Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-06-04
2002-08-13
Lambkin, Deborah C. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S429000, C568S854000, C568S853000
Reexamination Certificate
active
06433192
ABSTRACT:
The present invention relates to a process for preparing mixtures comprising 1,4-butanediol, tetrahydrofuran (THF) and &ggr;-butyrolactone (GBL) from the product gas stream from a reactor for the oxidation of butane by a) absorption of maleic anhydride (MA) from the product gas stream using a high-boiling alcohol, b) conversion of the maleic monoester formed into the maleic diester and c) hydrogenation of the latter in the liquid phase.
Numerous processes for converting MA into the corresponding monoesters and diesters and hydrogenating the latter are known.
EP-B 0 149 144, EP-B 0 206 194 and EP-B 0 212 121 describe processes for the continuous separation of MA from gaseous reaction mixtures which are obtained in the catalytic oxidation of hydrocarbons. Here, the MA-containing, gaseous reaction mixture is brought into contact with a monohydric alcohol. The gaseous materials formed are brought into contact with dicarboxylic diesters (EP-B 0 206 194 dibutyl fumarate or succinate, EP B 0 212 121 diesters of fumaric, succinic or maleic acid, EP-B 0 149 144 dibutyl maleate) in a countercurrent process and the liquid process product is taken off at the bottom. The liquid process product comprises predominantly the corresponding monoalkyl and dialkyl esters of maleic acid. These are heated at from 110° C. to 200° C. to complete the esterification and then provide a suitable starting material for the hydrogenation to form 1,4-butanediol.
A disadvantage of this process is that, apart from the alcohol, an additional material (dicarboxylic diester) which transfers the gaseous reaction products formed from alcohol and MA into the liquid phase is circulated. This must not be hydrogenated in a hydrogenation, so that it is always only possible to achieve incomplete conversion, which means complicated control of the hydrogenation. Furthermore, the dibutyl ester of a dicarboxylic acid used as absorption medium has to be separated from butanediol when the product is worked up by distillation, which complicates the work-up.
DE-A 31 06 819, too, describes a process for preparing 1,4-butanediol by catalytic hydrogenation of a mixture which is obtained by treatment of MA-containing, gaseous reaction mixtures with aliphatic alcohols. The absorption of the MA is carried out using monohydric or dihydric alcohols having boiling points above 180° C. An additional absorption medium is not necessary. The subsequent after-esterification of the absorption product is carried out at from 120° C. to 150° C. The diester-containing stream is finally catalytically hydrogenated, but the space-time yield (0.04 kg of butanediol/liter×hour) is low since the acid number after the after-esterification is too high.
Although the abovementioned processes can be carried out industrially, they have disadvantages which lead to high production costs. These disadvantages are, in particular, complicated control of the hydrogenation and a low space-time yield in the catalytic hydrogenation.
It is an object of the present invention to provide a process which requires very little absorption medium, achieves a good space-time yield in the catalytic hydrogenation using inexpensive catalysts and, in the separation of the desired products, forms no mixtures which are difficult to separate.
We have found that this object is achieved by a process for preparing 1,4-butanediol, tetrahydrofuran (THF) and &ggr;-butyrolactone (GBL) by oxidation of butane to give a product stream comprising maleic anhydride, absorption of maleic anhydride from the product stream using a high-boiling alcohol to give a liquid absorption product comprising monoesters and diesters of maleic acid and also high-boiling alcohol, after-esterification of the liquid absorption product and subsequent hydrogenation of the after-esterified product in the liquid phase. In the process of the present invention, the high-boiling alcohol is a polyhydric alcohol having a boiling point at atmospheric pressure of above 233° C. and the after-esterified product has an acid number of less than 30 mg KOH/g and a water content of less than 1% by weight.
In the context of the present invention, absorption means the separation of MA from a product stream obtained by oxidation of butane using a high-boiling alcohol to carry out this separation. In this absorption step, the MA reacts with the alcohol to give a maleic monoester which constitutes the main product in the absorption product.
In this process, a liquid process product is obtained directly by addition of the esterifying alcohol under the prevailing reaction conditions. The additional use of a high-boiling absorption medium such as a diester of a dicarboxylic acid is not necessary. By this means, a complicated, later separation of the desired products is avoided. Owing to the low acid number, the hydrogenation can be carried out using inexpensive catalysts and in good yields using the after-esterified product. This allows cost savings.
Catalytic oxidation of butane or another hydrocarbon in the gas phase over a vanadium pentoxide catalyst activated with, for example, MoO
3
gives a product stream comprising MA and by-products such as carbon dioxide, acetic acid and acrylic acid. In the process of the present invention, this MA-containing, gaseous product stream is brought into contact with a high-boiling alcohol to absorb the MA. In an advantageous embodiment of the invention, the reaction gas is fed in below the surface of the liquid, high-boiling alcohol, e.g. through an immersed tube. Preference is given to a process in which the reaction mixture is introduced directly from below into an absorption column in which the liquid, high-boiling alcohol flows toward the reaction mixture. Carrying out the MA absorption in a column or a plurality of columns connected in series is preferred.
Suitable columns are, for example, bubble cap tray columns, columns containing units of packing or columns packed with loose packing elements, with preference being given to using the latter. These can be provided with intermediate coolers in order to remove the heat of absorption.
The MA content of the product stream from the butane oxidation is not critical for the process of the present invention. In customary processes, it is in the range from 0.5 to 2% by volume. The temperature of the product gas stream is likewise generally not critical. It should, if possible, be not below the dew points and melting points of the individual components in order to avoid caking, i.e. it should preferably be at least 100° C.
The by-products occurring in the oxidation of butane, for example CO
2
, acetic acid and acrylic acid, are likewise not critical for the process. They are either mostly carried away with the waste gas stream or go into the absorption medium. If they do not react with the esterifying alcohol, they are removed in the thermal treatment of the liquid absorption product (partly with the water).
Alcohols used in the process of the present invention are polyhydric alcohols having a boiling point at atmospheric pressure of above 233° C., preferably above 250° C. As polyhydric alcohols preference is given to using dihydric to tetrahydric alcohols, particularly preferably dihydric alcohols (diols). Examples of alcohols used are polyethylene glycols, &agr;, &ohgr;-diols and cyclohexanedimethanols, e.g. 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,12-dodecanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, trimethylolpropane, neopentyl glycol, triethylene glycol, tetraethylene glycol and pentaethylene glycol, very particularly preferably 1,6-hexanediol and 1,4-cyclohexanedimethanol. As trihydric alcohol, it is possible to use glycerol; as tetrahydric alcohol, pentaerythritol. The alcohols can be used in pure form or as mixtures of various alcohols.
In general, the alcohol is used in a molar excess over the MA of up to 30, preferably up to 15, very particularly preferably up to 5.
In the absorption, a monoester of maleic acid is first formed from the MA and the alcohol. This monoester is high-boiling and thus no
Fischer Rolf
Kaibel Gerd
Pinkos Rolf
Rahn Ralf-Thomas
BASF - Aktiengesellschaft
Keil & Weinkauf
Lambkin Deborah C.
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