Patent GB-777232-A (GB)
Title: Crystalline synthetic zeolites
IPC: C07C11/00
Filed: 1954-12-21
Abstract: Crystalline synthetic zeolites having a formula expressed as oxides of <FORM:0777232/III/1> wherein M is hydrogen or ammonium or a metal of Groups I or II of the periodic table, or a transition metal, and where n is the valance of the metal and Y is a number not greater than 6, which zeolites have a specified X-ray diffraction pattern, are prepared by forming a sodium zeolite of the above formula and subsequently exchanging the sodium ion for the desired metal zeolite. In preparing a sodium zeolite the silica may be provided by silica gel, silicic acid or sodium silicate, the alumina as activated, gamma or alpha alumina or alumina trihydrate or sodium aluminate, and the sodium ion may be provided by sodium hydroxide or as sodium aluminate.  A solution of the reactants, for example, sodium silicate to which has been added a sodium aluminate and hydroxide solution, may be agitated to homogenize the mixture and break up any gel formed after which the mass is heated to a temperature of 20-175 DEG C., preferably a 100 DEG C. in order to crystallize the desired zeolite. The zeolite crystals are filtered and washed until the effluent wash water in equilibrium with the zeolite has a pH between 9 and 12, after which the crystals are dried at 25-150 DEG C.  Their size ranges from 0.01 to 100 microns.  A number of examples of preferred reactants and proportions are provided, the preferred reactant mixture compositions expressed as oxides being given by the ratios SiO2/Al2O3 0.5-25 Na2O/SiO2 from 0.8-3.0 and H2O/Na2O from 35-200. Compositions outside these ranges yield the zeolite of the invention in association with other crystalline sodium aluminium silicates and crystalline alumina.  The sodium cations of the formed zeolite may be replaced at least in part by mono or divalent cations such as lithium and magnesium, metal ions of Group I such as potassium or silver, Group II metals such as calcium or strontium, hydrogen or ammonium ions, or ions of the transitional metals namely Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Yt, Zr, Nb, Mo, Ru, Rh, Pa, Hf, Ta, W, Rh, Os, Ir, and Pt.  Thus hydrogen exchange may be effected by water or an aqueous hydrochloric acid solution, or metal exchange by nitrates or chloride solutions.  The zeolites when activated may be used as molecular sieve absorbents since they show a strong preference toward polar, polarizable and unsaturated molecules and are effective in absorbing molecules at low pressure and concentrations and high temperatures. The zeolites are preferably activated by heating at 350 DEG C. under a pressure of less than 0.1 millimetres of Hg absolute.  Data is provided comparing the absorption capacity of sodium zeolite according to the invention, silica gel and charcoal for methane, ethane and propane, oxygen and nitrogen, n butanol and isobutanol; the relative absorption capacity of potassium zeolite for water, oxygen, nitrogen, carbon dioxide, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, 2-butanol, butane, ipentane, n-octane, ethylene, butene-1 butene-2, i-butylene; the preferential absorption of oxygen over nitrogen at liquid air temperatures, whereby oxygen may be separated from krypton and methane and also from xenon hydrogen and helium; the effect of temperature on nitrogen and oxygen absorption where oxygen is absorbed in greater quantities at minus 196 DEG C. but nitrogen is preferentially absorbed at minus 75 DEG C. or higher; the relative absorption capacity for butene-1 and ethane at temperatures from 0-350 DEG C.; the preferential absorption of C1 and C2 straight chain saturated or unsaturated hydrocarbons over their homologues; the absorption of lower chain alcohols, whereby methanol, ethanol and propanol may be separated from long chain normal, isosecondary and tertiary alcohols, cyclic hydrocarbons having four or more atoms in the ring and all molecules whose maximum dimension of the minimum projected cross-section is as great or larger than that of propane; the absorption capacity of calcium and magnesium exchanged zeolites, which absorb molecules for minimum projected cross-section is 4.9A5.5A whereby they may be used to separate mixtures of straight and branch chained molecules or to separate straight chain molecules from cyclic compounds having four or more atoms in the ring; the effect of temperature and pressure at which the absorbent is activated on oxygen absorption; the effect of partial loading of the activated zeolite with water; the absorption of ethanol from a mixture thereof with benzene in the liquid phase; the relative absorption capacity of sodium calcium and magnesium zeolites at varying pressures and temperatures for water, carbon dioxide, sulphur dioxide, hydrogen sulphide, ammonia, carbon monoxide, acetylene ethylene, oxygen, nitrogen and methane, and the effect on water absorption with calcium zeolite of temperature.  The adsorbate may be desorbed from the zeolite by raising the temperature and reducing the pressure or by displacing the adsorbate by the adsorption of a more strongly absorbed molecule.  The zeolite may be pelleted with clay. Specification 774,233 is referred to.