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Preparation of Activated Carbon from Tobacco Stems and Application for Low Concentration Phosphine A

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Tutor: YiHongHong
School: Kunming University of Science and Technology
Course: Environmental Science
Keywords: Tobacco stems,Activated carbon,Pore ??structure,Phosphine,Adsorption capacity
CLC: X712
Type: Master's thesis
Year:  2011
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Abstract:
Activated carbon was an effective adsorbent, and was used for several applications. Recently, one of the focuses is to preparation activated carbons with adjustable pore size. The cheap agricultural waste was used as the carbonaceous materials. Additional tobacco stems of the tobacco product after picking tobacco will have received a lot of waste tobacco stems. The studies of sorbent were carried out on the preparation of activated carbon from tobacco stems with chemical activation, using conventional heating. The effects of carbonization temperature, activation parameters on the preparation of activated carbons from tobacco stems and adsorption properties of phosphine were studied. The texture features, surface functional groups microstructures and microcrystallinity of the activated carbons prepared were examined by N2 adsorption isotherm, Fourier transform infrared spectra, X-ray diffraction powder and scanning electron microscope techniques, respectively. And effects of various factors on the yield of activated carbon was studied, the best prepared conditions of activated carbon by conventional heating was obtained. The activated carbon produced from tobacco stems was modified for phosphine adsorption, while the regeneration of modified activated carbon and phosphine on the activated carbon adsorption thermodynamics were researched.The results showed that the optimum preparation conditions of activated carbon were: carbonization temperature of 700℃, activation temperature 850℃, KOH/C mass ratio of 2, Under these conditions, the activated carbon surface area, pore volume and pore content of the maximum were 2215m2/g,0.8968cm3/g,72.87%, the yield was 18.4%. Moderate carbonization temperature was conducive to the formation of microporous structure of activated carbon, high carbonization temperature can enhance activation, but the carbon edge was loss on ignition, resulting in micropore place loss on ignition hole collapse and widening of meso- and macropores. However, too high an activation temperature resulted in the burn-off of the carbon structures and the widening of micropores to meso- and macropores. As the activation temperature increased, the reaction of KOH and higher activity of carbon atoms increased, and the lower activity of KOH and the reaction of carbon atoms increases the odds, leading to more developed pore structure of activated carbon. The KOH-activated carbon was graphite-like structure to form carbon-ceramic, low-rise, more prone to form developed microporous. Activated carbon micro-surface morphology showed well-developed pore structure, and honeycomb voids, while the internal surface of honeycomb structure was extended in the channel wall, and rich in micropores. Too little or too much the amount of active agent was not conducive to the reaction of KOH-C, and was not conducive to generating carbon structure, particularly the production of porous structure. Microporous was the main factor of activated carbon to control the adsorption capacity.The modified activated carbon from tobacco stems had better adsorption purification for phosphine, the maximum adsorption capacity was up to 302mg/g. Thermal regeneration based on the modified activated carbon from tobacco stems has some practical application. Phosphine adsorption isotherms and isometric heat of adsoption on activated carbon were studied. It indicated that the phosphine adsorption was physical adsorption and chemical adsorption on modified activated carbon. Isometric heat of adsorption of phosphine was calculated using Clausius-Clapeyron equation according to adsorption isotherms. It was proved that isometric heat of adsorption of phosphine decreased, which is the heterogeneity of carbon surface caused.
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