FAU

Linde Type X

Si(55), Al(45)

Contributed by Hans Lechert and Philip Staelin

Verified by D. Ginter, by E. Basaldella, and by E. Fallabella Sousa-Aguiar

Type Material Na86Al86Si106O384 : wH2O (w ~ 260)

Method H. Lechert, H. Kacirek [1, 2]

Batch Composition NaAlO2 : 4 SiO2 : 16 NaOH : 325 H2Oa,b

Source Materials

distilled water
sodium hydroxide (99+% NaOH)
alumina trihydrate (Merck, 65% Al2O3) c
sodium silicate solution (27.35% SiO2, 8.30% Na2O, 1.37 g/mL)

Batch Preparation (for 42 g product)

(1) [100 g water + 100 g sodium hydroxide], stir until dissolved
(2) [(1) + 97.5 g alumina trihydrate], stir at 100íC until dissolved, cool to 25íC
(3) [(2) + 202.5 g water], mix
(4) [100 g of solution (3) + 612 g water + 59.12 g sodium hydroxide], mix until dissolved
(5) [219.7 g sodium silicate solution + 612 g water + 59.12 g sodium hydroxide], mix until dissolved
(7) [(4) + (5)], combine quickly and stir for 30 minutesd

Crystallization

Vessel: polyethylene bottles
Temperature: 90íC
Time: 8 hours
Agitation: none

Product Recovery

(1) Filter and wash to pH < 10
(2) Dry at 1000C, equilibrate over saturated aqueous NaCl
(3) Yield: near 100% on Al2O3

Product Characterization

XRD 100% FAU, a0 = 24.92 Å, competing phases: LTA, GIS, ANA, SOD
Elemental Analysis: NaAlO2. 1.24 SiO2f
Crystal Size and Habit: spherical aggregates, 0.8 um dia.
Click here to view XRD pattern

References

[1] H. Lechert, H. Kacirek, Zeolites 11(1991) 720
[2] H. Lechert, H. Kacirek, Zeolites 13 (1992) 192
[3] G. H. Kühl, Zeolites 7 (1987) 451

Notes

a. NaX zeolites are easily obtained with gel SiO2/NaAlO2 = 1.4-5.0, NaOH/NaAlO2 = 3.8-20 and H2O/NaAlO2 = 150-400.
b. Crystallization at lower water contents suffers from the high initial viscosities of the batches, thus preventing sufficient homogenization. NaX can be obtained without precautions down to H2O/NaAlO2 = 80. The crystallizing zeolite and its composition depend strongly on the alkalinity being held in the solution phase during the nucleation and growth of the zeolite. For a given batch composition, if the water content is decreased appreciably, the alkalinity will increase. If there are reasons to decrease the water content, the NaOH content should be decreased. Good results were obtained by reducing the alkali content proportional to the water content.
c. For the batch preparation, the authors would always prefer sodium aluminate instead of alumina trihydrate. Problems often occurred with the solubiity of the Al(OH)3 at the given NaOH concentration, depending on the alumina source. Sodium aluminate is usually available only in technical-grade quality. If only small quantities of NaX or pure substances are desired, it was preferable to use AlCl3 as the alumina source and to increase the NaOH content of the batch by 3 NaOH on the given batch composition to: AlCl3 : 4 SiO2 : 20 NaOH : 325 H2O. The resulting NaCl does not disturb the crystallization.
d. Longer times of homogenization give narrower particle size distributions.
e. Preferable crystallization temperatures: 670 to 970C. For safety the crystallization time should be increased to 12 to 14 hours. Experiments have shown that in the given batches up to 30 hours at 900C no other zeolite impurities were observed.
f. The Si/Al ratio of the product depends strictly on the NaOH concentration in the batch. Below 2.0 NaOH/liter, the nucleation rate of NaX goes almost to zero and nucleation of GIS occurs, which grows faster than NaX. Pure FAU with Si/Al> 1.5 in the product cannot be obtained without seeding. Above about 3.0 NaOH/liter, analcime or sodalite is obtained. Below Si/Al = 12.4, NaA appears. [3]