Sustainable Diesel from Rapeseed Oil Esters by Sequential Semi-Hydrogenation, Double Bond Isomerization, and Metathesis.

Rapeseed oil methyl esters (RME) have been converted to biofuel with a boiling point curve that fulfills the EN 590 specifications for modern diesel engines using a robust, three-step process. In the first step, the polyunsaturated esters of the RME were semi-hydrogenated in the presence of 20 ppm of a solvent-stabilized Pd colloid. The resulting mono-unsaturated fatty esters were further converted into a defined mixture of double-bond isomers by passing them over inexpensive, Brønsted-acidic Amberlyst 15 resin at high space-time yields (1.3 kg⋅L⋅h). The resulting mixture was then converted into a blend of terminally unsaturated olefins and monoesters, with <4.9 % diesters and <21 % saturated fatty esters by cross-metathesis with technical-grade ethylene. In this step, 50 ppm of a cyclic alkyl amino carbene (CAAC) Ru catalyst M1001 was used to achieve record-setting conversions (91 %) and selectivities (94 %). All three steps were conducted with neat feedstock at mild temperatures (60-100 °C). This demonstrates that sustainable diesel fuel for use in contemporary diesel engines is accessible from RME and ethylene via a short set of industrially viable reaction steps.