Optimization of Biodiesel Production from Waste Coffee Grounds by Simultaneous Lipid Extraction and Transesterification

Abstract

We previously optimized a conventional twostep process (TSP) for biodiesel production using waste coffee grounds (WCGs). In the present study, a novel process, one-step direct process (OSDP) comprised of lipid extraction and simultaneous transesterification in a reactor, was evaluated for biodiesel production for WCGs, and compared with TSP. Owing to a relatively low free-fatty acid content (2.3%), an alkaline catalyst, NaOH, was readily used in this process. We found that a mixture of methanol and n-hexane was the best combination for the OSDP. Optimization of OSDP was conducted by statistical technique, followed by one-factor-at-a-time and sensitivity analysis techniques. Using these techniques, 10.8% (gbiodiesel/ g-WCGs) biodiesel yield was achieved at 3.0 wt% of catalyst relative to WCGs, 3.0 mL methanol/g-WCGs, 4.5mL n-hexane/g-WCGs, 45°C, and 9 h of reaction time. Compared to the TSP, the OSDP saved methanol and n-hexane requirement by 69.7% and 67.2%, respectively, while the actual biodiesel yields based on the lipid amount in WCGs were similar in both processes. This study showed that the novel OSDP could be a promising alternative to TSP for economic biodiesel production from WCGs.