Recently, Prof. Zhen Fang was invited to write an Editorial in “Biofuels, Bioproducts and Biorefining” (He is also serving as advisory editorial board member for this Journal). He suggested to design and find a green and inexpensive solvent to solubilize lignocellulosic biomass at mild conditions for novel biorefineries.
Annual global biomass production is equivalent to 8 times the world’s energy consumption. Most of biomass is in lignocellulosic form that contains 75% sugar units (e.g., wood and grass plants: 50% cellulose and 25% hemi-cellulose). The key is how to release these abundant biopolymers to become water-soluble sugars that are easily subsequently converted into ethanol, lipids, other bio-fuels, various chemicals, foods, and medicines. There are three typical methods to hydrolyze lignocelluloses to sugars.
Typically, the three ways are used for hydrolysis: (i) enzymatic hydrolysis after pretreatment at low temperatures (e.g., 50 oC), (ii) catalytic hydrolysis at mild temperatures (e.g., 180oC), and (iii) fast hydrolysis at high temperatures near critical point (e.g., 350 oC). It is very important to solubilize biomass to form a homogenous phase for hydrolysis and pretreatment. The homogenous biomass solution (like petroleum not solid coal) is also easily processed in a flow system for practical applications. Organic solvents (e.g., γ-valerolactone), ionic liquids and supercritical fluids can dissolve actual biomass for hydrolysis.
After biomass solubilization, the three hydrolysis methods can be further improved for practical uses: (i) for enzymatic hydrolysis; enzymes, water and biomass molecules mix well in a homogenous phase for complete hydrolysis, pretreatment step is not required. However, how to recycle enzymes, keep high activity and reduce their cost should be considered for industrial production. (ii) For catalytic hydrolysis; a flow process can be built up to increase production efficiency. At the same time, solid catalysts may replace liquid acids for a green process. However, their stability and activity need study further. (iii) For fast hydrolysis; even though its high efficiency, however, owing to severe conditions (high temperature and pressure), engineering issues (such as reactor design, materials and continuous operation) become key obstacle to commercialize it.
- Zhen Fang*, How Can We Best Solubilize Lignocellulosic Biomass for Hydrolysis? Biofuels Bioproducts and Biorefining, 9, 621–622 (2015) (invited editorial).
