用Monte-Carlo方法研究八面沸石的脱铝过程

STUDIES ON DEALUMINIZATION PROCESS OF FAUJASITE BY MONTE-CARLO METHOD

八面沸石中的骨架铝可按其环境次邻位上出现的铝数分为4类。环境无次邻铝的铝离子形成分子筛的强酸中心;周围有1至3个次邻铝的铝离子形成的酸中心酸性较弱,与前者相比易于从骨架上解脱。基于一级动力学近似,用Monte-Carlo方法模拟八面沸石脱铝过程,得到4种类型铝离子的数目随硅铝比改变而演化的规律。预计硅铝比在6.68附近,脱铝八面沸石中的强酸中心数目达到极大值;如果强、弱酸中心铝离子的解脱速率差别较大,则脱铝八面沸石中强酸中心浓度较高。

In principle, four rypes of aluminum ions on the faujasite framework may be distinguished according to the next neighbour number (0,1,2,3) of aluminum appearing around their environment. The hydrogen ions associated with type-O aluminum ions are to be identified as 'strong' acid, and those associated with types 1,2 and 3, as 'weak' acid. In a dealuminization process, the 'weak acid' aluminum ions (types 1,2 and 3) are removed preferably over the 'strong acid' type-O. Based on first-order kinetics, the concentrations of all the four types aluminum ions upon dealuminization can be described in terms of the Monte-Carlo simulation of the dealuminization process of the faujasite. We conclude that the concentration of the strong acid center in dealuminization faujasites come up to its maximum around Si/Al 6.68. We also conclude that the more difference between dissolving rate constants for 'strong' and 'weak' aluminum ions the denser strong acid in dealuminization faujasite could be expected.