Conversion of biomass into value-added chemicals

Green house gas emissions, the depleting of non-renewable resources, and poor waste management have a detrimental environmental and socioeconomic impact. Consequantly, the development of alternative processes that alleviate these problems is imperative. Apart from being an energy source, biomass has the capability of providing solid, liquid and gaseous forms of energy carriers and chemicals that can be transformed into analogues of those originating from fossil fuels. This thesis provides some ways in which the aforementioned problems could be tackled with a focus on the development of novel catalytic conversion processes that transforming cellulose, sourced from plant biomass, into key platform chemicals. A general overview of biomass transformation technologies is provided in chapter 1. The conversion of various biomass derivatives into 5-hydroxymethylfurfural (HMF) has been identified as a key route as HMF serves as a precursor to numerous platform chemicals. We achieved significant improvements in downstream biomass processing pathways by performing an extensive design and detailed investigations into understanding the reaction mechanism and optimization of various catalytic systems. In particular, chapter 2 is dedicated to the design of a new ionic liquid that enhances the conversion of glucose into HMF, in combination with a CrCl2 pre-catalyst, affording HMF in a yield significantly superior to that obtained in other ionic liquids and allowing the process to operate under milder conditions to those required by other catalysts. In chapter 3 we describe the development of the transformation of more complex carbohydrates such as starch and cellulose, using novel ionic liquid mixtures. Here, we obtained high yields of HMF, whereas no product was observed when ionic liquids from the current state of the art were employed, demonstrating the efficacy of the new system. Although HMF is a key intermediate, its transformation into other value-added molecules is also important. A key derivative of HMF is 2,5-furandicarboxylic acid (FDCA), which is bio-based substitute of the petroleum-based monomer for the plastics industry. FDCA-derived polymers have outstanding properties that match or even excel the current market benchmark polymer, i.e. PET. In chapter 4 we present the development of a novel Pt-based catalyst for HMF oxidation, affording quantitative yields of FDCA, under mild conditions. In chapter 5 a new bimetallic rhodium-nickel catalyst for the hydrogenation of HMF is described. In water the catalyst is able to convert HMF into 3-hydroxymethylcyclopentanone (HCPN) in 90% yield whereas in organic solvents other products are obtained: e.g. 60% of 2,5-dimethylfuran (DMF) in 1,2-dimethoxyethane (DME)/formic acid (FA) mixture. These products have widespread uses as alternative fuels and have high commercial value for the market.