| As one of important products of pitch, spherical pitch-based activated carbon (SPAC) is widely used in bio-medicine, military protection, environmental purification and other fields, owing to the developed porosity, regular spherical structure, uniform packing density, good adsorption properties and high mechanical strength. The preparation process of SPAC includes the spheroidization, infusibilization, carbonization and activation steps. The process of infusibilization which was achieved through the pre-oxidation treatment becomes a bottleneck restricting the industrial production and application of SPAC for time-consuming and energy consuming. Domestic company is difficult to obtain the related technology information due to the few useful information which is mainly confidential patent, thus the industrial production of SPAC is almost blank. Therefore, exploring the preparation process of SPAC, regulating the microcosmic pore structure of SPAC, analysizing the relationship between the adsorption performance and pore structure have important practical significance for the preparation and development of SPAC.In this paper, SPAC with different pore structure was prepared through pre-oxidation, carbonization and activation of pitch spheres(20～36 mesh), which were prepared by suspension method from the raw material of pitch with the softening point of 280 ℃ Polarizing microscope, scanning electron microscope, nitrogen adsorption-desorption, adsorption kinetics and adsorption isotherm were used to analysis the sphericity, surface morphology, pore structure and adsorption performance of SPAC, respectively. Besides, the adsorption performance of SPAC for the methyl orange dye and physiological small molecules of creatinine were analysized.The pitch spheres were prepared by suspension method from pitch. The results showed that the spheroidization temperature and the sphericity could be controlled by the dosage of viscosity adjusting agent, spheroidization temperature and the stirring speed, respectively. And the rate of pre-oxidation heating influenced the surface morphology of pitch spheres. The spheroidization temperature decreased from 90 ℃ to 75 ℃, with the increasing from 40% to 50% of the dosage of viscosity adjusting agent. When the dosage of viscosity adjusting agent was 45%, the sphericity of pitch spheres prepared by suspension method was increased with the increasing of spheroidization temperature. But when the spheroidization temperature was too high, the sphericity decreased, thus the optimum spheroidization temperature was 80 ℃. When using suspension method to prepare pitch spheres containing 45% viscosity adjusting agent, the lower stirring speed was unfavourable to the dispersion of the blend pitch particles in the dispersion medium and the sphericity was lower. The sphericity was increased with the increasing of stirring speed, and the spherical structure of pitch spheres prepared at the sirring speed of 600 rpm/min was much better. Besides, the rate of pre-oxidation heating influenced the surface morphology of pre-oxidation pitch spheres, and the surface of pre-oxidation pitch spheres prepared at a lower heating rate was smooth. With the increasing of heating rate, the surface of pre-oxidation pitch spheres cracked gradually, thus the pre-oxidation process needed a lower heating rate of 0.5 ℃/min.The SPAC was prepared by one-step CO2 carbonization and activation from the pre-oxidation pitch spheres. Effect of activation temperature and activation time on the pore structure was investigated. The results showed that the yield of SPAC decreased with the increasing of activation temperature when the activation time was 2.0 h. Specific surface area, mesoporous ratio, total pore volume, average pore size, adsorption capacity of methyl orange and creatinine of SPAC increased gradually. However, the specific surface area, total pore volume, adsorption capacity of methyl orange and creatinine of SPAC decreased at the activation temperature of 950 ℃, thus the optimum activation temperature was 900 ℃. The yield of SPAC decreased with the prolonging of activation time when the activation temperature was 900 ℃, and the specific surface area, mesoporous ratio, total pore volume, average pore size, adsorption capacity of methyl orange and creatinine of SPAC increased gradually. However, the parameters of pore structure and adsorption performance of SPAC decreased when the activation time was prolonged to 4.0 h. Besides, yield of 28.02%, specific surface area of 816.92 m2/g, microporous ratio of 50.77% and total pore volume of 0.55 cm3/g could be achieved when the temperature and the time of CO2 activation were 900 ℃ and 3.0 h, respectively. And the adsorption capacity of methyl orange and creatinine of SPAC were 188.87 mg/g and 99.34 mg/g, respectively.The SPAC were prepared by KOH activation from the pre-oxidation pitch spheres, and the pore structure was controlled by the mass fraction of KOH and impregnation time. The results showed that the yield of SPAC decreased gradually with the increasing of mass fraction of KOH when the impregnation time was 1.5 h, and the parameters of pore structure and adsorption performance of SPAC increased gradually, thus the optimum mass fraction of KOH was 60%. The yield of SPAC decreased with the prolonging of impregnation time when the mass fraction of KOH was 60%, the specific surface area, total pore volume, average pore size, adsorption capacity of methyl orange and creatinine of SPAC increased gradually. However, the total pore volume, average pore size, adsorption capacity of methyl orange and creatinine of SPAC decreased when impregnation time was prolonged to 3.0 h. Besides, yield of 10.76%, specific surface area of 1074.64 m2/g, microporous ratio of 86.25% and total pore volume of 0.54 cm3/g could be obtained when the mass fraction of KOH and impregnation time were 60% and 3.0 h, respectively. And the adsorption capacity of methyl orange and creatinine of SPAC were 139.92 mg/g and 158.26 mg/g, respectively.The adsorption performance of SPAC prepared by CO2 activation for the methyl orange dye and physiological small molecule of creatinine were analysized. The results showed that the specific surface area and mesoporous concent influenced the adsorption rate of methyl orange and creatinine on SPAC. The specific surface area and the total pore volume influenced the adsorption capacity of methyl orange on SPAC, while the specific surface area and the micropore volume influenced the adsorption capacity of creatinine on SPAC. The adsorption kinetics of methyl orange on SPAC fitted successfully to the pseudo-second-order adsorption kinetics, and adsorption isotherm fitted to the Langmuir adsorption isotherm model, which was single molecule layer adsorption. But the adsorption kinetics of creatinine on SPAC fitted to the pseudo-first-order adsorption kinetics well, and adsorption isotherm fitted to the Freundlich adsorption isotherm model. |
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