Synthesis of biodiesel from acidified soybean soapstock using a lignin-derived carbonaceous catalyst

Biodiesel was produced from acidified soybean soapstocks by using lignin-derived carbonaceous catalyst (LCC). LCC was a solid acidic catalyst prepared by direct sulfonation of residual lignin from Xanthoceras sorbifolia Bunge hulls. The textural properties of the catalyst were characterized by 13C MAS NMR, X-ray diffraction, FT-IR, elemental analysis and BET surface area measurement. When 7 wt.% of LCC was used in the esterification, the maximum free fatty acids (FFAs) conversion (above 97%) could be achieved at a molar ratio of methanol/oil of 1:9 and a reaction temperature of 70 °C for 5 h. A comparison of catalytic activity between sulfuric acid and LCC revealed that LCC performed 3.5 times higher activity than sulfuric acid with the equivalent active group (SO3H). Additionally, LCC could be reused at least three times with high FFAs conversion (>80%).