Application: The Snamprogetti dimerization/hydrogenation technology is used to produce isooctene/isooctane—high-octane compounds (rich in C8 ) for gasoline blending.
Feed: C4 streams from steam cracker, fluid catalytic cracking (FCC) and isobutane dehydrogenation units with isobutene contents ranging from 15 wt% to 50 wt %.
Products: Isooctene and Isooctane streams contain at least 85 wt% of C8s with less than 5,000 ppm of oligomers higher than C12s.
Description. Depending on conversion and investment requirements various options are available to reach isobutene conversion ranging from 85 wt% to 99 wt%.
Oxygenates, such as methanol, methyl tertiary butyl ether (MTBE) and/or tert-butyl alcohol (TBA), are used as “selectivator” to improve selectivity of the dimerization reaction while avoiding formation of heavier oligomers.
A high conversion level of isobutene (99 wt%) can be reached with a double-stage configuration where, in both stages, water cooled tubular reactors (WCTR), (1) and (2), are used for the isobutene dimerization to maintain an optimal temperature control inside the catalytic bed.
The reactors effluents are sent to two fractionation columns (3) and (5) to separate the residual C4 from the mixture oxygenate-dimers. At the end, the oxygenates are recovered from raffinate C4 (6) and from dimers (column 4) and then recycled to reactors.
The isooctene product, collected as bottom of column (4), can be sent to storage or fed to the hydrogenation unit (7) to produce the saturate hydrocarbon stream—isooctane.
Due to a joint development agreement between Snamprogetti and Catalytic Distillation Technologies (CDTech) for the isobutene dimerization (Dimer8 process) the plant configuration can be optionally modified with the introduction of a catalytic distillation (CD Column), to have an alternative scheme particularly suitable for revamping of refinery MTBE units.
Licensor: Snamprogetti, a company of Saipem.