Butanediol Production from Maleic Anhydride

The process under analysis comprises three major sections: (1) DMM production; (2) Hydrogenation; and (3) Purification.

DMM production. After being preheated, fresh maleic anhydride, fresh methanol, and recovered methanol are fed to the reactive column, which consists of a counter-current column with trays containing ion-exchange resin catalysts. The reaction is carried out with excess of methanol, so as to push it towards equilibrium. On a molar basis, 99% of the maleic anhydride is converted to DMM. Since the reaction is exothermic, almost all water formed is vaporized and leaves the column as an overhead stream, also containing unreacted methanol. This stream is fed to the methanol column, in order to separate unreacted methanol from water.

Hydrogenation. The liquid stream from reactive column is vaporized and mixed with hydrogen, gamma-butyrolactone (GBL), and dimethyl succinate (DMS), while heavy organics obtained from the bottom of the vaporizer are burned as fuel. The vaporized stream is preheated and then fed to a fixed-bed reactor containing a hydrogenation and dehydration catalysts. In the reactor, the DMM is hydrogenated to Butanediol, which in turn is partially dehydrated to tetrahydrofuran (THF). The reaction product stream is cooled and routed to a knock-out drum, from which offgas rich in hydrogen is separated from the condensate and recycled to hydrogen stream.

Purification. The condensed stream, containing BDO, THF, and other by-products, is initially routed to a distillation column that strips off water, methanol, and THF. This stream is sent to another column that recovers THF. The product stream passes through another series of columns, in order to recycle methanol, DMS, and GBL. In the last column, high-grade Butanediol is obtained and heavy ends are burned as fuel.