A Kinetic Framework for Microwave-Irradiated Catalytic Conversion of Lignocelluloses to Biofuel Precursors by Employing Protic and Aprotic Ionic Liquids

Abstract

In this work, we present a kinetic framework for microwave-irradiated catalytic conversion of lignocelluloses such as Sunn hemp fibre (75.6% cellulose content, Crystallinity Index (CI) 80.1%) and June grass (82.3% cellulose, CI 54%) to biofuel precursors such as glucose, 5-Hydroxmethylfurfural, Levulinic, and Formic acids by employing protic (PIL) and aprotic (APIL) ionic liquids. While the APIL forms a large supramolecular complex, the PIL rapidly ionises to form a Lewis acid catalyst with metal chloride and water and creates a metal-aqua complex. Since the APIL and the PIL follow different reaction mechanisms for microwave-irradiated catalytic conversion, catalyst-substrate loading, IL-substrate loading, water concentration, temperature, and time are optimised to regulate the product distribution. The APIL functions better for the higher crystalline substrates (with CI > 70%) to produce glucose, whereas the PIL, which is much cheaper than the APIL, produces more high-value products such as 5-Hydroxmethylfurfural. Sunn hemp fibres produce a maximum glucose yield of 78.7% and 75.6% (using the APIL and PIL, respectively), while June grass produces a maximum glucose yield of 88.2% and 84.2%, and a maximum 5-Hydroxmethylfurfural yield of 23.4% and 34.9% (using the APIL and PIL, respectively). This work also explores the economic viability and the scale-up potential of the above processes.