Propylene Oxide Production from Propylene and Ethylbenzene

The process under analysis comprises 3 major sections: (1) Propylene Oxide (PO) Production; (2) PO Purification; and (3) Styrene Synthesis.

PO Production. The production of PO is based on two reactions. First, ethylbenzene is peroxidized with air in liquid phase yielding a solution of ethylbenzene hydroperoxide in ethylbenzene. This conversion is restricted to 10%. Then, this solution peroxidizes chemical grade propylene with molybdenum catalyst under high pressure, yielding propylene oxide. The epoxidation yields up to 99% reactant with 92-96% selectivity to PO.

PO Purification. Crude PO stream from PO production is fed to a series of columns, where C3s, phenyl ethanol, ethylbenzene, and other hydrocarbon impurities are removed. 99.9 wt% Propylene Oxide is obtained. The C3 stream is further separated into propane, used as fuel, and propylene, recycled to epoxidation. A stream containing phenyl ethanol, ethylbenzene, remaining reagents and other by-products is directed to next section.

Styrene Synthesis. The mixture is purified by means of four distillation columns. Residual ethylbenzene from such stream is removed, condensed and recycled to the Peroxidation, and impurities withdrawn are separated and burned for fuel. The stream rich in 1-phenylethanol and still containing acetophenone is fed to a dehydration reactor, where it is converted to styrene in the presence of an alumina catalyst. To increase the overall process economics, acetophenone, the main by-product from epoxidation, is extracted during the purification of the styrene and directed to a hydrogenation step, promoted by a copper-based catalyst, in which it is converted to 1-phenylethanol. The product stream is then recycled to the dehydration reactor, thus increasing styrene production.