Decolorization Of Polyester Degradation Product(BHET) By Modified Activated Carbon

Among the chemical fibers widely used at home and abroad,the production and use of polyester?PET?ranks first.A large amount of waste polyester is difficult to degrade in nature,posing a heavy burden on the environment.Over the years,domestic and foreign scholars have carried out a lot of research on the recycling of waste polyester,it was found that the glycolysis process is simple and easy to apply,and the obtained degradation products can be used as raw materials for various high value-added products,it has been applied in the industrial production of polyester recycling.Affected by the purity and polymerization degree of waste polyester,factories mainly use waste polyester bottles as raw material for recycling.polyester fibers and fabrics contain impurities such as dyes,so the application of their end products is limited.Therefore,how to decolorize the degradation products of polyester fibers and fabrics is the key to improving the recycling rate of waste polyesters.In this paper,activated carbon?AC?modified with HNO₃ and FeSO₄·7H₂O was used as decolorizing agent to improve the decolorization rate of BHET,and the decolorization effect as well as the feasibility of this method were verified from the perspective of industrial production.In the first part of this research,HNO₃ was choosen as the acid-modifier.To investigate how the modification conditions influence the physical and chemical properties of AC,modification temperature,concentration of HNO₃ and modification time was taken into account in the experiment.The results showed that the type and amount of oxygen-containing functional groups,such as carboxyl group,carbonyl group and lactone group on the surface of activated carbon increased with the raising modification temperature and raising concentration of HNO₃.When the modification temperature was higher than 90?,the original pore structure of the activated carbon was almost completely destroyed.In the decolorization process,it was found that when the mass ratio of ACs:BHET was 1:1,BHET could be completely decolorized within 2 h,and the maximum relative whiteness of BHET crystal could reach 99 after decolorization.Comparing the decolorization effect of modified AC and unmodified AC,it was found that the average decolorization rate of modified AC was higher than that of unmodified AC,and the average removal rate of AC-HNO₃-10M was13.01%higher than that of AC.The adsorption capacity and adsorption mechanism of dyes on ACs were further investigated by thermodynamics and kinetic experiments.The results showed that the adsorption of dyes on AC and AC-HNO₃-10M was a uniform monolayer distribution,and the chemical reaction was contained in the adsorption process,besides that,AC-HNO₃-10M showed a smaller adsorption capacity than AC.In order to improve the adsorption rate of AC without reducing the adsorption capacity of it,FeSO₄·7H₂O was used as the second modifier to prepare ion-modified AC.The effect of several factors,including concentration of Fe²⁺,ultrasonic time and calcination temperature on the physical and chemical properties of AC was explored by BET and TG tests.The results showed that with the increasing concentration of Fe²⁺,the amount of carboxyl and lactone groups in AC increased,and the amount of FeSO₄ in AC raised with the increasing ultrasonic time,but the type and quantity of oxygen-containing functional groups weren't affected by the length of ultrasonic time;high temperature calcination removed functional groups on the AC surface and made FeSO₄ break up into Fe₂O₃ and gases,calcination also destroyed the pore structure of AC and reduced its specific surface area.When using these modified ACs to decolorize BHET,it was founded that modified AC,except for those with calcination,all performed better than unmodified AC.Then the response surface method was used to optimize the modification conditions,when AC was modified with 1.224 mol/L FeSO₄ and4.93 h ultrasonic dispersion without calcination,the average decolorization rate for dye was93.48%,much higher than 85.04%of unmodified AC,and its adsorption capacity was about1.8 mg/g higher than unmodified AC.Finally,several important issues in the decolorization of BHET by using activated carbon in industrial production are explored,including adsorption methods,multiple use and regeneration of activated carbon.The results showed that under static adsorption conditions,the time required for AC-Fe²⁺-max to completely decolorize 100 ml of BHET solution with a concentration of 10 g/L was 120 min,while under dynamic adsorption conditions,the decolorization time was shortened to 30 min.The used activated carbon was applied for the decolorization of BHET repeatedly,it was found that under static and dynamic adsorption conditions,the decolorization rate of BHET solution by AC-Fe²⁺-max within 30 min at the fifth adsorption were 71.10%and 83.89%,respectively.The activated carbon was regenerated by calcination at high temperature,the final decolorization rate of the regenerated sample under dynamic adsorption conditions for BHET solution was 80%.In addition,the characteristics of undecolorized BHET samples and samples after being decolorized by AC and AC-Fe²⁺-max were compared.The results showed that for decolorized samples,the functional groups,melting points and thermal decomposition temperatures were consistent with the undecolorized samples,indicating that the activated carbon was only decolored during the adsorption process,and its other properties are not changed,which means that the decolorization of BHET by activated carbons was practical.