Studies On Preparation Of Activated Carbon By Using Residues In Extracting Diosgenin From Dioscorea Zingiberensis And Residues' Thermal Decomposition

Dioscorea zingiberensis is a special medicinal plant which is used to produce diosgenin in our country. It was wild before, but now it can be planted. In recent years, diosgenin production is a new developing industry based on the success of dioscorea zingiberensis' artificial planting. The residues in the process of diosgenin production are the remainder after dioscorea zingiberensis being distilled. Producing a ton of diosgenin can bring about 7～8 tons of residues. The unsettled residues not only destroy the soil ecological balance, but also bring water pollution and dust pollution, which have threatened the existent environment of human being. The main components of the residues in diosgenin production are xylogen and cellulose. The residues contain 48% of carbon. And they are the high quality material. So complex utilization of the residues will be of the good economic and social performance.This paper studies on the technological conditions of activated carbon prepared by using residues in extracting diosgenin from dioscorea zingiberensis. In experiments, the two-stage method is adopted, and zinc chloride is used as an activator. Through studying the influence of charring temperature, charring time, activation temperature, activation time, impregnation ratio, dipping time and mass fraction of ZnCl₂ on the activated carbon yield, iodine adsorption value and specific surface area, the optimal technological conditions are obtained: charring temperature is 300°C, charring time is 40min, activation temperature is 600°C, activation time is 105min, impregnation ratio is 6, dipping time is 20 hours, and mass fraction of ZnCl₂ is 40%. Under the optimal technological conditions, the activated carbon yield is 38.81%, its iodine adsorption value is 995.23 mg/g, its decolorizing capability to methylene blue is 14.5 ml/0.1g, its decolorizing capability to caramel is 115%, and its specific surface area is 1085.586 m²/g.By using static state method, this paper also studies adsorption capability and optimal conditions of the prepared activated carbon to Cr⁶⁺. Through studying the influence of the PH value of solution, the quantity of the activated carbon, surging time and temperature on the removal of Cr⁶⁺. The experiments determine the optimal conditions of the activated carbon adsorbing Cr⁶⁺: the PH value of solution is 4, the quantity of the activated carbon is 0.5g, surging time is 4 hours, and temperature is 20°C. 86.95% of Cr⁶⁺ can be removed by the prepared activated carbon. And the adsorption capability of the prepared activated carbon is18.45mgCr⁶⁺/g.Moreover, thermal decomposition experiments of the residues and the residues dipped by ZnCl₂ have been carried out in nitrogen, respectively. Decomposition processes of the residues and the dipped residues are analyzed, and the thermal decomposition kinetics of the dipped residues is studied. Without considering the kinetics model function, by using the Kisinger method and the Firedman method, the activation energy of the dipped residues is 29.84 kJ/mol and 44.45 kJ/mol in the first stage decomposition, respectively. And the activation energy of the dipped residues is 79.35 kJ/mol and 83.90 kJ/mol in the second stage decomposition, respectively. Furthermore, the activation energy is optimized by multivariate non-linear regression. The results of multivariate non-linear regression indicate that the first stage decomposition of the dipped residues is n-dimensional autocatalysis. The activation energy of the first stage decomposition is 42.87kJ/mol, and lgA is 3.0458. The f(α) can beexpressed as: f(α) = (1-α)ⁿ(1 + K_catX) , n=1.55, lgK_cat=-0.0828. The thermaldecomposition of the second stage decomposition is controlled by Ginstling-Brounslein three-dimensional phase boundary. The activation energy is 154.25kJ/mol, and lgA is 5.9101.The f(α) can be expressed as: . The research results of thethermal decomposition kinetics of the dipped residues provide the important parameters for designing reactor and assessing optimal technological conditions for production.