无溶剂快速合成ZSM-12分子筛

Solvent-free rapid synthesis of ZSM-12 zeolite

开发出一种无溶剂快速合成ZSM-12分子筛的方法。该方法分为两步。第一步是硅铝前体的制备:将正硅酸乙酯、铝酸钠、氟化钠、甲醇、水混合,在室温搅拌条件下反应3h后蒸干液体,得到硅铝前体。第二步是硅铝前体的晶化:将硅铝前体与晶种、四乙基氢氧化铵模板剂混合均匀后,移入反应釜中,在160℃条件下晶化24h得到ZSM-12分子筛产品。相比于已有的ZSM-12分子筛水热过程,无溶剂合成过程的晶化时间大大缩短。采用XRD、SEM、solid-state NMR、TG、FTIR等手段分析了硅铝前体的物化性质,跟踪了ZSM-12分子筛的晶化过程。结果表明,晶种的加入和硅铝前体中Si—O—Al键的提前构筑是ZSM-12分子筛快速晶化的原因。晶种为ZSM-12分子筛的生长提供表面,缩短诱导期;硅铝前体中Si—O—Al键的提前构筑促进结构重排,从而缩短生长期。

A solvent-free rapid synthesis method of ZSM-12 zeolite was developed.The method consists of two steps.The first step was to prepare Si-Al precursor.Tetraethylorthosilicate,sodium aluminate,sodium fluoride,methanol and water were mixed and reacted for 3h under agitation at room temperature.After reaction,the liquid phase was evaporated,resulting in the Si-Al precursor.The second step involves the crystallization of Si-Al precursor.The Si-Al precursor was mixed with seeds and tetraethylammonium hydroxide,and subsequently transferred to autoclave for crystallization for 24h at 160℃to obtain the ZSM-12 zeolite.The crystallization of ZSM-12 zeolite was faster in solvent-free synthesis system than in hydrothermal synthesis system.By using XRD,SEM,solid-state NMR,TG,and FTIR characterizations,the physicochemical properties of Si-Al precursor were analyzed,and the crystallization process of ZSM-12 zeolite was investigated.The results showed that the rapid crystallization was attributed to the addition of seeds and the formation of Si—O—Al in advance in Si-Al precursor.The seeds provided surface for the crystallization of ZSM-12 zeolite,thereby shortening the induction period.The formation of Si—O—Al bonds in the Si-Al precursor promoted structural rearrangement,and shortened the growth period.