March 4, 1969 3,431,070 METHOD OF TREATING AMMON IA AND HYDROGEN SULFIDE GASES To

6

INVENTOR. 274,725 ZA2ZZafar

17724ay

3,431,070 3 4 thiosulfate and sulfur. The sulfur dioxide reacts with the Where the initial feed gas contains hydrogen sulfide, but absorbed ammonia to form ammonium bisulfite according no ammonia, all of the thiosulfate formed by reaction (3) to the reaction: will be reduced to sulfur by reaction (4), resulting in no net yield of thiosulfate. If, on the other hand, ammonia is in excess, the mecha The remainder of the sulfur dioxide, in excess of that re nism of reacting the excess is believed somewhat different. quired to neutralize the ammonia, forms sulfurous acid In this case, reduction of the thiosulfate according to re as follows: action (4) is retarded as the ammonia raises the solution SO--HO->H+--HSO (2) pH. Since insufficient sulfur dioxide has been added to Complete reaction of the ammonia and hydrogen sul 10 convert all of the ammonia to ammonium bisulfite, the fide content of the feed gas to ammonium thiosulfate, to ammonia is probably in solution as a mixture of ammo sulfur, or to a mixture of ammonium thiosulfate and sul nium sulfite and ammonium bisulfite. The sulfite and bi fur requires 0.5 mole of sulfur dioxide per mole of the sulfite are reacted with the excess hydrogen sulfide to form total ammonia plus hydrogen sulfide reactant content of thiosulfate according to the reaction: the feed gas. Addition of the proper quantity of sulfur 15 dioxide is desirable, as the proportion of sulfur dioxide As previously mentioned, product distribution is af in part determines the completeness of reaction and ulti fected not only by feed gas composition, but by the amount mate yield of ammonium thiosulfate and sulfur. Insuffi of sulfur dioxide added. Although 0.5 mole of sulfur diox cient sulfur dioxide results in an incomplete reaction leav ide per mol of total ammonia plus hydrogen sulfide ing unreacted hydrogen sulfide, or, if ammonia is in excess 20 reactants are usually added to achieve complete reaction in the feed gas mixture, yields a product contaminated with of ammonia and hydrogen sulfide to ammonium thiosul ammonium hydrosulfide and other undesirable contami fate and/or sulfur, it is within the scope of my invention to nants. Excess sulfur dioxide merely forms additional am add more, or less, sulfur dioxide. monium bisulfite, sulfurous acid, or thiosulfuric acid, the Although the primary control of the chemical reactions particular byproduct depending on the proportions of am 25 and product yields is by the sulfur dioxide addition rate, monia and hydrogen sulfide in the initial feed gas. Thio pH may be used to monitor this control. The pH varies Sulfuric acid may further decompose to polythionates, sul from point to point within my process, depending on the fur, or sulfates, thereby adding additional impurities to particular reactions taking place and the proportion of the product. reactants. Ammonium thiosulfate in aqueous solution is The ammonium bisulfite and sulfurous acid content of 30 mildly acid, with a pH of about 4, the exact value depend the aqueous ammonium thiosulfate solution can be reacted ing on concentration and temperature. This pH is raised with hydrogen sulfide in the substantially ammonia-free by absorption of ammonia and lowered by absorption of gaseous product from the ammonia scrubbing step accord sulfur dioxide, the magnitude of the changes depending on ing to the reaction: the concentration of these reactants. For example, absorp 35 tion of equimolar quantities of ammonia and sulfur diox ide will first raise the pH of the solution as the ammonia Thiosulfate-forming reaction (3) proceeds moderately is absorbed, and then lower it on addition of the sulfur rapidly and is accompanied by a reduction in pH. If a dioxide, the pH of the resulting solution being about the proper quantity of sulfur dioxide has been added, either same as that of the original solution. On reaction with bisulfite or hydrogen sulfide will be in excess, depending 40 hydrogen sulfide, the solution pH is reduced as the am on the initial proportions of ammonia and hydrogen sul monium bisulfite and/or sulfurous acid are converted to fide in the feed gas. Subsequent reactions then occur stronger thiosulfuric acid and its ammonium salts. As the whereby additional ammonium thiosulfate and/or sulfur is lower thiosulfate reduction reaction (4) is completed, the formed, the exact mechanisms of these reactions again pH again increases to about the original level. depending on the proportions of ammonia and hydrogen 45 All of the reactions noted above occur in an aqueous sulfide in the feed gas. ammonium thiosulfate solution, a portion of which also Unless the feed gas initially contained at least 3.0 moles usually serves as an absorbent for the ammonia, although of ammonia per mole of hydrogen sulfide, a portion of the other solutions may also be used as absorbents. The prod thiosulfate formed according to reaction (3) will be re lucts of the hydrogen sulfide reactions are, except at the duced to sulfur by reaction with unreacted hydrogen 50 extremes of concentration range, an aqueous ammonium sulfide as follows: thiosulfate solution containing elemental sulfur crystals. Although these crystals are extremely finely divided, they can be removed by air flotation, filtration, or other sep Since hydrogen ions produced in reaction (3) are con aratory means. Thus, the final products of my process sumed in reduction reaction (4), the reaction is pH de 55 are finely divided elemental sulfur and a concentrated pendent and will not proceed where the solution pH is ammonium thiosulfate solution. As will be hereinafter above about 6.3, which condition can occur with insuffi described, the finely divided elemental sulfur can be fur cient sulfur dioxide addition or excess ammonia. ther processed to molten liquid sulfur, all or a portion of Where the initial feed gas contains equal molar propor which can then be oxidized to supply the sulfur dioxide tions of ammonia and hydrogen sulfide, an equivalent 60 requirement of the process. Minor amounts of polythionic quantity of sulfur dioxide is required and the reactions of acids can also be formed, but these react further with hy Equations 3 and 4 can be expressed by the net reaction: drogen sulfide to form thiosulfate and/or sulfur by reac tions such as: If the initial feed gas contains other than equal molar 65 H2SOs--H2S->2H2SO (8) quantities of ammonia and hydrogen sulfide, the excess In any event, no appreciable quantities of polythio reactant is consumed by further reactions, the particular nates are contained in the final product of my process, mechanism and final products depending on whether am thus constituting a marked advantage over some of the monia or hydrogen sulfide is in excess. In the case where prior art processes, such as that of U.S. Patent No. the initial feed contains hydrogen sulfide in excess of am 70 1,868,843 to Overdick, which yield considerable quanti monia, the excess hydrogen Sulfide reacts with a portion ties of polythionates. of the thiosulfate produced in the reaction of Equation 3 The above reactions are believed the mechanisms to form sulfur according to Equation 4. The net reaction whereby ammonia and hydrogen sulfide are converted to for the excess hydrogen sulfide can be expressed as: ammonium thiosulfate and sulfur in my process. Even 75 though the actual mechanism may not be completely 3,431,070 5 6 understood, or may be otherwise than as set forth above, any dissolved hydrogen sulfide from the ammonium thio I have conclusively demonstrated that ammonia and hy sulfate solution containing the absorbed ammonia pass drogen sulfide can be reacted to ammonium thiosulfate ing out of the bottom of absorber 1. Although carbon and/or sulfur by the method set forth herein. dioxide stripping is not absolutely necessary, it is ad Since the net reaction of my process is exothermic, heat vantageous particularly where inerts contained in the will build up which must be removed, either by radiation 5 sulfur dioxide are vented to the atmosphere. Thus, the losses to the atmosphere or by interchange of the hot section of the contacting zone of ammonia absorber 1 reaction media with a coolant. A desirable temperature below the point of feed gas entry is a stripping section range is from about 35° C. to about 70° C., although serving the sole purpose of preventing hydrogen sulfide temperatures up to about 100° C. or higher can be em from being retained in the ammonia thiosulfate solution ployed depending upon the system pressure, the upper 10 leaving absorber 1. Displacement of substantially all of limit being established by the boiling point of the solu the absorbed hydrogen sulfide is particularly important tion. The lower limit of the operable temperature range where the sulfur dioxide is obtained from combustion of is established by the temperature at which precipitation sulfur or byproduct recovery as absorbed hydrogen sulfide of salts commences. A higher temperature favors in 15 would be stripped from the solution on contact with the creased reaction rates, but reduces the absorptivity of the sulfur dioxide and vented with the inerts from the sulfur gases in the ammonium thiosulfate solution. Thus, the dioxide contacting step. effect of a temperature change on reaction rate depends The ammonia content of the feed gas is substantially on whether the reaction rate is, under those conditions, lowered by contact with the ammonium thiosulfate solu controlled by chemical reaction rate or by gas absorption 20 tion and if proper contacting is obtained can be substan TateS. tially completely removed. The substantially ammonia My process is suitable for treating gases at any pres free gaseous product from ammonia absorber 1 passes sure depending on the supply pressure and the required overhead through line 5 to hydrogen sulfide reactor 13, product pressure. In most applications, the inlet gas pres to be hereinafter described. The ammonium thiosulfate sure will vary from about atmospheric up to about 100 25 solution containing the absorbed ammonia passes out p.si.g. and the gas production pressure, if any gas is pro from the bottom of ammonia absorber 1 through line 6 duced, will be somewhat lower due to the pressure drop to sulfur dioxide absorber 7 wherein it is contacted with through the treating system. This range of pressures is gaseous sulfur dioxide passing countercurrent thereto. dictated by convenience, as there is no theoretical reason The aqueous ammonium thiosulfate solution containing why my treating process cannot be conducted at Subatmos 30 absorbed ammonia enters sulfur dioxide absorber 7 pheric pressures or at pressures substantially exceeding 100 through line 6 at the top thereof, in combination with p.si.g. Higher pressures increase gas absorptivities, there additional ammonium thiosulfate solution entering by reducing absorber sizes, and under conditions where through line 8 and valve 57 which has not been passed the reaction rate is limited by gas solubility, will increase through ammonia absorber 1. Sulfur dioxide absorber 7 the reaction rate. 35 is also a conventional liquid-gas contacting vessel com The process of my invention can be conducted either prising a vessel containing perforated trays, bubble cap batchwise or continuously depending on the nature of the plates or packed sections. The aqueous Solution of ammo feed stream and the purpose of the treatment. One en nium thiosulfate containing the absorbed ammonia from bodiment of a continuous version of my process can be ammonia absorber 1, passes downwardly through sulfur conducted in accordance with the attached flow diagram, 40 dioxide absorber 7 whereupon the ammonia is reacted with wherein is seen a feed gas entering ammonia absorber 1 sulfur dioxide passing upwardly therethrough to form through line 2. This feed gas can be a mixture of ammo ammonium bisulfite according to the reaction of Equa nia and hydrogen sulfide varying in composition from tion 1 or sulfurous acid according to the reaction of equal molar quantities of each of these gases to a mixture Equation 2. The sulfur dioxide gas enters at the bottom containing primarily hydrogen sulfide or a mixture con 45 of sulfur dioxide absorber 7 through line 11. Unreacted taining primarily ammonia. As noted above, ammonia sulfur dioxide gas and any inert gases contained in the conversion is limited to a quantity not exceeding an entering sulfur dioxide are vented from the top of ab amount equivalent to 3.0 moles of ammonia per mole of sorber 7 through line 9 and valve 10. The aqueous solu hydrogen sulfide. Alternately, various proportions of am tion of ammonium thiosulfate and the products of the monia and hydrogen sulfide can be in combination with 50 Sulfur dioxide absorption passes from the bottom of sul other gases or can be separately fed to the process. Where fur dioxide absorber 7 through line 12 to hydrogen sul the ammonia and the hydrogen sulfide are not admixed, fide reactor 13 wherein the main conversion reactions the ammonia can be fed through line 2 and the hydrogen CCC. sulfide through line 55 and valve 54, in which case valve Any convenient means of contacting the aqueous am 53 is closed. Where the feed gases are admixed, valves monium thiosulfate-bisulfite solution and the gaseous hy 52 and 54 are closed and valve 53 opened. Excess am drogen sulfide can be employed. A concurrent method monia or inerts contained in the ammonia feed, are vented is utilized in the embodiment described herein, wherein through line 51 and valve 52. Ammonia absorber 1 is a the gaseous hydrogen sulfide is introduced into the con conventional liquid-gas countercurrent contacting vessel tacting Zone at a plurality of points. Hydrogen sulfide re containing bubble cap plates, perforated trays or packed actor 13 can contain conventional gas-liquid contacting sections. The feed gas enters ammonia absorber 1 at a 60 means to achieve intimate contacting of the upward flow point somewhat above the bottom of the contacting Zone. ing gas with the upward flowing liquid. The substantially An aqueous solution of ammonium thiosulfate enters at ammonia-free feed gas is introduced to reactor 13 through the top of ammonium absorber 1 through line 3 and valve line 5 and internal distributors 5a, 5b, 5c and 5d. Any 56 and passes downwardly through the absorber in number of such distributors can be used as necessary to countercurrent contact with the upwardly flowing gas to 65 achieve distribution throughout the contact zone. Other absorb ammonia from the feed gas mixture. Although contacting devices such as baffles, mixers, dispersers, etc., only a portion of the recycled ammonium thiosulfate re may be employed to increase reaction rates by reducing action media is normally required for ammonia absorp gas bubbles sizes and improving gas distribution within tion, this amount depends on the feed rate and composi the reaction zone. Multiple internal distributors serve to tion, the absorption conditions and the efficiency of am 70 increase agitation throughout the reaction zone, thereby, monia absorber 1. in many cases, making mechanical mixers unnecessary. Carbon dioxide gas is introduced into ammonia ab Flow to the individual internal distributors can be con sorber 1 through line 4 and valve 50, at a point below trolled by valves 14a, 14b, 14c and 14d. Since it is de the contacting zone, in just sufficient quantity to displace 75 sirable to control the ammonium thiosulfate concentra 3,431,070 7 8 tion of the reaction media to avoid salt crystallization, On storage, ammonium thiosulphate solutions tend makeup water can be added to the aqueous Solution enter to decompose and precipitate colloidal sulfur unless the ing reactor 13 by means of makeup water line 15 and solution is maintained approximately neutral or slightly valve 16. Any unreacted gases exiting from hydrogen alkaline. The pH of the product ammonium thiosulfate sulfide reactor 13 pass overhead through line 17 and valve solution can be properly adjusted for storage by by 18. Alternately, valves 19 and 20 can be opened and gas passing a small slip stream of ammonia-rich ammonia recycled back to line 5 through line 21 and compressor 22. absorber bottoms through line 44 and valve 45 to the The hydrogen sulfide content of these gases is substan product solution discharged through line 43. tially reduced from that of the feed gases, and in fact The sulfur dioxide requirement can be supplied from in many cases the product gas will be substantially free of any convenient commercially available source, or it can hydrogen sulfide. Valve 18 can be closed and the total 0 be manufactured, or obtained from byproduct recovery. overhead gas recycled back to the reactor feed, particular The selection of a source of supply depends on availabili ly where the feed gas is a mixture of ammonia and hy ty and economics. One particularly suitable source of drogen sulfide without additional gaseous components. sulfur dioxide is combustion of the molten sulfur pro The aqueous liquid product from hydrogen sulfide re duced from the process. In such case, sulfur froth would actor 13 is withdrawn at the top of reactor 13 through be diverted to sulfur melter 37 to provide the necessary line 23 whereupon it passes to sulfur flotation separator sulfur dioxide on combustion. Sufficient sulfur will be 24. Air or other gas is introduced through line 25 and available to supply all the sulfur dioxide needed in any distributor 26, the gas passing upwardly through the liquid case where the amount of ammonia in the feed gas mix phase contained in separator 24 causing the sulfur to float 20 ture is equal to or less than the amount of hydrogen to the top, from which point it can be withdrawn as a sulfide contained therein. The remaining sulfur froth froth through line 27. A first substantially sulfur-free can be filtered or produced as molten sulfur, depending clarified ammonium thiosulfate solution is withdrawn on product demands. from the bottom of sulfur flotation separator 24 through Another source of sulfur dioxide can be found in the line 28. Any of the flotation gas which separates from combustion gases from a fuel source containing sulfur. the solution can be withdrawn through line 47 and The sulfur dioxide can be removed from the stack gases valve 48. by scrubbing with a portion of the ammonium thiosulfate The elemental sulfur formed by the reaction in hydrogen solution or with ammonium thiosulfate solution contain sulfide reactor 13 is in a finely divided crystalline state ing absorbed ammonia from the ammonia absorption suitable for agricultural or other purposes and can be re 30 step. Thus, not only is the necessary sulfur dioxide re covered by filtration. Alternately, the sulfur froth pro quirement supplied, but sulfur emission to the atmos duced in sulfur flotation separator 24 can be heated to melt phere is decreased, thereby reducing atmospheric the sulfur, thereby yielding a molten sulfur product. pollution. If desirable, a portion of the sulfur may be recovered One particular advantage of my ammonium thiosulfate by filtration and the balance thereof recovered by melt process is that the product is in the form of a concen ing. In the first instance, the sulfur slurry produced trated solution without further necessity of evaporation. from line 27 passes through line 29 and valve 30 to Thus, solution shipping costs are minimized and supple sulfur filter 31 wherein the solid crystalline Sulfur is mental evaporation costs are eliminated. More dilute solu separated from the aqueous ammonium thiosulphate So tions can be obtained by merely adding water to the lution. Solid sulfur passes from filter 31 through solids 40 ammonium thiosulfate product solution. Crystalline am conduit 32 and the aqueous filtrate is removed through monium thiosulfate can be produced from the concen line 33 as a second clarified ammonium thiosulfate solu trated solution, at minimum expense, by chilling or tion. The solid sulfur may be subjected to a Wash step evaporation. to remove occluded ammonium thiosulfate, if desired. The following example is illustrative of my invention, Any entrained flotation gas is vented from the filter but is not intended as a limitation thereof: chamber through line 34. Where a molten product is de sired, the sulfur slurry leaving the flotation Separator EXAMPLE I through line 27 is diverted through line 35 and valve 36 An equimolar mixture of ammonia and hydrogen to sulfur melter 37. Heat is provided by condensing steam sulfide is reacted according to the embodiment of my in coils 38, or by other suitable heating means, and the process shown in the process flow diagram hereof. A molten sulfur is withdrawn through line 39 and valve feed gas containing equal mol ratios of ammonia and 49. Any entrained flotation gas is removed through line hydrogen sulfide is fed to the ammonia absorber at a 40 and valve 46, and the sulfur free ammonium thio rate of 20,000 mols/hr. and at a temperature of 60° C. sulfate solution is produced through line 41 as a Second Absorption of the ammonia portion of the feed gas is clarified ammonium thiosulfate solution or in the case 5 5 obtained by countercurrent contact with 7,000 liters/hr. where a portion of the sulfur is recovered by filtration, of ammonium thiosulfate solution in the ammonia ab as a third clarified solution. Sulfur melter 37 must be Sorber. Hydrogen sulfide is stripped from the ammonia maintained under a slight positive pressure, usually not absorber bottoms by carbon dioxide gas introduced into exceeding 10 p.s.i.g., to prevent vaporization of water the absorber bottom at a rate of 225 mols/hr. The result at the elevated temperature of the melter. Pressure is 60 ing gas product, essentially free of ammonia, is passed regulated by valve 46 in vent gas line 40. The ammoni from the top of the ammonia absorber to the hydrogen um thiosulfate solution produced from sulfur flotation Sulfide reactor. The ammonia solution from the bottom separator 24 through line 28, from sulfur filter 31 through of the ammonia absorber is combined with the main line 33, and from sulfur melter 37 through line 41 are ammonium thiosulfate recycle stream, flowing to the combined in line 42 and returned to ammonia absorber 1 sulfur dioxide absorber at a rate of 43,000 liters/hr., and sulfur dioxide absorber 7 through lines 3 and 8 resulting in a total liquid entering the top of the sulfur respectively after passing through cooler 47 wherein dioxide absorber of approximately 50,000 liters/hr. This the ammonium thiosulfate solution temperature is reduced stream passes downwardly through the absorber in coun to an acceptable level usually between about 35° C. and tercurrent flow to the upward flowing sulfur dioxide gas about 70° C. Heat removal is necessitated because of the 70 entering the bottom thereof at a rate of 10,000 mols/hr. exothermic reactions and heat input to Sulfur melter The net liquid product obtained from this reaction 37. Alternately, the cooled solution may be filtered to amounts to approximately 50,500 liters/hr. of ammonium remove any residual sulfur crystals. Ammonium thio thiosulfate solution containing approximately 10,000 sulfate product solution is withdrawn from line 42 through mols/hr. of ammonium bisulfite. line 43. The 50,500 liters/hr. of ammonium bisulfite solution 3,431,070 10 and approximately 460 liters/hr. of makeup water are tion of said first gaseous mixture is separated from said fed to the hydrogen sulfide reactor for concurrent contact second Solution of ammonium thiosulfate. ing with the ammonia-free hydrogen sulfide gas from the 7. The process of claim 6 wherein at least a portion ammonia absorber. A net liquid product amounting to of said separated gases are recycled to combine with said approximately 51,160 liters/hr. is obtained. Air flotation Second gaseous mixture prior to said reaction to form results in approximately 5,360 liters/hr. of sulfur froth ammonium thiosulfate. and 45,800 liters/hr. of clarified product. The froth is 8. The process of claim 1 wherein the proportion of heated in the sulfur melter by condensing steam to yield Said ammonia is less than about 3.0 moles of ammonia approximately 320 kg./hr. of molten sulfur product and per mole of hydrogen sulfide, ammonium thiosulfate and 5,200 liters/hr. sulfur-free ammonium thiosulfate solution. O elemental Sulfur being produced by said reaction with The ammonium thiosulfate solution from the sulfur hydrogen sulfide, and including the step of removing said melter and the clarified solution from the separator are elemental sulfur from said second ammonium thiosulfate combined to yield 51,000 liters/hr. of solution, 1,000 Solution resulting from said reaction with said hydrogen liters/hr. of which is produced as net ammonium thio Sulfide, thereby yielding a first clarified solution of am Sulfate product at a concentration of 5.0 mols/liter. Net 15 monium thiosulfate substantially free of said elemental ammonium thiosulfate production amounts to 1,290 sulfur. kg./hr. of the salt. The remaining 50,000 liters/hr. of 9. The process of claim 8 wherein said elemental sul ammonium thiosulfate solution is returned to the process fur is removed from said second solution of ammonium as absorption and reaction media. The makeup water rate thiosulfate by: is set to maintain an ammonium thiosulfate concentra 20 passing a gas upwardly through a reservoir of said tion of 5.0 mols/liter in the circulating solution. If de Solution causing said elemental sulfur to rise to an sired, a portion of the ammonia absorber bottoms can be upper level of said reservoir to form a froth of said diverted to the final product for pH adjustment. elemental sulfur in a portion of said ammonium Various other changes and modifications of this inven thiosulfate solution; tion are apparent from the description thereof and fur 25 Withdrawing a remaining portion of said ammonium ther modifications and variations will be obvious to those thiosulfate solution from a lower level of said reser skilled in the art. Such modifications and changes are voir as said substantially elemental sulfur free first intended to be included within the scope of this inven clarified ammonium thiosulfate solution; and tion as defined by the following claims. withdrawing said sulfur froth from said upper level of I claim: 30 said reservoir. 1. A process for treating gases comprising: 10. The process of claim 9 including the steps of: contacting a first gaseous feed mixture comprising removing Said elemental sulfur from said sulfur froth hydrogen sulfide and ammonia, the proportion of to recover a second clarified ammonium thiosulfate said ammonia being not greater than about 3.0 moles Solution and an elemental sulfur product; of ammonia per mole of hydrogen sulfide, with an 35 combining said first and said second clarified ammo aqueous solution of ammonium thiosulfate to absorb nium thiosulfate solutions; a substantial portion of said ammonia from said first withdrawing a portion of said combined ammonium gaseous feed mixture, thereby yielding a second thiosulfate solution as final product; and gaseous mixture of reduced ammonia content and recycling a remaining portion of said combined ammo an ammonia-rich solution of ammonium thiosulfate; 40 nium thiosulfate solution to said sulfur dioxide ab removing any absorbed hydrogen sulfide from said Sorption step, a portion of said recycled ammonium ammonia-rich solution of ammonium thiosulfate to thiosulfate solution being diverted to said ammonia yield an ammonia-rich solution of ammonium thio absorption step prior to contacting said sulfur sulfate substantially free of hydrogen sulfide; dioxide. absorbing sulfur dioxide in said ammonia-rich solution 45 11. The process of claim 10 wherein said elemental sul of ammonium thiosulfate in the absence of any sub fur is removed from at least a portion of said sulfur froth stantial quantity of hydrogen sulfide; and by heating said Sulfur froth under superatmospheric pres contacting said second gaseous mixture with said Sure to melt said elemental sulfur, said superatmospheric ammonia-rich solution ofammonium thiosulfate con pressure being sufficient to prevent vaporization of water taining said absorbed sulfur dioxide whereby a hydro 50 from Said aqueous solution at the temperature required gen Sulfide portion of said second gaseous mixture to melt said sulfur, the molten sulfur formed thereby Sepa reacts with Said absorbed ammonia and said absorbed rating into a separate liquid phase from said ammonium Sulfur dioxide to form ammonium thiosulfate in a thiosulfate solution, withdrawing said molten sulfur from Second ammonium thiosulfate solution. said Sulfur phase, and withdrawing said second clarified 2. The process of claim 1 wherein a stoichiometric 55 ammonium thiosulfate solution from said ammonium thio quantity of 0.5 mole of said sulfur dioxide is absorbed in Sulfate solution phase, said withdrawn solution being sub said ammonia-rich solution for each mole of ammonia stantially free of said elemental sulfur. plus hydrogen sulfide reactant, thus obtaining substan 12. A process for converting ammonia and hydrogen tially complete reaction of said hydrogen sulfide and said Sulfide to ammonium thiosulfate and sulfur comprising: ammonia. 60 introducing a feed gas mixture comprising hydrogen 3. The process of claim 1 wherein said reaction with Sulfide and ammonia, the proportion of said am hydrogen sulfide is conducted at a temperature between monia being less than 3.0 moles of ammonia per about 35 C. and about 100° C. mole of hydrogen Sulfide, into an intermediate point 4. The process of claim 1 wherein said hydrogen sul of a first contacting Zone and introducing an aqueous fide is removed from said ammonia-rich solution of am 65 solution of ammonium thiosulfate into the top of said contacting Zone, said ammonium thiosulfate monium thiosulfate by stripping said solution with carbon Solution passing downwardly through said first con dioxide prior to contacting said solution with said sulfur tacting Zone countercurrently to said gaseous mix dioxide. ture flowing upwardly therethrough and absorbing 5. The process of claim 1 wherein said first gaseous O a Substantial portion of said ammonia from said feed mixture has an ammonia content of substantially gaSeous mixture, a substantially ammonia-free un 3.0 moles of ammonia per mole of hydrogen sulfide, the absorbed portion of said feed gas mixture passing product of said reaction with said hydrogen sulfide being overhead from said first contacting zone; essentially ammonium thiosulfate. introducing carbon dioxide into the bottom of said 6. The process of claim 1 wherein an unreacted por 75 first contacting Zone, said carbon dioxide passing 3,431,070 11 12 upwardly therethrough and displacing absorbed hy sulfate solution, said second clarified solution being drogen sulfide therefrom, said substantially hydro substantially free of said solid elemental sulfur; gen sulfide-free ammonium thiosulfate solution con combining said first and said second clarified ammo taining absorbed ammonia being withdrawn from the nium thiosulfate solutions; bottom of said first contacting Zone; cooling said combined first and second clarified am combining said ammonium thiosulfate solution contain 5 monium thiosulfate solution to a temperature be ing absorbed ammonia from said first contacting zone tween about 35 C. and about 100 C.; with substantially ammonia-free recycled ammonium withdrawing a portion of said combined ammonium thiosulfate solution; thiosulfate solution as final product; and introducing said combined ammonium thiosulfate solu 10 recycling a remaining portion of said cooled anno tion to the top of a second contacting zone and intro nium thiosulfate solution, a portion of said recycled ducing sulfur dioxide to the bottom of said second solution passing to the top of said first contacting contacting zone in the proportion of 0.5 mole of zone and a remaining portion of said recycled solu sulfur dioxide per mole of total hydrogen sulfide tion passing to the top of said second contacting Zone plus ammonia reactants in said feed gas mixture, together with said ammonium thiosulfate solution said combined solution passing downwardly through containing said absorbed ammonia from said first said second contacting zone countercurrently to said contacting Zone. sulfur dioxide passing upwardly therethrough, said 13. The process of claim 12 wherein unreacted gases sulfur dioxide being absorbed by said down-flowing passing upwardly through said third contacting zone and solution, and withdrawing said ammonium thio 20 exiting therefrom are separated from said aqueous solu sulfate solution containing said absorbed ammonia tion of ammonium thiosulfate having solid elemental sul and said absorbed sulfur dioxide from said second fur suspended therein, said unreacted gases being with contacting Zone; drawn therefrom. introducing said solution withdrawn from said second 14. The process of claim 13 wherein at least a portion contacting zone into the bottom of a third contact 25 of said withdrawn unreacted gases are recycled to said ing Zone, said solution passing upwardly there third contacting zone. through and introducing said substantially ammonia 15. The process of claim 12 wherein said solid ele free unabsorbed portion of said feed gas mixture mental sulfur is removed from at least a portion of said from said first contacting Zone into at least one point sulfur froth by heating under superatmospheric pressure of said third contacting zone, said unabsorbed gases 30 to melt said solid elemental sulfur, said superatmospheric passing upwardly through said third contacting zone pressure being sufficient to prevent vaporization of water concurrently with said ammonium thiosulfate solu from said aqueous solution at the temperature required tion, said hydrogen sulfide portion thereof reacting to melt said sulfur, the molten sulfur formed thereby sepa with said absorbed ammonia and said absorbed sul rating into a separate liquid phase from said ammonium fur dioxide to form a reaction product comprising 35 thiosulfate solution, withdrawing said molten sulfur from ammonium thiosulfate and solid elemental sulfur, said sulfur phase as a liquid sulfur product and withdraw the temperature of said third reaction zone being ing said second clarified ammonium thiosulfate solution between about 35 C. and about 100 C.; from said ammonium thiosulfate solution phase, said with withdrawing an aqueous solution of ammonium thio drawn solution being substantially free of said molten sulfate having solid elemental sulfur suspended 40 sulfur. therein from an upper level of said third contacting References Cited Zone; UNITED STATES PATENTS removing said solid elemental sulfur from said am monium thiosulfate solution by passing a gas up 1,079,291 11/1913 Field ------? 23-225 wardly through a reservoir of said solution causing 45 1,795, 121 3/1931 Hansen ------23-115 X said solid elemental sulfur to rise to an upper level 1,855,856 4/1932 Hansen ------23-3 X of said reservoir to form a froth of said solid ele 1,957,265 5/1934 Hansen ------23-130 ? mental sulfur in a portion of said ammonium thio 2,219,258 10/1940 Hill ------23-115 sulfate solution, said sulfur froth being withdrawn FOREIGN PATENTS from an upper level of said reservoir, and with 50 drawing a remaining portion of said ammonium thio 947,640 1/1964 Great Britain. sulfate solution as a first clarified ammonium thio OSCAR R. VERTIZ, Primary Examiner. sulfate solution, said withdrawn first clarified soiu EARL C. THOMAS, Assistant Examiner. tion being substantially free of said solid elemental 55 sulfur; removing said solid elemental sulfur from said sulfur lU.S. Cl. X.R. froth to form a second clarified ammonium thio 23-2, 130, 225