Kinetic Study Of The Air Oxidation Reaction Of Sodium Sulphide In Wastewater

Ethylene waste alkaline liquid after oil-water separation is difficult to meet the requirements of wastewater treatment due to its high sulphide content,which has become an environmental problem restricting the development of China’s ethylene industry.Therefore,the low-cost and harmless treatment of alkaline wastewater has attracted much attention.One of the more commonly used methods is wet oxidation,but most of the classical wet oxidation methods are carried out under high temperature and high pressure conditions,which are influenced by process mass transfer,huge equipment and low efficiency.In this paper,we aim to improve the efficiency and reduce the cost of air oxidation of sulphur-containing waste lye by simulating the oxidation of wastewater in a liquid-phase circulating reactor using a self-prepared sodium sulphide solution.The effect of the reaction conditions on the removal rate of sodium sulphide and the concentration distribution of the intermediate products sodium thiosulphate and sodium sulphite was investigated using a singlefactor controlled variable method at a reaction temperature of 313-363 K,a pressure of 0.2-1.0 MPa,an air flow rate of 100-500 m L/min,a circulation rate of 40-110 L/h and an initial concentration of 1000-15000 ppm.The experimental data required for the kinetic simulations were thus obtained.The kinetics of the air oxidation of sodium sulphide and the intermediate products sodium thiosulphate and sodium sulphite were simulated using MATLAB scientific computing software,assuming a one-stage reaction,and the effect of air pressure on the number of reaction stages on the simulation results was investigated.The results showed that the oxidation of sodium sulphide and the intermediate products sodium thiosulphate and sodium sulphite reacted to air pressure on a non-integer scale,and the reaction steps of sodium sulphide,sodium thiosulphate and sodium sulphite to air were 0.24,0.71 and 0.51,respectively.the average relative error of the sodium sulphide oxidation obtained using the model was 14.06%.Statistical tests showed that the resulting kinetic model was significant at the 95% confidence interval.Based on the above kinetic parameters,a continuous flow sulphurcontaining waste alkali air oxidation treatment reactor with liquid phase circulation was modelled and simulated to investigate the effect of the reaction operating conditions on the sodium sulphide removal rate.It was found that an increase in circulation volume,feed concentration and volume reduction were all beneficial for the removal of sulphur ions.A useful reference for subsequent reactor scale-up and improvement of process conditions is provided.