Authors: Vivek Mishra, Om Prakash Sondhiya
Abstract: Rice husk is a common lignocellulosic agricultural by-product produced in huge amounts across the world, with nearly 150 million tons generated every year. This work examines the preparation and assessment of bioethanol obtained from rice husk waste as an eco-friendly second-generation biofuel. The rice husk was collected, dried, powdered, and treated with 4% NaOH at 90°C for 2 h, followed by steam explosion at 121°C for 30 min to remove lignin and hemicellulose components. Enzymatic saccharification was carried out using cellulase (30 FPU/g) and xylanase (10 FPU/g) at pH 5.0 and 50°C for 72 h, producing 68.4 g/L reducing sugars. Fermentation was performed with Saccharomyces cerevisiae (MTCC 178) at 32°C for 96 h and resulted in 32.6 g/L bioethanol with 95.2% fermentation efficiency. The produced bioethanol was purified through double distillation and molecular sieve dehydration to reach 99.5% purity, and the product was analysed using GC-MS, FTIR, and NMR techniques. The physicochemical parameters, including density (789 kg/m³), calorific value (26.8 MJ/kg), and octane number (108), matched ASTM D4806 requirements. Engine testing on a 4-stroke, single-cylinder SI engine (5.2 kW, 1500 rpm) with E10, E20, E50, and E85 blends revealed that E20 decreased CO emissions by 38% and HC emissions by 32% relative to gasoline, with only a 3.5% decline in brake thermal efficiency. CFD analysis using ANSYS Fluent confirmed the experimental findings with an error lower than 6%. The results demonstrate that rice husk can serve as an effective feedstock for large-scale bioethanol manufacturing while supporting waste utilisation and renewable energy production.
