A comprehensive review of chemical treatments for biomass feedstock to enhance briquette characteristics

Abstract Converting biomass into briquettes offers a promising way to meet increasing global energy needs while reducing environmental issues. However, briquette performance is limited by low calorific value, high ash, and moisture contents. Materials such as corn cobs, groundnut shells, banana leaves, sugarcane bagasse, and rice husks contain ash levels exceeding the recommended 4%, resulting in slagging and reduced thermal performance. Chemical treatment with alkali, acid, and hydrothermal methods has become a practical approach to enhancing briquette quality. This review evaluates the effectiveness of these treatments by examining their influence on biomass characteristics. A structured narrative review methodology was applied, involving a comprehensive literature search of Google Scholar, Scopus, and other sources, covering peer-reviewed journals, grey literature, and case studies published in English between 2005 and 2025. Findings revealed sodium hydroxide as the most widely applied alkali, increasing calorific value by up to 16.2% in celosia argentea , cabbage, and banana leaf biomass. Among acids, sulphuric is the most effective, enhancing calorific value by up to 31.83% in rice stalks and watermelon biomasses, while hydrochloric achieves ash reduction of up to 96.26% in corn and soybean stalks. Briquettes for industrial application are classified according to DIN 51731 and ISO 17225 (class I1-I3 for industrial and B for standardized domestic heating) by ash content < 4%, moisture < 13%, volatile matter < 40%, net calorific value ≥ 14.5 MJ/kg, nitrogen < 0.6%, and sulphur < 0.8%. Despite demonstrated improvements, inhibitor formation, effluent disposal, and equipment corrosion hinder real-world application. Future research should optimize chemical treatment concentrations for heterogeneous biomasses and conduct post-treatment briquette analysis, including environmental and techno-economic implications.