Olefin Conversion Technology, also called the Phillips Triolefin Process, is the industrial process that interconverts propylene with ethylene and 2-butenes. The process is also called the ethylene to propylene (ETP) process. In ETP, ethylene is dimerized to 1-butene, which is isomerized to 2-butenes. The 2-butenes are then subjected to metathesis with ethylene. Rhenium- and molybdenum-containing heterogeneous catalysis are used. Nowadays, only the reverse reaction is practiced, i.e., the conversion of ethylene and 2-butene to propylene: CH2=CH2 + CH3CH=CHCH3 → 2 CH2=CHCH3