在(TPA)_2O-Na_2O-SiO_2-H_2O系统中MFI型硅沸石的结晶行为(Ⅰ)──结晶动力学的研究

Studies on the Crystallization Behavior of Zeolite Silicalite-1 in (TPA)_2O-Na_2O-SiO_2-H_2O System(Ⅰ)──Crystallization Kinetics

以四丙基溴化按作模板剂，以白炭黑（Ⅰ）、硅溶胶（Ⅱ）和水玻璃（Ⅲ）为不同硅源在140～180℃合成MFI型硅佛石（Silicalite－1）．反应物配比相同，其结晶动力学曲线有明显差异．从它们的成核诱导期及生长速度计算出各体系硅佛石晶核形成活化能与生长活化能，在体系（Ⅰ）中为46／76kJ／mol，体系（Ⅱ）中为41／43kJ／mol，体系（Ⅲ）中为38／78kJ／mol．产物结晶粒径的大小由各体系成核活化能与生长活化能的差值决定．合成产物的结晶度以白炭黑为硅源时最高．提高温度有利于提高产物结晶度．

Zeolite silicalite-1 was hydrothermally synthesized in (TPA)2O-Na2O-SiO2-H2O system. The silica sources used were fumed silica(Ⅰ), silica sol (Ⅱ) and waterglass(Ⅲ).There are different crystallization kinetic curves in the temperature range from 140℃ to 180 ℃ for different silica source systems with the same molar ratio of reactant. The activation energy for nucleation (En) and for crystallization (Ec), which are calculated from the induc-tion time and growing rate, are 46/76 kJ/mol in system (Ⅰ), 41/43 kJ/mol in system (Ⅱ),and 38/78 kJ/mol in system (Ⅲ), respectively. The crystal size obtained in each system de-pends on the difference between E. and Ec The highest product crystallinity determined both by XRD and by adsorption of n-hexane was obtained in fumed silica system. The quality of the zeolite obtained can be improved by increasing the temperature of crystallization.