Bio-ethanol Production from Wheat Straw Using Different Pre-treatment Approaches

Abdulsattar, Mohammed Oday

Abstract

The high level of pollution associated with greenhouse gas emissions and the rapid increase in energy demand across the globe raised the needs for clean, easily available, cheap and renewable energy sources to replace traditional fossil fuels. Among the different forms of renewable energy, bio-ethanol has been of great interest in recent decades since it has the ability to replace conventional transport fuel. A wide range of raw materials including food crops, molasses and lignocellulosic biomass have been utilised for bio-ethanol production. Among the variety of lignocellulosic biomass, agricultural waste such as Wheat Straw (WS) presents itself as a good candidate for bio-ethanol production on an industrial scale. In the current study, WS was pre-treated with several approaches including grinding, Steam Explosion (SE), Liquid Hot Water (LHW), microwave, Atmospheric Disk Refining (ADR) and pressurized disk refinering (PDR) with the aim to improve the total reduced sugar yield from Enzymatic Hydrolysis (EH). In grinding pre-treatment, WS was ground with a ceramic disk to various particle sizes (> 2000 μm to < 250 μm). The highest total reduced sugar yield after EH of 58.0% (wt/wt) was obtained from the sample with a particle size of < 250 μm. SE and LHW pre-treatment were carried out at the same severity of 4.65 and 3.35 by using distilled water or H2SO4 (3%, wt/wt), respectively. PDR pre-treatment experiments were conducted at a pressure ranging 4, 6, 8 and 10 bar. Moreover, the ADR pre-treatment was performed at the atmospheric pressure. Microwave pre-treatment time (min), temperature (°C), power (W) and distilled water volume (mL)effects on sugar recovery were investigated by the means of the Design of Experiments (DoE) software. Furthermore, microwave pre-treatment conditions were optimized. The maximum total reduced sugar yield of 92.1% was obtained from the WS pre-treated by the PDR at 10 bar. Meanwhile, the highest total reduced sugar yield obtained from the ADR was 74.6%.
The hemicellulose removal in the liquid fraction for the SE, LHW and microwave was reported. The overall sugar recovery (including the total reduced sugar yield after EH and the extracted sugars in the liquid fraction (if applicable)) yield was calculated and reported. The overall sugar recovery yield for the SE and LHW pre-treatment with H2O and H2SO4 (3%, wt/wt) was 72.4%, 82.7% and 69.5%, 85.6%, respectively. The highest overall sugar recovery yield of 93.4% was achieved by applying microwave pre-treatment method on the WS at 200 °C, 120 min, 900 W and with H2O volume 30 mL. The microwave pre-treatment conditions were optimized to reduce the pre-treatment time. The optimum microwave pre-treatment time was found to be 200 °C, 42.8 min, 900 W and 30 mL at which the overall sugar recovery yield was 88.4%.
Moreover, the effects of the pH value during the EH process was evaluated to find the optimum pH value in which the total reduced sugar yield reach its maximum potential. The ground WS to the particle size of < 250 μm was used to investigate the pH effect on the EH process. Different enzymes cocktails including Celluclast 1.5L supplements with Novozymes 188, Cellic CTec2 and endo-1, 4-β-Xylanase were used in the pH study (pH 3.0 to 7.0). The highest concentration of the total reduced sugar liberated during EH was obtained by carrying out the EH at pH 5.8 - 6.0 for all the different enzymes used in the current study. At the optimum pH value (5.8 and 6.0), the total reduced sugar concentration after the EH for Celluclast 1.5L with Novozymes 188, endo-1, 4-β-Xylanase and Cellic CTec2 were found to be 7.0, 7.4 and 10.8 g L-1, respectively.

Citation

Abdulsattar, M. O. (2019). Bio-ethanol Production from Wheat Straw Using Different Pre-treatment Approaches. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4912531

• Thesis Type: Thesis
• Deposit Date: Nov 12, 2024
• Publicly Available Date: Jan 6, 2025
• Keywords: Chemical engineering
• Public URL: https://hull-repository.worktribe.com/output/4912531
• Additional Information: Department of Chemical Engineering; University of Hull
• Award Date: Jun 1, 2019