United States Patent Office 2,345,134 Sodum Aluminate Product and Proc
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4-23-265 OR 2 345 l34. SR Search ROOT Patented Mar. 28, 1944 2,345,134 UNITED STATES PATENT OFFICE 2,345,134 SODUM ALUMINATE PRODUCT AND PROC. ESS OF PRODUCING THE SAME Frederick K. Lindsay, La Grange, and Benjamin F. Willey, Chicago, Ill, assignors to National Aluminate Corporation, Chicago, Ill., a corpo ration of Delaware No Drawing. Application November 27, 1939, Serial No. 306,292 12 Claims. (CI. 23-52) The present invention relates to a new and im droxide while still retaining the free and easy proved composition of matter consisting sub solubility of the product, coupled with substan stantially of a very soluble form of sodium tially permanent stability of the resulting solu aluminate which is further characterized by the tion. fact that solutions prepared therefrom will re 5 Thus it has already been proposed to prepare main stable Over long periods of time. a solution of sodium aluminate in which the One of the principal objects of the present molar ratio of sodium oxide to alumina is invention is a particularly desirable dry form Na2O:Al2O3::1.25:1 and then to take a COmpar of sodium aluminate containing up to 5% of a atively strong Solution of this product in Water stabilizing ingredient so thoroughly dispersed O and treat it at 100° C. with sugar to the extent therethrough that it will pass into solution sub of about 1.5% of the weight of the solution, con stantially simultaneously with the sodium alumi tinuing the heating for a period of about 2 hours, nate when the composition of the present inven it being stated by the previous workers in this tion is dissolved in water, with the result that field that such treatment will stabilize the re the Solution thus obtained will not become cloudy 5 sulting Solution. It should be noticed in this or precipitate aluminum hydroxide even upon connection, however, that there is 25% molar ex long standing. The composition is also charac cess of sodium oxide in the product, which in terized by the fact that the sodium aluminate itself is thereby rendered less likely to decom therein has an extraordinarily low ratio of so pose, simply by reason of its great excess of al dium oxide to alumina, namely, on the order kalinity. Furthermore, the previous workers in Of Na2O:Al2O3::1.11:1. this field found it necessary to heat Such solutions The invention also concerns a method of manu for several hours in Order to attain the desired facturing the above product in which particular stability. In accordance with our present inven care is taken to prevent decomposition of the tion, however, We find that such heating is en material by excessive temperatures during the 25 tirely unnecessary; and we are able to produce manufacturing operations. a finished product in dry form-flaked, granular, The present invention is a continuation in part or powdered-which will dissolve in cold water and yet produce a solution which is resistant to g f application Serial No. 141,244, filed May decomposition and the precipitation or separation AS is well known, two general methods have 30 of aluminum hydroxide. 25% heretofore been employed in the manufacture It has also been proposed to produce sodium of Sodium aluminate. The older of these meth aluminate by digesting aluminum hydroxide in ods is a dry process wherein aluminous material a caustic soda solution, using however a con to is calcined with soda ash. A more recent method siderable excess of the caustic soda in an at is a wet process wherein aluminum hydrate is 5 tempt to produce a suitable material. Thus, for digested with caustic soda to form sodium example, a ratio by weight of one part of alumina, x 2 (3 aluminate solution which is then evaporated to Al2O3, to one part of sodium hydroxide has been produce the solid product. Both wet and dry employed in the presence of water to produce a processes heretofore employed, however, have solution of sodium aluminate of sirupy con been characterized by certain disadvantages, for sistency, which was then allowed to solidify into despite repeated efforts no one has heretofore a cake which was then heated to a temperature Succeded in ascertaining and maintaining all the of from 300 to 450° C., resulting in a product fundamental conditions necessary consistently containing about 55% to 60% of soluble alumina to produce a product which is completely and and Soluble in water to such an extent that it rapidly soluble in Water, stable in aqueous so 5 would leave only about 0.1% of insoluble resi lutions, and characterized by a minimum con due. In connection with this prior proposal, tent of sodium carbonate or caustic soda. however, it was stated that the ratio by weight It has already been proposed, in the prior art, of alumina to sodium hydroxide was 0.9:1.1 and to produce various forms of Sodium aluminate; that if substantially lower ratios were used-that and methods have also been known for treating is to say, if there were less alkali than indicated Solutions of sodium aluminate so as to render by this weight ratio-the product would be un them stable. However, none of the prior art satisfactory, unstable and probably insoluble or methods have succeeded in producing a Com difficult to dissolve in water except in the pres paratively pure sodium aluminate in which there fence of an excess of sodium hydroxide. is but a very slight molar excess of sodium hy- 55 When calculating the molar ratio of Na2O to 2 2,845,134 Al2O3 in the just mentioned prior art product, nitely controlled conditions under which it is the following result Will be obtained: Let it be made and, furthermore, the temperature at assumed that one were to start with 100 grams which it is reduced to the dry state, which should of aluminum oxide, Al2O3, having a molecular not substantially exceed 350° C. and which pref weight of 102 and 122 grams of sodium hydroxide 5 erably is very much lower, namely, not exceed having a molecular weight of 40, which is a ing 200° C. Broadly speaking, the method of weight ratio of 0.9:1.1 described in this prior art manufacture of the composition consists in di method. However, inasmuch as sodium hy gesting alumina or aluminum hydroxide in an droxide has a molecular weight of only 40, it aqueous solution of Sodium hydroxide, using ap will at Once be apparent that here there are sub 0. propriate amounts of these two substances in ac stantially 3.0 mols of sodium hydroxide, NaOH, Cordance with the molar ratios herein mentioned which is equivalent to 1.50 mols of Na2O. This and heating the mixture until the aluminum hy product therefore has a 50% molar excess of so droxide has gone completely and entirely into a dium oxide over that required for the theoretical clear solution, whereafter the said solution is formation of Na2Al2O4, which is sodium alu 5 dried under conditions of high surface exposure minate. It is stated that such a product is solu so as to reduce it as rapidly as possible to a dry ble in Water, but this is readily accounted for condition, which can be most conveniently done by the fact that it contains this large molar ex on a suitable rotary drum drier, from the periph cess of Na2O. ery of which the product can be removed in dry It has also been proposed to produce a sodium 20 form by means of a doctor blade or similar de aluminate having a molar ratio of Na2O to Al2O3 vice. The stabilizing agent may be added in one of approximately 1:1 by the expedient of dissolv of two ways: It may be mixed very thoroughly ing aluminum hydroxide in an excess of sodium with the dry product obtained from the drum hydroxide, using about 2 mols of Na2O to one of drier or, and this method is more advantageous, Al2O3, and crystallizing from a mother liquor of 25 it may be added to the Solution of the alumina in this composition a sodium aluminate having a the sodium hydroxide solution, in which case 1:1 molar ratio. It is well known, however, that there will be assured a uniform distribution of such an aluminate, although soluble in water, the stabilizing agent throughout every particle almost immediately decomposes therein, with the of our product. formation of aluminum hydroxide, by reason of 30 As an exemplification of a commercial and the fact that there is no excess whatever of Na2O; practical metho anufacturing Our new and, while such a composition may be stable in product, we submit the following, without how the dry form, it is not stable when dissolved in ever in any way wishing to limit the invention Water. to the precise quantities expressed, provided only Attempts have also been made to combine alu 35 that the molar ratios be retained: 7112 pounds minum hydroxide or alumina directly with dry of sodium hydroxide solution containing 48% of Sodium hydroxide in the hope of obtaining a actual NaOH are heated in a steam-jacketed ket water-soluble sodium aluminate characterized by tle to a temperature of approximately 120° C. To stability of the resulting solutions, but this has this hot sodium hydroxide solution there are been obtained only by using a considerable ex 40 gradually added-for instance, being fed in by a cess of Sodium hydroxide amounting to from 1.2 screw conveyor-6279 pounds of aluminum hy to 1.5 mols calculated as Na2O.