Date of Award

4-20-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Faculty of Engineering

Department

Department of Chemical Engineering

Institution

Universiti Malaya

Abstract

Esterquats are cationic surfactants that are readily biodegradable and exhibit low aquatic toxicity. To produce esterquats via heterogeneous-catalyzed transesterification of methyl ester has become a preferred route to the conventional homogeneous catalysis as the approach can reduce the production cost through catalyst reuse and minimized water footprint through wastewater treatment. Many transesterification reactions catalyzed by pure calcium oxide (CaO) are attributed to its high basicity and it can be derived from a cheap, non-toxic, and environmentally friendly precursor. To enhance the performance and stability of CaO, a series of CaO-based catalysts were synthesized via a wet impregnation method. The catalytic activities of the synthesized catalysts were evaluated through the transesterification reaction between methyl palmitate and n-methyl diethanolamine. Physicochemical properties of the synthesized CaO-based catalysts were characterized via various analyses. The transesterification of methyl ester production using CaO-based catalysts was monitored by gas chromatography-flame ionization detector (GC-FID). Optimization of the transesterification of methyl ester and n-methyl diethanolamine via one-factor-at-time (OFAT) approach was established at 160 °C, 80 mbar, 4 wt% of catalyst dosage, 6 hours reaction time, methyl palmitate to n-methyl diethanolamine mole ratio of 2:1 and agitation speed of 150 rpm. The optimum catalyst preparative condition of Zn-doped CaO catalyst was established at calcination temperature of 700 °C and 20 wt% Zn loading. The optimum operating conditions for transesterification over optimum Zn-doped CaO catalyst attained via Response Surface Methodology (RSM) optimization were determined at 143 °C, vacuum of 288 mbar, 2:1 mole ratio (methyl ester: n-methyl diethanolamine) and 6 wt% of catalyst dosage. Under the optimum conditions, 86% of diester (DE) yield was predicted and 82.6% of actual DE yield was obtained. Meanwhile, the optimal regime for thermal activation and CaO loading onto γ-Al2O3 for CaO/γ-Al2O3 catalysts was established at 800 °C with 100 wt%, respectively. Transesterification employing the optimum supported catalyst which was established at 146 °C, vacuum of 101 mbar, 1.8:1 mole ratio and 4.1 wt% of catalyst dosage yielded 83.2% DE with a good agreement with the predicted of 83.9% DE by RSM. Pure CaO catalyst shows a loss of its activity after the first cycle, while Zn-doped CaO and CaO/γ-Al2O3 were able to be used for 3 cycles without significant deactivation. These synthesized catalysts gave higher stability characteristic and reusability than that of pure CaO catalyst. Deactivation of the used CaO-based catalyst were ascribed to a combination of surface area loss from particle agglomeration, deposition of organic matter onto the active sites and leaching of the active substance from the catalyst surface. By excluding the influence of internal and external diffusions, a kinetic model was proposed based on irreversible second-order kinetics. This model was the best-fitted experimental data with an overall reaction rate constants ranging between 0.0892 - 0.7077 L/mol.min at temperature of 100 oC – 160 oC and an activation energy (Ea) of 49 kJ/mol. The thermodynamic parameters such as enthalphy (ΔH) of 45.7 kJ mol-1, entrophy (ΔS) of -143.9 Jmol-1K-1 and Gibbs free energy (ΔG) of 108 kJ mol-1 were also determined.

Initial

khm

Additional Information

Thesis (PhD) - Faculty of Engineering, Universiti Malaya, 2026.

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