Design And Control Of A Reactive Distillation Column With Two Reactive Sections

Reactive distillation technique is an effective process intensification skill. For reversible chemical reactions, the integration of reactive operation with separation operation into one column overcomes the chemical equilibrium constraints and reduces the energy consumption and capital investment to a great degree. After decades improvement, reactive distillation columns are widely applied in the field of chemical industry, such as simple reactions, parallel reactions and two-step consecutive reactions. So far, most studies of the separation of two-step consecutive reactions focus on the reactive distillation column with single reactive section (RDC-SRS). However RDC-SRS can hardly coordinate the two reactions involved. It may lead to low conversion rate and selectivity, and even high energy consumption and capital investment. To solve this problem, a novel reactive distillation column with two reactive sections (RDC-TRS) is studied in this paper. The arrangement of two reactive sections in a single column will contribute to the coordination of the two reactions and improve the thermodynamic efficiency of system. The specific work of this paper is as below:In terms of hypothetical two-step consecutive reversible reactions, the software Mathematica is used to build up the model of this system. The dynamic performance of RDC-TRS is analyzed based on the study of its steady-state design. For obtaining the reasonable control scheme, relative gain array is adopted in the match of the inputs and outputs variables. After giving different disturbances, the close loop responses of RDC-TRS are compared with RDC-SRS. The results indicate that RDC-TRS shows better dynamic performance, stably and quickly returns to the set point when given feed flow rate disturbance and product set point disturbance. These dynamic results prove the feasibility of RDC-TRS.Besides, the complicated conditions such as azeotropy and liquid-liquid phase splitting often exist in realistic chemical industry. Taking the production of cyclohexanol from cyclohexene by two-step reactive process using formic acid as a reactive entrainer as an example, RDC-TRS is applied to this realistic system. In this process, the synthesis and design of the RDC-TRS is studied by the software Aspen Plus. The optimum structures are devised through a simple and effective procedure in terms of the minimization of total annual cost (TAC). Then RDC-TRS is compared with the conventional structure which is composed of two reactive distillation columns with single reactive section (CRDC). The results indicate that RDC-TRS provides additional design variables, and effectively improves the net reaction rate and the separating result. Through reinforcing internal mass integration and/or energy integration, RDC-TRS considerably reduces the capital investment and energy consumption.