Abstract: Light hydrocarbonisomerization usually takes C₅ and C₆ hydrocarbons as feedstocks, and C₇+ hydrocarbons in the process of isomerization are prone to a relatively severe cracking reaction, resulting in low yield of isomerized oil. As a novellow-temperature catalyst, ionic liquid has also poor adaptability to macromolecular hydrocarbon feedstocks.Therefore, in the process of macromolecular hydrocarbon isomerization, inhibiting side reaction and improving the yield of isomerized oil during the isomerization of larger hydrocarbons have been the difficulty and focus of research. Based on the mechanism of the alkane isomerization catalyzed by ionic liquid, isobutane criculation can inhibit side reaction and promote the isomerization reaction, which served to reduce the content of C₄ alkanes in the isomerization product and increase the yield of isomerized oil. The influence of process conditions such as the addition amount of isobutane, reaction temperature, reaction time, stirring rate and acid-to-alkane ratio on the n-heptane isomerization catalyzed by chloroaluminate ionic liquid was systematically studied. The results showed that the circulation of isobutane significantly decreased the yield of the by-product C₄ components. The reason was that the substantial presence of isobutane in the system could significantly accelerate the rate of hydrogen transfer during the reaction, effectively inhibit the secondary reactions such as cracking and disproportionation. Under the conditions of an isobutane dosage of 30%, a reaction temperature of 50℃,a reaction time of 1 h,a stirring speed of 1500 r/min and an acid-to-alkane ratio of 1, the n-heptane conversion reached 91.0%, with isomeric hydrocarbon selectivity and liquid yield of 87.2% and 93.5%, respectively. Compared to those of the reaction system without isobutane, the isomeric hydrocarbon selectivity and liquid yield of the reaction system with isobutane at similar conversion rate of n-heptane increased by 16.0 percentage points and 14.8 percentage points, respectively.

Key words: isomerization, ionic liquid, initiator, i-butane, n-heptane