| Methyl methacrylate(MMA) is a kind of important organic chemical raw materials. As polymeric monomers, methyl methacrylate can generate polymethyl methacrylate(organic glass, PMMA) after polymerization. And methyl methacrylate is widely used to paint, resin, textile, paper making and so on. At present, many methods have been explored to synthetise methyl methacrylate, such as acetone cyanohydrins method(ACH), ethylene method, isobutylene method, allylene method, propylene method, isobutane method. In recent years, a new method to synthetise methyl methacrylate developed gradually. Fristly, methylacrolein(MAL) was synthetised by using formaldehyde and propionaldehyde as raw materials. Then through one step oxidation, methylacrolein was oxidated to methyl methacrylate. And this method was gradually applied to the industry. Compared with other methods, this method has some advantages as follows: raw materials are easily obtained, reaction conditions are mild, simple and feasible, the selectivity of methylacrolein is high and so on. It has excellent application prospect.Ionic liquids(ILs) are taken for one of the “green solvents” and have been widely applied in chemical reaction, separation and analysis, electrochemistry, petrochemical industry and so on, for the unique charateristics. But ionic liquids are not completely harmless. The extensive use of ionic liquids will cause certain harm to the environment and humans. So it is important to realize the recycling and reusing of ionic liquids. This not only can solve the problem of environment but also can save the cost. At present, many methods have been explored for IL recovering, such as vacuum distillation, extraction, adsorption, aqueous biphasic systems, and membrane technology.In this paper, the reaction mechanism of the preparation process of methyl methacrylate by using formaldehyde and propionaldehyde as raw materials was studied. The recycling of ionic liquid catalyst was realized by aqueous two-phase system. The main content as follows:1)A novel ionic liquid diethylamine acetate was synthetised to catalyze the reaction of formaldehyde and propionaldehyde to generate methylacrolein. Results show that the conversion ratio of propionaldehyde is 99% and the selectivity of methylacrolein is 94%.2) The reaction mechanism of condensation reaction of formaldehyde and propionaldehyde as follows: in the acid condition, the carbonyl of formaldehyde was protonized and reacted nucleophilic addition reaction with diethylamine. Then the proton was removed, the electron of nitrogen was transferd, water was removed and imine ion intermediates(N- hydroxy methyl ethyl amine) were generated. Propionaldehyde was protonized and generated the enolate. As the electrophilic reagent, N- hydroxy methyl ethyl amine attacked the enolate that containing active hydrogen. Then the proton was removed and mannich base was generated. Finally, in the condition of heating, mannich base was decomposed into methylacrolein and water.3)Aqueous biphasic systems(ABS) were used for concentrating ionic liquids diethylamine acetate from wastewater of condensation reaction and the binidal curves, tie line and ternary phase diagram were drawn. The results show that the binodal curve data of aqueous biphasic system are fitted to Merchuk equation and tie line data are fitted to Othmer-Tobias and Bancroft equations. The recovery efficiency increases with the increase of the amount of inorganic salt and decreases with the increase of the initial concentration of diethylamine acetate.4)Aqueous biphasic systems were used for concentrating ionic liquids 1-ethyl-3-methylimidazolium chloride([Emim]Cl) from aqueous solutions and the binidal curves and tie line for aqueous biphasic systems were drawn. The results show that the binodal curve data of aqueous biphasic system are fitted to Merchuk equation and tie line data are fitted to Othmer-Tobias and Bancroft equations. Different inorganic salt will form different binodal curves and the phase separation ability of inorganic salt as follows: K3PO4>K2CO3>K2HPO4. The binodal curves of aqueous biphasic systems are associated with the molecular weight and hydrophobicity of IL. The binodal curves are not affected by operation temperature. The increase of PH is conducive to the separation of two phases but effect is not obvious.5)The effect factors of ionic liquid recycling were studied. The results show that the recovery efficiency increases with the increase of the amount of inorganic salt. When the same quality of inorganic salt were added to the IL solution, the order of recovery efficiency of IL as follows: K3PO4> K2CO3> K2HPO4. The recovery efficiency increases with the initial concentration of IL increases, but it becomes flat after the initial concentration of IL reaches about 25%. The recovery efficiency decreases with the increase of temperature. The recovery efficiency is not affected by PH. |
PDF Full Text Request