US Patent 8450550 Process and apparatus for producing propylene

A process for producing propylene, which including feeding at least one of dimethyl ether and methanol to a reactor to be reacted in the presence of a catalyst; supplying an obtained reaction product to a separator by which low-boiling compounds having a boiling point of −50° C. or lower at atmospheric pressure among the reaction product are separated; and recycling a proportion of at least 70% of a total amount of the separated low-boiling compounds to said reactor.