| Thousands of tons of waste textiles discarded each year, among which poly-cotton fabrics account for more than half, causing the waste of resources and environmental pollution. As a new biomass utilization technology, hydrothermal method can convert biomass into series of high value-added products under mild reaction conditions. In recent years, the hydrothermal method has received increasing attention because of its characteristics in no pollution, environment friendly and low cost.Polyester can hydrolysis into ethylene glycol(EG) and terephthalic acid(TPA) under hydrothermal conditions while cotton fiber carbonized into microsphere materials in subcritical water.With the reaction temperature, time, concentration and p H as theexperiment impact factors, the influence of EG and TPA on the hydrothermal carbonization of cotton fabrics were respectively explored in subcritical water. 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) Poly-cotton fabrics can take place decomposition reaction under the same hydrothermal conditions: polyester hydrolysis into EG and TPA while cotton fiber carbonized into carbon materials. The morphologies of carbon products are spheres and irregular particles when the poly-cotton blended ratio is below 55/45. Meanwhile, the morphologies of carbon products are rod and chip shapes when the poly-cotton blended ratio is over 55/45.(2) TPA can be recycled after separation and purification. TPA has little effect on cotton fiber hydrothermal carbonization when the mass ratio of TPA and cotton below 1. On the contrary, TPA has adverse effects on the structure and properties of hydro-char. Small amount of EG can promote the mass and energy yield of hydro-char. when the amount of EG is between 0.36 ~ 18 wt.%, the carbon productivity is higher than there is no EG in reaction system. The hydro-char has the largest yieldwhen EG concentration is 0.5wt.% while it has the highest calorific value and good thermal stability when EG concentration is 9wt.%.Continue to increase the concentration of EG, the yield of carbon and energy decreases and spherical carbon product disappears. When EG concentration is over 81 wt.%, the carbonization degree of cotton drastically reduced.(3) The existence of TPA and EG can decrease the carbonization temperature of cotton fiber. The starting carbonization temperature of TPA/cotton and EG/cotton respectively are 220℃ and 230℃ while pure cotton fiber is 240℃.(4) Compared with the hydrothermal carbonization of pure cotton fiber, reaction time has nothing to do with the increasing of hydro-char graphitization degree, but do adverse influence on hydro-char yield and TPA recycled rate when added TPA or EG into the reaction system. TPA recycle rate is the largest and hydro-char yield is high when the reaction hydrothermal temperature is 280 ℃ and time is 8h in TPA and cotton fiber reaction system. This reaction system obtained the biggest carbon productivity when the time is 6h while it requires 8h in EG and cotton fiber reaction system.(5) Analysis of TPA and EG on cotton carbonization show that, the yield of cotton fiber hydrothermal carbonization and the structure and properties of products will have a slightly increase while the poly-cottonblending ratio is less than 55/45, which equivalent to the TPA/cotton mass ratio and the content of EG are respectively below 1 and 0.36 wt.%.Conversely, it will act as an inhibition effect on cotton hydro-char productivity, structure and properties when the poly-cotton blending ratio is higher than 55/45. PH is the major factor on the morphology of hydro-char in TPA/cotton and EG/cotton hydrothermal carbonization systems. H+can significantly increase the amount of carbon microspheres. |
