Title : Rapid, ionic liquid mediated catalytic conversion of lignocellulosic Sunn hemp fibres to biofuel precursors
Abstract:
Lignocelluloses from non-food crops are considered to be the most important feedstock for second generation biofuel production since they do not conflict with food sources. We use non-edible cellulose-rich lignocellulosic Sunn hemp fibres – containing 75.6% cellulose, 10.05% hemicellulose, 10.32% lignin, with high crystallinity (80.17%) and degree of polymerization (650) – as a new non-food substrate for lignocellulosic biofuel production. Microwave irradiation is employed to rapidly rupture the cellulose’s glycosidic bonds and enhance glucose yield to 78.7% at 160°C in only 46 min. The reactants – long-chain cellulose, ionic liquid, transition metal catalyst, and water – form a polar supramolecular complex that rotates under the dual-mode microwave’s alternating polarity and rapidly dissipates the electromagnetic energy through molecular collisions, thus accelerating glycosidic bond breakage. In 46 minutes, 1 kg of Sunn hemp fibres containing 756 g of cellulose produces 595 g of glucose at 160 °C, and 203 g of hydroxymethyl furfural (furanic biofuel precursor) at 180°C. Yeast (Saccharomyces cerevisiae) mediated glucose fermentation produces 75.6% bioethanol yield at 30°C, and the ionic liquid is recycled for cost-effectiveness.
We also present experimental evidences of chemical chaos, which is observed when the Sunn hemp fibres are hydrolyzed using the same ionic liquid and the transition metal catalyst in well-mixed batch reactors heated to 110°C by an oil-bath instead of a microwave. The catalytic hydrolysis of lignocelluloses produces chaotic strange attractors with fractal dimensions and positive Lyapunov coefficients on the product phase spaces. All the 5 products (glucose, fructose, hydroxymethyl furfural (HMF), levulinic acid (LA), and formic acid (FA)) exhibit aperiodic (i.e., non-repetitive) temporal oscillations, peaking at 5 hours for water-addition rates ranging from 25 to 43 µl/gm/hr, when the hydrolysis system operates in the domain of chemical chaos. 37.5 µl/gm/hr of water-addition maximizes the concentrations of glucose, LA, FA at all times, with their average yields peaking at 5 hours to 67.5%, 12.4%, and 5%, respectively. At water-addition rates of 45 µl/gm/hr and higher, the system operates close to its thermodynamic equilibrium, resulting in the temporal oscillations to disappear completely, though the yields of glucose and HMF continue to peak at 5 hours. We show that the peak non-equilibrium yield of glucose obtained at the water-addition rate of 37.5 µl/gm/hr is 15% higher than its corresponding peak equilibrium yield at 45 µl/gm/hr of water addition, leading to a 15% increase in bioethanol production.
