Separation Of Benzene And N-Heptane By Extractive/Extractive Distillation With Furfural Comppsite Extractant

Benzene is an important basic chemical materials, which can be used to synthesize a variety of fine organic chemical intermediates. Its purity is expected very high with the great market demand, so it has great social effects to produce benzene products suitable for market demand economically. Benzene stems from the coal industry and petroleum chemical industry mainly. The former attracts more and more attention, as the latter becomes more expensive for the short petroleum supply in the global market. The main impurities are paraffins in benzene produced by coal, such as heptane, cyclohexane, which account for more than 90% of the impurity. Because the impurities have very close boiling point to benzene's, they cannot be separated by normal distillation. The common methods to remove the impurities in benzene are azeotropic distillation, extractive distillation, etc. But these methods have their own shortcomings.The salt effect was studied by theoretical analysis and experiments to meet the need of separation task in chemical engineering processes. Because there are differences among the interactions between the salt and each component, the relative volatility of each component will be changed. Therefore, by the way of adding a little salt, the separation is achieved. Compared with azeotropic distillation and extractive distillation, separation with salt is a competitive method. In this paper it is mainly investigated that n-heptane is separated from benzene by adding salt to the furfural.By the experiments, n-heptane can be extracted from benzene with the composite solvent composed of furfural and salt. Optimum conditions of salt extraction are investigated: the solvent ratio V (furfural and salt composite solvent)/V (n-heptane-benzene mixture) = 1.0-2.0/1, the mass percent of potassium rhodanate is 5.0%-10%. Experimental results showed that the composite solvent can increase the distribution coefficient of n-heptane and the selectivity coefficient greatly. At the meantime, the n-heptane recovery was improved. By the experiments of vapor-liquid-equilibrium, this paper reviewed the influences on the relative volatility of benzene and n-heptane, such as the solvent ratio, kinds of solvents and salts, etc. The results show that the addition of salt is advantageous to improve the relative volatility. When the furfural was used as solvent and the solvent ratio was 1.0, the relative volatility of n-heptane is 1.832 to benzene. With adding potassium rhodanate into the system, the relative volatility can reach 2.243. On the basis of the experiment, the Tan-Wilson equation was introduced to describe vapor-liquid-equilibrium of the n-heptane-benzene-furfural-salt system. And the calculative results fit the experimental data well as the mean square deviationis only 0.0083.