Pretreatment of Lignocellulosic Biomass Using Novel Methodologies

Abstract

Lignocellulose fractionation is a critical step in biorefineries to convert cellulose, hemicellulose, and lignin into sustainable fuels and chemicals. Conventional acid hydrolysis causes equipment corrosion, acid recovery challenges, excessive wastewater, and toxic by-products. To overcome this, solid acid ion exchange resins were investigated for the fractionation of lignocellulosic feedstocks in water and in ionic liquids. Characterisation of raw materials and pulp fractions via thermogravimetric analysis, X-ray diffraction, and other analytical techniques was used to evaluate its efficiency. After 2 hours at 110 °C in water, the highest cellulose retention (53 to 55 wt.%) and hemicellulose reduction (23 to18 wt.%) for miscanthus x giganteus (MxG) was observed with the commercial resin Amberlyst 70 (IER70) at a 1:8 mass ratio resin to biomass. When compared to equivalent proton concentrations of HCl and H₂SO₄, IER70 transformed better crystalline cellulose to amorphous forms achieving the largest changes in cellulose thermal degradation (10 °C). In the presence of triethylammonium hydrogen sulphate (IL-TS), IER70 enhanced the crystalline cellulose transformation to amorphous cellulose, reducing the cellulose peak degradation temperature from 269 °C to 257 °C. When compared to other six commercial ion exchange resins, IER70 overperformed them, due to its higher acid strength (117 kJ mol–1) and thermo-mechanical stability. The combination of IER70 with IL-TS was tested using three different feedstocks: MxG (high cellulose), brewery spent grains (low hemicellulose) and pine bark (high lignin). It was found this combination is most efficient for cellulose-rich biomasses, due to its stronger cellulose depolymerisation effect. In conclusion, IER70 enhanced biomass hydrolysis and fractionation in the presence of water and ionic liquids. Its solid form can reduce conventional hydrolysis issues (equipment corrosion and complex neutralisation and recovery steps). Thus, IER70 can enhance the pretreatment efficiency and enhance the feasibility of producing renewable chemicals and fuels from lignocellulosic biomass.