Energy recovery potential analysis of spent coffee grounds pyrolysis products

Spent coffee grounds are generated in a considerable amount as a processing waste during making the coffee beverage. This waste is attractive for biofuel production due to the high organic content. The aim of this study was to investigate the bioenergy production potential of the spent coffee grounds during pyrolysis at two different heating rates of 10 and 60 °C/min. During the process, three discrete stages of pyrolysis representing the thermal behaviour of the sample were identified as the evaporation of absorbed water, pyrolysis reactions and the decomposed residual solid. The gaseous volatile, CO2, CO and CH4 were shown to be the primary volatiles for the biogas. The heating rate of pyrolysis was found to have positive effects on the elemental composition in the bio-oil. The pyrolysis efficiency of spent coffee grounds was calculated accounting for the stoichiometric energy that can be produced from combustion of the pyrolysis products and the energy required to carry out the pyrolysis process. The pyrolysis efficiency was estimated at 77–85%, depending on the moisture content of the feedstock.