偏高岭土水热合成4A沸石晶化行为的研究

以偏高岭土为原料合成4A沸石,由于其合成过程工艺简单,成本低而一直受到普遍的关注,对于该法晶化过程的行为研究,近年来陆续出现报道,Rocha等^[1]研究认为偏高岭土在碱液中缓慢溶解,形成含SiO3^2-,SiOH基团和Al(OH)4^-的溶液,逐步缩合为硅铝酸钠凝胶,再进一步形成4A沸石晶粒并通过结构重排而转变为4A沸石,王建等^[2]研究提出偏高岭土在NaOH溶液中部分溶解,且迅速转变为偏高岭土,并伴有硅铝酸钠凝胶产生,同时偏高岭土也不断在碱液的作用下凝胶化,生成的凝胶再进一步转变为4A沸石,因而合成的4A沸石产品与化学合成法存在着较大的差异。对偏高岭土合成4A沸石的晶化历程,作者曾进行过研究^[3],发现偏高岭土在碱液中溶解很小,由偏高岭土转为4A沸石晶型,主要是在偏高岭土固相的基础上进行的。本文似从合成过程的机理方面,探讨偏高岭土合成4A沸石的晶化过程行为及其与化学法合成产品差异的关键所在。     

微波法煅烧高岭土及合成洗涤助剂4A沸石

本文用微波法煅烧高岭土并合成4A沸石.与传统高温热处理法相比,微波法煅烧的高岭土其活化深度好,增白程度高,粒度细,能耗大为降低,显示了明显的优越性.本文还采用煅烧后的活性高岭土为原料,在微波辐射下进行4A沸石的合成,并用XRD、DTA、SEM、白度计、钙离子交换度等进行表征.与传统水热处理法相比,微波法所得样品在结晶度、白度和钙离子交换能力方面均显优势,且大大地加快了沸石晶化反应速率.经动力学处理,发现微波法合成4A沸石的晶核形成及晶体成长的表观活化能均有所下降,说明微波辐射能促进新相的形成,加快整个晶化反应速率.     

高岭土合成4A沸石晶化历程

4A沸石是广泛用于催化、污水处理、洗涤剂助剂等领域的一种人工合成沸石分子筛[1,2].采用化学合成法,沸石分子筛是在无定形凝胶和水溶液共存的体系中生成[3].以高岭土为原料,在低温水热条件下进行4A沸石的合成时,由于高岭土并不完全溶解于碱性溶液中,因而这一固液两相体系的反应过程,可能是在偏高岭土无定形的表面上完成.本文通过对合成过程液相成分的变化和固相特征分析,探索了该条件下4A沸石晶核生成及其成长历程.81999-04-19收稿,1999-06-25修回内蒙古自然科学基金资助课题（971302-2）合成原料为n（StQ）：n（AI。O。）一2.06：1的…     

A形体过量β沸石的晶化过程

以四乙基氢氧化铵(TEAOH)为结构导向剂,在超浓水热条件下合成了手性多形体A(简称A形体)过量的β沸石,对初始凝胶的性质及晶化过程进行了深入研究,测定了相应的晶化曲线.研究结果表明,与晶化出A形体含量低于50%的普通β沸石的合成体系相比,晶化出A形体过量的β沸石的合成体系中含水量极低,凝胶中过量的水必须在晶化之前通过加热去除,但过度去除初始凝胶中的水则会显著延长晶化时间.在晶化初期,产物中己出现A形体过量特征,随着晶化的进行,A形体的过量程度无显著变化.     

偏高岭土水热合成NaY分子筛的机理研究

采用茂名高岭土水热合成NaY分子筛,用IR,XRD,NMR,SEM,HRTEM等分析了其晶化过程。结果表明：偏高岭土水热合成Y型分子筛是固相转变机理,晶化过程是一个扩散-成胶-原位重排的过程。     

沸石分子筛转晶的研究——4A转晶为NaY型沸石的机理

采用扫描电子显微镜、X-光衍射分析和高真空苯吸附量的测定等方法,研究了在一定的化学环境下沸石分子筛的介稳状态;探讨了不同转晶条件对沸石重新晶化的影响;分别研究了在Y型、AG_4型或Ω型沸石的合成条件下,加入其它型号的沸石转变为Y型、AG_4或Ω型沸石的过程;并研完了在Y型沸石合成的化学环境下,A型沸石向Y型沸石转变的过程,并探讨其机理。     

沸石转晶的研究(Ⅲ)——NaY型沸石的稳定性及NaPc型沸石的结构

研究了原始凝胶3、3Na_2O·A1_2O_3·10SiO_2·200H_2O在100℃NaY型沸石向NaPc型沸石转晶的晶化过程,应用电子显微镜、X-射线衍射、TMS-GC和固体高分辨Si~(29)-NMR方法研究了沸石晶核的形成、晶体粒度和外貌的变化及液、固相中硅酸根离子存在状况及转晶中沸石结构的变化,并提出了转晶的液相传质机理。     

洗涤助剂用硅铝酸盐制备

以苏州高岭土为原料,进行了新型高效无磷洗涤助剂硅铝酸盐活性体制备研究,确定了传统水热法合成硅铝酸盐活性体的适宜条件:高岭土在800℃焙烧活化2h,焙烧后的偏高岭土补加氢氧化钠、硅酸钠和水,调整SiO2:Al2O3:Na2O:H2O摩尔比为2:1:4.3:237,然后在60℃恒温水浴中老化3h,接着在95℃条件下晶化4h,最后所得固相即为钙镁离子交换性能优良的硅铝酸盐。该产品对钙镁吸附量均高于4A沸石和P型沸石,分别达到374.3mg/g和122.7mg/g;此外该产品对水溶液中铅离子也有很好的吸附性能。     

洗涤助剂用硅铝酸盐制备

以苏州高岭土为原料,进行了新型高效无磷洗涤助剂硅铝酸盐活性体制备研究,确定了传统水热法合成硅铝酸盐活性体的适宜条件:高岭土在800℃焙烧活化2h,焙烧后的偏高岭土补加氢氧化钠、硅酸钠和水,调整SiO2:Al2O3:Na2O:H2O摩尔比为2:1:4.3:237,然后在60℃恒温水浴中老化3h,接着在95℃条件下晶化4h,最后所得固相即为钙镁离子交换性能优良的硅铝酸盐。该产品对钙镁交换量均高于4A沸石和P型沸石,分别达到374.3mg/g和122.7mg/g;此外该产品对水溶液中铅离子也有很好的交换性能。     

以高岭土为原料合成沸石分子筛的相变规律

以天然粘土矿物高岭土为原料, 采用水热晶化法合成了NaX, NaP和SOD三类沸石. 利用XRD、 静态饱和水吸附等测试手段详细考察了晶化温度、 初始反应混合物的碱浓度对沸石结晶的影响. 通过实验研究得到了三类沸石的结晶相区和结晶变化规律, 并优化出最佳合成工艺条件和相转变规律.     

Hydrovapothermal conversion of tetraethoxysilane vapor to polycrystalline zeolite layer by in situ gelation

Zeolite membrane has been fabricated on porous alumina substrate in a single continuous process of gelation and subsequent crystallization while suppressing nucleation of zeolite powder in the bulk.     

UV-Raman and NMR spectroscopic studies on the crystallization of zeolite A and a new synthetic route

UV-Raman and NMR spectroscopy, combined with other techniques, have been used to characterize crystallization of zeolite A. In situ UV-Raman spectroscopy shows that the starting gel for crystallization of zeolite A contains a lot of four-ring (4R) building units and the appearance of six-ring (6R) building blocks is the signal for crystal formation. (29)Si NMR spectroscopy results suggest that the starting gel is double four-ring (D4R) rich and during crystallization of zeolite A both α and β cages appear. (27)Al NMR spectroscopy results indicate the absence of Al (2Si) species in the starting gel, suggesting the absence of single 4R building units in the starting gel. Furthermore, composition analysis of both solid and liquid samples shows that the solid rather than liquid phase predominates for the crystallization of zeolite A. Therefore, it is proposed that the crystallization of zeolite A mainly occurs in the solid phase by self-assembly or rearrangement starting from the zeolite building units mainly consisting of D4R. The essential role of D4R is directly confirmed by successful conversion from a solution of D4R to zeolite A in the presence of NaCl, and the importance of solid phase is reasonably demonstrated by the successful synthesis of zeolite A from a dry aluminosilicate gel. By considering that the solid phase has a major contribution to crystallization, a novel route was designed to synthesizing zeolite A from the raw materials water glass (Na(2)SiO(3) in aqueous solution) and NaAlO(2), without additional water and NaOH; this route not only simplifies synthetic procedures, but reduces water consumption.     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

超声波合成磁性4A沸石分子筛

为了解决微细粉末状沸石产品应用中与所处理溶液难以分离的问题, 在传统水热合成法合成4A沸石的晶化原料液中, 加入磁性Fe3O4微粒, 经过70 ℃, 功率为100 W的超声波晶化6 h, 合成了一系列Fe3O4含量不同的磁性4A沸石,并对其进行了XRD、SEM、IR、TG/DTA、EDX、磁化率及吸附性能等表征测试. 结果表明, 磁性4A沸石具有良好的磁稳定性, 其磁化率随Fe3O4含量的增加而增大; 磁性4A沸石对水中氟离子和六价铬的吸附与纯4A沸石性能相同, 其吸附速率可以用拟二级动力学方程来描述.     

高铝MAP沸石的非自发结晶动力学研究

在强碱性水溶液体系中,以水玻璃为硅源,以铝酸钠为铝源,在类质同晶高硅P沸石晶种导向作用下,反应物中自发生成的A型沸石可转晶为纯相高铝MAP沸石。升高反应温度有利于提高产物的结晶度。由不同温度下的晶化曲线计算出MAP沸石表观生长活化能为59.6kJ.mol^-^1。不用晶种时,同一反应物体系结晶产物为单一的A型沸石。在该反应物体系中,A型沸石的成核活化能与生长活化能分别为40.3和50.7kJ.mol^-^1。MAP高的生长活化能以及A型沸石相对低的成核与生长活化能揭示合成MAP沸石时使用晶种的原因。     

多级孔无铝Beta分子筛的合成与表征

研究了氟介质条件下,合成参数对前驱体黏度和无铝Beta分子筛晶化过程的影响.X射线衍射结果表明,高水硅比可降低前驱体的黏度,但抑制分子筛的晶化.当合成体系中加入成核促进剂(二氧化锗)和晶化促进剂(高氯酸根或磷酸根)后,即使水硅摩尔比高达20~30,在150℃水热合成4 d,仍可获得高结晶性、微米级球形或多面体形无铝Beta分子筛.热重和能谱分析结果表明,极少量高氯酸根和磷酸根可进入分子筛孔道,并影响模板剂四乙基铵根离子的热分解过程.氮气吸附-脱附、扫描电子显微镜、透射电子显微镜和选区电子衍射分析结果表明,所得无铝Beta分子筛具有多级孔结构,介孔尺寸在3.4~3.8 nm之间,由纳米晶体或纳米棒堆积而成.     

Kinetic Monte Carlo modeling of silicate oligomerization and early gelation†

We present a lattice-gas kinetic Monte Carlo model to investigate the formation of silicate oligomers, their aggregation and the subsequent gelation process. In the early oligomerization stage, the 3-rings are metastable, 5-rings and 6-rings are formed in very small quantities, 4-rings are abundant species, linear and branched species are transformed into more compact structures. Results reveal that the gelation proceeds from 4-ring containing species. A significant amount of 5-rings and 6-rings, sharing Si with 4-ring, form in the aging stage. These reveal the formation mechanism of silicate rings and clusters during zeolite synthesis.