U.S. patent number RE32,392 [Application Number 06/767,943] was granted by the patent office on 1987-04-07 for catalyst pellets with resin binder for decomposition of hypochlorite.
This patent grant is currently assigned to Pennwalt Corporation. Invention is credited to Roger T. Clark, David M. Gardner.
United States Patent |
RE32,392 |
Clark , et al. |
April 7, 1987 |
Catalyst pellets with resin binder for decomposition of
hypochlorite
Abstract
A porous catalyst matrix used for the decomposition of aqueous
hypochlorite solutions is disclosed along with the process for its
use. The catalyst is prepared by sintering a powdered mixture of a
particular metal oxide or hydroxide and a thermoplastic polyolefin
or halogenated polyolefin.
Inventors: |
Clark; Roger T. (Pottstown,
PA), Gardner; David M. (Collegeville, PA) |
Assignee: |
Pennwalt Corporation
(Philadelphia, PA)
|
Family
ID: |
26766138 |
Appl.
No.: |
06/767,943 |
Filed: |
August 21, 1985 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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081925 |
Oct 4, 1979 |
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Reissue of: |
216042 |
Dec 15, 1980 |
04400304 |
Aug 23, 1983 |
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Foreign Application Priority Data
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Mar 15, 1981 [BE] |
|
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888,204 |
Mar 19, 1981 [DK] |
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1244/81 |
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Current U.S.
Class: |
502/159; 210/763;
264/122; 264/125; 264/126; 264/127; 423/497; 502/402; 524/413;
524/431; 524/433; 524/435; 524/436; 524/545 |
Current CPC
Class: |
B01J
23/70 (20130101); B01J 23/75 (20130101); C02F
1/76 (20130101); B01J 37/0009 (20130101); B01J
31/08 (20130101); B01J 37/031 (20130101) |
Current International
Class: |
B01J
31/06 (20060101); C02F 1/76 (20060101); B01J
031/28 (); B01J 031/06 (); C08K 003/22 (); C02B
001/28 () |
Field of
Search: |
;502/159,402
;210/754,756,763 ;524/413,431,433,435,436,545
;264/122,125,126,127 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Konopka; P. E.
Parent Case Text
This application is a Continuation-in-part from application Ser.
No. 081,925, filed Oct. 4, 1979 now abandoned.
Claims
What is claimed is:
1. A porous catalyst matrix .[.in pellet form.]. consisting
essentially of a mixture of a powdered oxide or hydroxide of a
metal selected from the group consisting of iron, copper,
magnesium, nickel and cobalt, and a powdered thermoplastic organic
resin .[.comprising polyvinylidene fluoride.]. .Iadd.selected from
the group consisting essentially of solid polyolefins and
halogenated polyolefins and mixtures thereof .Iaddend.in a weight
ratio of oxide or hydroxide of metal to resin within .[.1:1 to
15:1.]. .Iadd.100:1 to 1:10.Iaddend., which mixture of powders has
been compacted into pellets and then thermally sintered at or about
the softening temperature of the resin, thereby forming a porous
.[.ctalyst.]. .Iadd.catalyst .Iaddend.matrix .[.in pellet form.].
which is stable in aqueous hypochlorite solutions.
2. The porous catalyst matrix .[.in pellet form.]. of claim 1
.Iadd.in pellet form .Iaddend.in which the pellet size is about
one-eight of an inch in diameter and three-sixteenths of an inch in
length.
3. The porous catalyst matrix of claim .[.1.]. .Iadd.2 .Iaddend.in
which the pellets have been crushed and screened to a particle size
of 18 to 35 mesh. .Iadd.
4. The porous catalyst matrix of claim 1 in which the powdered
thermoplastic solid organic resin is selected from the group
consisting essentially of polyvinylidene fluoride, polyethylene,
polypropylene, polytetrafluoroethylene, and mixtures thereof.
.Iaddend. .Iadd.5. The porous catalyst matrix of claim 4 wherein
the powdered oxide or hydroxide of said metal is supported with a
catalyst support material selected from the group of materials
consisting essentially of silica, diatomaceous earth, alkaline
earth metal and alkali metal silicates; aluminas; silicates and
mixed aluminum compounds of oxides, hydroxides and silicates;
magnesia and mixed magnesium compounds of oxides, hydroxides,
silicates and mixtures thereof. .Iaddend.
Description
.Iadd.This is an application for reissue of U.S. Pat. No. 4,400,304
granted Aug. 23, 1983. .Iaddend.
BACKGROUND OF THE INVENTION
Hypochlorite ions in aqueous solution are corrosive to many metals
and are highly toxic to aquatic life. Industrial waste streams
containing aqueous hypochlorite are produced by many processes such
as in the manufacture of chlorine-caustic and dry bleach. Before
these waste streams can be released into public waters, they
require treatment to remove hypochlorite ions.
Various methods including photochemically-, thermally-, and
chemically-induced decompositions have been proposed for removing
hypochlorite from dilute aqueous solutions. For large scale
industrial application, chemical methods are most commonly used.
Chemical methods, which include the use of hydrogen peroxide,
sodium hydrosulfide, hydrochloric acid and sulfur dioxide, or
example, are all expensive when very large quantities of dilute
aqueous hypochlorite are involved. Waste treatment systems which
consume large quantities of these chemicals create a substantial
economic burden on processes which they support.
There is a need for an ecologically efficient and economically
sound method for decomposing large quantities of dilute
hypochlorite. One basis for such a system is the decomposition of
hypochlorite by heterogeneous fixed-bed catalysts to give chloride
ion and oxygen. A number of such catalysts comprising the oxides
and hydroxides of iron, copper, magnesium, nickel and cobalt have
been described in the literature. Of these catalysts, those
prepared from cobalt are the most active.
Because of certain practical drawbacks, fixed-bed catalysts have
not seen widespread commercial application for hypochlorite
decomposition. For example, the high alkalinity of hypochlorite
solution causes the binder support of most tableted and extruded
catalysts to disintegrate, reducing the catalyst totally, or in
part, to a fine slurry. Because of the problems associated with
recovery and recycle of finely divided catalyst particles in
aqueous media, this technology has not seen widespread application.
Also, when fixed-bed catalysts are exposed to waste solutions
containing both calcium ions and hypochlorite, such as waste from
dry bleach manufacture, the catalyst rapidly loses activity due to
calcium carbonate deposition in the catalyst pores. Reactivation of
blinded catalyst is difficult.
Accordingly, it is an object of this invention to provide an
efficient and economically sound catalytic method of decomposing
hypochlorite contained in aqueous industrial waste streams,
including those containing dissolved and suspended calcium salts. A
further object of this invention is to provide a catalyst for use
in the present invention which is efficient, non-polluting and
long-lived.
BRIEF DESCRIPTION OF THE INVENTION
This invention relates to catalyst pellets, capable of decomposing
hypochlorite, which consists of a powdered active catalyst and a
resin binder. The catalyst pellets of this invention are
particularly suitable for treating waste waters containing
hypochlorite in fixed beds and have improved resistance to
disintegration compared to known tableted and extruded catalysts.
The use of the catalyst described herein in fixed-bed decomposition
of hypochlorite constitutes a second aspect of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous solutions containing hypochlorite which can be treated
in accordance with the process of this invention and with the
catalyst pellets described herein may be any aqueous solution which
contains hypochlorite ions such as hypochlorous acid or salts of
hypochlorous acids particularly the alkali metal and alkaline-earth
metal salts.
While the description of our invention uses the term "catalyst
pellets" it is to be understood that the catalyst can be used in
particulate form as well as in the preferred pellet form.
One common source of aqueous streams containing hypochlorite ions
is the waste water from scrubbing in a chlorine liquefaction plant
where the non-condensable "tail gases" are scrubbed with caustic
solution to prevent residual chlorine from entering the atmosphere.
This scrubbing stream contains alkali metal hypochlorite which must
be decomposed before discharge into public waters. Other sources of
aqueous waste waters containing hypochlorite which can be treated
by the method of the present invention occur in the manufacture of
chlorine-caustic and dry bleach.
The method of treating various chemical streams in a fixed-bed
reactor is well-known and does not, as such, constitute a part of
this invention. Similarly, a variety of catalytic materials
suitable for the decomposition of hypochlorite ion are known. The
use of these materials are only a part of the present invention. It
is the special form of the catalyst and its use in the
decomposition of hypochlorite that forms the basis of this
invention. In our invention, known catalysts for the decomposition
of hypochlorite are combined with an organic thermoplastic resin
binder to form a porous catalyst matrix in small paticle or pellet
form which is then utilized in the known process of decomposing
hypochlorite in a fixed bed.
Substances which are suitable for catalyzing the decomposition of
hypochlorite include oxides or hydroxides of iron, copper,
magnesium, nickel or cobalt. However, any substances serving this
function can be adapted for use in the catalyst pellets described
herein.
While these metal oxides and hydroxides can be used as such to
prepare the novel catalysts of our invention, it is preferable to
combine the metal oxides and hydroxides with a catalyst support.
When combined with a catalyst support additional catalyst surface
is exposed to the hypochlorite solutions and considerably greater
catalytic activity and catalyst efficiency are obtained. The
catalyst supports suitable for our new catalysts must be chemically
resistant to the strong hypochlorite and strong alkaline solutions
encountered in the decomposition of industrial aqueous hypochlorite
solutions.
Among the materials suitable as catalyst supports are silica,
diatomaceous earth, alkaline earth metal and alkali metal
silicates; aluminas; silicates and mixed aluminum compounds of
oxides, hydroxides and silicates; magnesia and mixed magnesium
compounds of oxides, hydroxides and silicates. Mixtures of the
various catalyst support materials can also be used.
The resin binder which forms the second essential component of the
catalyst pellets of this invention can be any of a wide variety of
solid thermoplastic organic resins. We have not found any
thermosetting resins which are suitable for this invention. It is
essential that the resin be relatively stable for long periods of
time under contact with hypochlorite and strong alkali and that it
be capable of forming a pellet which is not subject to mechanical
or chemical degradation in use. This excludes resins which are
susceptible to base attack such as epoxys, celluloses, phenolics,
acetates, polyesters, etc. In particular, it has been found that
solid thermoplastic polyolefins and halogenated polyolefins and
their mixtures are suitable. Representative of these materials are
polyethylene, polypropylene, polytetrafluoroethylene and
polyvinylidene fluoride.
The ratio between the substance capable of decomposing hypochlorite
and the organic resin binder can vary widely but generally will be
within the ratio of 100:1 to 1:10. Ratios of 1:1 to 15:1 are
generally preferred. The weight ratio of 2.3:1 to about 5:1 has
been found to be suitable where the substance capable of catalyzing
the decomposition of hypochlorite is cobalt oxide and the organic
resin is any one of a variety of thermoplastic polyolefins. The
essential criteria for selecting an appropriate ratio are that
sufficient thermoplastic organic resin must be present in order to
provide a matrix which is stable to mechanical handling and that
the amount of organic resin is not in excess of that which will
allow permeation of the catalyst pellets by the hypochlorite
solution.
The size of the pellets is not extremely critical. Consideration
should be given to ease of handling and the permeability of the
pellets. Therefore, extremely large pellets are undesirable because
of the possible difficulty of permeation by hypochlorite and the
consequent efficient utilization of the catalyzing ingredient.
Pellets in a cylindrical form having a diameter of about one-eighth
inch and the length of about three-sixteenths of an inch have been
found to be suitable for use in this invention. Smaller
granular-type catalyst particles have also been used with greater
efficiency than the pellets because of the relatively larger
available surface area. The preferred particle size is 18-35
mesh.
The pellets are prepared so that finely divided catalysts for
decomposing hypochlorite is intimately dispersed in the organic
resin matrix. One method for accomplishing this is to grind
powdered catalysts and powered organic resin, for example, in a
ball-mill, forming the intimately mixed powdered composition into
tablets or pellets by compacting them in a conventional machine and
then sintering the pellets at or about the softening temperature of
the organic resin. It is desirable that heating be conducted at a
temperature high enough for sintering to take place but not so high
that chemical degradation occurs or that the physical form of the
pellet is destroyed. The granular-type catalyst particles have been
made by crushing the pellets and sieving to a selected size range.
An equivalent catalyst can be made directly by extrusion followed
by sintering, thus eliminating compacting.
This invention can be used in decomposing hypochlorite waste
liquors which contain calcium ion. This presents special problems
since calcium ion apparently contributes to catalyst deactivation
by depositing calcium carbonate in the pores of the catalyst. In a
special aspect of this invention it has been found advantageous to
remove calcium ion by precipitiation of the calcium as an insoluble
salt, such as calcium carbonate, which is removed prior to allowing
the hypochlorite solution to contact the catalyst. However, it is
also possible to process hypochlorite solutions containing calcium
ion directly and to periodically regenerate the catalyst.
The process of decomposing hypochlorite is generally conducted at
ambient temperature to avoid the energy costs of heating the
hypochlorite liquor. It is recognized, however, that the higher the
temperature the greater is the catalyst activity obtained. The
process is always conducted in the liquid phase.
The following Examples will further illustrate the preparation of
the catalyst pellets of this invention and their use in a fixed-bed
system for decomposition of hypochlorite solutions.
EXAMPLE 1
A silica-supported cobalt oxide powder was prepared by slowly
precipitating cobalt hydroxide from an aqueous solution of cobalt
nitrate containing suspended kieselguhr by the addition of base.
The product was water-washed, dried and calcined at 450.degree. C.
for 2 hours. The resulting powder contained 35% cobalt by weight as
cobalt oxide.
To 15 g of the above powder is added 5 g of polyvinylidene fluoride
molding powder (Kynar 401). The mixture is placed in a size 000
ball mill along with 1/4 full capacity of ceramic balls and milled
for 1 hour. The powdered mixture is tableted into cylindrical
tablets approximately 1/8 inch in diameter and 3/16ths inch long at
9,600 lbs/in.sup.2 and the resulting tablets sintered in an oven at
180.degree. C. for 1 hour. The polymer matrix tablets are very
active for hypochlorite decomposition and retain their physical
integrity indefinitely under reaction conditions.
A fixed-bed catalytic reactor was charged with 100 grams of
catalyst. Simulated industrial hypochlorite waste liquor (prepared
as described below) treated for removal of soluble calcium (0.499%
available chlorine) was passed through the reactor at a rate of
2.25 mls/min. At 25.degree. C. a vent solution containing 0.058%
available chlorine was obtained, corresponding to an 88.5%
conversion of hypochlorite to chloride ion and oxygen.
Simulated industrial hypochlorite waste liquor was prepared by
dissolving 32.4 g of calcium hypochlorite (69.4% available
chlorine), 166 g of sodium chloride, and 74.1 g of calcium chloride
in 1000 ml. of distilled water. The resulting solution was
clarified by settling and the hypochlorite content determined by
titration with sodium thiosulfate (.about.1.25% available
chlorine). Other concentrations were made by successive
dilutions.
Calcium-free hypochlorite solution was prepared by treating the
above simulated industrial hypochlorite waste liquor with a
stoichiometric amount of sodium carbonate (one mole of carbonate
per mole of calcium). The resulting suspension was clarified by
settling and the clear supernatant liquor, after filtering, was
treated with the catalyst.
EXAMPLE 2
This example is identical to Example 1 with the exception that
nickel is substituted for cobalt.
EXAMPLE 3
This example is identical to Example 1 with the exception that
polyethylene powder is substituted for polyvinylidene fluoride
powder and the resulting tablets were sintered in an oven at
120.degree. C. for 1 hour.
The resulting polymer matrix tablets are active for hypochlorite
decomposition and retain their physical integrity indefinitely
under reaction conditions.
EXAMPLE 4
This example is identical to Example 1 with the exception that
tetrafluoroethylene is substituted for polyvinylidene fluoride
powder and the resulting tablets were sintered in an oven at
270.degree. C. for 1 hour.
The resulting polymer matrix tablets are active for hypochlorite
decomposition and retain their physical integrity indefinitely
under reaction conditions.
Catalyst samples prepared according to procedures described in
Example 1 through 4 were evaluated using both 1% sodium
hypochlorite solution (calcium free) and simulated industrial
hypochlorite waste liquor. With 1% sodium hypochlorite solution, no
fall-off in catalytic activity was measured over four weeks of
continuous operation. No disintegration of the catalyst was noted
and total cobalt in the vent liquor was less than 0.5 ppm.
When simulated industrial hypochlorite waste liquor was used as
feed to the reactor, substantial catalytic activity was lost within
48 hours. Catalyst deactivation was attributed to calcium carbonate
deposition in the pores of the catalyst. The catalyst activity was
restored using the procedure described in Example 5.
EXAMPLE 5
A fixed-bed catalytic reactor of cross sectional area 2.5 cm.sup.2
was charged with 100 grams (.about.100 cm.sup.3) of the cobalt
oxide/Kynar catalyst used in Example 1. Calcium-containing
simulated industrial hypochlorite waste liquor (.about.1.25%
available chlorine) prepared according to Example 1 was passed
through the reactor at a rate of 2.5 mls/min (25.degree. C.). After
one day of continuous operation, 93% of the hypochlorite fed to the
reactor was being converted to chloride ion and oxygen. After two
days the conversion was 88%, after three days the conversion was
83%, after four days the conversion was 77% and after five days the
conversion was 71%. At this point the catalyst was regenerated by
purging with fresh water at a rate of 300 mls/min for three hours.
Hypochlorite waste was again passed over the catalyst at a rate of
2.5 mls/min. Hypochlorite conversion after regeneration was 96.5%.
Continous operation followed by regeneration when conversions fall
below 80% was continued for 64 days with no indication that this
procedure cannot be continued indefinitely without a loss of
catalyst efficiency.
EXAMPLE 6
An alumina-supported cobalt oxide powder is prepared by
co-precipitation of cobalt hydroxide and aluminum hydroxide from an
aqueous solution of cobalt nitrate and aluminum nitrate by the
addition of base. The product was water washed, dried and calcined
at 450.degree. C. for 2 hours. The resulting powder contained 25%
cobalt by weight as cobalt oxide.
To 15 g of the above powder is added 5 g of polyvinylidene fluoride
molding powder (Kynar 401). The mixture is placed in a size 000
ball mill along with 1/4-full capacity of ceramic balls and milled
for 1 hour. The powdered mixture is tableted into cylindrical
tablets approximately 1/8 inch in diameter and 3/16 inch long at
9,600 lbs/in.sup.2 and the resulting tablets sinttered in an oven
at 180.degree. C. for 1 hour. The polymer-matrix tablets are very
active for hypochlorite decomposition and retain their physical
integrity indefinitely under reaction conditions.
EXAMPLE 7
A silica-magnesia-supported cobalt oxide powder is prepared by
impregnating a silica-magnesia powder (Davison SM-30) with aqueous
cobalt nitrate and calcining at 400.degree. C. for 2 hours. The
resulting powder contains 30% cobalt by weight as cobalt oxide.
To 15 g of the above powder is added 5 g of polyvinylidene fluoride
molding powder (Kynar 401). The mixture is placed in a size 000
ball mill along with 1/4-full capacity of ceramic balls and milled
for 1 hour. The powdered mixture is tableted into cylindrical
tablets approximately 1/8 inch in diameter and 3/16 inch long at
9,600 lbs/in.sup.2 and the resulting tablets sintered in an oven at
180.degree. C. for 1 hour. The polymer matrix tablets are very
active for hypochlorite decomposition and retain their physical
integrity ibndefinitely under reaction conditions.
EXAMPLE 8
A magnesia-supported cobalt oxide powder is prepared by
co-precipitation of cobalt hydroxide and magnesium hydroxide from
an aqueous solution of cobalt nitrates and magnesium sulfate by the
addition of base. The catalyst is water-washed, dried, and calcined
at 400-450.degree. C. for 2 hours.
To 15 g of the above powder is added 5 of polyvinylidene fluoride
molding powder (Kynar 401). The mixture is placed in a size 000
ball mill along with 1/4full capacity of ceramic balls and milled
for 1 hour. The powdered mixture is tableted into cylindrical
tablets approximately 1/8 inch in diameter and 3/16 inch long at
9,600 lbs/in.sup.2 and the resulting tablets sintered in an oven at
180.degree. C. for 1 hour. The polymer matrix tablets are very
active for hypochlorite decomposition and retain their physical
integrity indefinitely under reaction conditions.
* * * * *