Abstract:

The physical and chemical properties of the activated carbon have an important influence on the performance of carbon based catalysts for the dehydrochlorination reaction of tetrachloroethane(TeCA) to trichloroethylene (TCE). Activated carbons were pretreated by the use of acid or alkali solution. The surface oxygen-containing groups, physical structure, and the types and content of inorganic oxides of untreated and pretreated activated carbons were characterized by XRF, BET and Boehm titration. The physical structure and high boiling organic residues of the used activated carbon samples were obtained with the help of BET and GC-MS. The performances of different treated activated carbon samples for the reaction of TeCA to TCE were investigated. Furthermore, deactivation mechanism was discussed by the association of these physical and chemical properties and the stability of the activated carbon samples. The results showed that the treatments brought major change to the type and content of inorganic oxides rather than oxygen-containing groups and physical structure. The specific surface area and pore volume of the used carbon samples decreased with the generated 1,1,2,4,4-pentachlorobuta-1,3-diene. The main factor on the stability of activated carbon samples was not the surface oxygenic groups, but the Al and Fe. Water and Lewis acid like AlCl₃ and FeCl₃ were generated from the reaction of Al (Fe) oxides and by-product HCl. Under the effect of the Lewis acid,tetrachloroethane or trichloroethylene accelerates the formation of carbocation intermediate. Then, carbocation was polymerized with trichloroethene and undergone dehydrochlorination to give 1,1,2,4,4-pentachlorobuta-1,3-diene (1,1,2,3,4-pentachlorobuta-1,3-diene), even other polymerizations with longer molecular chains. These polymers were accumulated in the hole of activated carbon, leading to the decrease of the specific surface area and then the deactivation of the catalyst.

Key words: activated carbon, tetrachloroethane, trichloroethylene, catalyst

摘要：

活性炭表面物化性质是炭基催化剂催化TeCA脱HCl合成TCE反应性能的重要影响因素。采用酸、碱对活性炭进行调变处理,通过XRF、BET、Boehm滴定、GC-MS等对处理前后活性炭的物理结构、表面基团、无机氧化物种类和数量,以及反应后活性炭的物理结构和表面残留有机物的表征分析,研究了活性炭催化TeCA脱HCl反应性能与其表面物化性质的对应关系。结果表明:酸、碱等处理对活性炭物理结构和表面基团影响较小,但显著改变了无机氧化物种类和数量;反应后活性炭比表面积下降明显,表面残留有五氯丁二烯;活性炭中铝、铁氧化物与五氯丁二烯含量、孔道堵塞程度和失活速率呈密切对应关系。铝、铁与HCl生成的AlCl₃和FeCl₃ Lewis酸中心是促进TCE聚合进而导致孔道堵塞而失活的主要原因。

关键词: 活性炭, 四氯乙烷, 三氯乙烯, 催化剂