Extraction of lipids from post-hydrolysis spent coffee grounds for biodiesel production with hexane as solvent: Kinetic and equilibrium data

Spent coffee grounds (SCG), an agro-industrial residue produced after brewing of coffee beans contains appreciable amounts of lipids (similar to 16 wt%). One way of valorizing SCG is to subject it to dilute acid hydrolysis for the production of sugar-rich hydrolysate and lipid-dense post-hydrolysis residue. The post-hydrolysis spent coffee grounds (PHSCG) contains substantial amounts of lipids (similar to 26 wt%), making it necessary to gather lipid extraction kinetics and equilibrium data for process and equipment design. The effects of solvent-to-solid ratio (4-20 mL g(-1)) and temperature (30-60 degrees C) on the kinetics and equilibrium of lipid extraction from PHSCG using hexane as solvent was investigated. To appropriately describe the lipid extraction system, various kinetic models were fitted, with multi-step models best representing the extraction process (R-2 >= 0.99). Regardless of extraction temperature and SSR, washing step equilibrium is reached at a very short extraction time (<10 min) and over 90% of the lipids can be extracted in at least 1 h. Extraction of lipids from PHSCG required less amount of solvent to extract and recover the same amount of lipids present in SCG saving up to 40% of the solvent required for lipid extraction from SCG.