Reactive Dividing-Wall Distillation Column:Separation Of Low Selectivity And Low Conversion Reacting Mixtures

The separation of quaternary reversible reacting mixtures with low selectivity and low conversion requires a complex reactive distillation system to overcome the adverse thermodynamic characteristics and the adverse reaction kinetic characteristics.A large number of unconverted reactants and by-products are mixed in the product when the reacting mixtures is separated by conventional reaction distillation column.A common solution for this problem is to place distillation columns behind the reaction distillation column and send the unreacted reactants and by-products back to the reaction section to improve the selectivity and conversion of reacting mixtures.This not only increases the complexity of process design,but also fails to exploit the process intensification potential of the system.Although the Triple-unit reactive distillation system has achieved the separation of the above-mentioned reacting mixtures,the required device cost and heating demand is too considerable to the practical application and promotion of the separation process of the reacting mixtures.With reference to an ideal exothermic reaction,A+B?2C,accompanied by a side reaction A+C?2D(A,B,C and D are ideal components,αA>αc>αD>αB),a reactive double dividing-wall distillation column(R-DDWDCEX)has been developed by strengthening the Triple-unit reactive distillation system.The left part of R-DDWDCEX integrates the reaction operation and separation operation,and the right part integrates two separation operations.The effective cooperation of the two parts improves the mass and energy coupling of the system,reducing the device cost and heating demand of the separation equipment.The analysis of steady-state shows that the design structure of the R-DDWDCEX offers the satisfactory dynamic characteristics of the column.Based on the structure of R-DDWDCEX,a five-point temperature control system is designed.The liquid splitting ratio of the left dividing wall is closely linked to the operation of the two sides of the dividing wall,which ensures the control quality of R-DDWDCEX.In the case of large disturbance of feed flow and feed composition,the temperature of stage and the mole fraction of C in the product can be stabilized at their set values in a short time,and the steady-state error is small.In order to verify the universality of the design of the R-DDWDC,the separation problem in the case of the endothermic reaction is also studied in this paper,and a new reactive double dividing-wall distillation column(RDDWDCEN)is derived.The R-DDWDCEN is not only provided with satisfactory steady-state performance,but also its controllability is better than R-DDWDCEX(the adjustment time of R-DDWDCEN is shorter in the face of the same disturbance).These outcomes highlight that it is possible to employ the R-DDWDCEX or R-DDWDCEN for the separation of quaternary reacting mixtures with the most unfavorable ranking of relative volatilities,low selectivity,and low conversion.