Preparation Of Granular Activated Carbon By NaOH/urea Solvent System And Its Application

In this paper, granular activated carbons (GAC) with high abrasive resistance and good adsorption capacity were prepared from sawdust by chemical activation with NaOH/urea solvent system. The alkali urea system (NaOH/urea) was applied to the GAC preparation by using its good dissolution to cellulose, the formation of the adhesive system, then activation between NaOH and wood materials at a certain temperature without adding adhesives. At the same time, the chemical reaction between the residual alkali in activated carbon and sulfue dioxide has produced, so as to achieve the desulfueization in flue gas and widen the green-efficient application of GAC in the field of air pollution.In this work, granular activated carbons were prepared from fir sawdust by chemical activation with adding NaOH/urea solvent. The effect of the main conditions of preparation process (such as chemical ratio, kneading time, activation temperature and time) on the yield and adsorption capacities of GAC were studied to determine the optimum preparation parameters through the single factor tests and Response surface methodology. The textural structure and the surface functional groups were characterized by automatic adsorption instrument, Field emission scanning electron microscopy (FSEM), Fourier transform infrared spectra (FTIR) and strength test. The results showed that, under the better optimal parameters of chemical ratio 14wt% NaOH/24wt% urea, activation temperature 850 ℃, kneading time 2 h and activation time 1 h, the GAC was prepared with abrasive resistance of 99.83% , specific surface area (SBET) of 811.299 m2·g-1, total pore volumn of 0.5554 cm3/g, microporosity of 59.20% and average pore diameter of 2.74 nm is obtained. The raw materials were fully swelled and dissolved with the impregnation of NaOH/urea solvent, which was effectively facilitated the process of activation, thereby generated macro compact structure and micro porousity of GAC with high abrasive resistance. With the surface alkali catalysis and oxidation, the larger specific surface area and the residual alkali in carbons will benefit to improve the SO2 adsorption ability on granular activated carbon.In this study, the granular activated carbon prepared was used for flue gas desulfurization. The impact of SO2 inlet concentration on the desulfurization process of GAC was investigated. Then the adsorption isotherms and kinatics of desulfurization were analyzed. The results showed that both the breakthrough sulfur capacity and breakthrongh time decreased with the increase of SO2 inlet concentration. When the SO2 inlet concentration was 300 mg/L, the granular activated carbon has breakthrough sulfur capacity of 345 mg/g and breakthrongh time of 125 min. The main process of adsorption on the surface of GAC has divided into three segments, In the initial stage, the GAC has a high adsorption velocity of SO2 to increase adsorption capacity, and the removal rate of SO2 was close to 100%. The second stage appeared a rapid decline of adsorption velocity and removal rate and slow increase of adsorption capacity. The third stage has adsorption velocity closed to zero and reached adsorption equilibrium. Compared with Freundlich adsorption isotherm model presents better fitted resulted for SO2 adsorption equilibrium on the prepared granular activated carbon surface. The Bangham kinetic model can be described the kinetic of SO2 adsorption on GAC. The Bangham model fitting equation is q,=344(1-e-0.00061.1676).