The Chemical Engineering Department at the College of Engineering, University of Baghdad, held a Ph.D thesis examination titled:
“Kinetics and Optimization of Glycerol Esterification with Fatty Acid over Prepared MCM Silica“
By the student Badoor Muhsen Kurji and supervised by Prof. Dr. Ammar S. Abbas. The examination committee consisted of Prof. Dr. Wadood T. Mohammed as Chairman and the membership of Prof. Dr. Najwa Saber Majeed, Asst. Prof. Dr. Samar K. theydan, Asst. Prof. Dr. Sama Mohammed Abdullah, and Assist. Prof. Dr. Harith Hassoun Jassim. After conducting the public discussion and listening to the student’s defense, the thesis was accepted. The thesis was summarized as follows:
MCM-48 was used as a heterogeneous catalyst to produce glycerol oleates from the esterification of glycerol with oleic acid. MCM-48 was prepared using rice husk ash as a silica source by a hydrothermal autoclave reactor. X-ray diffraction revealed that rice husk ash has an amorphous structure; Whereas MCM-48 has a uniform hexagonal mesoporous structure. X-ray fluorescence showed that SiO2 was the main chemical constituent for rice husk ash and MCM-48. Field emission scanning electron microscopy showed that rice husk ash exhibited an irregular shape and tended to aggregate, while MCM-48 consisted of spherical particles with a narrow size distribution. Transmission electron microscopy showed the rice husk ash particles exhibit a generally spherical in shape with noteworthy agglomeration. Whereas, in MCM-48, the pore structure was regular over the whole particle. Atomic force microscopy showed that the average particle size of MCM-48 was in the mesoscale range and smaller than rice husk ash.
The textual properties of the rice husk ash and MCM-48 were studied using nitrogen adsorption-desorption at constant low temperatures. According to the International Union of Pure and Applied Chemistry, the adsorption-desorption isotherm proved that the studied materials have a mesoporous structure with type IV. The results obtained from Langmuir, Freundlich, and Brunauer–Emmett–Teller isotherm models showed that nitrogen adsorption followed Brunauer–Emmett–Teller isotherm.
The pore volume and surface area values for MCM-48 (312.5 cm3g-1 and 1360.14 m2g-1) were higher than those for rice husk ash (33.89 cm3g-1 and 147.51 m2g-1). The Barrett, Joyner, and Halenda model was used to determine pore size distribution based on the Kelvin equation. The pore size distribution for MCM-48 was narrower than rice husk ash, the pore diameter for MCM-48 was less than rice husk ash, and the average pore volume for MCM-48 was higher than the value of average pore volume for rice hush ash.
The esterification reactions were carried out in a batch reactor using as-prepared MCM-48 as a heterogenous catalyst at different temperatures (140, 160, and 200°C). MCM-48 was successfully employed as a heterogeneous catalyst to produce glycerol monooleate. The conversion and selectivity to glycerol monooleate were compared with the previous research that used a different type of heterogeneous catalyst. The conversion of oleic acid increases with temperature, while the selectivity of glycerol monooleate reduces with increased temperature.
Langmuir-Hinshelwood-Hougen-Watson, Eley-Rideal, and Power Law kinetic models were developed to describe the esterification reactions. The numerical solution for the models was computed by maximization of the correlation coefficient. The results show that the experimental rate was well-fitted with the Eley-Rideal model rate. The optimized rate constants for forward and backward reactions were estimated and used to obtain the activation energy, Arrhenius constant. Changes in enthalpy and entropy of the activation step for forward and backward reactions were calculated using the Eyring equation. The reactions of glycerol esterification with oleic acid were simulate depend on Eley-Rideal model to forecast the effects of glycerol and oleic acid ratio in feed, additionally the effect of water presence in feed. The result obtained by simulation showed; the increase the glycerol molar ratio caused increased in both conversion and desired product selectivity. Conversely, the increase the oleic acid molar ratio in feed caused decrease in both conversion and desired product selectivity. Regarding, the presence of water in feed result decrease in oleic acid conversion and rise the selectivity toward desired product. The reaction temperature of 140°C, 3:1 glycerol to oleic acid molar ratio, and absence of water in feed were suggest to be optimum condition for highest conversion and selectivity for desired product.
