A novel approach to biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More waste management, detailed in a recent review in BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More by Sun et al., investigates the transformation of bio-tar—a problematic byproduct of renewable energy production—into valuable bio-carbon materials. This innovative strategy not only tackles the persistent challenge of bio-tar formation in biomass pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More but also paves the way for creating high-performance carbon materials. The researchers highlight that this secondary thermoconversion of biomass offers a promising solution for sustainable waste utilization and advanced material development.

Bio-tar, a complex mixture primarily composed of aromatic compounds, is an unavoidable liquid byproduct of high-temperature biomass pyrolysis. Its inherent properties, such as high viscosity and volatility, have historically hindered the widespread adoption of pyrolysis technologies due to issues like pipeline clogging and environmental concerns from direct emissions. Traditional treatment methods, including physical removal, non-catalytic thermal cracking, and catalytic reforming, often face limitations like high energy consumption or catalyst deactivation. This new approach, which converts condensed bio-tar directly into bio-carbon through thermal polymerization, represents a significant step forward. The resulting bio-carbon boasts higher carbon content and lower ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More compared to conventional biochar, making it a superior material for various applications.

The polymerization mechanism of bio-tar is significantly influenced by specific oxygenated compounds. The review emphasizes the crucial role of oxygenated compounds containing carbonyl groups and furan rings as key precursors in this process. Their unsaturated oxygen-containing functional groups facilitate essential bond cleavage and recombination, driving the polymerization. For instance, furfural, a common furan, has been identified as an effective polymerization agent due to its active carbonyl group and electron-rich furan ring, which activate the polymerization of bio-tar and even promote cross-polymerization between bio-tar and biochar. While these insights are valuable, the complex nature of bio-tar components and the interaction mechanisms of condensation chemical reactions for synthesizing carbon skeletons still require further investigation.

Controlling the polymerization process is vital for optimizing bio-carbon yield and quality. Reaction parameters such as temperature, residence timeResidence time refers to the duration that the biomass is heated during the pyrolysis process. The residence time can influence the properties of the biochar produced.   More, and heating rate play a significant role. For example, studies show that while higher reaction temperatures promote the formation of stable bio-carbon, they can also lead to a decrease in bio-carbon yield due to the volatility of bio-tar components. Conversely, a longer reaction time generally enhances polymerization and improves bio-carbon yield. Lower heating rates also promote polymerization, especially at temperatures below 500∘C, leading to higher bio-carbon yields, with a 30% reduction in yield observed with increased heating rates.

To further enhance bio-carbon properties for specific applications, the incorporation of additives is crucial. Pre-treatment methods, such as air pre-oxidation or treatment with hydrogen peroxide and nitric acid, can improve the distribution of oxygen-containing functional groups in bio-tar, thereby promoting polymerization and enhancing the porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More of the resulting bio-carbon. Additionally, chemical additives like furfural can increase bio-carbon yield by inhibiting the evaporation of bio-tar components and delaying carbonization temperature. The use of templates like crab shells or activators such as KOH and NaOH , often combined with heteroatom dopants like urea for nitrogen doping , has been shown to significantly improve the pore structure and functional group characteristics of bio-carbon, leading to a specific surface area of up to 2489.62 m2g−1.

The high-value utilization of bio-carbon produced through this method is focused on creating high-performance carbon materials. Bio-carbon has shown promising potential across various applications, including adsorbents, energy storage electrode materials, catalysts, and fuels. As an adsorbent, bio-carbon with N/S dual-doping achieved a CO2​ adsorption performance of 2.21 mmol g−1 at 0∘C and a specific surface area of 957.44 m2g−1. For energy storage, bio-carbon derived from corn straw bio-tar showed a specific capacitance of 309.5 F g−1 at a current density of 0.5 A g−1 with an 80.1% retention rate after 10,000 cycles. Its low ash content and ease of aggregation make it an ideal precursor for high-performance electrode materials. As a fuel, bio-coal produced through bio-oil fraction polymerization achieved a mass energy density of 28.2 MJ kg−1, comparable to commercial coal, and demonstrated a potential reduction of 738 million tons of carbon dioxide equivalents annually by replacing the same amount of coal. While the potential is significant, further research is needed to improve cycling stability for energy storage , enhance catalytic stability , and achieve large-scale, cost-effective production for all applications.

Source: Sun, Y., Jia, J., Huo, L., Zhang, X., Zhao, L., Liu, Z., Zhao, Y., & Yao, Z. (2025). Preparation of bio-carbon by polymerization of bio-tar: a critical review on mechanisms, processes, and applications. Biochar, 7(90).