Studies On Preparation Of Styrene Epoxidation Catalyst And Process Optimization For1,2-Epoxyethylbenzene Production

1,2-epoxyethylbenzene is one of the most important fine chemicals and often used in the intermediate of pharmaceuticals and synthesis of perfume. Starting with the raw material of styrene, halogen alcohol method is widely adopted in industrial field. However, the defect of halogen alcohol method, such as high energy consumption, environment pollution and low efficiency, is also prevalent. So based on the oxygen source of hydrogen peroxide, a green and environment friendly synthesis process is proposed by the oxidation of styrene. The key problem of styrene oxidation system using hydrogen peroxide as the oxidant is to solve interface mass transfer limitation of water and oil phase, which caused by the immiscibility of these reactants. This paper focuses on the development of catalyst and the design of subsequent reaction and separation process.Firstly, the supported heteropoly acid catalyst is studied. Mesoporous MCM-41is modified with1-triethoxysilylpropyl-3-methylimidazolium chlorid ionic liquid so as to form a layer of imidazole cation group. The phosphomolybdic acid is immobilized onto the IL modified MCM-41(ILMCM-41) to prepare the PMo/ILMCM-41catalyst. The XRD, N2adsorption-desorption, and TEM results indicate that the sample retains mesoporous structure after ionic liquid modification and immobilization of phosphomolybdic acid. The FT-IR results indicate that the PMo/ILMCM-41possess the Keggin structure of [PMo12O40]3-and the Bmim cation. The amphiphilic catalyst can adsorb H2O2and styrene from aqueous and organic phase simultaneously to eliminate the disadvantage of mass interface transfer limitation. Styrene is selectively oxidized to1,2-epoxyethylbenzene, catalyzed by phosphomolybdic acid supported on ionic liquid modified MCM-41, using hydrogen peroxide as oxidant. Maximum activity including both of the optimal styrene conversion of95.4%and1,2-Epoxyethylbenzene selectivity of90.2%is observed at a loading of30wt.%phosphomolybdic acid on ionic liquid modified MCM-41under50℃and H2O2/styrene molar ratio of1.2within3h. The heterogeneous catalyst is easily separated by centrifugation and reused without deactivation after six runs.Aiming at the reaction subsystem, the attainable region-superstructure strategy for the synthesis of chemical reactor networks is proposed, which has complementary advantages between attainable region and superstructure-based approach. By searching feasible solutions efficiently in the key reactant and target product concentration spaces, this method has been successfully applied to1,2-epoxyethybenzene reaction system. Two-dimensional transfer model of micro reaction unit is derived and the state space superstructure based on the micro reaction units is developed to optimize heat/mass transfer and reaction simultaneously. To carry out discretization of PDEs, the Crank-Nicholson implicit difference method is applied, then a nonlinear programming model is generated. The preanalysis based on attainable region and ideal reactor network superstructure could determine the numbers of basic units and links between them, and also provide initials and bounds for variables, which will greatly decreace the computational complexity of the proposed model. The optimal reactor network consists of twenty tubular reactors with radius of0.1m and length of3.6m. And the outlet concentration of1,2-epoxyethybenzene is3.396mol·L-1. These data offer decision-making support for the design of subsequent production flowsheet.Dealing with the separation subsystem, computer aided molecular design (CAMD) is introduced to determine the optimal mass/energy separation agents. According to the property requirement of selectivity and solubility, a set of groups is pre-selected to assemble the objective molecular. The thermodynamic property of molecular is predicted by the UNIFAC (universal quasichemical functional group activity coefficient) group contribution method based on the topical solution theory. With the strategy of prediction-validation-improvement, a set of valid moleculars which have the specific properties are screening out. To avoid the combination explosion, an mixed integer nonlinear programming (MINLP) model is introduced and a divide and conquer solution strategy is proposed to select the best candidate extractors/entrainers of styrene epoxidation and1,2-epoxyethylbenzene. Furthermore, combined with the latest development of CAMD, a solid liquid equilibrium (SLE) model is introduced to calculate the solid liquid phase diagram. And a set of experiments are performed to valid the calculated relationship of styrene epoxidation and1,2-epoxyethylbenzene. Based on the results of the experiments, the cryogenic crystallization process is proved to be feasible and can be the thermodynamics foundation of the subsequent technical design.Then, the conceptual design for pilot-plant production of1800t·a-11,2-epoxyethybenzene is implemented based on simulation and heat exchanger network synthesis. The whole process contains four parts, including reaction, decanting separation, organic phase separation and1,2-epoxyethybenzene purification. According to the result of synthesis of optimal reactor network, fixed bed reactor is selected. The decanter process temperature is optimized as35℃with the feature of parameter sensitivity analysis of equipment and process. According to separation energy consumption of sequence flowsheet and inverted sequence flowsheet, organic phase components separation sequence is preferred. Different types of operations for1,2-epoxyethybenzene purification processes are proposed, which involve decompress distillation process, cryogenic crystallization process and cryogenic crystallization and decompress distillation combined processes. The purity of1,2-epoxyethybenzene is99.8%and the product recovery rate is above95%. The cryogenic crystallization-decompress distillation flowsheet has significant advantage in investments and operationg costs. To enhance energy recovery, heat exchanger network is synthesized based on pinch technology and mathematical programming. Cold and hot utility consumption is reduced by24.0%and46.8%respectively. No matter from economic or social benefit, the proposed pilot-plant is suited for large scale production.