Alkylation with diisopropyl sulfate

Nazareth, A. Joppich, M. Pauthani, A. Fisher, D. Giese, R.W. Alkylation with dialkyl sulfate and ethyl-diisopropyl amine. J. Chromatogr. 1985,319, 382-386. 

It was confirmed in the work at Midwest Research that propylene could be reacted with recycle alkylation acid to give a high yield of diisopropyl sulfate (DIPS), and that the DIPS could be extracted with hydrocarbon solvents, including isobutane. The isopropyl acid sulfate (IPS) is quite insoluble in hydrocarbons and only a small amount is extracted along with the DIPS. Since the reaction of propylene with sulfuric acid is an equilibrium reaction, some IPS is always present. It was found that some of the conjunct polymer is also extracted with the DIPS. It was anticipated that the water would stay in the acid phase or raffinate, and this was found to be the case. 

The used catalyst is reacted with propylene to convert the acid to diisopropyl sulfate. The diisopropyl sulfate is extracted with isobutane, the extract treated with a small amount of used catalyst, leaving a weak acid containing the conjunct polymer and water. The isobutane extract free of conjunct polymer and water is charged to alkylation, along with additional olefin and fresh make-up acid. A discussion of the reaction conditions required and the variables Involved In the four steps of the process are given. 

With propylene, higher temperatures and more concentrated sulfuric acid are needed to promote the desired reactions with isobutane (and the formation of alkylate). In many refineries, rather substantial fractions of the isopropyl sulfates do not react. The sulfates that do not react decrease acidity and increase acid consumption. The diisopropyl sulfates, which dissolve in the hydrocarbon phase, increase the need for either caustic or acid washing. Improved operating conditions have recently been developed to promote more complete reactions of these sulfates in the reactor (and hence higher yields of alkylate) plus lower acid consumption (26). 

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