High Quality Activated Carbon Preparation And Mechanism Analysis

As the accessional product of tobacco, a large amount of tobacco stems is produced after tobacco picked off in many places of our countryside. It is thrown away or burned for its no value, waste the usable resource and result environmental pollution. Eupatorium adenophorum spreng, known as a "vicious weed" in the world, has widely spread to Yunnan, Sichuan, Guizhou province and some other areas, make tremendous losing for the local economy. It is greatly necessary for us to make use of these resources availably. If so, we can protect the environment and create some value, the significance is greatly significant.In this paper, a series of granular activated carbon was produced from tobacco stems by physical activation and a series of activated carbon was produced from eupatorium adenophorum spreng by chemical activation, based on the review of the technology of preparation for activated carbon and application of microwave heating to preparation for activated carbon. The optimum preparation parameters have been obtained by study on the factors for the adsorption and yield of activated carbon. Furthermore, the activated carbons in optimum condition were tested by nitrogen adsorption at 77 K, and investigated the porous structures of the activated carbons. Activation mechanism was discussed too.(1) Study on the proportion of adhesive for preparation granular carbon with carbonization of tobacco stems, the best proportion is 30%, and using the granular carbon at best proportion as the materials of later activation test.(2) The optimum preparation parameters of granular activated carbon by traditional heating-CO₂ are obtained as follows: activation temperature is 900 ℃, activation time is 100min, and flow rate of CO₂ is 0.5L/min. The yield of granular activated carbon is 38.53% when the iodine number, the specific surface area, the methylene blue adsorption, reach 901.36 mg/g, 750.65m²/g, 8.0ml/0.1g and total pore volume is 0.42 ml/g.(3) The optimum preparation parameters of granular activated carbon by microwave heating-CO₂ are obtained as follows: microwave power is 700W, activation time is 70min and flow rate of CO₂ is 0.15L/min. The yield of granularactivated carbon is 43.37% when the iodine number, the specific surface area, the methylene blue adsorption, reach 960.39 mg/g, 847.41 m2/g, 13ml/0.1g and total pore volume is 0.48ml/g.(4) The optimum preparation parameters of granular activated carbon by traditional heating-water vapor are obtained as follows: activation temperature is 900 °C, activation time is 60min and flow rate of water vapor is 3.31g/min. The yield of granular activated carbon is 24.39% when the iodine number, the specific surface area, the methylene blue adsorption, reach 1028.49mg/g, 909.22m2/g, 19.0ml/0.1g and total pore volume is 0.61 ml/g.(5) The optimum preparation parameters of granular activated carbon by microwave heating-water vapor are obtained as follows: microwave power is 700W, activation time is 40min and flow rate of water vapor is 1.70g/min. The yield of granular activated carbon is 30.83% when the iodine number, the specific surface area, the methylene blue adsorption, reach 1060.81mg/g, 993.35m2/g, 17.5ml/0.1g and total pore volume is 0.82 ml/g.( 6) The optimum preparation parameters of activated carbon from by microwave radiation-K2CO3 are obtained as follows: drying for 2h at 120°C after ultrasound impregnating 20min, microwave power is 700W, microwave radiation time is 12min and the ratio of K2CO3and eupatorium adenophorum Spreng is 1.25:1. The yield of activated carbon is 16.35% when the iodine number, the specific surface area, the methylene blue adsorption, reach 1470.27mg/g, 1540.97m2/g, 30ml/0.1g and total pore volume is 0.93 ml/g.( 7 ) The optimum preparation parameters of activated carbon from by microwave irradiation-ZnCl2 are obtained as follows: drying for 2h at 120"C after ultrasound impregnating 30min, microwave power is 490W, microwave radiation time is 15min and the ratio of ZnC^and eupatorium adenophorum Spreng is 1. 5:1. The yield of activated carbon is 43.29% when the iodine number, the specific surface area, the methylene blue adsorption, reach 1107.61mg/g, 1538.81m2/g, 27ml/0.1g and total pore volume is 0.78 ml/g.(8) The iodine number of granular activated carbon by traditional heating- CO2 reached the second-grade of GB/T 13803.1-1999 and GB/T 13803.2-1999. The iodine number of granular activated carbon by microwave heating-CO> reached thesecond-grade of GB/T 13803.1-1999 and GB/T 13803.2-1999, the methylene blue adsorption reached the first-grade of GB/T 13803.1-1999 and GB/T 13803.2-1999. The iodine number and methylene blue adsorption of activated carbon by other method reached the first-grade.(9) The pore size distributions of activated carbons achieved at optimum conditions were analyzed by D-A equation, H-K equation, BJH method and DFT theory. The result shown that the pore diameter of granular activated carbon by water vapor activation is much wider than that by carbon dioxide, the pore diameter of granular activated carbon by traditional heating is much wider than that by microwave heating using the same activation agent, the pore diameter of activated carbon by zinc chloride activation is much wider than that by potassium carbonate activation. The micro-pore content of granular activated carbon by microwave heating is more than that by traditional heating using the same activation agent, thus the meso-pore content is fewer. The meso-pore content of granular activated carbon by water vapor activation is more than that by carbon dioxide activation by the same heating means. The micro-pore content of activated carbon by potassium carbonate activation is more than that by zinc chloride activation, thus the meso-pore content is fewer.(10) By analyzing the mechanism of activation, the result shown that molecule diameter of water vapor is bigger than that of carbon dioxide, the reaction rate of water vapor is much quicker than that of carbon dioxide. The active points by microwave heating is more than that by traditional heating, so the reaction rate by microwave heating is much quicker than that by traditional heating. The mechanism of chemical activation is relation to the character of activation agent.