Conversion of wet microalgae to biodiesel with microalgae carbon based magnetic solid acid catalyst

A microalgae carbon based magnetic solid acid catalyst (MCMSA) was prepared using microalgal residue after lipids extraction as carbon source through magnetization, carbonization and sulfonation. The effects of three preparation conditions of pore-forming agent type, carbonization temperature, and sulfonation agent type on the MCMSA were studied. The specific surface area, functional group, acidity and magnetism of MCMSA were studied to determine the optimized catalyst. The MCMSA prepared under the condition that the pore-forming agent is NaCl (1:1 m/m), the carbonization temperature is 800 °C, and the sulfonation agent is H2SO4 (1:10 m/v, 150 °C) has a high specific surface area (124.70 m2/g), high acidity (3.64 mmol/g) and high magnetism (1.042 emu/g), and shows good thermal stability at transesterification temperature of 90 °C with low loss of acid groups. MCMSA showed high conversion efficiency (98.51 %) in the microwave-assisted catalytic transesterification at 90 °C with MCMSA dosage of 5 wt% and methanol to wet microalgae ratio of 6.25:1 (v/m). It could maintain catalytic activity in five consecutive cycles without further treatment, and the average conversion efficiency was approximately 85.5 %. The results showed that the MCMSA could replace the traditional homogeneous acid catalyst for the preparation of microalgae biodiesel.