Analysis of long term catalytic performance for isobutane alkylation catalyzed by NMA–AlCl3 based ionic liquid analog

Isobutane alkylation with 2-butene to produce high-quality gasoline was catalyzed by N-methylacetamide (NMA)–AlCl3 based ionic liquid (IL) analog with a NMA/AlCl3 molar ratio of 0.75 and CuCl modification, which was marked as CuCl-modified 0.75NMA–1.0AlCl3. The long-term experiment was carried out in the autoclave operated in continuous mode to investigate the distribution of alkylate under different experimental nodes. The result indicated that the long-term alkylation was divided into three stages: rising, stable, and descending regions. C8 selectivity and molar ratio of trimethylpentanes (TMPs) to dimethylhexanes (DMHs) reached the highest level in the stable region, and research octane number (RON) of alkylate was as high as 97. Anionic Al species ([Al2Cl7]−, [AlCuCl5]−) and cationic Al species ([AlCl2L]+) from IL analog as two active Lewis acidic species played a catalytic role in the long-term alkylation, whereas the neutral Al species did not participate into the alkylation. Moreover, the structure of CuCl-modified 0.75NMA–1.0AlCl3 was destroyed after the deactivation, and CuCl was enriched in the CD2Cl2-insoluble substance, resulting in a decreasing TMP/DMH ratio. The catalytic lifetime of IL analog was similar with CuCl-modified 0.55Et3NHCl–1.0AlCl3 IL, but IL analog had a lower cost.