Gas phase process for the epoxidation of non-allylic olefins

Details Gas phase process for the epoxidation of non-allylic olefins Gas phase process for the epoxidation of non-allylic olefins

1999-12-16

2001-01-09

Trinh, Ba K. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S536000

Reexamination Certificate

active

06172245

ABSTRACT:

INTRODUCTION
This invention pertains to an improved gas phase process for the selective epoxidation of non-allylic olefins wherein the epoxidation is carried out in the presence of one or more volatile, nitrogen-containing, basic compounds. The presence of a nitrogen-containing basic compound in the olefin-containing reaction gas or vapor suppresses the formation of an organic resinous material which coats the catalyst, thereby decreasing catalyst activity. This resinous material (foulant) also can coat and foul process equipment, thereby impeding or obstructing gas flow through the reactor and associated equipment. The inclusion of a nitrogen-containing basic compound in the olefin-containing reaction gas also has been found to increase substantially the activity of the epoxidation catalyst.
BACKGROUND OF THE INVENTION
Processes for the selective epoxidation of olefins which contain no allylic hydrogen atoms (non-allylic olefins) or olefins which contain hindered allylic hydrogen atoms are described by Monnier and Muehlbauer in U.S. Pat. Nos. 4,897,498, 4,950,773, 5,081,096, 5,138,077 and 5,145,968. Stavinoha and Tolleson disclose in U.S. Pat. No. 5,117,012 the selective epoxidation of 1,3-butadiene (butadiene) to 3,4-epoxy-1-butene (EpB) by contacting a mixture comprising 1,3-butadiene, oxygen and methane with a supported silver catalyst at elevated temperatures. Stavinoha, Monnier, Hitch, Nolen and Oltean describe in U.S. Pat. No. 5,362,890 the advantages resulting from the use of a C
2
-C
6
paraffin hydrocarbon as an inert diluent in the feed gas in the epoxidation of certain olefins such as 1,3-butadiene.
The epoxidation of olefins such as butadiene in the presence of a modified, supported, silver catalyst to an epoxide such as 3,4-epoxy-1-butene according to known processes such as those described in the above referenced patents results in the co-production of a high-boiling, organic, resinous material. Generally, the rate of formation of the foulant material is dependent, at least in part, upon pressure within the epoxidation reactor with increased pressures resulting in increased rates of foulant formation. This foulant material coats the catalyst and thereby decreases catalyst activity which, in turn, results in lower conversion of the olefin reactant and production of the desired epoxide. This foulant also may coat and foul process equipment, thereby impeding or obstructing gas flow through the reactor and associated equipment. Build-up of the foulant material over extended periods of operation of the continuous epoxidation process significantly shortens the length of service of catalyst, results in an unacceptable pressure drop through the reactor during normal operation, lowers catalytic activity, and ultimately results in complete blockage of gas flow through the reactor. Removal of catalyst material coated or covered with the organic foulant from the reactor tubes typically used in the epoxidation of olefins is extremely difficult, requiring considerable time to remove the foulant from the reactor tubes and associated equipment downstream from the tubular reactor.
U.S. Pat. Nos. 5,618,954 and 5,905,161 are directed to reducing foulant formation during the epoxidation of butadiene. These patents disclose the use of 5-80% water in the feed gas to the epoxidation reactor to lower the rate of foulant formation. However, even with the water addition, fouling occurs and the supported silver catalyst requires frequent regeneration in a gas stream containing oxygen and water vapor. Furthermore, the addition of water to a process gas stream containing reactive epoxides can result in the formation of the corresponding diols, e.g., 3-butene-1,2-diol and 2-butene-1,4-diol, which are reactive species that can further react to form organic foulant residue. Although it is not known exactly how the organic foulant forms, it has been experimentally determined that 3,4-epoxy-1-butene, oxygen, and water are required for growth, or propagation of the organic foulant. Therefore, addition of water to suppress the formation of organic foulant is actually detrimental to the goal of lowering the rate of organic foulant formation. Finally, addition of high concentrations of water vapor described in the cited patents can result in the degradation of the modified silver catalysts that are employed to catalyze the formation of the olefin epoxides.
Inui and Tanabe,
Journal of Catalysis
, 52, 375-384(1978) discuss the effects of the addition of various levels of ammonia and substituted amines, such as monomethylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and ethanolamine, etc. to the reactor feedstream during ethylene epoxidation. The authors report that the addition of ammonia and such amines in the range of 200-34000 ppmv to the reactor feedstream resulted in decreases in the rate of ethylene oxide formation. At the higher levels, catalytic activity was completely suppressed.
BRIEF SUMMARY OF THE INVENTION
We have discovered that the rate of formation of resinous, high boiling, organic foulant during the epoxidation of olefins can be significantly reduced, and possibly eliminated, by including at least one nitrogen-containing basic compounds in the gaseous reaction mixture. Our invention, in its broader aspects, provides a process for the preparation of the monoepoxide of an olefin reactant selected from norbornene, norbornadiene and olefins having the general formula
wherein R
1
is hydrogen or alkyl and R
2
is an aryl radical or the group
provided that the olefins of formula (I) contain more than 2 carbon atoms and do not contain any allylic hydrogen atoms, which comprises contacting a reaction gas comprising said olefin reactant, oxygen, an inert diluent, and at least 5 parts per million by volume (ppmv) of at least one nitrogen-containing basic compound with a supported silver epoxidation catalyst at a temperature of about 175 to 230° C.; and recovering a gas containing said monoepoxide of the olefin reactant.
A more specific embodiment of the present invention is a continuous process for the preparation of the monoepoxide of an olefin reactant selected from norbornene, norbornadiene and olefins having the general formula
wherein R
1
is hydrogen or alkyl and R
2
is an aryl radical or the group
provided that the olefins of formula (I) contain more than 2 carbon atoms and do not contain any allylic hydrogen atoms, which comprises the steps of:
(1) continuously feeding a gas comprising about 3 to 30 mole percent of said olefin reactant, about 3 to 30 mole percent oxygen, about 40 to 90 mole percent of an inert diluent, and at least 5 parts per million by volume (ppmv) of at least one nitrogen-containing basic compound to an epoxidation zone containing a supported silver epoxidation catalyst and maintained at a temperature of about 175 to 230° C.; and
(2) continuously removing from the epoxidation zone a gas comprising about 0.5 to 5.0 mole percent of said monoepoxide of the olefin reactant, about 2 to 28 mole percent of said olefin reactant, about 2 to 28 mole percent oxygen and about 40 to 90 mole percent of the inert diluent.
The inclusion of the nitrogen-containing basic compound in the epoxidation zone or reactor suppresses foulant formation to a degree which permits operation of the epoxidation reactor at higher pressures which results in a higher rate of conversion of the olefin reactant and, thus, a higher rate of production of the monoepoxide. The nitrogen-containing basic compound in the epoxidation zone also results in an increase in the activity, e.g., an increase in activity of 10 to 30%, of the supported silver epoxidation catalyst. Another advantage provided by the present invention is that the nitrogen-containing basic compound fed to the epoxidation zone can provide the basic compound employed in the product recovery process described in U.S. Pat. No. 5,756,779 to reduce formation of butenediols.
DETAILED DESCRIPTION
The nitrogen-containing basic compounds which may be used in the present invention comprises ammonia and amines which exist in the

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