Overcoming the Humin Bottleneck in Levulinic Acid and Furfural Production from Biomass: A Review and Future Perspectives

High Resolution Image Download MS PowerPoint Slide Levulinic acid and furfural are two renewable platform chemicals with great potential for the future of the chemical industry. However, during the development of their production processes, many researchers have encountered challenges due to the formation of humins. Humins are generally considered waste products formed during the conversion of carbohydrate to levulinic acid and furfural under severe reaction conditions, typically associated with high temperatures (above 160–200 °C), acidic catalysts, and prolonged residence times. This account examines how humins form, the conditions that favor their formation, and the problems they pose for catalyst recovery and product purification. It also discusses strategies that combine mitigation with valorization. Rather than focusing only on kinetics, this work brings together reaction mechanisms, process design, and economic aspects to point out where improvements can be made. By examining 146 studies published between 1962 and 2025, we show that moving toward integrated process designs that include humin valorization is not only beneficial but also necessary to make biorefineries both more cost-competitive and environmentally sustainable.