Dynamics And Control Of Reactive Distillation Columns With Double Reactive Sections:Feed-Splitting Influences

Reactive distillation is the integration of reaction operations and separation operations in one processing unit,which makes the system have lower energy consumption and lower economic costs.It is a chemical process intensification technology with development potential.However,conventional reactive distillation columns with single reactive section are not useful for the separations of some reacting mixtures.When the reacting mixtures feature that reactants are the lightest and heaviest with the products in between,the separation effect of the reactive distillation columns with single reactive section is not as good as the traditional chemical industrial process.One solution to separate such reacting mixtures featuring the most unfavorable ranking of relative volatilities is to use the reactive distillation column with double reactive sections(RDC-DRS).The configuration of the RDC-DRS is to arrange two reactive sections at the top and bottom of the distillation respectively with one side product withdrawal,which is helpful to strengthen the material coupling and to make the system achieve a better steady-state performance compared to the reactive distillation column with single reactive section.On the basis of the scheme of the RDC-DRS,the steady-state performance can be further improved by adopting feed splitting,and that is using the reactive distillation column with double reactive sections and feed splitting(RDC-DRSFS).Although feed splitting is favorable for the steady-state performance of reactive distillation columns with double reactive sections,the influences of this technology on the dynamics and control of the system is still unknown,which is the crux of the feasibility of feed splitting.In this paper,the dynamics and control of the RDC-DRS and RDC-DRSFS are studied in detail,with particular attention to the influences of feed splitting.Due to the totally refluxed and totally reboiled operation mode plus an intermediate product withdrawal,the RDC-DRS is generally characterized by severe underdamping in the regulation path(between the reboiler heat duty and the intermediate product compositions)and severe asymmetry in the disturbance path(between the feed flow rate and the intermediate product compositions),consequently posing a great challenge to the process control.Compared to the RDC-DRS,with adoption of feed splitting in the RDC-DRSFS,these unfavorable dynamic characteristics are suppressed,thereby presenting favorable influences to process dynamics and controllability.Two reactive distillation systems,executing a hypothetical quaternary reversible reaction and the lactic acid esterification with methanol,are employed to inspect the dynamics and controllability of the RDC-DRS and RDC-DRSFS and verify influences of feed splitting on the dynamics and control of reactive distillation columns with double reactive sections.With using the same control schemes,the controllability of the RDC-DRSFS is better than the controllability of the RDC-DRS.The results reveals that feed splitting is not only an optimized process enhancement strategy,but also a effective booster for process dynamics and controllability.