Synthesis and characterization of carbon cryogel microspheres from lignin–furfural mixtures for biodiesel production

•Carbon cryogel has been synthesized from lignin and furfural.•The carbon cryogel produced has microspheres structure.•High total acidity and large surface area of hydrophobic amorphous carbon cryogel.•Carbon cryogel exhibits potential for catalyzing oleic acid esterification.

The aim of this work was to study the potential of biofuel and biomass processing industry side-products as acid catalyst. The synthesis of carbon cryogel from lignin–furfural mixture, prepared via sol–gel polycondensation at 90 °C for 0.5 h, has been investigated for biodiesel production. The effect of lignin to furfural (L/F) ratios, lignin to water (L/W) ratios and acid concentration on carbon cryogel synthesis was studied. The carbon cryogels were characterized and tested for oleic acid conversion. The thermally stable amorphous spherical carbon cryogel has a large total surface area with high acidity. Experimental results revealed the optimum FAME yield and oleic acid conversion of 91.3 wt.% and 98.1 wt.%, respectively were attained at 65 °C for 5 h with 5 wt.% catalyst loading and 20:1 methanol to oleic acid molar ratio. Therefore, carbon cryogel is highly potential for heterogeneous esterification of free fatty acid to biodiesel.