Chitosan-catalyzed biodiesel synthesis: Proof-of-concept and limitations

Second generation biodiesel uses cooking oil wastes, vegetal oils cultivated in marginal lands, or algae-based oils. The quest of heterogeneous catalysts for biodiesel synthesis is motivated by the option of by-passing saponification and neutralization steps, enabling proper catalyst recoveries, and performing esterifications and transesterifications simultaneously, as impure waste oils contain a significant concentration of free fatty acids (FFA). This paper evaluates the use of chitosan-cryogels as catalysts for (trans)esterification reactions of different oils with methanol. Being a worldwide available waste material, the use of chitosan as catalyst for biofuel production might add novel possibilities for the valorization of local areas. Chitosan-cryogels catalyzed successfully the transesterification of triolein and soybean oil with methanol to afford biodiesel yields of up to 90% (FAME) in 8–32 h at 100–150 °C. Chitosan beads could be partially recycled by washing them with tert-butanol and methanol to desorb fats and glycerol. To reach a practical use, further opportunities for research and development can be identified at the level of catalyst design, delivering chitosan-based novel catalysts – e.g. aerogels, layers, chitosan-based derivatizations, etc. –, that could enable more efficient catalytic rates and would display largely improved recyclability outcomes.