A physicochemical investigation of isobutane-olefin alkylation
Abstract
Alkylation reactions using sulfuric acid, H$\sb2$SO$\sb4,$ and hydrofluoric acid, HF, catalysts involve liquid-liquid dispersions in which the primary reactions occur at or near the acid-hydrocarbon interface while some secondary reactions occur in the acid phase. The selectivity of alkylation, therefore, can be driven in part by the degree of dispersion area available. In this investigation, for the first time, a method was developed to predict how the interfacial area for sulfuric acid-hydrocarbon dispersions varied with key operating variables: sulfuric acid composition in the range of 1-3 wt% water and 0-8 wt% acid soluble oils, volume% acid in the dispersion in the range 10-85%, temperature $-$3 to 15$\sp\circ$C, and the presence of surfactants. The dispersion studies were made in a stirred-baffled reactor with two glass windows for observation. Variations in acid composition were shown to result in interfacial areas per volume of dispersion, A$\sb{\rm disp},$ that changed by over 200% as the acid composition was changed to increased acid soluble oils and decreased water concentration. The interfacial area, A$\sb{\rm disp},$ was shown to reach a maximum at about 75 volume% acid in the dispersion while at less than 40 volume% acid very poor dispersions were obtained. Lower operating temperatures were also shown to result in significantly higher A$\sb{\rm disp}$ levels. Correlations were developed to predict the average drop size as a function of physical properties of the acid and volume fraction of the dispersed phase. A new acidity parameter, $(\rm H\sb2SO\sb4)\sb{u},$ was developed, which includes the effects of water and acid soluble oils that was used to correlate the kinetic rate constants of isooctane isomerization and degradation reactions and is also applicable to the alkylation reaction. A physicochemical model was derived, that incorporated the interfacial area of the dispersions in addition to the acidity parameter, to predict the selectivity of isobutane-olefin alkylation. The model was tested with existing alkylation data and found to correlate with temperature, rate of agitation, acid composition, and isobutane/olefin ratio. Process improvements were suggested as a result of these findings.
Degree
Ph.D.
Advisors
Albright, Purdue University.
Subject Area
Chemical engineering
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