Research On Recovery And Treatment Technology Of ADC Industrial Sewage Resources

ADC foaming agent is the abbreviation of azodicarbonamide,belonging to azo blowing agent,and the molecular formula is H₂NOCN=NCONH₂.It is widely used in many fields,due to lots of advantages such as large gas production,uniform and compact pore distribution,high decomposition temperature,decomposition products for any processing technology,and cheap price.The production of ADC foaming agent by urea method will consume a large amount of chlorine and sodium hydroxide,while China is a large chlor-alkali producing country,there are abundant and cheap chlorine and sodium hydroxide in the market.Therefore,the use of urea as a raw material to produce ADC foam agent is a very popular production process adopted by the vast majority of enterprises.The industrial wastewater of ADC foaming agent produced by urea mainly contains sodium chloride,ammonium chloride,unreacted urea and hydrazine hydrate,as well as reaction by-products,etc.The wastewater is characterized by high salt,high ammonia nitrogen,high COD,high toxicity and poor biodegradability.Therefore,nowadays the method how to efficiently remove COD from ADC foaming agent wastewater,make the wastewater meet the requirement standards of discharge or reuse,reduce the processing cost and,at the same time,improve the utilization ratio of resources in the wastewater is an important issue in the field of chemical industry and environmental protection.According to the composition and characteristics of the main pollutants in the wastewater of ADC foaming agent,the simulated wastewater was produced.Then,based on the simulated and the actual wastewater,the factors influencing the hydrolysis and oxidation of the main pollutants in the wastewater and the resource recovery effect of salt were researched in this work.When studying the hydrolysis of major pollutants in sewage,first,the simulated wastewater of the production process of ADC foaming agent is prepared with urea.The reaction temperature,the molar ratio of sodium hydroxide to urea,and the reaction time are first tested by the urea-formulated simulated wastewater.Through the orthogonal test,The reaction time,the molar ratio of sodium hydroxide to urea and the reaction temperature on the hydrolysis of urea decreases in turn,but all have significant effects.In order to overcome the limitation of multi-factors in the single-level test of orthogonal test,the single factor optimization of each condition is also carried out.The optimization experiment of simulated wastewater prepared by urea hydrolysis condition are carried out,and the experimental results are as follows.The urea hydrolysis rate will reach the peak value and the correlative TOC removal rate can reach 91.00%,when the initial concentration of urea is 20.00g/L,and the molar ratio of n?NaOH?:n?CO?NH₂?₂?=3:1 is controlled at the pressure of 0.12MPa in a high pressure reactor at 120?for 120 minutes,And the salinity of the solution will not obviously affect the hydrolysis of urea.The experiment of ADC foaming agent wastewater is also carried out under the same conditions with that of simulated wastewater,while its TOC removal rate can only reach 22.36%.The results of the NaClO urea oxidation experiment show that the removal rate of TOC will reach the maximum?83.9%?,when the initial concentration of urea is 20.00g/L,under atmospheric pressure,the reaction temperature is 50?,the mole ratio is n?NaClO?:n?CO?NH₂?₂?=3:1.the stirring speed is 200r/min,and the reaction time is 20min.The experimental results of ozone oxidizing urea show that ozone has little effect on the oxidation decomposition of urea.In addition,through analysis of the major contaminant components in the ADC foaming agent,the process of treating ADC foaming agent wastewater,namely“evaporative crystallization-cooling crystallization-salt refining-catalytic degradation–oxidation”,is proposed.After the treatment process,the NaCl and NH₄Cl solids were obtained,the purity of NaCl is 99.4%,which can be used directly for the electrolysis of salt water.And the purity of NH₄Cl is 85.8%,which can be used as an industrial raw material.At the same time,most of the urea and hydrazine hydrate in the wastewater are recycled.A small amount of urea,hydrazine hydrate and other organic pollutants can reach the discharge standard after treatment.Therefore,the process can reduce the cost of wastewater treatment and achieve the purpose of reuse of resources.