GB855301A - Attrition resistant adsorbents - Google Patents

Abstract

<PICT:0855301/III/1> Zeolitic molecular sieve crystals, prepared as described below, are treated with an aqueous sodium silicate solution containing 3 to 50% SiO2 based on the dry weight of the molecular sieve and the treated sieve crystals are thereafter dried and activated. The molecular sieves are prepared by mixing sodium aluminate and sodium silicate solutions in proportions such that the silica/alumina ratio of the mixture is from 0.5 to 1 to 3 to 1, at a temperature within the range of 160 to 215 DEG F., the sodium silicate employed having a Na2O/SiO2 ratio of at least 0.8/1 and the sodium aluminate having a ratio of Na2O/Al2O3 in the range of 1/1 to 3/1 . The sodium zeolite so produced may be treated with a metallic salt solution to convert the zeolite to, for example the calcium, copper, lithium, potassium, magnesium, barium, strontium, zinc, cadmium boron or aluminum form, either before or after compositing with the sodium silicate. As shown in the drawing, a sodium metasilicate of concentration 30 to 300 grams SiO2 per litre and sodium aluminate of concentration 40 to 400 grams Al2O3 per litre in vessels 2 and 4 respectively are mixed in vessel 10 preferably to give a silica/alumina ratio of 2/1 . The zeolitic sieve precipitates, preferably in the presence of seed crystals and is passed to a washing zone 16 and may be immediately treated with a calcium solution to form the corresponding calcium-sodium alumino-silicate. Preferably however the washed zeolitic sieve is withdrawn as a filter cake and slurried in a mixer 22 with a sodium silicate solution and the slurry so formed, may be spray dried. The dry products may be passed to an ion exchange zone 26 where they may be treated with calcium chloride solution, for example in a concentration of 2 to 25%. Such treatment converts the sodium sieve to the calcium form and also converts the sodium silicate coating to calcium silicate. The temperature is thereafter raised to 200 DEG F. and the sieve is withdrawn and washed and activated at 400 to 1000 DEG F. If the zeolite is required as the pellets for moving bed absorption operation, the moist zeolite initial crystals may be mixed with sodium silicate and a small amount of water into a uniform paste which is extruded, dried and calcined; the pellets so formed may be treated with a calcium salt solution. Specifications 548,905, 574,911 and 598,238 are referred to.