Process for making crystalline zeolites

摘要

The rate of crystallization of a crystalline sodium aluminosilicate molecular sieve described, claimed and designated zeolite A in Specification 777,232 from a recation mixture having a composition, expressed in terms of oxide-mol. ratios, within the following ranges: Na2O/SiO2 from 0.8 to 3.0 SiO2/Al2O3 from 0.5 to 2.5 H2O/Na2O from 35 to 200 is increased by introducing into or forming in said reaction mixture, prior to completion of said crystallization, a sufficient quantity to enhance the rate of crystallization occurring in said mixture, of crystalline sodium aluminosilicate zeolite A, said mixture being maintained at 20 DEG to 175 DEG C. until the crystals are formed. In a continuous process a portion of the reaction product is recycled as seed for further batches. At least 40% of the sodium ions of the crystalline sodium aluminosilicate produced as above may be exchanged for calcium ions whereby the pore size is increased from 4 Angstroms for the sodium form to 5 Angstroms for the calcium form. Ion exchange may also be effected with ions of Na, K, Ag, Cd, Li, Hg, Mg, Sr, Ni, Co, Pt, Cr, Fe, Sc, Ti, V, Mn, Yt, Zr, Ni, Mo, Ru, Rh, Pa, Hf, Ta, W, Re, Os or Ir. Suitable reagents for the preparation of sodium zeolite of the "A" series include silica sol, silica gel, silicic acid or sodium silicate as sources of silica; activated alumina, a -alumina, a -alumina, aluminium trihydrate or sodium aluminate as sources of alumina and sodium hydroxide is used as the source of sodium ions. Fig. 1 shows a system for continuously producing molecular sieves of the "A" series. Aqueous sodium silicate from vessel 10 and sodium aluminate and sodium hydroxide solution from vessel 13 are mixed in mixer 12 and the product introduced into reactor 16 in which the sodium aluminosilicate crystallizes out. A portion of the crystal containing reaction mixture is recycled through lines 18, 19 and 20 to the reactor; the stream of reaction product passing through line 17 is conducted to a filter 21 to remove the crystalline product from the aqueous phase and the latter (which consists of sodium hydroxide and sodium aluminate) is withdrawn through line 22 and recycled to vessel 13. The crystalline product obtained on filter 18 may be washed on the filter or transported to washing zone 25 and washed, preferably with salt free water, until the wash water reaches a pH of 9 to 12. The washed product is dried in zone 27 where the temperature is between 25 DEG and 150 DEG C. and then it is calcined in zone 29 in air at a temperature between 350 DEG and 525 DEG C. and the product passing through line 30 is a 4A molecular sieve. If any other molecular sieve of the "A" series is desired, the crystalline alumino-silicate product passing from washing zone 25 is conducted to the endless porous belt 32 where it is sprayed by sprayer 34 with a suitable ion-exchange solution, the ion of which serves to replace all or a portion of the sodium ions of the crystalline sodium alumino-silicate product, and then it is sprayed with water by sprayer 36 to wash the product free of water-soluble material. The product is then taken to drying zone 40 and calcining zone 42. Specification 777,233 also is referred to.