High-energy biofuels production via hydrothermal carbonisation of wet waste biomasses and bioenergy crops

The need of replacing fossil fuels with more environmentally friendly energy sources has boosted in recent years the search for alternative energy feedstock. Thermochemical conversion of wet, low valuable, residual biomasses (i.e. agricultural and agro-industrial residues, bioenergy crops that can be efficiently grown into semi-arid marginal lands, as well as the organic fraction of municipal solid waste) into high energy biofuels, can result in a circular-driven economy. Exploitation of such biomasses could lead to models for sustainable production. In this study, we report the influence of HTC operating conditions (temperature, residence time and dry mass solid to water ratio, b/w) on energy, thermal and morphology properties of four different feedstocks. The agricultural and agro-industrial residues: olive tree trimmings (OT) and olive mill pulp (OP) were carbonised at 120-250 °C, at fixed residence time of 0.5 h and b/w 0.25. The influence of the b/w (0.07-0.25) is examined for samples carbonised at 250 °C. The use of opuntia ficus indica as a bioenergy crop is also studied by HTC at 180-250 °C, 0.5-3 h and b/w 0.07-0.30. HTC of OFMSW is carried out at 120-260 °C, 3 h and b/w 0.15. The energy, thermal, chemical and morphology properties of raw materials and hydrochars were assessed by calorimetric, thermogravimetric, proximate and ultimate analyses, ATR-FTIR spectroscopy, SEM and EDS. Results show that both temperature and solid loads have a strong effect on energy and morphology features of hydrochars.