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Title: Heteropolyacids Based Heterogeneous Catalysts for the Transesterification of Triglycerides
Authors: Singh, Himmat
Supervisor: Ali, Amjad
Kumar, Davinder
Keywords: Transesterification;Triglyceride;Methanol;Waste Oil;Heteropolyacids
Issue Date: 17-May-2023
Abstract: The energy requirement is essential for human life, and the majority of need had been placed on non-renewable materials such as carbon fuels. Within that scenario, biofuel has become a feasible substitute for traditional diesel fuel which is also environmentally beneficial. In essence, biodiesel is made by transesterifying triglycerides throughout the presence of solid heterogeneous, homogeneous, or enzyme catalysts to produce methyl esters of fatty acid. NaOH and KOH, ordinary and conventional homogeneous basic catalysts, are incredibly effective for commercial-scale biodiesel generation. Though, that method delays the products that are contaminated with catalyst while producing a significant amount of waste material during the washing and refining procedures. As a result of their tolerance for water and free fatty acid, homogeneous alkali catalysts cannot be used to transesterify waste oils, necessitating the use of costly refined oil that has had free fatty acids and moisture freed from it. Supported heteropolyacids reusable and stable catalysts have gained enormous interest recently in an effort to circumvent the problems associated with uniphasic catalysts. In present thesis, three different heterogeneous catalysts K/TPA/Al2O3, K/TPA/SiO2, and K/TPA/GO were prepared. These catalysts were prepared utilising a wet impregnation process under normal air conditions rather than a severe hydrothermal method. The synthesized catalysts were characterised using a variety of analytical techniques, including powder XRD, FTIR, Raman, CO2 and NH3-TPD, TGA, FE-SEM, XPS, SEM-EDS, HRTEM, and Hammett indicator investigations. These catalysts were successfully applied to the generation of biodiesel from used cottonseed oil. Due to the generation of acidic and basic sites on its surface, the catalyst (K/TPA/Al2O3) was able to carry out the simultaneous esterification and transesterification reaction, and it took 1.25 h at 65 °C to complete the trans - esterification of used cottonseed oil (> 97 0% biodiesel yield). The catalyst displayed good recyclability by being active for the fourth consecutive run. Another catalyst (K/TPA/SiO2) was produced using a simple wet incipient technique. The catalyst was used to conduct both esterification and transesterification of triglycerides. The fact that very little metal leaching (< 2 ppm) was found in the fifth and sixth cycles, which was within ASTM defined limits, was a significant characteristic for the application of this catalyst. However, despite the presence of substantial levels of free fatty acids (up to 8.8 wt%) and moisture (up to 4 wt%) contents, the catalyst continued to operate efficiently. To minimize the reaction period, wet incipient technique was used to manufacture K and TPA imbued graphene oxide. The produced catalyst was used to synthesise biodiesel from waste cooking oil, and its activity was dependent on its acidic and basic strength. This catalyst could produce up to > 98.5% FAMEs in 1.5 hours, even when exposed to high externally supply free fatty acid (up to 8.76 wt%) and moisture content (up to 4 wt%). According to the regeneration study, the catalyst can be recycled for the sixth time without significantly reducing activity. The kinetic modelling study by using MATLAB software, indicate that transesterification reaction follow the pseudo first order kinetic law. The entropy of activation value shows that, the reaction of triglyceride to diglyceride proceed via associative pathway. As a result, the heterogeneous mode of action has been accurately reflected by all manufactured catalysts. All of the produced catalysts catalysed transesterification with (pseudo) first order kinetics and an experimentally measured activation energy of >25kJ/mol, indicating that the reaction was chemically regulated rather than by diffusion/mass transfer restrictions. The positive values of ΔH‡indicates that reaction were of an endothermic in nature and required external heat to proceed the reaction toward forward direction.
Description: Ph.D. Thesis
Appears in Collections:Doctoral Theses@SCBC

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