The Azeotropic Distillation Technology Research And Exploitation Of Acrylic Acid System

As an important basic chemical product, acrylic acid is currently manufacturedmainly through the two steps-oxidation of propene. The aqueous solution of acrylicacid obtained from the two steps-oxidation of propene cannot be separate directlythrough the common distillation method because of the hydrogen bond between waterand acrylic acid. The extraction, crystallization and heterogeneous azeotropedistillation method are primary methods in industry at present to purity acrylic acid.The main difference between the technologies of each company is the purity acrylicacid methods. The heterogeneous azeotrope distillation method is most widely useddue to its advantage in shortening the separation flowsheet, lowering the equipmentinvestment and increasing the product yield. Unfortunately, the patent has beenmonopolized by the Japanese company and the high patent fees have to be paid by thedomestic manufacturer if they want to use the technology. The scale of the productionhas also been restricted by the patentee. So it makes good sense to develop our ownentrainer and the heterogeneous azeotrope distillation technology to break themonopoly, reduce the processes consumption and promote the progress of thedomestic acrylic acid industry. The difficulty of the azeotrope distillation technologylies in the exploiting of the effective entrainer and the corresponding distillationtechnology. Most of the research work has also been done aimed at the developing ofthe more effective entrainer and the corresponding distillation technology.Considering the general rules for choosing entrainer and the character of theacrylic acid distillation process, the article has chosen the mixer of toluene andcyclohexane as new entrainer. In order to make use of ASPEN PLUS software todevelop the azeotrope distillation technology, following work had been done:vapor-liquid equilibrium (VLE) data for toluene+acrylic acid, toluene+acetic acid,and cyclohexane+acrylic acid systems have been determined at20kPa, whichshowed thermodynamics consistency, and all equilibrium data were fit to Wilson,NRTL, and UNIQUAC activity coefficient models to obtain the binary interactionparameters using ASPEN PLUS software; the simulation models had been set up inASPEN PLUS, the NRTL activity coefficient model combined with the Hayden and O’Connell equation were employed to calculate the vapor-liquid equilibriumproperties, the RadFrac module was used to simulate the rigorous distillation tower,the three phase flash tank was used to imitate the liquid-liquid phase splitter, theStandard method and the Wegstein method were applied to convergence thedistillation tower and the tear streams; twelve theoretical plates had been used for thedehydrating tower and the top pressure and the bottom pressure of which were15.47kPa and23.46kPa respectively, fifteen theoretical plates had been used for thedepickling tower and the top pressure and the bottom pressure of which were5.6kPaand15.6kPa respectively; simplified simulation flowsheet had been used to study theacrylic acid dehydrating and depickling process in detail with the traditional tolueneas entrainer, and the dosage of the new entrainer along with the best feed location andthe feed condition had been determined.The simulation results show that for the solution consists of acrylic acid (60.05%,wt), acetic acid (1.96%, wt), and water (37.99%, wt), when the mass flow of theentrainer was four times as much as the acrylic acid solution, the mass fraction oftoluene was four to two times as much as cyclohexane in the entrainer, the best effectcan be obtained if the acrylic acid solution feed on the6th or7th stage of thedehydrating tower. On this condition, the new entrainer shows only a little advantagecompare with toluene on the energy consumption and the distillation tower diameter,while the saving of entrainer lost was at least25percent and the saving of the acrylicacid lost was at least60percent per year, which shows that the new entrainer has itsown benefit contrast with the traditional toluene. The conclusion had lain a solidground for the further experimental verification and the practical application inindustry in future.