Patented Nov. 8, 1949 2,487,480 UNITED STATES PTENT. OFFICE PROCESS FOR PRODUCING AMMONIUM SULFAMATE Charles A. Rohrmann, Manoa, Pa., assignor to X E. I. du Pont de Nemours & Company, Wil mington, DeL, a corporation of Delaware No Drawing. Application April 26, 1945, Serial No. 590,505 2 Claims. (Cl. 23-414) 1 2 This invention relates to processes for pro stantially undissolved, and removing the undis ducing sulfamates of alkali metals and ammo solved sulfate from the solution. nium, and is more particularly directed to proc In the operation of a process of this invention esses in which a sulfamate or an alkali metal or an ammonium or alkali metal sulfamate solution ammonium, containing a sulfate, is dissolved in containing a sulfate is ?rst made up. This may substantially the minimum quantity of hot water be done by dissolving in water dry crystals of necessary to make a solution saturated with sulfamate containing sulfate. On the other respect to the sulfamate, whereby the sulfate re hand, it is preferred to use a solution prepared mains substantially undissolved, and the sulfate by neutralizing sulfamic acid with a base in is removed from the solution. l0 aqueous solution. Thus, sulfamic acid containing Sulfamates of alkali metals and ammonium are ammonium sulfate as an impurity may be neu commonly produced by neutralizing sulfamic tralized with ammonium hydroxide or ammonium acid with a suitable base, such as the hydroxide carbonate in aqueous solution to give a sulfamate or carbonate of the metal involved. Often it solution which may be treated to advantage ac is found that the sulfamic acid used contains ap 15 cording to this invention. Still other ways of preciable amounts of ammonium sulfate and sul obtaining a suitable solution may be used, as, for fu'ric acid. Since the neutralization of the sul instance, by effecting between anhydrous am~ famic acid with the base is usually carried out in monia and sulfur trioxide to- form ammonium aqueous solution it is customary to remove the im-idodisulfonate, hydrolyzing the ammonium imi sulfate impurity from mother liquors by pre dodisulfonate to ammonium sulfamate and am cipitating it as barium sulfate. Such a procedure monium acid sulfate, and neutralizing the acid at best is time consuming and with highly con— sulfate to normal ammonium sulfate with taminated solution requires large amounts of ammonia. relatively expensive barium compounds, thereby It will be understood that when reference to adding substantially to the cost of the sulfamate ' alkali metals is made it is intended to include produced. sodium, potassium, lithium, rubidium, and cae The expense of purifying the sulfamate product sium, although of these the ?rst two named are as above described may, of course, be reduced by by far the most important. starting with a sulfamic acid which is substan The sulfate impurity removed from a sulfamate tially free of sulfate as an impurity. Since such a 30 solution according to a process of this invention grade 'of sulfamic acid is ordinarily available only may have originated in the solution in various at increased cost, and in view of the need for ways. When obtained from the sulfamic acid eventual mothor liquor treatment or discard used to make up the sulfamate, the sulfate will the ultimate cost favors the processes herein dis be sulfuric acid, ammonium sulfate, or ammonium closed which utilize low cost technical quality 35 acid sulfate, originating from sulfamic acid hy drolysis. When obtained from the base used to acid. It is an object of this invention to provide neutralize sulfamic acid the sulfate will usually processes for the production of sulfamates of have a cation other than ammonium. In the’ sulfamate solution, of course, there will be ex alkali metals and ammonium which have a low 40 change of ions, so that irrespective of where the sulfate content. Another object .is to provide sulfate originated, it will be removed as the sul such processes in which the necessity for barium fate least soluble in the system. precipitation of sulfate impurities is avoided. The processes of the present invention may Another object is to provide such processes which be employed with especial advantage as a part permit the use of raw materials containing ap 45 of the operation of making sulfamates by neu preciable amounts of sulfate in making the sul tralizing technical grade sulfamic acid, con famate. Other objects will appear hereinafter. taining sulfates, with alkali metal or ammonium The foregoing and related objects of this inven bases in aqueous solution. In such an embodi tion are accomplished by processes comprising ment of the invention the proportion of Water dissolving a sulfamate, selected from the group 50 used in the neutralization is controlled at or consisting of sulfamates of alkali metals and adjusted to thatvproportion best suited for the ammonium, containing a sulfate, in substantially subsequent sulfate-removal step as hereinafter the minimum quantity of water necessary to make described. a solution saturated with respect to the sulfa The sulfamate containing sulfate as an im mate when hot, whereby the sulfate remains sub 55 purity is in a process of this invention dissolved 2,487,480 4 in substantially the minimum quantity of water The ?ltrate was cooled to 25° 0., whereby a crop necessary to make a solution saturated with of ammonium sulfamate crystals was formed. respect to the sulfamate. That is, the quantity These crystals were centrifuged to free them of of water ultimately present should be not appre excess mother liquor and then dried in air at ciably more than that required to dissolve or hold room temperature. Analysis showed that these in solution all of the sulfamate. This result may crystals contained 0.39% sulfate calculated as be achieved by carefully controlling the amount of S03. Analysis of the un-washed ?lter-cake, after water originally added, so that just enough is ' drying, showed it to consist of about ‘78% am used to dissolve all of the sulfamate but only monium sulfate and 22% ammonium-sulfamate. that amount of the sulfate required to saturate the 10 solution with sulfate. Alternatively, a lesser Example II amount of water may be used, so that, for a given A water slurry containing 70 grams of chemi quantity of crude sulfamate, the amount of water cally pure potassium carbonate was made up and used dissolves only a portion of the sulfate and a neutralized with sulfamic acid containing about larger portion, but not all, of the sulfamate. In 1% by weight of sulfate calculated as S03. The the latter case there is a sacri?ce of sulfamate proportions of carbonate, sulfamic acid, and yield, but by re-employing the residue in a vwater used were such as to give a saturated cyclic operation the yield may be improved. potassium sulfamate solution at 65° C. In the The solution used should be so concentrated saturated solution thus obtained there was ob with respect to the sulfamate that it is substan- . served a heavy, ?ne, white precipitate. The tially saturated When'hot. That is, the separa solution was ?ltered at about 70° C. By analysis tion of sulfate according to a process of this the precipitate obtained as a ?lter cake was invention has been found to be particularly effec shown to be potassium sulfate, and the potas tive at solution temperatures of about from 60° sium sulfamate was found to have experienced a C. to the boiling point of the solution, and the corresponding decrease in sulfate content. solution should be substantially saturated in this While in the foregoing description of this temperature range. This condition will, of course, invention there have ‘been shown certain speci?c be present when the solution is brought to sat processes, it will be understood that without uration by boiling off an excess of water until departing from the spirit of the invention one sulfamate starts to crystallize out. 30 skilled in the art may employ various processes Having brought the solution to the required for producing sulfamates of low sulfate content. concentration it will be found that the sulfate is I claim: present in an undissolved form. It is, of course, 1. In a process for the production of sulfamates immaterial whether the sulfate has been dissolved of low sulfate content the steps comprising sub in a more dilute solution and ice-precipitated 35 stantially neutralizing sulfamic acid containing upon concentration or has never been in solution a sulfate with an ammonium base to form the at all. The important fact is that the sulfate is corresponding sulfamate and sulfate, the neu present, under the conditions described, in an tralizaton being carried out in a quantity of insoluble form and accordingly can be removed Water not substantially greater than that neces by physical means. 40 sary to dissolve the sulfamate when hot, whereby The insoluble sulfate can be removed from the sulfate remains substantiallly undissolved, the solution by various methods. It can be and removing the undissolved sulfatefrom the allowed to settle out and the clear solution can be solution. decanted off, or the mixture of solution and sul 2. In a process for the production of am fate may be separated by centrifugal means or monium sulfamate of low sulfate content the by ?ltration. It is preferred that the separation steps comprising dissolving ammonium sulfamate be effected while maintaining the solution at containing ammonium sulfate in a quantity of elevated temperature, that is, above about the water not substantially greater than that neces saturation temperature, to avoid loss of sulfamate sary to dissolve the sulfamate at 60° 0., whereby due to crystallization. the sulfate remains substantially undissolved, The processes of this invention may be better and ?ltering off the sulfate from the solution.