Typical Microwave Heating Of Materials Preparation Of High Surface Area Activated Carbon And The Evolution Of Mechanisms

With the rapid development of social economy, the resource shortages and energy crisis has become increasingly prominent. However, the amount of solid wastes derived from industrial or agricultural production increases rapidly, resulting in the great waste of resources and environmental pollution. To deal with this problem, the recycle and reuse of solid wastes has become the focus of attention around the world in recent years. In view of the present status of solid waste resources and combined the advantages of microwave heating, three typical solid wastes of eupatorium adenophorum, walnut shells and solidification phenolic resin were used as raw materials to prepare high surface area activated carbon (HSAAC) by microwave heating. The process conditions with microwave treatment were optimized through analyzing the pyrolysis processes and systematically investigating the effects of carbonization temperature on the carbonization and activation process, respectively. The carbonization and activation mechanism as well as the regulation mechanism of pore structure were studied and analyzed systematically.The pyrolysis processes of the.three typical solid wastes were studied and analyzed by using thermogravimetric analysis method. The kinetics parameters of pyrolysis were calculated and the pyrolysis mechanism was discussed. The results showed that the heating rate had a significant influence on the yield of pyrolysis. The carbonization heating rates of the three materials were finally determined to 10℃/min. It was found that the pyrolysis kinetics of walnut shells, adenophorum and solidification phenolic resin are all diffusion-controled process.To understand the influence of carbonization temperature on the canonization process of the three materials, the pore structures, the microcrystalline structures and the surface chemical properties of the products obtained at different carbonization temperatures were characterized and analyzed. The results suggested that the carbonization temperature showed a significant effect on the structures and properties of the products. It was found that as the carbonization temperature increased, the yield of carbonized products, surface oxygen-containing functional groups and non-carbon components gradually decreased, resulting in the extension of the carbon-network structure to form a larger grid structure. Meanwhile, with the increase of carbonization temperature, the average interlayer distance (d002) of graphitic carbon decreased, but the stacking thickness Lc, crystallite diameter La and graphite crystallite sheet layer number increased, indicating the increase of graphitization degree of samples. With the gradual reduction of ordering degree, the samples were difficult to further graphitize. The specific surface area, total pore volume and the microstructures firstly increased and then decreased as the temperature increased, while the amount of mesopores and macropores gradually increased. This is according to the pore size distribution which firstly shifted to narrower pore size and then shifted to broader one with the increase of temperature.The effects of the carbonization temperature on the activation process by KOH with microwave heating were investigated systematically. The pore structures, microcrystalline structures, surface chemical properties and surface morphology of the activated products (HSAAC) with microwave heating were characterized and analyzed. It was found that the carbonization temperature had a crucial influence on the activation process. The optimum carbonization temperature for the preparation of HSAAC from walnut shell, eupatorium adenophorum and solidification phenolic resin respectively were determined, which provide a common standard and practice basis for the preparation of HSAAC. It was found that some infrared characteristic adsorption peaks belonged to surface functional groups weakened or showed various degrees of blue or red shifts, indicating the reduction of surface groups in activation process. After activation, tars and some particles which stuffed in the pores of carbon were removed, the surface became smoother, and the pore structures of the products were more developed. Furthermore, the graphite crystallite was damaged and the disordering degree of the products increased. The graphite crystallite sheet layer number significantly decreased but the crystallite diameter La remarkably increased, forming the activated carbon with typical disorder-layer structural characteristics. As the temperature increased, the porosity of the activated carbon products developed rapidly and the obtained HSAAC products mainly possessed micropore structures with abundant mesopore and macropore structures, resulting in a concentrated pore size distribution. It can be concluded that the preparation of the HSAAC opened a new path for the reuse of solid wastes.The effects of the microwave power, microwave heating time, hydroxide/carbon ratio and granularity of carbonized materials on properties of the resulting high surface area activated carbon (HSAAC) were studied, and the pore structures and the surface chemistry properties of the products were characterized. The optimum conditions were obtained as follows:the microwave power was 700W; the granularity of carbonized materials was bigger than 100 items; the hydroxide/carbon ratio was 3:4; and the heating time was 15-25min. Under the optimal conditions, the surface area of walnut shells, eupatorium adenophorum and the solidification phenolic resin were 4333,4227,4269m2/g, respectively. And the iodine adsorption number were 2531,2255 and 2384mg/g, respectively, reached the standard of activated carbon for electric double-layer capacitor (LY/T 1617-2004) Compared with the conventional heating method, microwave heating method is more efficient in that the process time of microwave heating was shortened over 72%, which significantly improved the property of activated carbon and realized the energy saving.Generally, a novel process of preparing high surface area activated carbon from three typical solid wastes of walnut shells, eupatorium adenophorum and solidification phenolic resin by microwave heating was put forward. The main factors influenced the preparation process of HSAAC were obtained and the HSAAC with the highest surface area in all HSAAC reported in current literatures was prepared successfully, which served as a good example for the efficient utilization of the solid wastes. The presented preparation process improved the quality of activated carbon products, shortened the heating time and lowered energy consumption, which is of great significance to ease the strain on the resources and realize the energy saving.