Design And Control Of Reactive Distillation Columns With Multiple Reactive Sections

As a process intensification device that integrating reaction operation and separation operation,the single reactive distillation column with a single reactive section(RDC-SRS)can break the limit of equilibrium reaction,improve the conversion rate of the reaction,and reduce equipment investment and operation energy consumption.However,when separating reacting mixtures with unfavorable thermodynamic and kinetic properties,it is difficult to effectively realize the potentials mentioned above.In order to solve the shortcoming of the RDC-SRS and expand the scope of application of reactive distillation technology,many scholars have proposed a variety of improvements,and the reaction distillation column with multiple reactive sections(RDC-MRS)is one of them.Although previous studies have found that the setting of multiple reaction sections can achieve better process intensification effects for the separation of multiple-stage consecutive reversible reactions,there is still a lack of systematic understanding of the effectiveness and feasibility of this design method,especially its impacts on process dynamics and controllability is not yet clear,so in-depth research is necessary.In this paper,the comparison and analysis of RDC-SRS and RDC-MRS are performed with respect to steady state performance and dynamic operation,thus comprehensively revealing the influences of setting multiple reaction sections when separating multiple-stage consecutive reversible reactions.For RDC-SRS,because multiple reactions are concentrated in the same reactive section,it lacks effective means to coordinate these reactions,which not only limits the improvement of reaction conversion rate,but also increases the difficulty in separating target product.For RDC-MRS,due to the setting of multiple reactive sections,it has more structural design variables and operational design variables,which include the number of the reactive sections,the number of trays in each reactive section,the number of trays in the separation section between the reactive sections,the flow rate and position of multiple feeds,etc.They provide more freedom for the synthesis and design of the system,which not only helps to coordinate the interrelationships between the multiple reactions,so that the reactions proceed in a favorable direction(that is,reduces the difficulty of separating the target product),but also helps to strengthen the mutual coupling between the reaction operation and the separation operation.Therefore,the setting of multiple reaction sections can effectively improve the steady-state performance of the reactive distillation column,that is,reducing the equipment investment cost and the operation energy consumption.In addition,since the setting of multiple reactive sections helps to coordinate the multiple reactions and the relationships between reaction operation and the separation operation involved,it will also have positive effects on the process dynamics of the reactive distillation column,that is weakening interaction between each product and reduce the time constant of the system.Obviously,both of them contribute to strict control of product quality.In this paper,the synthesis of diethyl carbonate by two-step consecutive reversible reactions and the preparation of silane by three-step consecutive reversible reactions are taken as examples to verify the effect of multiple reactive sections analyzed above.The experimental results of both examples show that RDC-MRS has better steady-state and dynamic performance than RDC-SRS.Therefore,the setting of multiple reactive sections can not only improve the steady-state performance of the reactive distillation column,but also improve its process dynamics and operation.It is reasonable to consider that the setting of multiple reactive sections is an effective and feasible strategy for process intensification in the case of the separation of multiple-stage consecutive reversible reactions.