Study On Hydrolysis And Carbonization Of Coloured Polyester And Cotton Fabric In Subcritical Water

With the continuous reform of ecological civilization system and the continuous improvement of the legal system and policies of green production and consumption,the disposal methods of waste and rubbish have attracted much attention.According to statistics,the tens of thousands of textiles are discarded every year,more than half of them are colored polyester and cotton textiles.Most of these waste textiles are burned or landfill,the recovery rate is only less than 1%,which not only caused a serious waste of resources,but also caused secondary pollution to the environment.Subcritical water has special physicochemical properties such as acid-alkali catalyst,separating solvent and replaceable organic solvent,the use of subcritical water can not only convert biomass into a series of high value-added products such as hydrothermal coke,but also completely hydrolyzed to ethylene glycol(EG)and terephthalic acid(TPA).Due to its environmental protection,low cost,simple operation and so on,it gradually arouses the attention of many scientific researchers.At the same time,it provides a new way to recycle and reuse of waste cotton.Therefore,the paper starts with the structure of the dye and uses the special properties of subcritical water to study the process of hydrolysis and carbonization of colored polyester fiber and cotton fiber in subcritical water.Firstly,the hydrothermal behavior of disperse dyes(disperse red S-BWFL/PET)and the hydrolysis behavior of colored polyester after dyeing disperse dyes were analyzed,and the influence of disperse dyes on the hydrolysis of polyester fiber was discussed emphatically.Secondly,the decomposition of reactive dyes(reactive red X-3B/Cotton and reactive blue KN-R/Cotton)in subcritical water were studied,and the hydrolysis and carbonization behavior of colored cotton fiber after dyeing with reactive dyes were also studied.The influence of reactive dyes on the hydrothermal carbonization of cotton fiber was analyzed emphatically.Finally,according to the hydrothermal behavior of colored cotton fabric,the hydrothermal carbonation path of colored cotton fiber in subcritical water was optimized by using formic acid as catalyst.The morphology,physical and chemical structure characteristics of the hydrothermally carbonized products(hydro-char)were investigated with scanning X-ray diffraction(XRD),fourier transform infrared spectrometer(FTIR),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),elemental analysis(EA)and thermal gravimetric analysis(TG).Results showed that:(1)After hydrothermal reaction,the ester and amide bonds of disperse red S-BWFL have been hydrolyzed or broken.The dye and PET have their own hydrolysis reaction,and the dye does not play any chemical role in the process of the polyester hydrolysis.(2)Disperse red S-BWFL dye does not affect the hydrolysis of PET,and has less influence on the physicochemical properties of TPA.In addition,the dye does not affect the yield of TPA,but it has a slight effect on the purity and acid value of TPA.(3)When the reaction temperature is 210~250 ? and the reaction time reaches 6 h,the reactive red X-3B and reactive blue KN-R almost complete hydrolysis.The hydrolysis rate of reactive red X-3B is higher than reactive blue KN-R,and organic acids formed by hydrolysis of cotton fiber promote the decomposition of dyes.However,the X-3B and KN-R will not affect the thermal carbonation conditions of cotton fiber,nor will it bring about obvious changes in physicochemical properties such as the appearance structure of hydrothermal products.(4)Compared with the carbonization of cotton fiber,the hydrolyzed products of reactive dyes are involved in the hydrothermal carbonation path of cotton fiber,and are wrapped in the inner layer of carbon microspheres.The content of carbonization products of different colored cotton fiber is distinguished.(5)When the reaction temperature is 250 ? and the concentration of formic acid is 1.5%,formic acid promotes the decomposition of reactive dyes and inhibits the cleavage of glucose.Reactive dyes are completely decomposed before the nucleation formed,and the small molecule matter is fully involved in the formation of the nucleation,and eventually stays within the carbon microspheres.