Synthesis Of Food Perfume Methyl Caprylate Catalyzed By Functionalized Acidic Ionic Liquids System

Methyl caprylate, a colorless to pale yellow oily liquid with winey, fruity and orange odour, has been taken as an allowed food perfume in the standards for uses of food additives GB2760-2011. It is mainly used as essence for food and cosmetics, intermediate for pharmaceuticals and fine chemicals, and also can act as plant growth regular and substitute for biodiesel. Hence, synthesis of methyl caprylate has received widespread attention due to people’s increasing demand. However, problems caused by conventional catalysts are not in conformity with the requirements of sustainable development, e.g., undesirable side reactions, equipment corrosion, environmental pollution, plaguy catalyst recovery and reuse. With the increasingly popular environmental protection movements and strict laws and regulations, it is of great academic and applied significance to perform clean synthesis of methyl caprylate.In this present work, kinds of ionic liquids were prepared and applied as catalysts to synthesize methyl caprylate. The correlations between catalytic activities and acid properties of ionic liquids were mainly studied. Effects of operating variables including methanol to caprylic acid molar ratio, catalyst amount, reaction time and temperature to the esterification were investigated and response surface methodology was utilized to optimize these variables. Furthermore, kinetic model for esterification of n-caprylic acid was established under the optimum conditions, which is reference for producting other esters.In the second chapter, a series of multi-SO3H functionalized Brφnsted acidic ionic liquids were prepared, and their structures and catalytic activies were investigated. The results showed that these ionic liquids had high thermal stabilities and strong acidities, among which N, N’, N", N’"-tetrapropane sulfonic hexamethylenetetramine tetrahydrosulfate [TshxH][HSO4]4showed an excellent catalytic activity in esterification of n-caprylic acid. The optimum reaction conditions were obtained by response surface methodology as follows:catalyst amount of0.3mmol, methanol to caprylic acid molar ratio of7.5:1, reaction time of2.5h and temperature of363K, generating a high methyl caprylate yield of94.8%. Under the optimized conditions, the kinetic equation was obtained to be the active energy was24.61kJ/mol. Under microwave irradiation, the optimum operating conditions were catalyst amount of0.3mmol, methanol to caprylic acid molar ratio of7:1, microwave power of400W, reaction time of35min and temperature of353K, leading to a high yield of96.2%. Compared with conventional heating, microwave irradiation had an "non-thermal effect" for its fast reaction rate.In the third chapter, the catalytic activities of Bronsted-Lewis acid ionic liquids such as [HSO3-pmim]+(1/2Zn2+)SO42-for synthesis of methyl caprylate were studied, indicating that synergy of Brφnsted and Lewis acid sites accouted for high activity. The optimum conditions in presence of [HSO3-pmim]+(1/2Zn2+)SO42-were obtained by response surface methodology as follows:catalyst amount of7wt%, methanol to caprylic acid molar ratio of6:1, reaction time of2.0h and temperature of363K, generating a high methyl caprylate yield of95.4%. Under the optimized conditions, the kinetic equation in2.0h was obtained to be the active energy was33.66kJ/mol.In the fourth chapter, catalytic activities of several phosphotungstic acid-based ionic liquids in esterification of caprylic acid were explored. The results showed that [MIM-PSHT]2.0HPW112O40manifested a high activity and stability, which might be ascribed to its strong acidity and steric effect. The optimum operating parameters were catalyst amount of4wt%, methanol to caprylic acid molar ratio of8:1, reaction time of3.0h and temperature of363K, leading to a ester yield of92.5%. Under the optimal conditions, the kinetic equation in3.0h could be expressed as the active energy was32.09kJ/mol. The phosphotungstic acid-based ionic liquid [MIM-PSH]2.0HPW12O40could be reused after simple treatment without considerable change in catalytic activity and mass. It is of great applied prospect in industry.In the fifth chapter, catalytic activities of a series of molybdovanadophosphoric heteropoly acid-based ionic liquids were evaluated, demonstrating that [MIM-PSH]2.0H2PVMo11O40possessed an excellent catalytic activity and stability in esterification of n-caprylic acid. The optimal conditions for synthesis of methyl caprylate catalyzed by [MIM-PSH]2.0H2PVMo11O40were obtained by response surface methodology as follows:catalyst amount of8wt%, methanol to caprylic acid molar ratio of7:1, reaction time of3.0h and temperature of363K, leading to a high yield of95.6%. Under the optimum conditions, the kinetic equation for synthesis of methyl caprylate in3.0h could be written as: the active energy was30.32kJ/mol.