Thermo-chemical conversion of spent coffee to bio-oil and biochar

Energy production from waste biomass/material is a more attractive alternative compared to use of feedstocks such as corn and soybean. This study presents total utilization of waste material- spent coffee grounds through a two-step process. In the first step, triglyceride oil was extracted from spent coffee grounds using hexane soxhlet extraction. The extracted oil properties were studied and found suitable for producing biodiesel. In the second step, the defatted spent coffee grounds was converted into bio-oil and biochar using a pyrolysis process at 450°C under nitrogen atmosphere. It was found that spent coffee grounds produced more bio-oil and less biochar compared to defatted coffee ground. The bio-oils were analyzed for their physical properties, such as viscosity, density, elemental composition, heating value, boiling point and molecular weight distribution. Structural characterization of bio-oils was carried out using advanced spectroscopic and chromatographic techniques, such as NMR, FTIR, TLC-FID, and GC-MS to obtain information on carbon and hydrogen distribution, functional groups, and hydrocarbon class type distribution. Two biochars produced from spent and defatted coffee grounds, and their respective feedstocks were characterized for elemental composition, BET surface area, ash, moisture and volatile content. These four samples were then used as soil amendment in a greenhouse experiment to study their effect on crop yields and to investigate if the use of biochar could help reduce the amount of chemical fertilizer, while at the same time maintaining or increasing crop yields.