Acid catalyzed carbohydrate degradation and dehydration

Facile commercial production of versatile polyfunctional compounds from biomass constitutes a great challenge in establishing a sustainable chemical industry. One such example is the production of furfural and hydroxymethyl furfural (HMF) via dehydration of pentoses and hexoses, respectively. These chemicals are of great interest as primary building blocks in the polymer industry. However, their large scale production is hindered due to several problems, such as feedstock availability, low product yields due to excessive side reactions and lack of an industrially feasible heterogeneous catalyst.;Organic acid functional groups incorporated onto mesoporous silica offer well defined catalytic sites in addition to the unique textural properties and thus give the material the potential to be a promising catalyst. However, a rational approach for fine tuning of the catalyst properties to meet the reaction system requirements entails detailed understanding of the nature of the catalytic sites in condensed phase under the conditions that mimic the reaction environment. Towards that aim, the current work presents a methodology for the characterization in condensed phase, using potentiometric titrations. Procedures for accurately determining the acidic strength and total acid capacity of the organic acid functionalized materials are presented. The results revealed that organic acid moieties of different strength display their characteristic acidity without being leveled in water. The strongest acid was the arene sulfonic group followed by propyl sulfonic, ethyl phosphonic and butyl carboxylic.;The results obtained for propyl sulfonic and arene sulfonic groups were not in complete agreement with literature. The discrepancy could be attributed to the fact that most of these previous studies had examined the interaction of the acidic group with a gas phase probe molecule, while the effect of solvation was neglected. In the present work, the effect of solvation on the acidic strength of these moieties was investigated via quantum chemical simulations. A change in the acidic strength trend was observed with the increasing number of water molecules, indicating that one-to-one interaction in the gas phase does not necessarily represent the interaction of the moiety with the solvent molecules.;The difference in the acidic strength for these organic acid groups incorporated onto mesoporous silica was not observed when they were tested for their activity on hexose and pentose dehydration due to poor hydrothermal stability of the materials at elevated temperatures. Sulfated zirconia doped mesoporous silica materials, which displayed high activity in cellobiose hydrolysis, did not provide desired hydrothermal stability either for dehydration reactions. Further research is focused on developing a hydrothermally stable catalyst for condensed phase reactions.;Although a lot of study has focused on monosaccharide decomposition, the information available in literature is highly unorganized and does not provide the insight about the catalytic properties or process conditions required for high yields. The current work presents a systematic study with homogeneous mineral and organic acids of varying strength to build a platform for catalyst comparison. The study revealed that depending on the pH of the solution, different mechanisms underlie the glucose decomposition in the presence of weak acids. Although lower acid concentration leads to higher selectivity toward HMF, this could not be considered as an industrially viable solution.;While attempting to develop an industrially feasible process to obtain high yield of HMF from glucose, it was discovered that addition of alkaline earth metals and application of pressure in the presence of acid catalyst activates the glucose ring resulting in high HMF yields. Further enhancement was obtained by addition of an organic phase for HMF extraction. This unprecedented process can be combined with polysaccharides hydrolysis and one pot HMF production from biomass. By further optimization of the parameters, an industrially feasible process for HMF production can be achieved.;Thus current work is very significant and relevant in providing perceptions for developing an industrially feasible process with heterogeneous acid catalysts to produce furanic compounds from biomass.