Process for the simultaneous production of maleic anhydride...

Details Process for the simultaneous production of maleic anhydride... Process for the simultaneous production of maleic anhydride...

2002-07-22

2003-09-16

Lambkin, Deborah C. (Department: 1626)

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S295000, C549S325000, C549S326000, C549S429000, C549S508000, C568S864000

Reexamination Certificate

active

06620949

ABSTRACT:

This application is a 371 of PCT/GB00/03805, filed Oct. 4, 2000.
This invention relates to a process for the co-production of C
4
compounds, more specifically maleic anhydride, butane-1,4-diol, &ggr;-butyrolactone, and tetrahydrofuran, from a hydrocarbon feedstock selected from C
4
hydrocarbons and benzene.
Maleic anhydride can be 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.
Depending on the nature of the feedstock a supported promoted vanadium pentoxide catalyst is typically used, while the reaction temperature is usually from about 350° C. to about 500° C. and the reaction pressure is from about 10
5
Pa to about 3×10
5
Pa. A substantial excess amount of air may be used in order to stay outside the explosive limits. The contact time is about 0.1 s. 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 hydrocarbon feedstock is within the flammable limits.
One design of reactor for such partial oxidation reactions comprises a tubular reactor including vertical tubes surrounded by a jacket through which a molten salt is circulated in order to control the reaction temperature. However, other designs of reactor can be used instead, including fixed bed reactors, fluidised bed reactors, or moving bed reactors.
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 acetic acid, acrylic acid, and unconverted hydrocarbon feedstock.
It is usual to recover and purify the maleic anhydride from this dilute reactor effluent stream in up to four steps. First, in an optional step, some conventional processes condense out part of the maleic anhydride by cooling the reactor effluent stream, typically to about 150° C. using a steam-producing heat exchanger and then cooling 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. Only partial condensation is effected because of the presence of water which reacts with maleic anhydride in the reactor effluent stream to form maleic acid, which may in turn isomerise to fumaric acid. Maleic acid has a melting point of 130° C., while fumaric acid has a melting point of 287° C., both of which are much higher than that of maleic anhydride (52.85° C.). As a result there is a tendency for deposits of solid maleic acid and fumaric acid to build up on the heat exchanger surfaces which require periodic removal, typically by use of water and/or sodium hydroxide solution which yields an aqueous solution that contains fumaric acid and maleic acid or their sodium salts and requires effluent treatment.
A second step that is conventionally used is to absorb essentially all of the remaining maleic anhydride from the effluent stream. The remaining gaseous effluent can then be vented to the atmosphere, possibly after incineration of carbon monoxide, unconverted hydrocarbon, and other organic compounds contained therein. In this absorption step an organic solvent can be used. Alternatively an aqueous solution can be used as the absorbent, in which case the maleic anhydride is mainly hydrolysed to form maleic acid.
Scrubbing with water or with an aqueous solution or slurry is described, for example, in U.S. Pat. No. 2,638,481. A disadvantage of such a procedure, however, is that 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 fouling problems.
Because of this isomerisation problem a variety of other anhydrous organic solvents have been proposed for absorption of maleic anhydride from vaporous streams, for example, dibutyl phthalate (British Patent Specifications Nos. 727,828, 763,339, and 768,551), dibutyl phthalate containing up to 10 weight % phthalic anhydride (U.S. Pat. No. 4,118,403) normally liquid intramolecular carboxylic acid anhydrides, such as a branched chain C
12-15
-alkenyl substituted succinic anhydride (U.S. Pat. No. 3,818,680), tricresyl phosphate (French Patent Specification No. 1,125,014), dimethyl terephthalate (Japanese Patent Publication No. 32-8408), dibutyl maleate (Japanese Patent Publication No. 35-7460), high molecular weight waxes (U.S. Pat. No. 3,040,059), diphenylpentachloride (U.S. Pat. No. 2,893,924), high boiling aromatic hydrocarbon solvents, such as dibenzylbenzene (French Patent Specification No. 2,285,386), dimethylbenzophenone (U.S. Pat. No. 3,850,758), polymethylbenzophenones, at least a portion of which contain at least 3 methyl groups, (U.S. Pat. No. 4,071,540), water-insoluble tertiary amines (U.S. Pat. No. 4,571,426), dialkyl phthalate esters having C
4
to C
8
alkyl groups and a total of 10 to 14 carbon atoms in both alkyl groups (U.S. Pat. No. 3,891,680), and esters of cycloaliphatic acids, for example dibutyl hexahydrophthalate (South African Patent Specification No. 80/1247).
A third step that is conventionally used is to recover the resulting solution of maleic anhydride or maleic acid from the absorbent. When the absorbent is an organic solvent, batch distillation or continuous distillation can be used to recover the maleic anhydride. On the other hand, when the absorbent liquid is water or an aqueous solution, the recovery step must include a dehydration step so as to re-convert the maleic acid back to maleic anhydride. One procedure that is used is to distil the maleic acid solution in the presence of xylene. This not only removes the water but also results in re-formation of maleic anhydride. In either event the elevated temperatures used tend to induce formation of fumaric acid which constitutes a further loss of potential product maleic anhydride.
U.S. Pat. No. 5,069,687 proposes recovery of maleic anhydride from a gaseous mixture by contact with an absorbent, following which water is removed from the enriched absorbent by contacting it with a water adsorbent or with a low humidity stripping gas. Maleic anhydride is then recovered from the dried enriched absorbent.
A growing use for maleic anhydride is in the production of butane-1,4-diol, and its co-products, i.e. &ggr;-butyrolactone, and tetrahydrofuran. Direct hydrogenation of maleic anhydride or maleic acid to these C
4
compounds is proposed in U.S. Pat. Nos. 3,948,805, 4,001,282, 4,048,196, 4,083,809, 4,096,156, 4,550,185, 4,609,636, 4,659,686, 4,777,303, 4,985,572, 5,149,680, 5,347,021, 5,473,086, and 5,698,749, and in European Patent Publication No. 0373947A.
Esterification of maleic anhydride with an alkyl alcohol to yield a dialkyl maleate followed by hydrogenation of the resulting dialkyl maleate has also been proposed in order to produce butane-1,4-diol, and its co-products, &ggr;-butyrolactone and tetrahydrofuran. Hydrogenation in the liquid phase is proposed in British Patent Specification No. 1,454,440. Vapour phase hydrogenation is taught in International Patent Publication No. WO 82/03854. Hydrogenation of a dialkyl maleate in two stages can be carried out as described in U.S. Pat. Nos. 4,584,419 and 4,751,334.
U.S. Pat. No. 4,032,458 proposes esterification of maleic acid with a C
2
to C
10
alkanol at elevated pressure and temperature followed by a two stage hydrogenation of the resulting dialkyl maleate using a slurry of a copper chromite catalyst and then by distillation.
U.S. Pat. No. 5,478,952 suggests a hydrogenation catalyst which can be used in aqueous solution to hydrogenate, for example, maleic acid, and which consists of a mixture of ruthenium and rhenium on carbon.
Processes and plant for the production of dialkyl maleates from maleic anhydride are described, for example, in U.

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