- Title
- Rational catalyst synthesis for the chemical conversion of propane-1,2-diol to value-added products
- Creator
- Akhter, Taslima
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The increased cost of fossil fuel extraction globally is becoming an increased concern, thus the use of biodiesel as a renewable fuel has gained the attention in the last decades due to the increase in energy demand, and the contribution of CO2 emissions to climate change. However, the development and establishment of a sustainable and profitable biodiesel industry is strongly subjected to the commercial value of the main yet undesirable by-product, glycerol that is major cost to the biodiesel industry, even though it is a low cost and readily available reactant. The study of new applications for crude glycerol is necessary to minimise the projected surplus supply as well as to improve the overall affordability of the biodiesel production. Several technological options are introduced by the conversion of glycerol into value added products by now, however, catalytic hydrogenolysis of glycerol into propane-1,2-diol is an important research attention due to its industrial prominence i.e., production of pharmaceuticals, food, cosmetics, in addition as engine coolant, de-icing agent, and the raw material for polyester resins. Substantial work has been carried out to the catalytic glycerol hydrogenolysis to propane-1,2-diol previously and these processes have the prospective to deliver a renewable and economic source of propane-1,2-diol. In this study, the primary objectives of the research were to advance one or more processes for the direct and continuous conversion of propane-1,2-diol into value-added chemicals on a unit operation that can be utilized to scale up for the industrial applications. Moreover, the minimisation of secondary reactions and by-products was preferred considering both economic and environmental benefit herein the analysis. Propionaldehyde is an important chemical intermediate used extensively in the manufacture of rubbers, plastics, paints, and pesticides; nonetheless, it is typically produced by petroleum-derived processes such as ethylene hydroformylation, propylene oxide isomerisation, and acrolein hydrogenation and so on. Overall, the currently available literature is mainly concerned with gas phase dehydration of 1,2-propanediol over acidic media, the main product formed is propionaldehyde. Due to increased petroleum costs and climate change concerns, the availability of processes to synthesise propane-1,2-diol from glycerol delivers the opportunity for a two-step process to propionaldehyde from glycerol that aids both environmental and economic incentives. Acidic catalysts such as ZSM-5 have been extensively used in various dehydration reaction of diols since these catalysts can preferentially remove a OH group from the diols. In the literature, the size and shape of ZSM-5 pores are also acknowledged to affect the product distribution in such dehydration reactions thus in this study H-ZSM-5 (SAR 30) was used. However, a secondary dehydration also occur that causes the formation of by-product: 2-ethyl-4-methyl-1,3-dioxolane and with proper measure reduction of such by-product was possible. In addition, selectivity to the dioxolane was found to be high at a greater GHSV and was independent of temperature. The formation of the propanol and propene were proportional towards the selectivity of dioxolane. However, the incorporation of the steam along with the reactant increased the overall conversion of propane-1,2-diol, and the selectivity towards propionaldehyde. The selectively of one reactive site relative to the other reactive sites must be higher in a multifunctional compound to proceed a chemical reaction, thus, protective group is introduced by chemical modification to temporarily decrease the reactivity of that functional group. Cyclic acetals are five or higher-membered monomers formed by the acid-catalyzed reaction of an aldehyde or ketone with a diol, are one of the carbonyl compound derivatives that are generally used in organic synthesis as the ‘protecting groups’ for aldehydes and ketones. According to the literature, the acetals are generally synthesized in the presence of corrosive acid catalysts, Nevertheless, the parameters for such acetals formations over H-ZSM-5 were not favourable, thus to achieve higher selectivity of such acetals, the higher GHSV was preferred leading to increasing coke formation thus subduing its use in the long-term application. In this study, another catalyst with the unique acid site (H-B-MFI) has been introduced to increase the selectivity of acetals over propionaldehyde. The modified hydrothermal synthesis of such catalyst was conducted in our laboratory for the purpose of this study. The characterization study resulted in findings that the incorporation of B in the MFI zeolite reduced the total surface area as well as the pore volume of the B-MFI sample and increased the external surface area. Additionally, a substantial rise in the weak acid site density for the boron containing species was also observed. This study relates to a process for preparing acetals, e.g., 4-methyl-1,3-dioxolane, 2,4-dimethyl-1,3-dioxolane ,2-ethyl-4-methyl-1,3-dioxolane and the like, by condensing an aldehyde of formula RCHO wherein R is a member of the class consisting of –H or -alkyl with propane-1,2-diol. In the preparation of acetals, the performance of the as synthesised catalyst H-B-MFI was found more effective than the H-ZSM-5 and the probable reason was the unique weak acid sites of H-B-MFI. The effects of reaction temperature have also been investigated; with the increase of temperature, the selectivity of acetals increases for both catalysts. To recognize and evaluate the catalytic activity and to identify the pathways of a reaction, it is important to measure the molecular properties. One of the dynamic properties, the activation energy of the reaction, is significant for the modelling of reaction kinetics and by using an appropriate rate of reaction equation. In this study, to understand the nature of the two-step reactions for the synthesis of the cyclic acetals, 2-ethyl-4-methyl-1,3-dioxolane, the overall activation energy of the catalytic dehydration of propane-1,2-diol was determined and that is 97 kJ.mol-1. In addition, the activation energy for the overall reaction of the condensation reaction of propane-1,2-diol with propionaldehyde was estimated. Comparing the value of these two activation energies, the slowest step was identified, and it can be illustrated that the rate-limiting step or slow step in the formation of 2-ethyl-4-methyl-1,3-dioxolane in the dehydration of propane-1,2-diol over H-ZSM-5 is the first step, that is the formation of propionaldehyde from propane-1,2-diol. This phenomenon also suggests that the second step is spontaneous if the concentration of the propane-1,2-diol remains higher. Moreover, this occurrence validates the effect of the molar ratio over the selectivity of 2-ethyl-4-methyl-1,3-dioxolane that has been summated. In this study, the primary objectives of the research were to advance one or more processes for the direct and continuous conversion of propane-1,2-diol into value-added chemicals i.e., Propionaldehyde, cyclic acetals that can be utilized not only to scale up for the industrial applications but also to minimise by-products taken into consideration of economic and environmental benefits. H-ZSM-5 (SAR 30) and (H-B-MFI) has been utilized for the production of propionaldehyde and acetals respectively. In the preparation of acetals, the performance of the as-synthesised catalyst H-B-MFI was found more effective than the H-ZSM-5 and the probable reason was the unique weak acid sites of H-B-MFI. The effects of reaction temperature have also been investigated; with the increase in temperature, the selectivity of acetals increases for both catalysts. None the less, one of the vital properties, the activation energy of the reaction that is significant for the modelling of reaction kinetics was calculated to understand the nature of the two-step reactions for the synthesis of the cyclic acetals, and the slowest step was also determined.
- Subject
- conversion; propane-1,2-diol; catalyst synthesis; value-added products
- Identifier
- http://hdl.handle.net/1959.13/1506582
- Identifier
- uon:55908
- Rights
- Copyright 2024 Taslima Akhter
- Language
- eng
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