GB777233A - Crystalline synthetic zeolites - Google Patents

Abstract

A crystalline synthetic zeolite having a composition expressed as oxides, of <FORM:0777233/III/1> where M is hydrogen, ammonium or a metal having a valence not more than 3, n is the valence of M, and Y is a number not above 8, and having a specified X-ray powder diffraction pattern as set forth in the Specification, is prepared by first forming a sodium aluminium silicate of the above characteristics and subsequently exchanging the sodium ion for the ion desired. The sodium zeolite may be prepared by forming a water mixture containing the following oxide molar ratios: SiO2/Al2O3 from 3.0 to 5.0, Na2O/SiO2\t from 1.2 to 1.5, H2O/Na2O from 35 to 60 and maintaining such a mixture at a temperature beween 20 and 120 DEG C. until crystals have formed. The source of silica may be silica gel, silicic acid, colloidal silica or sodium silicate; the alumina may be provided as activated or gamma alumina, aluminium trihydrate or sodium aluminate whilst sodium hydroxide may supply the sodium ion and also effect pH control. A number of examples of reactant solutions are given, the preferred reactants being sodium aluminate and hydroxide which are added with agitation to an aqueous solution of sodium silicate. The initial mixing, with agitation, may be done at room temperature whilst the subsequent formation and crystallization of the zeolite may be effected without agitation at 100 DEG C. The hot reaction magna is preferably cooled before filtering and the zeolite crystals recovered may be washed until the effluent wash water in equilibrium with the zeolite has a pH of 9 to 12. The crystals may then be dried at 25 to 150 DEG C. and in general will have a size of 0.1 to 100 microns. The zeolites of the invention, in admixture with a minor proportion of other sodium aluminium silicates having a different specified X-ray diffraction pattern may also be prepared from reaction mixtures whose compositions expressed as oxides are SiO2/Al2O3 from 2.4 to 30, Na2O/SiO2 from 0.4 to 6.5, H2O/Na2O from 10 to 90 and also from compositions where the SiO2/Al2O3 ratio is from 2 to 40, the Na2O/SiO2 ratio is from 0.6 to 6 and the H2O/Na2O ratio is from 10 to 30. The sodium cations of the zeolite may be replaced by ion exchange with for example lithium, hydrogen, silver, ammonium, magnesium, calcium, zinc, barium, cerium or manganese ions. Thus hydrogen exchange may be effected with water or an aqueous hydrochloric acid solution; potassium exchange may be effected with potassium chloride or hydroxide, lithium, magnesium, calcium, ammonium, nickel or strontium exchange by a solution of their chlorides whilst for zinc, silver and cerium a water solution of the nitrates is preferred. The zeolites may be employed as molecular sieve absorbents by heating to an activation temperature of 350 DEG C. and a prssure less than 0.1 mm. of mercury absolute. Preferential absorption is exhibited towards polar, polarizable and unsaturated molecules and the absorbents are effective at low pressures and concentrations and may be used for gas or liquid separations. Data is provided showing the absorption capacity of the zeolites for octane, benzene, m-dichlorobenzene and heptacosafluorotributylamine; the relative absorption ability of lithium, sodium and calcium zeolites for diphenyl methane; the effect on acetylene absorption of partial filling of the pores of the zeolite with water; a comparison of the water, acetylene and carbon dioxide absorption capacity of the sodium zeolite with silica gel and charcoal; the relative absorption of C2 and C3 hydrocarbons of varying degrees of unsaturation; the preferential absorption of carbon monoxide, a polar molecule, with argon, a nonpolar molecule of approximately the same size and volatility; the preferential absorption of toluene compared with cyclohexane; the selective absorption of thiophene from a liquid thiophene-benzene mixture and the absorption of tiophene from benzene vapour; the relative absorption capacity of sodium, calcium, magnesium, barium, manganese, lithium, and cerium zeolites for water, carbon monoxide, nitrogen, nhexane, and methyl cyclohexane. A further table compares the absorption capacity of sodium zeolite, silica gel and charcoal for water, carbon, dioxide, sulphur dioxide, hydrogen sulphide, ammonia, acetylene, ethylene, ethane, propylene and propane, isobutylene, hexane, cyclohexane, toluene, carbon monoxide, methanol, nitrogen, oxygen, argon, krypton, hydrogen, helium and methane. Exemplified uses of the zealites are drying of air; the recovery of traces of ethylene, acetylene, propylene, etc., from waste gas streams; the separation of volatile gases like hydrogen, and helium from oxygen, nitrogen, argon, and krypton; the separation of nitrogen from oxygen and argon; the removal of acetylene from mixtures with oxygen, nitrogen, hydrogen, carbon monoxide, carbon dioxide and methane and ethylene; the separation of ethylene from oxygen, nitrogen, hydrogen and carbon monoxide; the separation of carbon monoxide from hydrogen, nitrogen, oxygen, argon and methane; carbon dioxide may be separated from hydrogen, helium, nitrogen, oxygen, methane, ethane and ethylene; sulphur dioxide from hydrogen, nitrogen, oxygen, ethylene, carbon monoxide and dioxide; hydrogen sulphide from hydrogen, nitrogen, oxygen, carbon monoxide and dioxide, methane, ethane, propane, butane and pentane, and ammonia from hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, methane and ethane. The zeolites are operative at higher temperatures than normally used and a table compares the absorption capacity for water of calcium zeolite and silica gel at 25 and 100 DEG C. The zeolite may be activated or re-activated by heating in air or vacuum and by reducing the pressure; the absorbate may also be displaced by the absorption of a more strongly held absorbate, for example absorbed acetylene may be displaced by the absorption of water. The zeolites may be employed in pelleted form obtained by pressing a mixture of the zeolite with a bonding agent such as clay.