The Selection Of Cosolvent For Refining Rude Benzene By Extraction Distillation

Benzene is a kind of important chemical materials. Refining Rude Benzene is an important method to obtain pure benzene in China. Currently, German Krupp- Koppers (K-K) method whose solvent is N-Formylmorpholine (NFM) is an extractive process widely used.N-Formylmorpholine (NFM) has advanages of good selectivity and heat stability. But there is a bottleneck in the process, which is how to decrease the ratio of solvent in the extractive distillation column and increase the throughput of pure-benzene process while the content of benzene in the non-aromatic hydrocarbons in the top of the column is reduced.At present, multiple extracting agents are the trends of extractive distillation research, which is used to improve the condition of separated process. The vapor-liquid equilibrium (VLE) data of NFM containing systems is needed while studying on the effect of the factor to extractive distillation, such as the content of cosolvent, the ratio of solvent, and so on.As the mensurable components of rude benzene of the manufacturers are over 90 genus, benzene and cyclohexane are selected to carry out experiments as components to be separated for they are more difficult to separate than other components, and their content is the most, and they are the most representative. The VLE data of benzene- cyclohexane-NFM ternary system were measured at atmosphere and the ratio of solvent and relative volatility between cyclohexane and benzene were obtained as reference value of cosolvent selection. N, N-dimethylformamide (DMF), ethylene glycol, diethylene glycol and dimethyl sulfoxide were selected as cosolvent through researching a lot of literature. And the VLE data of benzene-cyclohexane-NFM-DMF, benzene-cyclohexane-NFM-ethylene glycol, benzene-cyclohexane-NFM-diethylene glycol and benzene-cyclohexane-NFM-dimethyl sulfoxide were measured at atmosphere, the ratio of solvent and relative volatility between cyclohexane and benzene were obtained. Compared with the reference value of NFM as the extractant (the total mass of solvent in the liquid phase is invariable), ethylene glycol (20 wt %) or dimethyl sulfoxide (10 wt %) is suited to be the coslovent. Vapor-liquid equilibrium (VLE) data for Ethylene glycol-NFM were measured at atmosphere with an improved Rose equilibria cell as supplementary data. NRTL equations were used to correlate the VLE data through the nonlinear least square method. The VLE data of benzene-cyclohexane-NFM-ethylene glycol quaternary system were compared with the data predicted by NRTL model from the VLE data of the correlative binary systems and the deviations are acceptable.