Patent ID: 7223895

Claim:
A method of producing propylene from ethane comprising the steps of: a. steam cracking an ethane or primarily ethane feedstock thereby producing a cracking product containing ethylene, hydrogen, ethane, methane, acetylene and C 3 and heavier hydrocarbons; b. treating said cracking product in an ethylene plant recovery section including removing said hydrogen, methane and C 3 and heavier hydrocarbons therefrom and converting said acetylene therein primarily to ethylene to thereby produce a treated cracking product containing primarily ethylene and ethane and including fractionating said treated cracking product in a C 2 fractionator and obtaining an ethylene fraction of chemical grade ethylene having an ethylene content of less than 99% by volume and a bottoms ethane fraction; c. recycling said bottoms ethane fraction to said steam cracking; d. reacting by dimerization in a dimerization section a first portion of said ethylene fraction thereby producing a butene-rich stream containing heavier hydrocarbons, ethylene and ethane; e. separating said heavier hydrocarbons in a butene separator from said butene-rich stream and feeding the remaining butene-rich stream containing ethylene, ethane and butene to said metathesis section; f. reacting by metathesis in said metathesis section the butene in said butene-rich stream with a second portion of said ethylene fraction thereby producing a propylene-rich stream containing propylene, ethylene and ethane; g. separating propylene from said ethylene and ethane in said propylene-rich stream, and h. recycling at least a first portion of said ethylene and ethane from said propylene-rich stream to said C 2 fractionator.