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. drate containing 62.25% of Al2O3. The addition Wherein the present invention totally differs of the aluminum hydrate being rather gradual, from the prior art is in the fact that the com it will require from 45 minutes to one hour to position not only has a low molar ratio of Na2O get it all into the sodium hydroxide Solution. The to Al2O3, which does not substantially exceed resulting mixture is then gently boiled at a tem 1.11:1.0, but also contains up to 5% of what we perature of approximately 120° C. until every bit prefer to call a stabilizing agent and which may of the aluminum hydroxide is dissolved and a consist of any one or a combination of a number clear sirupy solution is obtained. At this point of Substances such as Rochelle salts, tartaric 50 is added the stabilizing agent, which may be any acid and its salts, saccharates, gluconic acid and one of the Substances above enumerated and its salts, gallic acid and its salts, pyrogallic acid which bears a ratio of up to 5% of the weight and its salts, sugar, invert Sugar, dextrin, starch, of the inorganic constituents of the solution. In glycerols, glycols, phenols or phenolates, and gel the case of Rochelle Salts, We have found that atin. The amount of these stabilizing substances 85 pounds thereof is a satisfactory amount. The will vary, from a fraction of 1% up to 5% on the heating or digestion is thereupon continued until total weight of the inorganic Solids in the com complete solution of the added stabilizing agent position, and they are preferably so uniformly in this case the Rochelle saltS-is obtained. Me dispersed throughout the composition that they chanical agitation is, of course, provided in order will dissolve simultaneously with the sodium alu GO to blend the material and to assist in the solution minate when the composition is dissolved in thereof in the sodium hydroxide solution. When water, which will then form a solution charac the solution has become clear, it is fed into a terized by its stability over long periods of time. drum drier, preferably of the double-drum weir In its preferred embodiment, therefore, our feed type, the weir feedboxes of which are steam new composition comprises from 95% to 99--% jacketed so that, as the sirupy solution is fed to of sodium aluminate, Na2O.AlaO3, in which the the Weir boxes, some further evaporation and ratio of Na2O to Al2O3 does not substantially ex concentration of the solution is effected. The ceed 1.11:1, and also contains up to 5% of the liquor, when picked up by the drums as they stabilizing material from the above mentioned revolve past the weir feeds, is very heavy and group of products. In stating this composition, viscous. These drums are driven at a speed of constituent water has been disregarded. Ordi about a to 2% revolution per minute and are kept marily the commercial product may contain 20% at a temperature of from 150' to 160° C. The Of water. temperature may be higher than this, but we An important factor in the manufacture of the have found it very disadvantageous to raise it composition of the present invention is the defi- 75 higher than 350° C. and greatly prefer to operate O D.C. i.

2,345,134 3 at a temperature which is definitely below 200 aluminate of standardized and known properties C. and preferably is from 150 to 160° C., although from which he can prepare, by mere solution in somewhat lower temperatures can be used. As cold Water, a stable, clear, uniform and satisfac a result of the heat, input from the surfaces of tory solution of Sodium aluminate. The prior art the drying drums, the excess Water in the con products contained entirely too much sodium hy position is evaporated, so that the dry product droxide to permit of their use in these rather may be scraped from the drums by a doctor blade delicate processes. For example, in a process of or knife edge, coming off in the form of rather this type where aluminum sulfate is added to a large flakes, The dry product is then conveyed dilute suspension of paper fibers together with to a crusher, where the flakes are broken down 10 dissolved starch, and the starch is then precipi into smaller units, this constituting the finished tated by the addition of Sodium aluminate to the product which is ready for packaging and ship fiber-starch aluminum-sulfate mixture, alumi ping. From the batch described above, there is nunn hydroxide Will be formed from both the usually obtained about 8500 pounds of finished aluminum Sulfate and the Sodium aluminate, the product. 15 Only other by-product being sodium sulfate, If the above materials are calculated to molar which is harmless in the paper. However, if the ratios, it will be found that the product will have Sodium aluminate employed contains an unnec a ratio of sodium. Oxide to aluminum oxide of essarily large excess of sodium hydroxide, it will about 1.11:1, and we have found it quite in be seen that some of the aluminum sulfate will portant to maintain this ratio closely Within have been precipitated by the sodium hydroxide these limits. If we use too much Sodium hy to form aluminum hydroxide. It might appear droxide-that is, if the ratio becomes greater to be a matter of indifference whether the alumi than that mentioned, We then get into Our prod nunn hydroxide floc were formed from aluminum uct an undesirable excess alkalinity; and if We Sulfate cr sodium hydroxide, or from both the use less than that amount, we do not attain quite aluminum sulfate and the sodium aluminate. It the degree of solubility which we desire in the 25 has been found, however, that the physical char material. When using some of the other enun acteristics of the floc resulting from the precipi erated stabilizing agents, such as Sugar, gluconic tation Cf aluminum Sulfate by sodium hydroxide acid, glycerol, etc., they may likewise be added to is by no means as satisfactory as that produced the clear solution prior to application thereof to by the interaction between our product and alu the drum drier. In the case of perfectly dry ma 30 minum Sulfate. terials, however, such as Rochelle salts, gluconic A further advantage of our process lies in the acid, gallic and pyrogallic acids, these may be fact that by the proper choice of apparatus we added to the product which is removed from the can produce a material which is almost entirely drums, preferably after grinding, taking great free from iron and which therefore will not dis care thoroughly to disseminate the material as 35 cClor the paper in which it is employed. uniformly as possible throughout the mixture. It In the foregoing detailed description of the in will be readily seen, however, that its introduc vention it is apparent that many variations may tion into the solution will give much more uni be made without departing from the spirit and form distribution and is therefore the preferred 40 ScCpe thereof. Thus, for example, the rotary at embodiment of our invention, mospheric drum drier described in the foregoing In order to demonstrate the correctness of Our Specific example may be substituted by a drum method of operation as well as our theory, We drier Cf the vacuum type, if desired, or by any have prepared sodium aluminate having the same other type of evaporating equipment wherein the molar ratio of 1.11:1 but without the presence Solution may be heated to the desired and con of any stabilizing agent and have compared this trolled temperature in a condition of high sur with the product of cur invention. Thus, when face exposure. For example, the solution may be 0 grams of the product which does not contain Spread in the form of a film on a directly heated, the stabilizing agent are dissolved in, for exam flat metallic surface or an endless, flexible metal ple, 90 grams of distilled water, hydrolysis and belt maintained at the proper temperature, or the subsequent precipitation of aluminum hydrox material may be poured into large, shallow pans ide will take place almost immediately. We have and dried in a tunnel drier. Any method of dry never been able to obtain, without the use of a ing is satisfactory which will permit the conven stabilizing agent, a solution which remains sta ient maintenance of controlled temperatures up ble over 4 hours, and in most cases hydrolysis and to 350° C. This method of drying avoids the for precipitation begin in less than 30 minutes. We nation of the water-insoluble content present in do not consider a product which does not remain the Sodium aluminate previously available in the in solution for at least 4 hours as being stable art, since this insoluble material is due, to a great within the Sense of the term in Which We use it. extent, to the calcining of the material at a tem The material of our present invention, how (5) peratule in excess of 350° C. ever, when dissolved in the same proportions Our material contains approximately 20% of that is, 10 grams per 90 grams of distilled water, Water, although it is a dry product, and has an will remain stable for Over two Weeks; and a so apparent density of approximately 66 pounds lution of that kind is what we mean by a stable per Cubic foot. It is so soluble that about 90 solution. When it is considered that Sodium (55 grams thereof Will dissolve in 100 grams of water aluminate is now being employed on a large Scale to produce a solution containing 47% of solids in the manufacture of paper, particularly When Without the precipitation of any aluminum hy affixing or precipitating starch onto paper fibers droxide. This is a degree of solubility never be - during the formation of a paper sheet, in Which fore obtained in the art of manufacturing a case it is necessary to prepare large quantities of Sodium aluminate having a very low ratio of a very pure sodium aluminate Solution which is sodium cxide to aluminum oxide and presents a fed to the head box of the paper-making machine Very decided advance over anything that has under careful hydrogen-ion control, it will be been done along this line heretofore. seen that it is extremely important to be able to We again wish to emphasize that we wish to furnish to the paper manufacturer a sodium disclaim the preparation of solutions of sodium 4. 2,845,184 aluminate stabilized by the addition of stabiliz 6. A process of manufacturing a dry, com ing agents and which are shipped or sold as solu pletely and rapidly water-soluble composition tions; and we disclaim any sodium aluminate containing sodium aluminate, which comprises containing a Na2O:Al2O3 molar ratio substan adding aluminum hydrate in gradual increments tially above 1.11:1, for such sodium aluminates to a hot aqueous solution of caustic soda until are fairly stable but are entirely too alkaline to a Sufficient quantity of aluminum hydrate has be universally applicable. Our product contains been added whereby to obtain a water-soluble the lowest feasible amount of Na2O to Al2O3 Compound of Sodium oxide and aluminum oxide coupled with solubility as well as real stability having a slight molar excess of Na2O to Al2O3 of the resulting solution. 10 in the ratio of approximately 11:10, heating the We claim: reaction mixture until all the aluminum hydrate 1. A process of producing a composition Of is dissolved and a clear syrupy solution is matter consisting mainly of SOdium aluminate formed, the temperature of the heating not sub and up to 5% of an organic stabilizing agent, stantially exceeding 120° C.; spreading the solu which comprises dissolving aluminum hydrate 15 tion in the form of a thin film on a surface main in strong aqueous sodium hydroxide at a tem tained at a temperature sufficient to heat said perature not substantially exceeding 120° C. film to above about 150 C. and below about 200 until a clear solution is obtained, whereby to ob C. to produce thereby a thin dry film of solid tain a water-soluble compound of Sodium oxide material containing sodium aluminate; and in and aluminum oxide having a slight molar ex 2) Corporating with the sodium aluminate, at any cess of Na2O to Al2O3 in the ratio of approxi convenient step in said process, up to 5% by mately 11:10 adding up to 5% of an organic sta weight of an organic stabilizing agent selected bilizing agent to said solution, and drying the re form the group of polyhydroxy organic com sulting solution under conditions of high Sur pounds consisting of tartaric acid and its salts, face exposure in the form of a thin film main gluconic acid and its salts, gallic acid and its tained at a temperature not substantially ex 25 Salts, pyrogallic acid and its salts, and invert ceeding 200° C. Sugar. 2. A process of producing a composition of 7. A process of manufacturing a dry, com matter consisting mainly of sodium aluminate pletely and rapidly water-soluble composition and up to 5% of an organic stabilizing agent, COntaining SOdium aluminate, which comprises which comprises dissolving aluminum hydrate in adding aluminum hydrate in substantially stoi strong aqueous sodium hydroxide at a tempera chiometric quantities and in gradual increments ture not substantially exceeding 120° C. until a to a hot aqueous solution of caustic soda and di clear solution is obtained whereby to obtain a gesting said solution until a clear syrupy solu water-soluble compound of sodium oxide and tion is obtained, whereby to obtain a water-solu aluminum oxide having a slight molar excess of ble compound of sodium oxide and aluminum ox Na2O to Al2O3 in the ratio of approximately ide having a slight molar excess of Na2O to Al2O3 11:10; adding to said solution up to 5% of an in the ratio of approximately 11:10, thereafter organic stabilizing agent selected from the group spreading the solution in the form of a thin film of polyhydroxy organic compounds consisting of 40 on a surface maintained at a temperature suffi tartaric acid and its salts, gluconic acid and its cient to heat said film to above about 150° C. salts, gallic acid and its salts, pyrogallic acid and but below about 200° C., and incorporating with its salts, and invert sugar; drying the resulting said aluminate, at any convenient step in said solution under conditions of high surface expo process, a small quantity of an organic stabliz sure in the form of a thin film maintained at a ing agent consisting of Rochelle Salts. temperature not substantially exceeding 200 C.; 8. As a new composition of matter, a rapidly and comminuting the resulting dry product. Water-soluble compound of sodium oxide and 3. A process of manufacturing dry, completely aluminum oxide containing a slight molar ex and rapidly water-soluble composition contain cess of Na2O with respect to Al2O3 in a ratio of ing sodium aluminate, which comprises digest 50 approximately 11:10, in admixture with up to ing aluminum hydrate in an aqueous solution of sodium hydroxide until all of the aluminum hy prevent5% of EEEEEEESeparation of aluminum adaptedhydroxide to drate is dissolved and a clear syrupy Solution is from an aqueous Solution of said compound, said obtained whereby to obtain a water-soluble com composition being a dry product easily and com pound of sodium oxide and aluminum oxide hav 5 5 pletely soluble in water to form therewith a sub ing a slight molar excess of Na2O to Al2O3 in the stantially clear solution characterized by stabil ratio of approximately 11:10, thereafter evapo ity over long periods of time. rating water from the solution by heating the 9. The composition of claim 8 wherein Said same in a condition of high surface exposure in organic stabilizing agent is selected from the the form of a thin film maintained at a tempera 60 group of polyhydroxy organic compounds con ture below about 200° C., and incorporating with sisting of tartaric acid and its salts, gluconic acid the sodium aluminate an organic stabilizing and its salts, gallic acid and its salts, pyrogallic agent selected from the group of polyhydroxy acid and its salts, and invert sugar. o organic compounds consisting of tartaric acid 10. As a new composition of matter a rapidly and its salts, gluconic acid and its Salts, gallic 65 water-soluble compound of sodium oxide and acid and its salts, pyrogallic acid and its salts, aluminum oxide containing a slight molar excess and invert Sugar. of Na2O with respect to Al2O3 in a ratio not ex 4. The process of claim 3 wherein the evapo ceeding approximately 11:10, in admixture with ration is carried out at a temperature above 150 up to 5% of Rochelle salts effective to prevent C. but below about 200 C. 70 the separation of aluminum hydroxide from an 5. The process of claim 3 wherein said diges aqueous solution of said compound, said compo tion is carried out at a temperature not sub sition being a dry product, easily soluble in water stantially exceeding 120° C. and said evaporation to form therewith a substantially clear solution is carried out at a temperature of from about characterized by stability over long periods of 150° C. to below about 200 C. 5 time. 2,845,184 5 11. As a new composition of matter a rapidly ual increments to a hot aqueous solution of caus water-soluble compound of sodium oxide and tic soda and digesting said solution until a clear aluminum oxide containing a slight molar excess Syrupy solution is obtained, whereby to obtain a of Na2O with respect to Al2O3 in a ratio not ex water-soluble compound of sodium oxide and ceeding approximately 11:10, in admixture with b aluminum oxide having a slight molar excess of up to 5% of invert sugar effective to prevent the Na2O to Al2O3 in the ratio of approximately separation of aluminum hydroxide from an 11:10, thereafter spreading the solution in the aqueous solution of said compound, said con form of a thin film on a surface maintained at position being a dry product, easily soluble in a temperature sufficient to heat said film to water to form therewith a substantially clear So O about 150° C. but below about 200 C.; and in lution characterized by stability over long peri corporating with Said aluminate, at any conven ods of time. ient step, a Small quantity of an organic stabi 12. A process of manufacturing a dry, Com lizing agent selected from this group of polyhy pletely and rapidly water-soluble composition droxy organic compounds consisting of tartaric containing sodium aluminate characterized by 5 acid and its salts, gluconic acid and its salts, stability over long periods of time when dissolved gallic acid and its salts, pyrogallic acid and its in water, despite its low alkalinity, which proc Salts, and invert sugar. ess comprises adding aluminum hydrate in Sub FREDERICK K, LNDSAY. stantially stoichiometric quantities and in grad BENJAMN F. WILLEY.