摘要
鉴于以含氮生物质为原料,采用炭化碱活化两步法制备掺氮活性炭的工艺较长,该研究以大豆渣为原料,K2CO3为活化剂,尝试采用炭活化一步法制备含极微孔的掺氮活性炭,并考察活化温度对活性炭化学组成、孔结构及低压CO2吸附性能的影响。研究表明,该方法可用于制备富含极微孔的掺氮活性炭。当活化温度从560℃升高到650℃时,1）活性炭的氮元素皆均匀分布在体相及表面,其质量分数（4.1%~4.4%）变化不大,而其化学状态发生变化;2）比表面积、总孔容、微孔孔容均呈单调递增,但极微孔孔容先增大后减小。活化温度为600℃的样品,极微孔孔容较大（0.13 m L/g）,极微孔主要集中在0.42~0.70 nm,微孔孔容、总孔容、比表面积分别为0.40 m L/g、0.43 m L/g、948 m2/g。该样品在10 k Pa、0℃下的CO2吸附量达1.94 mmol/g,CO2/N2表观选择性为41.6,说明它对低压CO2能同时展现出较高的吸附量及表观选择性。该研究为含氮活性炭的便捷制备提供了参考。
So far, some studies have been conducted on preparation of nitrogen-doped（N-doped） active carbon from N-containing biomasses using alkalis as activators. In these studies, the commonly used preparation method was activation with alkali after biomass carbonization. Compared with this method, the one-step carbonization/activation method was simple and apt to reduce energy consumption, but its application in the preparation of N-doped active carbon was not investigated. In this research, N-doped active carbon with ultramicropores was prepared from waste soybean dreg using K2CO3 as activator via one-step carbonization/activation technology. The effects of activation temperature on chemical composition, pore structure, and low-pressure CO2 adsorption performances of the active carbon were investigated. To prepare active carbon, waste soybean dreg with particle size of 0.15-0.90 mm was impregnated with K2CO3 aqueous solution at K2CO3/dreg dry-basis weight ratio of 2：1, and after mixing uniformly, the mixture was sealed and kept for 4 h. Then, it was dried in an oven at 110℃ till constant weight was achieved. Subsequently, the dried mixture was heated to 500-650 ℃ at an average heating rate of 6℃/min and then kept for 75 min. Afterwards, the heated mixture was washed with distilled water until the pH value reached about neutral, and then dried at 110℃ for 12 h to produce active carbon. The obtained samples were subsequently characterized; pore structure and CO2 adsorption performance were measured with volumetric adsorption analyzers, elemental composition was measured with an elemental analyzer, surface chemistry was measured with an X-ray photoelectron spectroscopy, and surface morphology was measured with a scanning electron microscope（SEM） and a transmission electron microscope（TEM）. To gain an insight into the mechanism of pore formation, the soybean dreg and K2CO3-impregnated soybean dreg were pyrolyzed and analyzed using a thermogravimetric analyzer coupled with an infra-red spectrometer. The results showed that the technology could be successfully used to prepare N-doped active carbon with ultramicropores. As the activation temperature increased from 560 to 650℃, the N was distributed homogenously both on surface and in bulk of the active carbon; the N content（4.1%-4.4%） varied slightly, but the N chemical state changed. As the activation temperature rose, the specific surface area, total pore volume, and micropore volume of active carbon increased monotonously, but their ultramicropore volume first increased and then decreased. The activated carbon prepared at 600℃ possessed the maximum ultramicropore volume（0.13 mL /g）, and the pore diameter of the ultramicropores was mainly in the range from 0.42 to 0.70 nm. The micropore volume, total pore volume, and specific surface area of this kind of carbon were 0.40 mL /g, 0.43 mL /g and 948 m2/g, respectively. After characterizations of these carbon materials, the carbon materials were used for the adsorption of CO2. The CO2 uptakes of the obtained active carbon at low pressures（10, 15 and 20 kP a） first increased and then decreased with the increment in activation temperature, which coincided with the variation trend of their ultramicropore volume. This result indicated that the low-pressure CO2 uptake of the activated carbon prepared at 600℃ was ascribable to its developed ultramicropores. The carbon prepared by activation at 600℃ showed a CO2 uptake of 1.94 mmol/g at 10 kP a and 0℃, which was superior to the corresponding values ever reported for many biomass-based active carbon, indicating that the obtained sample could display a high CO2 uptake at low pressures. Besides, at 10 kP a, this sample displayed a selectivity for CO2/N2, 41.6 and 30.0 respectively at 0℃ and 25℃, which were high compared with the values of many biomass-derived N-deficient active carbon. The high CO2/N2 selectivity of the carbon was owing to the presence of N-containing groups on its surface. Finally, we found that the CO2 adsorption isotherm of the sample activated at 600℃ hardly changed after 5 successive runs of adsorption-desorption, indicating that the sample showed excellent recyclability. From the results derived from the CO2 adsorption tests, it is concluded that the active carbon prepared from N-containing biomass via one-step carbonization/activation technology can display a high uptake of low-pressure CO2, large selectivity of CO2/N2, and excellent recyclability.
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2015年第19期309-314,共6页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金(51206099)
中央高校基本科研业务费专项资金资助(15CX02024A)
浙江省林业工程重中之重一级学科开放基金(2014lygcz019)
关键词
活性炭
废弃物
工艺
吸附
氮掺杂
二氧化碳捕集
极微孔
activated carbon
wastes
technology
adsorption
N-doping
CO2 capture
ultramicropore
