Dynamic Simulation And Control Of PTA Hydrogenation Reaction

Pure terephthalic acid (PTA) is the main raw material for production of polyester. It contains two steps:the P-xylene(PX) oxidation and the hydrogenation reaction. And the hydrogenation reaction is that reducing the carboxyl benzaldehyde(4-CBA) which formed in the step of PX oxidation under high temperature and under high pressure.Steady simulation,dynamic simulation and control research are achieved based on ASPEN PLUS and ASPEN DYNAMICS in the article.Currently, the reactions kinetics and catalyst have been researched carefully by numbers of scholars and people even established steady simulation of hydrogenation reaction. However the dynamic characteristics of reactor is unknown in the steady simulation if the parameter disturbs.So according to the dynamic simulation requirements:the size of reactor,crystallizer, heat exchanger;the control loops,the steady simulation is turned into dynamic simulation.In the dynamic model of CTA hydrogenation unit, a series of step tests are added into the flow of CTA and saturated water and the dynamic response of product components have been analysised. The results show that when the flow of CTA increases, the concentration of all components will increase;when the flow of saturated water increases,the concentration of4-CBA,4-HMBA will increase.So in order to reduce the concentration of CTA,4-CBA and CO, a dual closed loop ratio control system and single-loop control systems-temperature controller, the hydrogen flow controller are designed.When the CTA flow increase, the dual closed loop ratio control system is adjusted to keeping the concentration of4-CBA stable,also,the temperature controller and hydrogen flow controller are regulating to promote of the hydrogenation and improve the quality of PTA.With the temperature control,hydrogen flow control coupling with the4-CBA,carbon monoxide(CO),single-loop control system can not meets needs, So an advanced controller is designed in this paper to solve the above problem.This controller is achieved through DMCplus.The control variables are the4-CBA,CO in the bottom of the reactor and the manipulated variables are reaction temperature, the flow of hydrogen. When the CTA flow increase and the concentration of4-CBA exceeds the upper limit,The DMCplus controller plays a role and the control variable4-CBA,CO is controlled within restraint space. The results show that the DMCplus controller has favorable control performance.