Activated carbons from yellow poplar and white oak by H3PO4 activation
Activated carbons from yellow poplar and white oak by H3PO4 activation
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DOI：
10.1016/s0008-6223(98)00082-7
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发表时间：
1998-01-01
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：
Jagtoyen, M;Derbyshire, F
结果提出了从磷酸活化硬木的持续调查。早期的工作与白色橡木已扩大到包括黄色白杨。发现两种前体发生相同的一般化学和物理变化。讨论了磷酸活化的可能机制，利用磷化合物作为木材和纤维素阻燃剂的广泛研究。磷酸似乎既用作酸催化剂以促进键断裂反应和经由诸如环化和缩合的过程形成交联，又用作与有机物质联合收割机以形成连接和交联生物聚合物片段的磷酸根和多磷酸根桥。磷酸基团的添加或插入驱动膨胀过程，在除去酸后，使基质处于膨胀状态，具有可接近的孔结构。认为无定形聚合物的活化主要产生微孔，而结晶纤维素的活化产生孔径的混合物。结晶纤维素的不同响应归因于比无定形聚合物可能的更大的结构膨胀潜力，除了其他因素之外，这是由于其更高的密度和其化学结构，其允许与磷酸更广泛程度的结合，并因此使细胞壁“膨胀”。从结晶纤维素获得的孔径分布可以通过增加HTT和/或酸与前体的比率来改变，使得最终结构主要是介孔的。在450摄氏度以上的温度下，当磷酸酯键变得热不稳定时，结构发生二次收缩。交联密度的降低允许聚芳族簇的生长和排列，从而产生更致密的堆积和更少的多孔结构。(C)1998爱思唯尔科技有限公司版权所有。
Results are presented from continuing investigations of the phosphoric acid activation of hardwoods. Earlier work with white oak has been extended to include yellow poplar. II is found that the same general chemical and physical changes occur with both precursors. A discussion is presented on the possible mechanisms of phosphoric acid activation, drawing upon extensive research on the use of phosphorous compounds as fire retardants for wood and cellulose. Phosphoric acid appears to function both as an acid catalyst to promote bond cleavage reactions and the formation of crosslinks via processes such as cyclization, and condensation, and to combine with organic species to form phosphate and polyphosphate bridges that connect and crosslink biopolymer fragments. The addition or insertion of phosphate groups drives a process of dilation that, after removal of the acid, leaves the matrix in an expanded state with an accessible pore structure. It is considered that activation of the amorphous polymers produces mostly micropores, while activation of crystalline cellulose produces a mixture of pore sizes. The different response of crystalline cellulose is attributed to a much greater potential for structural expansion than is possible with the amorphous polymers due, among other factors, to its higher density and its chemical structure that allows for a more extensive degree of combination with phosphoric acid, and hence "bulking" of the cell walls. The pore size distribution obtained from crystalline cellulose can be altered by increasing the HTT and/or the ratio of acid to precursor such that, eventually, the structure is dominantly mesoporous. At temperatures above 450 degrees C, a secondary contraction of the structure occurs when the phosphate linkages become thermally unstable. The reduction in crosslink density allows the growth and alignment of polyaromatic clusters, producing a more densely packed and less porous structure. (C) 1998 Elsevier Science Ltd. All rights reserved.