This work presents a new technology for rapid, microwave-irradiated ionic liquid-mediated one-pot synthesis of biofuel precursors from raw lignocellulosic biomass. We introduce two cellulose-rich (76-82% cellulose) non-edible lignocellulosic bioenergy crops, namely Sunn hemp fibre, with high crystallinity (80%) and degree of polymerization (650), and June grass, with a moderate crystallinity (48%) and a high degree of polymerization (1200). We convert these raw lignocelluloses using two different types of ionic liquids – Aprotic Ionic Liquid (APIL) and Protic Ionic Liquid (PIL) – and coper chloride (catalyst) and water (cross-catalyst) to biofuel precursors such as glucose, hydroxymethylfurfural (HMF), and levulinic acid (LA), in a microwave reactor at 160-200oC and 1-5 bar pressure in less than 46 minutes. The PIL (prepared in-house) rapidly ionizes to form a Lewis acid catalyst with copper chloride and water, and creates a hexa-aquo complex that reacts with the cellulose polymers in raw lignocelluloses to form a large electropositive complex, while the APIL forms a large supramolecular complex. These polar complexes align themselves along the microwave’s rapidly alternating electromagnetic field, resulting in frequent dipole rotations that lead to molecular collisions, and dissipation of electromagnetic energy as heat that increases the reaction temperature and the reaction rate, thus rapidly rupturing the glycosidic bonds in the cellulose [1]. Since the APIL and the PIL follow different reaction mechanisms, the nature of the ionic liquid (PIL vs. APIL), the reaction temperature, and the water concentration are optimized to regulate the product distribution. Sunn hemp fibres produce a maximum glucose yield of 76% and 79% (using the PIL and the APIL, respectively), at 160oC in 46 minutes, while June grass produces a maximum glucose yield of 88% with the APIL, and a maximum HMF yield of 34% with the PIL, both at 180oC and in 41 minutes. Glucose is microbially fermented to bioethanol (76% yield) in 15 hours, while HMF and LA can be catalytically converted to furanic fuels. The PIL-based conversion targeting HMF as the biofuel precursor molecule, with glucose and LA obtained as co-products, is recommended because of its high product:reactant cost ratio of 194.

Rapid, ionic liquid-mediated one-pot catalytic conversion of non-edible lignocelluloses to biofuel precursors

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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