Separation Of Binary Azeotrope Methanol-Benzene By Extractive Distillation

As important organic solvents, methanol and benzene have been widely used in fields like fine chemicals, pharmaceuticals etc. At the atmosphere pressure, methanol and benzene have the relative low volatility and the same lowest azeotropic point, and they can form azeotropic system. Therefore, they cannot be separated by conventional distillation method to yield high purity target products.The paper studied on the separation process of methanol-benzene binary azeotrope through extractive distillation using chlorobenzene as the solvent.Firstly, the vapor-liquid equilibrium curve methanol-benzene was determined by means of combining experimental data and reference data,Then, chlorobenzene was chosen as the solvent using UNIFAC group contribution method. And the separation effect of chlorobenzene was also verified through VLE experiment. The results showed that chlorobenzene could effectively improve the relative volatility of methanol-benzene, and when the solvent ratio was set at 1:1, their relative volatility could attain 3.54.Secondly, batch extractive distillation experiment was conducted to separate the methanol-benzene binary azeotrope using chlorobenzene as the solvent. And the hydrodynamics performance parameters of the distillation column, the number of total reflux theoretical plates and the range of the manipulating reflux ratio were tested and determined. In the experiment, chlorobenzene was added from the top of the distillation column in a sequential manner. When the solvent ratio was 1:1, and operating at the constant reflux ratio(R=3), 310 ml methanol product with a concentration of 92.8% was obtained at the top of the column and the recovery ratio of methanol was 71.9%.Finally, process simulation software Aspen Plus was employed to simulate the consecutive distillation process of methanol-benzene binary azeotrope and software ChemCAD was used to simulate the batch distillation process. And the effects of reflux ratio, feeding flow rate and feeding position of solvent on porduct purity were studied and optimal operation parameters were obtained in the end.The results showed that, during the batch extractive distillation process, when the number of stages was 30, the optimal reflux ratio R=3, solvent feeding position Ns=4, solvent ratio S=1.25, the purity of the product obtained could reach 0.95(mole fraction), and the product recovery rate could attain 97%. During the continuous process, when the number of stages was 30, the optimal reflux ratio R=3, solvent and raw material feeding positions Ns=8, Nf=23, solvent ratio S=1.2, the mole fraction of methanol product and chlorobenzene obtained was 99.2% and 96.4% respectively. These results could provide some reference basis for industrial production.