Technical valorisation of spent coffee grounds and food waste using sulphuric acid immobilised on silica

Biodiesel from spent coffee grounds and food waste was prepared using sulphuric acid immobilised on silica gel (H2SO4-SiO2) as a catalyst. Reactions were carried out under reflux conditions using 15 mmol methanol. Food waste lipid and spent coffee oil gave 97% and 92% of biodiesel, respectively, after 24 h of reaction. After completion of the reaction, the immobilised acidic catalyst was separated by gravity filtration. Subsequently, the catalyst was reused for three consecutive cycles. At the end of three cycles, a 22% decrease in catalytic activity was observed for reactions involving spent coffee oil, whereas a 13% decrease in activity was observed during the use of food waste lipid as a starting material.