Study On Flashing Evaporation Separation Process Of Isopropenyl Acetate In The Production Of Acetylacetone

As an important organic chemical intermediate, Acetyl acetone is generally prepared by ketene method. The process is that by the absorption of ketene with acetone in the presence of a strong acid catalyst, the absorption solution mainly contained isopropenyl acetate is obtained, and then after separation and purification, isopropenyl acetate is isomerizated into acetyl acetone at high temperatures. It is clear that the separation efficiency of isopropenyl acetate has a direct effect on the yield and purity of the acetylacetone. A common still was used to separate isopropenyl acetate in the present technology. As the residence time was long, solution in the still was continuing heated and heat sensitive materials deteriorate easily. A large amount of high viscosity materials, like acetic anhydride, polymer of ketene and acetyl sulfonylurea acetic acid catalyst, were gathered in the kettle at the end of distillation, which made coking happened extremely easy at the bottom of kettle and difficult to discharge the residue liquid. Therefore, the separation process should be completed quickly to avoid absorption solution staying at high temperatures for a long time. And improving separation efficiency of isopropenyl acetate in the condition of no coking will be the problem we should solve.On the analysis of the coking problem, the thermal stability of IPA and the kinetics of the thermal decomposition of IPA were investigated. The experiment results which have directive function for the condition of flash separation show that decomposition of IPA occur in acid condition under high temperature.The absorption solution was separated by a set of special flashing equipment and process. The influence of the nozzle, feeding flow, feeding temperature and pressure on flash vaporization rates was studied. As a result, optimal condition for single flash of the absorption solution is feeding temperature 150℃, flashing vacuum degree 0.085MPa with the round nozzle. Through mass balance calculation in this condition, vaporization rates were obtained:the total flash vaporization rate over 90%, IPA over 95%. And coking and blocking in the process did not occur. This process will provide a new method for continuing separation of isopropenyl acetate in the industrial production of acetyl acetone.