Turning agricultural waste into high-value chemicals is a critical step in moving away from fossil fuels. A recent article in the journal Resources Chemicals and Materials by Kamonwat Nakason, Saran Youngjan, Vorapot Kanokkantapong, and colleagues details a sustainable method to produce a key platform chemical, 5-hydroxymethylfurfural (HMF), from glucose using a novel biochar-based catalyst. HMF is a versatile compound with applications in bio-based polymers, fuels, and pharmaceuticals. Its sustainable production has been a major challenge, primarily due to the complex reaction steps involved and the need for environmentally friendly systems. This study addresses these issues by developing a bifunctional catalyst, labeled B-TsFe, derived from cassava rhizome (CR) biochar.

This innovative catalyst is built on the carbon-rich structure of cassava rhizome, a common agricultural byproduct in Thailand often disposed of by burning, which causes air pollution. The CR biochar is functionalized with p-toluenesulfonic acid to introduce Brønsted acid sites, and ferric chloride to introduce Lewis acid sites. This design provides the necessary dual acidity to efficiently convert glucose to HMF. The conversion process is a two-step sequence: Lewis acids catalyze the isomerization of glucose to fructose, followed by Brønsted acids catalyzing the subsequent triple dehydration of fructose to HMF. The synergistic combination of these two acid sites on the B-TsFe catalyst surface is crucial for its superior performance compared to catalysts with only one type of acid site. Characterization analyses confirmed the presence of both acid site types and a porous, mesoporous structure that facilitates the catalytic reaction. The catalyst’s total acidity was measured at 1.6 mmol/g, suggesting a high potential for this bifunctional activity.

The catalyst’s performance was evaluated in an eco-friendly biphasic solvent system of water and isopropanol . Isopropanol is considered a greener, low-boiling-point solvent that can be derived from 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 itself, enhancing the sustainability of the process compared to conventional fossil-derived organic solvents. The researchers systematically investigated the effects of reaction 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 the ratio. The results showed that temperature and reaction time were the dominant factors influencing HMF production. Under the optimal conditions the B-TsFe catalyst achieved a maximum HMF yield of 34.5 wt.% and a selectivity of 37.1%. This yield was notably higher than that achieved by the single-functionality catalysts, B-Ts (30.3 wt.%) and B-Fe (26.1 wt.%), clearly demonstrating the benefit of the Brønsted-Lewis hybrid design. Furthermore, the B-TsFe catalyst showed good stability, maintaining high activity over five consecutive reuse cycles with only a gradual decline in HMF yield from 34.5 wt.% to 25.4 wt.%, which is comparable to similar biomass-derived catalysts. This drop is primarily attributed to a small amount of acid site leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More and the unavoidable accumulation of polymeric by-products (humin) on the catalyst surface. The stability and reusability, along with the renewable origin of the cassava rhizome precursor and the use of a green solvent system, highlight the B-TsFe catalyst as a highly promising and sustainable solution for advanced biomass valorization. This study paves the way for efficient HMF synthesis and underscores the potential of agricultural waste to drive the bioeconomy. Future work will focus on enhancing the long-term durability of the catalyst and conducting comprehensive economic and life cycle assessments.

Source: Nakason, K., Youngjan, S., Kanokkantapong, V., Wanmolee, W., Kraithong, W., Chukaew, P., Riewklang, K., Eom, T., Khemthong, P., & Panyapinyopol, B. (2025). A biochar catalyst with functional Brønsted-Lewis acid sites for enhancing hydroxymethylfurfural production from glucose. Resources Chemicals and Materials.