Hydrothermal refining of biomass: An overview and future perspectives

Biomass is a promising alternative for the production of energy, novel materials, chemicals, and other valuable products. A certain degree of processing is required to achieve those results. Hydrothermal processes offer a unique way to obtain a wide range of biorefinery products. They can be considered as environmentally friendly processes, using solely water at different temperatures as a process medium to convert abundant and inexpensive biomass into products. We provide a short overview on hydrothermal processes that use water in its liquid state, including hot water extraction, pressurized hot water extraction, liquid hot water pretreatment, hydrothermal carbonization, and hydrothermal liquefaction. We also provide examples of current research and real-world findings. We then present a novel hydrothermal biorefinery concept for sequencing these single processes, giving concrete examples of possible raw materials and products. Sequencing gives new possibilities for biorefineries to exploit all the biomass components as valuable products with zero losses. The added value comes from the increased efficiency of the bio-based products' value chain, by reducing losses and generating higher-value products and services.