Study On Process Intensification And Optimization Of Oxidation Refining Of Hydrazine Hydrate Waste Salt Water By Sodium Persulfate

This thesis focused on the treatment of the by-product salt of hydrazine hydrate produced by keto nitrogenous method.The refining process of hydrazine hydrate waste salt water based on sodium persulfate（PS）oxidation was studied in order to realize the refined waste brine to meet the requirements of industrial chlor-alkali production.At first,a comparative study was conducted to demonstrate the possibility of total organic carbon（TOC）removal from hydrazine hydrate waste salt water by thermal-activated PS method.The influence law of reaction temperature,initial p H and initial sodium persulfate concentration on TOC removal from hydrazine hydrate waste salt water by thermal-activated PS method was studied by single-factor experiment.Response surface method was then employed to optimize the parameters of process of TOC removal from hydrazine hydrate waste salt water by thermal-activated PS method,and Design-Expert 12 software was used to simulate the process of TOC removal from hydrazine hydrate waste salt water by thermal-activated PS method.Finally,the TOC advanced removal of hydrazine hydrate waste salt water was studied through combining thermal-activated PS oxidation and salt washing processes.According to the experimental results,the main conclusions are as follows:（1）The comparative experimental study showed that the TOC of hydrazine hydrate waste salt water could hardly be removed by heating or adding sodium persulfate alone,and the organic matter in hydrazine hydrate waste salt water could be effectively d egraded by thermal-activated of PS.The removal of TOC could reach a high value of 86.3%by PS oxidation process activated at 90℃.（2）Single-factor experimental study showed that reaction temperature,initial p H and initial sodium persulfate concentration had significant effects on the removal of TOC from hydrazine hydrate waste salt water by thermal-activated PS process.High temperature was beneficial to improve the TOC removal efficiency of thermal-activated PS process through activating large amount of free radical SO₄^-·.The TOC removal from hydrazine hydrate waste salt water increased with the increase of initial sodium persulfate concentration.With increasing initial p H,TOC removal increased firstly,reached its highest value at the p H 9.0 and then decreased.（3）Response surface optimization study based on Box-Behnken method showed that the reaction temperature had the greatest effect on the removal of TOC from hydrazine hydrate waste salt water by thermal-activated PS method,and the initial p H had the least effect.By analyzing the response surface and contour plot,it was found that there was a significant interaction between reaction temperature and sodium persulfate concentration.（4）The simulated model based on software Design-Expert 12 predicted that the optimal parameters were sodium persulfate concentration 3.477 g/L,initial p H=9.443,reaction temperature 90℃,and reaction time 180 min.Under these conditions,an optimal TOC removal of 88.75%could be achieved.The average TOC removal obtained by three repeated experiments was 88.29%,which showed a very small difference compared with the predicted value,demonstrating the reliability of the simulated model.However,the TOC content of treated brine obtained under optimal conditions still cannot meet the requirements of chlor-alkali industry.（5）The study on the refining process of hydrazine hydrate waste salt water demonstrates that the advanced removal of organic matter in hydrazine hydrate waste salt water could be achieved by combining thermal-activated PS oxidation and salt washing processes.The salty water of the refined salt obtained through continuous refining experiment based on the hybrid process of thermal-activated PS and salt washing exhibited a TOC value between 2.6～5.8 ppm.During a 720-h experiment of ionic membrane electrolytic caustic soda production employing the above refined salt water,the current fluctuated steadily and the voltage fluctuated within the scope of 3.211～3.264V,demonstrating that the quality of purified brine could meet the requirements of chlor-alkali industry.