Preparation of biodiesel using s-MWCNT catalysts and the coupling of reaction and separation

A new process that coupled the reaction and separation in the production of biodiesel from feedstocks with Free Fatty Acids (FFAs) was studied. A novel solid acid catalyst, sulfonated-multiwalled carbon nanotubes (s-MWCNTs), was used in the synthesis of biodiesel from methanol and oleic acid in a 250 mL autoclave. s-MWCNTs with different concentrations of –SO3H were produced from the treatment of MWCNTs with concentrated H2SO4 (96%) at 120–210 °C, and were characterized by SEM/EDS and FTIR analysis. Recycling of the methanol phase was used to separate the water produced from the reaction mixture, which increased the esterification conversion substantially and decreased the acidity of the product. A conversion of oleic acid of 95.46 wt.% was obtained with a catalyst/oleic acid mass ratio of 0.20%, methanol/oleic acid molar ratio of 5.8, temperature of 135 °C, and reaction time of 1.5 h. By removing water from the reaction mixture and adding the recycling of the methanol steam, the conversion of oleic acid was increased to 99.10 wt.% after 1 h.