炭化温度对牛粪生物炭结构性质的影响

以牛粪为原料,在不同炭化温度下(200、300、400、500、600、700 ℃)采用热裂解法制备生物炭,借助扫描电子显微镜、元素分析仪、比表面积分析仪,结合Boehm滴定法、碘吸附及亚甲蓝吸附等,对所制得的牛粪生物炭的形貌特征、元素组成、比表面积、孔径、表面官能团和吸附性能等进行分析。结果表明:随着炭化温度升高,产率和挥发分含量降低,灰分和固定碳含量升高,pH值增加,制得生物炭的形貌特征更有规则且孔隙更加紧密。适当的升高炭化温度有利于孔隙的形成及微孔数量的增多,比表面积和孔容逐渐变大,而孔径逐渐减小。随炭化温度升高,牛粪生物炭的C含量增加,而H、O含量减小,N含量先增加后减小,H/C、(O+N)/C和O/C均下降,说明制得生物炭的芳香性和结构稳定性增强,但极性和亲水性减弱。表面官能团中羧基含量随炭化温度升高先增加后降低,羰基含量持续增加,而内酯基、酚羟基含量、酸总量和表面含氧官能团总量逐渐降低。碘吸附值和亚甲基蓝吸附值随炭化温度升高先增加后减小,在600 ℃下吸附值最大。

Effects of carbonization temperatures on structure and properties of cow dung biochars

A series of biochars were obtained under the limited oxygen cracking condition at different carbonization temperatures of 200, 300, 400, 500, 600, 700 ℃, respectively, with cow dung as raw material. The structures and properities of these biochars, i.e. surface morphology, element contents, specific surface area, pore size, surface functional groups and adsorption properties, were examined via scanning electronic microscopy, elemental analyzer, specific surface area and pore size distribution analyzer, and by means of Boehm titration, iodine adsorption and methylene blue adsorption. It was shown that the yields and volatile matter content decreased, while the contents of ash and fixed carbon and pH increased with the increasing carbonization temperature. Besides, the morphological features of biochars became more regular and the pores were denser. When the carbonization temperature was raised appropriately, it was beneficial to form pore and increase the number of micropores pore, the specific surface area and pore volume were increased, yet the pore size was decreased. With the increased carbonization temperature, the C contents of biochars increased, while the H and O contents decreased, and the N contents increased at first and then decreased, and the values of H/C,(O+H)/C and O/C were reduced, indicating that the aromatic properties and structural stability of biochars were enhanced, yet the polarity and hydrophilicity were both weakened. With the increasing carbonization temperatures, the carboxyl contents of surface functional groups were firstly increased and then decreased, the contents of carbonyl groups continuously increased, yet the contents of lactone and phenolic hydroxyl groups, the total contents of acid and oxygen-containing functional groups were gradually decreased. The adsorption value of iodine and methylene blue increased at first and then decreased with the increasing carbonization temperatures, andy both reached the highest value under 600 ℃.