Process for the production of spherical, bound zeolitic molecular sieves

Spherical zeolitic molecular sieves including clay as a binding agent are prepared by dropping or spraying a slurry containing zeolite powder and clay on to a powder or dust, whereby the drops of slurry become covered with dust and as a result of the surface tension take on a spherical shape. At least 10% of the clay particles have a diameter of less than 90 m , and the slurry comprises up to 80% of liquid, e.g. water. The powder or dust, e.g. coal dust, finely divided silicic acid, molecular sieve powder, clay powder, ion-exchange resin dust, meal dust, talc or kieselguhr, may be spread by means of a vibration sieve on to a conveyer belt or rotating vessel so that the slurry is continuously dropped or sprayed on to a fresh layer of powder. The slurry, containing sufficient finely divided clay for the final dried product to contain about 20% binder, may be sprayed by means of a dish sprayer, whose speed of rotation determines the size of the eventual spheroids. The product is dried at 100 DEG C., e.g. continously on the conveyer belt by infra-red radiation, calcined at 400-700 DEG C. and optionally sieved. Spheroids of diameter 0.3-0.4 mm. and bulk density 570-600 g./litre are so obtained. Slurries containing as little as 800 ml. water per kg. zeolite may be used when the binder is a clay such as bentonite which does not affect the characteristic bridge formation of the zeolite. Such thixotropic suspensions are allowed to flow under gravity through openings of 2-10 mm. diameter on to the powder, threads of material breaking up into drops. By this means spheroids of diameter 1.5 to 2.0 mm. and bulk density 650-680 g./litre are obtained. The spheroids may be further coated by e.g. the dragee process.