United States Patent Office 3,330,620 Patented July 11, 1967 2 3,330,620 aqueous solution is used and this base is selected from METHOD FOR OXEDZNG AMMONUMSULFTE TO AMMONUMSULFATE the group consisting of pyridine, picolines, lutidines, col Angel Vian-Ortino and Vicente Martin-Municio, Madrid, lidines, quinoline, pyridic coal-tar bases, pyridic bases Spain, assignors to Empresa Auxiliar de la Industria, derived from petro-chemical processes, bases containing S.A., Madrid, Spain 5 pyridinic condensed rings and derivatives thereof. No Drawing. Fied Apr. 22, 1963, Ser. No. 274,806 The method of the present invention of converting am Claims priority, application Spain, Apr. 23, 1962, monium sulfite into ammonium sulfate may also be car 276,718 ried out by forming a dispersion of an organic, nitro 15 Claims. (C. 23-119) gen-containing base in an aqueous solution of ammonium 10 sulfate and ammonium sulfite, the organic base being in The present invention relates to a process for the soluble in the aqueous solution and being present in an quantitative oxidation of ammonium sulfite and, more amount equal to between 10% and 80% of the volume particularly, for the oxidation of ammonium sulfite which of the dispersion, passing air through the dispersion while has been formed by absorption of sulfur dioxide in aque the same is maintained at an elevated temperature of be ous ammonia solutions. Thus, the present invention is also 5 tween 40 and 140 C. and at an absolute pressure of be concerned with the recovery of sulfur dioxide from waste tween 1 and 11 atmospheres so as to substantially com gases in the form of ammonium sulfate. pletely oxidize the ammonium sulfite of the solution to The recovery and utilization of small concentrations of ammonium sulfate, separating the base from the thus sulfur dioxide which are contained in waste gases dis formed substantial ammonium sulfite-free solution, and charged, for instance, from sulfuric acid plants, thermal 20 recovering ammonium sulfate from the solution. power stations, certain types of metallurgic foundries and Surprisingly, it has been found that the oxidation of Sul the like poses an important problem. It is desired not only fite to sulfate can be carried out with up to a substantial to prevent contamination of the surrounding atmosphere ly 100% yield by proceeding in accordance with the pres Such as would happen by allowing sulfur dioxide-contain ent invention, namely by oxidizing the aqueous solution ing gases to escape, but also to recover the sulfur diox of ammonium sulfite in the presence of a nitrogenous ide-even though present only in great dilution-and to organic base, and preferably under the conditions de convert the same into valuable products. scribed further below. It is well known to selectively absorb the sulfur dioxide To proceed in this manner has the further advantage of Such waste gases in aqueous dispersions and solutions that the nitrogenous base which is insoluble or immiscible of lime and in aqueous ammonia solutions. However, the 30 in the aqueous sulfite and/or sulfate solution will form a further treatment of the thus-formed sulfites is connected distinct separate layer when the mixture is allowed to with considerable difficulties. stand and thus, upon completion of the oxidation, the If a solution of ammonia in water or in a saline solu nitrogenous base can be easily separated by decantation tion is used as absorbent for the sulfur dioxide, it has from the aqueous ammonium sulafte solution. The thus been proposed to subject the thus-formed sulfur dioxide 35 obtained ammonium sulfate solution which preferably containing solution to contact with oxygen, for instance, will be a substantially Saturated solution maintained at an with the oxygen of the air, so as to transform the am elevated temperature, may then be cooled whereby the monium sulfite of the solution into ammonium sulfate solubility of the ammonium sulfate will be reduced and which then may be recovered as a crystallized product. a portion thereof will crystallize from the supersaturated However, in industrial practice, this direct oxidation poses 40 solution formed by cooling. It is, of course, also possible great difficulties inasmuch as due to the gradual change in to obtain crystallized ammonium sulfate by evaporation of the pH of the solution the yield of the oxidizing reaction the solution. The thus obtained solid product is suitable, diminishes gradually and eventually reaches zero. It has without further processing, for use in and as fertilizer or been attempted to overcome this difficulty by adding cata the like. The working conditions under which the am lysts such as certain cobalt, copper and iron salts as well 45 monium sulfate is recovered from the aqueous solution as by trying to control the pH, however, nevertheless, thereof are less critical than is the case in the separation still.after some time the oxidation practically comes to a stand and recovery of many other chemical compounds. The organic base which facilitates the oxidation of the It is, therefore, an object of the present invention ammonium sulfite and which should be finely dispersed to overcome the above discussed difficulties in the recov 50 throughout the aqueous solution during oxidation of the ery of Sulfur dioxide in the form of ammonium sulfate. same may be any nitrogenous base which is immiscible It is a further object of the present invention to pro with the aqueous solution and which is weaker than am vide a method by which ammonium sulfite contained in monia so that it will not cause freeing of ammonia from an aqueous solution can be substantially completely con the dissolved ammonium sulfite or sulfate. verted into ammonium sulfate in a simple and economical 55 Thus, heterocyclic aromatic, aliphatic, cycloparaffinic anner. and cycloolefinic amines, the heavy pyridic bases of the Other objects and advantages of the present invention type derived from coal-tar, xylidine, toluidines, quinoline, will become apparent from a further reading of the de dimethylaniline, methylamine, ethanolamines, cyclohexyl scription and of the appended claims. aniline, pyridine, lutidines, diphenylamine, picoline, col With the above and other objects in view, the present 60 lidine, methylethylpyridine and dipyridyl may be used as invention comprises in a method of oxidizing ammonium well as other compounds which are of pyridic character sulfite to ammonium sulfate, the step of contacting with or contain condensed pyridic rings, as well as nitrogen an oxygen-containing gas an aqueous ammonium sulfite containing basic derivatives thereof. containing solution having dispersed therethrough an or Preferably, the solution containing the ammonium sul ganic, nitrogen-containing base so as to oxidize the am 65 fite which is to be oxidized to ammonium sulfate will be monium sulfite of the Solution to ammonium sulfate there a concentrated solution of ammonium sulfate which con by forming an aqueous ammonium sulfate-containing tains between about 10 and 15% of ammonium sulfite. Solution which is substantially free of ammonium sulfite. When feasible it is desirable to control the absorption of According to a preferred embodiment of the present Sulfur dioxide from the waste gases or the like in such a invention, a nitrogen-containing organic base which is 70 manner that thereby a solution is formed which will be a Weaker than ammonium and which is insoluble in the concentrated solution of ammonium sulfate containing be. tween 10 and 15% of ammonium sulfite and the thus 3,330,620 4. t sulfate, sataurated at 20 C., is passed a gas stream which formed solution is then immediately subjected to oxidation contains 1.18 kg. of gaseous ammonia, and simultaneously in accordance with the present invention. Oxidation of the dissolved ammonium sulfite is carried or successively another stream of gas consisting of or con out according to the present invention by contacting the taining 2.22 kg. or SO2. To the resulting solution are ammonium sulfite-containing solution in the presence of added 0.625 kg. of water and 60 kg. of the fraction of a nitrogenous base with gaseous oxygen which may be in pyridic bases boiling between 140 and 170° C. The entire troduced in the form of air, or pure oxygen, or air which mixture is then introduced into a reactor, in the interior has been enriched with oxygen. The best results are ob of which exists an oxygen atmosphere, heated therein to tained if the oxidation is carried out at a somewhat ele 80° C. and vigorously stirred. The oxygen in the reactor is vated temperature such as between 40 and 140° C. and O replenished as it is consumed in the reaction, resulting in preferably at a temperature between 70 and 90° C., and a total consumption of 0.39 standard cubic meter of at an absolute pressure of between 1 and 11 atmospheres. OXygen. It is preferred to operate within the above described tem After one hour the oxidation is complete, and by fur perature and pressure ranges, however, the invention is ther treating the contents of the reactor in the same way not to be considered limited thereto. Generally, somewhat 15 as indicated in Example I, 4.8 kg. of ammonium sulfate higher pressures will be preferred in combination with in form of crystals are obtained, while at the same time somewhat lower temperatures, in other words, the tem a saturated (at (20 C.) ammonium sulfate solution is perature may be inverse to the utilized pressure. formed which is separated from the organic base by de The proportion of the organic base in the liquid mix cantation, or which may be re-used together with the ture containing ammonium sulfite which is to be oxidized 20 organic base for the absorption and oxidation of additional may vary within broad ranges and preferably will be main Sulfur dioxide. tained between 10 and 80% of the entire volume of the EXAMPLE III mixture. The most suitable proportion of the base which will give the best results in any given case can be easily To an aqueous solution of 100 kg. containing 41.7% ascertained and will depend on the specific nitrogenous 25 of ammonium sulfate, are added 50 kg. of 2-6-lutidine, base which is used, the degree of the dispersion of the the mixture is heated to 80 C. and intensely stirred in same and other operating conditions. an oxygen atmosphere and at an absolute pressure of 3 The process of the present invention, i.e., the oxida atmospheres. The solution will be completely oxidized tion of the ammonium sulfite solution can be carried out with an oxygen consumption of 4.03 standard cubic 30 meters. The 2-6-lutidine phase is decanted and an aque in any kind of apparatus which will afford intimate con ous solution containing 47.4% of ammonium sulfate is tact between the liquid and the oxidizing gas and which obtained, which is subjected to crystallization by cool will permit maintaining the nitrogenous base finely dis ing, while the saturated solution of ammonium sulfate tributed throughout the liquid. Thus, packing towers, plate formed thereby and the organic base can be re-used in towers, turbo-stirrers, etc., can be used for this purpose. 35 the same way as indicated in Example I. The effectiveness of a given proportion of the base will Without further analysis, the foregoing will so fully be improved, or the proportion of the base which is re reveal the gist of the present invention that others can quired will be reduced by favoring the interphasic dis by applying current knowledge readily adapt it for vari persion, for instance by stirring the reaction mixture dur ous applications without omitting features that, from ing oxidation of the same by anyone of the available con 40 the Standpoint of prior art, fairly constitute essential ventional methods. After oxidation of the dissolved ammonium sulfite has characeristics of the generic or specific aspects of this been completed, the reaction mixture is allowed to stand invention and, therefore, such adaptations should and until the immiscible nitrogenous base has formed a distinct are intended to be comprehended within the meaning and separate layer. Thereafter, the aqueous solution is and range of equivalence of the following claims. 4 5 What is claimed as new and desired to be secured by separated from the nitrogenous base preferably by sim Letters Patent is: ple decantation. 1. In a method of oxidizing ammonium sulfite to am The remaining aqueous solution of ammonium sulfate monium Sulfate, the step of contacting with an oxygen may then be crystallized, centrifuged and dried in a con containing gas an aqueous ammonium sulfite-containing ventional manner. The organic base is recycled from the Solution having dispersed therethrough, as the only sub decantation tank to the reaction vessel in which the oxida 50 stance promoting the reaction between said oxygen-con tion of the ammonium sulfite is carried out. taining gas and said ammonium sulfite, an organic, nitro The following examples are given as illustrative only gen-containing base so as to oxidize said ammonium sul of the present invention without, however, limiting the in fite of said solution to ammonium sulfate thereby form vention to the specific details of the examples. 55 ing an aqueous ammonium sulfate-containing solution EXAMPLE which is substantially free of ammonium sulfite. To 100 kg. of an aqueous ammonium sulfate solution, 2. In a method of oxidizing ammonium sulfite to am Saturated at 20° C., and containing 5.5 kg. of ammonium monium sulfate, the step of contacting with an oxygen sulfite, are added 40 kg. of 2-methyl-5-ethylpyridine. The containing gas an aqueous ammonium sulfite-containing thus-formed mixture is heated up to 90° C. and 7.6 stand 60 Solution having dispersed therethrough, as the only sub ard cubic meters of air are passed through under vigorous stance promoting the reaction between said oxygen-con stirring. In this manner the entire sulfite content of the taining gas and said ammonium sulfite, a liquid, organic, solution is oxidized to ammonium sulfate. nitrogen-containing base which is weaker than ammonia Thereafter, the 2-methyl-5-ethylpyridine phase and the So as to Substantially completely oxidize said ammonium 65 sulfite of said solution to ammonium sulfate thereby aqueous phase are separated by decantation, the latter now forming an aqueous ammonium sulfate-containing solu consisting of a concentrated solution of ammonium sulfate tion which is substantially free of ammonium sulfite. containing only an insignificant amount of 2-methyl-5-eth 3. In a method of oxidizing ammonium sulfite to am ylpyridine; the aqueous phase is cooled down to 20 C. monium sulfate, the steps of contacting with an oxygen and thereby 6.25 kg. of crystallized ammonium sulfate containing gas an aqueous ammonium sulfite-containing are obtained, and the original saturated ammonium sul 70 Solution having dispersed therethrough, as the only sub fate solution is regenerated. This solution can be re-used stance promoting the reaction between said oxygen-con in a subsequent oxidation cycle as described above. taining gas and said ammonium sulfite, a liquid, organic, EXAMPLE II nitrogen-containing base which is weaker than ammonia Through 100 kg. of an aqueous solution of ammonium 75 so as to Substantially completely oxidize said ammonium 3,330,620 5 6 sulfite of said solution to ammonium sulfate thereby 10. In a method of oxidizing ammonium sulfite to forming an aqueous ammonium sulfate-containing solu ammonium sulfate, the step of contacting with an oxygen tion which is substantially free of ammonium sulfite; and containing gas a substantially saturated aqueous am separating said organic base from said ammonium sulfite monium sulfate and ammonium sulfite-containing solu containing solution. tion having dispersed therethrough a liquid, organic, 4. In a method of oxidizing ammonium sulfite to am nitrogen-containing base which is weaker than ammonia monium sulfate, the steps of contacting with an oxygen so as to substantially completely oxidize said ammonium containing gas an aqueous ammonium sulfite-containing sulfite of said solution to ammonium sulfate thereby solution having dispersed therethrough, as the only sub forming an aqueous ammonium sulfate-containing solu stance promoting the reaction between said oxygen con O tion which is substantially free of ammonium sulfite, said taining gas and said ammonium sulfite, a liquid, organic, nitrogen-containing base being the only substance pres nitrogen-containing base which is weaker than ammonia ent which is capable of promoting reaction between said so as to substantially completely oxidize said ammonium ammonium sulfite of said solution and the oxygen of sulfite of said solution to ammonium sulfate thereby said gas. forming an aqueous ammonium sulfate-containing solu 15 11. A method of converting ammonium sulfite into tion which is substantially free of ammonium sulfite; ammonium sulfate, comprising the steps of forming a separating said organic base from said ammonium sul dispersion of an organic, nitrogen-containing base in an fate-containing solution; and recovering ammonium sul aqueous ammonium sulfite-containing solution, said or fate therefrom. ganic base being insoluble in said aqueous solution and 5. A method for the substantially quantitative oxida 20 being present in an amount equal to between 10 and tion of ammonium sulfite into ammonium sulfate, com 80% of the volume of said dispersion, said nitrogen-con prising the steps of forming an aqueous solution of am taining base being the only substance present which is monium sulfite; and contacting said solution in the pres capable of promoting reaction between said ammonium ence of an organic, nitrogen-containing base which is sulfite of said solution and the oxygen of said gas; pass weaker than ammonia and insoluble in said solution, 25 ing oxygen-containing gas through said dispersion so as with an oxygen-containing gas, said nitrogen-containing to substantially completely oxidize said ammonium Sul base being the only substance present which is capable fite of said solution to ammonium sulfate; separating of promoting reaction between said ammonium sulfite of said base from the thus-formed substantial ammonium said solution and the oxygen of said gas. sulfite-free solution; and recovering ammonium sulfate 6. A method of oxidizing sulfur dioxide, comprising 30 from said solution. the steps of absorbing sulfur dioxide in an aqueous am 12. A method of converting ammonium sulfite into monia-containing solution so as to form an aqueous am ammonium sulfate, comprising the steps of forming a monium sulfite-containing solution; and contacting the dispersion of an organic, nitrogen-containing base in an thus-formed solution in the presence of a finely dispersed aqueous ammonium sulfite-containing solution, said or organic, nitrogen-containing base which is weaker than 35 ganic base being insoluble in said aqueous solution and ammonia and insoluble in said solution, with an oxygen being present in an amount equal to between 10 and containing gas, said nitrogen-containing base being the 80% of the volume of said dispersion, said nitrogen only substance present which is capable of promoting containing base being the only substance present which is reaction between said ammonium sulfite of said solution capable of promoting reaction between said ammonium and the oxygen of said gas. 40 sulfite of said solution and the oxygen of said gas; pass 7. A method for the substantially quantitative oxida ing oxygen-containing gas through said dispersion while tion of ammonium sulfite into ammonium sulfate, com the same is maintained at an elevated temperature of prising the steps of forming an aqueous solution of am between 40 and 140° C. and at an absolute pressure of monium sulfite; and contacting said solution at a tem between 1 and 11 atmospheres so as to substantially com perature of between 40 and 140° C. in the presence of an 45 pletely oxidize said ammonium sulfite of said solution organic, nitrogen-containing base which is weaker than to ammonium sulfate; separating said base from the thus ammonia and insoluble in said solution, with an oxygen formed substantial ammonium sulfite-free solution; and containing gas, said nitrogen-containing base being the recovering ammonium sulfate from said solution. only substance present which is capable of promoting 13. A method of converting ammonium sulfite into reaction between said ammonium sulfite of said solution 50 ammonium sulfate, comprising the steps of forming a and the oxygen of said gas. dispersion of an organic, nitrogen-containing base in an 8. A method for the substantially quantitative oxida aqueous solution of ammonium sulfate and ammonium tion of ammonium sulfite into ammonium sulfate, com sulfite, said organic base being insoluble in said aqueous prising the steps of forming an aqueous solution of am solution and being present in an amount equal to be monium sulfite; and contacting said solution at a tem 55 tween 10 and 80% of the volume of said dispersion, said perature of between 40 and 140 C. and at an absolute nitrogen-containing base being the only substance pres pressure of between 1 and 11 atmospheres in the pres ent which is capable of promoting reaction between said ence of an organic, nitrogen-containing base which is ammonium sulfite of said solution and the oxygen of weaker than ammonia and insoluble in said solution, with said gas; passing oxygen-containing gas through said dis an oxygen-containing gas, said nitrogen-containing base persion so as to substantially completely oxidize said being the only substance present which is capable of pro ammonium sulfite of said solution to ammonium sulfate; moting reaction between said ammonium sulfite of said separating said base from the thus-formed substantial solution and the oxygen of said gas. ammonium sulfite-free solution; and recovering am 9. A method for the substantially quantitative oxida monium sulfate from said solution. tion of ammonium sulfite into ammonium sulfate, com 65 14. In a method of oxidizing ammonium sulfite to am prising the steps of forming an aqueous solution of am monium sulfate, the steps of contacting with an oxygen monium sulfite; and contacting said solution at a tem containing gas an aqueous ammonium sulfite-containing perature of between 70 and 90° C. and at an absolute solution having dispersed therethrough a liquid, organic, pressure of between 1 and 11 atmospheres in the pres nitrogen-containing base which is weaker than ammonia ence of an organic, nitrogen-containing base which is 70 and which is selected from the group consisting of pyri weaker than ammonia and insoluble in said solution, with dine, picolines, lutidines, collidines, quinoline, pyridic, an oxygen-containing gas, said nitrogen-containing base coal-tar bases, pyridic bases derived from petro-chemical being the only substance present which is capable of processes, bases containing pyridinic condensed rings and promoting reaction between said ammonium sulfite of derivatives thereof, so as to substantially completely oxi said solution and the oxygen of said gas. 75 dize said ammonium sulfite of said solution to ammonium 3,330,620 7 3 sulfate thereby forming an aqueous ammonium sulfate ing air through said dispersion so as to substantially com containing solution which is substantially free of am pletely oxidize said ammonium sulfite of said solution monium sulfite; and separating said organic base from to ammonium sulfate; separating said base from the thus said ammonium sulfate-containing solution. formed substantial ammonium sulfite-free solution; and 15. A method of converting ammonium sulfite into recovering ammonium sulfate from said solution. ammonium sulfate, comprising the steps of forming a dis persion of an organic, nitrogen-containing base in an References Cited aqueous ammonium sulfite-containing solution, said or UNITED STATES PATENTS ganic base being insoluble in said aqueous solution and 1,106,919 8/1914 Bosch ------23-119 being present in an amount equal to between 10 and 0 1/1961 Vian-Ortuno et al. --- 23-119 80% of the volume of said dispersion, said nitrogen-con 2,970,039 taining base being the only substance present which is OSCAR R. VERTIZ, Primary Examiner. capable of promoting reaction between said ammonium sulfite of said solution and the oxygen of said gas; pass EARL C. THOMAS, Examiner.