Studies On The Synthesis Of Nano-4A Molecular Sieves

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.