Design And Control Of Reactive Distillation Columns With Single And Double Reactive Sections:Esterification Of Ethylene Glycol With Acetic Acid

The reactive distillation column is widely applied to petrochemical industry. The combination of reaction operation and separation operation enables reactive distillation columns to be much more cost effective and thermodynamic efficient than the conventional design practice, i.e., a reactor plus a number of distillation columns. The main thrust originates essentially from the reinforcement of internal mass integration and internal energy integration between the reaction operation and separation operation involved. Up to now, considerable attention has been paid to the synthesis and design and dynamics and control of reactive distillation columns with single reactive section (RDC-SRS). It is generally favorable to the separations of reacting mixtures with the most or somewhat favorable ranking of relative volatilities. For the separations of reacting mixtures with the most unfavorable ranking of relative volatilities, the RDC-SRS succumbs completely to the conventional reactor plus distillation column scheme. Towards the two-stage consecutive reversible reaction of the esterification/etherification reaction, RDC-SRS are difficult to coordinate the relationship between the two step reactions, which is bad for internal mass integration and internal energy integration between the reaction operations and separation operation involved, thus limiting the RDC-SRS energy saving.Tung and Yu suggested using a reactive distillation column with two reactive sections (RDC-SRS) for the separations of quaternary reacting mixtures with the most unfavorable relative volatilities. Their RDC-DRS was characterized to have the two reactive sections arranged at top and bottom (including the top condenser and bottom reboiler as well) to favor internal mass integration between the reaction operation and separation operation involved. Our research group systematized their idea and presented the general configuration of the RDC-DRS,and applied it to the ideal two-stage consecutive reversible reaction and the reaction of methyl carbonate, RDC-DRS shows powerful energy saving.The esterification of ethylene glycol with acetic acid is characterized by two-stage consecutive reversible reaction kinetics and represents a challenging candidate for studying effective designs of reactive distillation columns. Two reactive distillation columns with single reactive section and double reactive sections (RDC-SRS and RDC-DRS) are designed for the separation of this complicated reacting mixture in terms of the minimization of total annual cost. The RDC-DRS is found to require less capital investment and utility consumption than the RDC-SRS and this is due to the fact that the former involves relatively more degrees of freedom than the latter to arrange internal mass integration and internal energy integration between the reaction operations and separation operation involved. Reboiler heat duty was reduced by 19.33%, CI, OC and TAC was reduced by 3.6%,20.7% and 3.6%, respectively.In terms of direct composition control strategy, dynamic controllability of the RDC-SRS and RDC-DRS is further studied and compared. The RDC-DRS is again found to be superior to the RDC-SRS in rejecting step disturbances from feed flow rate and tracking the variations in product purity set-points. These outcomes indicate that arranging two reactive sections in a reactive distillation column could favor process design and controllability and should be viewed as a potential option for the separation of complicated reacting mixture like the esterification of ethylene glycol with acetic acid.