Agro-industrial residue torrefaction to bio-coal: Its physico-chemical characterization and potential applications in energy and environmental protection

[Display omitted] •Torrefaction treatment improves the fuel characteristics of lignocellulose.•Temperature is a regulating factor for torrefied product’s properties.•Lignocellulosic biomass produces solids, liquids, and gas products during torrefaction.•Bio-coal has potential applications in energy, environment, agri-food, and polymer composite. Leveraging biofuel derived from biomass stands as a pivotal strategy in reducing CO2 emissions and mitigating the greenhouse effect. Biomass serves as a clean, renewable energy source, offering inherent benefits. However, despite its advantages, biomass encounters obstacles hindering its widespread industrial applications, including its relatively low calorific value, limited grindability, high water content, and susceptibility to corrosion. The torrefaction process has garnered significant attention as an effective method for enhancing the quality of raw biomass for energy production. In this review, we briefly discussed the mechanism of bio-coal preparation using biomass, physico-chemical characterization of different torrefied feedstocks, and the effect of torrefaction parameters, along with the effect of the different types of reactors on biomass torrefaction. Furthermore, bio-coal’s emission characteristics and fuel quality throughout the thermal treatment have been covered. Thus, bio-coal finds a wide range of applications in sustainable energy generation, environmental remediation, agri-food development, polymer composites, and others.