Study On Decolorization Of Alcoholysis Solution By Peroxicoagulation

Polyethylene terephthalate?PET?is an excellent material widely used in the textile industry and daily life,but the large amount of waste polyester generated every year places great pressure on the environment.At present,the most common method of degrading PET is to use ethylene glycol?EG?to degrade polyester into oligomers or monomers.After the reaction,the polyester alcoholysis solution contains a large amount of residual ethylene glycol,as well as some dyes,additives and other impurities.Direct discharge will pollute the environment.If it is not purified and then used to degrade polyester,then the impurities in it will affect the purity of the degradation product.Therefore,it is of great significance for the development of the polyester recycling industry to seek an effective method for decolorizing the polyester alcoholysis solution,so that the alcoholysis solution can be recycled.In this study,graphite was used as the main material to prepare the gas diffusion electrode,and the dye disperse yellow 114 was used as the target pollutant.A peroxicoagulation system was constructed to treat the polyester alcoholysis solution,and the effects of various parameters on the coupling system treatment efficiency were investigated.And initially explored the mechanism of dye decolorization.The main research contents are as follows:The subject firstly carried out the research on the treatment of polyester alcoholysis solution by electrocoagulation method using aluminum electrode and iron electrode respectively,and discussed the influence of voltage,initial pH value,electrolyte mass concentration and dye mass concentration on the decolorization rate during the treatment process using single factor.The results showed that the decolorization rate of the iron electrode was 86.2%after treating the alcoholysis solution under the best conditions for 80min.Compared with the iron electrode,the aluminum electrode electrocoagulation treatment polyester alcoholysis solution is better,when the voltage is 20 V,the initial pH value is 8,the electrolyte mass concentration is 0.8 g/L,and the dye mass concentration is 60 mg/L,the decolorization rate of the alcoholysis solution after electrolysis for 80 min was 96.4%.Although the performance of the iron electrode is not as good as the aluminum electrode in the electrocoagulation process,during the reaction of the iron electrode,the system will continue to produce ferrous ions and iron ions.The generation of ferrous ions in the system provides the possibility for the coupling reaction to proceed.Therefore,in order to overcome the shortcomings such as high energy consumption of electrocoagulation,we tried to couple electro-flocculation and Fenton and prepare graphite/polytetrafluoroethylene?PTFE?gas diffusion electrode.The preparation technology of graphite/PTFE cathode was studied,and the polyester alcoholysis solution was treated with graphite/PTFE cathode.The study found that ammonium bicarbonate is the most suitable pore-forming agent.When the mass ratio of graphite to PTFE is 3:1,the cathode activity is highest.The hydrophobicity has a great influence on the performance of graphite/PTFE cathode.The waterproof layer can effectively improve the H₂O₂ output of the graphite/PTFE cathode.The electrode prepared by the above optimization process under the condition of the initial pH value of the solution is3,and the concentration of H₂O₂ generated in the system can reach 94.8 mg/L after 120minutes of reaction;At a current density of 7 mA/cm²,an electrolyte pH of 7,and under continuous oxygen supply,the decolorization rate of the polyester alcoholysis solution after peroxicoagulation treatment reached 97.4%for 80 min,which is an increase of more than 10%compared with the effect of the single ferroelectric flocculation treatment under the best conditions.Finally,in order to improve the current efficiency of the cathode and the catalytic activity of oxygen reduction,graphite materials were treated with H₂O₂-H₂SO₄ to make the modified graphite/PTFE electrode.X-ray photoelectron spectroscopy,cyclic voltammetry,and other methods were used to analyze the chemical structure and electrochemical performance of the modified graphite-polytetrafluoroethylene?PTFE?electrode.The results showed that the modified electrode contained more defect sites and oxygen-containing groups.0.1 mol/L Na₂SO₄ solution was used as the electrolyte,when the current density is 7 mA/cm²,pH value is 3,the H₂O₂ output of modified electrode is 120.7 mg/L after 60 min,while unmodified electrode is only 76.8 mg/L.Treating polyester alcoholysis solution with modified electrode,the decolorization rate reached 98.3%after 50 min,which shortened the processing time by30 min.Compared with the electrocoagulation and electro-Fenton method alone,the processing efficiency of peroxicoagulation is better,and lower energy consumption is produced,it has higher application value.Purify the decolorized alcoholysis solution,and use the recovered ethylene glycol for the degradation reaction of the polyester fabric again.According to differential scanning calorimetry and thermogravimetric analysis,the degradation products are consistent with those obtained using fresh ethylene glycol.It proves that the glycol recovered from the decolorization of alcoholysis solution has the feasibility of being used for degrading polyester fabric again.