Propylene Oxide Production from Propylene and Chlorine

The process under analysis comprises three major sections: (1) Hypochlorination; (2) Epoxidation; and (3) Purification.

Hypochlorination. Initially, fresh, gaseous polymer grade propylene and chlorine are mixed with water, forming an aqueous solution. Such compounds react producing propene – chloronium complex, an intermediate which reacts with water yielding hydrochloric acid and propylene chlorohydrin (PCH) isomers. The gaseous effluent from the reactor is fed to a separator, which separates a solution containing PCH from the vent gas. The PCH solution is directed to the Epoxidation, while the vent gas is passed through a caustic scrubber and released.

Epoxidation. The PCH solution and a caustic solution (from a chlor-alkali unit) are fed to a saponifier, where a dehydrochlorination reaction takes place. Here, the PCH is converted to propylene oxide (PO) while organic impurities are stripped from the brine. The brine from saponifier bottom is directed to a treatment step, while a stream containing PO from saponifier overhead is routed to purification steps.

Purification. The stream rich in PO is distilled in a first column for obtaining a crude propylene oxide stream, removed from overhead. A solution containing 1,2-dichloropropane (DCP) from column bottom is decanted, yielding a DCP-rich stream and water. In a second column, residual light ends are stripped off from the crude PO stream and burned for fuel. The column’s bottom product is fed to a third column, which further purifies the PO from impurities. A 99.9 wt% Propylene Oxide is condensed and stored. Heavy ends are burned for fuel. The DCP-rich stream is treated for the neutralization, and for the removal of epoxidation by-products and other heavy components. The brine stream from Epoxidation and the wastewater from the first column are treated and returned to the chlor-alkali facility.