oxygen
containing gas. Consequently, the catalytic activity also
deteriorates within a short period such as within one hundred to
several hundreds hours. Thus, utilization of the
activated-carbon-containing catalyst was impossible in the
conventional wet oxidation for treating waste water.
[0011] Japanese Unexamined Patent Publication No. 11-179378
discloses a technique of oxidizing an oxygen-containing organic
compound having solely one carbon atom per molecule at a
temperature of 100.degree. C. or lower with use of a catalyst in
which a precious metal is supported on activated carbon. This
technique is not applicable to treating an organic compound having
two or more carbon atoms per molecule or inorganic compound. Also,
this publication does not fully consider durability (heat
resistance) of the catalyst in which a precious metal is supported
on activated carbon.
[0012] The above problems such as a possibility of combustion of
activated carbon itself and deterioration of catalytic activity
were also observed when treating waste water containing organic
and/or inorganic oxidizable substances at the time of temperature
rising by starting up the operation of the wet oxidation apparatus
and/or at the time of temperature lowering by suspending the
operation if the treatment is performed under the same oxidization
atmosphere as in the conventional system.
[0013] It is often the case that raising the pressure in the
apparatus is required so that the waste water retains its liquid
phase while raising the temperature of the waste water in the wet
oxidation. Therefore, it is a general practice to supply
oxygen-containing gas even in the absence of oxidizable substances
in order to maintain the pressure in the apparatus to a certain
level at the time of starting-up the apparatus. As a result, it is
likely that the catalytic activity of the catalyst containing
activated carbon is deteriorated at the time of starting up the
operation of the apparatus prior to actual treatment of waste water
as well as during suspension of the operation of the apparatus,
namely, suspension of supply of the waste water. In order to avoid
such a problem, there has been proposed a technique of supplying
gas which does not contain oxygen, e.g., nitrogen gas, into the
apparatus during starting-up operation of the apparatus or
suspension of the operation of the apparatus. This technique,
however, is not desirable in the aspect of cost performance and
necessity of cumbersome operation. There has also been a problem
that the catalytic activity is lowered due to existence of oxygen
that has remained in the apparatus or adsorbed to the catalyst even
during non-supply period of oxygen-containing gas.
[0014] Japanese Unexamined Patent Publication No. 4-300696
discloses a technique of initiating an operation of the apparatus
for catalytic wet oxidation. In this publication, disclosed is a
technique of omitting or simplifying a device that is required for
pre-heating of the apparatus during start-up operation, rapidly
initiating oxidation, and treating waste water with high
performance. This publication, however, does not propose a
technique of suppressing deterioration of catalytic activity.
[0015] Maintenance of high catalytic activity for a longer period
and carrying out the waste water treatment with high performance
have been strongly demanded recently. For instance, in the case
where the waste water contains oxidizable substances which are hard
to decompose, it is required to set the treating temperature at a
relatively high level in order to accomplish waste water treatment
with high performance. In such a case, durability of the
activated-carbon-containing catalyst is liable to deteriorate.
[0016] Activated carbon has a property of absorbing oxidizable
substances in the waste water. In the case where the decomposing
rate of the oxidizable substances that have been adsorbed to the
activated carbon is extremely slow, oxidation and decomposing
ability of the catalyst gradually decrease during waste water
treatment. Further, in the case where waste water treatment is
performed for a long period, a problem involved in waste water
treatment such as disorder of the apparatus and erroneous operation
of the apparatus cannot be avoided, which may deteriorate the
catalytic activity of the activated-carbon-containing catalyst.
[0017] In view of the aforementioned various problems, there has
been a demand for a technology of recovering the catalytic activity
of the activated-carbon-containing catalyst that has been once
deteriorated.
[0018] Several catalyst recovering techniques have been proposed
heretofore. For example, Japanese Examined Patent Publication No.
3-66018 proposes a technique of combining (a) acid washing process
and (b) liquid phase reduction process or combining (a) acid
washing process and (c) gaseous phase reduction process. The acid
washing is such that the catalyst is washed in an acidic aqueous
solution containing at least one component selected from the group
consisting of hydrochloric acid, nitric acid, phosphoric acid,
acetic acid, and propionic acid. The liquid phase reduction is such
that the catalyst is reduced with use of an aqueous solution
containing at least one component selected from the group
consisting of hydrazine hydrate, formaldehyde, sodium borohydride,
lithium aluminohydride, sodium tartrate, glucose, potassium
formate, and sodium formate. The gaseous phase reduction is such
that the catalyst is reduced with use of a gaseous reducing agent
containing hydrogen and/or carbon monoxide.
[0019] The above mentioned method, however, is not sufficient in
recovering the catalytic activity of the
activated-carbon-containing catalyst. Conversely, this process may
likely to cause deterioration of catalytic activity. Further more
the gaseous phase reduction employing hydrogen or carbon monoxide
also has a problem because it is difficult to implement the
reduction in a state that the catalyst is filled in a waste water
treating apparatus as itself. To carry out the water treating
process while employing the gaseous phase reduction, it is
necessary to take out the catalyst from a reactor and install a
furnace exclusively used for reduction and calcination. Such an
arrangement, however, is practically unexecutable.
[0020] Japanese Examined Patent Publication No. 4-45214 proposes a
technique of rendering the catalyst into contact with an aqueous
solution containing formic acid and/or oxalic acid at a
temperatures ranging from 40 to 85.degree. C. and heating the
catalyst to decompose the formic acid and/or oxalic acid, thereby
reducing the catalyst. This recovering process, however, does not
completely recover the catalytic activity of the
activated-carbon-containing catalyst. Conversely, this recovering
process may cause deterioration of the catalytic activity and
corrosion of the parts constituting the apparatus.
[0021] Japanese Unexamined Patent Publication No. 9-10602 proposes
a technique of contacting a solid catalyst whose catalytic activity
has been deteriorated due to oxidation resulting from oversupply of
oxygen, substantially without supply of oxygen, with a regenerated
solution which contains at least one ammonium salt selected from
the group consisting of ammonium sulfate, ammonium chloride, and
ammonium carbonate, or which contains ammonia and at least one
ammonium salt selected from the group consisting of ammonium
sulfate, ammonium chloride, and ammonium carbonate and has pH from
3 to 10. This technique is effective to some extent in recovering
the catalytic activity of the catalyst containing activated carbon.
However, there is room for further developing the technique to
achieve more improved recovering performance.
OBJECT OF THE INVENTION
[0022] The present invention has been accomplished to solve these
problems. Accordingly, an object of the present invention is to
provide a catalyst for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in the waste water by catalytic wet
oxidation efficiently in a stable manner and the preparation method
thereof.
[0023] Another object of the present invention is to provide a
method for treating waste water efficiently for a long period in a
stable manner by wet oxidation using a catalyst containing
activated carbon at low temperature and under low pressure.
[0024] Further object of the present invention is to provide a
method for suppressing deterioration of the catalytic activity of
the solid catalyst at the time of temperature rising when starting
up the operation of the wet oxidation and/or at the time of
temperature lowering when suspending the operation of the wet
oxidation.
[0025] Still further object of the present invention is to provide
a method for efficiently recovering the deteriorated catalytic
activity of the catalyst containing activated carbon.
SUMMARY OF THE INVENTION
[0026] The object mentioned above is accomplished by a catalyst for
the treatment of a waste water, which catalyst comprises activated
carbon, (a) component (also referred to as "first component") and
(b) component (also referred to as "second component").
[0027] (a) component is at least one selected from the group
consisting of Ti, Zr, Hf, Nb, Ta, Fe, Co, Mn, Al, Si, Ga, Ge, Sc,
Y, La, Ce, Pr, Mg, Ca, Sr, Ba, In, Sn, Sb and Bi.
[0028] (b) component is at least one selected from the group
consisting of Pt, Pd, Rh, Ru, Ir and Au.
[0029] The present inventive catalyst can be prepared by a method
for the production of the catalyst which method comprises the steps
of depositing (a) component on the activated carbon and depositing
(b) component on the activated carbon.
[0030] Another object of the present invention can be accomplished
by a method for oxidizing and/or decomposing organic and/or
inorganic oxidizable substances in waste water by wet oxidation
with a use of a catalyst, wherein the oxidizable substances are
oxidized and/or decomposed with an oxygen containing gas in the
presence of the catalyst under pressure such that said waste water
retains the liquid phase thereof at temperature of 50 to less than
170.degree. C., the catalyst contains activated carbon and
controlling an oxygen concentration in an exhaust gas in the range
from 0 to 5 vol %.
[0031] Further object of the present invention can be accomplished
by the method which is characterized in that a catalyst protection
liquid which contains easily decomposable substances is supplied at
the time of temperature rising when starting up a operation of the
wet oxidation and/or at the time of temperature lowering when
suspending the operation.
[0032] Still further object of the present invention is
accomplished by the method which is characterized in that a
catalyst recovering liquid which contains easily decomposable
substances is supplied to the catalyst under temperatures in the
range from 55.degree. C. to less than 200.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic diagram of the system for use in the
method of this invention.
[0034] FIG. 2 is a schematic diagram of the system for use in the
method of this invention.
[0035] FIG. 3 is a schematic diagram of the separation unit for use
in the method of this invention.
[0036] FIG. 4 is a schematic diagram of the separation unit for use
in the method of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0037] As a result of various studies, the present inventors have
found a method for oxidizing and/or decomposing oxidizable
substances in waste water with high efficiency. Such a method
comprises subjecting the waste water to wet oxidation treatment
using the catalyst containing an activated carbon under such
pressure as enables to waste water to retain the liquid phase
thereof intact and at a temperature in the range from 50.degree. C.
to less than 170.degree. C. while supplying an oxygen containing
gas. And also present inventors have found a method for treating
the oxidizable substances in the waste water stably by wet
oxidation with suppressing a deterioration of the catalyst for a
long period by controlling the oxygen concentration in a exhaust
gas, which is emitted after treating the waste water, to a
specified range.
[0038] Further more, the present inventors have found that (1)
deterioration of the catalyst can be suppressed by supplying a
catalyst protection liquid containing easily decomposable
substances to a catalyst bed at the time of temperature rising when
starting up a operation of the wet oxidation and/or at the time of
temperature lowering when suspending the operation. Still further,
(2) A catalyst containing activated carbon, which catalytic
activity for oxidizing and/or decomposing oxidizable substances is
deteriorated, can be recovered by operating the wet oxidation at a
temperature in the range from 50.degree. C. to less than
200.degree. C. while supplying a catalyst recovering liquid
containing easily decomposable substances to a catalyst bed.
[0039] According to the present invention, "oxidizable substances"
means organic and/or inorganic compound which can be oxidized
and/or decomposed by the wet oxidation process. Oxidizable
substances includes, but not limited to, organic compounds
including methanol, ethanol, acetaldehyde, formic acid, acetone,
acetic acid, propionic acid, tetrahydrofuran (THF), and phenol;
nitrogenous compounds including ammonia, hydrazine, nitrous acid
ion, dimethylformamide (DMF), and pyridine; sulfuric compounds
including thiosulfuric acid ion, sodium sulfide, dimethyl
sulfoxide, alkyl benzene sodium sulfonate; organic halogenated
compounds; and organic phosphorous compounds. These compounds may
be suspended or dissolved in the waste water.
[0040] A catalyst used in the present invention is a solid catalyst
containing at least activated carbon as a carrier. A type of
activated carbon for use in the present invention is not
specifically limited. As a raw material of activated carbon, such
as charcoal, coal, coke, peat, lignite and pitch are exemplified.
Also carbon fiber type activated carbon such as activated carbon
fiber of acrylonitrile family, phenol family, cellulose family, and
pitch family can be used as a material of activated carbon.
[0041] The shape of solid catalyst is not specifically limited, and
may be used as molded in various shapes such as, for example,
spheres, grains, pellets, rings, shredding and monolithic structure
such as honeycomb.
[0042] According to the present inventive method, depending on the
types and concentration of oxidizable substances in the waste
water, the catalyst consisting of activated carbon alone exhibits
enough catalytic activity required for oxidizing/decomposing the
oxidizable substances. The present inventive catalyst preferably
contains at least one selected from (b) component in addition to
activated carbon and more preferably contains elements selected
from both (b) component and (a) component in addition to activated
carbon is also effective for waste water treatment.
[0043] (a) component: at least one element selected from the group
consisting of Ti, Zr, Hf, Nb, Ta, Fe, Co, Mn, Al, Si, Ga, Ge, Sc,
Y, La, Ce, Pr, Mg, Ca, Sr, Ba, In, Sn, Sb and Bi.
[0044] (b) component: at least one element selected from the group
consisting of Pt, Pd, Rh, Ru, Ir and Au.
[0045] The catalyst containing the elements selected from both (a)
component and (b) component as a catalyst ingredient exhibits
excellent heat resistance compared with the catalyst containing
activated carbon and (b) component and with the catalyst consisting
of activated carbon alone. By improving the heat resistance,
deterioration of mechanical strength of the catalyst after using
the waste water treatment can be prevented and the decrease in the
catalyst amount by being combusted thereof and/or being powdered
thereof can be drastically suppressed. Further more, oxidation
resistance of the catalyst surface (surface of the activated
carbon) is improved which enables to suppress the deterioration of
the catalyst performance caused by the oxidation. With the
synergistic effect of the above mentioned advantages of the
catalyst, the present inventive catalyst maintains its excellent
performance of oxidizing/decomposing the oxidizable substances in
the waste water for long period.
[0046] The present inventive catalyst contains the element(s)
selected from (a) component and/or (b) component, where necessary,
which are deposited on activated carbon. (a) component improves
oxidation resistance of the catalyst (activated carbon) thereby
suppressing the deterioration of the catalyst performance caused by
the oxidation. The catalyst containing (a) component enables the
wet oxidation to conduct at higher temperature and under
considerably large amount of oxygen containing gas supply compared
to the catalyst without (a) component. (a) component heightens the
wet oxidation performance, the degree of purification, the
durability of the catalyst and the cost performance of the wet
oxidation. And also (a) component heightens the activity derived
from the (b) component, namely, the catalyst containing (a)
component exhibits high catalytic activity even with small amount
of (b) component. Considerably large amount of (b) component can be
deposited on the surface of carrier (activated carbon) and (b)
component can be highly dispersed into the carrier with suppressing
cohesion and movement of (b) component by containing the (a)
component in the carrier. In other words, (a) component acts as a
promoter having various effects such as improving the catalytic
activity and the durability of the catalyst.
[0047] Total amount of (a) component (relative to the total amount
of the catalyst) is not specifically limited but preferable amount
of (a) component in the solid catalyst is in the range from 0.1 to
10 mass %, more preferable lower limit is 0.3 mass %, and most
preferably 0.5 mass %. If the amount of (a) component is less than
lower limit, above mentioned (a) component effect may hardly
obtainable. And more preferable upper limit is 7 mass % and most
preferably 5 mass %. If the amount of (a) component exceeds upper
limit, the specific surface area and the pore volume of the
catalyst may be decreased by being covered its surface (surface of
activated carbon) by oversupplied (a) component and the suppression
of cohesion and movement of (b) component may be deteriorated. And
also excess amount of (a) component may lower the catalytic
activity by entrapping (b) component inside (a) component or may
lower the adsorbability of oxygen and oxidizable substances on the
catalyst.
[0048] It should be noted that among (a) component, preferable
element for obtaining above mentioned effect is at least one
selected from the group consisting of Ti, Zr, Fe, Mn, Ce and Pr,
and also more preferable element is at least one element selected
from the group consisting of Ti, Zr, and Fe. The most preferable
element is Ti or Zr. The form of (a) component contained in the
catalyst is not specifically limited as long as the component is
metal or metal compounds thereof. Preferable form of the (a)
component is metal or metal compounds thereof which is insoluble or
refractory to water and more preferable form is metal, oxide, or
composite oxide thereof which is insoluble or refractory to
water.
[0049] (b) component exhibits as main activity ingredients of the
catalyst for oxidizing/decomposing oxidizable substances. Total
amount of (b) component (relative to the total amount of catalyst)
is not specifically limited but preferable amount of (b) component
in the solid catalyst is in the range from 0.05 to 2 mass %, and
more preferable lower limit is 0.1 mass % and more preferable upper
limit is 1 mass %. If the (b) component amount is less than lower
limit, above mentioned (b) component effect may not be obtained. If
the (b) component amount is exceeds upper limit, the price of the
catalyst may be sacrificed.
[0050] Among (b) component, preferable element for obtaining above
mentioned effect is at least one element selected from the group
consisting of Pt, Pd and Ru, and also more preferable element is Pt
or Pd and the most preferable one is Pt. The form of (b) component
contained in the catalyst is not specifically limited as long as
the component is metal or metal compound thereof. Preferable form
of the (b) component is metal or metal oxide compound thereof and
more preferably metal.
[0051] The catalyst of this invention for treating the waste water
may incorporate in any of the catalyst mentioned above for treating
waste water and may incorporate in any catalyst used in wet
oxidation process other than mentioned above. Further more the
present inventive catalyst may incorporate with the wet oxidation
which is not designed for utilizing solid catalyst.
[0052] Property of the catalyst according to the present invention
is not specifically limited. Preferable specific pore volume having
pore diameter in the range from 0.1 to 10 .mu.m is in the range
from 0.1 to 0.8 ml/g and specific surface area of the catalyst
measured by the Brunauer-Emmett-Teller (BET) is in the range from
100 to 2500 m.sup.2/g. More preferable lower limit of the specific
pore volume is 0.15 ml/g and most preferably 0.2 ml/g. And also
more preferable upper limit of the specific pore volume is 0.7 ml/g
and most preferably 0.6 ml/g. Preferable lower limit of the
specific surface area is 500 m.sup.2/g, more preferably 800
m.sup.2/g and most preferably 900 m.sup.2/g. And preferable upper
limit of the specific surface area is 2000 m.sup.2/g, more
preferably 1700 m.sup.2/g and most preferably 1500 m.sup.2/g.
[0053] The property of activated carbon may be decreased when
preparing the catalyst by supporting (a) component.
[0054] Preferable specific pore volume having pore diameter in the
range from 0.1 to 10 .mu.m is preferably in the range from 0.15 to
0.6 ml/g and more preferably in the range from 0.2 to 0.5 ml/g. The
specific surface area of the catalyst measured by BET is preferably
in the range from 400 to 1600 m.sup.2/g, more preferably from 600
to 1200 m.sup.2/g and most preferably from 700 to 1100
m.sup.2/g.
[0055] According to the present inventive waste water treatment,
the pore having pore diameter in the range from 0.1 to 10 .mu.m,
namely micro pore, have an great influence on diffusion of oxygen
and oxidizable substances contained in the waste water into the
catalyst. If the bulk of the solid catalyst consists of pore having
pore diameter of 0.1 to 10 .mu.m, oxygen and the oxidizable
substances are readily diffused into the catalyst which promotes
the wet oxidation efficiency at low temperature and under low
pressure. If the specific pore volume having pore diameter in the
range from 0.1 to 10 .mu.m is less than 0.1 ml/g, oxygen and the
oxidizable substances are hard to diffuse into the catalyst which
may be resulted in deteriorating the adsorption of the oxidizable
substances to active site of the catalyst and also which may be
resulted in deteriorating the usability of oxygen for decomposing
oxidizable substances and excess oxygen may cause the activated
carbon itself to be combusted.
[0056] Further more, if the specific pore volume having pore
diameter in the range from 0.1 to 10 .mu.m exceeds 0.8 ml/g, the
catalyst may suffer a decrease in the mechanical strength.
Accordingly, the catalyst having above mentioned specific pore
volume having pore diameter from 0.1 to 10 .mu.m is
recommended.
[0057] If the specific surface area of the catalyst is less than
100 m.sup.2/g, the catalyst may suffer a decrease in adsorption of
oxidizable substances to the active site and the purification of
the waste water may be attained incompletely. If specific surface
area of the catalyst exceeds 2500 m.sup.2/g, the catalyst may
suffer a decrease in the mechanical strength. Accordingly, the
catalyst having above mentioned specific surface area of the
catalyst is recommended.
[0058] The decrease value of the specific pore volume having 0.1 to
10 .mu.m pore diameter after (a) component is deposited on
activated carbon is preferably in the ranging of 0.01 to 0.5 ml/g,
more preferably from 0.05 to 0.4 ml/g and most preferably 0.1 to
0.3 ml/g compared with the specific pore volume of the activated
carbon. The decrease value of the specific surface area of the
catalyst after (a) component is deposited on the activated carbon
is preferably of from 50 to 800 m.sup.2/g, more preferably from 100
to 700 m.sup.2/g and most preferably 200 to 600 m.sup.2/g.
[0059] The catalyst which is satisfied with above mentioned
catalyst property and the property derived from the decrease value
is suitable for treating the waste water. If the decrease value of
the specific pore volume is less than 0.01 ml/g and the decrease
value of the specific surface area is less than 50 m.sup.2/g, the
pore portion of the activated carbon may be covered by (a)
component inefficiently and the catalyst may suffer a decrease in
catalytic activity and durability. If the decrease value of the
specific pore volume exceeds 0.5 ml/g and the decrease value of the
specific surface area exceeds 800 m.sup.2/g, pore portion of the
activated carbon, which facilitates the oxidation/decomposition,
may be covered by (a) component and the catalyst may suffer
decrease in catalytic activity. It is also recommended to adjust
the heat treatment condition when preparing the catalyst to
suppress the decrease in the catalyst property.
[0060] When oxidation treatment or reduction treatment is applied
to activated carbon, the property of activated carbon have been
understood that the activated carbon changes its property
drastically by introducing polar group into the surface of the
activated carbon or by removing polar group from its surface.
Similarly, the catalyst used in the present inventive method
changes its properties and its performance considerably in
accordance with the amount of polar group introduced into the
catalyst. According to the present invention, especially the
relationship between the amount of polar group introduced and the
property of catalytic activity depends on the oxidizable substances
in the waste water. If the oxidizable substances are mostly organic
substances and/or inorganic anion substances, the catalyst contains
a small amount of polar group and which requires the catalyst a
high hydrophobic property. Accordingly, reduction treatment applied
catalyst (explained later) tends to exhibit higher catalyst
activity. If the oxidizable substances are mostly inorganic cation
substances such as ammonia and hydrazine, the amount of polar group
in the catalyst containing activated carbon needs to be large.
Accordingly, oxidation treatment applied catalyst (explained later)
tends to exhibit higher catalytic activity.
[0061] The present inventors considered that the change in the
catalyst properties and performances depends largely on the
adsorption readiness of the oxidizable substance to the catalyst.
Most of the polar group in the catalyst is oxygen containing
functional group such as hydroxyl group and carboxyl group.
Therefore, the present inventive catalyst containing activated
carbon has correlation with, not limited to, the polar group amount
in the catalyst and a the ratio of oxygen amount and carbon amount
(herein after may be referred to as "oxygen/carbon ratio") in the
catalyst. This correlation indicates that when the catalyst
contains small quantities of the polar group, the value of the
oxygen/carbon ratio is small. On the contrary, when the catalyst
contains large quantities of the polar group, the value of the
oxygen/carbon ratio is large. With the oxygen/carbon ratio, the
present inventive catalyst can be classified as favorable catalyst
and as unfavorable catalyst for treating oxidizable substances. To
be more specific, when the oxidizable substances are organic
substances or inorganic anion substances, the favorable catalyst
for treating these oxidizable substances indicates the
oxygen/carbon ratio in the range from 0 to 0.12, more preferably
from 0 to 0.10 and most preferably from 0 to 0.08. On the contrary
when the oxidizable substances are inorganic cation substances such
as ammonia and hydrazine, the favorable catalyst for treating
thereof indicates the oxygen/carbon ratio in the range from 0.08 to
0.30, more preferably from 0.10 to 0.25 and most preferably from
0.12 to 0.20. If the oxygen/carbon ratio exceeds above mentioned
range, the catalyst may suffer a decrease in the mechanical
strength.
[0062] The catalyst used in present inventive method is not limited
to any specific types as long as the catalyst contains activated
carbon, but it is recommended to adjust the value of the
oxygen/carbon ratio to meet the desired purposes by applying a wide
variety of treatment to the catalyst during its preparation.
Specifically, for preparing the catalyst containing small
quantities of the polar group with small oxygen/carbon ratio, a
reduction treatment is preferably applied to the catalyst. As the
reduction treatment, such as gaseous phase reduction using
hydrogen, and liquid phase reduction using reductant (e.g. sodium
sulfite, hydrazine) are exemplified. During the reduction
treatment, active ingredient of the catalyst is reduced and/or
activated carbon (surface of the activated carbon) is hydrogenated
whereby the catalyst having high activity to inorganic anion
compounds and organic compounds is prepared. Generally used
activation treatment applied to a production process of activated
carbon can be employed as reduction treatment. Such an activated
treatment as contacting the catalyst with vapor, carbon gas, or
nitrogen gas at high temperature is employable.
[0063] For preparing the catalyst containing large quantities of
polar group with large oxygen/carbon ratio, a oxidation treatment
is preferably applied to the catalyst. As the oxidation treatment,
such as gaseous phase oxidation using oxygen containing gas, ozone,
or NOx, and liquid phase oxidation using oxidant (i.e. hydrogen
peroxide, ozone aqueous solution, bromine water, permanganate,
dichromate, hypochlorite, nitric acid and phosphoric acid) are
exemplified. During the oxidation treatment, active ingredient of
the catalyst is oxidized and/or polar group such as functional
groups having oxygen is introduced to activated carbon (surface of
the activated carbon) whereby the catalyst having high activity to
inorganic cation compounds such as ammonia and hydrazine is
prepared. A treatment such as nitration, sulfonation, amination and
a treatment by alkali metal compounds can be applied to the
catalyst during its production process.
[0064] As mentioned above, the catalyst for use in the present
invention having an excellent adsorption property of oxidizable
substances on the catalyst exhibits higher catalyst activity.
Property of the present inventive catalyst can be measured by
adsorption property of oxidizable substances. As an example, when
the waste water contains organic compounds as a oxidizable
substances, the adsorption property can be measured based on the
adsorbability of organic compounds and its oxidized/decomposed
substances on the catalyst. Further more, when the organic
compounds consist of more than 2 carbon atoms per molecule, acetic
acid tends to remain in treated water (a water treated by wet
oxidation). The catalyst containing activated carbon having
excellent adsorbability of acetic acid exhibits higher catalytic
activity for organic compound. On the contrary, the catalyst
containing activated carbon having excellent adsorption ability of
ammonia exhibits higher catalytic activity to inorganic cation
compounds when the waste water contains inorganic cation compounds
such as ammonia and hydrazine as a oxidizable substances. Activated
carbon contained in the catalyst having excellent adsorbability of
oxidizable substances is evaluated as an activated carbon having
higher adsorbability of oxidizable substances. Accordingly, the
activated carbon having excellent adsorbability of oxidizable
substances is preferably employed for preparing the present
inventive catalyst.
[0065] "Excellent adsorbability" herein means the adsorption amount
of the catalyst when conducting adsorption test under certain
condition by measuring saturated adsorption amount of object
ingredients per activated carbon unit. Activated carbon having
excellent adsorbability exhibits larger saturated adsorption
amount. And also, excellent adsorbability can be means the rate of
the adsorption under certain condition. Activated carbon having
faster adsorption rate of oxidizable substances excels in
adsorption property. The adsorption rate can be measured at any
time of the adsorption test and the rate can be expressed by using
any method. The adsorption rate at the beginning of the adsorption
test is preferably employed in the present invention. The catalyst
containing activated carbon having faster adsorption rate at the
beginning of the test exhibits excellent adsorptivity and higher
catalytic activity.
[0066] Since the present inventive catalyst can be defined with a
wide variety of property, the present inventive catalyst is not
limited to the catalyst having above mentioned property. The
present inventive catalyst can be further defined by using
properties such as amount of functional groups, amount of ash
content, amount of impurities, structure of carbon, acidity, volume
amount of pore other than macro pore (i.e. meso pore, micro pore
and sub-micron pore), ratio of the pore (i.e. meso pore, micro pore
and sub-micron pore), outer surface area, inner surface area and
the ratio of outer and inner surface area of the present inventive
catalyst.
[0067] The method for producing the catalyst containing both (a)
component and/or (b) component is not specifically limited. Various
methods are available for producing the catalyst such as depositing
(a) component and/or (b) component on activated carbon. The
catalyst can be molded into various shape after depositing (a)
component and/or (b) component on the activated carbon,
subsequently (a) component and/or (b) component can be further
deposited on the molded catalyst. Among them preferable production
method for preparing the present inventive catalyst is to deposit
(a) component and/or (b) component on activated carbon.
[0068] Various method can be taken for depositing (a) component and
(b) component on activated carbon such as depositing (b) component
after (a) component is deposited on activated carbon, depositing
(a) component after (b) component is deposited on activated carbon,
and depositing both (a) component and (b) component at the same
time. Among them preferable depositing method is to deposit (b)
component after depositing (a) component on activated carbon for
preparing the present inventive catalyst which exercises its effect
brought by adding (a) component and (b) component which excels in
catalyst performance. The reason for the excellent catalyst
performance, which is brought by the above mentioned preferable
catalyst preparation process, is not completely clarified, the
present inventors have considered as following.
[0069] The catalyst prepared by depositing (a) component on the
activated carbon before depositing (b) component may have the
following structure:
[0070] (a) component is deposited on the surface of the activated
carbon and inside the pore thereof.
[0071] (b) component is deposited on the further outer surface of
the activated carbon and on the further outer surface of the pore
compared with that of the (a) component deposited on the activated
carbon, and also (b) component is deposited on the surface of the
(a) component. Namely, the presence of (b) component placing on the
outer surface thereof greatly improves the catalytic activity. With
the aid of (a) component, (b) component can be prevented from being
deposited on the deep inside of the pore, which is hardly
susceptible to the oxidation/decomposition of the oxidizable
substances. And also distributed (a) component on the surface of
activated carbon exercise distribution effect as block for
suppressing the cohesion and the movement of (b) component. Taking
the above mentioned catalyst structure, (a) component feeds oxygen
to (b) component effectively thereby promotes the
oxidation/decomposition of the oxidizable substance and leading to
prevent activated carbon from being oxidized/deteriorated by
oxygen. Accordingly, the catalyst having above structure can
exercise each component ability effectively.
[0072] The catalyst prepared by depositing (a) component after
depositing (b) component on activated carbon, or the catalyst
prepared by depositing both (a) component and (b) component at the
same time has smaller amount of (b) component existed on the
surface of activated carbon, namely on (a) component, than that of
the catalyst prepared by depositing (b) component after depositing
(a) component on activated carbon.
[0073] When depositing (a) component before depositing (b)
component on activated carbon, applying a treatment for stabilizing
(a) component is recommended. The effective treatment for
stabilizing (a) component can be heat treatment as exemplified
following. After depositing (a) component with the treatment such
as impregnation method or adsorption method, thus obtained catalyst
precursor is preferably processed by heat treatment (e.g. drying or
calcination). The heat treatment can be conducted in oxidizing
atmosphere (e.g. in the air) or in inactive gas atmosphere (e.g.
nitrogen). Inactive gas is preferably employed for suppressing the
oxidation and deterioration of activated carbon. When the precursor
is heat treated in oxidizing atmosphere (e.g. in the air), the
temperature thereof is preferably in the range from 80 to
500.degree. C., more preferable lower limit is 150.degree. C. and
most preferably 200.degree. C. And also, more preferable upper
limit is 400.degree. C. and most preferably 300.degree. C. When the
precursor is heat treated in an inactive gas atmosphere, the
temperature thereof is preferably in the range from 80 to
600.degree. C. and more preferable lower limit is 150.degree. C.
and most preferably 200.degree. C. And also, more preferable upper
limit is 500.degree. C. and most preferably 450.degree. C.
[0074] According to the present inventive method, heat treatment is
also effective for stabilizing (b) component after (b) component is
deposited on the precursor. The heat treatment can be conducted in
oxidizing atmosphere (e.g. in the air), in inactive gas atmosphere
(e.g. nitrogen) or in reducing atmosphere (e.g. hydrogen containing
gas). Among them reducing atmosphere is preferably employed in view
of improving the catalytic activity, if (b) component exists as
metal thereof (in most cases (b) component exists as metal thereof
when the oxidizable substances are organic compound) and if the
catalyst exhibits higher hydrophobic property by removing polar
group such as hydroxyl group and carbonyl group of activated
carbon. When the precursor, on which (b) component is deposited, is
heat treated in oxidizing atmosphere or in inactive gas atmosphere,
the temperature thereof is preferably selected in ranging from 80
to 400.degree. C. and more preferable lower limit is 150.degree. C.
and more preferable upper limit is 300.degree. C. When the
precursor is heat treated in reducing atmosphere, the temperature
thereof is preferably selected in the range from 150 to 600.degree.
C., more preferable lower limit is 200.degree. C. and most
preferably 250.degree. C. Also, more preferable upper limit is
500.degree. C. and most preferably 450.degree. C. With the heat
treatment other than mentioned above, (b) component can be
stabilized such as by reducing agent (e.g. sodium borohydride).
[0075] When adding (a) component and (b) component to activated
carbon, varieties of compounds containing (a) component and/or (b)
component can be employed in accordance with the needs and
preferable compounds may be water soluble compounds, or inorganic
compounds containing (a) compound and/or (b) component. Also, the
compounds may be emulsion form, sully form, and colloid form, or
simple substance thereof can be used.
[0076] For increasing the effect derived from (b) component,
preferably 90 mass % of the (b) component contained in the catalyst
exists within surface depth of 600 .mu.m. Namely, the catalyst
containing (b) component forms preferably egg shell type catalyst
or egg white type and more preferably egg shell type catalyst. To
meet this requirement, any method can be applied to deposit (b)
component within the above mentioned surface depth of the catalyst.
As an example, the activated carbon is impregnated with liquid
containing (b) component by the impregnation method. The liquid
containing (b) component is prepared by adding predetermined amount
of inorganic salt of (b) component to water. The water is prepared
so that the amount of water is in proportion to water absorption
coefficiency of the activated carbon. And after activated carbon is
uniformly impregnated with the liquid containing (b) component, the
catalyst (activated carbon) is dried uniformly in inactive gas
atmosphere whereby (b) component can be uniformly deposited on the
surface area of the catalyst. As an preparation method of the
catalyst having above mentioned properties, absorption method and
spraying method can be employable instead of impregnation
method.
[0077] If the present inventive catalyst consists essentially of
activated carbon as a carrier, (a) component and (b) component as a
catalyst ingredients, the present inventive catalyst can exhibit
above mentioned excellent effect. In this case, the catalyst may
possibly contain as extraneous matter therein such substances and
impurities as are entrained by the precursor of the catalyst and
such substances and impurities as are admitted in the catalyst in
the process of production. If the catalyst of this invention
contains these substances in minute amounts, their functions as a
catalyst will not be impaired at all unless these substances
produce an appreciable influence on the physical properties of the
catalyst.
[0078] The present invention will be explained with the reference
to the Figures. FIG. 1 is a schematic diagram of the system for use
in the method of this invention. It should be noted that the
apparatus of FIG. 1 is just an example of an apparatus usable in
the method of the present invention, and the present invention does
not necessarily use this apparatus.
[0079] Waste water supplyed from a waste water supply source (not
shown) is fed to a heater 3 through line 6 by waste water feed pump
5. Oxigen containing gas (e.g. air) is supplied through
oxygen-containing gas supply line 8 and pressurized by compressor 7
and the oxigen containing gas is supplyed to the water before the
waste water is fed to the heater 3. The supply amount of the oxigen
containing gas is controled by oxygen-containing gas flow control
valve 9. Oxigen added waste water heated by the heater 3 is
introduced into the reactor 1 from its head with mesureing the
pressure thereof by pressure gauge indicator PI.
[0080] The reactor 1 is equipped with electric heater 2 which
maintains the temperature in the reactor 1 at predetermined desired
level. The reactor 1 is also charged with the catalyst bed (not
shown) by which the oxidizable substances in the waste water is
oxidized and/or decomposed. The space velocity at catalyst bed
(namely passing rate of the waste water through the catalyst bed)
is not specifically limited, and preferably in the range from 0.1
hr.sup.-1 to 10 hr.sup.-1, more preferably from 0.2 hr.sup.-1 to 5
hr.sup.-1 and most preferably from 0.3 hr.sup.-1 to 3 hr.sup.-1. If
the space velocity is less than 0.1 hr.sup.-1, the amount of the
waste water to be treated will be unduly small and the facility
will be unduly large. If the space velocity exceeds 10 hr.sup.-1,
the efficiency of the decomposition/oxidation of oxidizable
substances will be unduly low. It should be noted that the oxygen
containing waste water is introduced into the reactor 1 from its
head and treated waste water (e.g. treated water) is extracted from
its bottom. The gas-liquid (e.g. oxigen containing gas and the
waste water) flow type at the catalyst bed is gas-liquid concurrent
descending. Namely, the reactor 1 is tricle-bed reactor.
[0081] After the waste water is decomposed/oxidized in the reactor
1, thus obtained treated water flows from the bottom of the reactor
1 to cooler 4 for cooling down. And then the liquid ejected from
pressure control valve 12 is fed to gas-liquid separator 11. The
pressure control valve 12 maintained the pressure inside the
reactor 1 at predetermined pressure level in accordance with the
value obtained from the pressure gauge indicator PI.
[0082] Gaseous components are separted from the treated water in
gas-liquid separator 11. The gaseous componets (exhaust gas) are
ejected via conduit 13 and the liquid is ejected via conduit 15 by
treated water exhaust pump 14. The concentration of oxygen
contained in the exhaust gas is mesured by concentration meter 16
in the separator 11. Liquid level is detected by liquid level
controler LC and the liquid level is controled by adjusting the
pump 14 to maintain a certain liquid level.
[0083] FIG. 2 is a schematic diagram of the system for use in the
method of this invention. Expranation to the process which is using
similar apparatus with the aforementioned apparatus used in FIG. 1
is ommited (same number may be attached to the apparatus in FIG. 2,
FIG. 3 and FIG. 4 as that in FIG. 1.)
[0084] According to FIG. 2, the waste water heated at the heater 3
is supplied to the reactor 21 from its bottom. After the waste
water is treated in the reactor 1, thus obtained treated water is
extracted from its head. The gas-liquid flow type at the catalyst
bed is gas-liquid concurrent ascending.
[0085] FIG. 3 is a schematic diagram of the system for use in the
method of this invention in which reactors 31 and 32 having same
flow type (gas-liquid concurrent descending) with FIG. 1 are
arranged in series. Oxygen containing gas is supplied to the waste
water through valve 35 and valve 9.
[0086] According to the present invention, the number, kind, and
shape of the reactor are not specifically limited, and one or more
reactors which have been conventionally used in wet oxidation may
be employed. For example, the reactor may be of a single-tube type
or a multiple-tube type. For treating the waste water with high
oxydizable substance concentration, which may bring high heating
value by treating thereof, multiple-tube type reactor having high
heat elimination capability is preferably employed. For treating
the waste water with low oxydizable substance concentration,
multiple-tube type reactor having heat adding capability is
preferably employed. Further more, when employing the plurality of
reactors, the reactors may be installed in parallel or in series
according to needs.
[0087] The temperature for the catalytic wet oxidation treatment
according to this invention is in the range from 50.degree. C. to
less than 170.degree. C. If the temperature of this treatment is
less than 50.degree. C., the treatment of organic oxidizable
substances and inorganic oxidizable substances may be effected with
unduly low efficiency and the purification of the waste water may
be attained incompletely.
[0088] The preferable temperature is not less than 80.degree. C.,
more preferably not less than 100.degree. C. and most preferably
not less than 110.degree. C. If the temperature is less than
100.degree. C., organic compound having one carbon atom per
molecule such as methanol, formic acid and formaldehyde can be
decomposed by using the present inventive catalyst. For treating
the waste water containing organic compound having 2 or more carbon
atoms per molecule, the temperature is preferably set at
100.degree. C. or more. If the temperature of this treatment
exceeds 170.degree. C., activated carbon itself is liable to be
brought into combustion and the catalyst losts economic
application. Preferable upper limit of the temperature is at
160.degree. C., more preferably at 150.degree. C. and most
preferably at 140.degree. C.
[0089] The pressure under which the waste water is treated is
suitably selected, depending on the relation between this pressure
and the treating temperature. It has no particular restriction
except for the requirement that the sufficient pressure is applyied
for enabling the waste water to retain the liquid phase thereof. It
is often the case that a pressure is selected in the range from
atmospheric pressure to 1 MPa (Gauge) is selected. If the
temperature for the catalytic wet oxidation treatment excells
50.degree. C. and less than 95.degree. C., atmospheric pressure can
be applyied for economical operation and preferably adding suitable
pressure to the waste water is reccommended for improving the
efficiency of the waste water treatment. If the temperature exceeds
95.degree. C., the waste water may be no longer capable of
retaining the liquid phase thereof under atmospheric pressure and
applying pressure in the range from 0.2 to 1 MPa (Gauge) is needed
to keep its liquid phase. If the pressure exceeds 1 MPa (Gauge) at
this temperature, the treatment may incur heavy operational cost.
If excessive pressure is applied, the activated carbon itself is
liable to be conbusted and/or the catalystic activity may be
deteriorated. According to the present invention, for avoiding
aforementioned problem, the pressure can be adjusted by controlling
output pressure of the reactor 1 with pressure control valve 12 so
as to the waste water can keep its liquid phase in the reactor 1.
For improving the wet-oxydation performance and the durability of
the catalyst, the pressure fluctuation shall be within plus or
minus 20%, more preferably within plus or minus 10% and most
preferably plus or mius 5%.
[0090] According to the present invention, the concentration of
oxygen in the exhaust gas needs to be maintained in the rang of
from 0 to 5 vol %. The oxygen concentration in this range gives an
effective purification of the waste water and a highly effective
treatment of the oxidizable substances in the waste water for a
long period. If the concentration exceeds 5 vol %, the activated
carbon may be liable to be combusted by redundant supply of oxygen
and which resulted in unstable operation. Accordingly the
wet-oxidation is preferably operated with supplying enough oxygen
for oxidizing/decomposing the oxidizable substances. The preferable
oxygen concentration in the exhaust gas is close to 0 vol % which
is not under-supply condition for oxidizing/decomposing the
oxidizable substances. If oxygen is under-supplied, the treatment
of the waste water may suffer unduly low efficiency in accordance
with the increase of oxygen deficiency. If the oxygen concentration
is slightly less than the upper vol % of the oxygen concentration,
the catalytic activity of the present inventive catalyst and the
efficiency of the waste water treatment may be improved. The
slightly oxygen deficiency condition improves durability of the
catalyst and the wet-oxidation enjoys stable waste water treatment
for a long period. According to the present invention, The upper
limit of oxygen concentration is preferably 4 vol %, more
preferably 2 vol % and most preferably 1 vol %.
[0091] According to the present invention, if the oxygen supply
amount is slightly less than 5 vol %, the catalytic activity of the
present inventive catalyst and the efficiency of the waste water
treatment will be improved. The factor of this trend may be that
the active point of the catalyst surface (e.g. the active point of
the activated carbon) and/or the (b) component in the catalyst
become reduction state under the slightly oxygen deficiency
condition which resulted in improving the catalytic activity. And
also under the slightly oxygen deficiency condition, the activated
carbon is reduced to give improved hydrophobic property to the
surface thereof. If the oxidizable substances are organic
compounds, the activated carbon enjoys improved adsorbability of
the oxidizable substances and this invention can treat waste water
with high efficiency.
[0092] The concentration of oxygen can be suitably controlled
within the above mentioned range with variety of method, for
example the concentration meter 16 can be employed for measuring
the concentration of the oxygen in the exhaust gas and the oxygen
supply amount can be controlled by the valve 9 based on the result
obtained from the concentration meter 16. Any types of
concentration meter can be employed such as zirconia type oxygen
analyzer, oxygen dumbbell type oxygen analyzer and gas
chromatograph.
[0093] When starting up the wet oxidation process with supplying
oxygen containing gas, the oxygen supply amount is preferably
adjusted to the amount slightly less than that of needed for the
oxidation/decomposition. This invention preferably treats the waste
water under the slightly oxygen deficiency condition such as 0 vol
% of oxygen concentration in the exhaust gas. Starting from 0 vol %
of the oxygen concentration, the oxygen supply amount is gradually
increased until it reached most suitable oxygen amount for
sufficiently oxidizing/decomposing the oxidized substances when
starting up the wet oxidation process. The supply amount of the
oxygen containing gas may be controlled by the result of oxygen
concentration in the exhaust gas or by the analyzed result of the
treated water. When starting up the wet oxidation deterioration of
the catalyst, which is caused by oversupply of the oxygen, can be
avoided By properly controlling the oxygen supply amount. Further
more, the catalytic activity may be improved by providing the
reduction treatment, as needed, to the catalyst when treating the
waste water. The catalyst can deal with the change of the
oxidizable substance concentration and the change of the ingredient
in the waste water. If the waste water treatment suffers unduly low
efficiency due to the shortage of the oxygen supply, the treated
water can be processed by the present inventive method again for
obtaining highly purified water. This invention does not
particularly prohibit a waste water from being treated by the
conventional method of purification.
[0094] According to the present invention, the term "oxygen
concentration in the exhaust gas" means the oxygen concentration in
the gas phase obtained by treating the waste water with the use of
the catalyst. In general, the oxygen concentration is determined by
measuring the oxygen concentration in the gas-liquid separator as
shown in FIG. 1 and FIG. 2.
[0095] According to the present invention, the supply amount of the
oxygen containing gas need to be adjusted in accordance with the
actual processing efficiency for efficiently oxidizing/decomposing
organic and/or inorganic oxidizable substances contained in the
waste water.
[0096] The preferable condition for controlling the oxygen
concentration in the exhaust gas within the range from 0 to 5 vol %
is to set [oxygen amount in the oxygen containing gas
supplied]/[oxygen demand of the waste water at maximum waste water
treatment efficiency](hereinafter may be referred to as "D
value")=0.8 to 1.3. The durability and the performance of the
catalyst can be remarkably improved by adjusting the oxygen supply
amount to the aforementioned D value.
[0097] The [oxygen demand of the waste water at maximum waste water
treatment efficiency] is measured by changing the oxygen containing
gas supply amount under the fixed condition of the temperature, the
pressure, LHSV, gas-liquid current type, and the catalyst to be
used for the wet-oxidation. In other words, [oxygen demand of the
waste water at maximum waste water treatment efficiency] means
required oxygen amount of the waste water when the waste water
treatment efficiency rate indicates its maximum efficiency rate
under above condition. The D value can be used as an index for
indicating excess and deficiency of the oxygen supply amount. For
example, if the treatment efficiency in terms of the chemical
oxygen demand (COD(Cr) is 90% at maximum when treating the waste
water by changing the oxygen supply amount with the predetermined
wet oxidation condition, D value=1.0 can be obtained with the
supply of oxygen containing gas at a rate of O.sub.2/COD=0.9. If
the oxygen containing gas is supplied at a rate of O.sub.2/COD=1.1,
D value is 1.11. [oxygen demand in the waste water at maximum waste
water treatment efficiency], which is denominator of D value, does
not necessarily equals to the value of "oxygen supply amount in the
waste water at maximum waste water treatment efficiency" If the
O.sub.2/COD(Cr)=90% at maximum and aforementioned oxygen containing
gas supply amount is O.sub.2/COD(Cr)=0.9, oxygen containing gas
supply amount equals to D value. If the COD(Cr)=90% at maximum and
the O.sub.2/COD(Cr)=2.0, D value is 2.22.
[0098] If D value exceeds 1.3, the oxygen gas supply amount exceeds
the amount required for the oxidation/decomposition treatment and
the activated carbon itself may be liable to be combusted. If D
value is less than 0.8, the oxygen supply amount is less than the
amount required for the oxidation/decomposition treatment and the
treatment of oxidizable substances may be effected with unduly low
efficiency which is economically unacceptable. The preferable lower
limit of D value is 0.9 and more preferably 0.95. The preferable
upper limit is 1.2 and more preferably 1.1.
[0099] The term "the waste water treatment efficiency", which is
represented by [oxygen demand in the waste water at maximum waste
water treatment efficiency] can be expressed by any treatment
efficiency to meet the purification object of ingredient contained
in the waste water and such a treatment efficiency can be
exemplified as COD treatment efficiency, TOC treatment efficiency,
nitrogen treatment efficiency, BOD treatment efficiency, TOD
treatment efficiency and any other specific substance treatment
efficiency.
[0100] The kinds of the oxygen containing gas to be used in this
invention is not specifically limited as far as it contains oxygen
molecules. As examples such a gas include, but not limited to, pure
oxygen, oxygen enriched gas, air, and exhaust gas containing oxygen
from other plants. And also these oxygen containing gas can be used
by diluting with inactive gas. The air is inexpensive and
advantageously used. The activated carbon may be liable to be
combusted and/or the catalytic activity may be deteriorated by
using oxygen enriched gas containing 50 vol % or more of oxygen
concentration and pure oxygen. The activated carbon may not be
combusted and the solubility of oxygen in the waste water is
increased by using oxygen enriched gas containing preferably less
than 40 vol %, and more preferably less than 35 vol % of the oxygen
concentration. Thereby this invention enjoys the improved wet
oxidation performance. A production process for preparing the
oxygen enriched gas suitable for the present invention is not
specifically limited but can be exemplified such as chilled method,
PSA method. As an process for preparing the oxygen enriched gas
with less cost and simple safe operation, oxygen enrichment
membrane is preferably employed to regulate the oxygen
concentration. Instead of using the oxygen containing gas, hydrogen
peroxide aqueous solution can be used.
[0101] According to the present invention, stable and efficient
treatment of the waste water can be achieved with any gas-liquid
flow type at the catalyst bed as long as the oxygen concentration
in the exhaust gas is maintained within the range from 0 to 5 vol
%. Among them, gas-liquid concurrent descending such as shown in
FIG. 1 and FIG. 3 is recommended. The gas-liquid concurrent
descending promotes gas-liquid contact rate which resulted in
increasing oxygen dissolving amount in the waste water and in
inclreasing the treatment efficiency. With gas-liquid concurrent
flow, the waste water containing plenty of oxidizable substances is
contacted with the gas having high oxygen concentration at the
entrance of the catalyst bed and which prevents the activated
carbon from being combusted. On the contrary, with gas-liquid
countercurrent flow, the waste water containing reduced amount of
oxidizable substances is contacted with the gas having high oxygen
concentration at the exist of the catalyst bed which may cause the
activated carbon to be combusted and the catalytic activity may
suffur unduly deterioration.
[0102] Further more, when the wet oxidation is conducted under
pressure in the range from atmospheric pressure to 1 MPa (Gauge)
with gas-liquid concurrent ascending flow in the reactor such as
shown in FIG. 2, the oxygen supply amount is preferably 1.5 times
or more and more preferably 2.0 times or more of the theoritical
oxygen demand for promoting the treatment efficiency. Thereby the
gas-liquid concurrent ascending flow may be unsuitable for
improving the treatment efficiency when using the present inventive
catalyst with the gas having oxygen concentration in the range from
0 to 5 vol %.
[0103] The term "theoretical oxygen demande" means an amount of
oxygen required for decomposing/oxidizing the oxidizable substances
in the waste water into such as water, carbon dioxide gas, nitrogen
gas, inorganic salts, ash content and so on.
[0104] According to the present invention, the method of supplying
oxygen containing gas is not specifically limited and as an
example, all the amount of the oxygen containing gas can be
supplied from the upstream of the catalyst bed entrance and more
preferably, supplying the oxygen containing gas from at least two
location by dividing the total amount of the gas into predetermined
ratio (herein after may be referred to as "dividing method"). The
dividing method reduces the total oxygen containing gas supply
amount compared with the supply amount of the non-dividing method.
Thereby activated carbon can be prevented from being combusted and
the wet oxidation enjoys improved catalytic activity. In the
treatment with dividing method, the present inventive catalyst
manifests satisfactory durability and treats the waste water with
high satiability for a long period. When utilizing the dividing
method, the oxygen containing gas can be supplied at any location
and recommended are supplying the oxygen containing gas at least
from the upstream of the catalyst bed entrance and from the midway
of the catalyst bed. The supply amount at each location is not
specifically limited but the concentration of the oxygen at the
supply means for supplying the oxygen containing gas to the midway
of the catalyst bed is preferably in the range from 0 to 5 vol %
and more preferably from 0 to 3 vol %. With the decrease in oxygen
concentration, the catalyst manifests satisfactory durability for a
long period.
[0105] Further more, when utilizing the dividing method, the amount
of the oxygen containing gas supplied to the midway of the catalyst
bed can be predetermined by measuring the concentration of the
oxygen in the gas which is to be supplied. The concentration of the
oxygen may be different from the concentration at each gas
supplying location.
[0106] The term "oxidation/decomposition treatment" includes
variety of oxidation and/or decomposition of substances contained
in the waste water such as decomposing easily decomposable
substances into nitrogen gas, carbon dioxide gas, water and ash
content; and oxidizing/decomposing hard to decomposable substances
such as organic compounds and nitrogen compounds into low molecular
weight compounds. More specifically, oxidizing/decomposing acetic
acid into water and carbon dioxide; decarboxylation/decomposition
of acetic acid into carbon dioxide and methane, hydrolysis of urea
into ammonia and carbon dioxide; oxidizing/decomposing ammonia and
hydrazine into nitrogen gas and water; oxidizing/decomposing
dimethyl sulfoxide into carbon dioxide, water, and ash content such
as sulphate ion; oxidizing dimethyl sulfoxide into dimethyl sulfone
and methane sulfoxide are exemplified.
[0107] According to the present inventive method, the activated
carbon may suffer decrease in mechanical strength and the activated
carbon may be liable to be combusted by passing the water having
temperature of 50.degree. C. or more through the catalyst bed with
the supply of oxygen containing gas. And thus obtained catalyst may
exhibit insufficient catalytic activity for treating the waste
water. For obtaining sufficient catalytic activity and the
durability of the catalyst even if the temperature of the reactor
exceeds 50.degree. C. at the time of starting up the wet oxidation
operation and at the time suspending the operation, supplying or
circulating a liquid containing oxidizable substances is
recommended and the liquid is preferably exchanged with waste water
before the temperature reaches 50.degree. C.
[0108] The treated water may be given an aftertreatment by the
conventional purifying method.
[0109] The oxidizable substances such as organic acid (e.g. acetic
acid) and ammonia contained in the treated water can be treated by
using reverse osmosis membrane having high salt rejection rate
(e.g. polyamide type composite membrane). The reverse osmosis
membrane is able to remove oxidizable substances from the treated
water, and thus obtained permeated liquid is highly purified.
Impermeated liquid contains concentrated oxidizable substances and
which can be purified by the conventional purifying method or by
recycling to the wet oxidation treatment.
[0110] According to the present invention, the durability of the
catalyst can be increased by packing the present inventive catalyst
into plurality of containers when charging the catalyst in the
reactor and/or when taking out the catalyst from the reactor. In
the method for treating the waste water by catalytic wet oxidation,
catalytic reaction is facilitated excessively at the catalyst bed
entrance compared with the catalytic reaction at the catalyst bed
exit. At the catalyst bed entrance, hotspot (overheat) may be
generated by the excessive catalytic reaction and the catalyst may
suffer a decrease in its durability. By employing the plurality of
containers for charging the catalyst in the reactor, all the
catalyst charged in the reactor does not need to be exchanged with
new set of catalyst. The plurality of containers ease the catalyst
exchanging process and prolong the life span of the catalyst.
[0111] According to the present inventive waste water treatment
method, fluidized bed can be employed as the catalyst bed in the
reactor. The catalyst containing activated carbon enables to employ
the fluidized bed easily, which lowers the possibility of
generating the hotspot, compared with the fixed catalyst bed. The
fluidized bed is preferably employed for treating the waste water
having high oxidizable substance concentration compared with the
treatment utilizing fixed bed. The wet oxidation employing the
fluidized bed can treat the waste water containing certain
substances which may lower the durability of the catalyst while
replacing deteriorated catalyst with new catalyst. On the contrary,
in the wet oxidation using fixed catalyst bed, catalytic activity
may be deteriorated due to the fact that the active ingredient of
the catalyst moves to the rear side of the catalyst bed. The wet
oxidation employing fluidized bed can solve the problem reside in
the conventional wet oxidation by moving the catalyst itself. The
wet oxidation employing fluidized bed can adopt the catalyst having
smaller particle diameter compared with the conventional fixed
catalyst bed. The wet oxidation with the catalyst having smaller
particle diameter enjoys increased gas-liquid contact rate and
treats the waste water with high efficiency. Further more, the wet
oxidation employing fluidized bed enables to treat the waste water
containing small amount of solid matter which is hardly treated in
the fixed bed wet oxidation due to reactor clogging problem. The
wet oxidation employing the fluidized bed can treat wide variety of
waste water.
[0112] The number of the reactor employed for the wet oxidation is
not specifically limited when employing the fluidized bed but
considering the operational easiness and the operational cost,
utilizing one reactor with fluidized bed is recommended. The type
of the reactor is not specifically limited but the vessel type of
the reactor may be a reactor having single room for the treatment
or a reactor having multiple rooms for the treatment such as a
reactor having baffle plates. The reactor having multiple rooms
excels in wet oxidation performance and in operation control.
[0113] As the waste water to be treated in the wet oxidation
according to the present invention, any waste water that contains
organic compounds and/or nitrogen compounds can be treated, and for
example, waste water discharged from various industrial plants such
as chemical plants, electronic parts, manufacturing plants, food
processing plants, metal processing plants, plating plants,
printing plate making plants, photographic processing plants,
electric power plants (e.g. heat power plants and atomic power
plants) can be used. To be more specific, waste water discharged
from electrooculography (EOG) manufacturing plants and alcohol
production plants such as methanol, ethanol, and higher alcohol is
exemplified. Especially, waste water containing organic compounds
such as discharged from production plants of aliphatic carboxylic
acids (e.g. acrylic acid, acrylic ester, methacrylic acid,
methacrylic ester or esters thereof), aromatic carboxylic acids
(e.g. terephthalic acid and terephthalic ester and aromatic
carboxylic acid esters). It also may be waste water containing
nitrogen compounds such as amine, imine, ammonia and hydrazine, or
waste water containing sulfur compounds such as thiosulfuric acid
ion, sulfide ion and dimethyl sulfoxide. Further more, waste water
can be domestic waste water such as sewage and excrements can be
used. In addition, it may be waste water containing organic
halogenated compounds and environmental hormones such as dioxins,
flons, diethyl hexyl phthalate, and nonyl phenol.
[0114] The pH value of the waste water to be treated is not
specifically limited and can be suitably adjusted as long as the pH
value is in the range from 1 to 14.
[0115] The deterioration of the catalytic activity of the present
inventive catalyst can be suppressed effectively by supplying
catalyst protection liquid which contains easily decomposable
substances at the time of temperature rising when starting up a
operation of the wet oxidation and/or at the time of temperature
lowering when suspending the operation. The catalyst protection
liquid needs to be supplied to the catalyst bed directly or
indirectly and the preferably supplying the enough amount of the
catalyst protection liquid so as to the easily decomposable
substances in the protection liquid is remained in the liquid
passed through the catalyst bed.
[0116] The oxygen may exist in the form of adsorbed state to the
catalyst or in the gaseous phase inside the catalyst bed. Even at
low temperature the oxygen in the catalyst bed is consumed by
oxidizing/decomposing the easily decomposable substances. Thus the
catalyst bed becomes oxygen deficiency state. The oxygen deficiency
state in the catalyst bed prevents the catalyst from being
combusted and the catalytic activity from being deteriorated.
[0117] Existence of the catalyst protection liquid may prevent the
catalyst from deterioration of its durability caused by the heat.
After pre-heating the wet oxidation unit, the protection liquid is
exchanged with the waste water to be treated before starting up the
wet oxidation operation. If the protection liquid is remained in
the catalyst bed before starting up the operation, initial reaction
of the wet oxidation is facilitated.
[0118] If the catalyst bed is free from the protection liquid at
the time of starting up the wet oxidation operation, the catalyst
may be liable to be combusted due to excessive oxygen whereby the
waste water treatment may suffer incomplete purification of the
waste water at the initial stage thereof.
[0119] If the waste water is exchanged with the protection liquid
at the time of suspending the wet oxidation operation, the waste
water treatment enjoys complete purification of the waste water at
the end of the operation and thus obtained highly purified waste
water contains almost no harmful substances contained in the waste
water. Further more, if the wet oxidation operation is suspended
without exchanging the waste water with the protection liquid, the
activity of the catalyst may be decreased, and the oxidizable
substances are not fully decomposed at the end of the operation,
furthermore, the waste water treatment at the beginning of the
following wet oxidation operation may be deteriorated.
[0120] The deterioration of the catalytic activity can be
suppressed by increasing the contact rate of the catalyst with the
easily decomposable substances throughout the catalyst bed even if
insufficient amount of the protection liquid is remained at the
exit of the catalyst bed. The deterioration of the catalytic
activity can be suppressed without protecting all the catalyst in
the catalyst bed if the amount of oxygen remained at the end half
of the catalyst bed, where the easily decomposable substances are
diminished, is in small quantity.
[0121] The method for protecting the catalyst is applied to the wet
oxidation operation at the time of temperature rising when starting
up the operation and/or at the time of temperature lowering when
suspending the operation. And also aforementioned catalyst
protecting method can be applied when maintaining the temperature
of the wet oxidation unit (e.g. reactor) during which the waste
water is not supplied to the reactor. Accordingly the term starting
up the operation and suspending the operations includes the time
"maintaining the temperature of the wet oxidation".
[0122] In the aforementioned catalyst protecting method, the
temperature at which the protection liquid is supplied has no
particular restriction but considering the object of the inventive
protection method, the liquid is preferably supplied to the heated
catalyst bed. Especially, the catalyst protection method is to
protect the catalyst at the time of temperature rising when
starting up the operation and/or at the time of temperature
lowering when suspending the operation. In this case, the
temperature of supplying the protection liquid is lower than the
temperature of treating the waste water. The protection liquid is
preferably supplied before the temperature reached at 50.degree.
C., and more preferably at 60.degree. C. When the temperature is
lower than the temperature at which waste water is treated within
5.degree. C., the protection liquid is preferably exchanged with
the waste water. Therefore the protection liquid is preferably
supplied before the temperature reached at 50.degree. C., and more
preferably at 60.degree. C. when starting up the operation with
pre-heating the unit. Also, the waste water is preferably exchanged
with the protection liquid shortly after suspending the operation
and the protection liquid is preferably supplied continuously until
the temperature decreased to 50.degree. C. or less and more
preferably 60.degree. C. or less.
[0123] The same pressure value for treating the waste water is
preferably applicable as the pressure for supplying the protection
liquid as long as the protection liquid maintains its liquid
phase.
[0124] According to the inventive catalyst protection method, the
protection liquid can be supplied without supplying oxygen
containing gas to the catalyst bed at a time when starting up the
operation and/or when suspending the operation. The pressure may be
difficult to control without the presence of the gas and the
unstable pressure may brought adverse effect on the catalyst. By
supplying the gas from downstream of the catalyst bed, the pressure
inside the reactor can be maintained and the stable pressure
control can be attained. With utilizing this technique, the
deterioration of the catalytic activity is efficiently suppressed
since oxygen is not provided to the catalyst bed. The gas used for
treating waste water such as oxygen containing gas is preferably
employed as a gas for the protective method in view of the economic
efficiency and the operational easiness.
[0125] After suspending the operation and during storage of the
catalyst, it is preferable to keep the catalyst in the low oxygen
concentration atmosphere. When the catalyst is kept in the reactor
after suspending the operation, decreasing the oxygen concentration
in the reactor is recommended. And more preferably, with the
decrease of oxygen concentration, the protection liquid is present
in the reactor.
[0126] The liquid to be used as the protection liquid is not
specifically limited as long as the liquid contains easily
decomposable substances. The easily decomposable substances herein
means the substances which can be easily oxidized/decomposed by the
present inventive catalytic wet oxidation at temperatures in the
range from 50.degree. C. to less than 170.degree. C., preferably in
the range of form 50.degree. C. to less than 140.degree. C., more
preferably in the range from 50.degree. C. to less than 120.degree.
C., further preferably in the range from 50.degree. C. to less than
100.degree. C. and most preferably in the range form 50.degree. C.
to less than 90.degree. C.
[0127] And also the pH value of the protection liquid is preferably
in the neutral zone. If the pH value of the liquid is acidic or
alkaline zone, a problem of corrosion and deterioration of the unit
or the catalyst may be occurred. As the protection liquid, liquid
containing alcohol is preferably employed. Specifically, the liquid
may contains alcohol such as methanol, ethanol, and propanol and
also the liquid may contains glycol or glycerine. For obtaining
better result the liquid is desired to be decomposed easily by the
above mentioned condition, such as alcohol having 1 to 4 carbon
atoms per molecule are preferably used, more preferably methanol,
ethanol, and propanol, and most preferably methanol. The waste
water containing methanol can be treated in the present inventive
method and the waste water to which methanol is added can be
treated. It should be noted that the protection liquid is not
intended to limit to the above exemplified liquid and variety of
liquid containing easily decomposable substances. As further
examples, organic compounds such as acetaldehyde, formaldehyde,
acetone, tetrahydrofuran, phenol and formic acid; also inorganic
compounds such as sodium sulfite, sodium hydrogen sulfite can be
counted as easily decomposable substances.
[0128] The concentration of the protection liquid, which is to be
supplied, is not specifically limited but the concentration in
terms of COD(Cr) is preferably in the range from 0.1 to 50 g/L, and
more preferable lower limit is 0.5 g/L and more preferable upper
limit is 30 g/L. If the concentration is less than 0.1 g/L, the
catalyst protecting effect brought by the protection liquid may be
decreased. If the concentration excels 50 g/L, the treatment may
incur heavy cost with the increase of the oxidizable substances in
the protection liquid.
[0129] Also the concentration of the protection liquid after passed
through the catalyst bed is not specifically limited but the
protecting effect brought by the protection liquid is increased if
the oxidizable substances in the protection liquid is remained in
the liquid passed through the catalyst bed. The preferable
concentration of the oxidizable substances in the liquid passed
thorough the catalyst bed is in the range from 0.05 to 50 g/L
(COD(Cr)), more preferable lower limit is 0.1 g/L, and more
preferable upper limit is 30 g/L. If the concentration is less than
0.05 g/L, the catalyst protecting effect may be decreased. If the
concentration excels 50 g/L, the treatment may incur heavy cost and
aftertreatment of the liquid may be needed.
[0130] The method of supplying the protection liquid at the time
when starting-up the operation with pre-heating the unit is not
specifically limited. Easily oxidizable substances dissolved in
water may be supplied to the wet oxidation unit directly via pump
(e.g. pump 5 in FIG. 1) or may be added to waste water in the waste
water reserve tank (not shown) and supplying thus easily oxidizable
substances added waste water to the wet oxidation unit. The method
of supplying the protection liquid at the time when suspending the
operation with cooling down the unit is not specifically limited.
the easily oxidizable substances dissolved in water may be supplied
to the wet oxidation unit via the pump 5 shortly after suspending
the supply of the waste water. The protection liquid can be
supplied from the upstream of the wet oxidation unit via another
pump which is different from the pump used for feeding the waste
water.
[0131] The space velocity at the catalyst bed (namely passing rate
of the protection liquid through the catalyst bed) is not
specifically limited, and the same condition with the space
velocity for treating waste water can be applicable. The space
velocity (LHSV) at the catalyst bed is preferably in the range from
0.1 hr.sup.-1 to 10 hr.sup.-1, more preferably from 0.1 hr.sup.-1
to 5 hr.sup.-1, and most preferably from 0.1 hr.sup.-1 to 3
hr.sup.-1. If the space velocity is less than 0.1 hr.sup.-1,
excessive time, which is commercially unacceptable, may be needed
for obtaining sufficient protecting effect. If the space velocity
exceeds 10 hr.sup.-1, large amount of the protection liquid may be
needed for obtaining sufficient protecting effect.
[0132] Spent protection liquid may contains easily decomposable
substances. When spent protection liquid contains easily
decomposable substances, the spent protection liquid may be given
an aftertreatment such as conventional purifying method (e.g.
biological treatment and chemical treatment) before dumping. As an
aftertreatment, the spent protection liquid can be treated
with/without the waste water by the present inventive wet oxidation
by adding to the waste water reserve tank. The spent protection
liquid can be reused as a protection liquid.
[0133] When starting-up the operation with pre-heating the unit
and/or when suspending the operation with cooling down the unit,
the concentration of oxygen in the exhaust gas (a gas passed
through the catalyst bed) is preferably maintained in the range
from 0 to 5 vol %. The oxidation concentration in this range
suppresses the deterioration of the catalytic activity and gives an
effective protecting effect at the time of temperature rising when
starting up a operation and/or at the time of temperature lowering
when suspending the operation. If the concentration exceeds 5 vol
%, the activated carbon may be liable to be conbusted by
oversupplied oxygen. Accordingly the wet-oxydation is preferably
conducted with supplying enough oxygen for oxdizing/decomposing the
oxydizable substances. The closer to 0 vol % of the oxygen
concentarion, the better protecting effect can be obtained. The
most preferable lower limit is 0 vol %. Also, preferable upper
limit of the concentration is 4 vol %, more preferably 2 vol % and
most preferably 1 vol %. If the pressure of the unit can maintains
at certain level needed for operating the wet oxidation, less
amount of oxygen is preferably supplied for surpressing the
degradation of the catalitic activity. It should be noted that if
the oxygen containing gas is under supplied, difficulty may arise
when the protection liquid is exchanged with the waste water at the
time starting-up the operation. And in this case, the treatment of
the oxidizable substances in the waste water will be effected with
undly low efficiency and the purification of the waste water may be
attained incompletely.
[0134] If the temperature at which the protection liquid is
supplied is unduly low compared with the catalyst bed temperature
at which the waste water is treated when starting-up the operation
and/or when suspending the operation, the radical deterioration of
the catalytic activity is surprised even if oxygen is present in
the catalyst bed. Therefore when the temperature is less than
50.degree. C., and in most cases less than 60.degree. C., the
oxygen concentration in the exhaust gas can exceed 5 vol % and the
catalyst bed can be free from the protection liquid. If the
temperature at which the waste water is treated exceeds 90.degree.
C., the oxygen concentration in the exhaust gas can exceed 5 vol %
without deteriorating the catalytic activity within short period
(i.e. within 24 hours, more preferably 12 hours) at the temperature
in the range from 50.degree. C. to less than 80.degree. C. under
the condition that the protection liquid is existed in the catalyst
bed.
[0135] The concentration of oxygen can be suitably adjusted within
above mentioned range with variety of method, for example the
concentration meter 16 can be employed for measuring the
concentration of the oxygen in the exhaust gas and the oxygen
supply amount can be controlled by valve 9 based on the result
obtained from the concentration meter 16. And aforementioned
concentration meter can be employed.
[0136] The term "oxygen concentration in the exhaust gas" herein
means the oxygen concentration in the gas phase passed through the
catalyst bed when starting-up the operation and/or suspending the
operation. In general, the oxygen concentration is obtained by
measuring the oxygen concentration in the gas-liquid separator as
shown in FIG. 1.
[0137] The catalyst protection treatment can be conducted
with/without supplying oxygen containing gas. Small amount of the
oxygen containing gas is preferably supplied when operating the
catalyst protection treatment. In general, the waste water
treatment is operated with the application of pressure, the
pressure inside the reactor need to be maintained to some extent
when starting-up the operation and/or when suspending the
operation. Supplying small amount of gas is recommended for
maintaining the pressure stably.
[0138] In stead of the oxygen containing gas, oxygen free gas such
as nitrogen gas and inert gas can be employed. The oxygen
containing gas used for treating waste water is preferably employed
for economic efficiency and for process easiness.
[0139] The oxygen concentration in the exhaust gas during the
protecting treatment is preferably in the range of form 0 to 5 vol
%. The preferable condition for controlling the oxygen
concentration within the rang from 0 to 5 vol % is to set [oxygen
amount in the gas supplied]/[oxygen demand in the protection liquid
at maximum catalyst protecting efficiency] (hereinafter may be
referred to as "D1 value")=0 to 1.3. The deterioration of the
catalytic activity can be remarkably suppressed by controlling the
oxygen supply amount to the aforementioned D1 value. And also, it
is preferable to control the protection liquid supply amount so as
to easily decomposable substances are remained in the liquid passed
through the catalyst bed. If the D1 value=1.0 to 1.3, the easily
decomposable substances may not be remained in the liquid passed
through the catalyst bed. If the D1 value exceeds 1.0, especially
exceeds 1.3, the oxygen supply amount may be increased for
oxidizing/decomposing the easily decomposable substances contained
in the protection liquid and also the activated carbon may be
liable to be combusted by the oversupplied oxygen. For avoiding
these problems, preferable upper limit is 0.8, more preferably 0.6
and most preferably 0.4.
[0140] [oxygen demand in the protection liquid at maximum catalyst
protecting efficiency] is measured by changing the oxygen
containing gas supply amount under the fixed condition of the
temperature, pressure, LHSV, gas-liquid current type, and the
catalyst. In other words, [oxygen demand in the protection liquid
at maximum catalyst protecting efficiency] means required oxygen
amount of the protection liquid when the protection treatment
efficiency rate indicates its maximum efficiency rate under above
condition. The D1 value can be used as an index for indicating
excess and deficiency of the oxygen supply amount. The maximum
catalyst protecting efficiency is changed with the change in
temperature according to the present invention. The highest
temperature of supplying the protection liquid is employed for
measuring the D1 value. According to the present invention, the
higher the temperature, the better the catalyst protecting
efficiency is obtained. The D1 value can be used as an index for
indicating excessive rate of oxygen supply amount when conducting
the catalyst protecting treatment. The concept of D1 value is the
same as the concept of aforementioned D value.
[0141] According to the present inventive method,
oxidation/decomposition performance deteriorated catalyst can be
recovered efficiently by supplying a catalyst recovering liquid
which contains easily decomposable substances under temperatures in
the range from 55.degree. C. to less than 200.degree. C.
[0142] For recovering the deteriorated catalyst, supplying the
recovering liquid containing easily decomposable substances to the
catalyst bed is needed according to the present invention. And the
supply amount of the recovering liquid is preferably controlled so
as to the easily oxidizable substances in the liquid are remained
in the liquid passed through the catalyst bed. The deterioration of
the catalytic activity is caused by the following reason.
[0143] 1) The catalyst, especially activated carbon is liable to be
oxidized by oxygen existed in the form of adsorbed state to the
catalyst or in the gas phase inside the catalyst bed.
[0144] 2) The catalytic activity is deteriorated by being covered
its active site by hard to decompose oxidizable substances
contained in the waste water when conducting the waste water
treatment for a long period.
[0145] According to the present inventive catalyst recovering
method, the catalyst property can be modified by contacting the
recovering liquid with the catalyst. And also the recovering liquid
exhibits the effect of removing adsorbed substances from the active
site easily. To be more specific, the recovering liquid is
decomposed by heat and thus obtained heat decomposed substances of
the recovering liquid facilitates desorping the adsorbed substances
from the active site by decomposing the adsorbed substances thereof
under the oxygen deficiency condition or without supplying oxygen
containing gas. And also, easily decomposed substances in the
recovering liquid is readily oxidized with the supply of oxygen
containing gas and the oxidation readiness property of the
recovering liquid facilitates the catalytic reaction. With the
oxidation of the substances in the recovering liquid, the hard to
decomposed substances adsorbed to the catalyst is easily
oxidized/decomposed and removed form the active site. For improving
the aforementioned effect, the supply amount of the recovering
liquid is preferably controlled so as to the easily oxidizable
substances in recovering liquid are remained in the liquid passed
through the catalyst bed. If the easily oxidizable substances are
not remained in the liquid passed through the catalyst bed,
aforementioned effect may not be attained. By employing the present
inventive catalyst recovering method, the catalytic activity is
protected by the recovering liquid from deterioration when
conducting the catalyst recovering process under high temperature.
With the present inventive recovering method, the catalytic
activity is improved by the recovering liquid.
[0146] The catalytic activity can be recovered to a certain level
by contacting the recovering liquid with the most part of the
catalyst bed even if the easily oxidizable substances do not remain
in the liquid passed through the catalyst bed. It should be noted
that all the catalyst in the catalyst bed dose not need to be
recovered for improving the waste water treatment efficiency. The
waste water treatment efficiency can be improved by recovering the
enough amount of the catalyst to meet the supply amount of the
easily decomposable substances in the waste water.
[0147] The liquid to be used as the recovering liquid is not
specifically limited as long as the liquid contains easily
decomposable substances. The liquid used for protection liquid can
be preferably used as the recovering liquid.
[0148] The concentration of the recovering liquid, which is to be
supplied, and the concentration of the recovering liquid after
passed through the catalyst bed is not specifically limited. The
concentration of aforementioned protection liquid is preferably
applied to the concentration of the recovering liquid.
[0149] The method of supplying the recovering liquid and the
aftertreatment of spent recovering liquid are not specifically
limited and aforementioned protection liquid supply method and
spent protection liquid aftertreatment are preferably applied.
[0150] And the recovering operation can be conducted with/without
supplying oxygen containing gas. The condition of aforementioned
protecting operation is preferably applied to the recovering
operation.
[0151] The oxygen concentration in the exhaust gas during the
recovering operation is preferably in the range form 0 to 5 vol %.
The preferable condition for adjusting the oxygen concentration in
the rang from 0 to 5 vol % is to set [oxygen amount in the gas
supplied]/[oxygen demand in the recovering liquid at maximum
catalyst recovering efficiency] (hereinafter may be referred to as
"D2 value")=0 to 1.3. The regenerating effect can be improved by
adjusting the oxygen supply amount to the aforementioned D2
value.
[0152] According to the recovering operation, if the D2 value=1.0
to 1.3, the easily decomposable substances may not be remained in
the liquid passed through the catalyst bed. If the D2 value exceeds
1.0, and especially exceeds 1.3, the oxygen supply amount is
increased for oxidizing/decomposing the easily decomposable
substances contained in the recovering liquid and also the
activated carbon may be liable to be combusted by the oversupplied
oxygen. For avoiding these problems, the preferable upper limit is
0.8, more preferably 0.6 and most preferably 0.4. It should be
noted that excess amount of oxygen may be required for decomposing
the oxidizable substances adsorbed to the activated carbon which is
formed during the long period of waste water treatment operation.
Therefore it is effective to change the oxygen supply amount during
the recovering operation. Namely, at the initial stage of the
recovering operation, adjusting the oxygen supply amount to obtain
D2=1.0 to 1.3 is recommended. And at the end stage of the
recovering operation, adjusting the oxygen supply amount to obtain
D2=0 to 1.0, preferably D2=0 to 0.8, and more preferably D2=0 to
0.4 is recommended.
[0153] The [oxygen demand in the recovering liquid at maximum
catalyst recovering efficiency] is measured by changing the oxygen
containing gas supply amount under the fixed condition of the
temperature, the pressure, LHSV, gas-liquid current type, and the
catalyst. In other words, [oxygen demand in the recovering liquid
at maximum catalyst recovering efficiency] means required oxygen
amount of the recovering liquid when the recovering treatment
efficiency rate indicates its maximum efficiency rate under above
condition. The maximum catalyst recovering efficiency may not be
changed with the change in temperature according to the present
invention if the most oxidizable substances contained in the
recovering liquid are easily oxidizable substance. If this is the
case, the recovering efficiency rate is changed in accordance with
the oxygen supply amount. That is, when the oxygen supply amount is
constant, D2 value may not be changed even if the temperature is
changed. The D2 value can be used as an index for indicating
excessive amount rate of the oxygen supply amount. The concept of
D2 value is the same as the concept of aforementioned D and D1
value.
[0154] The temperature of supplying the recovering liquid is
preferably higher than the temperature at which waste water is
treated about from 5 to 100.degree. C., preferably from 10 to
60.degree. C., and more preferably 15 to 40.degree. C. It should be
noted that the operation is conducted less than 200.degree. C. If
the temperature exceeds 200.degree. C., activated carbon may be
liable to be combusted and the catalyst may suffer a decrease in
catalytic activity. Accordingly preferable upper limit is at
170.degree. C., more preferably at 160.degree. C. and most
preferably at 50.degree. .degree. C.
[0155] The heat treatment time is not specifically limited. The
heat treatment may be conducted about from 1 to 100 hours,
preferably from 3 to 50 hours, and more preferably from 5 to 24
hours.
[0156] And also for recovering the catalyst containing (a)
component and (b) component, reduction treatment can be applied to
the catalyst at higher temperature than the temperature mentioned
above. To be more specific, reduction treatment can be conducted
under oxygen containing gas deficiency state or without supplying
oxygen containing gas at the temperature less than 300.degree.
C.
[0157] The recovering operation may need to be conducted at high
temperature for decomposing the oxidizable substances adsorbed to
the activated carbon which is formed during the long period of
waste water treatment operation. Therefore it is effective to
change the temperature within above mentioned recovering operation
temperature during the recovering operation.
[0158] Namely, preferably 20 to 100.degree. C., more preferably 25
to 80.degree. C. and most preferably 30 to 60.degree. C. added
temperature to the temperature at which waste water is treated is
preferably employed at the initial stage of the recovering
operation as long as the temperature remains above mentioned
recovering operation temperature and the temperature at the end
stage of the recovering operation is preferably selected in the
range from lower than the temperature at the initial stage of the
recovering operation. And most preferably selected in the range
from higher than the temperature at which waste water is treated
and lower than the temperature at the initial stage of the
recovering operation. It has no particular restriction except for
the requirement that the sufficient pressure is applied for
enabling the recovering liquid to retain the liquid phase
thereof.
[0159] Hereinafter, the present invention will be further
illustrated in detail with reference to several inventive examples
and comparative examples below, which are not directed to limiting
the scope of the invention.
EXAMPLES
Example 1 to 5
[0160] 500 hours of waste water treatment was performed under the
following conditions with using the equipment illustrated in FIG.
1. A reactor 1 having cylindrical shape (a diameter of 26 mm.phi.
and a length of 3000 mm) was used in the treatment. Into the
reactor, loaded were 1 liter (380 g) of pellet type solid catalysts
having a diameter of 4 mm .phi. to give a catalyst bed height of
1880 mmH. The solid catalyst had activated carbon and platinum as
main components and included 0.3 mass % of platinum with respect to
the total amount of the solid catalyst. In addition, as the waste
water to be treated in the present examples, used was waste water
exhausted by manufacturing facilities of aliphatic carboxylic acids
and aliphatic carboxylate. The waste water contained organic
compounds having 2 or more carbon atoms per molecule such as
alcohol, aldehyde and carboxylic acid. The COD (Cr) concentration
of the waste water was 20000 mg/liter and pH thereof equaled 2.8.
In addition, 55% of the total TOC component was acetic acid. This
waste water did not include any of alkali metal ion, ammonium ion
and inorganic salt.
[0161] The aforementioned waste water was fed with pressure rising
by waste water feed pump 5 at the flow rate of 1 liter/h.
Subsequently, the waste water was heated up to 120.degree. C. by
heater 3 and then supplied to reactor 1 from its upside to make a
gas-liquid downward concurrent flow for the treatment. Air was also
introduced through oxygen-containing gas supply line 8, followed by
being compressed by compressor 7. The oxygen-containing gas (air)
was then supplied to the waste water according to the ratios shown
in table 1 prior to the waste water was heated by to heater 3.
[0162] In reactor 1, the waste water temperature was maintained to
be 120.degree. C. by electric heater 2 to perform
oxidation/decomposition treatments. The obtained treated water was
cooled to 30.degree. C. by cooler 4. Subsequently, it was exhausted
through pressure control valve 12 with its pressure being
recovered, followed by separating gas from liquid in the exhausted
water by gas-liquid separator 11. In this process, at pressure
control valve 12, pressure controller PC detected and controlled
the pressure in reactor 1 to keep the pressure at 0.5 MPa (Gauge).
In addition, oxygen concentration of the exhaust gas in gas-liquid
separator 11 was measured by using oxygen content meter 16. The COD
(Cr) concentration of the treated water in gas-liquid separator 11
was also measured. On temperature rising in reactor 1, the waste
water was supplied to reactor 1 under the condition of oxygen
deficiency in order to suppress deterioration of the catalyst
therein.
[0163] The results were shown in table 1. In examples 2 to 5, the
waste water treatments was continued for evaluation of the catalyst
durability even after the treatment time reached 500 hours and then
about 5000-hour endurance test were conducted. After 5000-hour
treatment, the catalyst was extracted from the reactor to be
observed. As a result, it was found that any catalyst in these
examples stayed unchanged after the treatments.
Example 6
[0164] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 4, except that the treatment temperature
was set to 140.degree. C. This result was also shown in table 1. In
addition, after 5000-hour treatment, the catalyst was extracted
from the reactor to be observed. As a result, it was found that the
catalyst in this experiment stayed unchanged after the
treatment.
Example 7
[0165] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 1 except for the following 3 points: 1) the
treatment temperature was set to 95.degree. C.; 2) the treatment
pressure was set to the atmosphere pressure; and 3) the supply
amount of oxygen-containing gas was adjusted to 0.40 in term of
O.sub.2/COD. This result was also shown in table 1. In addition,
after 5000-hour treatment, the catalyst was extracted from the
reactor to be observed. As a result, it was found that the catalyst
in this experiment stayed unchanged after the treatment.
1TABLE 1 COD(Cr) COD(Cr) Treatment Treatment Efficiency Efficiency
After Oxygen After 500 Hour Concentration 5000 Hour Treatment In
Exhaust Treatment O.sub.2/COD D Value (%) Gas (vol %) (%) Example
0.75 0.79 77 0 -- 1 Example 0.85 0.89 86 0 86 2 Example 0.95 1.00
95 0.2 95 3 Example 1.00 1.05 93 1.5 92 4 Example 1.10 1.15 93 3.5
90 5 Example 1.00 1.00 99.8 0 94 6 Example 0.40 1.03 39 0.5 39
7
Comparative Example 1
[0166] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 3, except for setting the treatment
temperature to 200.degree. C. and the treatment pressure to 3 MPa
(Gauge). In this treatment, the supply amount of oxygen-containing
gas was adjusted to satisfy O.sub.2/COD=0.95 and D value=0.95 (that
is, in case of O.sub.2/COD=1.0, the initial COD (Cr) treatment
efficiency under the treatment conditions equaled to 100%).
[0167] Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 95% and the oxygen concentration in the
exhaust gas was 0 vol %. This waste water treatment was continued
for evaluation of the catalyst durability. As a result, after about
450-hour treatment, it was observed that the catalyst was flowing
out along with the treated water through the liquid vent of the wet
oxidation treatment equipment. The pressure rising was also
observed according to the pressure gauge indicator PI that was
provided on the gas-liquid inlet side of reactor 1. For these
reasons, the treatment was stopped to extract the catalyst from the
reactor. Consequently, it was observed over the catalyst bed that
the catalyst had lost its shape and the amount thereof had
decreased.
Comparative Example 2
[0168] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 1, except that the supply amount of
oxygen-containing gas was adjusted to satisfy O.sub.2/COD=1. 5 and
D value=1.6.
[0169] Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 86% and the oxygen concentration in the
exhaust gas was 9.5 vol %. This waste water treatment was continued
for evaluation of the catalyst durability. As a result, the COD
(Cr) treatment efficiency after 500-hour treatment was 30%.
Therefore, the treatment was stopped to extract the catalyst from
the reactor. Consequently, it was observed over the catalyst bed
that the catalyst had lost its shape and the amount thereof had
decreased.
Example 8
[0170] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 1, except that the supply amount of
oxygen-containing gas was adjusted to satisfy O.sub.2/COD=0.2 and D
value=0.21.
[0171] Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 20% and the oxygen concentration in the
exhaust gas was 0 vol %. This waste water treatment was continued
for evaluation of the catalyst durability. As a result, the COD
(Cr) treatment efficiency after 500-hour treatment was 20%.
[0172] In this example, the treatment efficiency was low resulting
from oxygen deficiency due to such a small supply amount of oxygen
containing gas. However, the catalyst deterioration was not
observed. In addition, after this treatment, the oxygen containing
gas supply amount was increased to the same amount as that in
example 3. This resulted in 95% of COD (Cr) treatment efficiency of
the waste water.
Comparative Example 3
[0173] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 7, except that the supply amount of
oxygen-containing gas was adjusted to satisfy O.sub.2/COD=2.0 and D
value=5.1.
[0174] Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 39%. This waste water treatment was
continued for evaluation of the catalyst durability. As a result,
the COD (Cr) treatment efficiency after 1500-hour treatment was
27%. Therefore, the treatment was stopped to extract the catalyst
from the reactor. Consequently, it was observed over the catalyst
bed that the catalyst had lost its shape and the amount thereof had
decreased.
Example 9
[0175] A 500-hour treatment was performed under the following
conditions with using the equipment illustrated in FIG. 2. In the
treatment, reactor 21 had a cylindrical shape having a diameter of
26 mm.phi. and a length of 3000 mm. Into the reactor, loaded were 1
liter (380 g) of the same pellet type solid catalysts as the one
used in example 1 to give a catalyst bed height of 1880 mmH. In
addition, the same waste water as the one used in example 1 was
treated in the present example. Moreover, the same treatment
processes as the ones in example 3 were applied in the present
example, except that the supply port, through which the waste water
heated by heater 3 was supplied to reactor 21, was provided on the
bottom of reactor 21 and thereby the waste water treatment was
conducted in the state of gas-liquid upward concurrent flow. In
addition, the supply amount of oxygen-containing gas was adjusted
to satisfy O.sub.2/COD=0.95 and D value=1.12. Furthermore, the
maximum efficiency for treating the waste water was given when the
oxygen-containing gas was supplied with satisfying O.sub.2/COD=2.0
as described in comparative example 4. The treatment efficiency of
COD (Cr) in this case was 85%.
[0176] Consequently, the COD (Cr) treatment efficiencies after
100-hour and 500-hour treatments were 75% and the oxygen
concentrations in the exhaust gas were both 4.5 vol %. This waste
water treatment was continued for evaluation of the catalyst
durability even after the 500-hour treatment. Then about 2500-hour
endurance test were conducted, resulting in 69% of COD (Cr)
treatment efficiency. During the test, the oxygen concentration of
exhaust gas was gradually rising. The supply amount of air was
therefore reduced little by little to keep the oxygen concentration
of the exhaust gas at 4.5 volt.
Comparative Example 4
[0177] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 9, except that the supply amount of
oxygen-containing gas was adjusted to satisfy O.sub.2/COD=2.0 and D
value=2.35. Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 85% and the oxygen concentration of the
exhaust gas was 12 vol %. This waste water treatment was continued
for evaluation of the catalyst durability. As a result, the COD
(Cr) treatment efficiency after 500-hour treatment was 30%.
Therefore, the treatment was stopped to extract the catalyst from
the reactor. Consequently, it was observed over the catalyst bed
that the catalyst had lost its shape and the amount thereof had
decreased.
Comparative Examples 5 and 6
[0178] 100-Hour treatments were performed in the same manner
including the same treatment processes, treatment conditions and
equipment as in example 1 except for the following points: 1) 1
liter (1050 g) of pellet type solid catalysts having a diameter of
4 mm.phi. was loaded into reactor 1 to give a catalyst bed height
of 1880 mmH; and 2) the solid catalyst had titania and platinum as
main components and included 0.3 mass % of platinum. As a result,
the COD (Cr) treatment efficiency was too low and, in other words,
the waste water could not well-purified.
2 TABLE 2 COD(Cr) Oxygen Treatment Concentration In O.sub.2/COD
Efficiency (%) Exhaust Gas (vol %) Comparative 0.35 34 0.7 Example
5 Comparative 1.0 35 14 Example 6
Example 10
[0179] A 500-hour treatment was performed under the following
conditions with using the equipment illustrated in FIG. 3. The
equipment has a couple of front and back reactors as mentioned
above and thereby it is also possible to supply oxygen containing
gas through the portion between the front and back reactors. The
front reactor had a cylindrical shape having a diameter of 26
mm.phi. and a length of 3000 mm. The back reactor was also a
cylindrical shape having a diameter of 26 mm.phi. and a length of
3000 mm. Into each of the reactors, loaded were 1 liter of the same
solid catalyst as the one used in example 1. That is, 2 liters of
the catalyst was loaded totally. The treatment was performed in the
same manner including the same catalyst and treatment processes as
in example 3 except for setting the supply amount of the waste
water to 2 liter/hour and supplying the oxygen-containing gas to
the waste water in two stages as mentioned below.
[0180] In the method of supplying the oxygen-containing gas, air
was introduced though oxygen-containing gas supply line 8 and
compressed by compressor 7. The air was then supplied to the waste
water with satisfying the ratio of O.sub.2/COD=0.7 prior to the
waste water was heated by to heater 3. The air was further supplied
through the port between the front and back reactors with
satisfying the ratio of O.sub.2/COD=0.27.
[0181] Consequently, the COD (Cr) treatment efficiency after
500-hour treatment was 97% and the oxygen concentration in the
exhaust gas was 0.1 vol %. This waste water treatment was continued
for evaluation of the catalyst durability even after the 500-hour
treatment. Then about 5000-hour endurance test was conducted. The
obtained COD (Cr) treatment efficiency was also 97%. After
5000-hour treatment, the catalyst was extracted from the reactors
to be observed. As a result, the catalyst was found to stay
unchanged after this treatment. The D value at this point was
1.00.
Examples 11 and 12
[0182] 500-Hours treatments were performed under the following
conditions with using the same equipment as the one used in example
1. Into reactor 1, loaded were 1 liter (450 g) of pellet type solid
catalysts having a diameter of 3 mm.phi. to give a catalyst bed
height of 1880 mmH. The solid catalyst had activated carbon and
platinum as main components and included 0.6 weight % of platinum.
In addition, as the waste water to be treated in the present
examples, used was waste water exhausted by electric generating
plants. The waste water contained ammonium sulfate, sodium ion and
carbonic acid ion. The ammonium concentration of the waste water
was 4200 mg/liter and pH thereof equaled 7.8. The treatment was
performed in the same manner including the same treatment processes
and same equipment as in example 1 except for setting the treatment
temperature and pressure respectively to 130.degree. C. and 0.9 MPa
(Gauge) and supplying the oxygen-containing gas (air) according to
the ratios shown in table 3.
[0183] The results were also shown in table 3. The waste water
treatments were continued for evaluation of the catalyst durability
even after the 500-hour treatments and then about 2500-hour
endurance tests were conducted. After 2500-hour treatments, the
catalyst was extracted from the reactors to be observed. As a
result, it was found that any catalyst in these examples stayed
unchanged after the treatments.
Example 13
[0184] A treatment was performed in the same manner as in example
11 except for the following points: 1) 1 liter (430 g) of pellet
type solid catalysts having a diameter of 3 mm .phi. were loaded to
give a catalyst bed height of 1880 mmH; 2) the solid catalyst had
activated carbon and palladium as main components and contained 1.0
mass % of palladium. The result was also shown in table 3.
3TABLE 3 Ammonia Treatment Efficiency Ammonia Oxygen After
Treatment Concentration 2500 Hour Efficiency In Exhaust Treatment
O.sub.2/COD D Value (%) Gas (vol %) (%) Example 0.85 0.88 85 0 84
11 Example 0.98 1.01 97 0.25 96 12 Example 0.98 1.03 95 0.7 95
13
Comparative Example 7
[0185] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 11, except that the supply amount of
oxygen-containing gas was adjusted to satisfy O.sub.2/COD=1.5 and D
value=1.55. Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 97% and the oxygen concentration of the
exhaust gas was 8 vol %. This waste water treatment was continued
for evaluation of the catalyst durability. As a result, the COD
(Cr) treatment efficiency decreased to 73% after about 500-hour
treatment. Therefore, the treatment was stopped to extract the
catalyst from the reactor. Consequently, it was observed over the
catalyst bed that the catalyst had lost its shape and the amount
thereof had decreased.
Example 14
[0186] A 500-hour treatment was performed under the following
conditions with using the same type of the wet oxidation treatment
equipment as the one used in example 1. The equipment had
cylindrical reactor 1 having a diameter of 200 mm.phi. and a length
of 3000 mm. 60 Liters (24.6 kg) in total of pellet type solid
catalysts having a diameter of 5 mm.phi. were divided into 3
cassette cases (i.e., each case has 20 liters (8.2 kg) of the
catalyst) and the 3 cases of the catalyst were loaded into reactor
1. Each case had a cylindrical shape having an internal diameter of
180 mm.phi. and a length of 900 mm and the 3 cases were set in
series in reactor. The waste water to be treated in the present
example was solvent-type waste water containing a large amount of
alcohols such as ethyl alcohol and propyl alcohol. The COD (Cr)
concentration of the waste water was 30 g/liter and pH thereof
equaled 7.1.
[0187] In addition, this waste water did not include any of alkali
metal ion, ammonium ion and inorganic salt. Then the heat
temperature by the heater was set to 100.degree. C., the
temperature in the reactor was kept at 130.degree. C., the
treatment pressure was set to 0.6 MPa (Gauge) and the
oxygen-containing gas (oxygen-enrichment gas) was supplied to the
waste water according to the following ratio. Also, the supply
amount of the waste water was set to 30 liter/h. The equipment was
operated in the same manner as in example 1 for the waste water
treatment. As the oxygen-enrichment gas, used was gas having 30 vol
% of oxygen concentration that had been manufactured from air
according to an oxygen enrichment membrane apparatus. As a result,
in case of supplying the oxygen-containing gas with satisfying
O.sub.2/COD=0.94 and D value=1.01, the COD (Cr) treatment
efficiency after 100-hour treatment was 93% and the oxygen
concentration in the exhaust gas was 0.25 vol %.
[0188] Subsequently, the oxygen-containing gas was supplied so as
to give the supplying amount ratio of O.sub.2/COD=0.92 and D
value=0.99, and this treatment was continued with keeping the
oxygen concentration of the exhaust gas below 0.1 vol %. As a
result, the COD (Cr) treatment efficiency after 5000-hour treatment
was 92%. After the 5000-hour treatment, the catalyst was extracted
from the reactor to be observed. In consequence, it was found that
the catalyst in the second case and the bottom case in the reactor
stayed unchanged after the treatment. However, it was observed that
the catalyst in the top case tended to have a slightly decreased
catalyst activity.
[0189] Therefore, for further continuation of the waste water
treatment, the bottom and top catalyst cases in reactor 1 were
replaced with each other to perform the further treatment. As a
result, the COD (Cr) treatment efficiency immediately after the
replacement was 92%. The COD (Cr) treatment efficiency after
further 5000-hour treatment (i.e., after 10000-hour treatment in
total) was also 92%. After this treatment, the catalyst was
extracted from the reactor to be observed. In consequence, it was
observed that the catalyst in the cases located on the top and
bottom in the reactor in the further treatment (i.e., when the
treatment time was between 5000 to 10000 hours) tended to have a
slightly decreased catalyst activity. However, no critical catalyst
deterioration was observed.
Example 15
[0190] A 500-hour treatment was performed under the following
conditions with using the same equipment as the one used in example
1. Into reactor 1, loaded were 1 liter (440 g) of pellet type solid
catalysts having a diameter of 3 mm.phi. to give a catalyst bed
height of 1880 mmH. The solid catalyst had activated carbon as main
component. In addition, the waste water treated in the present
example contained 1000 mg/liter of hydrazine that had exhausted by
semiconductor manufacturing plants and pH of the waste water
equaled 8.6. In the treatment, the treatment temperature was set to
90.degree. C., the treatment pressure was set to the atmosphere
pressure and the supply amount of the waste water was adjusted to 3
liter/h. In addition, the oxygen-containing gas (air) was supplied
to the waste water in such a manner that the supplied oxygen amount
equaled to the required oxygen amount for decomposition of the
hydrazine and satisfied D value=1.0. The equipment was operated in
the same manner as in example 1 to treat the waste water.
[0191] As a result, the hydrazine treatment efficiency after
500-hour treatment was 100% and the oxygen concentration in the
exhaust gas was less than 0.1 vol %. The waste water treatment was
continued for evaluation of the catalyst durability even after the
500-hour treatment and then about 5000-hour endurance test was
conducted. Consequently, the hydrazine treatment efficiency in the
test was 100%. Additionally, after 5000-hour treatment, the
catalyst was extracted from the reactor to be observed. It was
found that the catalyst stayed unchanged after the treatment.
Comparative Example 8
[0192] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 15, except that the supply amount of the
oxygen-containing gas was adjusted in such a manner that the
supplied oxygen amount was twice as large as the required oxygen
amount for decomposition of the hydrazine.
[0193] As a result, the hydrazine treatment efficiency after
100-hour treatment was 100% and the oxygen concentration in the
exhaust gas was 11 vol %. In addition, the waste water treatment
was continued for evaluation of the catalyst durability. It
resulted in the decrease of the hydrazine treatment efficiency to
88% after about 2000-hour treatment. Therefore, the treatment was
stopped to extract the catalyst from the reactor. Consequently, it
was observed over the catalyst bed that the catalyst had lost its
shape and the amount thereof had decreased.
Examples 16 and 17
[0194] 500-hour treatments were performed under the following
conditions with using the equipment illustrated in FIG. 1. Into
reactor 1, loaded were 1 liter (350 g) of pellet type solid
catalysts having a diameter of 4 mm.phi. to give a catalyst bed
height of 1880 mmH. The solid catalyst had activated carbon and
platinum as main components and included 0.15 weight % of platinum.
In addition, the waste water to be treated in the present examples
contained methanol and the COD (Cr) concentration thereof was 10000
mg/liter. Then the treatment temperature was set to 80.degree. C.
and the treatment pressure was set to the atmosphere pressure.
Also, the oxygen-containing gas (air) was supplied to the waste
water according to the ratios shown in table 4. The supply amount
of the waste water was set to 0.5 liter/h. Moreover, the equipment
was operated in the same manner as in example 1.
[0195] The results were shown in table 4. The waste water
treatments were continued for evaluation of the catalyst durability
even after the 500-hour treatment and then about 5000-hour
endurance tests were conducted. After the 5000-hour treatment, the
catalyst was extracted from the reactor to be observed. As a
result, it was found that any catalyst in these examples stayed
unchanged after the treatments.
4TABLE 4 COD(Cr) COD(Cr) Treatment Treatment Efficiency Efficiency
After Oxygen After 500 Hour Concentration 5000 Hour Treatment In
Exhaust Treatment O.sub.2/COD D Value (%) Gas (vol %) (%) Example
0.85 0.89 85 0 84 16 Example 0.95 1.00 95 0 95 17
Comparative Example 9
[0196] The treatment was performed in the same manner including the
same catalyst, treatment processes, treatment conditions and
equipment as in example 16, except that the supply amount of the
oxygen-containing gas was set to satisfy O.sub.2/COD=2.0 and D
value=2.11. Consequently, the COD (Cr) treatment efficiency after
100-hour treatment was 85% and the oxygen concentration in the
exhaust gas was 12 volt. In addition, the waste water treatment was
continued for evaluation of the catalyst durability. It resulted in
the decrease of the COD (Cr) treatment efficiency to 68% after
about 1000-hour treatment. Therefore, the treatment was stopped to
extract the catalyst from the reactor. Consequently, it was
observed over the catalyst bed that the catalyst had lost its shape
and the amount thereof had decreased.
Example 18
[0197] A waste water treatment was performed with using the
equipment illustrated in FIG. 1. Into the reactor 1, loaded were 1
liter (390 g) of pellet type solid catalysts having a diameter of 4
mm.phi. to give a catalyst bed height of 1880 mmH. The solid
catalyst had activated carbon and platinum as main components and
included 0.3 weight % of platinum.
[0198] This equipment was started up according to the following
processes. First of all, the catalyst protection liquid having
15000 mg/liter of COD (Cr) containing about 10 g/liter of methanol
was pressurized by waste water feed pump 5 at the flow rate of 1
liter/h. Air (oxygen-containing gas) was supplied to the catalyst
protection liquid prior to the protection liquid was heated by
heater 3. The air supply amount was adjusted so that the
aforementioned D1 value was 0.3 when the internal temperature of
reactor 1 was 120.degree. C. The heated gas-liquid mixture by
heater 3 was supplied to reactor 1 from its upside to give a
gas-liquid downward concurrent flow. On starting the gas-liquid
supply, the internal temperature in reactor 1 was 20.degree. C. In
addition, when the internal temperature of reactor 1 was
120.degree. C., the maximum efficiency for treating the catalyst
protection liquid was given when the oxygen-containing gas was
supplied with satisfying O.sub.2/COD (Cr)=0.99. The treatment
efficiency of COD (Cr) in this case was 100%.
[0199] The catalyst protection liquid supply was started as
mentioned above. After confirming the catalyst protection liquid
being exhausted by the reactor through pressure control valve 12,
the rising of the treatment temperature was started by heater 3 and
electric heater 2. During the temperature rising, the catalyst
protection liquid was constantly fed into the catalyst bed to
suppress deterioration of the catalyst activity. The pressure in
reactor 1 was controlled to keep the pressure at 0.6 MPa (Gauge).
According to the pressure control, the pressure in reactor 1
increased gradually, through it was the atmosphere pressure on
starting the air supply. It was then stabilized at 0.6 MPa (Gauge)
after the temperature in reactor 1 reached higher than 100.degree.
C. On starting-up, the oxidizable substances (methanol) contained
in the protection liquid was constantly made to stay in the liquid
passed through the catalyst bed. This process of starting up the
equipment according to the catalyst protection liquid supply
continued until the internal temperature of reactor 1 reached
120.degree. C. When the internal temperature reached 120.degree.
C., the concentration of the catalyst protection liquid in
gas-liquid separator 11 was COD(Cr)=10400 mg/liter. In addition,
the oxygen concentration in the exhaust gas during the temperature
rising was constantly 0 vol % after the internal temperature of
reactor 1 reached higher than 60.degree. C.
[0200] After the internal temperature of reactor 1 reached
120.degree. C., the supply of the catalyst protection liquid was
stopped, immediately followed by changing over to the supply of the
waste water to be treated. The waste water to be treated was
supplied through waste water feed line 6, as was the case with the
catalyst protection liquid. In addition, as the waste water to be
treated, used was water exhausted by manufacturing facilities of
aliphatic carboxylic acids and aliphatic carboxylate. The waste
water contained an organic compound having 2 or more carbon atoms
per molecule such as alcohol, aldehyde and carboxylic acid. The COD
(Cr) concentration of the waste water was 15000 mg/liter and pH
thereof equaled 2.8. In addition, 40% of the total TOC component
was acetic acid.
[0201] In the treatment process of the waste water, heater 3 and
electric heater 2 were controlled to keep the internal temperature
of reactor 1 at 130.degree. C. The air supply amount was controlled
by oxygen-containing gas flow control valve 9 to keep the oxygen
concentration of the exhaust gas in gas-liquid separator 11 at 0.2
vol %. The controlled air supply amount was 0.96 in term of
O.sub.2/COD(Cr) ratio. Moreover, the liquid level of the treated
water in gas-liquid separator 11 was detected by a liquid-level
controller LC and kept a constant liquid level by the control of
treated water exhaust pump 14. Except for these, the treatment was
performed in the same manner as in the process of starting up the
equipment. Furthermore, the treated water that had flowed out from
treated water exhaust pump 14 was then exhausted trough treated
water exhaust line 15, to be sampled at pleasure for measurement of
COD (Cr) concentration thereof. When the treatment was stabilized
after the 50-hour operation of the equipment, the COD (Cr)
treatment efficiency was 96%.
Comparative Example 10
[0202] A treatment was performed with using the equipment
illustrated in FIG. 1 in the same manner as in example 18 except
for using water in the starting up process instead of the catalyst
protection liquid having 15000 mg/liter of COD (Cr) containing
about 10 g/liter of methanol. The supply amount of
oxygen-containing gas (air) equaled to the air supply amount in
example 18. Accordingly, the oxygen concentration of the exhaust
gas in gas-liquid separator 11 was constantly 21 vol %.
[0203] Subsequently, after the temperature rising to 120.degree.
C., the liquid to be supplied was changed over from water to the
waste water as in the case with example 18, to start the treatment
of the waste water. In addition, the waste water to be treated was
same as the one used in example 18. Also, as in the case with
example 18, the internal temperature of reactor 1 was set to
130.degree. C. and oxygen-containing gas flow control valve 9 was
controlled so as to keep the oxygen concentration of the exhaust
gas in gas-liquid separator 11 at 0.2 vol %.
[0204] As a result, after the 50-hour supply of the waste water,
the COD (Cr) treatment efficiency was 65%. In addition, the air
supply amount on this point was 0.65 in term of the ratio of
O.sub.2/COD (Cr).
Examples 19 to 23
[0205] Treatments were performed in the same manner including the
same processes and same conditions as in example 18 except for
using liquids shown in table 5 as the catalyst protection liquid
instead of the liquid containing about 10 g/liter of methanol. The
waste water to be treated was also the same as that used in example
18. Each catalyst protection liquid had a COD (Cr) concentration of
15000 mg/liter. The results were shown in Table 5. Additionally,
the waste water to be treated was also used as the catalyst
protection liquid in example 23. In other words, the liquid to be
used as the catalyst protection liquid was the same as the waste
water to be treated after the temperature rising. In case of the
internal temperature of reactor 1 being 120.degree. C., the maximum
efficiencies for treating the catalyst protection liquids in
examples 19 to 22 were given when air was supplied with satisfying
O.sub.2/COD=about 1.0. The treatment efficiencies of COD (Cr) in
this case were 100%. On the other hand, in case of the internal
temperature of reactor 1 being 120.degree. C., the maximum
efficiency for treating the catalyst protection liquid in example
23 was given when supplying air with satisfying O.sub.2/COD=0.82.
The treatment efficiency of COD (Cr) in this case was 82%.
Accordingly, air was supplied with satisfying O.sub.2/COD=about
0.25 in example 23 in order to obtain a D1 value of 0.3.
5TABLE 5 Remained COD(Cr) Oxygen Concen- COD(Cr) Concen- tration
Treatment tration In The Efficiency The Catalyst In Exhaust
Protection Of The Protection D1 Gas Liquid Waste Liquid Value (vol
%) (mg/L) Water (%) Example Ethanol 0.3 0 10,400 95 19 Example
Propanol 0.3 0 10,400 93 20 Example Formic Acid 0.3 0 10,400 93 21
Example Formaldehyde 0.3 0 10,400 92 22 Example Waste Water 0.3 0
11,300 95 23 To Be Treated
Examples 24 to 27 and Comparative Examples 11 and 12
[0206] The treatment was performed in the same manner including the
same catalyst protection liquid, waste water, catalyst, treatment
conditions and equipment as in example 18, except for setting the
aforementioned D1 values to values shown in table 6. The results
were shown in table 6.
6TABLE 6 Remained COD(Cr) Concentration COD(Cr) Oxygen In The
Treatment Concentration Protection Efficiency Of D1 In Exhaust
Liquid The Waste Value Gas (vol %) (mg/L) Water (%) Example 24 0.1
0 12,900 96 Example 25 0.7 0 4,400 94 Example 26 0.9 0 1,200 93
Example 27 1.2 3.5 0 84 Comparative 1.5 7.0 0 69 Example 11
Comparative 2.0 10.5 0 68 Example 12
Example 28
[0207] The waste water treatment was performed with using the
equipment illustrated in FIG. 1 in the same manner as in example 18
except for the following conditions. Into the reactor, loaded were
1 liter (440 g) of pellet type solid catalysts having a diameter of
5 mm.phi. to give a catalyst bed height of 1880 mmH. The solid
catalyst had activated carbon and palladium as main components and
contained 0.5 weight % of palladium. As the catalyst protection
liquid, used was the liquid having 10000 mg/liter of COD (Cr)
containing about 6 g/liter of methanol. The liquid was fed with
pressure rising by waste water feed pump 5 at the flow rate of 2
liter/h. In addition, pressure control valve 12 was controlled to
keep the pressure in reactor 1 at 0.5 MPa (Gauge).
[0208] The air supply amount was controlled so that the
aforementioned D1 value was 0.4 when the internal temperature of
reactor 1 was 110.degree. C. This process continued until the
internal temperature of reactor 1 reached 110.degree. C. according
to the catalyst protection liquid supply. When the internal
temperature reached 110.degree. C., the density of the catalyst
protection liquid at the catalyst bed exit (in gas-liquid
separator) was COD(Cr) 5800 mg/liter. In addition, the oxygen
concentration of the exhaust gas during the temperature rising was
constantly 0 vol % after the internal temperature of reactor 1
reached higher than 60.degree. C.
[0209] In case of the internal temperature of reactor 1 being
110.degree. C., the maximum efficiency for treating the catalyst
protection liquid in example 6 was given when air was supplied with
satisfying O.sub.2/COD=0.99. The treatment efficiency of COD (Cr)
in this case was 100%.
[0210] As soon as the maximum efficiency was given, the supply of
the catalyst protection liquid was stopped, immediately followed by
changing over to supply the waste water to be treated. The waste
water to be treated in the present example was solvent-type waste
water containing a large amount of alcohols such as ethyl alcohol
and propyl alcohol. The COD (Cr) concentration of the waste water
was 30000 mg/liter and pH thereof equaled 7.1. This waste water did
not include any of alkali metal ion, ammonium ion and inorganic
salt.
[0211] Additionally, in this waste water treatment, heater 3 and
electric heater 2 were controlled to keep the internal temperature
of reactor 1 at 115.degree. C. The air supply amount was controlled
by oxygen-containing gas flow control valve 9 so that the oxygen
concentration of the exhaust gas in gas-liquid separator 11 was
kept at 0.5 vol %. The controlled air supply amount was 0.97 in
term of the ratio of O.sub.2/COD (Cr).
[0212] Consequently, when the treatment was stabilized after the
50-hour supply of the waste water, the COD (Cr) treatment
efficiency was 95%.
Comparative Example 13
[0213] A process of starting up the equipment was performed in the
same manner as in example 28, except for using water instead of
supplying the catalyst protection liquid during the temperature
rising of the equipment. The air supply amount was set to the same
air amount supplied in example 28. Accordingly, during the
temperature rising, the oxygen concentration of the exhaust gas in
gas-liquid separator 11 was constantly 21 vol %.
[0214] Subsequently, after the temperature rising to 110.degree.
C., the liquid to be supplied was changed over from water to the
same waste water as the one used in example 28, i.e., solvent-type
waste water containing a large amount of alcohols such as ethyl
alcohol and propyl alcohol, to start the treatment thereof. Also,
as in the case with example 28, oxygen-containing gas flow control
valve 9 was controlled so that the oxygen concentration of the
exhaust gas in gas-liquid separator 11 was kept at 0.5 vol %.
[0215] As a result, after 50-hour supply of the waste water, the
COD (Cr) treatment efficiency was 55%. In addition, the air supply
amount was 0.56 in term of the ratio of O.sub.2/COD (Cr).
Example 29
[0216] The equipment illustrated in FIG. 2 was used in the present
example. The same amount of the same solid catalyst as the one used
in example 18 was loaded into the reactor. Then the waste water
treatment was performed in the same manner (same waste water,
treatment processes and treatment conditions) as in example 18.
[0217] The temperature rising was conducted with using the catalyst
protection liquid. When the internal temperature of reactor 21
reached 120.degree. C., the density of the catalyst protection
liquid at the catalyst bed exit (in gas-liquid separator 11) was
COD(Cr)=10400 mg/liter. In addition, the oxygen concentration in
the exhaust gas on the temperature rising was constantly 0 vol %
after the internal temperature of reactor 21 reached higher than
60.degree. C.
[0218] As a result, when the treatment was stabilized after 50-hour
supply of the waste water, the COD (Cr) treatment efficiency was
88%. The air supply amount on treating the waste water was
controlled by oxygen-containing gas flow control valve 9 in such a
manner that the oxygen concentration of the exhaust gas in
gas-liquid separator 11 was kept at 0.2 vol %. The air supply
amount on this point was 0.89 in term of the ratio of O.sub.2/COD
(Cr).
Example 30
[0219] A waste water treatment was performed with using the
equipment illustrated in FIG. 4. The equipment illustrated in FIG.
4 has the same structure as that of the equipment illustrated in
FIG. 1 except that an additional air supply location, which is for
keeping the pressure in the equipment when starting up the
equipment, is provided to rearward of reactor 1. In other words,
the equipment in FIG. 4 has oxygen-containing gas supply line 41
connected between reactor 1 and pressure control valve 12 in
addition to the equipment structure illustrated in FIG. 1. This
oxygen-containing gas supply line 41 makes it possible to supply
air from the aforementioned oxygen-containing gas supply line 8 to
the upstream side of pressure control valve 12 through
oxygen-containing gas flow control valve 42.
[0220] The treatment was then performed in the same manner as in
example 18 except for supplying air through oxygen-containing gas
supply line 41 when starting up. That is, the treatment was
performed in the same manner as in example 18 except for the
followings. The supply air amount when starting up was controlled
by oxygen-containing gas flow control valve 42 to adjust the
aforementioned D1 to 1.5. In addition, the location for supplying
the air was changed from that in example 18. Accordingly, the
oxygen concentration of the exhaust gas in gas-liquid separator 11
was constantly 21 vol % in the process of starting up. However,
after the pressure rising, the oxygen concentration of the gas
phase in reactor 1 is considered to be 0 vol % (i.e., the
aforementioned D1 value equals to 0), since no air is supplied into
reactor 1 (solid catalyst bed). In addition, the density of the
catalyst protection liquid at the catalyst bed exit (in gas-liquid
separator 11) was 14800 mg/liter.
[0221] The waste water treatment was performed immediately after
the above-mentioned starting up in the same manner as in example
18. The waste water treatment resulted in 96 of the COD (Cr)
treatment efficiency.
Example 31
[0222] After the waste water treatment was performed as described
in example 18, a process of cooling down the equipment was
subsequently carried out according to the following method. In this
process of cooling down, heating by electric heater 2 and heater 3
were firstly stopped to start cooling the equipment. At the same
time, the oxygen-containing gas supply amount was adjusted to 0.82
in term of O.sub.2/COD (Cr). Then, immediately after the internal
temperature of reactor 1 reached 120.degree. C., the liquid to be
supplied was changed over from the waste water to the catalyst
protection liquid that was used for starting up in example 18, in
order to suppress deterioration of the catalyst activity. In
addition, the oxygen-containing gas amount was reduced in such a
manner that the D1 value equaled to 0.3. At this time, the
oxidizable substances in catalyst protection liquid was made to
stay in the liquid passed through the catalyst bed exit.
[0223] As a result, the oxygen concentration of the exhaust gas,
which was 0.2 vol % during the waste water treatment, gradually
decreased and then it was constantly 0 vol % until the temperature
of reactor 1 decreased to about 60.degree. C.
[0224] After the equipment temperature decreased to 30.degree. C.,
the temperature was subsequently raised in the same manner as in
example 18, followed by another waste water treatment in the same
manner as in example 18. In consequence, when this treatment was
stabilized after 50-hour supply of the waste water, COD (Cr)
treatment efficiency was 96%.
Comparative Example 14
[0225] A treatment was performed in the same manner as in example
31 except for using water for cooling down the equipment instead of
the catalyst protection liquid having 15000 g/liter of COD (Cr)
containing about 10 g/liter of methanol. In the cooling, the oxygen
concentration of the exhaust gas in gas-liquid separator 11
increased rapidly, through it was about 0.2 vol % immediately after
the changing over from the waste water to water. And it was beyond
20 vol %, when the temperature of reactor 1 reached about
110.degree. C.
[0226] After the equipment temperature decreased to 30.degree. C.,
the temperature was subsequently raised in the same manner as in
example 18, followed by starting another waste water treatment in
the same manner as in example 18. In consequence, when this
treatment was stabilized after 50-hour supply of the waste water,
COD (Cr) treatment efficiency was 71%.
Examples 32 to 36
[0227] The waste water treatment in example 19 was followed by a
cooling process of the equipment in example 32 as described below
with using the catalyst protection liquid shown in table 7. In
addition, the waste water treatment in example 20 was followed by a
cooling process of the equipment in example 33, the waste water
treatment in example 21 was followed by a cooling process of the
equipment in example 34, the waste water treatment in example 22
was followed by a cooling process of the equipment in example 35
and the waste water treatment in example 23 was followed by a
cooling process of the equipment in example 36. All these cooling
processes were performed in the same manner as in example 31. Also,
the respective catalyst protection liquid used in the above cooling
processes was the same liquid as used in the corresponding example
19 to 23.
[0228] In the respective examples, after the equipment temperature
decreased to 30.degree. C., the temperature was raised again in the
same manner as in the corresponding examples 19 to 23. It was
followed by another waste water treatment in the same manner as in
example 18. Shown in table 7 were the results of COD (Cr) treatment
efficiencies obtained when the treatments in the examples were
stabilized after 50-hour supply of the waste water.
7 TABLE 7 The Catalyst COD(Cr) Treatment Protection Efficiency Of
The Liquid D1 Value Waste Water (%) Example Ethanol 0.3 95 32
Example Propanol 0.3 93 33 Example Formic Acid 0.3 93 34 Example
Formaldehyde 0.3 92 35 Example Waste Water To 0.3 95 36 Be
Treated
Example 37
[0229] A treatment was performed with using the same catalyst
protection liquid, waste water, treatment conditions and equipment
as those in example 31 except for adjusting the oxygen-containing
gas supply amount on cooling to 1.1 in term of the D1 value.
[0230] As a result, the oxygen concentration gradually increased
and it reached about 2 vol % at 110.degree. C. In addition, the
remaining COD (Cr) concentrations of the catalyst protection liquid
in gas-liquid separator 11 at 110.degree. C. and 80.degree. C. were
both less than 100 mg/liter. The waste water treatment was then
performed in the same manner as in example 18, resulting in 88% of
the COD (Cr) treatment efficiency.
Examples 38 to 42
[0231] First of all, a standard waste water treatment was performed
with using the equipment illustrated in FIG. 1. Into the reactor,
loaded were 1 liter (390 g) of pellet type solid catalysts having a
diameter of 4 mm.phi. to give a catalyst bed height of 1880 mmH.
The solid catalyst had activated carbon and platinum as main
components and included 0.3 weight % of platinum. In addition, as
the waste water for the standard treatment, used was water
exhausted by manufacturing facilities of aliphatic carboxylic acids
and aliphatic carboxylate. The waste water contained an organic
compound having 2 or more carbon atoms per molecule such as
alcohol, aldehyde and carboxylic acid. The COD (Cr) concentration
of the waste water was 15000 mg/l and pH thereof equaled 2.8. In
addition, 53% of the total TOC component was acetic acid.
[0232] The waste water was pressurized at the flow rate of 1
liter/h. Subsequently, the waste water was heated up to 120.degree.
C. by heater 3 and the internal temperature was kept at 120.degree.
C. by electric heater 2. The oxygen-containing gas (air) was then
supplied to the waste water prior to the waste water was heated by
to heater 3. The pressure in reactor 1 was controlled to keep the
pressure at 0.6 MPa (Gauge).
[0233] During the first 50-hour operation of the equipment, the air
supply amount was controlled so that the oxygen concentration of
the exhaust gas was 0.5%. As a result, the COD (Cr) treatment
efficiency was 94% after the 50-hour operation.
[0234] Then, when the operation time was between 50 to-100 hours,
the air supply amount was controlled so that the oxygen
concentration of the exhaust gas was 10% in order to deteriorate
the catalyst activity. Furthermore, when the operation time was
between 100 to 150 hours, the air supply amount was controlled so
that the oxygen concentration of the exhaust gas was again 0.5%.
This 150-hour operation decreased the COD (Cr) treatment efficiency
to 66%.
[0235] (Recovering Treatment Process)
[0236] The following recovering treatments were respectively
performed to the catalyst whose COD (Cr) treatment efficiency had
decreased from 94% to 66% in the above-mentioned treatments.
[0237] In the recovering treatment process, a catalyst-recovering
liquid was fed with pressure rising by waste water feed pump 5 at
the flow rate of 1 liter/h. Subsequently, the recovering liquid was
heated up to 140.degree. C. by heater 3 and then supplied to
reactor 1 from its upside to make a gas-liquid downward concurrent
flow. The catalyst recovering liquid used in this recovering
process was a liquid containing about 10 g/liter of methanol and
having 15 g/liter of COD (Cr). The oxygen-containing gas (air) was
then supplied to the recovering liquid according to the respective
ratios shown in table 8 prior to the recovering liquid was heated
by heater 3.
[0238] After the recovering liquid passed through the catalyst bed,
it was cooled by cooler 4. Subsequently, it was exhausted through
pressure control valve 12 with its pressure being recovered,
followed by separating gas from liquid in the exhausted water by
gas-liquid separator 11. In this process, at pressure control valve
12, the pressure in reactor 1 was controlled to keep the pressure
at 0.6 MPa (Gauge).
[0239] This recovering treatment was continued for 5 hours in
respective tests in the present examples. Then another 50-hour
waste water treatment was conducted under the same conditions as in
the respective former waste water treatments. The remaining amounts
of the recovering liquid in the recovering process and the waste
water treatment efficiencies in the waste water treatment process
were shown in table 8.
[0240] In example 42, nitrogen gas was supplied in the recovering
treatment process instead of the oxygen-containing gas. The supply
amount of the nitrogen gas was set to be equal to that of the
oxygen-containing gas in example 39.
8 TABLE 8 Oxygen Concen- Remaining Treatment tration COD(Cr)
Efficiency In The Concen- Of The Exhaust Gas tration Waste Water
During The In The After Recovering Recovering Recovering O.sub.2/
D2 Treatment Treatment Treatment COD Value (%) (mg/L) (%) Example
0.2 0.2 0 11,800 94 38 Example 0.5 0.5 0 7,400 94 39 Example 0.8
0.8 0 3,000 91 40 Example 1.0 1.0 0.1 <100 83 41 Example 0 0 0
14,500 94 42
Examples 43 to 46, Comparative Example 15
[0241] The recovering treatment was performed in the same manner
including the same catalyst, treatment processes, treatment
conditions and equipment as in example 39, except for setting
recovering treatment temperature as shown in table 9. The results
were also shown in table 9.
[0242] The temperature in example 46 was set to 160.degree. C. and
the pressure was set to 0.9 MPa (Gauge). The temperature in
comparative example was set to 220.degree. C. and the pressure was
set to 2.5 MPa (Gauge).
9 TABLE 9 Oxygen Concen- Remaining Treatment tration COD(Cr)
Efficiency Recover- In The Concen- Of The ing Exhaust Gas tration
Waste Water Treatment During The In The After Temper- Recovering
Recovering Recovering ature D2 Treatment Treatment Treatment
(.degree. C.) Value (%) (mg/L) (%) Exam- 80 0.5 0 7,500 78 ple 43
Exam- 100 0.5 0 7,500 82 ple 44 Exam- 125 0.5 0 7,400 93 ple 45
Exam- 160 0.5 0 7,300 92 ple 46 Comp- 220 0.5 0 3,200 60 arative
Exam- ple 15
Example 47 to 52
[0243] The recovering treatment was performed in the same manner
including the same catalyst, treatment processes, treatment
conditions and equipment as in example 39, except for changing
treatment time as shown in table 10. The results were also shown in
table 10.
[0244] The temperature in example 51 and example 52 was set to
125.degree. C. and the treatment was performed in the same manner
as in example 45.
10 TABLE 10 Oxygen Concen- Remaining Treatment tration COD(Cr)
Efficiency In The Concen- Of The Recover- Exhaust Gas tration Waste
Water ing During The In The After Treatment Recovering Recovering
Recovering Time D2 Treatment Treatment Treatment (Hr) Value (%)
(mg/L) (%) Exam- 2 0.5 0 7,400 90 ple 47 Exam- 24 0.5 0 7,400 94
ple 48 Exam- 80 0.5 0 7,400 93 ple 49 Exam- 500 0.5 0 7,400 91 ple
50 Exam- 24 0.5 0 7,400 94 ple 51 Exam- 500 0.5 0 7,400 93 ple
52
Example 53 to 59
[0245] The recovering treatment was performed in the same manner as
in example 39, except for changing COD(Cr) concentration of the
recovering liquid containing methanol as shown in table 11. The
results were also shown in table 11. The recovering treatment in
example 57 and example 58 was conducted for 24 hours and the
treatment was performed in the same manner as in example 48 and the
supply amount of oxygen-containing gas in example 53 to 58 was
adjusted to O.sub.2/COD=0.50. The recovering treatment in example
59 was conducted for 5 hours and the supply amount of
oxygen-containing gas was adjusted to O.sub.2/COD=0.20.
11 TABLE 11 Oxygen Treatment Concentration In Efficiency Of COD(Cr)
The Exhaust Gas Remaining COD(Cr) The Waste Water Concentration Of
During The Concentration In After The Recovering Recovering The
Recovering Recovering Liquid (mg/L) D2 Value Treatment (%)
Treatment (mg/L) Treatment (%) Example 53 1,000 0.5 0 500 78
Example 54 5,000 0.5 0 2,400 92 Example 55 30,000 0.5 0 14,000 94
Example 56 60,000 0.5 0 28,000 94 Example 57 1,000 0.5 0 500 86
Example 58 5,000 0.5 0 2,400 94 Example 59 5,000 0.2 0 3,900 94
Example 60 to 64
[0246] The recovering treatment was performed in the same manner
including the same catalyst, treatment processes, treatment
conditions and equipment as in example 39, except for using the
recovering liquid containing ethanol, propanol, acetone and
tetrahydrofuran each of which has COD(Cr)=15 g/L. The results were
shown in table 12.
[0247] In example 64, the waste water exhausted by manufacturing
facilities of aliphatic carboxylic acids and aliphatic carboxylate
was used. The waste water contained alcohols having 1 to 4 carbon
atoms per molecule. The COD(Cr) concentration of the waste water
was 23 g/L and the air supply amount in example 60 to 64 was
O.sub.2/COD (Cr)=0.5.
12 TABLE 12 Oxygen Treatment Concentration In Efficiency Of The
Exhaust Gas Remaining COD(Cr) The Waste Water During The
Concentration In After Recovering D2 Recovering The Recovering
Recovering Liquid Value Treatment (%) Treatment (mg/L) Treatment
(%) Example 60 Ethanol 0.5 0 7,400 93 Example 61 Propanol 0.5 0
7,400 89 Example 62 Formic Acid 0.5 0 7,500 85 Example 63
Formaldehyde 0.5 0 7,500 83 Example 64 Waste Water 0.5 0 10,500 92
To Be Treated
Comparative Example 16, 17
[0248] The recovering treatment was performed in the same manner
including the same catalyst, treatment processes, treatment
conditions and equipment as in example 39, except for setting the
air supply amount as shown in table 13. The results were also shown
in table 13.
13 TABLE 13 Oxygen Treatment Concentration In Efficiency Of The
Exhaust Gas Remaining COD(Cr) The Waste Water During The
Concentration In After Recovering The Recovering Recovering
O.sub.2/COD D2 Value Treatment (%) Treatment (mg/L) Treatment (%)
Comparative 1.5 1.5 7.8 <100 64 Example 16 Comparative 2.0 2.0
11.0 <100 63 Example 17
Example 65
[0249] The waste water treatment was performed using the equipment
illustrated in FIG. 2. The treatment was performed in the same
manner including the same waste water and treatment conditions as
in example 39. The COD (Cr) treatment efficiencies after 50-hour
treatments were 87%. Following the waste water treatment, the
recovering treatment was performed in the same treatment conditions
as in example 39. The result was shown in table 14. The air supply
amount was O.sub.2/COD (Cr)=0.5.
14TABLE 14 Oxygen Concentration In Remaining COD(Cr) Treatment
Efficiency The Exhaust Gas During Concentration In The Of The Waste
Water The Recovering Treatment Recovering Treatment After
Recovering D2 Value (%) (mg/L) Treatment (%) Example 65 0.5 0 7,400
87
Example 66
[0250] The recovering treatment was performed in the same manner
including the same catalyst, treatment processes, treatment
conditions and equipment as in example 39, except for changing the
temperature in accordance with the treatment time as follow.
[0251] The temperature was set to 160.degree. C. for 1 hour from
the start (0 to 1 hour) and then the temperature was set to
125.degree. C. for next 2 hours (1 to 3 hour). The result was shown
in table
15TABLE 15 Oxygen Concentration Remaining COD(Cr) Treatment
Efficiency In The Exhaust Gas Concentration In The Of The Waste
Water During The Recovering Recovering Treatment After Recovering
O.sub.2/COD D2 Value Treatment (%) (mg/L) Treatment (%) Example 66
0.5 0.5 0 7,400 94
Example 67 and 68
[0252] The waste water treatment was performed using the equipment
illustrated in FIG. 1. Into the reactor, loaded were 1 liter (420
g) of pellet type solid catalysts having a diameter of 3 mm.phi. to
give a catalyst bed height of 1880 mmH. The solid catalyst had
activated carbon and palladium as main components and included 0.6
mass % of palladium with respect to the total amount of the solid
catalyst. In addition, as the waste water to be treated in the
present examples, used was water exhausted by electric power
plants. The waste water contained ammonium sulfate, sodium ion and
carbonic acid ion. The ammonia concentration of the waste water was
4200 mg/liter and pH thereof equaled 7.8.
[0253] The aforementioned waste water was fed with pressure rising
at the flow rate of 1 liter/h. Subsequently, the waste water was
heated up to 130.degree. C. by heater 3. The oxygen-containing gas
(air) was then supplied to the waste water prior to the waste water
was heated by to heater 3.
[0254] In reactor 1, the waste water temperature was maintained to
be 130.degree. C. by electric heater 2. The pressure in reactor 1
was controlled to keep the pressure at 0.9 MPa (Gauge).
[0255] During the first 50-hour operation of the equipment, the air
supply amount was controlled so that the oxygen concentration of
the exhaust gas was 0.5%. As a result, the ammonia treatment
efficiency was 95% after the 50-hour operation.
[0256] Then, when the operation time was between 50 to 100 hours,
the air supply amount was controlled so that the oxygen
concentration of the exhaust gas was 10% in order to deteriorate
the catalyst activity. Furthermore, when the operation time was
between 100 to 150 hours, the air supply amount was controlled so
that the oxygen concentration of the exhaust gas was again 0.5%.
This 150-hour operation decreased the ammonia treatment efficiency
to 54%.
[0257] (Recovering Treatment Process)
[0258] The following regeneration treatments were respectively
performed to the catalyst whose ammonia treatment efficiency had
decreased from 95% to 54% in the above-mentioned treatments.
[0259] In the recovering treatment process, a catalyst recovering
liquid was supplied with pressure rising by waste water feed pump 5
at the flow rate of 1 liter/h. Subsequently, the recovering liquid
was heated up to 150.degree. C. by heater 3 and then supplied to
reactor 1 from its head to make a gas-liquid downward concurrent
flow. The catalyst recovering liquid used in this recovering
process was a liquid containing about 8 g/liter of methanol and
having 12 g/liter of COD (Cr). The oxygen-containing gas (air) was
then supplied to the recovering liquid according to the respective
ratios shown in table 16 prior to the recovering liquid was heated
by heater 3.
[0260] After the recovering liquid passed through the catalyst bed,
it was cooled by cooler 4. Subsequently, it was exhausted through
pressure control valve 12 with its pressure being recovered,
followed by separating gas from liquid in the exhausted water by
gas-liquid separator 11. In this process, at pressure control valve
12, the pressure in reactor 1 was controlled to keep the pressure
at 0.9 MPa (Gauge).
[0261] This recovering treatment was continued for 7 hours in
respective tests in the present examples. Then another 50-hour
waste water treatment was conducted under the same conditions as in
the respective former waste water treatments. The result was shown
in table 16.
16 TABLE 16 Oxygen Concentration Remaining COD(Cr) Treatment
Efficiency In The Exhaust Gas Concentration In The Of The Waste
Water During The Recovering Recovering Treatment After Recovering
O.sub.2/COD D2 Value Treatment (%) (mg/L) Treatment (%) Example 67
0.5 0.5 0 5,500 95 Example 68 0.8 0.8 0 1,700 92
[0262] Catalyst Preparation 1
[0263] Pellet type activated carbons (an average particle diameter
of 4 mm and an average length of 5.5 mm) having specific surface
area of 1200 m.sup.2/g by BET method and specific pore volume
having pore diameter in the range from 0.1 to 10 .mu.m of 0.63 ml/g
by mercury penetration method was used for a catalyst preparation.
Titanyl sulfate aqueous solution was deposited on the pellets by
impregnation method and the pellets was dried in the nitrogen
atmosphere at 90.degree. C. Thus obtained was calcined in the
nitrogen atmosphere at 400.degree. C. for 3 hours to obtain
titania-deposited-activated-carbon pellets. Platinum nitrate
aqueous solution was deposited on the pellets by impregnation
method and the pellets were dried in nitrogen gas at 90.degree. C.
After that thus obtained pellets were calcined in hydrogen
containing gas at 300.degree. C. for 3 hours to obtain catalysts
(A-1). Main component and mass ratio of the catalyst (A-1) were
shown in Table 17. The contents and the composition of titan and
platinum were expressed by converted into metal thereof. The
average mechanical strength of the catalyst was declined to 6.4 kg
per particle, the specific surface area was declined to 900
m.sup.2/g by BET method and the specific pore volume having pore
diameter in the range from 0.1 to 10 .mu.m of 0.48 ml/g by mercury
penetration method.
[0264] Catalyst Preparation 2 to 8
[0265] The catalyst was prepared in the same manner including-the
same processes, pellet type activated carbon and conditions as in
catalyst preparation 1 except that following solution was used
instead of titanyl sulfate aqueous solution;
[0266] Catalyst preparation 2: zirconyl nitrate aqueous
solution
[0267] Catalyst preparation 3: iron nitrate aqueous solution
[0268] Catalyst preparation 4: manganese nitrate aqueous
solution
[0269] Catalyst preparation 5: cerium nitrate aqueous solution
[0270] Catalyst preparation 6: praseodymium nitrate aqueous
solution
[0271] Catalyst preparation 7: tin sulfate aqueous solution
[0272] Catalyst preparation 8: bismuth nitrate aqueous solution
[0273] Thus obtained catalysts (A-2 to A-8 respectively) was shown
in Table 17. Main component and mass ratio of the catalyst (A-2 to
A-8) were shown in Table 17. The average mechanical strength of
each catalysts was almost same with that of catalyst A-1. The same
decline value in the specific surface area and specific pore volume
having pore diameter in the range from 0.1 to 10 .mu.m of the
catalyst A-1 was shown in that of A-2 to A-8.
[0274] Catalyst Preparation 9 to 10
[0275] The catalyst was prepared in the same manner including the
same processes, pellet type activated carbon and conditions as in
catalyst preparation 1 except that following solution was used
instead of nitric acid platinum aqueous solution;
[0276] Catalyst preparation 9: palladium nitrate aqueous
solution
[0277] Catalyst preparation 10: ruthenium nitrate aqueous
solution
[0278] Thus obtained catalysts (B-1 and B-2 respectively) was shown
in Table 17. Main component and mass ratio of the catalyst (B-1 and
B-2) were shown in Table 17. The average mechanical strength of
each catalysts was almost same with that of catalyst A-1. The same
decline value in the specific surface area and specific pore volume
having pore diameter in the range from 0.1 to 10 .mu.m of catalyst
A-1 was shown in that of B-1 and B-2.
[0279] Catalyst Preparation 11 to 12
[0280] The catalyst was prepared in the same manner including the
same processes, pellet type activated carbon and conditions as in
catalyst preparation 1 except that the ratio of titanyl sulfate
supported on the pellets was changed as shown in Table 17.
[0281] Thus obtained catalysts (C-1 and C-2 respectively) was shown
in Table 17. Main component and mass ratio of the catalyst (C-1 and
C-2) were shown in Table 17. The average mechanical strength of
each catalysts was almost same with that of catalyst A-1. The
specific surface area of the catalyst C-1 was declined to 1100
m.sup.2/g by BET method and the specific pore volume having pore
diameter in the range from 0.1 to 10 .mu.m of 0.55 ml/g by mercury
penetration method. The specific surface area of the catalyst C-2
was declined to 700 m.sup.2/g by BET method and the specific pore
volume having pore diameter in the range from 0.1 to 10 .mu.m of
0.43 ml/g by mercury penetration method.
[0282] Catalyst Preparation 13 to 14
[0283] The catalyst was prepared in the same manner including the
same processes, pellet type activated carbon and conditions as in
catalyst preparation 1 except that zirconyl nitrate aqueous
solution as used in catalyst preparation 2 was used instead of
titanyl sulfate aqueous solution and the ratio of the zirconyl
nitrate supported on the pellets was changed as shown in Table
17.
[0284] Thus obtained catalysts (C-3 and C-4 respectively) was shown
in Table 17. Main component and mass ratio of the catalyst (C-3 and
C-4) were shown in Table 17. The average mechanical strength of
each catalysts was almost same with that of catalyst A-1. The
specific surface area of the catalyst C-3 was declined to 1100
m.sup.2/g by BET method and the specific pore volume having pore
diameter in the range from 0.1 to 10 .mu.m of 0.54 ml/g by mercury
penetration method. The specific surface area of the catalyst C-4
was declined to 800 m.sup.2/g by BET method and the specific pore
volume having pore diameter in the range from 0.1 to 10 .mu.m of
0.45 ml/g by mercury penetration method.
[0285] Catalyst Preparation 15
[0286] Titanyl sulfate and of platinum nitrate aqueous solution
used in the catalyst preparation 1 were thoroughly mixed. The
produced mixture was supported on the pellet type activated carbon
used in the preparation 1 by impregnation method and thus obtained
pellets was dried in the nitrogen atmosphere at 90.degree. C. and
then was calcined in hydrogen containing gas at 300.degree. C. for
3 hours to obtain catalyst (D-1).
[0287] Main component and mass ratio of the catalyst (D-1) were
shown in Table 17. The average mechanical strength of each
catalysts was almost same with that of catalyst A-1. The same
decline value in the specific surface area and specific pore volume
having pore diameter in the range from 0.1 to 10 .mu.m of catalyst
A-1 was shown in that of D-1.
Example 69
[0288] 500 hours of waste water treatment was performed under the
following conditions with using the equipment illustrated in FIG.
1. A reactor 1 having cylindrical shape (a diameter of 26 mm.phi.
and a length of 3000 mm) was used in the treatment. Into the
reactor, loaded were 1 liter (410 g) of catalyst A-1. In addition,
as the waste water to be treated in the present examples, used was
waste water exhausted by chemical plants. The waste water contained
organic compounds such as acetic acid and propionic acid. The COD
(Cr) concentration of the waste water was 25 g/liter.
[0289] The aforementioned waste water was fed with pressure rising
by waste water feed pump 5 at the flow rate of 1 liter/h.
Subsequently, the waste water was heated up to 130.degree. C. by
heater 3 and then supplied to reactor 1 from its head to make a
gas-liquid downward concurrent flow for the treatment. Air was also
introduced through oxygen-containing gas supply line 8, followed by
being compressed by compressor 7. The oxygen-containing gas (air)
was then supplied to the waste water prior to the waste water was
heated by to heater 3. The supply amount of the oxygen-containing
gas was adjusted by oxygen-containing gas flow valve 9 so that the
oxygen concentration in the exhaust gas was in the range from 0.1
to 0.5%.
[0290] In reactor 1, the waste water temperature was maintained to
be 130.degree. C. by electric heater 2 to perform
oxidation/decomposition treatments. The obtained treated water was
cooled by cooler 4. Subsequently, it was exhausted through pressure
control valve 12 with its pressure being recovered, followed by
separating gas from liquid in the exhausted water by gas-liquid
separator 11. In this process, at pressure control valve 12,
pressure controller PC detected and controlled the pressure in
reactor 1 to keep the pressure at 0.4 MPa (Gauge). In addition,
oxygen concentration of the exhaust gas in gas-liquid separator 11
was measured by using oxygen content meter 16. The COD (Cr)
concentration of the treated water in gas-liquid separator 11 was
also measured. On temperature rising in reactor 1, the waste water
was supplied to reactor 1 under the condition of oxygen deficiency
in order to suppress deterioration of the catalyst therein.
[0291] The results was shown in table 17. As a result, it was found
that the properties (specific surface area, specific pore volume
having pore diameter in the range from 0.1 to 10 .mu.m, pore
diameter distribution and mechanical strength) of catalyst A-1
stayed unchanged after the treatments.
Example 70 to 82
[0292] In examples 70 to 82, the treatment was performed in the
same manner including the same waste water, treatment processes,
treatment conditions and equipment as in example 69, except that
the catalysts A-2 to A-8, B-1, B-2, and C-1 to C-4 was used in each
examples respectively instead of catalyst A-1. The results were
shown in table 17. As a result, it was found that the properties
(specific surface area, specific pore volume having pore diameter
in the range from 0.1 to 10 .mu.m, pore diameter distribution and
mechanical strength) of these catalysts stayed unchanged after the
treatments.
Example 83
[0293] In example 83, the treatment was performed in the same
manner including the same waste water, treatment processes,
treatment conditions and equipment as in example 69, except that
the catalyst D-1 was used in each examples respectively instead of
catalyst A-1. The results were shown in table 17. As a result, it
was found that the properties (specific surface area, specific pore
volume having pore diameter in the range from 0.1 to 10 .mu.m, pore
diameter distribution and mechanical strength) of these catalysts
stayed unchanged after the treatments.
Example 84
[0294] The treatment was performed in the same manner including the
same catalyst, treatment processes and equipment as in example 69
except for the following 4 points: 1) waste water to be treated was
waste water containing formic acid as a main ingredient and COD(Cr)
concentration was 8000 mg/L; 2) the treatment temperature was set
to 95.degree. C.; 3) the treatment pressure was set to the
atmosphere pressure; and 4) the supply amount of waste water was
adjusted to 0.75 L/h.
[0295] After 500 hour treatment, COD(Cr) treatment efficiency of
the waste water was 98% and the properties (specific surface area,
specific pore volume having pore diameter in the range from 0.1 to
10 .mu.m, pore diameter distribution and mechanical strength) of
these catalysts stayed unchanged after the treatments.
Example 85
[0296] The treatment was performed for 500 hours in the same manner
including the same catalyst, waste water, treatment processes and
equipment as in example 69 except for the following 3 points: 1)
the treatment temperature was set to 190.degree. C.; 2) the
treatment pressure was set to 2.5 MPa (Gauge); and 3) the supply
amount of the waste water 2.0 L/h.
[0297] After 500 hour treatment, COD(Cr) treatment efficiency of
the waste water was 100%.
[0298] Following the first 500-hour treatment, the treatment was
continued in the same manner including treatment processes and
treatment conditions as in example 69 except that the treatment
temperature was set to 130.degree. C. and the treatment pressure
was set to 0.4 MPa (Gauge). The supply amount of the oxygen
containing gas was controlled so that the oxygen concentration in
the exhaust gas maintained in the range from 0.1 to 0.5 vol %.
[0299] After 100 hour treatment, COD(Cr) treatment efficiency of
the waste water was 89% and the properties (specific surface area,
specific pore volume having pore diameter in the range from 0.1 to
10 .mu.m, pore diameter distribution and mechanical strength) of
these catalysts stayed unchanged after the treatments. it was
observed over the catalyst bed that the catalyst kept its shape and
the amount thereof had maintained.
Example 86
[0300] The treatment was performed for 500 hours at 190.degree. C.
in the same manner including the same waste water, treatment
processes, treatment conditions and equipment as in example 85
except that catalyst C-2 was used instead of catalyst A-1. After
500-hour treatment, COD(Cr) treatment efficiency of the waste water
was 100%. After next 100 hours treatment at 130.degree. C., COD(Cr)
treatment efficiency was the same as that of example 80 (i.g.
COD(Cr) treatment efficiency of the waste water was 93%) and the
properties (specific surface area, specific pore volume having pore
diameter in the range from 0.1 to 10 .mu.m, pore diameter
distribution and mechanical strength) of these catalysts stayed
unchanged after the treatments. it was observed over the catalyst
bed that the catalyst kept its shape and the amount thereof had
maintained.
Example 87
[0301] The treatment was performed in the same manner including the
same catalyst, waste water, treatment processes, treatment
conditions and equipment as in example 70 except in that the supply
amount of the oxygen-containing gas was adjusted so that the oxygen
concentration in the exhaust gas was in the range from 10 to
11%.
[0302] After 500 hour treatment, COD(Cr) treatment efficiency of
the waste water was 87% which was the same value of COD(Cr)
treatment efficiency after 100 hour treatment. The wastewater was
treated stably throughout the treatment and the properties
(specific surface area, specific pore volume having pore diameter
in the range from 0.1 to 10 .mu.m, pore diameter distribution and
mechanical strength) of these catalysts stayed unchanged after the
treatments.
17 TABLE 17 Catalyst COD(Cr) Treatment No. Weight Ratio Of Catalyst
Efficiency (%) Remarks Catalyst A-1 Activated Carbon/Ti/Pt = 92
Example 69 Preparation 1 98.7/1.0/0.3 Catalyst A-2 Activated
carbon/Zr/Pt = 94 Example 70 Preparation 2 98.7/1.0/0.3 Catalyst
A-3 Activated carbon/Fe/Pt = 89 Example 71 Preparation 3
98.7/1.0/0.3 Catalyst A-4 Activated carbon/Mn/Pt = 71 Example 72
Preparation 4 98.7/1.0/0.3 Catalyst A-5 Activated carbon/Ce/Pt = 88
Example 73 Preparation 5 98.7/1.0/0.3 Catalyst A-6 Activated
carbon/Pr/Pt = 86 Example 74 Preparation 6 98.7/1.0/0.3 Catalyst
A-7 Activated carbon/Sn/Pt = 62 Example 75 Preparation 7
98.7/1.0/0.3 Catalyst A-8 Activated carbon/Bi/Pt = 66 Example 76
Preparation 8 98.7/1.0/0.3 Catalyst B-1 Activated carbon/Ti/Pd = 81
Example 77 Preparation 9 98.7/1.0/0.3 Catalyst B-2 Activated
carbon/Ti/Ru = 67 Example 78 Preparation 10 98.5/1.0/0.5 Catalyst
C-1 Activated carbon/Ti/Pt = 76 Example 79 Preparation 11
99.2/0.5/0.3 Catalyst C-2 Activated carbon/Ti/Pt = 93 Example 80
Preparation 12 96.7/3.0/0.3 Catalyst C-3 Activated carbon/Zr/Pt =
80 Example 81 Preparation 13 99.2/0.5/0.3 Catalyst C-4 Activated
carbon/Zr/Pt = 96 Example 82 Preparation 14 96.7/3.0/0.3 Catalyst
D-1 Activated carbon/Ti/Pt = 60 Example 83 Preparation 15
98.7/1.0/0.3
EFFECT OF THE INVENTION
[0303] In the method of oxidizing/decomposing organic and/or
inorganic oxidizable substances in the waste water by catalytic wet
oxidation, the present invention provides a method for treating
waste water efficiently for a long period in a stable manner by wet
oxidation using a catalyst containing activated carbon at low
temperature and under low pressure.
[0304] The present invention also provides a method for suppressing
deterioration of the catalytic activity of the solid catalyst at
the time of temperature rising when starting up the operation of
the wet oxidation and/or at the time of temperature lowering when
suspending the operation of the wet oxidation.
[0305] The present invention further provides a method for
efficiently recovering the degraded catalytic activity of the
catalyst containing activated carbon.
[0306] This application is based on Japanese patent application
serial No. 2000-5198 filed on Jan. 5, 2000, No. 2000-102629 filed
on Apr. 4, 2000, and Nos. 2000-114130 and 2000-114131 filed on Apr.
14, 2000, whose priorities are claimed under Paris convention, thus
the contents thereof is incorporated by reference.
[0307] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiment is therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalence of such
metes and bounds are therefore intended to embraced by the
claims.
* * * * *