Reactive Distillation Processes:Fundamentals And Extensive Technologies

In chemical industry processes, chemical reaction and distillation separation are usually carried out in two individual equipments. If the operations of reaction and distillation can be integrated in a single multi-functional process unit, this new integration concept is therefore called’reaction distillation’. When the heterogeneous catalysts are applied, the term’catalytic distillation’is often used. As advantage of this integration, chemical equilibrium limitations can be overcomed, higher selectivities can be achieved, and the heat of reaction can be used in situ for the distillation. Reactive distillation has therefore been frequently used in the petrochemical and fine chemical industries, especially in the esterification, etherification, and hydration processes. However, despite the fact that the basic idea of combing reaction and distillation is proposed for a long time and it has a good development in many aspects, the design, simulation and extensive applications of reactive distillation are still faced with many difficulties due to the rigorous coupling between reaction and distillation. The packing structure of solid catalyst in reactive distillation column is the key factor to determine the proceeding of reaction distillation process, and green catalyst of high catalytic activity is also highly conceived to replace cation-exchange resins and solid acids for the reactive distillation process. Therefore, the esterification reaction was choosed as the research object owing to its widespread popularity. It is very important to thoroughly study the coupling effect derived from reaction and separation, to investigate the influence of hardware configuration on the hydrodynamics and mass-transfer performance, and to explore a new reactive distillation esterification processes based on ionic liquids. Through these efforts, it is not only effective to enhance the integration efficiency, but also change the traditional esterification technology and match the aim of energy saving and emission reduction. In addition, these achievements can also be applied and promoted to other reaction processes.The present work aimed at the research of green production of n-butyl acetate and methyl acetate via the reactive distillation processes. A flow guided hardware configuration with plug-in units installed in the sieve tray column was proposed and primarily studied. Then the hydrodynamics, mass-transfer, and catalytic performance of solid catalyst packing structure were investigated, and its effect on reaction and distillation separation was also obtained. In addition, several Bransted acidic ionic liquids (BAILs) composed of different cations were designed and synthesized. The kinetics of esterification reaction catalyzed by BAILs was studied systemically, and the possibility of BAIL-based catalytic distillation processes was also discussed. And investigations were further carried out on the behavior of thermodynamics of the esterification system containing BAILs. The ASPEN PLUS software was also used to simulate the BAIL-based reactive distillation processes, to provide the basic data and the theoretical analyses for the design of those processes. Therefore, several important results have been obtained in two research sections and summarized as follows:The fist part of the thesis concerns the design of solid catalyst packing structure. A flow guided hardware configuration with plug-in units installed in the sieve tray column was primarily proposed. The hydrodynamics, mass-transfer, and catalytic performance of solid catalyst packing structure were therefore investigated. It was shown that the dry plate pressure drop and wet pressure drop were not increased too much with the introduction of catalytic packing structure on the sieve tray, and the weeping and entrainment of catalytic sieve tray were reduced obviously. It is reasoned that the flow guided framework can rectify the liquid flow well and wire mesh is of good eliminating foam effect. In addition, the catalyst packing structure was further tested to be of excellent mass-transfer efficiency and catalytic activity. Therefore, it is demonstrated that the flexibility and stability of the sieve tray column with the introduction of catalyst packing are improved in comparison to the normal sieve tray column. These experimental results also verify the feasibility and innovation of catalytic packing installed on the tray.The second part of the thesis concerns the design and simulation of B AILs-based reactive distillation processes, and this part is introduced in three aspects. First, several BAILs composed of different cations were designed and synthesized. For the esterification reaction in the presence of BAILs, it is found that the catalytic activity of BAIL is relevant to its acidity and hydrophilicity. The stronger acidity or hydrophilicity the BAIL has, the higher the catalytic activity. It is also demonstrated that a combination of reactive distillation with a BAIL as catalyst is effective to drive the reaction equilibrium further to the product side and lead up to the completion of esterification, primarily due to the nature of BAIL to enable liquid-liquid biphasic catalysis. The feasibility of a combination of reactive distillation with a BAIL as catalyst is also verified. Second, on the basis of presious study, the kinetics of esterification reaction catalyzed by BAILs was studied systemically. A pseudo-homogeneous (PH) kinetic model was utilized to correlate the experimental data. The experimental results indicated that the acidity and hydrophilicity of BAILs have a synergistic effect on the performance of esterification. It is validated from the comparison between experimental data and the PH model values that the PH model can give a good representation of the esterification kinetic behavior at a low catalyst loading. The optimization of reaction conditions were reaction temperature of373.15K, catalyst loading of25%w/w and molar ratio of the reactants of2:1. Third, investigations were further carried out on the behavior of thermodynamics of the esterification system containing BAILs. The vapor-liquid equilibrium and liquid-liquid equilibrium for the esterification system containing BAILs were measured, and the corresponding thermodynamics model was also established. Binary interaction parameters were therefore obtained by solving those equations. Then, the BAILs-based reactive distillation process was simulated by using the ASPEN PLUS software. The effects of theoretical plate number, feed location, and molar ratio of the reactants on the concentration of acetic acid in the top and the mole fraction of ester in the bottom were also explored in detail. As a result, the product of ester can be purified to over99.6%in the bottom of reactive distillation column.