TGA study examining the effect of pressure and peak temperature on biochar yield during pyrolysis of two-phase olive mill waste

In this paper, a factorial design of experiments was proposed to investigate the effect of the absolute pressure (in the range 0.1–1.5 MPa) and the peak temperature (in the range 400–550 °C) on the pyrolysis behaviour of two-phase olive mill wastes (TPOMW). Pyrolysis experiments were conducted in a thermogravimetric analyser (TGA) under nitrogen atmosphere and at a linear heating rate of 5 K min−1. The response variables (biochar yield, fixed-carbon yield, and the temperature at which the maximum rate of weight loss is reached) were analysed using regression models. From results of regression analyses, the following main conclusions can be drawn: (a) biochar yield from pyrolysis of TPOMW decreases when both peak temperature and pressure increases; (b), an increase of both peak temperature and pressure results in a higher fixed-carbon yield; and (c), a significant increase of the overall devolatilisation rate was observed for experiments conducted at intermediate pressure values (0.8 MPa). In addition to this, kinetic parameters describing TPOMW pyrolysis were estimated adopting a devolatilisation scheme based on separate volatilised fractions generated from three pseudo-components. The quality of the fit between experimental weight-loss data and computed values (using an independent parallel reaction kinetic model) was found to be remarkably good.

► The aim of this work is to investigate the effect of the pressure and the peak temperature on the pyrolysis of two-phase olive mill wastes. ► The response variables were biochar yield, fixed-carbon yield, and the temperature at which the maximum rate of weight loss was reached. ► An increase of both peak temperature and pressure results in a higher fixed-carbon yield. ► A significant increase of the overall devolatilisation rate was observed for experiments conducted at intermediate pressure values. ► Kinetic parameters describing TPOMW pyrolysis were estimated adopting a devolatilisation scheme based on separate volatilised fractions.