Biochar structure development during slow pyrolysis of pellets from barley straw and bran

In recent years, there has been a significant drive to incorporate circularity into products by finding cost-effective methods to recycle and reuse industrial waste. Agricultural biomass, a widespread waste stream, has great potential as a raw material for producing sorbents. However, the common practice of waste incineration negates this opportunity, as valuable resources are lost. This study aims to demonstrate that biomass pyrolysis can be used to create value-added products such as sorbents. Prior to pyrolysis, the optimal granulation process for integrating barley straw with bran was determined, yielding durable pellets composed of 90% barley straw and 10% bran (BSB). The study comparatively analyzed biochar obtained from BSB pellets, which were first pelletized and then subjected to pyrolysis at different temperatures (600, 700, and 800 °C) and holding times (1, 2, and 3 h). Key properties examined included biochar yield, carbon and nitrogen content, specific surface area, pore size distribution, and BET surface area. Pyrolysis was carried out at a constant heating rate of 5 °C·min⁻¹. Increasing the holding time and pyrolysis temperature positively influenced the surface area and broadened the pore size distribution of the resulting biochar. The most favorable results were observed for the sample obtained at 800 °C. The total pore volume of samples BSB800-2 h and BSB800-3 h was notably higher than that of BSB800-1 h. Prolonged holding time at the final temperature led to an expansion in pore size range and a corresponding increase in total pore volume and surface area.