Pyrolysis of spent coffee ground: optimization of operating parameters on product yield

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Abstract
This research aims to optimize the pyrolysis process of spent coffee grounds (SCG) utilizing a fixed bed reactor system. Response surface methodology (RSM) with central composite design (CCD) was employed to determine the optimal conditions for maximizing the yield of bio-char, bio-oil, and bio-gas. The study examined the impact of pyrolysis temperature and residence time, identifying 545.19 °C and 52.87 minutes as the optimal conditions. Under these parameters, the highest bio-oil, bio-char, and bio-gas yields were 44.70%, 27.32%, and 27.98%, respectively. All process parameters were significant (p-value < 0.05), with pyrolysis temperature emerging as the most influential factor based on the highest F-value. The bio-char’s proximate analysis revealed that increased pyrolysis temperature and prolonged residence time reduced moisture content to 3.69 wt% and enhanced fixed carbon content to 74.97 wt%. Functional group analysis of bio-oil demonstrated a complex composition with various organic compounds such as C-H, C=O, CH2, CH3, C-O, P-O-C, and C-Cl, highlighting its diverse chemical properties and potential applications. In conclusion, optimizing pyrolysis conditions effectively converts SCG into valuable bio-products, presenting a sustainable waste management solution for Malaysia’s increasing coffee consumption.

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