LTA

Zeolite Alpha

Si(75), Al(25)

Contributed by Günter Kühl

Verified by S. Mintova and by Zhaolan

Type Material Na4(TMA)2[Al6Si18O48] (TMA = tetramethylammonium)

Method G. H. Kühl [1]

Batch Composition 1.07 Na2O : 2.37 (TMA)2O : Al2O3 : 10 SiO2 : 120 H2O

Source Materials

distilled water
sodium aluminate (MCB, 28.5% Na2O, 42.75% Al2O3)
tetramethylammonium hydroxide solution (25% TMAOH) a
precipitated silica (PPG Corp. Hi-Sil 233, 88% SiO2) b

Batch Preparation (for 36 g product)

(1) (46.4 g water + 15.6 g sodium aluminate], stir at room temperature until dissolved c
(2) [(1) + 111.7 g tetramethylammonium hydroxide solution], mix
(3) ((2) + 44.5 g precipitated silica], add silica to the aluminate solution gradually with stirring d
(4) Stir or blend for 30 minutes d

Crystallization

Vessel polypropylene bottle
Incubation: 48 h at room temperature
Time: 24- 30 hours e
Temperature: 900C
Agitation: none

Product Recovery

(1) Dilute reaction mixture with water
(2) Filter on a dense filter, such as Whatman #5, or separate by decantation, then reslurry sediment, flocculate,f and and wash with water g
(3) Dry at room temperature or at 1100C
(4) Yield: 36 g (near 100% on Al2O3)

Product Characterization

XRD: LTA (contracted unit cell); competing phase: high-silica sodalite
Elemental Analyses: 0.6 Na2O : 0.4 (TMA)2O : Al2O3 :6 SiO2
Crystal size and habit: cubes, <1 um on edge
Click here to view XRD pattern

Reference

[1] G. H. Kühl, US Patent 4 191 663

Notes

a. TMA salts cannot be used because the anions tend to cause nucleation of high-silica sodalite (SiO2/Al2O3 = 10).

b. Hi-Sil 233 has a median particle size of 18-19 um; precipitated silica of larger particle size tends to be insufficiently reactive. Ultrasil 320 is an acceptable substitute. If less reactive silica is to be used in this preparation, 10% of the silica should be slurried in the (TMA)OH solution prior to combining the (TMA)OH with the NaAlO2 solution.

c. Small amounts of iron may be removed by filtration although this iron does not affect the crystallization. If the sodium aluminate does not dissolve completely, it probably contains AI(OH)3 and cannot be used.

d. Slow addition of Hi-Sil is recommended for proper dispersion. Silica-rich gel particles tend to cause nucleation of high-silica sodalite.

e. The longer crystallization time improves the crystallinity, unless sodalite nuclei are present.

f. Avoid flocculating in the presence of mother liquor because colloidal silica will coagulate.

g. Alternatively, use repeated decantation and reslurrying sequences (settling may be accelerated by centrifuging), and optionally, flocculation h after having removed the bulk of the alkalinity.

h. See Introductory Article on "Product Recovery."