PEP Review 2009-14
C3-C4 Oligomerization for Gasoline
Published: December 2009
Oligomerization is a process that converts light olefins, usually propylene, butylene or their mixtures, contained in mixtures with light paraffins from catalytic or steam cracking, visbreakers, cokers or Fischer-Tropsch units into gasoline or, obtained with hydrogenation, even jet fuel blendstocks. Paraffinic LPG is a by-product. These olefinic LPG streams are too volatile for direct blending into gasoline.
In the net reaction, one olefin reacts with one or more of the same or different olefins to form a heavier olefinic compound. The product may be hydrogenated downstream to meet specifications of the motor fuel. Two types of processes are commercial: solid acid catalyzed or homogeneously catalyzed.
Oligomerizing light olefins can increase refinery profit by providing an outlet for these light olefins at relatively low capital expenditure usually through increased gasoline sales. The process is especially attractive in situations where olefin alkylation or separation into petrochemical grade olefins is not attractive due to unavailability of isobutane, smaller refinery capacity or local market conditions.
We review the chemistry and technology of light olefin oligomerization with emphasis on producing gasoline blendstock. We determine the economics of two cases: oligomerizing an FCC mixed C3-C4 stream with solid phosphoric acid catalyst and dimerizing an FCC mixed C3 stream with a homogeneous catalyst. Each grassroots plants capacity is 3,333 BPSD (530 m3/SD) of fresh feed. Each plant is operating in a fuels refinery on the U.S. Gulf Coast.