Catalytic production of Jatropha biodiesel and hydrogen with magnetic carbonaceous acid and base synthesized from Jatropha hulls

Graphical abstract: Jatropha seeds were extracted oil for biodiesel production and the hulls were carbonized to load active sites as magnetic carbonaceous solid acid and base catalysts. Crude Jatropha oil was esterified to decrease its acid value to 1.3 from 17.2 mg KOH/g by the solid acid, and subsequently transesterified to biodiesel (96.7% yield) catalyzed by the solid base. After 3 cycles and magnetically separated, the deactivated base was catalyzed the hydrothermal gasification of biodiesel by-product (crude glycerol) with gasification rate of 81% and 82% H₂ purity. - Highlights: • High acid value (AV) crude oil was extracted from Jatropha seeds with waste hulls produced. • Carbonizing the hulls and loading active sites produced magnetic carbonaceous acid and base. • The acid reduced AV of crude oil to 1.3 from 17.2 mg KOH/g and separated for 3 cycles. • The base achieved 97.5% biodiesel yield and magnetically separated for recycles. • After 3 cycles, the deactivated base catalyzed the hydrothermal gasification of glycerol. - Abstract: Magnetic carbonaceous solid acid (C-SO₃H@Fe/JHC) and base (Na₂SiO₃@Ni/JRC) catalysts were synthesized by loading active groups on the carbonaceous supporters derived from Jatropha-hull hydrolysate and hydrolysis residue. Characterization of their morphology, magnetic saturation, functional groups and total acid/base contents were performed by various techniques. Additional acidic functional groups that formed with Jatropha-hull hydrolysate contributed to the high acidity of C-SO₃H@Fe/JHC catalyst for the pretreatment (esterification) of crude Jatropha oil with high acid values (AV). The AV of esterified Jatropha oil dropped down from 17.2 to 1.3 mg KOH/g, achieving a high biodiesel yield of 96.7% after subsequent transesterification reaction with Na₂SiO₃@Ni/JRC base that was cycled at least 3 times with little loss of catalysis activity. Both solid acid and base catalysts were easily recovered by magnetic force with average recovery yields of 90.3 wt% and 86.7%, respectively. After washed by ethanol, the catalysts were cycled for 10 times. The AV of esterified oil and biodiesel yield using the recycled catalysts remained below 2.0 mg KOH/g and above 85%, respectively. The existence of catalyst ions and residual methanol contributed to high H₂ yield (81.0%) and high purity (81.7%) in the hydrothermal gasification of glycerol by-product using the deactivated solid base.