EVOLUTION OF CARBON STRUCTURE IN CHEMICALLY ACTIVATED WOOD
EVOLUTION OF CARBON STRUCTURE IN CHEMICALLY ACTIVATED WOOD
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DOI：
10.1016/0008-6223(95)00067-n
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发表时间：
1995-01-01
期刊：
影响因子：
10.9
通讯作者：
DERBYSHIRE, F
中科院分区：
文献类型：
--
作者：
SOLUM, MS;PUGMIRE, RJ;DERBYSHIRE, F
采用~（13）C NMR和FTIR分析方法研究了磷酸活化白色橡木制得的活性炭的化学结构随热处理温度（HTT）的变化与孔隙率的关系。在低HTT下通过酸处理实现的化学变化是：到50 ℃，木质素结构有显著改变;到100 ℃，纤维素的显著部分已经反应，形成酮和酯;磷酸酯的形成在150 ℃左右变得明显;交联反应在低于150 ℃下开始，这与化学活化中获得的较高碳产率一致;并且通常芳香性增加，脂肪族、羧基和羰基损失。低温现象先于并涉及多孔性和结构膨胀的发展，多孔性和结构膨胀在250摄氏度左右开始，并在350至450摄氏度之间达到最大值。高达450摄氏度，发现孔体积与交联密度相关。高于450摄氏度，存在尺寸收缩和孔隙率降低。伴随的现象包括：纤维素磷酸盐和氧官能团的消除;以及估计的芳香族簇大小的急剧增加。后者将需要降低交联密度以促进簇生长，并且所得的结构重排和簇的增加的对齐将产生具有降低的孔隙率的更致密堆积的结构。
C-13 NMR and FTIR analyses have been employed to follow the evolution of chemical structure in relation to porosity development, as a function of heat treatment temperature (HTT), for activated carbons produced from white oak by phosphoric acid activation. The chemical changes effected by acid treatment at low HTT are: by 50 degrees C there is significant alteration of the lignin structure; by 100 degrees C a significant portion of the cellulose has reacted, with the formation of ketones and esters; the formation of phosphate esters becomes apparent around 150 degrees C; crosslinking reactions are initiated below 150 degrees C, consistent with the higher carbon yield obtained in chemical activation; and generally there is an increase in aromaticity and loss of aliphatic, carboxyl, and carbonyl groups. The low temperature phenomena precede, and relate to, the development of porosity and structural dilation that commences around 250 degrees C, and attains a maximum between 350 and 450 degrees C. Up to 450 degrees C, pore volume is found to correlate with crosslink density. Above 450 degrees C, there is a dimensional contraction and a reduction in porosity. Among the accompanying phenomena are: the elimination of cellulose phosphates and oxygen functionalities; and a dramatic increase in the estimated aromatic cluster size. The latter would require a reduction in crosslink density to facilitate cluster growth, and the resulting structural rearrangement and increased alignment of clusters would produce a more densely packed structure with reduced porosity.