Valorization of glycerol for commodity chemicals through vapour phase hydrogenolysis over supported platinum catalysts
Creators: name: Samudrala, Santhi Priya
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 340307
subject: Structure and dynamics of materials
classificationCode: 340601
subject: Catalysis and mechanisms of reactions

description: The global demand for energy, fuels and chemicals, along with the decline in fossil fuel resources has significantly led to the rise of renewable energy sources. In this regard, biomass represents one of the most promising, alternative resources for the sustainable production of fuels and chemicals. Biodiesel derived from plant biomass is a renewable fuel produced on a large scale over the past decade by the transesterification of oils. Glycerol is considered to be a promising three carbon feedstock, obtained in large quantities as a by-product during biodiesel production. Since glycerol can be obtained from renewable sources, it clearly emerged as a versatile feedstock instead of petroleum based chemicals. This generated a lot of interest in developing new valorisation technologies to produce high value tonnage chemicals from glycerol by sustainable processes. One such attractive application is the catalytic hydrogenolysis of glycerol to value-added chemicals such as propanediols and propanols. Due to the broad applications of these compounds, glycerol hydrogenolysis has been extensively studied in the past decade, both in liquid phase and in vapour phase, for which various metal-based catalysts have been explored, including supported Rh, Ni, Ru, Pt and Cu.<br><br>Present research work is mainly focussed on the selective production of 1,3-propanediol and propanols through glycerol hydrogenolysis over platinum-based catalysts in vapour phase at moderate reaction temperatures and atmospheric pressure. In this work, various supported platinum catalysts have been synthesised by wet impregnation method. The supports used in the study include zirconia, sulphated zirconia, gamma alumina, aluminium phosphate, activated carbon, Y-zeolite, H-mordenite and SBA-15. In addition, metal acid bifunctional catalysts such as Pt-HPAs/ZrO2 and Pt-WO3/SBA-15 have been synthesized via sequential and co-impregnation methods. The prepared catalysts were well characterized by various spectro-analytical techniques and the catalytic properties were evaluated for selective hydrogenolysis of glycerol to 1,3-propanediol and propanols in vapour phase under atmospheric pressure. A detailed study investigated the influence of metal loading, reaction temperature, reduction temperature, glycerol concentration, hydrogen flow rate, feed flow rate, catalyst amount and time on stream studies. In addition, structural aspects of spent catalysts were also evaluated to study possible catalyst deactivation. The investigated catalysts exhibited moderate to high activity towards glycerol hydrogenolysis with optimal conversion and selectivity. Metal dispersion and acidity of the catalysts were found to be the key parameters for the catalytic performance of various supported platinum catalysts in glycerol hydrogenolysis as evidenced by the results obtained from various characterization techniques.<br><br>It is proposed that glycerol hydrogenolysis proceeds via a two-step mechanism involving the dehydration of glycerol to 3-hydroxy propionaldehyde over acidic sites and further hydrogenation into 1,3-propanediol over metal sites. The sequential hydrogenolysis of propanediols over strong acidic sites leads to the formation of lower alcohols such as 1-propanol and 2-propanol. The present study was successful in providing a sustainable and economically viable methodology to convert biomass-derived glycerol into value-added chemicals, such as 1,3-propanediol and propanols. The supported platinum catalysts were proven to be highly efficient catalysts for selective glycerol hydrogenolysis with excellent conversions and selectivities towards the desired products.