【作者】 周洲；

【导师】 郭锡坤；

【作者基本信息】 汕头大学 ， 工业催化， 2001， 硕士

【摘要】 4A分子筛广泛用作洗涤剂助剂，需求量很大。已经发现，其粒径越小，性能越好。例如，粒径为0.5—1mm比粒径为2—8mm的4A分子筛，其悬浮性、钙镁离子吸附量、低温下的金属离子吸附能力都有很大提高。目前研究结果又表明，小粒径的4A分子筛不但在以上性能上可能有大幅度提高，而且随着表面积的增加，在作为催化剂的载体和吸附剂的性能上也可能会有显著改善。因此，如何合成更小粒径以至为纳米级的4A分子筛，是目前受重视的研究课题。 本文以溶胶凝胶—超临界干燥法制备具有一定硅铝比的超细氧化物粉末，以它为原料，不但可以将原料的粒径控制在纳米级，硅铝氧化物均匀混合，而且可以使原料中的硅铝比易于精确调控，从而适合小粒径分子筛的合成。本文又对的传统水热合成法进行改进，合成了纳米分子筛。通过探讨成胶温度、陈化时间、碱度等条件，以及不同铝络合剂对合成体系的影响，从而确定了较佳的反应条件。实验结果表明，控制原料硅铝摩尔比为1.4，反应体系H₂O/Na₂O（摩尔比）为30，SiO₂/Na₂O（摩尔比）为2.2，首先在冰浴中形Si-Al凝胶，并在0℃陈化24h，加入适量柠檬酸作为铝络合剂，可以合成出粒径为50nm左右的4A分子筛；如果加入乙酸作为铝络合剂，则可以合成出粒径为45nm左右的P型分子筛。 通过比较不同反应条件和添加不同铝络合剂时合成的分子筛的粒径、纯度、以及各种条件下的晶化曲线，探讨了纳米分子筛的合成机理，以及添加铝络合剂对反应产生影响的机理。本文的实验结果发现，随着铝络合剂络合能力的增强，晶化速度加快，分子筛在合成时为固相转化机理。由于这些络合剂和OH^-一起与铝生成了比较稳定的络合物，增加了溶液相中的铝含量，有利于分子筛的成核以及晶体的生长。因此4A分子筛的晶化速度增加，晶粒度减小。但是，由于EDTA的络合能力过强，晶化速度过快，反而抑制了晶核的形成，使得晶粒度比柠檬酸作为络合剂的要大。通常认为过高的碱度是4A分子筛转晶为方钠石的原因，但是我们的实验结果表明，提高碱度后，并没有观察到方钠石的衍射峰。通常获得方钠石的系统的铝源一般都是铝酸钠，这种系统在溶液碱度不变的情况下，反应硅铝胶中的钠离子的含量就会明显偏高。采用超细氧化物作为硅源和铝源，与铝酸钠系统的区别就在于体系中钠离子的数量比较少，而且在反应中不变。更多还原

【Abstract】 4A zeolite is one kind of wash additive. It has been found that the capatility of 4A zeolite will be much more better when the granularity is smaller. And as the superficial area of 4A zeolite is increased, it抯 suspend property, absorption of Ca2~ and Mg2~ will be improved. In the synthesis of 4A and P zeolite, nano-SiO, and A1203 were used as alumina source and silica source, and the batches had the molar ratio of 3-8 Na-,O :1-2 SiO-, : AL,03: 200-400H,O. When the batches had high alkalinity andlor hi concentration of alumina, the rate of crystallization was accelerated and the average crystal size of 4A zeolite reduced. This may be due to the promotion of hydroxide ions to the nucleation and growth of zeolite crystals. It is showed the average crystal size can be reduced and the crystallization rate presents faster by forming Si-Al gel at low temperature (00C) and prolonging the aging time to about 24 hours. By adding different kind of complexing agent of aluminum, the crystallization time and the average crystal size can be greatly reduced from 200nm to about 5Onm. Nano-4A molecular sieves can be synthesized by adding citric acid, and Nano-P molecular sieves can be synthesized by adding acetate. By forming Si-Al gel at low temperature 00C, prolonged aging time of nucleation gel (24hr). Comparing to the conventional synthesis method reported in literature, the above method also presents the faster crystallization rate. These are interpreted that more nuclei were formed under the suggested crystallization conditions. To obtain further reduce the crystal size of 4A zeolite, an improved method basing on the above was also developed, the complexing agents of aluminum were added into the batches. It is shown that the crystallization time and the average crystal size of zeolite 4A zeolite could be greatly reduced by adding the complexing agents of aluminum. The amount of the ?III ? ~IJc}拁Tg~ I~2L~SC additives was also found to obviously affect the crystallization. With the amount of citrate increased, the crystallization time and crystal size of zeolite 4A exhibited a regularity of decreasing followed by increasing. The above promotion could be interpreted at that the additional amount of tetra-coordinated aluminum species was formed in batches, which is active for nucleation and crystallization of zeolite 4A, when the complexing agent of aluminum were added.更多还原