U.S. patent application number 10/855428 was filed with the patent office on 2004-11-04 for process and apparatus for treating gas containing fluorine-containing compounds and co.
This patent application is currently assigned to EBARA CORPORATION. Invention is credited to Mori, Yoichi.
Application Number | 20040219086 10/855428 |
Document ID | / |
Family ID | 18891514 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219086 |
Kind Code |
A1 |
Mori, Yoichi |
November 4, 2004 |
Process and apparatus for treating gas containing
fluorine-containing compounds and CO
Abstract
The purpose of the present invention is to provide a process and
an apparatus for efficiently treating a gas containing
fluorine-containing compounds and CO to be discharged, for example,
from the step of dry cleaning the inner surfaces and the like of a
semiconductor manufacturing apparatus or the step of etching
various types of formed films such as oxide films in the
semiconductor industry. In order to accomplish the above-mentioned
purpose, the gas treating process according to the present
invention is a process for treating a gas containing
fluorine-containing compounds and CO which comprises contacting the
above described gas with O.sub.2 and H.sub.2O at a temperature of
850.degree. C. or higher to oxidize the CO to CO.sub.2; and then
contacting the gas with .gamma.-alumina at a temperature of 600 to
900.degree. C. to decompose the fluorine-containing compounds.
Inventors: |
Mori, Yoichi;
(Chigasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
EBARA CORPORATION
11-1, Haneda Asahi-cho, Ohta-ku
Tokyo
JP
|
Family ID: |
18891514 |
Appl. No.: |
10/855428 |
Filed: |
May 28, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10855428 |
May 28, 2004 |
|
|
|
10060224 |
Feb 1, 2002 |
|
|
|
6764666 |
|
|
|
|
Current U.S.
Class: |
423/240S |
Current CPC
Class: |
B01D 2257/502 20130101;
B01D 2251/00 20130101; B01D 53/864 20130101; B01D 2251/102
20130101; B01D 53/86 20130101; B01D 2257/2027 20130101; B01D
53/8659 20130101 |
Class at
Publication: |
423/240.00S |
International
Class: |
B01D 053/68 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2001 |
JP |
26750/2001 |
Claims
1-2. (Canceled)
3. An apparatus for treating a gas containing fluorine-containing
compounds and CO which comprises a heat oxidation vessel having a
hollow inside enabling the passage of the above described gas
therethrough, a heating means capable of heating the temperature of
the gas in the hollow inside to 850.degree. C. or higher, a gas
inlet, an O.sub.2 inlet and H.sub.2O inlet; and a catalytic
reaction vessel which is under fluid-communicating condition with
the heat oxidation vessel and has been filled with
.gamma.-alumina.
4. The apparatus of claim 3, wherein the catalytic reaction vessel
further has a heating means capable of heating the .gamma.-alumina
to 600 to 900.degree. C.
5. The apparatus of claim 3, wherein the .gamma.-alumina has a
crystal structure which exhibits diffraction lines having an
intensity of 100 or more at five angles of 33.degree..+-.1.degree.,
37.degree..+-.1.degree., 40.degree..+-.1.degree., 46.degree.35
1.degree. and 67.degree..+-.1.degree. of the angles of diffraction
2.theta.measured by an X-ray diffraction apparatus.
6. The apparatus of claim 3, wherein the heat oxidation vessel
further has a contact auxiliary means for enhancing the contact
efficiency of the CO in the gas with O.sub.2 and H.sub.2O.
7. The apparatus of claim 4, wherein the heat oxidation vessel
further has a contact auxiliary means for enhancing the contact
efficiency of the CO in the gas with O.sub.2 and H.sub.2O.
8. The apparatus of claim 5, wherein the heat oxidation vessel
further has a contact auxiliary means for enhancing the contact
efficiency of the CO in the gas with O.sub.2 and H.sub.2O.
9. An apparatus for treating a gas having fluorine-containing
compounds and CO, comprising: a heat oxidation vessel having a
hollow inside for a passage of the gas therethrough, a heater for
heating the gas in the hollow inside to a temperature of
850.degree. C. or higher and the heated gas contacting with
H.sub.2O and O.sub.2 to oxidize the CO in the hollow inside, and a
catalytic reaction vessel filled with .gamma.-alumina, wherein the
catalytic reaction vessel having fluid-communicating with the heat
oxidation vessel for receiving the gas passed through the heat
oxidation vessel to treat the fluorine-containing compounds with
the .gamma.-alumina.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a process for treating a
gas containing fluorine-containing compounds and CO, and
particularly it relates to a process and an apparatus for
efficiently treating an exhaust gas containing fluorine-containing
compounds and CO which are discharged in the step of dry cleaning
the inner surfaces and the like of a semiconductor manufacturing
apparatus, the step of etching various types of formed films such
as oxide films and the like in the semiconductor industry.
[0002] In the semiconductor industry, various types of harmful
gases are being used in the semiconductor manufacturing steps and
the environmental pollution by discharging them to the environment
is a matter of concern. Particularly, in an etching step, a CVD
step and the like in the semiconductor industry, fluorinated
hydrocarbons such as CHF.sub.3 and fluorine-containing compounds
such as perfluoro-compounds including CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, C.sub.4F.sub.8, C.sub.5F.sub.8, SF.sub.6 and
NF.sub.3 (hereinafter referred to as "PFC") are being used. It is
of urgent necessity to establish a system of removing the
fluorine-containing compounds present in the exhaust gas from these
steps as the global warming gases. Further, the exhaust gas from
these steps sometimes contains CO as the processing gas or
frequently contains CO which has been generated by exposing a mixed
gas of PFC with O.sub.2 to a plasma in a chamber.
[0003] As the method of removing PFC in a gas, a gas treating
method using an alumina based catalyst obtained by incorporating
various metals into alumina; a gas treating method using alumina
having an Na content as the metal of not greater than 0.1% by
weight; a gas treating method comprising contacting a molecular
oxygen with a gas in the presence of alumina; a gas treating method
using an aluminum-containing catalyst in the presence of steam at a
temperature of 200 to 800.degree. C.; a gas treating method using
various types of metal catalyst in the presence of a molecular
oxygen and water; and the like have been proposed. Furthermore, as
described in the specification of Japanese Patent Application No.
2000-110668, a gas treating method using .gamma.-alumina having a
specific crystal structure (which exhibits diffraction lines having
an intensity of 100 or more at the five angles of
33.degree..+-.1.degree., 37.degree..+-.1.degree.,
40.degree..+-.1.degree.- , 46.degree..+-.1.degree. and
67.degree..+-.1.degree. of the angles of diffraction 2.theta.
measured by an X-ray diffraction apparatus) as the catalyst has
been proposed.
[0004] On the other hand, as the method for removing CO in a gas,
there is a method comprising oxidizing CO using a hopcalite
oxidation catalyst (a composite oxide of Cu and Mn, an Ni oxide,
and the like) and O.sub.2 to CO.sub.2 which is then removed.
However, the technique of simultaneously treating
fluorine-containing compounds and CO has not yet been reported.
[0005] Accordingly, in order to treat both fluorine-containing
compounds and CO in a gas according to the conventional technique,
it is necessary to adopt a method comprising forming a two-stage
catalytic reaction vessel having a CO oxidation catalyst arranged
in the previous stage and .gamma.-alumina arranged in the later
stage and passing a gas therethrough to oxidize CO in the previous
stage and to decompose the fluorine-containing compounds in the
latter stage. However, in this instance, there is a problem that
the fluorine in the fluorine-containing compounds present in the
gas comes to a catalytic poison against the CO oxidation catalyst
to remarkably lower the CO oxidative power in the reaction vessel
of the previous stage and as a result, the CO cannot be treated to
a threshold limit value-time weighted average concentration
(TLV-TWA value) of 25 ppm or smaller in a short period of time.
[0006] Furthermore, in order to treat a gas containing
fluorine-containing compounds and CO according to the conventional
technique, there are such problems that each component has to be
treated with a different catalyst, which needs to use different
heating vessels to be individually filled with different catalysts,
and the treating temperature for each heating vessel has to be
individually controlled, and further a wide space for installing
the apparatuses is necessary, and the temperature control becomes
complicated. Further, there is a problem of complicating the
control of catalysts since the period of exchanging the catalyst
differs due to the difference in the lives of individual catalysts.
In addition, there is a problem of an increase in the running cost
such as the expense necessary for periodically exchanging the
catalysts.
[0007] Then, the object of the present invention is to solve the
above described problems according to the conventional technique
and to provide a process and an apparatus for treating a gas
containing fluorine-containing compounds and CO which can
simultaneously and efficiently treat fluorine-containing compounds
and CO and are low in the running cost and can be simply
controlled.
SUMMARY OF THE INVENTION
[0008] In order to solve the above described problems, the present
inventors have made strenuous investigations, and found that the
above described object can be achieved by first reacting a gas
containing fluorine-containing compounds and CO with O.sub.2 and
H.sub.2O without using a CO treating catalyst at a specified
temperature or higher to oxidize the CO to CO.sub.2, and then
contacting the gas with .gamma.-alumina as the catalyst to
decompose the fluorine-containing compounds, in treating the gas
containing the fluorine-containing compounds and CO.
[0009] Namely, according to the present invention, there is
provided a process for treating a gas containing
fluorine-containing compounds and CO which comprises contacting the
above described gas with O.sub.2 and H.sub.2O at a temperature of
850.degree. C. or higher to oxidize the CO to CO.sub.2; and
subsequently contacting the gas with .gamma.-alumina heated at 600
to 900.degree. C. to decompose the fluorine-containing
compounds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic perspective view showing one preferred
embodiment of the apparatus for treating a gas containing
fluorine-containing compounds and CO according to the present
invention. In FIG. 1, each referential numerals have the following
meaning.
[0011] 1: PFC exhaust gas treating apparatus;
[0012] 20: heat oxidation vessel;
[0013] 20b: oxidation reaction zone;
[0014] 21: PFC exhaust gas inlet;
[0015] 22: O.sub.2 inlet;
[0016] 23: H.sub.2O inlet;
[0017] 28: ceramic heater;
[0018] 29: baffles;
[0019] 30: catalytic reaction vessel;
[0020] 31: .gamma.-alumina;
[0021] 32: ceramic heater;
DETAILED DESCRIPTION OF THE INVENTION
[0022] The gas containing fluorine-containing compounds and CO
which can be treated by the present invention may include exhaust
gases which are discharged in the step of dry cleaning the inner
surfaces of a semiconductor manufacturing apparatus and the step of
etching various types of formed films in the semiconductor industry
and the like. Further, the above described fluorine-containing
compounds may include fluorinated hydrocarbons such as such
CHF.sub.3, perfluoro-compounds such as CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, C.sub.4F.sub.8, C.sub.5F.sub.8, SF.sub.6 and
NF.sub.3 and the like.
[0023] In the present invention, the temperature at which the above
described gas is contacted with O.sub.2 and H.sub.2O is 850.degree.
C. or higher, preferably 870.degree. C. or higher. When the
temperature is lower than 850.degree. C., the CO in the gas is not
sufficiently oxidized and remains, and thus such temperatures are
not preferred.
[0024] In the present invention, the gas containing
fluorine-containing compounds and CO (hereinafter referred to as
"PFC exhaust gas" for brevity) is first contacted with O.sub.2 and
H.sub.2O at the above described temperature to cause the reactions
in the gas phase as shown by the following formulae, whereby CO is
oxidized to CO.sub.2.
2CO+O.sub.2.fwdarw.2CO.sub.2
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
2H.sub.2+O.sub.2.fwdarw.2H.sub.2O
[0025] Subsequently, the gas is then contacted with .gamma.-alumina
at a temperature of 600 to 900.degree. C., by which, the
fluorine-containing compounds in the gas is decomposed. For
example, when the gas contains CF.sub.4as the PFC, the CF.sub.4 is
decomposed to CO.sub.2 and HF by the reaction as shown by the
following formula.
CF.sub.4+2H.sub.2O .fwdarw.CO.sub.2+4HF
[0026] In the present invention, the amounts of O.sub.2 and
H.sub.2O to be contacted with a PFC exhaust gas are preferably
sufficient to decompose all of CO and fluorine-containing compounds
in the PFC exhaust gas to be treated to CO.sub.2 and HF. In a
preferred embodiment, the amount of O.sub.2 to be added to the PFC
exhaust gas is preferably at least molar amount necessary for the C
atoms in the fluorine-containing compounds and the C atoms of CO
which are present in the PFC exhaust gas to come to CO.sub.2
(minimum molar amount), more preferably the amount of at least
molar amount obtained by adding one mole to the minimum molar
amount. Further, the amount of H.sub.2O to be added to the PFC
exhaust gas is preferably at least molar amount necessary for the F
atoms in the fluorine-containing compounds to come to HF (minimum
molar amount), more preferably, the molar amount corresponding to 6
to 20 times of one mole of the fluorine-containing compounds. In
this instance, H.sub.2O is preferably introduced in a gaseous state
and, for example, H.sub.2O is sent from an H.sub.2O tank to a
vaporizer by means of a pump and heated to 100.degree. C. or higher
to render the entire amount steam, and furthermore it is preferred
to introduce an H.sub.2O with a pressure of an inert gas such as
N.sub.2.
[0027] In the present invention, the .gamma.-alumina to be
contacted with the PFC exhaust gas acts as a catalyst for
decomposing fluorine-containing compounds. In the present
invention, the contact of the PFC exhaust gas with .gamma.-alumina
is preferably conducted at a temperature of 600 to 900.degree. C.,
preferably 650 to 850.degree. C., more preferably 750.degree. C.
When the contact temperature of the PFC exhaust gas with the
.gamma.-alumina is lower than 600.degree. C., the activity of the
alumina as a catalyst is lowered to decrease the decomposition
ratio of the PFC, and thus such temperatures are not suitable, and
conversely temperatures of higher than 900.degree. C. cause crystal
transition and there is a fear of vitrifying the .gamma.-alumina,
and thus such temperatures are not suitable. It is preferred to
heat the .gamma.-alumina catalyst to the above described
temperature by a heating means.
[0028] As the .gamma.-alumina which can be used in the present
invention, the .gamma.-alumina having a crystal structure which
exhibits diffraction lines having an intensity of 100 or more at
five angles of 33.degree..+-.1.degree., 37.degree..+-.1.degree.,
40.degree..+-.1.degree.- , 46.degree..+-.1.degree. and
67.degree..+-.120 of the angles of diffraction 2.theta. measured by
an X-ray diffraction apparatus as proposed in Japanese Patent
Application No. 2000-110668 can be preferably used. The Na.sub.2O
content in the alumina is preferably not greater than 0.02% by
weight based on the entire amount of the .gamma.-alumina in
consideration of the decomposition performance of the
fluorine-containing compounds. The .gamma.-alumina having such a
crystal structure can be obtained, for example, by firing an
alumina sol as the spherical alumina hydrogel
[Al(OH).sub.y.nH.sub.2O]. Although the .gamma.-alumina which is
used in the present invention is not particularly limited in its
shape as far as it has the above described crystal structure, it is
preferably spherical from the standpoint of handling properties.
Further, although the particle size of the .gamma.-alumina may be
within the range which does not increase a pressure drop when the
gas to be treated is passed, it is preferably fine to increase the
contact area with the gas components to be treated and is
preferably in the range of 0.8 mm to 2.6 mm.
[0029] Further, according to the present invention, there is
provided an apparatus for treating a gas containing
fluorine-containing compounds and CO. The apparatus for treating a
gas containing fluorine-containing compounds and CO comprises a
heat oxidation vessel having a hollow inside enabling the passage
of the above described gas therethrough, a heating means capable of
heating the temperature of the gas in the above described hollow
inside to 850.degree. C. or higher, a gas inlet, an O.sub.2 inlet
and an H.sub.2O inlet; and a catalytic reaction vessel which is
under fluid-communicating condition with the above-described heat
oxidation vessel and has been filled with .gamma.-alumina.
[0030] In the PFC exhaust gas treating apparatus of the present
invention, the heat oxidation vessel and the catalytic reaction
vessel may be arranged under fluid-communicating condition, and
they may be formed as one body or as separate bodies. Further,
although the material of the heat oxidation vessel and the
catalytic reaction vessel is not particularly limited, it is
preferably formed of a material which is stable in a high
temperature atmosphere and inert to the gas components to be
treated and, simultaneously, excels in thermal conductivity, and
particularly preferably formed of stainless steel.
[0031] In the PFC exhaust gas treating apparatus of the present
invention, a heating means of the heat oxidation vessel is not
particularly limited as far as it can heat the gas phase portion
formed in the hollow inside of the heat oxidation vessel to
850.degree. C. or higher, preferably to 870.degree. C. or higher
and, for example, a ceramic heater such as a ceramic electric
tubular furnace is preferably arranged on the outside of the heat
oxidation vessel.
[0032] In the heat oxidation vessel of the PFC exhaust gas treating
apparatus of the present invention, at least a PFC exhaust gas
inlet, an O.sub.2 inlet and an H.sub.2O inlet are provided. These
inlets are preferably provided at the top portion of the heat
oxidation vessel, and each is connected to a PFC exhaust gas
generation source such as an exhaust gas line from a semiconductor
manufacturing apparatus, an O.sub.2 supply source, or an H.sub.2O
supply source through piping. It is preferred to introduce H.sub.2O
in a gaseous form, and thus in a preferred embodiment, the H.sub.2O
supply line to be connected to the H.sub.2O inlet is constituted of
an H.sub.2O (liquid) tank of the H.sub.2O supply source, a
vaporizer which vaporizes the liquid H.sub.2O to be supplied from
the H.sub.2O tank, a piping which connects the tank with the
vaporizer, a water pump provided on the piping, and a supply source
of an inert gas such as N.sub.2 for pumping the vaporized H.sub.2O
to the H.sub.2O inlet of the heat oxidation vessel, and a heating
means such as a band heater is installed on the piping connected to
the H.sub.2O inlet.
[0033] Further, it is preferred to install a contact auxiliary
means to enhance the contact efficiency of the CO in the gas with
O.sub.2 and H.sub.2O in the inside of the heat oxidation vessel.
The contact auxiliary means is not particularly limited as far as
it can cause a turbulence in the gas phase portion to be formed in
the hollow inside of the heat oxidation vessel and may include, for
example, baffles formed by arranging a plurality of plates, fins or
the like on the inner wall of the heat oxidation vessel spirally or
alternately so as to face one another in the radial direction,
fillers having a small pressure loss and the like. In the case of
using baffles as the contact auxiliary means, the surfaces of the
baffles may be coated with a metal such as Ni.
[0034] The catalytic reaction vessel of the PFC exhaust gas
treating apparatus of the present invention is filled with
.gamma.-alumina. The volume of the catalytic reaction vessel is not
particularly limited as far as it can be filled with
.gamma.-alumina. As the .gamma.-alumina to be filled in the
catalytic reaction vessel, the .gamma.-alumina having the above
described specified crystal structure can preferably be used.
[0035] Further, in a preferred embodiment, the catalytic reaction
vessel is provided with a heating means to heat .gamma.-alumina to
600 to 900.degree. C., preferably 650 to 850.degree. C., more
preferably 750.degree. C. This heating means is not particularly
limited and the same heating means as provided in the heat
oxidation vessel can be used, and the heating means as described
above in connection with the heat oxidation vessel can be
preferably be used.
[0036] Moreover, if necessary or required, the PFC exhaust gas
treating apparatus of the present invention may be combined with an
apparatus for separating solid substances such as a water splaying
tower to separate solid substances which might be present in the
gas, or an apparatus for removing an acid gas such as a water
splaying tower to remove an acid gas such as HF to be obtained
after the PFC exhaust gas treatment of the present invention.
[0037] With reference to the Figure attached hereto, the PFC
exhaust gas treating apparatus of the present invention will now be
explained in more detail but the present invention should not be
limited thereto. In the following description, in order to simplify
the explanation, fluorine-containing compounds are supposed to be
perfluoro-compounds such as CF.sub.4 and abbreviated to merely
"PFC" for explanation.
[0038] FIG. 1 is a schematic view showing one preferred embodiment
of the PFC exhaust gas treating apparatus of the present invention.
The PFC exhaust gas treating apparatus of the present invention 10
has a heat oxidation vessel 20 which allows a PFC exhaust gas to
contact with O.sub.2 and H.sub.2O at a temperature of 850.degree.
C. or higher to effect oxidation treatment of CO in the gas, and a
catalytic reaction vessel 30 which allows the oxidation treated gas
to contact with .gamma.-alumina at a temperature of 600 to
900.degree. C. to decompose the PFC in the gas. The heat oxidation
vessel 20 and the catalytic reaction vessel 30 are arranged in such
a fluid-communicating condition that the PFC exhaust gas flows down
from the heat oxidation vessel 20 arranged at the upper stage to
the catalytic reaction vessel 30 arranged at the lower stage. In
the present embodiment, the heat oxidation vessel 20 and the
catalytic reaction vessel 30 comprise cylindrical stainless steel
mini-columns having the same size.
[0039] At the top portion 20a of the heat oxidation vessel 20, a
gas inlet 21, an O.sub.2 inlet 22 and an H.sub.2O inlet 23 are
provided. The gas inlet 21 is connected to a PFC exhaust gas supply
source (not shown in the Figure) such as an exhaust gas line of a
semiconductor manufacturing apparatus through piping. The O.sub.2
inlet 22 is connected to an O.sub.2 supply source (not shown in the
Figure) through piping. The H.sub.2O inlet 23 is connected to a
vaporizer 25 through piping 24 wrapped with a band heater, and the
vaporizer 25 is connected to an H.sub.2O (liquid) tank 26 through
piping on which a water pump 27 is installed. In addition, the
vaporizer 25 is connected to an inert gas (N.sub.2) supply source
through piping.
[0040] The inside of the heat oxidation vessel 20 is rendered
hollow, and the hollow inside has an oxidation reaction zone 20b
into which an PFC exhaust gas, O.sub.2 and H.sub.2O are introduced
to advance the oxidation reaction of CO. The oxidation reaction
zone 20b has a plurality of baffles 29 as the contact auxiliary
means to enhance the contact efficiency of CO in the PFC exhaust
gas with O.sub.2 and H.sub.2O. The baffles 29 are plates or fins
having a size slightly longer than the inner radius of the heat
oxidation vessel 20 and are spirally arranged on the inner wall of
the heat oxidation vessel 20 or are alternately arranged on the
inner wall of the heat oxidation vessel 20 so as to face one
another in the radial direction. At the outer periphery of the heat
oxidation vessel 20, a ceramic electric tubular furnace 28 is
provided as the heating means capable of heating the temperature of
the oxidation reaction zone 20b to 850.degree. C. or higher.
Further, in order to measure the temperature of the oxidation
reaction zone, a thermocouple (not shown in the Figure) is provided
at the center of the hollow inside of the heat oxidation
vessel.
[0041] Downstream of the heat oxidation vessel 20, a catalytic
reaction vessel 30 is provided in a fluid-communicating condition
with the heat oxidation vessel 20. The inside of the catalytic
reaction vessel 30 is filled with .gamma.-alumina. The
.gamma.-alumina having the above described specific structure is
preferably used.
[0042] Furthermore, at the outer periphery of the catalytic
reaction vessel 30, a ceramic electric tubular furnace 32 is
preferably provided as the heating means capable of heating the
.gamma.-alumina at 600 to 900.degree. C. This ceramic electric
tubular furnace 32 may be either integrated with or separated from
the ceramic electric tubular furnace 28 provided for the heat
oxidation vessel 20. Further, in order to measure the temperature
of the inside of the catalytic reaction vessel 30, a thermocouple
(not shown in the Figure) is installed in the inside of the
catalytic reaction vessel 30.
EXAMPLES
[0043] The present invention will be more concretely explained
below on the basis of examples.
Example 1
[0044] The relationship between the temperature of the gas phase
portion in a heat oxidation vessel and the removal ratio of CO was
observed as the CO treatment properties in a gas with no
catalyst.
[0045] As the heat oxidation vessel, a stainless steal mini-column
having an inner diameter of 27 mm and a height of 500 mm amounted
in a ceramic electric tubular furnace was used. In order to measure
the temperature of the gas phase portion in the hollow inside of
the heat oxidation vessel, a thermocouple was installed nearly at
the center of the hollow inside of the heat oxidation vessel. The
temperature was varied stepwise from 500 to 900.degree. C. while
monitoring the temperature of the gas phase portion with the
thermocouple.
[0046] Carbon monoxide (CO) diluted with N.sub.2 which was used as
an artificial test exhaust gas, O.sub.2 and H.sub.2O were
introduced into the hollow inside of the heat oxidation vessel so
as for the O.sub.2 and H.sub.2O to come to at least equimolar
amounts at a total gas flow rate of 410 sccm. At this instance, the
concentration of the CO introduced was set at 1.22 to 1.33%; that
of O.sub.2 introduced was set at 3.7 to 3.9%; and the flow velocity
of H.sub.2O was set at 0.079 mL/min. The treatment time was set at
30 minutes.
[0047] In order to observe the disposal performance in the heat
oxidation vessel, CO, CO.sub.2, O.sub.2 and H.sub.2 in the gas at
the outlet of the column were analyzed using a gas chromatograph
apparatus equipped with a mass detector ("AGS-7000U", manufactured
by Anelva Co., Ltd.). The results are set forth in Table 1.
1TABLE 1 Treating Gas at Inlet Gas at Outlet CO Temperature CO
O.sub.2 H.sub.2O CO CO.sub.2 O.sub.2 H.sub.2 Removal (.degree. C.)
(%) (%) (mL/min) (ppm) (ppm) (%) (ppm) Ratio (%) 500 1.28 3.8 0.079
11200 470 3.8 <2 13 600 1.22 3.9 0.079 9960 1470 3.8 <2 18
700 1.23 3.8 0.079 7160 3600 3.6 <2 42 750 1.27 3.8 0.079 3770
6310 3.4 <2 70 800 1.23 3.8 0.079 500 10500 3.2 <2 96 850
1.29 3.8 0.079 12 9470 3.2 <2 99.9 870 1.28 3.7 0.079 <2
11000 3.2 <2 100 900 1.31 3.9 0.079 <2 11300 2.9 <2
100
[0048] As would be understood from Table 1, when the temperature of
the gas phase portion of the heat oxidation vessel was 850.degree.
C., CO was reduced to 12 ppm (removal ratio of 99.9%) which was
lower than the tolerance concentration (25 ppm), and when the
temperature was 870.degree. C., CO was reduced to lower than the
detection limit (25 ppm). At this time, the CO.sub.2 in the gas at
the outlet (11000 ppm) was nearly equal to the concentration of the
CO introduced and H.sub.2 was not detected, and accordingly it can
be considered that CO has all been oxidized to CO.sub.2.
Comparative Example 1A
[0049] The same experiment as in Example 1 was carried out with the
use of the apparatus of Example 1 by introducing CO at a
concentration of 1.33% and H.sub.2O at a flow velocity of 0.079
mL/min at a total gas flow rate of 410 sccm into the inside of the
heat oxidation vessel without the addition of O.sub.2 at a
temperature of the gas phase portion of the heat oxidation vessel
of 870.degree. C. for 30 minutes of the treating time. The results
are set forth in Table 2.
[0050] As would be understood from Table 2, even when the
temperature of the gas phase portion was 870.degree. C., by the
addition of H.sub.2O alone, the removal ratio of CO was merely 38%,
and thus the disposal performance of CO was low.
Comparative Example 1B
[0051] The same experiment as in Example 1 was carried out with the
use of the apparatus of Example 1 by introducing CO at a
concentration of 1.24% and O.sub.2 at a concentration of 3.8% at a
total gas flow rate of 410 sccm without the addition of H.sub.2O at
a temperature of the gas phase portion of the heat oxidation vessel
of 870.degree. C. for 30 minutes of the treating time. The results
are set forth in Table 2.
[0052] As would be understood from Table 2, even when the
temperature of the gas phase portion was 870.degree. C., the
addition of O.sub.2 alone could not completely remove CO, and 200
ppm of CO which greatly exceeded the tolerance concentration (25
ppm) were detected in the gas at the outlet.
2 TABLE 2 Gas at Inlet Gas at Outlet Removal CO O.sub.2 H.sub.2O CO
CO.sub.2 O.sub.2 H.sub.2 Ratio (%) (%) (mL/min) (ppm) (ppm) (%)
(ppm) of CO (%) Example 1 1.28 3.7 0.079 <2 11000 3.2 <2 100
(870.degree. C.) Comparative 1.33 0 0.079 8330 3220 <0.3 <2
38 Example 1A Comparative 1.24 3.8 0 200 11600 3.1 <2 98 Example
1B
Example 2
[0053] The disposal performance of the PFC exhaust gas treating
apparatus according to the present invention was observed. As the
PFC exhaust gas treating apparatus, an apparatus 10 having a
structure shown in FIG. 1 was used. As the heat oxidation vessel 20
and the catalytic reaction vessel 30, stainless steel mini-columns
having an inner diameter of 27 mm and a height of 500 mm were used.
As the .gamma.-alumina, "Neobead GB-08" (a product of Mizusawa
Chemical Co., Ltd., Na.sub.2O content of not greater than 0.01% by
weight) having a particle diameter of 0.8 mm and a crystal
structure which exhibits diffraction lines having an intensity of
100 or more at five angles of 33.degree..+-.1.degree.,
37.degree..+-.1.degree., 40.degree..+-.1.degree.,
46.degree..+-.1.degree. and 67.degree..+-.1.degree. of the angles
of diffraction 2.theta. measured by an X-ray diffraction apparatus
was filled in the catalytic reaction vessel 30 to a height of 100
mm (a filled amount of 57 mL). As the heating means for the heat
oxidation reaction vessel 20 and the catalytic reaction vessel 30,
ceramic electric tubular furnaces 28 and 32 were used. Within these
furnaces, the heat oxidation reaction vessel 20 and the catalytic
reaction vessel 30 were mounted. The temperatures of the oxidation
reaction zone 20b in the heat oxidation vessel 20 and the inside of
the catalytic reaction vessel 30 were measured by thermocouples
(not shown in the Figure) installed at their center portion.
[0054] The temperature of the oxidation reaction zone 20b in the
heat oxidation reaction vessel 20 was heated to 870.degree. C. and
that of .gamma.-alumina in the catalytic reaction vessel 30 was
heated to 750.degree. C., and CO and CF.sub.4 diluted with N.sub.2
as an artificial test PFC exhaust gas and at least equimolar
amounts of CO.sub.2 an O.sub.2 were introduced into the heat
oxidation vessel 20 at a total gas flow rate of 410 sccm. The
concentrations introduced were set at CO: 1.24%, CF.sub.4: 1.61%,
and O.sub.2: 5.6%, respectively, and the flow velocity of H.sub.2O
was set at 0.079 mL/min.
[0055] In order to confirm the disposal performance of the present
apparatus, concentration of CO, CF.sub.4, CO.sub.2, O.sub.2 and
H.sub.2 in the gas at the outlets of the heat oxidation vessel and
the catalytic reaction vessel were analyzed by a gas chromatograph
apparatus equipped with a mass detector ("AGS-7000U", manufactured
by Anelva Co., Ltd.). The results are set forth in Table 3.
3 TABLE 3 Gas at Outlet Sampling Point CO(ppm) CF.sub.4(ppm)
CO.sub.2(%) O.sub.2(%) H.sub.2(ppm) At Outlet of Heat <1 15400
1.19 4.5 <2 Oxidation Vessel At Outlet of <1 <1 2.79 3.9
55 Catalyst Reaction Vessel
[0056] As would be clear from Table 3, at the outlet of the heat
oxidation vessel, CO was disposed to lower than the detection limit
(2 ppm) but CF.sub.4 was not removed. At the outlet of the
catalytic reaction vessel, both CF.sub.4 and CO were disposed to
lower than the detection limit (1 ppm for CF.sub.4 and 2 ppm for
CO). Accordingly, it has been confirmed that the present apparatus
which combines a heat oxidation vessel with a catalytic reaction
vessel has enabled good treatment of both CO and CF.sub.4.
Comparative Example 2
[0057] In order to observe the effect of treating CO without
passing a PFC exhaust gas through the heat oxidation vessel, an
artificial test exhaust gas and O.sub.2 and H.sub.2O were directly
passed through the catalytic reaction vessel under the same
conditions as in Example 2 excepting the heat oxidation vessel to
carry out a comparative example. The results are set forth in Table
4.
4 TABLE 4 Gas at Outlet of Catalyst Reaction Vessel CO(ppm)
CF.sub.4(ppm) CO.sub.2(%) O.sub.2(%) H.sub.2(ppm) Example 2 <1
<1 2.79 3.9 55 Comparative 3700 <1 2.42 4.1 39 Example 2
[0058] As would be clear from Table 4, although the disposal of
CF.sub.4 was possible only by the catalytic reaction vessel, CO
removal ratio was as low as 70%, and CO could not be disposed to
lower than the tolerance concentration.
[0059] From the above described Examples and Comparative Examples,
it could be understood that the use of the gas treating apparatus
according to the present invention which comprises a heat oxidation
vessel and a .gamma.-alumina-filled catalytic reaction vessel
enables efficient treatment of a gas containing CO and
fluorine-containing compounds.
[0060] According to the present invention, a gas containing
fluorine-containing compounds and CO can be disposed to carry out
oxidation of CO and decomposition of the fluorine-containing
compounds efficiently and simultaneously, whereby the running cost
becomes low and effective treatment becomes possible.
[0061] According to the present invention, treatment with each
different catalyst, heating vessels to fill different catalysts,
control of the treating temperature for each heating vessel and a
wide space for installing apparatuses are not needed in treating a
gas containing fluorine-containing compounds and CO, and the
temperature control is rendered easy.
[0062] Further, since the use of different catalysts each having a
different life is not required, the control of the catalyst is
rendered easy. Furthermore, no specific catalyst for removing CO is
necessary, and thus the running cost such as the expense in an
periodical exchange of the catalyst can be lowered.
* * * * *