废旧聚酯碱性水—甲醇溶液高效解聚回收对苯二甲酸

Efficient depolymerisation of waste polyester in alkaline water-methanol solution forterephthalic acid recovery

为了高效解聚废旧聚酯回收对苯二甲酸,本文采用水—溶剂热技术,以碱性水—甲醇溶液高温高压处理废聚酯粒料,再用硫酸析出对苯二甲酸,并优化了碱性水—甲醇溶液解聚聚酯的工艺条件。结果表明,浴比为1︰20时,质量浓度50 g/L的氢氧化钠与100 mL/L的甲醇混合溶液,160℃条件下处理聚酯粒料2.5 h,对苯二甲酸产回收率为94.9%;红外光谱、核磁共振谱和高效液相色谱分析表明,所得分离产物的化学性质与对苯二甲酸标准品高度吻合,其纯度为90.53%。标准化视觉和数字色彩评定仪分析表明,所得对苯二甲酸与商业品存在较大色差(16.02),含有少量淡黄色杂质。

Polyester,especially polyethylene terephthalate(PET),is widely used in the textile and apparel industries due to its excellent thermal,mechanical,and chemical stability.However,with increasing consumption,the environmental impact of waste polyester fibers has become increasingly pronounced.The problem in biodegrading PET poses technical challenges for the recycling and reuse of waste polyester,particularly in terms of efficient depolymerization and the recovery of valuable chemical monomers.Traditional methods for dealing with waste polyester are plagued by low efficiency,high costs,cumbersome processes,and significant environmental pollution.Therefore,developing efficient,economical,and energy-conserving recycling technology for waste polyester is significant for alleviating environmental pressure and achieving resource recycling.This study aims to explore a novel water-solvent thermal technology for the efficient depolymerization of waste polyester and the recovery of terephthalic acid(TPA),providing a new approach for the high-value recycling of waste polyester.To efficiently depolymerize waste polyester and recover TPA,this study employed water-solvent thermal technology.Waste polyester pellets were treated with an alkaline water-methanol solution under high temperature and pressure,followed by the precipitation of TPA using sulfuric acid.The process conditions for the depolymerization of polyester in the alkaline water-methanol solution were optimized.Various analytical techniques,including Fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance(NMR)spectroscopy,and high-performance liquid chromatography(HPLC),were used to characterize the chemical properties and purity of the obtained TPA.Additionally,the VeriVide DigiEye(Roachelab)system was used to evaluate the color characteristics of the product.The use of hydro-solvent thermal technology in this study achieved efficient depolymerization of waste polyester,and the use of sulfuric acid facilitated the efficient precipitation of TPA.The systematic optimization of depolymerization process parameters provided a basis for further improving the recovery rate and reducing costs.The experimental results showed that when waste polyester granules were treated in a mixture containing 50 g/L of sodium hydroxide and 100 mL/L methanol at 160℃for 2.5 hours,with a bath ratio of 1︰20,the recovery rate of TPA was calculated to be 94.9%.The chemical properties of the separated product,as indicated by FTIR,NMR,and HPLC analysis,were highly consistent with the TPA standard,showing a purity of 90.53%.However,the color difference between commercial TPA and the obtained TPA was 16.02 according to the VeriVide DigiEye(Roachelab)system,indicating the presence of a small amount of light yellow impurities.This study has significant value in practical application and environmental protection.The optimization of depolymerization conditions provides key reference information for the industrial-scale recycling of waste polyester,which can help improve production efficiency and effectively reduce economic costs.Moreover,this study proposes a new method for the efficient recovery of TPA from waste polyester,which not only reduces the potential environmental impact of waste polyester fibers but also promotes the further development of the circular economy.However,there are some limitations in the research process that point the way for future work.For example,the TPA product obtained in the experiment shows a significant color difference compared to the standard one,indicating that the product contains a certain amount of impurities.This necessitates the exploration of more effective purification technologies in future research to improve the purity and quality of the product.Additionally,during the experimental process,ethylene glycol(EG)was observed in the hydrolysate,but due to its low content,it is difficult to achieve effective separation.This issue also needs to be resolved in future research to fully recover and utilize all valuable components in waste polyester.In summary,although this study has made positive progress in the depolymerization of waste polyester and the recovery of TPA,further research and improvement are still needed to overcome current challenges and achieve a more efficient and environmentally friendly recycling process.