One step cracking/transesterification of vegetable oil: Reaction–regeneration cycles in a capillary fluidized bed

• CaO/Al2O3 transesterifies and cracks fats in the gas phase above 300 °C.
• Maximum biodiesel (BD) yield was 44 %, with less than 10 % COx.
• Short catalyst regeneration times (trg<1min) favors BD over hydrocarbons.
• BD selectivity increases with oil reaction time (trx):SBD=9trx-1.5·trgtrx0.5.
• Coke preserves active sites that are selective to convert oil to biodiesel.

CaO/Al2O3 catalytically transesterifies and cracks vegetable oils in the gas phase at temperatures beyond 400 °C. The products are biodiesel (fatty acid methyl esters) and hydrocarbons. Oil conversion was complete with excess methanol in the feed. The gas residence time was less than 1 s and the weight-hourly-space velocity in the capillary fluidized bed was on the order of 5 h−1 (0.12 mg min−1 oil feed rate with 1.6 g of catalyst). Periodic regeneration cycles with O2 converted the coke on the catalyst to CO and CO2. Regenerated catalyst is initially less selective towards biodiesel. Coke preserves the active sites that are selective for the conversion of the triglycerides into biodiesel. The biodiesel yield was highest (44 %) dosing the catalyst with oil for 5 min then regenerating it for 1 min.

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