An insight into the thermokinetics of the pyrolysis of invasive grass Sorghum halepense towards its bioenergy potential

In the present study, an attempt was made to investigate the physicochemical characteristics of Sorghum halepense, often called Johnson grass, and its performance in pyrolysis. For this, the pyrolytic process of the S. halepense under thermogravimetric scale was first acquired using three heating rates (5, 10, and 20 degrees C min(-1)). Following this, the pyrolytic behavior of S. halepense was kinetically admitted as a two-step devolatilization process. By using an isoconversional kinetic analysis and integral master-plot methods, it was verified that the first devolatilization stage matched with the three-dimensional diffusion-reaction model (D3), and the average activation energy was within 182.9-192.0 kJ mol(-1), while the second devolatilization stage followed the first-order reaction model (F1) with the average activation energy in a range of 166.9-184.4 kJ mol(-1). As estimated from Kissinger's method, the pre-exponential factor was found around 3.84 x 10(15) min(-1) and 2.59 x 10(15) min(-1) for the first and second devolatilization stages, respectively. The overall kinetic expression from the estimated kinetic triplets is a good way to characterize the pyrolysis kinetics of the S. halepense since it can reproduce the conversion rate. The results in terms of thermodynamic parameters evidence S. halepense as a viable feedstock for pyrolysis, presenting Delta H > 0, Delta G > 0, and Delta S > 0. It is concluded that S. halepense has a considerable bioenergy potential, proportional to the established bioenergy feedstocks.

Automated summary

This study investigates the physicochemical characteristics and pyrolysis performance of Sorghum halepense. The pyrolysis behavior of S. halepense is found to involve a two-step devolatilization process, with the first step following a three-dimensional diffusion-reaction model and the second step following a first-order reaction model. The estimated kinetic parameters indicate that S. halepense has considerable bioenergy potential as a feedstock for pyrolysis.