Pre-functionalized and lipid-dense post-hydrolysis rice bran as feedstock for FAME production via non-isothermal in-situ (trans)esterification with subcritical methanol

Abstract

In-situ (trans)esterification (ISTE) of lipids in post-hydrolyzed rice bran (PHRB) with methanol under subcritical conditions has proven to be a suitable feedstock for fatty acid methyl ester (FAME) production. The lipids from PHRB had a fatty acid profile which was primarily composed of oleic (39 wt%) and linoleic (36 wt%) acids, and could potentially result in biodiesel with favorable properties. The PHRBs which were lipid-dense (31.35 and 48.98 wt% on a dry basis) and pre-functionalized (0.55 and 1.21 mmol H+/g dry and lipid-free PHRB), were successfully processed non-isothermally from 30 to 150 °C at high reactor loading of 85% and a solvent-to-solid ratio (SSR) of 4–6 mL/g dry PHRB, which resulted in yields of 26.48 and 35.11 g/100 g dry PHRB, equivalent to a conversion of ∼90% of the fatty acids. Due to the acquired acid sites in the collected PHRB, no additional catalyst was required. Elemental analysis and FT-IR spectroscopy were carried out to test the presence of sulfur and sulfonic sites in the PHRB residues. Furthermore, the recovered solids still exhibited substantial acid sites which were tested for activity through the esterification of oleic acid in methanol and were reused up to 7 cycles.