Butadiene-butylene separation process

Although not a separate process, isomerization plays an important role in pretreatment of the alkene feed in isoalkane-alkene alkylation to improve performance and alkylate quality.269-273 The FCC C4 alkene cut (used in alkylation with isobutane) is usually hydrogenated to transform 1,3-butadiene to butylenes since it causes increased acid consumption. An additional benefit is brought about by concurrent 1-butene to 2-butene hydroisomerization. Since 2-butenes are the ideal feedstock in HF alkylation, an optimum isomerization conversion of 70-80% is recommended.273... 

Butadiene Separation. Solvent extraction is used in the separation of butadiene (qv) [106-99-0] from other C-4 hydrocarbons in the manufacture of synthetic mbber. The butadiene is produced by catalytic dehydrogenation of butylene and the Hquid product is then extracted using an aqueous cuprammonium acetate solution with which the butadiene reacts to form a complex. Butadiene is then recovered by stripping from the extract. Distillation is a competing process. 

The C4 stream from steam crackers, unlike its counterpart from a refinery, contains about 45% butadiene by weight. Steam crackers that process significant amounts of Hquid feedstocks have satellite faciUties to recover butadiene from the stream. Conventional distillation techniques are not feasible because the relative volatihty of the chemicals in this stream is very close. Butadiene and butylenes are separated by extractive distillation using polar solvents. 

The most important olefins and diolefins used to manufacture petrochemicals are ethylene, propylene, butylenes, and hutadiene. Butadiene, a conjugated diolefin, is normally coproduced with C2-C4 olefins from different cracking processes. Separation of these olefins from catalytic and thermal cracking gas streams could he achieved using physical and chemical separation methods. However, the petrochemical demand for olefins is much greater than the amounts these operations produce. Most olefins and hutadienes are produced hy steam cracking hydrocarbons. 

---