Research On The Degradation Of PVA Textile Materials By Ozone Oxidation/Wet Oxidation Combined Process

Nonwovens made of water-soluble PVA fibers are widely used in the field of disposable textiles.For example,it can be used to manufacture the one-off work clothes for special industries.These disposable textiles need to be dealt with after being used.The traditional treatments are landfill and dump,which will cause serious permanent damage to the soil and the waste of space.Nowadays,the most commonly used way of treatment is to dissolve it in water for subsequent processing.However,PVA water solution has good stability,the effect of traditional physicochemical and biochemical methods is not obvious.As a research hotspot,advanced oxidation technology has been successfully applied to the treatment of PVA and other toxic and hazardous wastewater.In the existing studies,advanced oxidation techniques for degrading PVA wastewater mostly use catalysts.The use of the catalyst is easy to bring secondary pollution,so that the effluent quality can not reach the ideal condition.Even if the catalyst components in the effluent are treated,a large amount of sludge will be brought,and the environmental protection can not be truly realized.Based on the current state of the society is paying more and more attention to environmental protection and the current technology for degrading PVA will involve the problem of secondary pollution and other issues.In this paper,ozonation/wet oxidation combined process was applied to environmental degradation of PVA textile materials.According to the technical and economical of the process,the process conditions for the ozonation pretreatment process and the wet oxidation deep degradation process were optimized,and the reaction mechanism was preliminarily explored.Finally,experiments were carried out to verify the engineering practicality of the ozonation/wet oxidation combined process,main research contents and related conclusions are as follows:?1?PVA textile materials were pretreated with ozonation process.The effects of reaction temperature,ozone penetration rate and initial pH value of solution on the degradation of PVA were investigated by single factor effect experiments.The results showed that the degradation effect gradually became worse with the increase of the reaction temperature,became better and then worse with the increase of ozone penetration rate,and the degradation effect was better in the neutral and weak alkali system,but poor in the strong alkaline and acid system.According to the economics of the process,the appropriate process conditions were determined,namely,the reaction temperature was 20°C,the ozone penetration rate was 18 g/h,and the initial pH value of the solution was kept unchanged at 7.Under this condition,ozone was used to pretreat100 mL PVA textile material solution whose concentration was 20 g/L.After 4 h,the concentration of PVA decreased to 0.286 mg/L and the PVA degradation rate was almost 100%.The GPC molecular weight distribution of the solution also changed significantly,the peak molecular weight decreased from 130191 to 2424,indicating that PVA macromolecules had been completely degraded to low molecular weight substances.?2?Under the optimized process of ozone pretreatment PVA textile materials,a certain concentration of hydroxyl radical trapping agent CO₃^2-was added to the original PVA textile material solution.It was found that the degradation effect of ozone on the PVA textile material was obviously worse at this time,indicating that the degradation of PVA by ozone was achieved through the indirect oxidation of hydroxyl radicals.According to the GC-MS analysis results of the effluent after reaction of 6 h,the reaction pathway of ozonation was predicted.First,the ozone molecules in the solution react with OH^-to produce hydroxyl radicals,then the hydroxyl radicals attacked the carbon atoms linked to the hydroxyl group in the PVA chain,causing the carbon chain to break randomly,electronic rearrangement and transfer of hydrogen radicals oxidized the chain-broken products to carbonyl compounds.?3?The COD value of the ozone-pretreated PVA effluent after reaction of 6 h was measured.It was found that the COD value was still as high as 42140 mg/L,and the removal rate of COD was only 57.383%,which required further degradation.The wet oxidation process was used to deeply degrade the ozone-pretreated PVA effluent.The effects of reaction time,reaction temperature,oxygen partial pressure,and initial pH on the COD removal rate of the solution were investigated by single-factor and orthogonal optimization experiments.According to the economy of the process,the suitable process conditions were determined,namely,the reaction time was 3 h,the reaction temperature was 275°C,the oxygen partial pressure was 0.8 MPa,and the initial pH value of the solution was 2.5.After the reaction,the COD removal rate of the solution increased from 57.383%to 93.715%,and the molecular weight distribution of GPC changed obviously,the peak molecular weight decreased from 2216to 401,realizing the purpose of the deep degradation of the ozone-pretreated PVA effluent.And after the experiment,the final effluent solution remained colorless and clear,and no turbidity was generated,and there was no secondary pollution,which met the requirements of environmental degradation.?4?The ozone-pretreated PVA effluent and the final effluent were freeze-dried.It was found that the former still had many substances left after the removal of water,while the latter had very few substances left after the removal of water,indicating that the process of wet oxidation deep degradation produced a lot of volatile molecules with very small molecular weight,as well as H₂O,CO₂,resulting in the very few remaining substances after the water was removed from the final effluent.According to the results of infrared analysis and GC-MS analysis,the reaction mechanism of the wet oxidation deep degradation process was preliminarily explored,and the reaction pathway was predicted:in a high-temperature closed system,the hydroxyl radicals oxidized the aldehydes and ketones in the ozone-pretreated PVA effluent to carboxylic acids,and attacked the organic molecules to cause the carbon chain to break.?5?Ozonation/wet oxidation combined process was used to degrade other types of PVA under optimized process conditions.All of their COD value reduced greatly,COD removal rate was over 90%,and the molecular weight was also greatly reduced.PVA macromolecules were degraded to small molecular weight substances.After various types of PVA were degraded,the aqueous solution remained colorless and clear.There was no turbidity,no secondary pollution.The environmental degradation of various types of PVA had been achieved,indicating that the ozonation/wet oxidation combined process had good engineering practicability.