Zeolite Catalysts for the Selective Conversion of Sugars into Polymer Monomers

The current society is highly dependent on materials derived from fossil feedstock, but the emergent environmental issues impose urgent changes in the production of chemicals. However, the transition to the use of sustainable sources requires the development of new technologies capable of processing the chemical functionality of the new starting materials. The Cat2BioChem project aimed to develop methodologies for the production of bio-based monomer polymers. In particular, the work performed in this thesis focused on the conversion of carbohydrates into different hydroxy esters using stannosilicate catalysts. The study started with understanding the already known process for the production of methyl lactate from hexoses using Sn-Beta zeolite as the catalyst. Methyl lactate is the monomer of polylactic acid, the most common bio-based biodegradable plastic, and the optimization of the parameters of the chemocatalytic production process can widen the applicability of the material. The use of 1D and 2D NMR techniques allowed following the formation of intermediates and products over time. In the thesis, the role of methyl glycosides during the conversion of carbohydrates in methanol using zeolite catalysts is discussed in detail and a kinetic model for the formation of methyl lactate from hexoses is proposed. Fructose was identified as central reactive specie during the reaction starting from both sucrose and glucose. Thus, a method for the production of fructose from the cheaper and more available sucrose using commercial zeolite catalysts is also presented. The work continued with the study of the conversion of glycolaldehyde under similar conditions to the process for methyl lactate considered previously. In this case, the ability of the Lewis acidic catalyst to promote aldolic pathways led to the formation of a four-carbon hydroxy ester, methyl vinyl glycolate (MVG), as the main product. The molecule of MVG includes functionalities interesting for polymer applications and represents a new building block for the creation of bio-based materials. Different parameters involved in the process were studied and a kinetic model for the formation of MVG from glycoladehyde is currently under investigation. The last part of the thesis focuses on the optimization of the catalytic system used for the conversion of carbohydrates into hydroxy esters. Modifications in the procedure for the synthesis of Sn-Beta zeolite can improve the performances of the catalyst and facilitate the application in industrial processes. Thus, the effect of different parameters involved during the preparation of the catalysts was explored. Mesoporous stannosilicates showed improved activity during the conversion of large substrates at short times. Moreover, the catalytic materials were characterized using different techniques in order to investigate the structure-activity relation. The study analyzed the interaction between the catalyst and additives, such as alkali salts, in order to achieve better understanding of the structures active in the formation of the desired products and help in the future design of new catalysts. In conclusion, this thesis contributes to enlarge the current knowledge about the processes for the production of bio-based monomers, explaining the parameters relevant for the conversion of carbohydrates and considering routes for the optimization of the catalytic system.