Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Halogen or compound containing same
Reexamination Certificate
2002-06-18
2003-01-07
Siegel, Alan (Department: 1621)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Halogen or compound containing same
C502S228000, C502S307000, C502S314000, C502S315000, C502S320000
Reexamination Certificate
active
06503865
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of preparing pentafluoroethane, catalysts for fluorination and a preparation method thereof.
PRIOR ART
Generally, since saturated halogenated hydrocarbons containing hydrogen (hereinafter sometimes referred to as alternative flon) have an extremely low possibility of destroying the ozone layer, they have attracted much attention as an alternative to halogenated carbons without hydrogen (for example, chlorofluoroethanes: hereinafter sometimes referred to as specific flon) which have been used on the market.
In particular, pentafluoroethane is expected to satisfy a wide range of uses as a refrigerant, a foaming agent, a solvent, and a dry etchant. Further, pentafluoroethane is a useful substance because it is an inert and low-toxicity gas under normal temperatures and pressures.
In the conventional preparation methods for pentafluoroethane, it has been known that a gas phase fluorination reaction of tetrachoroethylene or halogenated hydrocarbons [C
2
HCl
x
F
(s-x)
; wherein x is 1-5] uses a chromium oxide catalyst or an alumina catalyst carrying metals and so on.
However, it has been obvious that the conventional known reaction cannot avoid the generation of chlorofluoroethanes (specific flon) as by-products, in addition to the objective product, pentafluoroethane and halogenated hydrocarbons represented as C
2
HCl
x
F
(s-x)
(where x is 1-5) which can be recycled in the reaction system as the starting material.
In addition, chlorofluoroethanes [C
2
Cl
x
F
(6-x)
; where x is 1-5] of this specific flon cannot be recycled in the reaction system as the starting material, resulting in a production loss, difficulty in separation from the objective product (pentafluoroethane) in the purification process leading to a cost increase for the purification equipment and lower purification, especially in the case of 1-chloro-1,1,2, 2,2,-pentafluoroethane (hereinafter referred to as CFC-115). Further, much expense is required for the treatment.
First, the conventional methods of preparing pentafluoroethane using a chromium oxide catalyst or an activated carbon catalyst carrying chromium or chromium oxide are described.
For example, it is disclosed in U.S. Pat. No. 3,755,477 that pentafluoroethane is produced using 2,2-dichloro-1,1, 1-trifluoroethane (hereinafter referred to as HCFC-123) as a starting material in the presence of a chromium oxide catalyst. JP Open. No. 8-38904 illustrates that pentafluoroethane is generated from perchloroethylene in the presence of a chromium oxide catalyst treated reductively. Further, in WO No. 92/19576, it is disclosed that pentafluoroethane is produced from HCFC-123 in the presence of a chromium oxide prepared from (NH
4
)
2
Cr
2
O
7
. It is also disclosed in EP No. 456552 that pentafluoroethane is produced using HCFC-123 as a starting material in the presence of an activated carbon catalyst carrying Cr.
However, since the conventional methods using said catalysts, such as a chromium oxide catalyst and an activated carbon catalyst carrying chromium or chromium oxide, are limited in reducing the problematic chlorofluoroethane by-products as described above, improvement in the problem of generating chlorofluoroethanes is still insufficient.
Especially in any of the said methods, it is difficult to lower the ratio of the total yield of chlorofluoroethane by-products to not more than 1% of the yield of the objective product, pentafluoroethane.
Another method of preparing pentafluoroethane is known using alumina or aluminum fluoride catalysts carrying metals.
For example, the methods of preparing pentafluoroethane are disclosed using starting materials such as perchloroethylene, 1,1,2-trichloro-2,2-difluoroethane (hereinafter referred to as HCFC-122) or HCFC-123 in the presence of the catalysts: Cr
2
O
3
/Al F
3
in EP No. 638535; Mn (or Co, Cr)/AlF
3
in JP Publ. No. 3-505328; Zn/alumina in WO No. 92/16482; Co/Ce/alumina in JP Open. No. 4-29940; and Cr/Ni/Al oxide catalyst in EP No. 609124.
Compared to the cases using chromium oxide catalysts, the cases using these catalyst with alumina or aluminum fluoride as a carrier lead to a low reactivity being forced to react at a high temperature. Consequently, it not only creates conditions for an increase in generation of the by-products, but also leads to increase both in equipment costs for heat of reactors and running costs. Further, the larger reactor made of a higher quality material is required resulting from the necessity for a large amount of the catalyst.
New catalysts for the preparation of pentafluoroethane are proposed in which the catalyst is a chromium catalyst such as chromium oxide or fluorinated chromium oxide which has been made to carry metals.
However, in most of these, the yield of the chlorofluoroethane by-products is not considered. In addition, they do not illustrate the preparation methods of pentafluoroethane showing a highly-active fluorination; namely, a high yield of pentafluoroethane and a controlled generation of chlorofluoroethane by-products. For example, in JP Open. No. 2-178237, pentafluoroethane is prepared by fluorination of perchloroethylene using a catalyst Fe
2
O
3
—Cr
2
O
3
with a good yield. In JP Open. No.7-61944, pentafluoroethane is obtained by using HCFC-123 as a starting material and a catalyst In/CrO
x
F
y
(the catalyst shown in the published patent gazette is specified with a composition that gives a Cr valence of +3.0) treated with hydrogen at 400° C. for 4 hr. In JP Open. No. 8-108073, preparation of pentafluoroethane is also disclosed using HCFC-123 as a starting material and a catalyst Ga/CrO
x
F
y
(the catalyst shown in the published patent gazette is specified with a composition that gives a Cr valence of +3.0) treated with hydrogen at 400° C. for 4 hr. Both gazettes show the controlled effect on lowering the activity due to an increase in the reaction pressure and the long life of the catalyst.
However, none of the said examples show findings relating to the generation of chlorofluoroethane by-products.
Namely, although WO No.95/27688 discloses a method of preparing pentafluoroethane using catalysts of Zn/Cr oxides, this does not illustrate the finding relating to the total yield of chlorofluoroethane by-products. The amount of CFC-115 is shown, however, in the example using perchloroethylene as a starting material, the ratio of CFC-115 to pentafluoroethane generated is 0.59%. Further, in the example using HCFC-123 as a starting material, even the ratio of CFC-115 to the combined amount of HFC-125 with HCFC-124 already reaches 1.46%; accordingly, the reducing effect on chlorofluoroethanes is insufficient.
Further, a method of preparing pentafluoroethane from perchloroethylene using an Mg/Cr oxide catalyst is disclosed in EP No. 733611. However, large amounts of chlorofluoroethane by-product are obviously generated in all examples shown there, compared with the comparative example, and the ratio of the total amount of chlorofluoroethane generated to the amount of pentafluoroethane generated is high, and in the range of 2.9 to 7.0%.
In another fluorination reaction of 2-chloro-1,1,1-trifluoroethane (hereinafter referred to as HCFC-133a), a chromium oxide catalyst with the addition of some metals is also proposed.
For example, the fluorination reaction of HCFC-133a is disclosed in JP Open. No. 2-172933 using a catalyst comprised of halogenated compounds or oxides containing Cr and at least one element selected from a group composed of Al, Mg, Ca, Ba, Sr, Fe, Ni, Co, and Mn. The fluorination reaction of HCFC-133a is also disclosed in EP No. 546883, where the catalyst composed of a base material of an oxide of Cr mixed with Ni prepared by a hydroxide sol of Cr
3+
with Ni
2+
is used. However, this literature does not show findings relating to activity and selectivity of the generation reaction of pentafluoroethane or the yield of chlorofluoroethanes. Also, the reactivity of the generation reaction of pentafluoroethane cannot be easily predicted. Further, since
Kanemura Takashi
Shibanuma Takashi
Armstrong Westerman & Hattori, LLP
Daikin Industries Ltd.
Siegel Alan
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