Solid biofuel production from spent coffee ground wastes: Process optimisation, characterisation and kinetic studies

•The food wastes (spent coffee grounds) can be used as slow pyrolysis feedstock.•Biochar conversion were optimised by response surface methodology.•Biochar-SCG possessed great yield (29.94%) and excellent energy yield (41.60%).•The biochar-SCG was a favourable solid fuels with low activation energies. The massive generation of spent coffee ground wastes has become an environmental concern around the world. Thus, in this research work, spent coffee grounds of Coffea arabica species were evaluated as potential feedstock for solid biofuel production to reduce solid waste and to generate value products. Pyrolysis temperature, pyrolysis time and heating rate were the dominating factors affecting the biochar and energy yields from the response surface methodology analysis. The spent coffee ground biochar (SCG-biochar) was then optimised of its pyrolysis parameters, with promising biochar yield (29.94%) and high energy yield (41.60%). The optimised SCG-biochar was characterised and found to possess favourable fuel characteristics such as high carbon percentage (80.35%), low oxygen percentage (12.43%), low H/C ratio (0.44), low O/C (0.12) and high fuel ratio (6.75), which will contribute to higher energy generation and lesser emission of greenhouse gases. The optimised SCG-biochar possessed high thermal efficiencies with low activation energies (63.24 kJ mol−1 –122.93 kJ mol−1) with attractive unit cost of $ 7.22 per kg which can be used in combustion process effectively. Therefore, the fuel and combustion characteristics of SCG-biochar signifies a promising development of feasible biofuels for energy generation.