| Calcium magnesium acetate(CMA) is a mixture of calcium acetate and magnesium acetate; it is an environment-friendly organic acid salt which is substitute of highway snow (ice) melting agent sodium chloride. And the recent research results have found that CMA can remove NOx and SO2 emitted from coal combustion and HCl emitted from polyvinyl chloride combustion, to reduce the air pollution. But due to the high cost of its normal producing method, the application of the CMA is limited.In this paper, the green chemical of calcium magnesium acetate was prepared from acetic acid wastewater by extraction. The sulfonated polyethersulfone hollow-fiber membrane was used for extraction with trialkylamine(7301)/n-octanol/kerosene as extractant, afterwards, back-extraction was carried out to get CMA with CaO-MgO as back-extractant. The optimum conditions for extraction and bake-extraction are studied simultaneously. The effect of acetic acid concentration, flow velocity of organic phase and water phase, flow ratio, time as well as membrane swelling on extraction was studied; and the effect of amount of back-extractant, molar ratio of Ca to Mg, back-extraction time as well as back-extraction temperature when adopt CaO-MgO as back-extractant on back-extraction ratio was studied either. Based on this, the economic balance has been made for the membrane extraction. The results showed that:(1) The optimum conditions for the single stage extraction are as follows: The mass fraction of wastewater acetic acid is 2%, the water flow in tube and the organic flow in shell are countercurrent, the flow ratio of organic phase to water phase is 1.30, and the water flow is 0.23mL/min. The extraction ratio of the single stage can reach 74%, the total mass transfer coefficient is 3.06×10-7m/s and extraction ratio of the two-stage can reach 95%.(2) For countercurrent circulate extraction, the total extraction effect of two-stage extraction is better than that of single stage extraction under the same amount of organic extractant. Swelling makes the structure of membrane loose, which causes membrane flux increased, the total mass transfer coefficient rises, and the extraction ratio is increased.(3) The optimum conditions for back-exaction are as flows: CaO-MgO emulsion mass concentration 100g/L, molar ratio of CaO-MgO to acetic acid 1.0:2.0, molar ratio of Ca to Mg 2.9:7.1, back-extraction time 30 min and room temperature. The back-extraction efficiency can reach 97%. (4) It solved the problems of solvent entrainment loss of complexation extraction by adopting the membrane extraction, which could reduce the secondary pollution and producing cost, and provided a new method for the recycle of acetic acid wastewater as well as the CMA producing.The results of this research have provided theoretical foundation for the industrialization of acetic acid wastewater treatment to recover the green chemical CMA.
|
PDF Full Text Request