Application: The Snamprogetti Dimerization/Hydrogenation Technology is used to produce Iso-octene/Iso-octane—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: Iso-octene and Iso-octane streams contain at least 85 wt% of C8s with less than 5,000 ppm of oligomers higher than C12s.
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%) can be reached with a double-stage configuration where, in both stages, water-cooled tubular reactors (WCTR), (1, 2), are used for the isobutene dimerization to maintain optimal temperature control inside the catalytic bed.
The reactors effluents are sent to two fractionation columns (3, 5) to separate residual C4 from the mixture oxygenate-dimers. At the end, the oxygenates are recovered from raffinate C4 (6) and from dimers (4) and then recycled to reactors.
The Iso-octene product, collected as bottoms of column (4), can be sent to storage or fed to the hydrogenation unit (7) to produce the saturate hydrocarbon stream Iso-octane.
Due to a joint development agreement between Saipem 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 refinery MTBE units.