The two-step alkylation of isobutane with butenes using sulfuric acid as a catalyst
Abstract
A new two-step process of the sulfuric acid catalyzed alkylation of isobutane with butenes was investigated. A sealed batch reactor and feed charging system was employed to produce the intermediates and to study the effects of the various process variables. Process variables investigated include the molar acid-to-olefin ratio (A/O), isobutane-to-olefin ratio (I/O), temperature, agitation, and acid composition. The properties of conjunct polymers, acid-soluble hydrocarbons produced via olefin polymerization reactions, were studied for three different sulfuric acid catalysts. In the first step of the sequence, the desired reactions are between H$\sb2$SO$\sb4$ and n-butene to form s-butyl sulfates; equilibrium mixtures containing di-s-butyl sulfate (DBS), s-butyl hydrogen sulfate (MBS), n-butene, and H$\sb2$SO$\sb4$ resulted. In the second step, the desired reactions are between the s-butyl sulfates produced in the first step, sulfuric acid, and isobutane to form trimethylpentanes. The alkylates produced were of exceptionally high qualities, research octane numbers (RON) of up to 101. Isobutylene polymerized during first-step reactions, resulting in mostly C$\sb{12}$, C$\sb{16}$, and C$\sb{20}$ unsaturated hydrocarbons. These unsaturated hydrocarbons in the second step formed a relatively low quality alkylate with a RON of about 90. The DBS and MBS intermediates were produced at A/O ratios of 0.15 to 0.75 and were identified using proton magnetic resonance, infrared absorption, hydrolyses, and mass balances. At A/O ratios up to 0.75, the intermediate products were stable at temperatures up to at least 30$\sp\circ$C. The composition of the mixtures were strongly dependent on the A/O ratios and on the water content of the phases. Other variables affecting first-step reactions were temperature and I/O ratio; DBS is soluble in isobutane. In the second step (A/O ratios of 5 to 10), the quality of the alkylate was strongly dependent on the reaction temperature. At $-20$ to $-15\sp\circ$C, alkylates were produced with RON's of 100 to 101. At higher temperatures, however, some of the s-butyl sulfates decomposed, resulting in alkylates with lower qualities. Several commercial applications of the results are proposed. These proposals will reduce both the energy requirements and acid consumption for the new alkylation process.
Degree
Ph.D.
Advisors
Eckert, Purdue University.
Subject Area
Chemical engineering
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