Development of novel homogeneous and magnetic heterogeneous catalysts using paracetamol-based deep eutectic solvents for esterification of free fatty ACIDS / Andrew Yeow Tze Hao

Andrew Yeow , Tze Hao (2024) Development of novel homogeneous and magnetic heterogeneous catalysts using paracetamol-based deep eutectic solvents for esterification of free fatty ACIDS / Andrew Yeow Tze Hao. Masters thesis, Universiti Malaya.

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Abstract

Oil palm milling processes generate large quantities of byproducts such as low-quality crude palm oil (LPO) that contain high free fatty acid (FFA) content. The use of these high FFA raw materials present major challenges as feedstocks for biodiesel production due to saponification reactions. Therefore, esterification reaction is the typical pretreatment process for high FFA feedstocks using methanol and acidic catalysts (such as sulphuric acid). In the works of this thesis, new homogeneous and heterogeneous acidic catalysts were developed. The homogeneous acid catalysts were developed based on deep eutectic solvents (DESs). Herein, paracetamol (PCM) was reported as a novel DES formed with Brønsted acids (5-sulfosalicylic acid (SSA) and benzenesulfonic acid (BZSA)) at a 3:1 molar ratio. At the optimized reaction conditions of 1.5 wt% DES catalyst dosage, 8:1 methanol-to-oil molar ratio, 50 °C reaction temperature for 50 min reaction time, the [3BZSA:PCM] DES achieved high FFA conversion at 86.4 %. On the other hand, at the optimized conditions of 2.5 wt% DES catalyst dosage, 16:1 methanol-to-oil molar ratio, 60 °C reaction temperature for 90 min reaction time, the [3SSA:PCM] DES achieved similarly high FFA conversion at 86.0 %. The activation energy was determined for the catalytic reaction using [3BZSA:PCM] and [3SSA:PCM] DESs, as 40.91 and 50.89 kJ/mol respectively, following the pseudo first order rate of reaction. Through the Eyring-Polanyi thermodynamic study, the DES-catalysed esterification reactions were endothermic, non-spontaneous and endergonic. However, the homogeneous DES catalysts exhibit challenges in recyclability and separation despite its high catalytic efficiency. Magnetic composites (Fe3O4/PVA) as support materials for acid catalysts is a viable protocol in improving the recyclability and separation performances. Therefore, SSA, BZSA, p-toluenesulfonic acid (PTSA) and their DES counterparts (formed with paracetamol at 3:1 molar ratio) were investigated to be supported on Fe3O4/PVA to yield heterogeneous catalysts for FFA esterification in LPO. From the screening results, Fe3O4/PVA/PTSA was determined as the best catalytic activity for FFA esterification reaction. The optimized reaction conditions were determined: 10 wt% catalyst loading, 20:1 methanol-to-oil molar ratio, 5 h of contact time and at 60 °C, resulting in an FFA conversion of 79.81 %. Fe3O4/PVA/PTSA exhibited fair recyclability performances and stability with > 65 % FFA conversion after five successive runs. FFA esterification reaction using Fe3O4/PVA/PTSA was determined to require an activation energy of 43.72 kJ/mol following the pseudo first order rate of reaction. By comparing the operating conditions of both types of catalysts, the heterogeneous Fe3O4/PVA/PTSA magnetic catalyst required double the reaction conditions compared to the homogeneous DESs in catalysing the esterification reaction. However, from the perspective of catalyst recyclability, the magnetically recoverable Fe3O4/PVA/PTSA catalyst can be recycled for five times with improved stability, while the homogeneous DESs exhibited significant challenges in catalyst recycling. Additionally, the pristine sulphonic acids exhibited better compatibility to be supported on Fe3O4/PVA magnetic composite than their DES counterpart, with Fe3O4/PVA/PTSA being a viable catalyst for the pretreatment of low-quality oils through FFA esterification.

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