Патент USA US2412607код для вставки
2,412,607 Patented Dec. 17, 1946 UNITED A STTES "PATENT OFFICE I ’ 2,412,507 , AMMONIUM THIOSULFATE Henry V. Farr, Ferguson, Mo., and John R. Ruho?, Bronxville, N. Y., assignors to Mallin ckrodt Chemical Works, St. Louis, Mo., a cor poration of Missouri No Drawing. Application October 21, 1943, I Serial No. 507,178 7 Claims. (Cl. 23-115) 1 2 This invention relates to ammonium thio sulfate, and more particularly to methods for the preparation of this compound. Among the objects of this invention are the provision of an improved method for the prepara tion of ammonium thiosulfate; the provision of an improved method for preparing ammonium thiosulfate in crystalline form; the provision of an improved method for the provision of a stable will not undergo decomposition under ap propriate storage conditions. Ammonium thiosulfate is prepared in accord ance with the present invention by the reaction ammonium thiosulfate solution; the preparation of anhydrous ammonium thiosulfate; the prepa ration of anhydrous ammonium thiosulfate in stable form; and the provision of anhydrous ammonium thiosulfate and ammonium thiosul fate‘ solutions, bothcf which are stable and do not decompose under appropriate conditions‘of storage. Other objects will be in Part obvious and in part pointed out hereinafter. _ The invention accordingly comprises the steps , of ammonium sul?te and sulfur in the presence of sul?de ions. The probable course of the re action is as follows when ammonium sul?de is used: (NH4)ZS (NH4)2SOa+S —'—_> (N?dzszos Ammonium sul?te may be prepared by any convenient means, such as by the reaction of sulfur dioxide with ammonia in the presence of water to produce ammonium sul?te solution. ' Where ammonium thiosulfate has in the past been prepared by the reaction of ammonium sul?te and sulfur, the reaction has not pro ceeded smoothly. The reaction is extremely slow, and apparently requires conditions of tempera and sequence of steps, and features of manipu 20 ture and concentration which make it economi lation, which will be exempli?ed in the methods cally unfeasible. It has been found, however, and products hereinafter described, and the scope that where, as in the present invention, the re of the application of which will be indicated in action is carried out in the presence of sul?de the following claims. ions, the reaction itself takes place easily in a comparatively short time interval and may be ,. Ammonium thiosulfate has long been known to be awsuperior photographic ?xing agent. It carried out at a wide range of temperatures. Since, as indicated in the foregoing reaction, the ammonium sul?de is not consumed by the re sodium thiosulfate, the customarily employed ?x 30 action, only a relatively small proportion is re quired. The ammonium sul?de apparently acts ing agent. Ammonium thiosulfate, however, has as a carrier or solubilizer for the sulfur which not been widely used because it has been ex reacts with the ammonium sul?te to form am pensive to produce and because a product su?i ciently free from impurities for photographic use monium thiosulfate. The above reaction is, however, preferably car has not been available. Such small quantities 35 ried out by keeping the reaction temperature of ammonium thiosulfate as have been used have low, and by having present in the reaction mix customarily been marketed in the form of a con ture an excess of ammonium hydroxide. The centrated solution, chie?y because economical reaction is preferably carried out between sulfur, methods of preparing a stable crystalline product, particularly one in the anhydrous state, have not 40 ammonium sul?de and ammonium sul?te in the presence of such an amount of ammonium hy been known. The transportation of a solution droxide that the ?nal reaction solution is about is difiicult because it has, in the case of am 1N in ammonium hydroxide. Ammonium sul?de monium thiosulfate, been shipped in glass car is preferably employed to provide the sul?de ions, boys, which adds greatly to the cost because the carboys themselves are expensive and must be 45 since it does not introduce an undesired cation. Other sul?des could be substituted but would in shipped back to the manufacturer when empty. e?ect contaminate the reaction product. The This greatly increases transportation costs. reaction is preferably carried out at a tempera It has now been found that in accordance with ture of from 30 to 55° C. the present invention, ammonium thiosulfate can At the end of the reaction, ‘the liquors con be easily and economically prepared as a product 50 tain ammonium hydroxide, ammonium sul?de of great purity, and that it may, if desired, be or polysul?de, and excess sulfur, in addition to made in the iormof an anhydrous crystalline the ammonium thiosulfate product, the am solid. The ammonium thiosulfate prepared in monium sul?te, having been substantially com accordance with the present invention, either in has the advantage that it will ?x the photo graphic image at a much more rapid rate than the‘form of a solution or as a solid, is stable and 55 pletely converted to the thiosulfate. The am 2,412,607 3 4 monium thiosulfate could be isolated directly proves the stability of the ammonium thiosulfate, and also aids in the subsequent drying step. The from this solution. However, from an economic viewpoint it is preferable to treat the solution so that more ammonium thiosulfate is formed at the expense of the impurities present in the reaction solution. This is accomplished by the careful addition of ammonium bisul?te solution to the reaction mixture. This addition neutral ammonium sul?te need not be present in the mother liquor, but the salt can be washed with ammonium sul?te solution if it is desired to introduce additional proportions of ammonium sul?te to stabilize the drying step. The factors pointed out above for the evapora tion of ammonium thiosulfate solutions also sul?te, and the ammonium sul?te is converted to 10 apply to the drying of moist crystalline am monium thiosulfate. Ammonium thiosulfate is ammonium thiosulfate by reaction with the am not a stable product, and dissociates substan monium sul?de remaining in the solution. Neu tially over normal drying temperature ranges. tralization of the ammonia favors the reaction of It has been customary therefore, where such the ammonium sul?de and the ammonium sul?te, which may thereby be made to take place readily 15 drying has been carried out, to effect it in a izes the excess ammonia to form ammonium and substantially completely. By proper selec tion of the reaction conditions and concentra tions, and by careful addition of the ammonium vacuum over a drying agent, such as sulfuric acid, and at a temperature of about room tem perature. bisul?te, the ?nal solution will contain " insig In accordance with the present invention it ni?cant amounts of ammonium sul?de, am 20 has been found that ammonium thiosulfate can be dried at temperatures above those at which monia, and ammonium sul?te, when considered decomposition would ordinarily occur, if am in the light of commercial speci?cations for am monia is present in suf?cient quantity in the monium thiosulfate. The percentages may be of atmosphere in the drying chamber. The higher the order of from O to 1% ammonium sul?de, from 0 to 1.5% ammonia, and from 0.5 to 1% 25 the temperature of drying, the greater the pro portion of ammonia which must be present in ammonium sulfite. the atmosphere in order to prevent the dissocia The solution may contain a small amount- of tion of the ammonium thiosulfate. We believe colloidal sulfur, and is preferably therefore ?l that the partial pressure of the ammonia present tered, with or without a prior adjustment by the addition of ammonium bisul?te. At this 30 must be at least as great as the dissociation pressure of the ammonium thiosulfate at the tem point a controlled amount of ammonium hy perature of treatment in order to prevent dis droxide is preferably also added to aid in the sociation of the ammonium thiosulfate. As long preservation and stabilization of the ammonium as the ammonia is present to at least this ex thiosulfate. The ?ltered solution is hen ready tent, the ammonium thiosulfate will dry with for sale as such, or may be used as feed for . out decomposition. However, whatever the cor the evaporator if crystalline anhydrous am rect explanation may be, this drying may be monium thiosulfate is desired. carried out at atmospheric pressures, or under Ammonium thiosulfate solutions are unstable vacuum, or by placing the thiosulfate in a cabi in the presence of heat, and concentration of such solutions has in the past been carried out 40 net containing trays of a drying agent, such as calcium oxide or merely in an ordinary heated usually at temperatures in the neighborhood of pipe drier, provided always that su?icient am 30° C. by operation under a high vacuum. monia is present in the atmosphere. It has been found, however, that in accord~ In all of the above processes in which ammonia ance with the present invention, ammonium is employed, the ammonia. is of course preferably thiosulfate solutions can be concentrated at at recovered from the moisture-laden atmosphere mospheric pressure if this is carried out in the removed from the concentrating or drying cham presence of ammonia, or of ammonium sul?te or both. Pressures below atmospheric may be employed if desired, but this is not necessary. bers. » The following description is given by way of Ammonium thiosuliate solutions may thus be concentrated under atmospheric pressure by heating and simultaneously blowing ammonia example to indicate one form in which the in vention can be carried out: In general, ammonium thiosulfate is prefer mixture, allowing the mixture to stir for about 1800 pounds of water, 2890 pounds of am monium white and 140 pounds of 28% ammo gas into the solution. The ammonia is recovered nium hydroxide solution are placed in a tank of from the vapors. If ammonium sul?te is pres 560 gallons capacity equipped with an agitator. ent, the solution can be heated to a higher tem 90 pounds of ammonium sul?de solution of 40% perature and hence less ammonia is required to concentration and 800 pounds of sulfur are then evaporate the same quantity of water, and the added, and the mixture is vigorously agitated. higher the percentage of ammonium sul?te, the The temperature at which this agitation takes hotter the solution can be heated. Ammonium sul?te is not essential, and the evaporation can 60 place may vary over fairly wide limits, but it is preferred to maintain the temperature between be carried out with ammonia alone in the sub 30 and 50° C. As the agitation proceeds the stantially complete absence of ammonium suliite liquid gradually turns yellow due to the forma if desired. tion of ammonium polysul?de, and the appear If the concentration is carried out under re ance of this yellow color indicates that the main duced pressure, a smaller proportion of ammonia reaction is terminated since the ammonium poly is required. The lower the pressure, the less sul?de can only form after the ammonium sul?te ammonia will be necessary. Likewise, if am has been completely converted to ammonium monium sul?te is present, less gaseous ammonia thiosulfate. With the agitation continuing, am is needed. Aqueous ammonia may be substituted for gaseous ammonia, but in this event more 70 monium bisul?te solution of any suitable con centration, but preferably of about 66% strength, water will have to be evaporated, although the is then added in small portions to the reaction concentration can be carried out. ably crystallized from liquors containing of the 10. minutes between each addition. order of 3% of ammonium sul?te. This'im tion mixture is tested from time to time for the The reac 2,412,607 5 6 . absence of sul?te ions, and the presence of sul ?de ions. This is simply accomplished by allow containing eiiiuent vapors from the drying chamber through a scrubbing tower, or by any ing the reaction mixture to stir for a time and other convenient means. observing whether the yellow color reappears. The reappearance of the yellow color indicates obtained is substantially stable over an inde? absence of sul?te, and also presence of ammonium sul?de. The total acidity of the solution is also nitely long period of time, when stored in gas tight containers. If stored in ammonia-tight periodically checked to determine the amount of excess ammonium hydroxide. When the point containers containing an atmosphere of am The anhydrous ammonium thiosulfate thus monia the anhydrous salt is substantially free is ?nally reached at which the addition of a small 10 from any tendency to decompose. It has been found in addition that the solution of ammonium thiosulfate is likewise stable, and may be stored for extended periods. The solution, test is shown to be free from sul?de, the reac if this is the desired ?nal form, is preferably con tion is considered to be completed. This solution is then ?ltered through a ?lter 15 centrated to contain 60% of ammonium thio'sul amount of ammonium bisul?te gives a perma nently water white solution which by additional press in order to remove such excess sulfur and colloidal sulfur as may be present, and dis charged into a second tank. At this point su?i fate. Such a 60% solution will not deposit crys tals unless it is subjected to low temperatures, and is quickly and easily mixed with other ingredi ents to form a photographic ?xing bath, for ex remove from the solution all of the remaining 20 ample. Attention is directed to our copending applica sul?de ion, and during this stage a slight amount of colloidal sulfur may precipitate out. Am tion, Serial No. 666,811, ?led May 2, 1946. monium hydroxide is then added to preserve and In view of the above, it will be seen that the several objects of the invention are achieved and stabilize the ammonium thiosulfate. The amount other advantageous results attained. to be added at this point is largely optional, As many changes could be made in the above but suf?cient to produce a solution of about pH 8 cient ammonium sul?te is added to completely is preferred. The solution is again ?ltered through a ?lter press to remove any solid ma terial, and is then ready for sale as such, or is suitable for feed to the evaporator. About 400 gals. of 60% ammonium thiosulfate solution are placed in a 500 gal. stainless steel tank equipped with a stainless steel internal heat ing coil and a stainless steel agitator. The liquor methods and products Without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a lim iting sense. We claim: 1. The method of concentrating ammonium thiosulfate solutions which comprises evaporat is agitated to avoid local overheating and is heated ing such solutions in contact with ammonia. as rapidly as possible. When the temperature 2. The method of concentrating ammonium reaches about 80° C‘. anhydrous ammonia is thiosulfate solutions which comprises evaporat bubbled into the solution through a stainless steel ing said solution in contact with ammonia and tube extending nearly to the bottom of the tank. ammonium sul?te. The solution is heated to approximately 105° C. 40 3. The method of dehydrating ammonium and the anhydrous ammonia is bubbled in at the thiosulfate which comprises evaporating water rate of approximately 1 lb. per hour. After about from hydrous ammonium thiosulfate in contact 3 hours the rate of addition of ammonia is in creased to about 11/2-2 lbs. per hour. The with gaseous ammonia. temperature is not allowed to exceed 105° 0. Gen erally 6 or 7 hours evaporation will concentrate the solution to such an extent that crystals of ammonium thiosulfate will separate from it on cooling. The concentrated solution is then ?l thiosulfate which comprises evaporating Water from hydrous ammonium thiosulfate in contact 4. The method of dehydrating ammonium with gaseous ammonia at a partial pressure at least equal to the dissociation pressure of the ammonium thiosulfate under the dehydration tered while still hot and permitted to crystallize. 50 conditions. The crystals are separated from the liquors by 5. The method of making stable anhydrous any convenient means. In the moist state the ammonium thiosulfate which comprises mixing crystals are subject to accelerated rates of de ammonium vsul?te and sulfur in the presence of composition and should preferably be exposed to a substantial proportion of ammonium sul?de air as short a time as possible. 55 and of ammonium hydroxide, neutralizing the re The mother liquors from the crystallization may sulting solution with ammonium bisul?te and be returned to the evaporator and again con evaporating the resulting solution in the pres centrated to yield further crops of ammonium ence of ammonia and ammonium sul?te. 6. The method of dehydrating ammonium thiosulfate, or, if desirable, they can be mixed with fresh feed solution prior to evaporation. 60 thiosulfate crystals which contain water, which Drying the moist ammonium thiosulfate crys comprises evaporating water from said crystals tals may be accomplished following conventional in contact with gaseous ammonia from an out drying practices, if, as has been pointed out, salt side source. 7. The method of dehydrating ammonium is maintained in an ammonia-containing atmos phere throughout the drying operation. We have 65 thiosulfate crystals which contain water, which comprises evaporating water from said crystals found it convenient to place trays of ammonium thiosulfate in a drying chamber, gradually heat ing the chamber to a temperature in the neigh borhood of 50° C. while continually passing a stream of gaseous ammonia into the chamber 70 during the drying operation. The ammonia may be recovered by passing the moist, ammonia in contact with gaseous ammonia from an out side source at a partial pressure at least equal to the dissociation pressure of ammonium thio sulfate under the dehydration conditions. HENRY V. FARR. JOHN R. RUI-IOFF.