U.S. patent application number 10/676013 was filed with the patent office on 2004-04-08 for process for treating fluorine compound-containing gas.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Arato, Toshiaki, Azuhata, Shigeru, Ikeda, Shinzo, Irie, Kazuyoshi, Kanno, Shuichi, Tamata, Shin, Yamashita, Hisao, Yasuda, Ken.
Application Number | 20040067185 10/676013 |
Document ID | / |
Family ID | 26338096 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040067185 |
Kind Code |
A1 |
Kanno, Shuichi ; et
al. |
April 8, 2004 |
Process for treating fluorine compound-containing gas
Abstract
A gas stream containing at least one fluorine compound selected
from the group consisting of compounds of carbon and fluorine,
compounds of carbon, hydrogen and fluorine, compounds of sulfur and
fluorine, compounds of nitrogen and fluorine and compounds of
carbon, hydrogen, oxygen and fluorine is contacted with a catalyst
comprising at least one of alumina, titania, zirconia and silica,
preferably a catalyst comprising alumina and at least one of nickel
oxide, zinc oxide and titania in the presence of steam, thereby
hydrolyzing the fluorine compound at a relatively low temperature,
e.g. 200.degree.-800.degree. C., to convert the fluorine of the
fluorine compound to hydrogen fluoride.
Inventors: |
Kanno, Shuichi;
(Hitachi-shi, JP) ; Arato, Toshiaki;
(Hitachinaka-shi, JP) ; Ikeda, Shinzo; (Naka-gun,
JP) ; Yasuda, Ken; (Tokyo, JP) ; Yamashita,
Hisao; (Hitachi-shi, JP) ; Azuhata, Shigeru;
(Hitachi-shi, JP) ; Tamata, Shin;
(Higashiibaraki-gun, JP) ; Irie, Kazuyoshi;
(Hitachi-shi, JP) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
26338096 |
Appl. No.: |
10/676013 |
Filed: |
October 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10676013 |
Oct 2, 2003 |
|
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|
09005006 |
Jan 9, 1998 |
|
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Current U.S.
Class: |
423/239.1 ;
423/240S |
Current CPC
Class: |
B01D 53/8671 20130101;
C01B 7/191 20130101; A62D 3/20 20130101; A62D 2101/49 20130101;
B01D 2257/204 20130101; Y02C 20/30 20130101; B01D 2255/2092
20130101; B01D 2258/0216 20130101; B01D 53/8662 20130101; B01D
53/8659 20130101; A62D 2101/22 20130101 |
Class at
Publication: |
423/239.1 ;
423/240.00S |
International
Class: |
B01D 053/70 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 1997 |
JP |
09-004349 |
Jun 20, 1997 |
JP |
09-163717 |
Claims
What is claimed is:
1. A process for treating a fluorine compound-containing gas, which
comprises contacting a gas stream containing at least one of
compounds of carbon and fluorine, compounds of carbon, hydrogen and
fluorine, compounds of sulfur and fluorine, compounds of nitrogen
and fluorine and compounds of carbon, hydrogen, oxygen and fluorine
with a catalyst containing at least one of alumina, titania,
zirconia and silica in the presence of steam, thereby hydrolyzing
the fluorine compound to convert the fluorine of the fluorine
compound to hydrogen fluoride.
2. A process according to claim 1, wherein the catalyst is selected
from the group consisting of alumina, titania, zirconia, silica, a
mixture of titania and zirconia, a mixture of alumina and magnesia,
a mixture of alumina and titania and a mixture of alumina and
silica.
3. A process according to claim 1, wherein the catalyst comprising
a mixture of alumina and titania is in a weight ratio of alumina to
titania of 75-98:25-2.
4. A process according to claim 3, wherein the catalyst comprising
a mixture of alumina and titania is a catalyst prepared from
boehmite as an alumina raw material.
5. A process according to claim 3, wherein the catalyst comprising
a mixture of alumina and titania is a catalyst prepared from
titanium sulfate as a titania raw material.
6. A process according to claim 3, wherein the catalyst comprising
a mixture of alumina and titania is a catalyst prepared by adding
sulfuric acid thereto during the catalyst preparation.
7. A process according to claim 3, wherein the catalyst comprising
a mixture of alumina and titania contains sulfate ions.
8. A process according to claim 1, wherein the catalyst comprises a
mixture of alumina, titania and at least one member selected from
the group consisting of zirconia, tungsten oxide, silica, tin
oxide, ceria, bismuth oxide, nickel oxide and boron oxide and
having a weight ratio of at least one member selected from the
group consisting of zirconia, tungsten oxide, silica, tin oxide,
ceria, bismuth oxide, nickel oxide and boron oxide to sum total of
alumina and titania being 0.1-10:99.9-90.
9. A process for treating a fluorine compound-containing gas, which
comprises contacting a gas stream containing a compound comprising
carbon and fluorine with a catalyst comprising a mixture of
alumina, titania and zirconia, and having a weight ratio of alumina
to titania being 75-98:25-2 and a weight ratio of zirconia to sum
total of alumina and titania being 2-10:98-90, thereby hydrolyzing
the compound comprising carbon and fluorine.
10. A process according to claim 1, wherein the catalyst comprises
a mixture of alumina and at least one member selected from the
group consisting of zinc oxide, nickel oxide, iron oxide, tin
oxide, cobalt oxide, zirconia, ceria, silica and platinum and has
an atomic ratio of aluminum of the alumina to at least one element
of at least one of the member except for platinum being 50-99:50-1,
and the content of platinum being 0.1 to 2% by weight per 100% by
weight of the alumina.
11. A process according to claim 10, wherein the catalyst further
contains 0.1-20% by weight of sulfur on the basis of the
catalyst.
12. A process according to claim 12, wherein the catalyst
containing sulfur comprises a mixture of alumina and nickel
oxide.
13. A process for treating a fluorine compound-containing gas,
which comprises contacting a gas stream containing a fluorine
compound comprising C.sub.2F.sub.6 with a catalyst comprising
alumina and titania having a weight ratio of alumina to titania
being 65-90:35-10, thereby hydrolyzing the fluorine compound to
convert the fluorine in the gas stream to hydrogen fluoride.
14. A process for treating a fluorine compound-containing gas,
which comprises contacting a gas stream containing a fluorine
compound comprising C.sub.2F.sub.6 with a catalyst comprising
alumina, titania and zirconia and having a weight ratio of alumina
to titania being 65-90:35-10 and a weight ratio of zirconia to sum
total of alumina and titania being 2-10:98-90, thereby hydrolyzing
the fluorine compound to convert the fluorine in the gas stream to
hydrogen fluoride.
15. A process for treating a fluorine compound-containing gas,
which comprises contacting a gas stream containing a fluorine
compound comprising at least one member selected from the group
consisting of C.sub.2F.sub.6, CF.sub.4, C.sub.4F.sub.8 and
CHF.sub.3 with a catalyst comprising a mixture of alumina and zinc
oxide and having an atomic ratio of aluminum to zinc being
90-70:10-30, thereby hydrolyzing the fluorine compound to convert
the fluorine in the gas stream to hydrogen fluoride.
16. A process for treating a fluorine compound-containing gas,
which comprises a gas stream containing a fluorine compound
comprising at least one member selected from the group consisting
of C.sub.2F.sub.6, CF.sub.4, C.sub.3F.sub.8, C.sub.4F.sub.8,
CHF.sub.3, NF.sub.3 and SF.sub.6 with a catalyst comprising a
mixture of alumina and nickel oxide and having an atomic ratio of
aluminum to nickel being 95-60:5-40, thereby hydrolyzing the
fluorine compound to convert the fluorine in the gas stream to
hydrogen fluoride.
17. A process for treating a fluorine compound-containing gas,
which comprises contacting a gas stream containing a fluorine
compound comprising C.sub.4F.sub.8 with a catalyst comprising a
mixture of alumina and nickel oxide, thereby hydrolyzing the
fluorine compound to convert the fluorine in the gas stream to
hydrogen fluoride.
18. A process according to claim 16, wherein a reaction temperature
is 650.degree.-800.degree. C. for the hydrolysis of C.sub.2F.sub.6,
600.degree.-800.degree. C. for the hydrolysis of CF.sub.4 and
CHF.sub.3, 700.degree.-800.degree. C. for the hydrolysis of
C.sub.3F.sub.8, 650.degree.C. -800.degree. C. for the hydrolysis of
C.sub.4F.sub.8, 600.degree.-800.degree. C. for the hydrolysis of
NF.sub.3 and 500.degree.-800.degree. C. for the hydrolysis of
SF.sub.6.
19. A process according to claim 15, wherein a reaction temperature
is 650.degree.-800.degree. C. for the hydrolysis of C.sub.4F.sub.8
and 600.degree.-800.degree. C. for the hydrolysis of CF.sub.4 and
CHF.sub.3.
20. A process for treating a fluorine compound-containing gas,
which comprises a hydrolysis step of contacting a gas discharged
from a semiconductor-etching or cleaning step using a gas stream
containing at least one fluorine compound selected from the group
consisting of compounds of carbon and fluorine, compounds of
carbon, hydrogen and fluorine, compounds of sulfur and fluorine,
compounds of nitrogen and fluorine and compounds of carbon,
hydrogen, oxygen and fluorine, after addition of air and steam to
the gas, with a catalyst comprising at least one of alumina,
titania, zirconia and silica, thereby hydrolyzing the fluorine
compound to convert the fluorine in the gas to hydrogen fluoride,
as a poststep to the semiconductor-etching or cleaning step.
21. A process according to claim 20, which further comprises an
alkaline washing step of contacting the gas from the hydrolysis
step with an alkaline washing solution, thereby washing the gas as
a poststep to the hydrolysis step.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The present invention relates to a process for efficient
decomposition treatment of a gas containing fluorine compounds such
as C.sub.2F.sub.6, CF.sub.4, C.sub.3F.sub.8, C.sub.4F.sub.8,
CHF.sub.3, SF.sub.6, NF.sub.3, etc. at a low temperature.
[0003] 2) Related Art
[0004] Fluorine compound gases such as CF.sub.4, C.sub.2F.sub.6,
etc. are used in a large amount as a semiconductor etchant, a
semiconductor cleaner, etc. However, it was found that these
compounds, once discharged into the atmosphere, turn into warming
substances causing global warming. Post-treatment of these
compounds after their use would be subject to a strict control in
the future.
[0005] Compounds having a high fluorine (F) content as a molecule
constituent such as CF.sub.4, C.sub.2F.sub.6, etc. have a higher
electronegativity of fluorine and thus are chemically very stable.
From this nature it is very hard to decompose such fluorine
compounds, and it is thus in the current situations that no
appropriate processes for such decomposition treatment are not
available yet.
[0006] JP-B-6-59388 (U.S. Pat. No. 5,176,897) discloses a
TiO.sub.2--WO.sub.3 catalyst for hydrolysis of organic halogen
compounds. The catalyst contains 0.1 to 20% by weight of W on the
basis of TiO.sub.2 (i.e. 92% to 99.96% of Ti by atom and 8 to 0.04%
by atom of W) and has a decomposition rate of 99% at 375.degree. C.
for a duration of 1,500 hours in treatment of CCl.sub.4 in ppm
order. JP-B-6-59388 suggests that organic halogen compounds having
a single carbon atom, such as CF.sub.4, CCl.sub.2F.sub.2, etc. can
be decomposed, but shows no examples of decomposition results of
fluorine compounds.
[0007] JP-A-7-80303 discloses another
Al.sub.2O.sub.3--ZrO.sub.2--WO.sub.3 catalyst for decomposition of
fluorine compound gases. The catalyst is directed to
combustion-decomposition of CFCs (chlorofluorocarbons) and has a
decomposition rate of 98% for a duration of 10 hours in treatment
of CFC-115 (C.sub.2Cl.sub.5) by combustion-decomposition reaction
at 600.degree. C. The disclosed process needs addition of
hydrocarbons such as n-butane, etc. as a combustion aid, resulting
in a higher treatment cost. Among organic halogen compounds to be
treated, fluorine compounds are less decomposable than chlorine
compounds. Furthermore, the more the carbon atoms of organic
halogen compound, the less decomposable. Decomposition of compounds
consisting only of carbon and fluorine such as C.sub.2F.sub.6, etc.
are much less decomposable than CFC-115. but no examples of
decomposition results of such compounds are shown therein.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a process
for efficient decomposition treatment of compounds of carbon and
fluorine, compounds of carbon, hydrogen and fluorine, compounds of
sulfur and fluorine, compounds of nitrogen and fluorine and even
compounds of carbon, hydrogen, fluorine and oxygen such as
C.sub.2F.sub.6, CF.sub.4, C.sub.3F.sub.8, C.sub.4F.sub.8,
CHF.sub.3, SF.sub.6 and NF.sub.3.
[0009] The present invention provides a process for treating a
fluorine compound-containing gas, which comprises contacting a gas
stream containing at least one fluorine compound selected from the
group consisting of compounds of carbon and fluorine, compounds of
carbon, hydrogen and fluorine, compounds of sulfur and fluorine,
compounds of nitrogen and fluorine and compounds of carbon,
hydrogen; oxygen and fluorine with a catalyst containing at least
one of alumina, titania, zirconia and silica in the presence of
steam, thereby hydrolyzing the fluorine compound to convent
fluorine of the fluorine compound to hydrogen fluoride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a block diagram showing a process for treating a
fluorine compound-containing gas according to one embodiment of the
present invention.
[0011] FIG. 2 is a graph showing performances of various catalysts
for decomposing a fluorine compound.
[0012] FIG. 3 is a graph showing performances of various catalysts
for decomposing a fluorine compound.
[0013] FIG. 4 is a graph showing performances of various catalysts
for decomposing a fluorine compound.
[0014] FIG. 5 is a graph showing performances of various catalysts
for decomposing a fluorine compound.
[0015] FIG. 6 is a graph showing performances of various catalysts
for decomposing a fluorine gas.
[0016] FIG. 7 is a graph showing performance of catalysts with
various composition ratios for decomposing a fluorine gas.
[0017] FIG. 8 is a graph showing performance of catalysts with
various composition ratios for decomposing a fluorine gas.
[0018] FIG. 9 is a graph showing relations between reaction
temperature and decomposition rate of various fluorine
compounds.
[0019] FIG. 10 is a graph showing relations between reaction time
and decomposition rate of a fluorine compound.
[0020] FIG. 11 is a graph showing relations between reaction
temperature and decomposition rate of CHF.sub.3, CF.sub.4 and
C.sub.4H.sub.8 by an Al.sub.2O.sub.3--ZnO catalyst.
[0021] FIG. 12 is a graph showing relations between reaction
temperature and decomposition rate of SF.sub.6 and C.sub.3F.sub.8
by an Al.sub.2O.sub.3--NiO catalyst.
[0022] FIG. 13 is a graph showing relations between reaction
temperature and decomposition rate of C.sub.4F.sub.8 by an
Al.sub.2O.sub.3--NiO--ZnO catalyst.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] As a result of extensive studies on development of catalysts
for decomposition of fluorine compound-containing gases, the
present inventors have found that catalysts must contain a metallic
component capable of forming an appropriately strong bond with
fluorine as the nature of catalysts, and further have found that
catalysts containing a metallic component having a higher fluoride
formation enthalpy show a higher decomposition activity
particularly in case of compounds consisting of carbon and
fluorine, because molecules of such compounds are stable by
themselves. Formation of too stable a bond will gradually lower the
decomposition activity of catalysts, because fluorine compounds are
less releasable from the catalyst surface, whereas too weak a
bonding force will not attain a satisfactory decomposition rate.
C.sub.2F.sub.6, one of gases to be treated according to the present
invention, is a compound of poor reactivity because of a higher
intramolecular force, and it is said that a temperature of
1,500.degree. to 2,000.degree. C. is required for combustion of
such a gas.
[0024] As a result of tests on various catalysts, the present
inventors have found that catalysts of alumina (Al.sub.2O.sub.3),
titania (TiO.sub.2), zirconia (ZrO.sub.2), silica (SiO.sub.2), a
mixture of titania and zirconia, a mixture of alumina and magnesia
(MgO), a mixture of alumina and titania, or a mixture of alumina
and silica can hydrolyze fluorine compounds, and further have found
that the fluorine compounds can be decomposed at a lower
temperature than 800.degree. C. thereby.
[0025] Among these catalysts, it has been found that a catalyst
based on a mixture of alumina and titania has the highest activity
and particularly a catalyst comprising 75 to 98% by weight of
alumina and 25 to 2% by weight of titania has a particularly high
activity. It can be presumed that the alumina of the catalyst based
on a mixture of alumina and titania acts to attract fluorine
compounds onto the catalyst, whereas the titania acts to depart the
fluorine compounds from the catalyst surface.
[0026] The present inventors further have found that catalysts
based on the mixture of alumina and titania further containing at
least one member selected from the group consisting of zirconia,
tungsten oxide, silica, tin oxide, ceria, bismuth oxide, nickel
oxide and boron oxide can hydrolyze fluorine compounds. It has been
found that above all the catalyst containing zirconia has a higher
decomposition activity on fluorine compounds. It has been further
found that the content of at least one member selected from the
group consisting of zirconia, tungsten oxide, silica, tin oxide,
ceria, bismuth oxide, nickel oxide and boron oxide is preferably
0.1 to 10% by weight on the basis of sum total of alumina and
titania and particularly the content of zirconia is preferably 2 to
10% by weight on the basis of sum total of alumina and titania. It
seems that these additive members exist in the form of single
oxides or composite oxides and contribute to an improvement of
decomposition activity on fluorine compounds.
[0027] In catalyst preparation, it has been found that it is
preferable to use boehmite for alumina raw material and a titanium
sulfate solution for a titania raw material. It has been confirmed
that there are sulfate ions, SO.sub.4.sup.2-, in the catalysts
prepared from the titanium sulfate solution and the decomposition
activity on fluorine compounds can be improved by the presence of
sulfate ions. It has been found that addition of sulfuric acid is
preferable during the catalyst preparation.
[0028] The present inventors further tested catalysts containing
other components besides alumina and titania, specifically
catalysts containing alumina and one of zinc oxide (ZnO), nickel
oxide (NiO), iron oxide, tin oxide (SnO.sub.2), platinum (Pt),
cobalt oxide, zirconia (ZrO.sub.2), ceria (CeO.sub.2) and silica
(SiO.sub.2). As a result, it has been found that these catalysts
can hydrolyze fluorine compounds and particularly catalysts
containing zinc oxide or nickel oxide have a higher activity than
catalysts based on the mixture of alumina and titania. It has been
further found that catalysts comprising alumina and nickel oxide,
admixed with sulfuric acid during the catalyst preparation have a
higher activity than the catalyst without admixing with sulfuric
acid. It has not been confirmed in which forms iron oxide or cobalt
oxide of the catalysts containing the iron oxide or the cobalt
oxide exists. Probably it seems to exist in the form of
Fe.sub.2O.sub.3 or Co.sub.3O.sub.4.
[0029] It has been found that the catalysts comprising alumina and
one of Zinc oxide, nickel oxide, iron oxide, tin oxide, cobalt
oxide, zirconia, ceria and silica as other components preferably
contain 50 to 1% by atom of one metallic element of the other
components, the balance being aluminum of the alumina, and the
content of platinum is preferably 0.1 to 2% by weight on the basis
(100% by weight) of alumina. It has been further found that these
catalysts can further contain sulfur and the content of sulfur is
preferably 0.1 to 20% by weight on the basis of the alumina
catalyst.
[0030] Fluorine compounds to be treated according to the present
invention include, for example, CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, C.sub.4F.sub.8, C.sub.5F.sub.8, CHF.sub.3,
CH.sub.2F.sub.2, CH.sub.3F, C.sub.2HF.sub.5, C.sub.2H.sub.2F.sub.4,
C.sub.2H.sub.3F.sub.3, C.sub.2H.sub.4F.sub.2, C.sub.2H.sub.5F,
CH.sub.2OCF.sub.2, SF.sub.6, NF.sub.3, etc., among which CF.sub.4,
C.sub.2F.sub.6, C.sub.3F.sub.8, C.sub.4F.sub.8, CHF.sub.3, SF.sub.6
and NF.sub.3 are used as etchants for semiconductors and CF.sub.4,
C.sub.2F.sub.6 and NF.sub.3 are used as cleaners for
semiconductors.
[0031] According to the present invention, all of these fluorine
compounds can be hydrolyzed. Hydrolysis temperature depends upon
kinds of fluorine compounds and catalyst components, and is usually
200.degree. to 800.degree. C., preferably 400.degree. to
800.degree. C. According to the present process fluorine of
fluorine compound gases can be converted to hydrogen fluoride.
[0032] Hydrolysis of fluorine compounds can proceed typically
according to the following reaction equations:
CF.sub.4+2H.sub.2O.fwdarw.CO.sub.2+4HF (1)
C.sub.2F.sub.6+3H.sub.2O.fwdarw.CO.sub.2+6HF (2)
CHF.sub.3+H.sub.2O.fwdarw.CO+3HF (3)
SF.sub.6+3H.sub.2O.fwdarw.SO.sub.3+6HF (4)
NF.sub.3+{fraction (3/2)}H.sub.2O.fwdarw.NO+1/2O.sub.2+3HF (5)
[0033] Hydrolysis according to reaction equations (2) and (3) can
produce CO. The present catalysts also have an ability to oxidize
CO, and thus CO can be further oxidized to CO.sub.2 in the presence
of oxygen.
[0034] The present invention provides a process for hydrolyzing a
fluorine compound-containing gas by a catalyst comprising at least
one member selected from the group consisting of alumina, titania,
zirconia, silica, a mixture of titania and zirconia, a mixture of
alumina and magnesia, a mixture of alumina and titania and a
mixture of alumina and silica.
[0035] Furthermore, the present invention provides a process for
treating a fluorine-containing gas by a catalyst comprising alumina
and titania, further containing 0.1 to 10% by weight, on the basis
of alumina and titania, of one of zirconia, tungsten oxide, silica,
tin oxide, ceria, bismuth oxide, nickel oxide and boron oxide.
[0036] Still furthermore, the present invention provides a process
for treating a fluorine compound-containing gas by a catalyst
comprising alumina and at least one member selected from the group
consisting of zinc oxide, nickel oxide, iron oxide, tin oxide,
cobalt oxide, zirconia, ceria, silica and platinum as other
components, a ratio of aluminum of alumina to the metallic element
of at least one of other components by atom is 50 to 99:50-1, and
further by the catalyst further containing 0.1 to 20% by weight of
sulfur on the basis of the alumina. These additive components can
contribute to improvement of decomposition activity of the
catalysts on fluorine compounds in the form of single oxides or
composite oxides with aluminum and/or other additive
components.
[0037] Still furthermore, the present invention provides a process
for converting fluorine in a gas to hydrogen fluoride, which
comprises contacting a gas stream containing a fluorine compound
comprising C.sub.2F.sub.6 with a catalyst comprising a mixture of
alumina and titania and having a weight ratio of alumina to titania
being 65 to 90:35 to 10, thereby hydrolyzing the fluorine
compounds. Still furthermore, the present invention provides a
process for converting fluorine in a gas stream to hydrogen
fluoride, which comprises contacting a gas stream comprising a
fluorine compound comprising C.sub.2F.sub.6 with a catalyst
comprising a mixture of alumina, titania and zirconia and having a
weight ratio of alumina to titania being 65 to 90:35 to 10 and a
weight ratio of zirconia to sum total of alumina and titania being
2 to 10:98 to 90, thereby hydrolyzing the fluorine compound.
[0038] Still furthermore, the present invention provides a process
for converting fluorine in a gas stream to hydrogen fluoride, which
comprises contacting a gas stream containing at least one fluorine
compound selected from the group consisting of C.sub.2F.sub.6,
CF.sub.4, C.sub.4F.sub.8 and CHF.sub.3 with a catalyst comprising a
mixture of alumina and zinc oxide and having an atomic ratio of
aluminum to zinc being 90 to 70:10 to 30, thereby hydrolyzing the
fluorine compound.
[0039] Still furthermore, the present invention provides a process
for converting fluorine in a gas stream to hydrogen fluoride, which
comprises contacting a gas stream containing at least one fluorine
compound selected from the group consisting of C.sub.2F.sub.6,
CF.sub.4, C.sub.3F.sub.8, CHF.sub.31 NF.sub.3 and SF.sub.6 with a
catalyst comprising a mixture of alumina and nickel oxide and
having an atomic ratio of aluminum to nickel of 95 to 60:5 to 40,
thereby hydrolyzing the fluorine compound.
[0040] Still furthermore, the present invention provides a process
for converting fluorine in a gas stream to hydrogen fluoride, which
comprises contacting a gas stream comprising a fluorine compound
comprising C.sub.4F.sub.8 with a catalyst comprising a mixture of
alumina, nickel oxide and zinc oxide, thereby hydrolyzing the
fluorine compound.
[0041] Still furthermore, the present invention provides a process
for converting fluorine in a gas stream to hydrogen fluoride, which
comprises a hydrolysis step of contacting a gas discharged from a
semiconductor-etching or cleaning step using a gas stream
containing at least one fluorine compound selected from the group
consisting of compounds of carbon and fluorine, compounds of
carbon, hydrogen and fluorine, compounds of sulfur and fluorine,
compounds of nitrogen and fluorine and compounds of carbon,
hydrogen, oxygen and fluorine, after addition of air and steam to
the gas, with a catalyst comprising at least one of alumina,
titania, zirconia and silica, thereby hydrolyzing the fluorine
compound to convert the fluorine in the gas to hydrogen fluoride,
as a poststep to the semiconductor-etching or cleaning step.
[0042] Still furthermore, the present invention provide a process
for treating a fluorine compound-containing gas, which further
comprises an alkaline washing step of contacting the gas from the
hydrolysis step with an alkaline washing solution, thereby washing
the gas as a poststep to the hydrolysis step. As the alkaline
washing solution, there can be used conventional ones such as a
solution of NaOH, Ca(OH).sub.2, Mg(OH).sub.2, CaCO.sub.3, etc., a
slurry of Ca(OH).sub.2, etc.
[0043] In contacting of the gas stream containing a fluorine
compound with the catalyst, the concentration of the fluorine
compound in the gas stream is preferably 0.1 to 10% by volume,
particularly preferably 0.1 to 3% by volume, and the space velocity
is preferably 100 to 10,000 h.sup.-1, particularly preferably 100
to 3,000 h.sup.-1. Space velocity (h.sup.-1) is defined by reaction
gas flow rate (ml/h)/catalyst volume (ml).
[0044] In the hydrolysis of the fluorine compound, it is desirable
to add steam as a hydrogen source for hydrolysis to the gas stream
so as to make the amount of hydrogen atoms (H) at least equal to
the amount of fluorine atoms (F) contained in the fluorine
compound, thereby making the fluorine atoms (F) of decomposition
products into the hydrogen fluoride (HF) form that allows easy
post-treatment. Hydrogen, hydrocarbons, etc. can be used as a
hydrogen source besides the steam. In case of hydrocarbons as a
hydrogen source, hydrocarbons can be combusted on the catalyst,
thereby effectively reducing the heat energy to be supplied.
[0045] By adding an oxidizing gas such as oxygen, etc. to the
reaction gas, oxidation reaction of CO can be carried out at the
same time. When the oxidation reaction of CO is incomplete, the
decomposition product gas is brought into contact with the CO
oxidizing catalyst, after removal of HF from the decomposition
product gas, to convert CO to CO.sub.2.
[0046] In the hydrolysis (decomposition) of fluorine compound, the
reaction temperature is preferably about 200.degree. to about
800.degree. C. Above about 800.degree. C., a higher decomposition
rate can be obtained, but the catalyst will be rapidly
deteriorated, and also the corrosion rate of apparatus structural
materials will be abruptly increased, whereas below about
200.degree. C. the decomposition rate will be lowered.
[0047] As the step of neutralizing and removing the formed HF,
washing by spraying an alkaline solution is efficient and
preferable because of less occurrence of clogging in pipings due to
crystal deposition, etc. Bubbling of the decomposition product gas
through the alkaline solution or washing with the alkaline solution
through a packed column may be used for the neutralization and
removal of the formed HF. Alternatively, HF can be absorbed in
water, followed by treatment with an alkaline solution or
slurry.
[0048] As the raw material for aluminum (Al) for preparing the
present catalyst, .gamma.-alumina and a mixture of .gamma.-alumina
and .delta.-alumina can be used besides boehmite. However, it is
preferable to use boehmite as a raw material for Al to form an
oxide through final firing.
[0049] As the raw material for titanium (Ti), titania sol, titanium
slurry, etc. can be used besides titanium sulfate.
[0050] As the third metallic components for silica (Si), magnesium
(Mg), zirconium (Zr), etc., their various nitrates, ammonium salts,
chlorides, etc. can be used.
[0051] The present catalyst can be prepared by any of ordinary
procedures for preparing catalysts, such as precipitation,
impregnation, kneading, etc.
[0052] The present catalyst can be used as such or upon molding
into a granular form, a honeycomb form, etc. by an desired molding
procedure such as extrusion molding, tabletting, tumbling
granulation, etc., or as a coating on ceramic or metallic
honeycombs or plates.
[0053] Only a catalytic reactor for decomposing fluorine compounds
and a facility for neutralizing and removing acid components in the
decomposition product gas are required for an apparatus for
carrying out the present process for treating fluorine
compound-containing gas.
[0054] The present invention will be described in detail below,
referring to Examples which are not limitative of the present
invention.
[0055] FIG. 1 shows an example of using the present process for
hydrolysis treatment of a fluorine gas in a cleaning step in a
plasma CVD apparatus in the semi-conductor production process.
[0056] The plasma CVD apparatus is an apparatus for vapor
depositing a SiO.sub.2 film on a semiconductor wafer surface. Since
the SiO.sub.2 film tends to deposit on the entire interior surfaces
of the apparatus, and thus it is necessary to remove SiO.sub.2
depositions from unwanted surfaces. To clean the unwanted surface
to remove SiO.sub.2 therefrom, gases containing fluorine compounds
such as C.sub.2F.sub.6, CF.sub.4, NF.sub.3, etc. are used as a
cleaning gas. Cleaning gas 1 containing these fluorine compounds is
led to a CVD chamber to remove SiO.sub.2 under plasma excitation.
Then, the chamber is flushed with a N.sub.2 gas 2, thereby diluting
the cleaning gas to a desired lower fluorine compound
concentration, and the diluted cleaning gas is discharged from the
chamber. The discharged gas is admixed with air 3 to further lower
the fluorine compound concentration by dilution with air 3 and the
air-diluted discharged gas is further admixed with steam 4 and the
resulting reaction gas 5 is led to a decomposition step, where the
reaction gas is brought into contact with a catalyst at a desired
space velocity (h.sup.-1), which is defined by reaction gas flow
rate (ml/h)/catalyst volume (ml) and at a desired temperature. In
that case, the reaction gas may be heated or the catalyst may be
heated by an electric oven, etc. The resulting decomposition gas 6
is led to an exhaust gas washing step, where the decomposition gas
6 is sprayed with an aqueous alkaline solution to remove acid
components from the decomposition gas 6 and the resulting exhaust
gas 7 freed from the acid components is discharged to the system
outside.
[0057] CF.sub.4, C.sub.2F.sub.6 and NF.sub.3 can be used as
etchants for semiconductors, etc., and CHF.sub.3, C.sub.3F.sub.6,
SF.sub.6 and C.sub.4F.sub.8 can be also used as etchants besides
the above-mentioned fluorine compounds. These etchants can be
treated and decomposed in the same manner as in FIG. 1 except that
the cleaning step of FIG. 1 is only replaced with an etching
step.
[0058] Activities or performances of various catalysts for
composing fluorine compounds were investigated, and results thereof
will be described below:
EXAMPLE 1
[0059] A C.sub.2F.sub.6 gas having a purity of 99% or more was
diluted with air, and further admixed with steam to prepare a
reaction gas. Steam for the admixture was prepared by feeding pure
water into a reactor tube from the top at a flow rate of 0.11
ml/min. by a microtube pump and gasified. The reaction gas had a
C.sub.2F.sub.6 concentration of about 0.5%. Then, the reaction gas
was brought into contact with various catalysts heated to
700.degree. C. in a reactor tube at a space velocity of 3,000
h.sup.-1. Heating of the catalyst was carried out by heating the
reactor tube in an electric oven.
[0060] Reactor tube was an Inconel reactor tube having an inner
diameter of 19 mm, where a catalyst bed was fixed at the center of
the reactor tube and had an Inconel thermowell for a thermo couple,
3 mm in outer diameter, inside the catalyst bed. Decomposition
product gas discharged from the catalyst bed was bubbled through an
aqueous sodium chloride solution an then discharged as an exhaust
gas. C.sub.2F.sub.6 decomposition rate was calculated by the
following equation by determining concentration of C.sub.2F.sub.6
in the reaction gas at the inlet to the reactor tube and
concentration of C.sub.2F.sub.6 in the decomposition gas at the
outlet from the alkaline washing step by FID (flame ionization
detector) gas chromatography and TCD (thermal conductivity
detector) gas chromatography: 1 Decomposition rate = 1 -
Concentration of discharged fluorine compound Concentration of fed
fluorine compound .times. 100 ( % )
[0061] Catalyst 1:Al.sub.2O.sub.3
[0062] Granular alumina (NKHD-24, trademark of a product
commercially available from Sumitomo Chemical Co., Ltd., Japan) was
pulverized, sieved to obtain a fraction of 0.5-1 mm grain sizes,
followed by drying at 120.degree. C. for 2 hours and firing (or
calcining) at 700.degree. C. for 2 hours.
[0063] Catalyst 2:TiO.sub.2
[0064] Granular titania (CS-200-24, trademark of a product
commercially available from Sakai Chemical Industry Co., Ltd.,
Japan) was pulverized, sieved to obtain a fraction of 0.5-1 mm
grain sizes, followed by drying at 120.degree. C. for 2 hours and
firing at 700.degree. C. for 2 hours.
[0065] Catalyst 3:ZrO.sub.2
[0066] 200 g of zirconyl nitrate was dried at 120.degree. C. for 2
hours and fired at 700.degree. C. for 2 hours. The resulting
powders were placed in a mold and compression molded under a
pressure of 500 kgf/cm.sup.2. The molded product was pulverized and
sieved to obtain zirconia grains having grain sizes of 0.5-1
mm.
[0067] Catalyst 4:SiO2
[0068] Granular silica (CARIACT-10, trademark of a product
commercially available from Fuji Silysia Co., Ltd., Japan) was
pulverized and sieved to obtain a fraction of 0.5-1 mm grain sizes,
followed by drying at 120.degree. C. for 2 hours and firing at
700.degree. C. for 2 hours.
[0069] Catalyst 5:TiO.sub.2--ZrO.sub.2
[0070] Granular titania (CS-200-24) was pulverized to grain sizes
of 0.5 mm and under. 100 g of the resulting powders was admixed
with 78.3 g of zirconyl nitrate and kneaded while adding pure water
thereto. After the kneading, the kneaded mixture was dried at
120.degree. C. for 2 hours and fired at 700.degree. C. for 2 hours.
The resulting powders were placed in a mold and compression molded
under a pressure of 500 kgf/cm.sup.2. The molded product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Ti:Zr=81:19 and in a weight ratio of
TiO.sub.2:ZrO.sub.2=73.5:26.5.
[0071] Catalyst 6:Al.sub.2O.sub.3--MgO
[0072] Granular alumina (NKHD-24) was pulverized to grain sizes of
0.5 mm and under. 100 g of the resulting powders were admixed with
56.4 g of magnesium nitrate and kneaded while adding pure water
thereto. After the kneading, the kneaded mixture was dried at
120.degree. C. for 2 hours and fired at 700.degree. C. for 2 hours.
The resulting powders were placed into a mold and compression
molded under a pressure of 500 kgf/cm.sup.2. The molded product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Mg=90:10 and in a weight ratio of
Al.sub.2O.sub.3:MgO=91.9:8.1.
[0073] Catalyst 7:Al.sub.2O.sub.3--TiO.sub.2
[0074] Granular alumina (NKHD-24) was pulverized to grain sizes of
0.5 mm and under. 100 g of the resulting powders were admixed with
17.4 g of dried powders of a metatitanic acid slurry and kneaded
while adding pure water thereto. After the kneading, the kneaded
mixture was dried at 120.degree. C. for 2 hours and fired at
700.degree. C. for 2 hours. The resulting powders were placed in a
mold and compression molded under a pressure of 500 kgf/cm.sup.2.
The molded product was pulverized and sieved to obtain grains
having grain sizes of 0.5-1 mm. The resulting grain composition for
catalyst was in an atomic ratio of Al:Ti=90:10 and in a weight
ratio of Al.sub.2O.sub.3:TiO.sub.2=85.2:14.8.
[0075] Catalyst 8:Al.sub.2O.sub.3--SiO.sub.2
[0076] Granular alumina (NKHD-24) was pulverized to grain sizes of
0.5 mm and under. 100 g of the resulting powders were admixed with
13.2 g of dried powders of SiO.sub.2 sol and kneaded while adding
pure water thereto. After the kneading, the kneaded mixture was
dried at 120.degree. C. for 2 hours and fired at 700.degree. C. for
2 hours. The resulting powders were placed in a mold and
compression molded under a pressure of 500 mgf/cm.sup.2. The molded
product was pulverized and sieved to obtain grains having grain
sizes of 0.5-1 mm. The resulting grain composition for catalyst was
in an atomic ratio of Al:Si=90:10 and in a weight ratio of
Al.sub.2O.sub.3:SiO.sub.2=88.3:11.7.
[0077] Test results of-the above-mentioned catalysts 1 to 8 are
shown in FIG. 2, from which it is evident that the
Al.sub.2O.sub.3--TiO catalyst is preferable as a hydrolysis
catalyst for a C.sub.2F.sub.6 gas.
EXAMPLE 2
[0078] In this Example, influences of changes in composition ratios
of alumina to titania in Al.sub.2O.sub.3--TiO.sub.2 catalysts upon
C.sub.2F.sub.6 decomposition rate were investigated under the same
test procedure and conditions as in Example 1. The results are
shown in FIG. 4.
[0079] Catalyst 19:Al.sub.2O.sub.3
[0080] Boehmite powders (PURAL SB, trademark of a product
commercially available from Condea Co., Ltd.) were dried at
120.degree. C. for 2 hours. 200 g of the resulting dried powders
were fired at 300.degree. C. for 0.5 hours and further fired at an
elevated temperature of 700.degree. C. for 2 hours. The resulting
powders were placed into a mold and compression molded under a
pressure of 500 kgf/cm.sup.2. The molded product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm, and tested.
It was found that boehmite powders used as an alumina raw material
had a higher catalytic activity than granular alumina.
[0081] Catalyst 20:Al.sub.2O.sub.3--TiO.sub.2
[0082] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were kneaded with
248.4 g of an aqueous 30% titanium sulfate solution, while adding
about 200 g of pure water thereto. After the kneading, the kneaded
mixture was dried at 250.degree.-300.degree. C. for about 5 hours
and then fired at 700.degree. C. for 2 hours. The resulting powders
were placed into a mold and compression molded under a pressure of
500 kgf/cm.sup.2. The molded product was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm and tested. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=90:10 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=85.65:14.35.
[0083] Catalyst 21:AlO.sub.3--TiO.sub.2
[0084] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were kneaded with
about 100 g of an aqueous solution containing 78.6 g of 30% titania
sol in pure water. After the kneading, the kneaded mixture was
dried at 120.degree. C. for about 2 hours and then fired at
700.degree. C. for 2 hours. The resulting powders were placed into
a mold and compression molded under a pressure of 500 kgf/cm.sup.2.
The molded product was pulverized and sieved to obtain grains
having grain sizes of 0.5-1 mm and tested. The resulting grain
composition for catalyst was in an atomic ratio of Al:Ti=91:9 and
in a weight ratio of Al.sub.2O.sub.3:TiO.sub.2=86.25:13.75- .
[0085] It was found that the catalyst prepared from the titanium
sulfate solution as a titanium raw material had the highest
catalytic activity, probably because of the presence of sulfate
ions SO.sub.4.sup.2- in the catalyst.
EXAMPLE 3
[0086] In this Example, influences of changes in composition ratios
of Al.sub.2O.sub.3 to TiO.sub.2 in Al.sub.2O.sub.3--TiO.sub.2
catalysts upon C.sub.2F.sub.6 decomposition rate were investigated
under the same procedure and conditions as in Example 1.
[0087] Catalyst 22:Al.sub.2O.sub.3--TiO.sub.2
[0088] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 100 g of the resulting dried powders were kneaded with
82.4 g of an aqueous 30% titanium sulfate solution while adding
about 120 g of pure water thereto. After the kneading, the kneaded
mixture was dried at 2500-300.degree. C. for about 5 hours and then
fired at 700.degree. C. for 2 hours. The resulting powders were
placed into a mold and compression molded under a pressure of 500
kgf/cm.sup.2. The molded product was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm and tested. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=93:7 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=90.0:10.0.
[0089] Catalyst 23:Al.sub.2O.sub.3--TiO.sub.2
[0090] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 100 g of the resulting dried powders were kneaded with
174.4 g of an aqueous 30% titanium sulfate solution while adding
about 70 g of pure water thereto. After the kneading, the kneaded
mixture was dried at 250.degree.-300.degree. C. for about 5 hours
and then fired at 700.degree. C. for 2 hours. The resulting powders
were placed into a mold and compression molded under a pressure of
500 kgf/cm.sup.2. The molded product was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm and tested. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=87:13 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=80.9:19.1.
[0091] Catalyst 24:AlO.sub.3--TiO.sub.2
[0092] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 100 g of the resulting dried powders were kneaded with
392 g of an aqueous 30% titanium sulfate solution while adding the
latter to the former. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 5 hours and then
fired at 700.degree. C. for 2 hours. The resulting powders were
placed into a mold and compression molded under a pressure of 500
kgf/cm.sup.2. The molded product was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm and tested. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=75:25 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=65.4:34.6.
[0093] Activities of catalysts 19, 20 and 22-24 are shown in FIG.
5, from which is evident that the highest C.sub.2F.sub.6
decomposition rate can be obtained at an alumina content of about
85% by weight.
EXAMPLE 4
[0094] In this Example, an influence of sulfuric acid during the
preparation of the Al.sub.2O.sub.3--TiO.sub.2 catalyst upon the
C.sub.2F.sub.6 decomposition rate was investigated.
[0095] Catalyst 25:Al.sub.2O.sub.3--TiO.sub.2
[0096] Boehmite powders (PURAL SB) was dried at 120.degree. C. for
one hour. 150 g of the resulting dried powders were kneaded with
58.5 g of 30% titania sol (CS-N, trademark of a product
commercially available from Ishihara Sangyo Kaisha, Ltd., Japan)
and an aqueous solution prepared by diluting 44.8 g of 97% sulfuric
acid with 250 ml of pure water. After the kneading, the kneaded
mixture was dried at 250.degree.-300.degree. C. for about 5 hours
and then fired at 700.degree. C. for 2 hours. The resulting powders
were placed into a mold and compression molded under a pressure of
500 kgf/cm.sup.2. The molded product was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm and tested. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=91:9 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=86.3:13.7.
[0097] Sulfate ions were present in the catalyst. Test conditions
were the same as in Example 1, except that the space velocity was
changed to 1,000 h.sup.-1. The test results revealed that a
C.sub.2F.sub.6 decomposition rate of 80% was obtained at a reaction
temperature of 650.degree. C.
EXAMPLE 5
[0098] In this Example, C.sub.2F.sub.6 decomposition rates were
investigated by adding various components to the
Al.sub.2O.sub.3--TiO.sub- .2 catalysts. The catalysts were prepared
as follows, but test procedure and conditions were the same as in
Example 1.
[0099] Catalyst 9:Al.sub.2O.sub.3--TiO.sub.2
[0100] Granular alumina (NKHD-24) was pulverized and sieved to
obtain grains having grain sizes of 0.5-1 mm, followed by drying at
120.degree. C. for 2 hours. Then, the dried grains were impregnated
with 176 g of an aqueous 30% titanium sulfate solution. After the
impregnation, the grains were dried at 250.degree.-300.degree. C.
for about 5 hours and then fired at 700.degree. C. for 2 hours. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Ti=90:10 and in a weight ratio of Al.sub.2O:TiO.sub.2=85.1:14.9.
The catalyst thus prepared was designated as catalyst A.
[0101] Catalyst 10:Al.sub.2O.sub.3--TiO.sub.2--ZrO.sub.2
[0102] 50 g of Catalyst A grains were impregnated with an aqueous
solution of 6.7 g of zirconyl nitrate dihydrate in 38.4 g of
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al:Ti:Zr=90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:ZrO.sub.2=80.2:14.0:5.8.
[0103] Catalyst 11:Al.sub.2O.sub.3--TiO.sub.2--WO3
[0104] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 6.5 g of ammonium paratungstate in H.sub.2O.
After the impregnation, the grains were dried at 120.degree. C. for
2 hours and then fired at 700.degree. C. for 2 hours. The resulting
grain composition for catalyst was in an atomic ratio of
Al:Ti:W=90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:WO.sub.3=76.6:13.4:10.0.
[0105] Catalyst 12:Al.sub.2O.sub.3--TiO.sub.2--SiO.sub.2
[0106] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 7.5 g of 20 wt. % silica sol in H.sub.2O. After
the impregnation, the grains were dried at 120.degree. C. for 2
hours and then fired at 700.degree. C. for 2 hours. The resulting
grain composition for catalyst was in an atomic ratio of
90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:SiO.sub.2=82.6:14.5:2.9.
[0107] Catalyst 13:Al.sub.2O.sub.2--TiO.sub.2--SnO.sub.2
[0108] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 5.6 g of tin chloride dihydrate in H.sub.2O.
After the impregnation, the grains were dried at 120.degree. C. for
2 hours and then fired at 700.degree. C. for 2 hours. The resulting
grain composition for catalyst was in an atomic ratio of
Al:Ti:Sn=90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:SnO.sub.2=79.1:13.9:7.0.
[0109] Catalyst 14:Al.sub.2O.sub.3--TiO.sub.2--CeO.sub.2
[0110] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 10.9 g of cerium nitrate hexahydrate in
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al:Ti:Ce =90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:CeO.sub.2=78.4:13.7:7.- 9.
[0111] Catalyst 15:Al.sub.2O.sub.3--TiO.sub.2--MnO.sub.2
[0112] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 7.2 g of manganese nitrate hexahydrate in
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al:Ti:Mn=90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:MnO.sub.2=81.6:14.3:4.- 1.
[0113] Catalyst 16:Al.sub.2O.sub.3--TiO.sub.2--Bi.sub.2O.sub.3
[0114] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 12.13 g of bithmus nitrate hexahydrate in
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al:Ti:Bi=90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:Bi.sub.2O.sub.3:85.1:1- 4.8:1.1.
[0115] Catalyst 17:Al.sub.2O.sub.3--TiO.sub.2--NiO
[0116] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 7.3 g of nickel nitrate hexahydrate in
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al Ti:Ni =90:10:0.025 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:NiO=82.0:14.4:3.6.
[0117] Catalyst 18:Al.sub.2O.sub.3--TiO.sub.2--BO.sub.4
[0118] 50 g of Catalyst A grains were impregnated with 38.4 g of an
aqueous solution of 1.36 g of ammonium borate octahydrate in
H.sub.2O. After the impregnation, the grains were dried at
120.degree. C. for 2 hours and then fired at 700.degree. C. for 2
hours. The resulting grain composition for catalyst was in an
atomic ratio of Al:Ti:B=90:10:0.005 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2:BO.sub.4=85.65:14.827:- 0.008.
[0119] It was found from FIG. 3 that the
Al.sub.2O.sub.3--TiO.sub.2--ZrO.s- ub.2 catalyst had the highest
activity.
EXAMPLE 6
[0120] In this Example, various catalysts containing alumina as one
member were investigated for C.sub.2F.sub.6 decomposition rates
under the following conditions:
[0121] A C.sub.2F.sub.6 gas having a purity of 99% or more was
diluted with air, and the diluted gas was further admixed with
steam to prepare a reaction gas. Steam was prepared by feeding pure
water to a reactor tube from the top at a flow rate of about 0.2
ml/min. by a microtube pump to gasify the pure water. The reaction
gas had a C.sub.2F.sub.6 concentration of about 0.5%, and was
brought into contact with a catalyst heated to 700.degree. C. by
external heating of the reactor tube in an electric oven at a space
velocity of 2,000 h.sup.-1.
[0122] The reactor tube was an Inconel reactor tube having an inner
diameter of 32 mm and had a catalyst bed fixed at the center of the
reactor tube. An Inconel thermowell for a thermocouple, 3 mm in
diameter, was inserted into the catalyst bed. Decomposition product
gas from the catalyst bed was bubbled through an aqueous calcium
fluoride solution and discharged to the system outside.
[0123] The following catalysts were prepared for the test under the
foregoing conditions:
[0124] Catalyst 26
[0125] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders zinc nitrate
hexahydrate and the mixture was kneaded. After the kneading, the
kneaded mixture was dried at 250.degree.-300.degree. C. for about 2
hours and then fired at 700.degree. C. for 2 hours. The fired
product was pulverized and sieved to obtain grains having grain
sizes of 0.5-1 mm and tested. The resulting grain composition for
catalyst was in an atomic ratio of Al:Zn=91:9 and in a weight ratio
of Al.sub.2O.sub.3:ZnO=86.4:13.6.
[0126] Catalyst 27
[0127] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 50.99 g of nickel sulfate hexahydrate and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=91:9 and in a weight ratio of
Al.sub.2O.sub.3:NiO=87.3:12.7.
[0128] Catalyst 28
[0129] Boehmite powder (PURAL SB) were dried at 120.degree. C. for
one hour. 300 g of the resulting dried powders were admixed with an
aqueous solution of 125.04 g of nickel nitrate hexahydrate and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=91:9 and in a weight ratio of
Al.sub.2O.sub.3:NiO=87.3:12.7.
[0130] Catalyst 29
[0131] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 300 g of the resulting dried powders were kneaded with
354.4 g of an aqueous 30% titanium sulfate solution while adding
about 300 g of pure water thereto. After the kneading, the kneaded
mixture was dried at 250.degree.-300.degree. C. for about 5 hours
and then fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm and tested. The resulting grain composition for catalyst was in
an atomic ratio of Al:Ti=91:9 and in a weight ratio of
Al.sub.2O.sub.3:TiO.sub.2=86.6:13.4.
[0132] Catalyst 30
[0133] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 115.95 g of iron nitrate nonahydrate and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 25020 -300.degree. C. for about 2 hours and then fired at
700.degree. C. for 2 hours. The fired product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm, and tested.
The resulting grain composition was in an atomic ratio of
Al:Fe=91:9.
[0134] Catalyst 31
[0135] Boehmite powder (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 95.43 g of tin chloride hydrate and the mixture
was kneaded. After the kneading, the kneaded mixture was dried at
250.degree.-300.degree. C. for about 2 hours and then dried at
700.degree. C. for 2 hours. The fired product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm and tested.
The resulting grain composition for catalyst was in an atomic ratio
of Al:Sn=91:9 and in a weight ratio of
Al.sub.2O.sub.3:SnO.sub.2=77.4:22.6.
[0136] Catalyst 32
[0137] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution prepared by diluting 22.2 g of a dinitrodiamino
Pt(II) nitric acid solution (Pt concentration: 4.5 wt. %) with 200
mg of pure water, and the mixture was kneaded. After the kneading,
the kneaded mixture was dried at 250.degree.-300.degree. C. for
about 2 hours and then fired at 700.degree. C. for 2 hours. The
fired product was pulverized and sieved to obtain grains having
grain sizes of 0.5-1 mm and tested. The resulting grain composition
for catalyst was in a weight ratio of
Al.sub.2O.sub.3:Pt=100:0.68.
[0138] Catalyst 33
[0139] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 300 g of the resulting dried powders were admixed with an
aqueous solution of 125.87 g of cobalt nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm and tested. The resulting grain composition was in an atomic
ratio of Al:Co=91:9.
[0140] Catalyst 34
[0141] Boehmite powder (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 76.70 g of zirconyl nitrate dihydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm and tested. The resulting grain composition for catalyst was in
an atomic ratio of Al:Zr=91:9 and in a weight ratio of
Al.sub.2O.sub.3:ZrO.sub.2=80.7:19.3.
[0142] Catalyst 35
[0143] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 124.62 g of cerium nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm and tested. The resulting grain composition for catalyst was in
an atomic ratio of Al:Ce=91:9 and in a weight ratio of
Al.sub.2O.sub.3:CeO.sub.2=75.0:25.0.
[0144] Catalyst 36
[0145] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 300 g of the resulting dried powders were admixed with an
aqueous solution of 129.19 g of 20 wt. % silica sol, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm and tested. The resulting grain composition for catalyst was in
an atomic ratio of Al:Si=91:9 and in a weight ratio of
Al.sub.2O.sub.3:SiO.sub.2=89.6:10.4.
[0146] Test results of the foregoing catalysts 19 and 26-36 at a
reaction temperature of 700.degree. C. are shown in FIG. 6,
C.sub.2F.sub.6 decomposition activity is highest with the
Al.sub.2O.sub.3-ZnO.sub.2 catalyst and is lowered in the order of
the Al.sub.2O.sub.3-NiO catalyst, and the
Al.sub.2O.sub.3--TiO.sub.2 catalyst. The highest activity of
catalyst 26 seems to be due to the effect of S.
EXAMPLE 7
[0147] In this Example, changes in the activity of
Al.sub.2O.sub.3--NiO catalyst 28 were investigated by changing
atomic ratios of Al:Ni. Test procedure and conditions were the same
as in Example 6 except that the C.sub.2F.sub.6 concentration was
changed to 2% and the feed rate of pure water to 0.4 ml/min.
[0148] Catalyst 28-1
[0149] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powder were admixed with an
aqueous solution of 8.52 g of nickel nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=99:1 and in a weight ratio of
Al.sub.2O.sub.3:NiO=98.5:1.5.
[0150] Catalyst 28-2
[0151] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 300 g of the resulting powders were admixed with an
aqueous solution of 66.59 g of nickel nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=95:5 and in a weight ratio of
Al.sub.2O.sub.3:NiO=92.8:7.2.
[0152] Catalyst 28-3
[0153] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 210.82 g of nickel nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=80:20 and in a weight ratio of
Al.sub.2O.sub.3:NiO=73.2 26.8.
[0154] Catalyst 28-4
[0155] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 361.16 g of nickel nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al Ni =70:30 and in a weight ratio of
Al.sub.2O.sub.3:NiO=61.4:38.6.
[0156] Catalyst 28-5
[0157] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with
562.1 g of nickel nitrate hexahydrate, and the mixture was kneaded
while adding water thereto. After the kneading, the kneaded mixture
was dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=60:40 and in a weight ratio of
Al.sub.2O.sub.3:NiO=50.6:49.4.
[0158] C.sub.2F.sub.6 decomposition rate 6 hours after the start of
test is shown in FIG. 7. It was found that the Ni content of
Al.sub.2O.sub.3--NiO catalysts is in a range of 5 to 40 atom %,
preferably 20 to 30 atom %.
EXAMPLE 8
[0159] In this Example, changes in the activity of
Al.sub.2O.sub.3--ZnO catalyst 26 was investigated by changing
atomic ratios of Al:Zn. Test procedure and conditions were the same
as in Example 6 except that the C.sub.2F.sub.6 concentration was
changed to 2% and the feed rate of pure water to 0.4 ml/min.
[0160] Catalyst 26-1
[0161] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 215.68 g of zinc nitrate hexahydrate and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Zn=80:20 and in a weight ratio of
Al.sub.2O.sub.3:ZnO=71.5:28.5.
[0162] Catalyst 26-2
[0163] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with
369.48 g of zinc nitrate hexahydrate and the mixture was kneaded.
After the kneading, the kneaded mixture was dried at
250.degree.-300.degree. C. for about 2 hours and fired at
700.degree. C. for 2 hours. The fired product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Zn=70:30 and in a weight ratio of
Al.sub.2O.sub.3:ZnO=59.4:40.6.
[0164] Catalyst 26-3
[0165] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 126.65 g of the resulting dried powders were admixed with
an aqueous solution of 96.39 g of zinc nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Zn=85:15 and in a weight ratio of
Al.sub.2O.sub.3:ZnO=78.0:22.0.
[0166] C.sub.2F.sub.6 decomposition rate 6 hours after the start of
test is shown in FIG. 8. It was found that the Zn content of
Al.sub.2O.sub.3--ZnO.sub.2 catalysts is in a range of 10 to 30 atom
%, preferably 10 to 15 atom %.
EXAMPLE 9
[0167] In this Example, decomposition of CF.sub.4 and CHF.sub.3 was
carried out with a Al.sub.2O.sub.3--NiO catalyst 28-3 under the
same test procedure and conditions as in Example 6, except that the
space velocity was changed to 1,000 h.sup.-1 and the fluorine
compound was diluted with nitrogen in place of air. Test results at
various reaction temperatures are shown in FIG. 9. It was found
that the decomposition activity of Al.sub.2O.sub.3--NiO catalyst
upon CF.sub.4 gas and CHF.sub.3 gas is higher than upon
C.sub.2F.sub.6 gas and the Al.sub.2O.sub.3--NiO catalyst is a
preferable hydrolysis catalyst for CF.sub.4 or CHF.sub.3.
Furthermore, it was found that a preferable reaction temperature is
600.degree.-700.degree. C. for the decomposition of CF.sub.4 and
CHF.sub.3, and 650.degree.-700.degree. C. for the decomposition of
C.sub.2F.sub.6. The higher the reaction temperature, the higher the
decomposition rate. However, substantially 100% decomposition rate
can be obtained at 700.degree. C., and thus a higher reaction
temperature than 700.degree. C. will be meaningless, and a reaction
temperature must be as high as 800.degree. C.
EXAMPLE 10
[0168] In this Example, influences of steam upon C.sub.2F.sub.6
decomposition were investigated under the same test conditions as
in Example 6 except that the space velocity was changed 1,000
h.sup.-1. Al.sub.2O.sub.3--NiO catalyst 28-3 was used at a reaction
temperature of 700.degree. C. while supplying steam for 2 hours
from the start of test, then interrupting supply of steam for 3
hours, and then starting to supply steam again. Test results are
shown in FIG. 10. It was found that during the supply of steam the
C.sub.2F.sub.6 reaction rate was elevated due to the occurrence of
C.sub.2F.sub.6 hydrolysis.
EXAMPLE 11
[0169] In this Example, decomposition of SF.sub.6 was investigated
with Al.sub.2O.sub.3--NiO catalyst 28-3 under the same test
conditions as in Example 6 except that a SF.sub.6 gas having a
purity of 99% or more was used, the space velocity was changed to
1,000 h.sup.-1 and the SF.sub.6 gas was diluted with nitrogen in of
air. The reaction temperature was 700.degree. C. Concentration of
SF.sub.6 in the reaction gas at the inlet to the reactor tube and
concentration of SF.sub.6 in the decomposition gas at the outlet
from the alkaline washing step were determined by TCD gas
chromatography and the decomposition rate was calculated by the
following equation. It was found that the decomposition rate was
99% or more. 2 Decomposition rate = 1 - Concentration of discharged
SF 6 Concentration of fed SF 6 .times. 100 ( % )
EXAMPLE 12
[0170] In this Example, decomposition of NF.sub.3 was investigated
with Al.sub.2O--NiO catalyst 28-3 under the same test conditions as
in Example 11 except that a NF.sub.3 gas having a purity of 99% or
more was used. Reaction temperature was 700.degree. C.
Concentration of NF.sub.3 in the reaction gas at the inlet to the
reactor tube and concentration of NF.sub.3 in the decomposition gas
at the outlet from the alkaline washing step were determined by TCD
gas chromatography and the decomposition rate was calculated
according to the following equation. It was found that the
decomposition rate was 99% or more. It was found preferable to
carry out the decomposition of the NF.sub.3 gas with the
Al20.sub.3--NiO catalyst at a temperature of
600.degree.-800.degree. C. 3 Decomposition rate = Concentration of
discharged NF 3 Concentration of fed NF 3 .times. 100 ( % )
EXAMPLE 13
[0171] In this Example, activity of Al.sub.2O.sub.3--ZnO catalyst
upon hydrolysis of a CF.sub.4 gas, a C.sub.4F.sub.8 gas and a
CHF.sub.3 gas was investigated. Decomposition of a CF.sub.4 gas was
carried out in the following manner:
[0172] At first, a CF.sub.4 gas having a purity of 99% or more was
diluted with air, and the diluted CF.sub.4 gas was further admixed
with steam. Concentration of CF.sub.4 in the reaction gas was about
0.5%, and steam flow rate was adjusted to about 50 times as high as
that of the fluorine compound, i.e. CF.sub.4. The reaction gas was
brought into contact with the catalyst heated to a predetermined
temperature in a reactor tube in an electric oven at a space
velocity of 1,000 h.sup.-1. Decomposition product gas from the
catalyst bed was bubbled through an aqueous sodium hydroxide
solution and then discharged to the system outside. Decomposition
rate of CF.sub.4 was determined by TCD gas chromatography.
[0173] The Al.sub.2O.sub.3--ZnO catalyst used for the test was
prepared in the following manner:
[0174] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 126.65 g of the resulting dried powders were admixed with
96.39 g of zinc nitrate hexahydrate, and the mixture was kneaded.
After the kneading, the kneaded mixture was dried at
250.degree.-300.degree. C. for about 2 hours and then fired at
700.degree. C. for 2 hours. The fired product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm. The
resulting grain composition for catalyst was in an atomic ratio of
Al:Zn85:15 and in a weight ratio of Al.sub.2O.sub.3:ZnO=78:22.
[0175] FIG. 11 shows decomposition rates of CF.sub.4 at various
reaction temperatures and also those of CHF.sub.3 and
C.sub.4F.sub.8 as fed and decomposed in the same manner as above.
Decomposition rates of CHF.sub.3 and C.sub.4F.sub.8 were determined
by FID gas chromatography, whereby it was found that the
Al.sub.2O.sub.3--ZnO catalyst had a higher activity upon the
CF.sub.4 gas, the C.sub.4F.sub.8 gas and the CHF.sub.3 gas. It was
also found that a higher decomposition rate can be obtained
preferably at a reaction temperature of 650.degree. C. or higher
for the hydrolysis of the C.sub.4F.sub.8 gas and even at a reactor
temperature of 600.degree. C. or lower for the hydrolysis of the
CHF.sub.3 gas or the CF.sub.4 gas.
EXAMPLE 14
[0176] In this Example, the decomposition activity of as
Al.sub.2O.sub.3--NiO catalyst upon a C.sub.3F.sub.8 gas, a
C.sub.4F.sub.8 gas and a SF.sub.6 gas was investigated in the same
manner as in Example 13. The concentration of C.sub.4F.sub.8 in the
reaction gas after decomposition of C.sub.4F.sub.8 was 0.1% by
volume. The Al.sub.2O.sub.3--NiO catalyst used for the test was
prepared in the following manner:
[0177] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with an
aqueous solution of 210.82 g of nickel nitrate hexahydrate, and the
mixture was kneaded. After the kneading, the kneaded mixture was
dried at 250.degree.-300.degree. C. for about 2 hours, and then
fired at 700.degree. C. for 2 hours. The fired product was
pulverized and sieved to obtain grains having grain sizes of 0.5-1
mm. The resulting grain composition for catalyst was in an atomic
ratio of Al:Ni=80:20 and in a weight ratio of
Al.sub.2O.sub.3:NiO=73.2:26.8.
[0178] FIG. 12 shows decomposition rates at various reaction
temperatures, where the decomposition rate of C.sub.3F.sub.8 and
C.sub.4F.sub.8 was determined by FID gas chromatography and that of
SF.sub.6 by TCD gas chromatography. It was found from the test
results that the Al.sub.2O.sub.3--NiO catalyst had a higher
activity upon the hydrolysis of the SF.sub.6 gas, C.sub.3F.sub.8
gas and the C.sub.4F.sub.8 gas, and the reaction temperature was
preferably 500.degree. C. or higher for the hydrolysis of the
SF.sub.6 gas and preferably 700.degree. C. or higher for the
hydrolysis of the C.sub.3F.sub.8 gas. In the case of C.sub.4F.sub.8
gas, the reaction temperature for the hydrolysis was preferably
650.degree. C. or higher.
EXAMPLE 15
[0179] In this Example, decomposition activity of an
Al.sub.2O.sub.3--NiO--ZnO catalyst upon C.sub.4F.sub.8 was
investigated in the same manner as in Example 13. The
Al.sub.2O.sub.3--NiO--ZnO catalyst used for the test was prepared
in the following manner:
[0180] Boehmite powders (PURAL SB) were dried at 120.degree. C. for
one hour. 200 g of the resulting dried powders were admixed with
210.82 g of nickel nitrate hexahydrate and 152.31 g of zinc nitrate
hexahydrate, and the mixture was kneaded while adding pure water
thereto. After the kneading, the kneaded mixture was dried at
250.degree.-300.degree. C. for about 2 hours and then fired at
700.degree. C. for 2 hours. The fired product was pulverized and
sieved to obtain grains having grain sizes of 0.5-1 mm. The
resulting grain composition for catalyst was in atomic ratios of
Al:Ni80:20 and Al:Zn=85:15 and in a weight ratio of
Al.sub.2O.sub.3:NiO:ZnO=60.7:22.2:17.1.
[0181] FIG. 13 shows decomposition rates at various reaction
temperatures, where the decomposition rate of C.sub.4F.sub.8 was
determined by FID gas chromatography.
* * * * *