| In the background of carbon peak and carbon neutrality,the treatment and reuse of printing and dyeing wastewater is crucial for the green,low energy consumption and recycling development of the textile industry.Printing and dyeing wastewater has the characteristics of complex water quality,tremendous amounts of discharge,high chromatic value,and high content of organic pollutants,which brings great challenges to its efficient purification and treatment.Cellulose porous microspheres have the characteristics of wide range of cellulose sources,low cost,non-toxicity and biodegradability,and the characteristics of porous materials such as large specific surface area and lots of active sites,which have significant preponderances as biological adsorbents for the purification of printing and dyeing wastewater.However,there are still some problems such as complex preparation process,single adsorption pollutant type,and low adsorption efficiency,which limit the practical application potential of cellulose porous microspheres.In order to solve the above problems,this thesis used the drop phase separation method and two-step chemical modification method to prepare amphoteric cellulose porous microspheres(ACM)with high porosity,high mechanical properties,and both carboxyl and amino active groups.Taking cationic dye methylene blue(Me B)and anionic dye methyl orange(MO)as dye pollutant models.We investigated the static adsorption performance of ACM on dyes under different conditions and the adsorption mechanism.At the same time,the treatment of secondary sedimentation printing and dyeing wastewater in textile industry by ACM was investigated.Based on ACM excellent adsorption performance and low mass transfer resistance,a packed adsorption column was constructed using ACM as the adsorption filler to study the dynamic adsorption performance of ACM.The specific research contents and results were as follows:(1)Preparation and physical and chemical properties of amphoteric cellulose porous microspheres:cellulose was used as the basic raw material,and cellulose microspheres were prepared by phase separation method.After carboxylation and amino functionalized surface modification,ACM with both carboxyl and amino active groups was obtained.By studying the preparation process of ACM,it was found that the content of carboxyl group and amino group of ACM prepared under optimal conditions was as high as 1.51mmol/g and 1.52 mmol/g,respectively,indicating that it had abundant carboxyl and amino groups.At the same time,the porosity of ACM was investigated,and it was found that there were abundant pores on the surface and inside of ACM,with a specific surface area of 123.97 m~2/g and a porosity of 89.22%,showing a good pore structure.In addition,the mechanical properties and stability of the microspheres were investigated.It was found that the crystallite of ACM was 38.2%,and the thermal decomposition temperature was of ACM 332℃.Besides,the compressive strength of ACM attained 591.9 k Pa,which still maintained the original compressive strength of 63%after 40 times compression,indicating that it had good structural stability and mechanical strength.(2)Static adsorption performance of amphoteric cellulose porous microspheres:Me B and MO were used as dye pollutant models to explore the static adsorption behavior of ACM to dyes under different conditions(initial p H value,initial concentration,contact time,adsorption temperature).The maximum adsorption capacity of ACM for Me B and MO was 616.12 mg/g and 345 mg/g,respectively,indicating that ACM has excellent adsorption performance.After 8 cycles of adsorption experiments,the adsorption capacity could still be maintained at 80%of the original adsorption capacity,indicating that ACM has good recycling usability.To explore its ability to separate dyes,ACM was able to separate anionic and cationic dyes by adjusting the p H value of the mixed dyes,indicating that ACM has good separation performance.Through the adsorption isotherm,adsorption kinetics and chemical correlation structure changes before and after adsorption,it was proved that the adsorption process of ACM was mainly chemisorption at the monolayer interface.Further,the effect of ACM on the treatment of real printing and dyeing wastewater in the textile industry was investigated,and it was found that the effect of ACM on the color,total nitrogen and total phosphorus in the secondary sedimentation wastewater was particularly prominent,which were reduced by 87.20%,74.44%and56.67%,respectively.(3)Study on the dynamic adsorption performance of amphoteric cellulose porous microspheres:Based on the excellent mechanical properties,high functional group content and low mass transfer resistance of ACM,a packed adsorption column device was constructed,using Me B dye wastewater as a pollution model,the effects of different device parameters(filler height,liquid inlet concentration and liquid inlet flow rate)on ACM dynamic adsorption were studied.It was found that the dynamic adsorption efficiency of adsorption column can be improved by reducing the initial concentration,increasing the loading height and slowing down the liquid inlet speed.0.8 g of microspheres could treat 7.5 L of dye-containing wastewater,indicating that ACM has a good dynamic adsorption capacity for Me B dye.The Thomas,Yoon-Nelson and Bohart-Adams models were used to fit the dynamic adsorption behavior of ACM,and it can be found that the dynamic adsorption behavior of ACM was consistent with the Thomas and Yoon-Nelson models,indicating that the dynamic adsorption of ACM occurred on the surface of a single molecular layer.In this paper,cellulose microspheres with high porosity,high mechanical strength and high recyclability were prepared by phase separation method with cellulose as raw material.After chemical modification,the microstructure of the microspheres was not affected,and the microspheres were rich in carboxyl and amino groups,showing amphoteric surface characteristics,which could realize the efficient adsorption and separation of anionic and cationic dyes.Based on these excellent properties,as a biodegradable and recyclable ecological adsorbent,it shows excellent potential for the purification of printing and dyeing wastewater. |
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