Liquid-liquid Extraction And Recovery Of N, N? Dimethylacetamide From The Salinity Pharmaceutical Wastewater

N, N-dimethylacetamide, referred to here in after as DMAC, a nonproton solvent with high polarity, which chemical formula is CH3C(O)N(CH3)2. It is widely used as an excellent organic solvent inpharmaceutical, heat-resistant synthetic fiber, plastic film,acrylonitrile spinning, petroleum processing, organic pigment and other areas of the industry because of its high hydrothermal stability, low corrosivity and toxicity, steady chemical property, fine solubility, difficult to hydrolysis, high boiling points and good solubility for polyurethane resin, polyimide resin as well. Especially in the production of pharmaceutical intermediate cefuroxime acid intermediates, the waste liquor is usually drained off with 5-17 wt% DMAC and a small quantity of dichloromethane(DCM). Due to the high cost of large distillation separation energy, direct emissions will cause a loss of DMAC and significant pollution. Therefore, to recover DMAC from the waste liquor and make the energy consumption less than recification the extraction method by using low boiling point solvents is adopted, which makes the extracting agent recovering more easily.Since a small amount of DCM and salts exists in the wastewater at the same time the system of extraction becomes complicated. The DCM extraction agent was selected to complete this work in order not to cause secondary pollution.Liquid-liquid extraction with multi-stage countercurrent and recovery of DMAC from the salinity pharmaceutical wastewater by using low boiling point DCM as an extracting reagent has been researched in this article, The single factor effect experiment has taken the liquid-liquid equilibrium cell made by our group in the water bath to analyze the data.Distribution coefficients(D) and selectivity coefficients(S) were measured to evaluate the extracting capability. The experimental results illustrates that adding salt to the system is beneficial to increase the selectivity of solvent, floating in a small range of the concentration of DMAC in waste still can effective extraction, tending alkaline is in favor of extraction and recovery of DMAC from the salinity pharmaceutical wastewater. The optimal operating conditions of extraction are determined in the experiment, which is pH=8, phase ratio=1, extraction and recovery of DMAC from the salinity pharmaceutical wastewater with DCM as extraction agent at room temperature and at mospheric pressure.The LLE data of the salt-removed DCM + water + DMAC + NaCl system were used to determine the theoretical stage number of 5 by the stepwise graphing method, and at last the extracting separations have been finished for the simulated wastewater and industrial wastewater. The comparison between experimental values and calculated values and that between the simulated wastewater and industrial wastewater are performed. Experimentalresults show that the content of DMAC in simulation waste liquor reduces to 0.74 %,the extraction recovery is 94.37 %, with the relative error between the theoretical and experimental results is 3.92 %, and while that in actual waste liquor reduces to 0.78 % and the extraction recovery is 92.53 %, with the relative error between the theoretical and experimental results is 6.41 %.Based on the optimal operating conditions, the theoretical stage number, and experimental related data, the extraction column has been design and calculation. The comparison between the extracting separations for the extraction packing column and the extraction tower with agitator has been finished. Experimental results show that the content of DMAC in the extraction packing column reduces to 0.98 %, the extraction recovery is85.82 %, with the relative error between the theoretical and experimental results is 25.51 %,while that in the extraction tower with agitator reduces to 0.85% and the extraction recovery is 88.53 %, with the relative error between the theoretical and experimental results is 14.12 %.