Study On The Reactive Distillation Technique For Acetate Ester Production Via Esterification Catalyzed By [HSO₃-BMIM][HSO₄]

Ester i.e.ethyl acetate（EtAc）and n-butyl acetate（BuAc）,are essential chemicals.They are widely used in chemical synthesis due to the excellent solubility.Esterification is usually used to synthesis EtAc and Bu Ac,where concentrated sulfuric acid（H₂SO₄）applied as catalyst.However,the high catalytic efficiency of H₂SO₄ also leads to the serious waste liquid pollution and equipment corrosion.Therefore,to develop an alternative catalyst to replace H₂SO₄ in the esterification has always been a research hotspot in chemical engineering.Ionic liquids（ILs）are novel materials that have highly activity and good stability,which have great potential to replace H₂SO₄.Screen the results according to the studies of ILs,a sulfuric acid IL that has multiple protons（H⁺）activity groups（1-sulfobutyl-3-methylimidazolium hydrogen sulfate,[HSO3-BMIM][HSO₄]）is used as catalyst to synthesise EtAc and Bu Ac in esterification.The macroscopic reaction kinetics of [HSO3-BMIM][HSO₄]-catalyzed esterification was studied.The catalytic activity of [HSO3-BMIM][HSO₄] was compared with traditional catalysts.The reactive distillation（RD）processes for the production of EtAc and Bu Ac via esterification catalyzed by [HSO3-BMIM][HSO₄] were designed and simulated in Aspen Plus,while the RD experiment of [HSO3-BMIM][HSO₄] catalyzing esterification was carried out in a laboratory-scale distillation tower.In order to reduce the corrosion of [HSO3-BMIM][HSO₄],ILs were immobilized on SiO₂ by Sol-Gel method and impregnation to prepare supported ILs（SILs）.Then the catalytic performance of SILs in the esterification of acetic acid could be studied.The main achievements are as follows:（1）[HSO3-BMIM][HSO₄] was used to catalyze the esterification of acetic acid（HAc）and ethanol（EtOH）to synthesize EtAc.The influences of reaction temperature,catalyst concentration,reactants molar ratio on the conversion of HAc(X_HAc)were studied.Based on the reaction mechanism of the esterification catalyzed by Br（?）nsted acid,the enhancement of the self-catalysis effect in the esterification and its interaction with the addition of ILs were investigated.The interactions between reactants and ILs were studied by introducing self-catalysis term to modify the conventional homogeneous reaction kinetics models then obtained the modified ideal homogeneous IH（M）model and modified non-ideal homogeneous NIH（M）model.By comparing the mean absolute squared error（MASE）between modeling results and experimental data,NIH（M）model has exact fitting and prediction of the reaction rate（r_a）and X_HAc,and the NIH（M）model equation is as follows:（?） The catalytic efficiency of [HSO3-BMIM][HSO₄] was compared with the traditional catalysts e.g.H₂SO₄ and ion exchange resin Amberlyst-15 in the esterification of HAc and Et OH.Results showed that [HSO3-BMIM][HSO₄] was more efficiency than Amberlyst-15,while the corrosiveness of [HSO3-BMIM][HSO₄] was less than that of concentrated H₂SO₄.[HSO3-BMIM][HSO₄] could be reused for 6 runs without deactivation.（2）[HSO3-BMIM][HSO₄] catalyst was used to produce BuAc in the esterification of HAc and n-butanol（n-BuOH）.The macroscopic reaction kenitics was studied,and the homogeneous models were used to predict the reaction rate（rb）and X_HAc.Results show that NIH（M）model has exact fitting and prediction of rb and X_HAc,the rate equation of NIH（M）model is as follows:（?） The catalytic activities of [HSO3-BMIM][HSO₄] and other Br（?）nsted acidic ILs（BAIL_s）and Amberlyst-15 in the esterification of HAc and n-Bu OH were compared.It was found that the ILs which contained-HSO₄ and sulfonic acid group in the cation and anion had great catalytic activity.[HSO3-BMIM][HSO₄] showed faster rb and higher X_HAc than other BAIL_s catalysts,while rb and X_HAc were not decreased significantly after IL being reused for 6 runs.（3）The RD process of [HSO3-BMIM][HSO₄]-catalyzed esterification reaction was designed and simulated in Aspen Plus.（a）The RD process for EtAc production was conducted in a plate tower.RD tower operating conditions,for example,plate number,feed location of reactants,flow rates,catalyst concentration,reflux ratio,liquid holdup on tray and reboiler,were optimized.Results showed that the EtAc content in the product was 93.59%（97.76 wt %）,and the impurity content was less than 4%.（b）A packed RD tower was designed for Bu Ac production.The packed tower parameters i.e.packing section height,tower inner diameter,fed stage,fed mode,flow rate,reflux ratio,flow ratio of bottom to feed,liquid holdup of packing stage and reactor,condenser pressure,and the tower pressure drop were optimized.The optimized result indicated that Bu Ac concentration in the conventional RD（CRD）process was 70.93%（91.05 wt %）,and it could be improved to 77.95%（95.02 wt %）in the intensified RD（IRD）process,and the mole fractions of HAc and n-Bu OH were less than 1.5%.X_HAc increased from 90.94% to 99.72% by RD process intensification.IRD process reduced the TAC by 26%.[HSO3-BMIM][HSO₄] showed higher catalytic activity than resin A in the IRD process.（4）The [HSO3-BMIM][HSO₄]-catalyzed RD process was conducted in a laboratory-scale packed tower to produce EtAc.The continuous RD process and bottom liquid recycle RD process experiments were performed.The influences of the design parameters such as reflux ratio,liquid holdup,ccat and RHAc:Et OH on the EtAc purity in products were studied.The purity of EtAc in the continuous RD process was 87.23 wt %,and the EtAc purity in the bottom liquid recycle RD process was 83.15 wt %.The simulated results of Aspen differed from the experimental values by 1.59 wt %.（5）SILs were synthesized and applied to the esterification of HAc and Et OH to produce EtAc.The characteristics of SILs were analyzed by infrared spectroscopy,thermogravimetric,nitrogen adsorption desorption and scanning electron microscopy.Results indicated that the Sol-Gel method was more effectively than impregnation in ILs immobilization at the conditions of RA:E0 = 1,T in the range of 323.15 K–338.15 K,and xcat:HAc in the range of 5%–15%.The SILs synthesized by Sol-Gel method,[HSO3-BMIM][HSO₄]/SiO₂,showed fast reaction rate,X_HAc exceeded 50% at the first 30 min,which achieved 70% of the equilibrium conversion(X_HAc = 68%).The X_HAc（t = 4 h）of reused [HSO3-BMIM][HSO₄]/SiO₂ exceeded 60% in the repeatability experiment,which was decreased at 6 runs.The catalytic activity and stability of SILs prepared by Sol-Gel method were better than impregnation.Results show that Sol-Gel method is suitable for the preparation of SILs.