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Hydrolysis of Esters

A methyl acetate-water mixture is produced in large quantities by the purification of terephthalic acid (PTA). The manufacture of poly vinyl alcohol (PVA) also produces large quantities of methyl acetate (1.68 kg/kg PVA). Methyl acetate is a comparatively low-value solvent, hence it has to be sold at a lower price. Alternatively, it can be hydrolyzed efficiently to recover methanol and acetic acid for reuse in the process [26-28].

The conventional process for the hydrolysis of methyl acetate uses a fixed-bed reactor followed by a complex arrangement of several distillation/extraction columns. The conversion is limited by unfavorable equilibrium (equilibrium constant 0.14-0.2) and a large amount of unconverted methyl acetate needs to be separated and recycled. The reaction is carried out in a fixed-bed reactor and the product stream contains all four components. It needs four additional columns to separate the methanol and acetic acid streams and recycle unconverted methyl acetate along with methanol to the reactor.

Fuchigami developed an RD process at laboratory level for the hydrolysis of methyl acetate using an ion-exchange resin catalyst in a special form [26] (Fig. 1.4). Converting the process from conventional to RD can eliminate many complicated steps. The use of solid acid catalysts obviates the need for spent acid recovery and exotic construction materials. The resin was molded into 7 mm X 7 mm pellets using polyethylene powder. The distillation column was

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