Sanphawat Phromphithak. Lignocellulosic biomass pretreatment with green ionic liquid-based solvents and applications. Doctoral Degree(Energy Engineering). Chiang Mai University. Library. : Chiang Mai University, 2024.
Lignocellulosic biomass pretreatment with green ionic liquid-based solvents and applications
Abstract:
Fossil fuels have served as the primary source of energy for an extended period, despite the considerable environmental risks such as greenhouse gas emissions. The pursuit of renewable alternatives to fossil materials has led to the study of producing energy and fuel from lignocellulosic biomass. However, the efficiency of converting lignocellulosic biomass is limited due to the network of lignin-carbohydrate complexes acting as a barrier to efficient biomass conversion. To overcome the limitation and enhance the efficiency of converting lignocellulosic biomass, these components can be improved through fractionation and delignification. The pretreatment of biomass with ionic liquid-based solvents has proven to be effective in achieving these results. Machine learning (ML) can be used as a tool for understanding the biomass pretreatment with ionic liquid-based solvents. The remaining solid residue resulting from the extraction of hemicellulose and lignin led to an increase in cellulose content as known as cellulose-rich material (CRM). Machine learning algorithms were employed to predict CRM properties, particularly cellulose enrichment factor (CEF) and solid recovery (SR), utilizing 23-feature datasets that include biomass characteristics, operating conditions, solvent system identities, and catalyst. The random forest algorithm demonstrated the highest prediction accuracy. The important features in making predictions were primarily related to biomass characteristics and solvent treatment operating conditions. One- and two-way partial dependence plots were used to elucidate the multi-dimensional relationships among the most important features. The lignocellulosic biomass was employed to investigate the effects of reaction temperatures (60150 °C), residence times (615 h), molar ratio of ionic liquid-based solvents with choline chloride to glycerol (1:0.5-4), biomass type (corncob, giant juncao grass, and inflorescence hemp), ionic liquid types in systems (choline chloride, choline acetate, and choline hydroxide), and pretreatment methods (conventional heating and microwave-irradiation heating). The results demonstrated the effective extraction of hemicellulose and lignin from raw biomass resulting in the production of the CRMs. These results in each variant led to a better understanding of lignocellulosic biomass pretreatment with ionic liquid-based solvents. The microwave-irradiation heating exhibits high performance in lignocellulosic fractionation compared to conventional heating. Additionally, the process allows for the optional preservation of hemicellulose at lower temperature or its extraction at higher temperature. Corncob, a common agricultural biomass waste found in many countries, was selected as a representative of typical lignocellulosic biomass. It was chosen as precursor materials for producing absorbents for capturing CO2. The corncob was employed to produce CRMs, which then underwent hydrothermal carbonization to produce hydrochars. The corncob, CRMs, and hydrochars were utilized as feedstock to produce activated chars. The feedstocks activated chars and activated chars were then analyzed to evaluate their characteristic properties. Furthermore, the activated chars were tested for CO2 adsorption capacity to demonstrate their efficiency. The results indicated that, the pretreatment of biomass with an ionic liquid-based solvent is effective in achieving delignification, while hydrothermal carbonization has the potential to further fractionation. The activated feedstock exhibited differences in morphology, thermal stability, crystallinity of cellulose, and chemical functional groups. These differences in the feedstock resulted in specific characteristics in each activated char. The pretreatments and hydrothermal carbonization had an influence on the morphology of the activated chars. These processes led to an increase in specific surface area and changes in pore structure parameters. Overall, the activated chars produced through pretreatments and/or hydrothermal carbonization showed an enhanced CO2 adsorption capacity. The highest CO2 adsorption capacity, approximately 78 mg CO2/g char, was achieved through a combination of ionic liquid-based solvents pretreatment and hydrothermal carbonization.