Purification of biodiesel using deep eutectic solvents in liquid membrane separator with activated carbon and graphene / Khalid Mohsin Abed`

Khalid Mohsin , Abed` (2024) Purification of biodiesel using deep eutectic solvents in liquid membrane separator with activated carbon and graphene / Khalid Mohsin Abed`. PhD thesis, Universiti Malaya.

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Abstract

The biodiesel industry is an essential aspect of renewable energy, but it has limitations due to contaminants, in particular the soap content. The present study focuses on the development of a water-free downstream process to remove the soap from crude biodiesel. Emulsion liquid membrane (ELM) technique has been employed, and it has been used for purifying different contaminants. Green solvents such as deep eutectic solvents (DESs) is used as a stripping phase, and carbon materials (activated carbon and graphene) are integrated to enhance the DES for soap removal. Activated carbon (AC) was synthesized from palm raceme-derived biomass due to its plentiful supply and environmental sustainability. Lipase activity was utilized as an indicator to assess the optimal AC under different parameters as well as to investigate the biocompatibility of AC and DES. The results showed that the optimum conditions of AC’s synthesis were 0.5 impregnation ratio, 150 minutes, and 400 °C. DES prepared from alanine/sodium hydroxide exhibited good biocompatibility with AC. AC was integrated with two different techniques which are DES-based liquid-liquid extraction and novel DES-based ELM for soap removal from biodiesel. Additionally, computational screening of different DESs via COSMO-RS was used in the ELM system for soap removal. This particular study highlights the potential of COSMO-RS in predicting the best DES candidate as a stripping phase in the ELM system based on solvent capacity. The DESs were prepared from two salts, namely tetramethylammonium chloride (TMAC) and choline chloride (ChCl), with different hydrogen bond donors (HBD) such as lactic acid (LA), glycerol (Gly), ethylene glycol (EG), diethylene glycol (DEG) and triethylene glycol (TEG). ELM results illustrated a superior soap removal efficiency of 1.87 ppm in comparison to liquid-liquid extraction results which was 23.23 ppm. The highest removal efficiency of 99.75% was achieved for TMAC:LA under the following conditions: 2 wt.% of the surfactant, 0.5 wt.% of AC, 1:4 DES molar ratio, 1:1 DES: BD ratio, 400 rpm mixing speed, and 6 min extraction time. LA-based DES as natural DES also showed high removal efficiency (99.6%) under the following conditions: 2 wt.% of the surfactant, 0.3 g of graphene, 1:4 DES molar ratio, 1:1 DES: BD ratio, 400 rpm mixing speed, and 6 min extraction time. Novel DESs were successfully prepared from TEG as hydrogen bond donors with TMAC and ChCl as ammonium salts. These two DESs were combined with AC for soap removal and the efficiency were 99.1% and 97.5% for TMAC:TEG and ChCl:TEG, respectively, with a salt:HBD molar ratio of 1:4, DES:biodiesel ratio of 1:1, 2 wt% surfactant, 10 min, 400 rpm, 0.5 treatment ratio and 0.5 wt% AC dosage. The kinetics of sodium ion transport during ELM system adheres to the first-order kinetic model. The overall mass transfer coefficient, mass transfer coefficient of the external phase in an agitated reactor, and the interfacial reaction rate constant of 5.188×10−9,1.373×10−7 , and 5.392×10−9 m/s, respectively. Overall, the integration of DES and carbon materials in the ELM system provides a new cleaner, more effective, and simpler route for biodiesel downstream processing.

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