Research On Extractive Distillation Separation Process Of Diethylene Glycol Monomethyl Ether(MDG)and N-Methyl Formamide(NMF)

Diethylene glycol monomethyl ether(MDG)and N-methylformamide(NMF)belong to close-boiling system in recovery process of photoresist waste stripping solution.High cost will be required when direct distillation is used to separate this mixture.Thus new separation technology should be studied and developed.Works haved been done for the separation of MDG and NMF mixture.First the mixture was separated by solvent extraction and melt crystallization,but the separation effect was not ideal.Secondly the extraction distillation of MDG and NMF were studied.According to the properties of MDG and NMF,the extractant was preliminarily selected.The extractant was quantitatively selected by using COSMO-RS theory.Experiments were carried out to verify the results of theoretical calculation.The appropriate extractant for MDG-NMF system was finally determined to be diethylene glycol.Further,the batch extraction distillation experiments were carried out.The relation of the purity(mass fraction)of the components at the top of the tower with the amount of extractant and the process parameters of the batch extractive distillation tower were obtained.The results showed that diethylene glycol as the extractant can meet the separation requirements.The binary vapor-liquid equilibrium data between MDG-NMF-diethylene glycol were obtained by using the improved vapor-liquid equilibrium reactor.The thermodynamic consistency of the experimental data was checked by using the area test method.According to the properties of the system,the NRTL model was selected to correlate with the experimental data,and the binary interaction parameters of the NRTL model were obtained.Finally,the continuous extractive distillation process of diethylene glycol was designed through Aspen plus.The influences of the main process parameters such as the amount of extractant and the number of theoretical trays on the separation process were analyzed respectively.Based on the analysis the main process parameters of the optimized distillation column were obtained.The results showed that compared with direct distillation,extractive distillation can significantly reduce the number of theoretical plates.