Abstract:
Catalytic distillation (CD) is a typical intensification technology of chemical process via coupling catalytic reaction and product separation into one operation unit and has been widely used in the industrial field. In a CD column, some chemical reaction systems can adopt either homogeneous catalyst or heterogeneous catalyst, although the corresponding operation processes and control structures may not be the same. However, there have been few works focusing on the comparison between the homogeneous and heterogeneous CD processes for a sequential-competitive reaction system aiming at selectivity, especially from the aspect of dynamic control performance. In this paper, the synthesis of ethylene glycol monobutyl ether (EGMBE) using ethylene oxide and
n-butanol is taken as an example to illustrate the differences between the homogeneous and heterogeneous CD processes. The steady state performance, the control structure design, and dynamic characteristics are analyzed and compared. Moreover, the homogeneous and heterogeneous EGMBE production processes are firstly set up in the Aspen Plus platform and designed with the same feed flowrates, conversion and selectivity objectives and product purity targets. Steady state simulations are carried out to obtain the basic operating conditions and equipment sizing parameters. The relative gain array (RGA) matrix is used to analyze the homogeneous and heterogeneous CD processes, based on which a two-temperature control loop is determined for both processes. The control structures are then designed and set up in Aspen Dynamics, in which dynamic simulations are carried out. By adding a ±10% disturbance of
n-butanol feed flow rate in both processes, the dynamic response and control effect are investigated. The results show that the proposed control structures of both homogeneous and heterogeneous CD processes can provide effective control and meet the control requirements. Moreover, the control structure of the heterogeneous CD process has faster closed-loop response, lower steady-state offset and faster recovery to the set point than that of the homogeneous CD process. Besides, there is no variation in catalyst concentration along the heterogeneous CD column.