Study On Recovery Of DMF From Meropenem Wastewater

N,N-dimethylformamide(DMF)is an important chemical raw material,widely used in polyurethane synthetic leather,fiber,medicine,petrochemical,and other fields.Due to the high concentration of DMF and salt in the production wastewater of meropenem,in this paper,chloroform was used as an extractant to recover DMF from salt-containing pharmaceutical wastewater by solvent extraction.The liquid-liquid equilibrium data of H2O-DMF-CHCl3 system at different NaCl concentrations were determined.On this basis,the process simulation of liquid-liquid extraction and the evaluation of extraction performance on reciprocating sieve plate extraction column(RPEC)were carried out.The main research contents and conclusions are as follows:(1)An analytical method combining gas chromatography(FID)internal standard method,Karl-Fischer moisture method,drying method and normalization method was established.The liquid-liquid equilibrium data of H2O-DMF-CHCl3 in the presence of NaCl with various concentrations of 0,2.5,5.0,7.5,10.0,13.3 wt%at 25℃ were determined.The effect of salting-out effect on phase equilibrium was investigated.The reliability of the experimental values was verified through the Eisen-Joffe equation,the correlation coefficient R2 of which is more than 0.9981.The NRTL thermodynamic model was applied to correlate the experimental data with RMSD less than 0.0062,indicating that the experimental values were basically the same with the calculated values.The consistency of the model parameters was checked by topological analysis of mixed Gibbs energy function,and the fitting results met the Gibbs stable equilibrium condition.(2)The process simulation and experimental verification of multi-stage cross flow and multi-stage countercurrent extraction of DMF from wastewater were carried out.The optimal mass ratio of extractant to feed was determined to be 2.5:1.The DMF recovery rate of the five-stage cross-flow extraction was 99.94%,and that of the five-stage countercurrent extraction was 99.92%.The difference between the simulated and experimental recovery rate was less than 0.05%.(3)The separation effect of extracting DMF in RPEC was studied.The calculated and experimental results show that the extraction performance and operation elasticity are better when the dispersed phase is salt-containing DMF wastewater,and the continuous phase is chloroform.The increase of agitation rate enhances the mass transfer but also aggravates the back-mixing.More than 90%of the tower height is used to compensate for the adverse effects of axial mixing.Within the operating range,under the conditions of agitation rate Af of 0.06 m·s-1 and mass transfer direction of d→c,the maximum recovery rate of DMF is 95.3 1%.At this time,the content of DMF in the raffinate phase is about 1.173wt%,and the error between the calculated and the experimental value is within 15%.