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

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Spent coffee grounds (SCG), an agro-industrial residue produced after brewing of coffee beans contains appreciable amounts of lipids (~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 (~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 °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 (R2 ≥ 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.