Comparison of Isobutane/n-Butenes Alkylation over Y-Zeolite Catalyst in CSTR, Fixed Bed and Circulating Flow Reactors

Abstract

Isobutane/olefin alkylation is an important route to obtain high-quality gasoline. There is an apparent interest to apply zeolite based catalysts for this process to eliminate large scale usage of liquid catalysts such as H2SO4 and HF. Solid catalysts require a specific reactor system design involving frequent catalyst regeneration and operation at low concentration of the olefin. The aim of this work was to compare different reactor types: CSTR, “once-through” fixed bed type and circulating flow reactors (CFR), which are typically considered as suitable options for industrial implementation. The experiments were done on decationated Y-zeolite catalyst. Different paraffin/olefin ratios, temperature and circulation rates were studied. Catalysts and process performance are discussed based on the catalyst lifetime and the alkylate octane number. Analysis of diffusion limitations in different reactor types and optimization of the circulation rate in CFR were done. It was found that isobutane alkylation in a circulating flow reactor shows approximately the same catalyst lifetime even at a high circulation rate not exhibiting any positive impact of back-mixing on this process. However, a circulating flow reactor has demonstrated a much better quality of alkylate with the research octane number higher by 4.9 points. Additional operational costs related to the reactor effluent recycle are fully covered by the alkylate quality improvement even at a high circulation ratio.