Design And Control Of Distillation System For Methylal/Methanol Separation Using Extractive Distillation And Pressure Swing Distillation

In this paper, two methods for methylal/methanol separation is presented usingextractive distillation (ED) and fully heat integrated pressure swing distillation (PSD).Rigorous steady state and dynamic simulations for this neat operation areimplemented on commercial simulators (Aspen Plus and Aspen Dynamics). For ED,N,N-dimethylformamide was selected as an suitable entrainer by comparing infinitedilution relative volatilities. On the basis of global economic optimization, a designwith optimized operation conditions for this process is developed. For dynamicsimulations, feed flow rate and feed composition disturbances are used to evaluate thedynamic performance of several control structures. The results reveal that the controlstructure with fixed reflux ratio can handle all disturbances well, except one kind ofcomposition disturbance. An improved control structure with R/F ratio scheme is usedto maintain the two products’ purity requirements. Dynamic simulation results revealthat this control structure can handle feed flow rate and composition disturbancesquite effective. For PSD, based on the proposed partially optimization and globaleconomical optimization, an optimized configuration for this fully heat integratedpressure swing distillation is developed. Several control structures for this fully heatintegrated pressure swing distillation system are presented. The dynamic simulationresults reveal that the proposed basic control structure is unable to maintain the twobottom product at their quality specification. This problem can be resolved by using apressure-compensated temperature control scheme. The dynamic responses show thatthis control structure works pretty well for this fully heat integrated pressure swingdistillation, even for large feed flowrate and composition disturbances. From thesimulation results, it is found that the process via fully heat integrated pressure swingdistillation is more competitive than the one via extractive distillation from theeconomical view. Contrast between the dynamic controllabilities of extractivedistillation process and pressure swing distillation process is also made. Results showthat the dynamic performances of the two alternative processes are somewhat similar.