Complementary Technologies (Ethylene Production)

Olefins Conversion (OCT)

Olefins Conversion Technology (OCT) employs metathesis and isomerization chemistry to produce propylene from reacting ethylene with C4 and/or C5 olefins. This is the only commercially demonstrated route to propylene using metathesis chemistry. The source of the C4 and C5 olefins can be from steam cracking, refinery processes, MTO or ethylene dimerization. Polymer grade propylene is readily produced in a simple catalytic fixed bed reactor without the use of super fractionators since no paraffins are formed in the metathesis or isomerization reactions. In addition, the metathesis reactions are mildly exothermic. There is no energy input into the reaction step, making OCT the only route to propylene that does not require energy input to the reaction step. This reduces operating costs and greenhouse gas emissions. Further, since OCT has a selectivity to propylene of over 95%, very few by-products are produced, which offers superior operating economics and low capital investment. OCT is the most selective route to propylene of all demonstrated routes. Worldwide, there are 49 OCT units either in operation or under design, producing over nine million metric tons of propylene—more than 10% of worldwide capacity. Unit capacity ranges from 60 kta of polymer grade propylene to 800 kta of propylene. 


OCT can be readily integrated with a steam cracker. When integrated with a naphtha cracker, the maximum propylene to ethylene ratio can be increased from 0.6 to 1.2, essentially doubling the amount of propylene produced. Both the C4 and C5 raffinate streams are increased in value from feed or gasoline blending value to polymer grade propylene value. In addition, the ethylene plus propylene yields are increased by as much as two and one half times relative to recycle cracking of the raffinates. When integrated with an ethane cracker, which as a standalone unit produces very little propylene, OCT combined with ethylene dimerization can be used to produce any desired quantity of PG propylene, making it the only route of ethane feed to propylene product.      

OCT can also utilize the C4 and C5 raffinate from various refinery processing schemes or the C4 and C5 raffinate from MTO units. When integrated with refinery streams, ethylene can be recovered from refinery off-gas streams and used as feed for the OCT. Doing so will upgrade the recovered ethylene from fuel value to PG propylene value, and the C4/C5 raffinate from alkylate or gasoline blending value to propylene value. When integrated with an MTO unit, ethylene plus propylene production increases by up to 15%. Mild operating conditions lead to a design that is essentially all carbon steel material. Utility consumption is very low and limited to the product recovery utility consumers. The high selectivity limits feed consumption and by-product quantities. The non-noble metal catalyst offers long cycle times between regeneration, long life, and comprises less than 1% of the operating costs. These features combine to offer the lowest capital costs for PG propylene production and the highest return on investments.