Studies On Preparation And Application Of Activated Carbon From Ramie Stalk

Activated carbon is an effective adsorbent, it is widely used since its well-developed porous structure, stable chemical properties and considerable surface functional groups with high quality. In recent years, the research on the hotspot is to synthesize activated carbon with excellent performance, using low-cost agriculture wastes as raw materials and by simple preparing process.The pyrolysis of ramie stalk was carried out by means of the thermo-gravimetric analyzer in high pure N2 atmosphere. According to the TG-DTG curves, the influences of different heating rates on the pyrolysis process were investigated and the pyrolysis mechanism was discussed. The results showed that the non-isothermal pyrolysis process of discarded waste ramie stalk includes the following four stages:dehydration, pre-pyrolysis, principle decomposition and low-speed decomposition. According to the pyrolysis dynamics of ramie stalk waste, it was found that the entire pyrolysis reaction agreed with chemical reaction mechanism, the activation energy and frequency factor increased as temperature rose.In this study, activated carbon was prepared from the linen fabric waste by KOH as activator. There were two steps, carbonization and activation in the production of linen-based activated carbon. The method of factor analysis and the orthogonal design were employed to investigate the characteristics of activated carbon. The preparation factors (the ratio of alkali to carbon, activation temperature, activation time, impregnation time), which effect the adsorption properties of iodine and methylene blue and the yield of activated carbon were discussed and the technological conditions were optimized. Results showed that it was appropriate to use ramie stalk as raw materials for activated carbon preparation. The optimum preparation conditions were the ratio of alkali to carbon 2:1, activation temperature 750℃with activation time 150min, carbonization temperature 500℃and impregnation time 24h. The basic adsorption properties of sample were the iodine capacity 1374.78 mg/g, the methylene blue capacity 314.51 mg/g and the yield of activated carbon 26%.Specific surface area and pore size distribution analyzer was employed to determine the N2 adsorption-desorpion of several samples at 77K. The Langmuir equation, BET equation, t figure and BJH method were used to calculate the specific surface area, pore volume and pore size distribution. The scan electric microscope (SEM), X-ray diffraction (XRD) and FT-IR were also used to investigate the morphology, crystallite structure and chemistry structural characteristics, respectively. Adsorption of Cr(Ⅵ) from aqueous solution onto activated carbon prepared from ramie stalk waste was investigated in a batch system. At the same time, Adsorption kinetics, thermodynamics and mechanism were discussed in this study. Adsorption studies were carried out to investigate influence of different conditions on the adsorption effect, such as initial pH value, adsorption time, dosage of activated carbon, temperature et al. The experimental results of Cr(Ⅵ) adsorption onto the ramie stalk showed that the pH value of Cr(Ⅵ) solution is the most important factor to effect on the Cr(Ⅵ) adsorption capacity of activated carbon. Under the conditions of the initial pH=2 approximately, the concentration of Cr(Ⅵ):150mg/L, the dosage of LAC:0.1mg and adsorption time:150min, the activated carbon revealed relatively strong capability of adsorbing Cr(Ⅵ). In addition, Langmuir and Freundlich isotherms were used to analyze the adsorption equilibrium data. The results showed that the Langmuir adsorption isotherms can agree with the adsorption behavior of Cr(Ⅵ) on activated carbon from ramie stalk. The adsorption data were analyzed by using pseudo-first-order and pseudo-second-order kinetic models, and the adsorption kinetics was found to follow the pseudo-second-order kinetic model. The regeneration of waste powder activated carbon is in very important applications. In this paper, the acid alkali reclaiming method was discussed for the regeneration of waste activated carbon. The result showed that the percent of primary recycling can reach approximately 80% by acid-alkali regeneration.