Catalyst development for biomass conversion to fuel and high value added chemicals
Creators: name: Ravi, Krishnan
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340601
subject: Catalysis and mechanisms of reactions

description: Concerns about the depletion of petroleum resources and the environmental impact of CO2 emissions have sparked a growing interest in developing alternatives to fossil fuels. Biomass, including lignocellulosic biomass, is indeed a valuable resource for the production of chemicals, fuels, and materials to meet future societal needs. Lignocellulosic biomass comprises cellulose, hemicellulose, and lignin, which are complex and highly oxygenated compounds. The high oxygen content and structural complexity of lignocellulose present challenges for its conversion into carbon-based materials or chemicals. One of the main hurdles is the recalcitrance of lignocellulose, which refers to its resistance to being broken down or converted. The recalcitrance of lignocellulosic biomass arises primarily from the strong hydrogen bonding within its  structure. The hydrogen bonds make the biomass more rigid and resistant to chemical and biological degradation. 

Breaking down these bonds and efficiently converting lignocellulosic biomass into valuable products require specialized catalysts and processes. Researchers are  actively investigating various strategies to overcome the challenges associated with lignocellulosic biomass conversion. These include pretreatment techniques to weaken the biomass structure, enzymatic or microbial methods to break down the complex carbohydrates into simpler sugars, and catalytic processes to convert these sugars into desired chemicals or fuels. Efforts are also being made to develop catalysts that can effectively depolymerize lignin, the aromatic component of lignocellulosic biomass. Lignin is particularly challenging due to its complex and heterogeneous nature. However, advancements in catalysis and biomass processing technologies are improving the efficiency and selectivity of lignin valorization. The development of cost-effective and sustainable processes for lignocellulosic biomass conversion is crucial for realizing itsfull potential as a renewable feedstock. Such advancements can contribute to reducing the global reliance on petroleum resources, mitigating CO2 emissions, and promoting a transition to a more sustainable and environmentally friendly bio-based economy. 

The research described in chapters 3 and 4 of the thesis focuses on using sugarcane bagasse, a type of lignocellulosic biomass, to synthesize various carbon materials. The synthesis process involves hydrothermal treatment, followed by high temperature pyrolysis. Two specific carbon materials are explored: N-doped carbon and SO3H functionalized hydrochar. N-doped carbon refers to carbon materials that have been modified with nitrogen-containing functional groups. These materials were synthesized using sugarcane bagasse as the precursor. The N-doped carbon materials synthesized from sugarcane bagasse were then investigated for their catalytic properties in the reductive amination of bio-derived aldehydes. Bio-derived aldehydes, such as furfural, 5-methylfurfural, 5-hydroxymethylfurfural, and vanillin, are important intermediates in biomass valorization processes. The N-doped carbon catalysts showed promise in facilitating the reductive amination reactions of these aldehydes. The second carbon material investigated is SO3H functionalized hydrochar. Hydrochar is a carbonaceous material obtained from the hydrothermal treatment of biomass. In this case, sugarcane bagasse was used as the feedstock. The hydrochar material was functionalized with SO3H groups, which are sulfonic acid functional groups. The SO3H functionalized hydrochar catalysts were then employed in alcoholysis, followed by ring-opening reactions of furfuryl alcohol to produce alkyl levulinates. Alkyl levulinates are valuable chemicals that can find applications as solvents or fuel additives. Additionally, the same SO3H functionalized hydrochar catalysts were used in the acetalization of glycerol with carbonyl compounds to produce solketal derivatives. Solketal is a cyclic acetal derived from glycerol and is used as a solvent or fuel additive. The catalysts were also employedin the hydroxyalkylation reaction of 2-methylfuran with carbonyl compounds to synthesize fuel precursors. Hydroxyalkylation involves the addition of hydroxyl groups to the carbonyl compounds, which can enhance their fuel properties. Overall, the research presented in the thesis explores the synthesis of carbon materials from sugarcane bagasse and theirapplications in biomass valorization processes. The N-doped carbon and SO3H functionalized hydrochar catalysts derived from sugarcane bagasse show potential in catalyzing various important reactions involved in biomass conversions, such as reductive amination, alcoholysis, ring-opening reactions, acetalization, and hydroxyalkylation. These findings contribute to the development of sustainable and efficient processes for utilizing biomass resources and producing valuable chemicals and fuels. 

In Chapter 5 of the thesis, the focus is on the synthesis of levulinic acid from sugarcane bagasse through hydrothermal treatment. By utilizing sugarcane bagasse as the feedstock, the hydrothermal treatment process aims to convert the biomass into levulinic acid, which can then be further processed into value-added products. During the hydrothermal treatment, solid residues are formed as byproducts. These solid residues are utilized as catalyst supports in hydroformylation reactions. The solid residues derived from the hydrothermal treatment of sugarcane bagasse act as catalyst supports, facilitating the hydroformylation reaction directly from olefins. By using the solid residues as catalyst supports, the aim is to directly convert olefins into fuel precursors. 

In Chapter 6 of the thesis, the focus is on the synthesis of a basic catalyst through direct amine functionalization on sugarcane bagasse. Sugarcane bagasse, a lignocellulosic biomass, is modified by introducing amine functional groups onto its surface. The amine-functionalized sugarcane bagasse is then treated with n-butyl bromide to synthesize tethered quaternary ammonium salts. The formation of quaternaryammonium salts on the sugarcane bagasse surface is confirmed through X-ray photoelectron spectroscopy (XPS) analysis, which provides information about the elemental composition and chemical bonding of the material. The resulting quaternary ammonium salt functionalized sugarcane bagasse serves as a catalyst for the additive-free cycloaddition of carbon dioxide (CO2) with various epoxides. By utilizing the quaternary ammonium salt functionalized sugarcane bagasse as a catalyst, the aim is to promote the cycloaddition reaction between CO2 and epoxides without the need for additional additives. This approach simplifies the reaction process and reduces the reliance on external catalysts or co-catalysts. 

In the final chapter of the thesis, the focus is on the synthesis of mesoporous Al SBA-15, a type of mesoporous material, using the true liquid crystal templating method. After synthesizing mesoporous Al-SBA-15, the material is then impregnated with Rh nanoparticles. High-resolution transmission electron microscopy (HRTEM) topography images are employed to characterize the synthesized material. The images clearly reveal the presence of channels within the mesoporous Al-SBA-15 structure. These channels play a crucial role in facilitating the diffusion of reactants and products during catalytic reactions. The Rh nanoparticles loaded onto the mesoporous Al-SBA-15 serve as a catalyst for the one-pot synthesis of fuel precursors directly from tandem olefin hydroformylation. By utilizing the Rh catalyst supported on mesoporous Al-SBA-15, the aim is to enable the direct synthesis of fuel precursors in a single-step reaction. The mesoporous structure of Al-SBA-15 provides a large surface area and accessibility, while the Rh nanoparticles act as active sites for the catalytic conversion of olefins to aldehydes.