Repeated Biodiesel Production from Waste Coffee Grounds via a One-step Direct Process with a Cartridge Containing Solid Catalysts Manufactured from Waste Eggshells

In this study, biodiesel was produced from waste coffee grounds (WCGs) using solid catalysts manufactured from waste eggshells (WESs). A one-step direct process (OSDP), comprising extraction of lipids from WCGs and simultaneous transesterification of these lipids with methanol in a reactor, was employed. To facilitate reuse of the solid catalysts, a cartridge containing the solid catalysts was devised and applied in the OSDP. The optimal reaction conditions of the OSDP with the cartridge were 100 wt% catalyst relative to WCGs, the mixture of 4.0 mL methanol and 4.0 mL n-hexane per gram WCG, 45 degrees C, 9 h, and 200 rpm. Under these optimal conditions, an 8.7% biodiesel yield (g-biodiesel/g-WCGs) was achieved. Solid catalysts retained in the cartridge were successfully reused for seven rounds of repeated batch operation and, using this approach, a biodiesel yield exceeding 92% of that of the first batch operation was maintained.