Propylene Oxide Production from Propylene and Isobutane

The process under analysis comprises two major sections: (1) Reactions; and (2) Purification.

Reactions. Isobutane is reacted with oxygen yielding a solution of tertiary butyl hydroperoxide (TBHP) and tertiary butyl alcohol (TBA) by-product. While the reaction is exothermic, reaction conditions are regulated such that the reaction mixture is constantly boiling, so that reaction heat is removed by reaction media vaporization. Accordingly, the oxidation product - a vapor mixture - is removed from the reactor and cooled, in such a way that TBHP, TBA, unreacted isobutane and other readily condensable components are condensed and partially routed to an isobutane recovery step and then to epoxidation reaction system. The second reaction, epoxidation, occurs by mixing the peroxide solution in TBA with propylene. The reaction is carried out in the liquid phase, in the presence of a homogeneous molybdenum catalyst, yielding Propylene Oxide (PO). As in the peroxidation, the heat of epoxidation reaction is removed by the medium vaporization. The epoxidation product is then separated into a distillate stream containing unreacted propylene, propylene oxide and TBA, and a heavy organic stream, comprising high boiling by-products and dissolved molybdenum catalyst. The catalyst-rich stream is submitted to a thermal treatment before being recycled to epoxidation.

Purification. The distillate from epoxidation reaction system is sent to the propylene column, which strips off propylene, propane and residual light ends from the epoxidation effluent stream. The C3 stream is further treated in a column for recovery of a propylene-rich stream that can be recycled to the epoxidation. The C3-free epoxidation product, in turn, is fed to the TBA recovery, where a crude PO stream is obtained after a TBA-rich stream is separated, treated for impurities removal, and recycled to the epoxidation reaction. The crude PO stream is further purified by means of an extractive distillation process followed by another distillation column, from which high-purity Propylene Oxide is obtained as overheads product.