Process for preparing tetrahydrofuran

Details Process for preparing tetrahydrofuran Process for preparing tetrahydrofuran

1992-01-31

1994-05-10

Ivy, C. Warren

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D30708

Patent

active

053109546

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for the recovery of tetrahydrofuran from mixtures containing tetrahydrofuran, one or more lower alkanols and water.


RELATED ART

A problem arises in attempting to recover pure tetrahydrofuran from a mixture that contains also water and a lower alkanol because tetrahydrofuran forms azeotropes with water and also with lower alkanols, such as methanol and ethanol.
Mixtures containing both a lower alkanol and water, in addition to tetrahydrofuran, are formed, for example, in the production of butane-1,4-diol and/or gammabutyrolactone by hydrogenation of a (di-C.sub.1 - to C.sub.4 -alkyl) maleate, fumarate, succinate, or a mixture of two or more thereof, according to the teachings of EP-A-0143634, WO-A-86/03189, and WO-A-86/07358. These mixtures contain, besides butane-1,4-diol and gamma-butyrolactone, varying amounts of tetrahydrofuran as well as water and a lower alkanol corresponding to the C.sub.1 - to C.sub.4 -alkyl moiety of the starting ester, such as ethanol. In addition such mixtures may contain a minor amount of dialkyl succinate and small amounts of "heavies", such as the corresponding C.sub.1 - to C.sub.4 -alkyl 4-hydroxybutyl succinate and other compounds, some of which have not been identified and hence can be classed as "unknowns".
Various processes have been described enabling substantially pure tetrahydrofuran to be recovered from such mixtures. One method of separating such mixtures is disclosed in GB-A-2175894. In this proposal it is stated: operated under vacuum at a pressure of 0.27 bar with a head temperature of 48.degree. C. The "light ends", i e. a mixture of tetrahydrofuran, ethanol, water, and n-butanol, are stripped off in column 5, recovered overhead in line 6, and passed to a second distillation column 7. Column 7 is operated at 1.2 bar at a head temperature of 58.degree. C. A first tetrahydrofuran/water azeotrope is recovered overhead in line 8 and is passed to a third distillation column 9 which is operated at 7.0 bar with a head temperature of 126.degree. C. Essentially pure tetrahydrofuran is recovered as a bottom product from third distillation column 9 in line 10. The overhead product in line 11 from third column 9 is a second tetrahydrofuran/water azeotrope which is markedly richer in water than the first tetrahydrofuran/water azeotrope from the second column 7. This second azeotrope is recycled from line 9 by way of line 6 to the second column 7"
Similar proposals appear in EP-A-0255400, and WO-A-88/00937.
Extractive distillation with butane-1,4-diol has been proposed in GB-A-2207429. Another proposal involving extractive distillation with butane-1,4-diol or another polyol is disclosed in GB-A-2207431.
Extractive distillation using water to separate one or more aliphatic alcohols selected from the group consisting of methanol, ethanol, iso-propanol and t-butanol from a tetrahydrofuran stream comprising tetrahydrofuran, one or more of said alcohols and optionally water is disclosed in U.S. Pat. No. 4,175,009.
In U.S. Pat. No. 4,105,667 a tetrahydrofuran/water stream in line 42 "is further purified in column 44 where water is separated as a bottom stream through line 45, and THF is withdrawn as an overhead stream through line 46."
DD-A-137188 describes recovery of tetrahydrofuran from technical mixtures, such as condensed vapours from polybutylene terephthalate manufacture, by a process which involves extractive distillation with an added solvent such as butane-1,4-diol.
Extractive distillation using, for example ethylene glycol, is used in the separation of methanol and ethanol in the process of SU-A-1025709.
DD-A-237056 describes a process for extractive distillation to separate a methanol/tetrahydrofuran azeotrope obtained in the course of preparation of polybutylene terephthalate, using as selective extraction medium dilute solutions of alkali metal or alkali earth metal hydroxides in polyhydric alcohols, such as glycols; ethylene glycol and butane-1,4-diol are proposed as suitable polyhydric alcohols.
JP-A-53/3

REFERENCES:
patent: 4105667 (1978-08-01), Thom
patent: 4175009 (1979-11-01), Copelin
patent: 4665205 (1987-05-01), Yamada et al.
patent: 4912236 (1990-03-01), Palm et al.
Ind. Eng. Chem. Process Res. Dev., vol. 24, 1985, Samir I. Abu-Eishah et al.: "Design and Control of a Two-Column Azeotropic Distillation System", pp. 132-137.
"Distillation", Kirk Othmer Encyclopedia of Chemical Technology, vol. 7, pp. 869-870 (1979).

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