Wheat straw pyrolysis fundamentals during production of biochar

Wheat straw has significant potential as a biomass source for production of biochar, syngas and biofuel. Its lignocellulosic origin, low sulphur content and carbon neutrality make it an important substitute for fossil fuels. The present study was undertaken to examine the potential of wheat straw for production of biochar by pyrolysis for its application as a soil amendment and determine the effect of biomass constituents, hemicellulose, cellulose and lignin, on biochar formation mechanism. Raw wheat straw was pyrolysed to 500 °C at a heating rate of 10 °C min⁻¹ in the presence of nitrogen. Biomass had a moisture content of 10.5% and a carbon content of 46.16%, while the biochar had a higher carbon content of 73% suitable for use as a soil amendment. Wheat straw biochar exhibited low particle density and contained all the essential elements to promote soil health and plant growth. Its alkaline nature further justified its use as a soil amendment. The pyrolytic behaviour of wheat straw was studied using computational thermal analysis method, while gas chromatographic and mass spectroscopic techniques were employed to study biogas and bio-oil composition. The results from thermal investigation of lignocellulosic components also corresponded well with wheat straw biomass. The thermal analysis revealed the thermal regions of decomposition of the wheat straw with the major thermal reaction recorded in the temperature region between 250 and 400 °C related to decomposition of the hemicellulose, cellulose and lignin components of the wheat straw. CO₂ was the most prominent gas evolved during the pyrolysis followed by CO, while CH₄ was the major hydrocarbon gas evolved. The GC–MS analysis showed that phenols were the most dominant compounds in the bio-oils. The FTIR analysis of individual lignocellulosic components revealed the major breakdown bands in all the three components related to the bands detected in wheat straw biochar spectrum. The analysis elucidated the behaviour of lignocellulosic components as wheat straw undergoes pyrolysis by showing the sequential changes starting from water absorption, followed by bending and stretching of OH and CO groups, leading to biomass degradation and char generation.