Lignocellulosic biomass has the potential to partially displace fossil fuels in the production of energy, materials, chemicals and transportation fuels. In order to realize this potential, cost-effective and low-energy fractionation of biomass into different product streams is necessary.
This work uses low-cost protic ionic liquids to deconstruct and fractionate lignocellulosic biomass, with a focus on agricultural residues, energy crops and woody biomass. It aims to demonstrate process intensification and scale-up leading to potential cost reductions. Firstly, the use of triethylammonium hydrogen sulfate was investigated as an alternative to expensive, thermally unstable aprotic ionic liquids for pretreatment of high-ash and high-lignin agroresidues. Pretreatment of sugarcane bagasse, rice husk and rice straw was shown to give up to 90% glucose release under mild conditions. 100-fold scale-up of ionoSolv pretreatment from the 10 mL to the 1 L-scale was performed, enabling evaluation of key parameters expected to impact process economics, including solids loading, feedstock particle size and stirring speed. It was shown that excellent performance could be maintained using a biomass to solvent ratio of 1:2 g/g. Use of larger particle sizes up to 10 mm offered significant potential to reduce comminution energy.
Attention was then turned to utilization of the lignin stream derived from ionoSolv biorefining. Fine-tuning of the process severity (temperature, time, acidity) enabled control of lignin molecular weight and functionality. Fast pyrolysis of mildly treated lignins gave the highest bio-oil yields with maximal energy recovery in the liquid product. Fractional precipitation produced lignin fractions with narrow polydispersity and low molecular weight of 1000 g mol-1 with yields of up to 14 wt%. Potential applications of lignin were assessed based on HSQC NMR, 31P NMR, gel permeation chromatography and thermal analysis. Lignin condensation and re-precipitation were identified as the most important parameters affecting both glucose yields and valorization potential of lignin.