Comprehensive evaluation of the life cycle of liquid and solid fuels derived from recycled coffee waste

In this study, the potential advantages of fuels derived from coffee waste were evaluated and quantified over the entire life cycle. Life cycle evaluation is important for achieving robust understanding because it covers the entire sequence of stages of fuel production and utilization. Coffee waste collection and transport, oil extraction, and biodiesel production and transport are the stages covered under the first life phase, called well-to-pump. Extensive engine tests were also conducted to assess the second life phase, pump-to-wheel. Environmental, economic, energetic, and technical criteria were encapsulated within the frame of each phase, and various evaluation tools that fit each life stage were adopted. The results showed that coffee biodiesel contributes to an 80.5% reduction in CO2 emissions compared with the hydrocarbon diesel during its life cycle. Moreover, the conversion efficiency of the raw material energy to fuel energy in the case of coffee biodiesel was 10% higher than that of the petro-diesel. An energy amount of 3.45 MJ is associated with coffee biodiesel for each 1 MJ consumed in its life cycle. The economic viability of coffee biodiesel was found to be very sensitive to the price of the coffee solid fuel (biomass pellets). The entire project is feasible only when the price of pellets is 40% of that of wood pellets or higher. Substantial reduction of tailpipe emissions was attained for CO, CO2, and HC, with 45.3%, 5.7%, and 23.6% reductions, respectively, for B20. Reductions of 10.3% and 7.5% were observed in the brake thermal efficiency and brake power, respectively. Thus, coffee biodiesel has significant advantages and potential, and its technological development merits further research.