Process for the preparation of butane-1,4-diol,...

Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

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C568S864000, C549S508000

Reexamination Certificate

active

06204395

ABSTRACT:

This invention relates to the production of butane-1,4-diol, &ggr;-butyrolactone and tetrahydrofuran.
Butane-1,4-diol, together with variable amounts of &ggr;-butyrolactone and tetrahydrofuran, can be produced by hydrogenolysis of maleic anhydride. A major use of butane-1,4-diol is as a feedstock for the plastics industry, particularly for the production of polybutylene terephthalate. It is also used as an intermediate for the production of &ggr;-butyrolactone and of the important solvent, tetrahydrofuran.
Maleic anhydride is normally produced by vapour phase oxidation of a hydrocarbon feedstock, such as benzene, mixed C
4
olefins, or n-butane, in the presence of a partial oxidation catalyst. In the partial oxidation of benzene there is typically used a supported vanadium pentoxide catalyst promoted with MoO
3
and possible other promoters. The reaction temperature is form about 400° C. to about 455° C. and the reaction pressure is form about 1 bar to about 3 bar, while about 4 times the theoretical amount of air is used in order to stay outside the explosive limits. The contact time is about 0.1 s. When the feedstock is a mixed C
4
olefin feedstock, i.e. a mixed butanes feedstock, then the partial oxidation catalyst may be vanadium pentoxide supported on alumina. Typical reaction conditions include use of a temperature of from about 425° C. to about 485° C. and a pressure of from about 1.70 bar to about 2.05 bar. The volume ratio of air to butanes may be about 75:1 in order to stay below explosive limits. Alternatively it is possible, according to more modern practice, to design the plant so that satisfactory safe operation can be achieved, despite the fact that the feed mixture of air and butanes is with in the flammable limits. In the case of n-butane as feedstock, the catalyst is typically vanadium pentoxide and the reaction conditions include use of a temperature of from about 350° C. to about 450° C. and a pressure fo from about 1 bar to about 3 bar. The air: n-butane volume ratio may be about 20:1, even though this may be within the flammable limits. One design of reactor for such partial oxidation reactions comprises vertical tubes surrounded by a jacket through which a molten salt is circulated in order to control the reaction temperature.
In each case a hot vaporous reaction mixture is recovered from the exit end of the reactor which comprises maleic anhydride vapour, water vapour, carbon oxides, oxygen, nitrogen, and other inert gases, besides organic impurities such as formic acid, acetic acid, acrylic acid, and unconverted hydrocarbon feedstock.
One way of recovering maleic anhydride from such a reaction mixture is to cool it to about 150° C. using a stream-producing stream and then to cool it further to about 60° C. by cooling it against water in order to condense part of the maleic anhydride, typically about 30% to about 60% of the maleic anhydride present. The remainder of the stream is then scrubbed with water.
Scrubbing with water or with an aqueous solution or slurry is described, for example in U.S. Pat. No. 2,638,481. Such scrubbing results in production of a solution of maleic acid which is then dehydrated, by distilling with xylene, for example, so as to remove the water and re-form the anhydride. A disadvantage of such a procedure, however, is that an unacceptable proportion of the product remains in the vapour phase. In addition, some of the maleic acid is inevitably isomerised to fumaric acid. The byproduct fumaric acid represents a loss of valuable maleic anhydride and is difficult to recover from the process system since it tends to form crystalline masses which give rise to process problems.
Because of this isomerisation problem a variety of other anhydrous scrubbing liquids have been proposed. For example, dibutyl phthalate has been proposed as scrubbing liquid in GB-A-727828, GB-A-763339, and GB-A-768551. Use of dibutyl phthalate containing up to 10 weight % phthalic anhydride is suggested in U.S. Pat. No. 4,118,403. U.S. Pat. No. 3,818,680 teaches use of a normally liquid intramolecular carboxylic acid anhydride, such as a branched chain C
12-15
-alkenyl substituted succinic anhydride, for absorption of maleic anhydride from the reaction mixture exiting the partial oxidation reactor. Tricresyl phosphate has been proposed for this purpose in FR-A-1125014. Dimethyl terephthalate is suggested for this duty in JP-A-32-8408 and dibutyl maleate in JP-A-35-7460. A high molecular weight was as scrubbing solvent is taught in U.S. Pat. No. 3,040,059, while U.S. Pat. No. 2,893,924 proposes scrubbing with diphenylpentachloride. Use of an aromatic hydrocarbon solvent having a molecular weight between 150 and 400 and a boiling point above 140° C. at a temperature above the dew point of water in the vaporous reaction mixture, for example dibenzylbenzene, is suggested in FA-A-2285386. Absorption of maleic anhydride from the vaporous partial oxidation reaction mixture in dimethylbenzophenone followed by distillation in described in U.S. Pat. No. 3,850,758. Polymethylbenzophenones, at least a portion of which contain at least 3 methyl groups, can be used as liquid absorbent for maleic anhydride according to U.S. Pat. No. 4,071,540. Dialkyl phthalate esters having C
4
to C
8
alkyl groups and a total of 10 to 14 carbon atoms in both alkyl groups are proposed for absorption of maleic anhydride from the reaction mixture in U.S. Pat. No. 3,891,680. An ester of a cycloaliphatic acid, for example dibutyl hexahydrophthalate, is suggested as absorption solvent for maleic anhydride in ZA-A-80/1247.
It has also been proposed to effect direct condensation of maleic anhydride from the reaction mixture exiting the partial oxidation reactor. However, this procedure is inefficient because an unacceptable proportion of the maleic anhydride remains in the vapour phase.
The maleic anhydride product recovered following condensation or by scrubbing or absorption and distillation can then be subjected to hydrogenation to yield butane-1,4-diol, together with variable amounts of &ggr;-butyrolactone and tetrahydrofuran, as described in U.S. Pat. No. 5,347,021 and EP-B-0373947 the disclosure of which is herein incorporated by reference.
It would be desirable to improve the production of butane-1,4-diol, &ggr;-butyrolactone and tetahydrofuran, from maleic anhydride by hydrogenation. In particular it would be desirable to reduce the capital cost of construction of such a plant and also to reduce its running costs, thereby making butane-1,4-diol, &ggr;-butyrolactone and tetrahydrofuran more readily available.


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Vapour Phase Hydrogenation of Maleic Anhydride to &ggr;-Butyrolactone; 3. Reaction Pathway and New ctalyst Compositions, pp. 174-178; BD. 48, Heft 4/5, Apr./May 1995.

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