Characterization of structural and chemical modifications during the steam activation of activated carbons
Characterization of structural and chemical modifications during the steam activation of activated carbons
复制标题
DOI：
10.1016/j.micromeso.2020.110549
复制
发表时间：
2020-12-15
影响因子：
5.2
通讯作者：
Bathen, Dieter
中科院分区：
文献类型：
--
作者：
Muthmann, Johanna;Blaeker, Christian;Bathen, Dieter
在富含水蒸气的氮气流中活化低孔隙度的无烟煤基材料，以产生四种活性炭，它们在结构和化学性质上系统地不同。通过体积测量和压汞法对基质和活化材料的结构性质进行表征。通过元素分析对化学成分进行了一般分类。通过Boehm滴定分析表面化学。通过测量选定探针分子（丙酮（极性）、正庚烷（非极性）和甲苯（芳香族））的过量等温线和负载依赖性吸附焓来研究吸附性能。假设选择性吸附的分布规律，由过量吸附等温线估算出表面基团的摩尔比，这些方法的结合使得能够观察和区分活化过程中炭的结构和表面化学变化。例如，可以表明，在活化过程中出现的中孔比例增加的更宽的孔宽度分布导致更明显的能量不均匀性。还发现，随着活化时间的增加，表面积的增加伴随着芳香族表面基团的增加和极性和非极性表面基团的减少。特别是极性探针分子丙酮的吸附揭示了表面化学的异质性，这与异质性的结构组成一起导致吸附焓随负载量的增加而明显降低。
An anthracite-based material of low porosity was activated in a nitrogen stream enriched with water vapor to produce four activated carbons, which differ systematically in their structural and chemical properties. Characterization of the structural properties of the base and the activated materials was carried out by volumetric measurements and mercury porosimetry. A general classification of chemical composition was done by ultimate analysis. The surface chemistry was analyzed by Boehm titration. The adsorption performance was investigated by measuring excess isotherms and load-dependent adsorption enthalpies of selected probe molecules: acetone (polar), n-heptane (non-polar) and toluene (aromatic). Assuming distribution rules for selective adsorption, the molar ratios of the surface groups were estimated from the excess isotherms.The combination of these methods enables the observation and differentiation of structural and surface chemical changes of the carbons during activation. For example, it could be shown that the broader pore width distribution with an increasing proportion of mesopores occurring in the course of activation leads to a more pronounced energetic heterogeneity. It was also found that an increase in surface area with increasing activation time is accompanied by an increase in aromatic surface groups and a reduction of polar and non-polar surface groups. Especially the adsorption of the polar probe molecule acetone revealed the heterogeneity of the surface chemistry, which together with the heterogeneous structural composition resulted in a distinct decrease of the adsorption enthalpy with increasing loading.