Alkylation reacts isobutane with olefins such as butene and propylene to create octane and other fuels. The Salt Lake City unit, the first commercial ionic liquid-based alkylation unit to be installed in the US, has a capacity of about 5,000 barrels of alkylate per day. Chevron ran a demonstration unit for about 5 years before it moved forward with a revamp of its HF-based unit.
Ionic liquid salts are made by pairing organic cations with organic or inorganic anions. Their irregular structures delocalize their charges, leading to properties—such as sub-100 °C melting points—of interest to chemists. Scientists are investigating them for use in petrochemical processes, cellulose extraction, and battery electrolytes.
The chloroaluminate ionic liquids Chevron uses have strong acid properties, which allow them to take the place of the hydrofluoric and sulfuric acids used in alkylation.
Helin Cox, business director for alkylation and treating at Honeywell UOP, which helped Chevron develop the process and is licensing it under the ISOALKY name, says the strong acidity means that only about 3-6% of the contents of the alkylation reactor is ionic liquid, compared with 50% for the conventional acids. “It significantly reduces the handling requirements and the volume requirements in the reactor,” she says.
Among other advantages, Cox says, less ionic liquid is consumed in alkylation than is with hydrofluoric or sulfuric acid in the conventional processes. The ionic liquid is also safer to handle and can be regenerated inexpensively on site.
UOP has already signed up a licensee, Sinochem Hongrun Petrochemical, which will soon build an ISOALKY unit in China. UOP also designed an HF-to-ISOALKY conversion for an unnamed North American customer and will complete another design later this year.
“I definitely do see Chevron’s plant as a milestone, as this plant is a fully operable commercial unit using ionic liquids in a large-scale market segment,” Roland Kalb, founder of the Austrian custom ionic liquid maker Proionic, tells C&EN in an e-mail.
UOP does have competition. Another ionic liquid-based alkylation process—developed at China University of Petroleum and licensed by the Canadian firm Well Resources—has been deployed at 6 units in China. Most recently, Sinopec installed it in a 7,500-barrel-per-day unit that replaces an HF unit at its refinery in Wuhan.
Two other ionic liquid markets that Kalb sees as “picking up speed” are electrolytes for energy applications and solvents for biomass extraction. “These segments do have the potential for us to create an annual multimillion $ volume within the next few years,” he writes.