Research On The Recovery Of DMAC In The Waste Liquid

As an important industrial solvent, N,N-dimethylacetamide(DMAC) has a strong ability of dissolution for many compounds, which frequently encountered in the manufacture of rubbers, resins and fibers. At the same time, it is an important reaction medium in the manufacture of polyether sulfone hollow fiber membrane. However, a lot of DMAC waste liquid inpour into water area during manufacture, use and disposal every year. Losses of these toxic substances to the ambient water may lead to an adverse environment impact on the water quality and thus endanger public health and welfare. In this dissertation, the feasibility and conditions of DMAC's recovery is our research's emphases through extraction and rectification processes.A liquid-liquid extraction process is studied for recovering DMAC from waste liquid. In contrast with other low boiling point extractats, we choose chloroform as the extractant. For the purpose of quick analysis, an ultraviolet absorption spectrophotometry for determining DMAC at wave length 198nm was established. Correlation between the absorbency and composition of the binary solution is reported: CDMAC-10. 509A-0. 3.The effects of several variables such as temperature, pH and dosage of extractant are investigated. Through mensurating the phase of DMAC-Chloroform-Water ternary systems, the theoretic stage and the effect of extraction are studied. The five experimental stages with counter-current and four experimental stages with downstream extraction are operated. It is showed that under the conditions normal temperature and chloroform being the extractant. the DMAC concentration in the aqueous effluent canbe decreased from 30%(w/w) to about 300mg/l by 5-stage counter current extraction when the ratio of organic phase to aqueous phase is 2:1. The value of pH has obvious influence on extraction efficiency; higher pH value is advantages to extraction.The date of both the refractive index and composition were measured by refractivemeter. Correlation between the refractive index and composition is reported: n25D =1.3286 + 0.1684x_DMAC-0.0572x2_DMAC liquid equilibrium data of DMAC-Water system have been determined by double circle vapor-liquid equilibrium kettle. Because there is no constant boiling point and boiling temperature between DMAC and Water has a very large gap, the target of separation can be obtained by the means of rectification. We adopt the way of area, which was suggested by Herrington, to verify thermodynamics coherence. The results show that data fit to thermodynamics relation.The DMAC and Water mixture was separated in a laboratory rectification tower, and the effects of several variables such as reflux ratio, pressure and accumulative batch distillation is investigated. During the process of operation, the content of DMAC in the bottom of the rectification tower increase smoothly. In the first period we keep the content of rectification solution constant and increase the reflux ratio. In the second period we make reflux ratio equal to 3 and extracted middle rectification solution. In this way, not only economize energy and shorten the time of operation, but also we can gain pure DMAC. So the effects of separation are good and can be reused in the manufacture.In this dissertation, the recovery of DMAC is determined in two processes. In the rectification process, we find DMAC decompounded into dimethylamine on account of long time distillation. We think the extraction process is the better in these two processes because the rectification process consumes plentiful energy in long time distillation.Since the extensive application of DMAC as solvent and reaction medium has been increased in textile and paper making fields, the obtained results are very useful in reducing production cost, reproduction expending and environment protection.