Design And Comparison Of Methyl Acetate External Recycled Dividing-wall Reactive Distillation Columns

Nowadays,the chemical industry is considered as a high-consumption and heavily polluting industry,how to realize energy saving and recycling economy effectively has always been the important issue to achieve national sustainable development,solving resource strain,energy shortage and environmental pollution is very significant to scientific research and practical application.Reactive distillation as a coupling reaction and separation process,has been widely used in chemical reactions.Although traditional reactive distillation columns have advantages in terms of saving energy,improving product selectivity and the coversion of reactants,they are difficult to recycle the unconverted reactants to the reaction section for all kinds of reaction systems due to structural drawbacks,leading to system performance degradation.For example,when traditional reactive distillation columns are used for the separation of the quaternary reacting mixtures with somewhat unfavorable relative volatilities ranking,the unconverted light and heaviest reactants tend to accumulate in the bottom and the top of the reactive section,respectively,and this leads to the reduce of conversion of the reaction.To deal with this problem,there are three different external recycles solutions available.The first is to only recycle the unconverted heaviest reactant back to the reactive section,the second is to only recycle the unconverted light reactant back to the reactive section,and the third is to recycle the unconverted light and heaviest reactants back to the reactive section at the same time.It should be pointed out that a vertical dividing wall must be set within the column in order to achieve the purpose of recycle the unconverted light reactant back to the reactive section.The esterification of acetic acid with methanol was employed as an illustrated example to investigate this problem,and according to the above mentioned three external recycles solutions,three different dividing-wall reactive distillation columns with external recycles were designed respectively and compared on the improvement of the system performance.Results show that the dividing-wall reactive distillation column with double external recycles,because of reinforcing the internal mass and energy interactive to the utmost,has the best system performance among the three structures.