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How does polymerization convert propylene and butylene into gasoline components?

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Aerial view of an oil refinery complex near New Orleans, Louisiana, with storage tanks, industrial structures, and smoke rising from the facility, surrounded by open land. — petroleum refining Aerial view of an oil refinery near New Orleans.

In petroleum refining, polymerization is a conversion process used to transform light, gaseous olefins—specifically propylene and butylene—into high-octane gasoline components.12

During this process, these light olefins are induced to combine, or polymerize, into larger hydrocarbon molecules that are two to three times their original molecular weight. This effectively shifts these gaseous by-products into the liquid gasoline boiling range.12

The reaction requires specific industrial conditions to proceed:
* Catalysts: The process typically employs phosphoric acid supported on pellets of kieselguhr, a porous sedimentary rock.1
* Operating Conditions: High pressures ranging from 30 to 75 bars (400 to 1,100 psi) are maintained at temperatures between 175 and 230 °C (350 to 450 °F).1

The resulting product, known as polymer gasoline, is a valuable blending component because it possesses an octane number above 90, which helps improve the antiknock quality of the final fuel mixture.13