二丙胺的结构微调对磷酸铝分子筛晶化过程影响的凝胶组成依赖性

Initial-Gel-Composition-Dependence of Dipropylamine-Structure-Fine-Tuning Influence on the Crystallization Pathways of Aluminophosphate Molecular Sieve

以二丙胺异构体(二正丙胺DPA和二异丙胺D-i PA)为结构导向剂,在200℃加热2组反应原料物质的量之比不同的初始凝胶,合成出了高结晶度的磷酸铝分子筛Al PO4-11。利用X射线粉末衍射分析、元素分析等表征手段,研究了凝胶的晶化过程和液相的p H值以及Al和P的浓度演化。初始凝胶各组分物质的量之比为nAl2O3∶nP2O5∶nDPA/D-i PA∶nH2O=1.0∶1.0∶1.2∶75时,以DPA为结构导向剂,晶化过程中无中间相生成,而以D-i PA为结构导向剂时,晶化过程中生成了具有12元环孔道结构的磷酸铝分子筛Al PO4-5中间相;初始凝胶各组分物质的量之比为nAl2O3∶nP2O5∶nDPA/D-i PA∶nH2O=1.0∶1.0∶1.0∶75时,以DPA为结构导向剂,晶化过程中生成了具有18元环孔道结构的磷酸铝分子筛VPI-5中间相,而以D-i PA为结构导向剂时,晶化过程中同时出现了VPI-5及Al PO4-5两种中间相。表明对于同一种有机胺,凝胶物质的量之比的改变影响了其结构导向效应。理论计算结果显示质子化的DPA及D-i PA中N原子上的电荷有差异,表明有机胺的结构微调影响其结构导向效应,但该影响依赖于凝胶组成。

The structure-directing effect of dipropylamine isomers, i.e., di-n-propylamine （DPA） and diisopro- pylamine （D-iPA）, was investigated. By heating the initial gels with certain composition at 200 ℃ for 24 h, highly crystalline aluminophosphate molecular sieve A1PO4-11 was obtained. The crystallization processes were investigated using X-ray diffraction, elemental analysis and pH value measurement. For the crystallization process of the initial gel with nA12O3：np205/nDPA/D.iPA ：nH2O=l.0：l.0：1.2：75, no intermediate phase was formed when the DPA was used as the structure-directing agent, whereas intermediate phase of aluminophosphate molecular sieve A1PO4-5 was observed when the D-iPA was used as the structure-directing agent. For the crystallization process of the initial gel with nAl2O3 ：nP2O5：nDPA/D-iPA ：nH2O =1.0：1.0：1.0：75, intermediate phase of aluminophosphate molecular sieve VPI-5 was formed when the DPA was used as the structure-directing agent, whereas intermediate phases of both VPI-5 and A1PO4-5 were observed when the D-iPA was used as the structure-directing agent. Theoretical calculation showed that the charge on the N of the protonated DPA was different with that on the N of the protonated D-iPA. The results indicate that the structure-directing effect of amine can be affected by the composition of the initial gel and the fine-tuning of the structure of amine can influence its structure-directing effect. However, such influence is affected by the composition of the initial gel.