【摘要】 为了研究木质素基炭微观结构演变规律,以阔叶材酶解木质素及其尿素改性和三聚氰胺改性木质素为原料,在300～900℃之间炭化制备木质素基炭。采用X射线衍射、氮气吸附/脱附等温线、电阻率测试和扫描电镜分析了木质素基炭的微观结构、导电性和孔隙结构,全面分析了改性处理对木质素基炭的微观结构和孔隙结构演变过程的影响。研究结果表明:不管木质素是否改性,当炭化温度从600℃升高到700℃时,木质素基炭的导电性急剧提高,并从绝缘体转变为半导体,木质素基炭的类石墨微晶结构快速发展。然而,尿素和三聚氰胺改性导致类石墨微晶中碳网平面层间距的缩小,且氮含量越高的三聚氰胺改性变化更加明显;同时可以明显提高炭化温度低于700℃时炭化得到的木质素基炭的导电性,并降低炭化温度高于700℃时炭化得到的炭的导电性。非常突出的是,尿素和三聚氰胺改性显著阻碍了木质素基炭孔隙结构的发展,甚至完全抑制了微孔的形成。在700℃下制得的未改性、尿素改性和三聚氰胺改性木质素基炭的比表面积分别为524、 102和69 m~2/g。更多还原

【Abstract】 Three series of lignin-based chars were prepared from three raw materials, hardwood enzymatic hydrolysis lignin and their urea-modified and melamine-modified counterparts, through carbonization in the temperature range of 300-900 ℃ in order to elucidate the microstructure evolution of lignin chars. X-ray diffraction, nitrogen adsorption, electric resistivity analysis and scanning electron microscope were employed to characterize the graphite-like microcrystallite structure, electric conductivity and pore structure of their lignin-based chars. The results consistently showed that when the carbonization temperature was increased from 600 ℃ to 700 ℃, the electronic resistivity of the chars was sharply promoted leading to the rapid transition of lignin-based chars from an insulator to a semiconductor, and the development of the graphite-like microcrystallite component in the chars was remarkably enhanced, whether lignin as raw materials was modified by nitrogen-containing substances or not. However, urea or melamine modification lead to a reduction of interlayer spacing in the graphite-like microcrystallites, with a more reduction for melamine modification of more nitrogen content. Moreover, urea or melamine modification could obviously promote the electron conductivity of the chars prepared below 700 ℃ but lessen a little for the char prepared above 700 ℃. Outstandingly, urea and melamine modification remarkably suppressed the development of pore structure of lignin-based chars, especially totally the formation of microporosity. Specifically, the surface area of the chars prepared from the unmodified lignin, urea-modified one and melamine-modified one have a big difference with the value of 524,102 and 69 m~2/g, respectively.更多还原