Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-06-28
2001-05-29
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S508000, C568S864000
Reexamination Certificate
active
06239292
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 diesters of maleic acid, fumaric acid and mixtures thereof. 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.
The maleate and fumarate diesters used as feedstock for the production of butane-1,4-diol by such a hydrogenolysis route are conveniently prepared from maleic anhydride, which is itself 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 possibly other promoters. The reaction temperature is from about 400° C. to about 455° C. and the reaction pressure is from 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 butenes 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 butenes 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 butenes is within 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 of 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 steam-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 wax 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 FR-A-2285386. Absorption of maleic anhydride from the vaporous partial oxidation reaction mixture in dimethylbenzophenone followed by distillation is 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 is then reacted with a suitable C
1
to C
4
alkanol, such as methanol or ethanol, to yield the corresponding di-(C
1
to C
4
alkyl maleate. This di-(C
1
to C
4
alkyl) maleate may contain a minor amount of the corresponding di-(C
1
to C
4
alkyl) fumarate, besides traces of the corresponding mono-(C
1
to C
4
alkyl) maleate and/or fumarate. It is then subjected to hydrogenolysis to yield a mixture of butane-1,4-diol, together with variable amounts of &ggr;-butyrolactone and tetrahydrofuran, depending upon the hydrogenolysis conditions that are selected, and of the C
1
to C
4
alkanol which can be recycled to produce further di-(C
1
to C
4
alkyl) maleate.
Processes and plant for the production of dialkyl maleates from maleic anhydride are described, for example, in U.S. Pat. No. 4,795,824 and in WO-A-90/08127. This last mentioned document describes a column reactor containing a plurality of esterification trays each having a predetermined liquid hold-up and containing a charge of a solid esterification catalyst, such as an ion exchange resin containing pendant sulphonic acid groups. A liquid phase containing, for example, a carboxylic acid component flows down the column from one esterification tray to the next lower one against an upflowing stream of vapour of the lower boiling component of the esterification reagents, typically the C
1
to C
4
alkanol. Water of esterification is removed from the top of the column reactor in a vapour stream, while ester product is recovered from the sump of the reactor. As the liquid flows down the trays it encounters progressively drier reaction conditions and the esterification reaction is driven further towards 100% ester formation. This column reactor may be followed by a polishing reactor operating under liquid phase reaction conditions, the ester-containing stream from the bottom of the column reactor being admixed with further C
1
to C
4
alkanol prior to
Hiles Andrew George
Tuck Michael William Marshall
Wood Michael Anthony
BASF - Aktiengesellschaft
Dentz Bernard
Nixon & Vanderhye P.C.
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