Acid-catalyzed isobutane-isobutylene alkylation in liquid carbon dioxide solution

Liquid carbon dioxide was studied as a solvent for the isobutane-isobutylene alkylation. The acid catalysts in the reaction were anhydrous HF (AHF), pyridinium-poly(hydrogen fluoride) complex (PPHF), concentrated sulfuric acid and trifluoromethanesulfonic acid (TFSA). The effect of the acid-hydrocarbon volume ratio, temperature and residence time on the alkylate quality were studied over the temperature range of 50 ≥ T ≥ 0°C. Carbon dioxide as a competing weak base decreases the acidity of the system which parallels the alkylate quality. In the case of HF and TFSA catalysts, solvent CO₂ increased the octane number of the alkylate product (RON 95.6 for HF- and 88.0 for TFSA-catalyzed alkylation with CO₂ solvent).