United States Patent (19) 11, 3,937,793 Metzger Et Al

United States Patent (19) 11, 3,937,793 Metzger et al. (45) Feb. 10, 1976

(54) PROCESS FOR THE CONTINUOUS (56) References Cited MANUFACTURE OF CRYSTALLIZED UNITED STATES PATENTS AMMONIUM THIOSULFATE

2,219,258 10/1940 Hill...... 423154 (75) Inventors: Adolf Metzger, Wiesbaden; 3431,070 3/1969 Keller ...... 423154 Karl-Heinz Henke, Frankfurt am 3,473,891 10/1969 Mack...... 4231514 Main; Horst Schreiber, Kelkheim, Taunus, all of Germany Primary Examiner-Earl C. Thomas (73) Assignee: Hoechst Aktiengesellschaft, Attorney, Agent, or Firm-Curtis, Morris & Safford Frankfurt am Main, Germany 57 ABSTRACT 22 Filed: June 18, 1973 Crystallized ammonium thiosulfate is manufactured by (21) Appl. No.: 370,686 converting ammonia with oxygen containing sulfur di oxide in ammonium thiosulfate solution to ammonium bisulfite and ammonium sulfite in a first step, while 30 Foreign Application Priority Data maintaining a pH of from 5.5 to 7.0 and a reaction June 20, 1972 Germany...... 223OOO5 temperature of up to 80°C. In a second step, the am monium bisulfite and ammonium sulfite in the solution 52 U.S. Cl...... 4231514; 423/519 are converted with ammonia and sulfur to ammonium 51 Int. Cl.’...... C01B 17/64 thiosulfate. 58 Field of Search...... 423/514 3 Claims, 1 Drawing Figure

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W va - U.S. Patent Feb. 10, 1976 3,937,793

3,937,793 1. 2 A modification of the process comprises in the first PROCESS FOR THE CONTINUOUS step introducing continuously oxygen containing sulfur MANUFACTURE OF CRYSTALLIZED dioxide into a circulated ammonia, ammonium bisulfite AMMONUM THOSULFATE and ammonium sulfite containing ammonium thiosul fate solution maintained at a pH of from 5.5 to 7.0 and The present invention relates to a process for the a temperature of from 60 to 80°C, and taking off the manufacture of ammonium thiosulfate from SO, con circulation system ammonium bisulfite and ammonium taining flue or sulfur combustion gases. sulfite containing ammonium thiosulfate solution, and, It is known to convert ammonium sulfite containing in a second step, adding ammonia and sulfur, and recy solutions or suspensions to ammonium thiosulfate by 1 0 cling the sulfite-deficient ammonium thiosulfate solu means of a slight excess of sulfur at temperatures of tion into the first step. 80°C and more in the presence of free NHa. The ammo A further modification of the process comprises con nium sulfite containing thiosulfate solution is generated verting the ammonium bisulfite being in the solution to in an ammonium thiosulfate mother liquor by feeding ammonium sulfite by means of ammonia in a second in NH and SO. Usually, the reaction temperature of 5 step, and in a third step reacting the ammonium sulfite with sulfur. these processes is maintained at 50°C by cooling. The The reaction of the process of the invention proceeds gaseous reactants may be fed in in the presence or in the first step according to the following scheme: absence of sulfur. 2NH - SO - HO re (NH4)2SOs Furthermore, it is known to incite the formation of 20 NH -- SO + HO ste (NH4)HSO ammonium sulfite under conditions which already re The ratio of bisulfite to sulfite is controlled by the sult in a partial conversion of the sulfite to thiosulfate, amount of NH3. which shortens the reaction time necessary for the In the subsequent second step, the ammonium thio conversion of ammonium sulfite to thiosulfate. The sulfate solution saturated with ammonium sulfite and reaction is generally further accelerated by operating at 25 ammonium bisulfite is converted to ammonium thiosul elevated temperatures (from 110 to 130°C). fate according to the following scheme: (NH)SO - S -> (NH)SOs In these processes, the mother liquor may be circu (NH)HSO - S - NH -> (NH)SOs lated, but in industrial practice it has been observed This conversion of the second step may be carried out that in this case a perfect crystallization of the ammo in one single as well as in two separated operations, nium thiosulfate is only possible when the amount of 30 which may be continuous or batchwise. ammonium sulfate in the mother liquor does not ex Advantageously, the solution is saturated with am ceed about 1%. monium sulfite and ammonium bisulfite in the first step In order to avoid the formation of ammonium sulfate in such a manner that after the reaction of the second as far as possible all known processes use oxygen-free step a saturated mother liquor containing about 70% SO. According to Forster and Haufe however, ammo 35 of ammonium thiosulfate is obtained. nium sulfate is formed also in this case, the reaction When from the crystallization an ammonium thiosul corresponding to the following scheme: fate solution saturated at 20°C (about 60% of ammo 4HSO -> SO -- SO - 2HO nium thiosulfate is obtained for reuse in the first step, in When oxygen containing SO, gases are used, the this first step a solution is prepared which contains. manufacturing process is additionally complicated by 40 about 53% of ammonium thiosulfate and 12.0% of the oxidation conversion of ammonium sulfite or am SO, and which consists of from about 55 to 75% of monium bisulfite to ammonium sulfate. This reaction, sulfite and from 45 to 25% of bisulfite. This ammo as Chertkov in J. appl. chem. USSR 32 (1959), pp. nium sulfite/ammonium hydrosulfite ratio corresponds 2687-2690 has proved, is catalyzed by the presence of to a pH of from 5.5 to 7.0 in the reaction solution. thiosulfate in the following manner: 45 SO + O., +SO + 3H - SO + OH + H2O Under these process, conditions, the formation of and sulfate decreases at the same rate as the periods of SO -- 20H +SO + 2H-> SO + 2HO contact with the oxygen containing SO, gas decrease. SO + H.O - SO + SO + 2H Therefore, for carrying out this process step, a reaction His tests prove that increasing thiosulfate concentra apparatus is suitable which ensures a gas/liquid contact tions accelerate considerably the oxidation conversion 50 time as short as possible, for example, a Venturi scrub to sulfate. ber. Moreover, it is advantageous to keep the residence Furthermore it is generally known that ammonium time of the reaction solution in the first step as short as thiosulfate (heavily depending on its concentration) possible, for example from 0.1 to 1 second in the reac transforms into sulfur dioxide and sulfur in acidic solu tion zone. This process may also be carried out under tion, while in alkaline solution ammonium thiosulfate 55 conditions in which the reaction solution exceeds the decomposes into ammonium sulfate. solubility limit. The salt obtained in this case does not It has now been found that ammonium thiosulfate disturb the operation of the apparatus. can be manufactured continuously with only insignifi The process is carried out at reaction temperatures of cant formation of sulfate in the presence of oxygen about 60 to 80°C. Intense cooling is therefore not containing sulfur dioxide. The process of the invention 60 necessary. From the heat balance results that a temper comprises converting ammonia with oxygen containing ature of 70°C in the first step is advantageous for the sulfur dioxide in ammonium thiosulfate solution to further conversion in the second step. However, also ammonium bisulfite and ammonium sulfite in a first another temperature range is possible when required step, while maintaining a pH of from 5.5 to 7.0 and a for any reasons. reaction temperature of up to 80°C, and, in a second 65 The apparatus is advantageously a Venturi scrubber. step, converting the bisulfite and sulfite being in the The present invention will be further understood by solution with ammonia and sulfur to ammonium thio reference to the FIGURE which shows a Venturi scrub sulfate. ber consisting of trap 1, in which the reaction solution 3,937,793 3 4 to be saturated is fed in via supply duct 2. By means of Under these conditions, an ammonium thiosulfate circulation pump 3, the reaction solution is pumped to containing less than 1% of ammonium sulfate is ob jet 5 of the Venturi scrubber, thereby passing heat tained. exchanger 4. In jet 5, the reaction solution is distrib uted into the gas stream which is fed in via duct 6. EXAMAPLE 2 Waste gas is let off via exhaust 7. NH (8) is added also Under analogous operation conditions as indicated in by means of pump 3. For further reaction in the second Example 1, the batch of the first step is 182 kg/h of step, the reaction solution is discharged via duct 9 and ammonium thiosulfate mother liquor containing 60.50 forwarded to reactor 10, where the solution of the first weight % of ammonium thiosulfate and 0.75 weight % step is converted to thiosulfate with the aid of NH 10 of ammonium sulfate. 43.8 Nm per hour of gas are (supply duct 11) and sulfur (supply duct 12). The thio introduced which contains 16 volume 7% of sulfur diox sulfate is forwarded via duct 13 into a crystallizer 15 ide, 79 volume 96 of nitrogen and 5 volume % of oxy which is drawn in broken lines. The ammonium thiosul gen. In addition, also 7.2 kg/h of NH3 are introduced, fate mother liquor obtained in the crystallizer is recy which results in a pH of 6.4 to 6.5. The solution dis cled into the first step via duct 14 which is also drawn 15 charged from the first step contains in broken lines. 53.50 weight % of ammonium thiosulfate The following examples illustrate the invention. 6.18 weight % of annonium sulfite 0.87 weight % of ammonium sulfate EXAMPLE 9.85 weight % of ammonium bisulfite. 140.0 kg of a 64 weight % ammonium thiosulfate mother liquor containing 0.68 weight % of ammonium Maintaining the conditions indicated in Example 1, an sulfate are introduced per hour into the first reaction amount of ammonia of 3.6 kg/h is introduced as well as step. For saturation of this solution with ammonium 9.8 kg/h of sulfur. 221.2 kg/h of ammonium thiosulfate sulfite and ammonium bisulfite, an amount of gas of 25 solution containing 70.9 weight % of ammonium thio 43.8 Nm (Nm-Standard cubic meter)per hour is sulfate are obtained. introduced which contains 12 volume % of sulfur diox After crystallization, the mother liquor is recycled ide, 79 volume % of nitrogen and 9 volume % of oxy into the first step. gen. By feeding in 5.9 kg/h of NHa, the pH is kept What is claimed is: constant at 6.1 to 6.2. The amount of charge of the first 1. A process for the continuous manufacture of crys step is 551, the amount circulated per hour 2.5 m. By tallized ammonium thiosulfate which comprises: react cooling, the temperature is maintained at 61°C. A solu ing ammonia with oxygen containing sulfur dioxide in tion containing the following components is obtained: an ammonium thiosulfate solution to form ammonium bisulfite and ammonium sulfite at a pH of from 5.5 to 56.9 weight % of ammonium thiosulfate 35 7.0 and a temperature of up to 80°C; and, in a second 7.91 weight % of ammonium sulfite 0.70 weight % of ammonium sulfate step, converting the ammonium bisulfite and ammo- . 8.52 weight % of ammonium bisulfite nium sulfite in the solution formed with ammonia and sulfur to ammonium thiosulfate at a temperature of 105°C, said temperature being obtained by heating, if which solution is forwarded to the second step. In this 40 necessary. second step, the ammonium bisulfite is converted to 2. A process as claimed in claim 1, which comprises ammonium sulfite by introducing 2.3 kg/h of ammonia. in the first step introducing continuously oxygen con For the conversion of ammonium sulfite to ammonium taining sulfur dioxide into a circulated ammonia, am thiosulfate, also 7.2 kg/h of sulfur are added, advanta monium bisulfite and ammonium sulfite containing geously in regular little portions or continuously. In 45 ammonium thiosulfate solution maintained as a pH of addition to this, a constant excess of about 1 to 2 from 5.5 to 7.0 and a temperature of from 60 to 80°C, weight% of sulfur is maintained in the reaction solution and thereby forming ammonium bisulfite and ammo by introducing once a corresponding amount. The re nium sulfite containing ammonium thiosulfate solution; action time is 4 hours at 105°C; if necessary, this tem adding ammonia and sulfur to the solution formed to perature is attained by heating. The reaction proceeds 50 convert the ammonium bisulfite and ammonium sulfite in a weakly alkaline medium (pH of from 7.5 to 8.0, to ammonium thiosulfate; removing ammonium thio measured at 20°C). sulfate from the solution by crystallization; and recy By this operation mode, a solution containing 74.9 cling the remaining solution to the first reaction step. weight % of ammonium thiosulfate is obtained. No 3. A process as claimed in claim 1, which comprises ammonium sulfate is formed in the second step. 55 converting the ammonium bisulfite in the solution to After filtration, the ammonium thiosulfate is sepa ammonium sulfite by means of ammonia in a second rated from the mother liquor by crystallization. After step, and in a third step reacting the ammonium sulfite removal of the crystallized portion, the mother liquor is with sulfur. recycled into the first step. sk k k 60