(546b) Isopentane and Ethylene Alkylation Using Ionic Liquid Catalyst

Modern refineries employ many upgrading units such as fluid catalytic cracking (FCC), hydrocracking (HCR) and PenHex paraffin isomerization. As results, these refineries produce a significant amount of isopentane. Historically, isopentane was a desirable blending component for gasoline having higher octane (92 RON), although it exhibited high volatility (20.4 Reid vapor pressure, RVP). As environmental laws began to place more stringent restrictions on gasoline volatility, the use of isopentane in gasoline was limited because of its high volatility. As a consequence, the problem of finding uses for by-product isopentane became serious, especially during the summer season. Moreover, as more gasoline composition contain ethanol as their oxygenate component, more isopentane must be kept out of the gasoline pool in order to meet the gasoline volatility specifications.

We explored upgrading of isopentane by alkylation with either ethylene or propylene to produce C7 or C8 alkylate using ionic liquid catalysts. Higher reactivity of the ionic liquid catalyst achieved nearly complete conversion of ethylene. This was surprising initially since conventional alkylation catalysts (HF or H2SO4 acid catalysts) cannot alkylate ethylene. We have studied impact of process variables for alkylate product quality and identified process conditions for scale-up. Continuous microunit runs were conducted to examine the impact of extended operation on catalyst aging.

We also examined potential low cost source of ethylene from a refinery. A dilute stream of ethylene is available from the FCC offgas. Currently the FCC offgas is sent to furnace for steam generation. By consuming the ethylene in the FCC offgas, refinery fuel gas yield would be lowered and high-value alkylate product can be created. This concept was particularly attractive since we are combining two low value refinery streams to produce clean, low RVP C7 gasoline. Integrated process concept for this technology was generated. C2 stream separation from the FCC offgas is a costly step in the process, and we are looking into ways to lower the overall process cost.

This talk will present the catalysis of isopentane alkylation and development of the technology.