Study On Bactericidal And Corrosion Inhibition Mechanism Of ClO₂ And Organophosphorus In Circulating Cooling Water

The water quality of circulating cooling water will affect the stability and safe operation of the commercial unit,which is a particular concern of enterprises.However,fungicide and scale inhibitor are usually the first choice for treatment of circulating cooling water.Taking the circulating cooling water of a coal chemical enterprise in Heilongjiang province as the research object,this paper compares and evaluates the bactericidal effect of non-oxidizing fungicide-sodium dichloroisocyanurate and oxidizing fungicide-ClO₂ through production test.As well as,static experiments were conducted to study the bactericidal effect of ClO₂ on typical bacteria and its corrosion characteristics on metal.Moreover,in the presence of fungicide ClO₂,the inhibition scale and comprehensive properties of organic phosphine agents were also studied,and a compatible agent with good inhibition performance was simultaneously optimized by response surface method.Meanwhile,the corrosion mechanism of ClO₂ on carbon steel and the corrosion inhibition mechanism of compound corrosion inhibitor on carbon steel were clarified by means of quantitative calculation,in order to provide support for the application of organic phosphine corrosion inhibitor.The main research contents and results were as follows.The bactericidal effect of chlorine dioxide on heterotrophic bacteria and sulfide bacteria were studied,and the germicidal effects of different fungicides were also compared and evaluated.In addition,the corrosion effect of chlorine dioxide on different metals were also investigated.The results showed that chlorine dioxide had obvious bactericidal effect on the two kinds of bacteria.The sterilization rate of ClO₂ for two kinds of bacteria could achieve at least 90 %,when the dose of ClO₂ was 0.6 mg/L,p H = 7.0,the temperature was 20.0℃,within 15 min.Meanwhile,the increase of ClO₂ concentration,temperature and reaction time would promote the bactericidal effect of ClO₂.Through the productive experiments of the bactericidal effect of ClO₂,it was found that the presence of ClO₂ could significantly make the bacteria in the circulating cooling water reaching the standard of GB50050-17 “Codefor design of industrial recirculating cooling water treatment” comparing with the addition of sodium dichloroisocyanurate and 1227 corrosion and scale inhibitor.Furthermore,the presence of ClO₂ could cause different degrees of corrosion to the metals through studying on the corrosion properties of different metals by different chlorine bactericidal fluids（ClO₂,liquid chlorine and their mixture）.When the concentration of the ClO₂ was 10.0 mg/L,temperature was（40.0 + 1.0）℃,rotating time was 720 h,p H value was 8.0,the corrosion rate of carbon steel,aluminum,copper and stainless steel were 0.5966 mm/a,0.0610 mm/a,0.0166 mm/a and 0.0048 mm/a,respectively.In addition,it was found that ClO₂ had a certain degree of corrosion inhibition effect on carbon steel through the corrosion study of liquid chlorine,ClO₂ and their mixture.By the calculation of quantum chemistry,compared with ClO₂ corrosion of carbon steel,HCl O is more likely to react with iron atoms,that is,liquid chlorine is more likely to corrode carbon steel.In addition,Fe2+ could also provide electrons to ClO₂ to generate Fe3+,which could form the precipitation of iron hydroxide on the surface of carbon steel,preventing the corrosion of carbon steel and showing corrosion inhibition characteristics.The corrosion,scale inhibition and combination properties of PBTCA,HEDP and ATMP on carbon steel were studied by adding ClO₂ fungicide.When the concentration of ClO₂ was 7.0 mg/L,temperature was（40.0 + 1.0）℃,p H = 9.0,rotation response time was 72 h,the average corrosion rate of the three kinds of organophosphorus corrosion inhibitor could reach more than 80 %.Meanwhile,response surface curve method was applied to mix ClO₂,organophosphorus corrosion inhibitor and inorganic corrosion inhibitor,and a compound agent was optimized with high corrosion inhibition efficiency.The optimized compounding scheme was that the additive concentration ratio of PBTCA and HEDP was 1.45（8.88 mg/L,6.12 mg/L）,the concentration of zinc ion was 2.86 mg/L,the concentration of chlorine dioxide was 6.76 mg/L,the p H value was 7.43,the temperature was（40.0 + 1.0）℃,and the rotating reaction time was 72 h.Under the optimal combination scheme,the experimental value of corrosion inhibition rate was 98.82 %,and the corrosion rate was 0.0089 mm/a,which was very close to the predicted value of corrosion inhibition rate response,98.16 %,and the corrosion rate was 0.0138 mm/a.At the same time,it was found that the change of Zn²⁺ concentration indicated the inhibition effect of the inhibitor in circulating water.When the concentration of Zn²⁺ suddenly increased,the inhibition performance of the indicator inhibitor decreased,so it was necessary to continue adding the inhibitor.Finally,the corrosion inhibition mechanism of organic phosphorus compound corrosion inhibitor on carbon steel was analyzed by combining the theoretical calculation of quantum chemistry,molecular dynamics simulation and SEM detection.It was also proved that the adsorption of organophosphorus inhibitor on metal surface followed Langmuir monolayer chemical adsorption.The results of molecular dynamics simulation showed that the three organophosphorus inhibitor molecules were vertically distributed on the metal surface to effectively isolate the metal surface from the water molecules.The adsorption energies of three organophosphorus inhibitor molecules（PBTCA,HEDP and ATMP）interacting with Fe（0 01）surface were 305.64 k J/mol,131.29 k J/mol and 101.45 k J/mol,respectively.Based on DFT algorithm,three kinds of organophosphorus corrosion inhibitors acted as electronic buffer.The positively charged phosphorus atoms of PBTCA received electrons from the iron atoms,while the negatively charged oxygen and nitrogen atoms of the three organophosphate corrosion inhibitors provided electrons to zinc and ferrous iron ions in the water,which resulted in a double layer of complex layer forming in the circulating cooling water and adhered to the iron surface so as to prevent the corrosion of carbon steel.Because circulating water is usually at a higher temperature,organic phosphine corrosion inhibitors have certain decomposition characteristics.Thus,after a period of time of drug action,the complexed Zn²⁺ can be dissociated,resulting in a sudden change in the concentration of Zn²⁺.Then the corrosion inhibition performance of the compound agent decreased,indicating that we need to supplement the corrosion inhibitor in the water to ensure a certain corrosion inhibition efficiency.