Insights into olive pomace pyrolysis conversion to biofuels and biochars: Characterization and techno-economic evaluation

This work demonstrates, experimentally and economically the potential of Olive Pomace Waste (OPW) to produce renewable biofuels (pyrolytic oil and gas) and biochars through slow pyrolysis to evaluate the scale up of commercial pyrolysis. Experimental pyrolysis runs were conducted at 500, 600 and 700 °C as final pyrolysis temperature, 15, 20 and 25 °C/min as heating rate and 1 h as residence time, in a fixed bed pyrolyzer. In the optimum pyrolysis conditions (600 °C and 15 °C/min), 33 wt% of oil, 30.00 wt% of char and 37 wt% of gas were produced. Recovered pyrolytic oil presents good energy value (HHV between 15.96 and 20.94 MJ/kg) with a great bioactive potential. The released permanent gases show an interesting energy content (LHV up to 11 MJ/kg) which emphasizes their application in a gas engine to provide renewable electricity in rural olive groves area. The recovered OPW biochar presents a high carbon (C: 72.54 wt%) and nutrients contents (up to 8.42 mg/g of Ca, up to 8.69 mg/g of K and up to 2.02% of total N) which make it suitable for soil amendment and for long-term carbon sequestration. Kinetic study of OPW pyrolysis, performed using the Distributed Activation Energy Model (DAEM), gives a low activation energy value ranging from 121.6 to 151.6 kJ/mol encouraging the scaling-up. The economic results support the feasibility of OPW pyrolysis, with a payback period of 2.83 years and a profit of about 226.4 USD per ton of OPW.