Utilization of coffee waste for biofuel production through catalytic microwave-assisted pyrolysis approach

Given the global prominence of coffee as a widely consumed beverage, the disposal of coffee waste in landfills poses significant environmental challenges. Addressing this issue through waste treatment measures can play a crucial role in waste management efforts. Presently, there is a lack of information on microwave-assisted pyrolysis (MAP) of coffee waste. Therefore, this study employs a MAP approach to convert spent coffee grounds (SCG) waste into bio-oil. Various catalysts, including ZSM-5, Ga-impregnated ZSM-5, potassium hydroxide, and titanium oxide, were investigated to enhance the quality and yield of the products. Several analytical techniques, such as simulated distillation analysis (SimDist), gas chromatography-mass spectrometry (GC-MS), proton nuclear magnetic resonance (¹H-NMR), and Fourier-transform infrared spectroscopy (FTIR), were employed to examine the chemical composition of the produced pyrolytic bio-oil. The results indicate that the bio-oil obtained from this process demonstrates significant potential for producing chemical compounds and liquid fuels, offering a promising and beneficial solution for managing coffee waste. Furthermore, GC-MS analysis revealed the presence of phenolics, alkanes, ketones, and nitrogen compounds, with the highest formation of phenolic compounds observed when using the TiO₂ catalyst. Graphical abstract: (Figure presented.)