Various biomass pyrolysis conditions influence the porosity and pore size distribution of biochar

Abstract

Biochar is obtained from the pyrolysis of biomass in the absence of oxygen and has great potential as a sorbent or as a carbon sequestration material. Although numerous studies have investigated biochar characteristics, the biochar porosity and sorption properties obtained with different pyrolysis conditions are still largely unclear. The objective of this study was to determine the interrelationships among temperature, material grain size, heating rate, and retention time, as well as the effects of the interactions of these variables on the surface morphology of biochar made from wheat straw. The sorption, porosity, and pore size distribution of biochars prepared at different pyrolytic temperatures were determined. Elemental analysis, BET-N2 surface area analysis, ICP‒OES, and Fourier transform infrared spectroscopy were used to characterize 19 wheat straw biochars obtained via pyrolysis at different temperatures (500–700 °C), heating rates (20 and 30 °C/min), and residence times (5 and 15 min). Based on a full factorial design method and variance analysis, the optimal conditions for wheat straw pyrolysis and the variables that have a statistically significant effect on biochar quality were determined. A high surface area of 400 m2/g and an average pore size of approximately 2.34 nm were obtained at 700 °C for a grain size of 0.5–1.0 mm at a heating rate of 20 °C/min and a residence time of 5 min.