Chevron embraces ionic liquids

Chevron will convert the alkylation catalyst used in its Salt Lake City refinery from the toxic and corrosive chemical hydrofluoric acid to an ionic liquid. The planned switch takes ionic liquids a step closer to becoming mainstream materials and could presage big changes in the refining industry as well.

The big oil firm began developing ionic liquids as alkylation catalysts in 1999 and has run a demonstration unit in Salt Lake City for the past five years. It plans to start building a full-scale alkylation plant next year. After the plant is completed in 2020, Chevron will remove all HF-specific equipment and its inventory of HF from the site.

Ionic liquids, salts that are liquid at temperatures below 100 °C, have long fascinated chemists, but they have often seemed like a technology in need of an application. Two successful applications are BASF’s use of ionic liquids as acid-scavenging agents and Petronas’s ionic-liquid-based process for removing mercury from natural gas.

Tom Welton, a professor at Imperial College London who studies ionic liquids, says Chevron’s project will represent the largest-scale chemical synthesis using ionic liquids to date. “It will certainly have the greatest impact of any process introduced so far,” he says, noting that the new facility’s output will end up in the fuel that powers our cars.

The Chevron technology could also have a big impact on how the refining industry carries out alkylation. Refiners use alkylation to combine low-molecular-weight alkanes and alkenes into high-octane gasoline components. Today, more than half of the alkylation capacity in the U.S. is based on HF, according to the energy consulting firm Stratas Advisors. HF releases in Texas and Pennsylvania have prompted calls for the phaseout of HF in refineries.

Chevron says it developed the new process not for safety reasons but for the lower catalyst consumption and ease of on-site regeneration it offers. Chevron has licensed the technology to Honeywell UOP, which will market it to the refining industry and supply the catalyst, a chloroaluminate ionic liquid with a proprietary composition.

Honeywell calls the process, named Isoalky, the first successful liquid alkylation technology to be introduced in 75 years.