Patented July 20, 1937 2,087,325 UNITED STATES PATENT OFFICE 2,087,325 PROCEss FoR THE PRODUCTION of UREA AND AMMONUM SATS Charles K. Lawrence, Syracuse, N. Y., and Her man A. Beekhuis, Jr., Petersburg, Va., assign ors, by mesne assignments, to The Solvay Proc ess Company, New York, N. Y., a corporation of New York Application September 13, 1933, serial No. 689,246 15 Claims, (C. 260-125) This invention relates to a process for the method for the production of valuable am- . production of urea and ammonium salts such monium salts from the unconverted ammonia in as annonium carbonates, ammonium chloride, the urea synthesis effluent which obviates the ammonium nitrate or ammonium sulfate. necessity of recovering both the ammonia and 5 It is known to produce urea by heating am carbon dioxide for re-use in the urea Synthesis monia and carbon dioxide under pressure to process itself and in which the value of the an 5 convert the materials into urea in accordance monium salt compensates for the cost involved with the following equation: in its production. It is furthermore an object 0. of this invention to provide a novel method for This reaction under the conditions employed for the effective elimination of unconverted am O carrying it out does not go to completion so that monia and carbon dioxide from a urea. Synthesis the reaction product recovered from an autoclave effluent and the recovery from the gaseous mix in which Synthesis of urea is carried out contains ture obtained in the treatment of the urea. Syn in addition to the urea and water (the products thesis effluent of ammonia in the form of an am of the above reaction) a considerable proportion gasmonium which salt may and be a readily concentrated and economically carbon dioxide re 5 of ammonia and carbon dioxide which may be turned to the urea Synthesis. present principally in the form of ammonium In carrying out the process of this invention, carbamate or carbonate. It is frequently desir ammonia and carbon dioxide are heated under able, furthermore, to employ in the synthesis of pressure to a temperature promoting the forma urea an excess either of ammonia or of carbon tion of urea. The resulting product is passed 20 dioxide over that corresponding to the stoi in contact with an inert gas such as air to strip chiometric proportions for the formation of urea unconverted ammonia and carbon dioxide from and, in Such a case, the reaction product from the product. The mixture of gases thus ob 25 the urea. Synthesis may contain uncombined am tained is then treated to separate the ammonia, monia or carbon dioxide in addition to am and carbon dioxide from the inert gas. This 25 monium carbamate or carbonate. separation may be accomplished by cooling the One of the major problems in developing a gases to a temperature at which the ammonia commercially satisfactory method for the syn and carbon dioxide combine to form ammonium thesis of urea, from ammonia and carbon dioxide carbonate-carbamate; i. e., a product which may has been the provision of satisfactory methods consist principally of normal ammonium car 30 for recovering the unconverted ammonia and car bonate, ammonium bicarbonate or of ammonium bon dioxide from the effluent of the urea, auto carbamate, together with more or less of the clave. Heretofore it has been proposed to heat other named compounds, the exact composition 35 the effluent to drive out the unconverted am of the product depending upon the ratio of am monia and carbon dioxide and return these ma monia and carbon dioxide in the cooled gas and 35 terials to the autoclave for the production of the proportion of water combined with the am further quantities of urea. In one process, the monia and carbon dioxide. This cooling of the ammonia and carbon dioxide distilled from the gases to form ammonium carbonate-carbamate 40 autoclave effluent are directly compressed with may be accomplished by passing the gases in out separation for return to the autoclave. This contact with a solution of ammonium carbonate, 40 compression, however must be carried out at Or the gases may be passed in contact with a high temperatures to avoid the formation of solution of an ammonium salt such as am Solid ammonium carbamate, which high tem monium nitrate, ammonium sulfate, and the 45 perature compression involves mechanical dif like, to, form a solution of ammonium carbonate. ficulties and low efficiencies of the compression It is apparent that in order to accomplish this 45 step. It has also been proposed to separate the separation of the ammonium carbonate-car ammonia from the carbon dioxide as, for ex bamate or ammonium carbonate from the inert ample, by selective absorption of the ammonia, gas, the inert gas used is one which, like air, is 50. and then recovering the gases separately and not condensed at temperatures at which the separately recompressing them and returning gaseous ammonia, and carbon dioxide combine 50 them to the urea Synthesis autoclave. Such a to form solid ammonium carbonate-carbamate mode of operation, however, is costly and adds Or, in the presence of Water, a solution of am- : appreciably to the cost of the urea synthesis. monium carbonate. The Solution of ammonium 55 It is an object of this invention to provide a carbonate, or the ammonium carbamate-car 55 2 .. a,087,825 bonate solid obtained as described, is treated top of a stripper 4, where it is passed in direct with an acid such as nitric acid, sulfuric acid, contact with air which is introduced into the phosphoric acid, or the like, to form an aim bottom of stripper 4. Stripper 4 is operated at monium salt and to liberate a concentrated car a pressure materially below that of autoclave 3; bon dioxide gas, which may be returned to the for example, a pressure of a few pounds gauge, urea synthesis step. and as the effluent from the autoclave at an ele Instead of treating with an acid a solution wated temperature is introduced into the stripper of ammonium carbonate obtained as described at the lower pressures, ammonia and carbon di oxide are evolved from the melt. The liquor or above, or prepared by dissolving the solid am 0. O monium carbamate-carbonate recovered from melt in the top of the stripper may have a tem the gases in water, a salt such as sodium chlor perature of, for example 100° C., which is below ride, sodium nitrate or sodium sulfate may be the boiling point of the liquor. The air intro dissolved in the solution and it is then carbon duced into the stripper may be preheated or the ated by absorbing carbon dioxide in it to pre stripper may contain heating coils whereby the 5 cipitate sodium bicarbonate. The sodium bicar heatrequired for the evolution of the uncon bonate may be filtered from the Solution COn verted carbon dioxide and ammonia in addition taining ammonium chloride, ammonium nitrate to the heat already contained in the autoclave or ammonium sulfate and heated to evolve a effluent may be supplied. Also, steam may be concentrated carbon dioxide gas and form the introduced with the air entering the bottom of . 20 normal sodium carbonate. In case the am the stripper to Supply a desired amount of heat. 20 monium carbonate solution in which the Sodium If desired, this steam may be introduced into salt is dissolved originally contains ammonium the stripper at an intermediate point instead of bicarbonate, the carbonating of the Solution ob into the bottom of the stripper. tained after dissolving the sodium salt may be A solution of urea substantially free from am 25 Omitted or materially curtailed. monia and carbon dioxide foWS off from the bot 2 5 Ammonium Sulfate may also be prepared in tom of stripper 4 and may be treated in any accordance with this invention by mixing the desired manner for the recovery of the urea. A ammonium carbonate solution obtained as de gaseous mixture of air, ammonia and carbon di scribed above with finely divided calcium Sulfate, oxide is drawn off from the top of the stripper 30 whereby calcium carbonate is precipitated and and conducted to a cooler or absorber 5 while 30 a Solution of ammonium sulfate formed. After maintaining the gases at a temperature of, for separation of the calcium carbonate from the example, 75°C., which is above the temperature solution the ammonium sulfate may be recovered at which the ammonia and carbon dioxide would by concentrating and crystallizing the ammo combine to precipitate a Solid ammonium car 35 nium sulfate from the Solution. The calcium bamate-carbonate in the pipes leading from the 3. 5 carbonate may then be decomposed with an acid, Stripper to the absorber. Absorber 5 contains an for example, nitric acid, to recover the carbon aqueous solution of ammonium carbonate which dioxide. is maintained at a temperature of about 40 C. The process of this invention further comprises This temperature regulation may be accom 40 the modifications of processes described above plished by circulating cooling water through coils 40 which involve the direct absorption of the ammo submerged in the ammonium carbonate Solution. nia and carbon dioxide in the gases obtained by The ammonia, and carbon dioxide are absorbed distilling the effluent from a urea, Synthesis auto in the ammonium carbonate Solution and water clave in Solutions of Sodium Salts such as Sodium is continuously added at a rate sufficient to Sup chloride, Sodium nitrate or sodium sulfate, or a ply the desired proportion of Water for combi 45 Suspension of Calcium sulfate whereby ammo nation with the ammonia, and carbon dioxide to nium chloride, ammonium nitrate.or ammonium form ammonium carbonate and to give a solution Sulfate is directly formed in the solution. Such of a desired composition. The air separated from a procedure simplifies the production of these the ammonia, and carbon dioxide may be returned ammonium Salts by not requiring a separate from absorber 5 for reuse in stripper 4. 50 treatment of the ammonia, and carbon dioxide The ammonium carbonate solution is passed gas for the intermediate production of an ammo from absorber 5 into a carbonating column 6 nium carbonate Solution. into which Sodium chloride is introduced and In the accompanying drawings, Fig. 1 shows dissolved in the ammonium carbonate Solution 55 diagrammatically a process for the production and carbon dioxide' is passed in contact With the 55 of urea, and of ammonium chloride, and Fig. 2 resulting solution to precipitate Sodium bicar a process for the production of urea and ammo bonate. The slurry of sodium bicarbonate and nium nitrate, which are illustrative of this inven solution containing ammonium chloride is passed tion, to a filter for renoval of the Sodium bicar 60 Referring to Fig. 1 of the drawings, ammonia, bonate, and this is heated in a kiln 8 to evolve gas is compressed and liquefied in an ammonia, carbon dioxide and to form soda, ash (sodium. liquefying System and carbon dioxide is com carbonate). The carbon dioxide evolved in kiln pressed and liquefied in a carbon dioxide lique 8 may be returned to liquefying System 2 and fying System 2. The liquid ammonia and liquid thence to the urea, synthesis or may in part be 65 carbon dioxide in the proportions of about 2 mols returned to carbonating column 6 for treatment 65 of ammonia, for every 1 mol. of carbon dioxide of further quantities of ammonium carbonate are continuously passed into an autoclave 3 in Sodium chloride solutions. If desired, a relative which the reaction mixture is heated at a tem ly dilute carbon dioxide gas may be employed for perature of about 150° to 200°.C. while main the treatment of the liquor in carbonating col 70 taining it under a pressure of 100 to 300 atmos umn 6, and the carbon dioxide thus absorbed pheres. The ammonia and carbon dioxide react recovered as a concentrated gas from kiln 8. The to form urea and a product containing this ma Solution containing ammonium chloride sepa terial, together with water and unconverted am rated from the Sodium bicarbonate in filter monia, and carbon dioxide, is continuously with may be passed to an evaporator 9 where the solu 5 drawn from the autoclave and passed into the tion is concentrated. Solid ammonium chloride 2,087,825 3 may be recovered from the concentrated solution. be recovered from the resulting solution by cool Other ammonium salts such as ammonium ni ing. trate or ammonium sulfate may be obtained by Fig. 2 illustrates a process for the production dissolving the corresponding sodium salt in the of ammonium nitrate in accordance with this in ammonium carbonate solution introduced into vention. In this process an ammonia liquefying carbonating column 6 in the process above de System O, carbon dioxide liquefying system , Scribed. It is also possible to omit the carbonat urea autoclave 2, and stripper 3 are operated as ing of the solution by forming in absorber 5 a. in carrying out the process of Fig. 1 described Solution of ammonium bicarbonate. This may above. The gases from stripper 3 are passed O be accomplished by introducing into the absorber into an absorber 4 where they are treated with O carbon dioxide in desired proportion in addition an aqueous solution of ammonium nitrate con to the carbon dioxide obtained in the gases com taining about 50% NH4NO3 maintained at a ing from stripper 4, or by employing in the urea temperature of about 50° C. The ammonium ni Synthesis an excess of carbon dioxide over the trate solution cools the gases from stripper 3 and 5 proportions of 2NH3 to 1CO2 so that the gases absorbs the ammonia and carbon dioxide. The from stripper 4 contain ammonia and carbon Solution is treated until it is substantially satu dioxide in the ratio of 1NH3 to 10O2. rated with ammonium carbamate-carbonate. Instead of treating the ammonium carbonate The resulting solution is withdrawn to a neutral solution from absorber 5 in the manner described izing vessel 5, where it is treated with 40% ni 20 above, this solution containing about 30% tric acid to form ammonium nitrate and evolve (NH4)2CO3 at about 40° C. may be agitated with a concentrated carbon dioxide gas, which is re finely divided gypsum (CaSO4.2H2O) in the pro turned to liquefying system f. The ammonium portions of about 100 parts of the ammonium nitrate solution, which may be neutral or slightly carbonate solution to about 53 parts of the gyp acid, is then evaporated in an evaporator 6 to 25 sum. The ammonium carbonate and calcium obtain a concentrated solution from which solid sulfate react to form ammonium sulfate and cal ammonium nitrate may be recovered by cooling cium carbonate. The calcium carbonate is fill or the solution may be evaporated under a re tered from the solution of ammonium sulfate and duced pressure to crystallization in evaporator 6 the Solution evaporated and ammonium sulfate and the crystals recovered by filtration. A por 30 Crystallized out. The calcium carbonate may tion of the Solution from neutralizing vessel f S then be reacted with nitric acid to obtain calcium may be returned to absorber 4 for recovery of nitrate with the evolution of carbon dioxide gas ammonia, and carbon dioxide from the gases which is returned to the urea, synthesis. passed through the absorber. The process of Fig. If desired, the gases containing ammonia and 2 may be operated continuously, if desired. If Carbon dioxide from stripper 4 may be passed di desired, the neutralization of the ammonium : rectly into a suspension of finely divided gypsum carbamate-carbonate solution formed in absorber in water to form ammonium carbonate and am 4 may be accomplished by introducing the acid monium sulfate. Either natural gypsum or a by into the solution in the absorber itself, in which product gypsum such as is obtained by treating case the absorption of the ammonia, and carbon 40 phosphate rock with nitric acid and precipitat dioxide may be continuously carried out by em 40 ing the calcium by addition of ammonium sul ploying duplicate absorption vessels 4 and while fate, may be utilized for the production of the One is serving for the treatment of the gases ammonium sulfate. Other ammonium salts such from the stripper, the solution in the other is as ammonium nitrate or ammonium chloride may treated with acid. also be obtained by treating the corresponding The process of this invention presents, numer 45 calcium salt (calcium nitrate or calcium chloride) Ous practical advantages over the methods here with the ammonium carbonate solution to pre tofore employed for the recovery of unconverted cipitate calcium carbonate and leave a solution ammonia and carbon dioxide from urea synthe of ammonium nitrate or ammonium chloride. It sis effluents. The expenses involved in the treat 50 is also Sometimes advantageous, where an am ment of the gases from the effluent are compen monium salt is to be formed from a sodium salt, Sated for by the valuable ammonium salts ob to directly absorb the ammonia and carbon diox tained. Furthermore, the urea synthesis itself ide in the sodium salt solution, for example sodi may be operated under conditions most favorable um chloride solution, and then to carbonate the with respect to the cost of production of the urea, resulting Solution to precipitate out sodium bi and With respect to the plant construction and carbonate. Operating conditions, without being limited by Instead of treating the ammonium carbonate the requirements with respect to completeness of solution from absorber 5 for the conversion of . the reaction imposed by the processes heretofore the ammonium carbonate into ammonium sul required for recovery of unconverted ammonia, 60 fate, ammonium nitrate or ammonium chloride, and carbon dioxide. For example, a considerable 60 ammonium carbonate itself may be recovered as excess of ammonia may be employed in the urea a solid from this solution. For example, the am synthesis step itself with the attendant advan monium carbonate solution at 40° C. from ab tages derivable therefrom, and this ammonia eco sorber 5 may be cooled to 25° C. to crystallize nomically recovered as a valuable ammonia salt 65 ammonium carbonate therefrom. The crystal product. A further advantage of the process of line ammonium carbonate is separated from the this invention which uses an inert gas such as mother liquor and the latter returned to absorber air for stripping the unconverted ammonia and 5 for the treatment of further quantities of gas carbon dioxide from urea synthesis melts, is with from stripper 4. Ammonium bicarbonate may respect to the completeness of recovery of these be obtained by introducing additional CO2 into materials from the melt. While the hot product the gas mixture coming from stripper 4 so that leaving the urea synthesis autoclave, upon reduc the gas contains about 1 mol. ammonia to 1 mol. tion of the pressure, will evolve a considerable carbon dioxide. This gas is then passed in Con proportion of the ammonia, and carbon dioxide, tact with an ammonium bicarbonate solution at the complete stripping of the melt by means 75 about 25° C. and solid ammonium carbonate may of heat alone involves a Supply of considerable 75 4. 2,087,825. quantities of heat at elevated temperatures. and introducing an acid into the solution to These elevated temperatures promote a decomr form the corresponding ammonium salt and position of the urea and are thus inimical to the evolve concentrated carbon dioxide gas. recovery from the autoclave effluent of all of its 4. The process for the production of urea and urea content. By employing an inert gas in the an ammonium salt which comprises heating am 5 stripping operation, heat at lower temperatures, monia and carbon dioxide at a urea-forming which are below the boiling point of the melt it temperature, and pressure, passing the resulting self may be utilized. This is not only economical product containing urea, ammonia and carbon but has the advantage of decreasing the losses, dioxide in contact with an inert gas substan due to decomposition of urea in the melt. and at tially free from ammonia and carbon dioxide at 0. the same time, the melt may be substantially con a temperature, below the boiling point of said pletely freed of uncombined ammonia and carbon product, at which the gas strips from the prod dioxide. uct annonia and carbon dioxide while main We claim: taining the resulting mixture of gases at a tem 1. The process for the production of urea and perature at which the ammonia and carbon 15 an ammonium salt which comprises heating am dioxide remain in the gaseous phase, said inert monia and carbon dioxide at a urea-forming gas being one which is not condensed at tem temperature and pressure, passing the resulting peratures at which gaseous ammonia and carbon product containing urea, ammonia and carbon dioxide combine to form ammonium carbonate dioxide in contact with an inert gas substan carbamate, cooling said mixture of gases to a 20 tially free from ammonia and carbon dioxide at temperature at which the ammonia and carbon a temperature, below the boiling point of Said dioxide combine to form ammonium carbonate product, at which the gas strips from the prod carbamate, separating said ammonium carbo uct ammonia and carbon dioxide, said inert gas nate-carbamate from said inert gas, and treat being one which is not condensed at tempera ing the thus separated carbonate-carbamate 25 tures at which gaseous ammonia and carbon With an acid to convert it into an ammonium dioxide combine to form ammonium carbonate Salt and carbon dioxide gas. carbamate, cooling the resulting gaseous mix 5. The process for the production of urea and an annonium salt which comprises heating am ture containing ammonia, and carbon dioxide to monia, and carbon dioxide at a urea-forming 30 recover an amnonium carbanate-carbonate temperature and pressure, passing the resulting material therefrom, separating Said Carbamate product containing urea, ammonia and carbon carbonate material from the inert gas and dioxide in contact with an inert gas substan treating the thus separated material to form an tially free from ammonia and carbon dioxide ammonium salt and carbon dioxide gas there 35 5 from. at a temperature, below the boiling point of said 2. The process for the production of urea, and product, at which the gas strips from the prod an ammonium salt which comprises heating an uct ammonia and carbon dioxide, said inert gas monia, and carbon dioxide at a urea-forming being one which is not condensed at tempera tures at which gaseous ammonia, and carbon temperature and pressure, passing the resulting 40 40 product containing urea, ammonia, and carbon dioxide combine to form ammonium carbonate dioxide in contact with an inert gas substan carbamate, passing the gaseous mixture contain tially free from ammonia, and carbon dioxide at ing ammonia and carbon dioxide in contact with a temperature, below the boiling point of said an aqueous solution of an ammonium salt at a product, at which the gas strips from the prod temperature at which the ammonia and carbon uct ammonia and carbon dioxide, said inert gas dioxide combine to form ammonium carbonate, 45 being one which is not condensed at tempera Separating the resulting solution of ammonium tures at which gaseous ammonia and carbon carbonate from the inert gas and introducing dioxide combine to form ammonium carbonate an acid into the solution containing ammonium carbamate, passing the resulting mixture of carbonate to form the corresponding ammonium gases in contact with an aqueous liquor at a Salt and to evolve concentrated carbon dioxide 50 gaS. temperature at Which the ammonia, and carbon 6. The process for the production of urea and dioxide are absorbed in the liquor, separating ammonium nitrate which comprises heating am the resulting Solution from Said inert gas, treat monia and carbon dioxide at a urea-forming ing the solution to convert its ammonia content 55 5 5 into an ammonium salt and recover carbon diox temperature and pressure, passing the resulting ide as a gas, and reacting the recovered carbon product containing urea, ammonia and carbon dioxide with ammonia to form urea. dioxide in contact with air at a temperature, 3. The process for the production of urea, and below the boiling point of said product, at which the air strips unconverted ammonia and carbon an ammonium salt which comprises heating am 60 60 monia and carbon dioxide at a urea-forming dioxide from the product while maintaining the temperature and pressure, passing the resulting resulting mixture of air, ammonia and carbon product containing urea, ammonia and carbon dioxide at a temperature above that at which the ammonia and carbon dioxide combine to dioxide in contact with an inert gas substan form ammonium carbonate, passing the result tially free from ammonia, and carbon dioxide at 65 65 a temperature, below the boiling point of said ing gases in contact with an aqueous solution product, at which the gas strips from the prod of ammonium nitrate at a temperature at which uct ammonda, and carbon dioxide, said inert gas the ammonia and carbon dioxide combine to being One which is not condensed at tempera form ammonium carbonate, separating the re tures at Which gaseous ammonia and carbon Sulting Solution from the air, neutralizing the dioxide combine to form ammonium carbonate solution containing ammonium carbonate with 70 carbamate, passing the resulting gaseous mix nitric acid and reacting the carbon dioxide ture containing ammonia and carbon dioxide in evolved from the solution with additional am contact with an aqueous liquor to absorb am monia for the production of urea therefrom. 7. The process for the production of urea, and monia and carbon dioxide from said gases, sep 75 75 arating the resulting Solution from the inert gas an ammonium Salt which comprises heating ann 2,087,825 5 monia, and carbon dioxide at a urea-forming temperature and pressure, passing the resulting temperature and pressure, passing the resulting product containing urea, ammonia and carbon product containing urea, ammonia and carbon dioxide at a pressure of a few pounds gauge in dioxide in contact with an inert gas substantially contact with air at a temperature, below the boil free from ammonia, and carbon dioxide at a tem ing point of said product at which the air strips perature, below the boiling point of said product, therefrom ammonia, and carbon dioxide, main at which the gas strips from the product am taining the resulting mixture of gases while in monia and carbon dioxide, said inert gas being contact with said product and Subsequent thereto one which is not condensed at temperatures at 10 at a temperature at which the ammonia and car which gaseous ammonia, and carbon dioxide COm bon dioxide remain in the gaseous phase, cool 10 bine to form ammonium carbonate-carbamate, ing Said mixture of gases after removal from said inert gas being one which is not condensed contact with said product to a temperature at at temperatures at which gaseous ammonia and which the ammonia, and carbon dioxide combine carbon dioxide combine to form ammonium car 5 to form ammonium carbonate-carbamate, sepa bonate-carbamate, cooling the resulting mixture rating the ammonium carbonate-carbamate 15 of gases in contact with a solution of ammonium from the air and treating said ammonium car carbamate-carbonate to absorb ammonia and carbon dioxide from the gases, separating the re bonate-carbamate to form an ammonium salt sulting solution from the inert gas and reacting and concentrated carbon dioxide gas therefrom. 20 11. The process for the production of urea and the resulting solution with finely divided calcium an ammonium salt which comprises heating am 20 sulfate to form ammonium sulfate and calcium monia and carbon dioxide at a urea-forming carbonate. temperature and pressure, passing the resulting 8. The process for the production of urea. So dium bicarbonate and ammonium chloride which melt containing urea, ammonia and carbon di comprises heating ammonia, and carbon dioxide oxide at a pressure of a few pounds gauge in in the proportions of about 2 mois of ammonia contact with a stream of air which is continuous 25 for every 1 mol. of carbon dioxide at a urea-form ly recycled in a gas circulatory system in which ing temperature and pressure, passing the re the melt is treated with the air at a temperature, sulting product containing urea, ammonia and below the boiling point of the melt, at which the 30 air strips therefrom ammonia, and carbon dioxide carbon dioxide in contact with air at a tempera and the resulting mixture of gases is Subsequent 30 ture, below the boiling point of said product, at ly cooled to a temperature at which the ammonia, which the air strips unconverted ammonia and and carbon dioxide combine to form an ammo carbon dioxide from the product while maintain nium carbonate-carbamate material, removing ing the resulting mixture of air, ammonia and said material from contact with the air in said 35 carbon dioxide at a temperature above that at circulatory system, and then treating the ann which the ammonia and carbon dioxide combine monium carbonate-carbamate material to form to form ammonium carbonate, passing the re an ammonium salt and concentrated carbon di sulting gases in contact with an aqueous solution Oxide gas therefrom. of ammonium carbonate at a temperature at 12. The process for the production of urea and 40 which the ammonia, and carbon dioxide combine an ammonium salt which comprises heating ann 40 to form a carbonate of ammonia and reacting monia and carbon dioxide at a urea-forming the carbonate of ammonia, with sodium chloride temperature and pressure, passing the resulting to form sodium bicarbonate and ammonium product containing urea, ammonia, and carbon chloride. dioxide at a pressure of a few pounds gauge in 45 9. The process for the production of urea, So contact with a stream of an inert gas which is 45 dium bicarbonate and ammonium chloride which continuously recycled in a gas circulatory SyS comprises heating ammonia and carbon dioxide tem in which the melt is treated with the inert in the proportions of about 2 mols of ammonia gas at a temperature, below the boiling point for every 1 mol. of carbon dioxide at a urea-form of the melt, at which the gas strips therefrom 50 ing temperature and pressure, passing the re ammonia and carbon dioxide and the resulting 50 sulting product containing urea, ammonia, and mixture of gases is subsequently cooled to a tem carbon dioxide in contact with air at a tempera perature at which the ammonia and carbon di ture, below the boiling point of said product, at oxide combine to form an ammonium carbonate which the air strips unconverted ammonia and carbamate material, removing said material from 55 carbon dioxide from the product while maintain contact with the inert gas in Said circulatory 55 ing the resulting mixture of air, ammonia and system, and then treating the ammonium car carbon dioxide at a temperature above that at bonate-carbamate material to form an ammo which the ammonia, and carbon dioxide Combine nium salt and concentrated carbon dioxide gas to form ammonium carbonate, passing the re therefron. 80 sulting gases in contact with an aqueous Solution 13. The process for the production of urea and 60 of ammonium carbonate at a temperature at an ammonium salt which comprises heating am which the ammonia, and carbon dioxide combine monia, and carbon dioxide at a urea-forming tem to form a carbonate of ammonia, dissolving sodi perature and pressure, passing the resulting prod um chloride in the solution of carbonate of am uct containing urea, ammonia and carbon di 65 monia, thus prepared and carbonating the solu oxide at a pressure of a few pounds gauge in 65 tion to precipitate sodium bicarbonate therefron, contact with a stream of an inert gas which is separating the precipitated sodium bicarbonate continuously recycled in a gas circulatory System from the solution containing ammonium chloride, in which the melt is treated with the inert gas heating the sodium bicarbonate to evolve carbon at a temperature, below the boiling point of the 70 dioxide gas therefrom and reacting the carbon melt, at which the gas strips therefrom ammonia. 70 dioxide thus obtained with ammonia for the pro and carbon dioxide and the resulting mixture of duction of urea, therefrom. gases is subsequently passed in contact with an 10. The process for the production of urea and aqueous liquor to absorb ammonia, and carbon an ammonium salt which comprises heating an dioxide from said gases, separating the resulting 75 monia and carbon dioxide, at a urea-forming solution from the inert gas and introducing an 6 2,087,325 acid into the solution to form the corresponding temperature, passing the resulting product COs ammonium salt and evolve concentrated carbon taining urea, ammonia and carbon dioxide in dioxide gas. contact with an inert gas substantially free from 14. The process for the production of urea and ammonia and carbon dioxide at a temperature, an ammonium salt which comprises heating am below the boiling point of said product, at which monia and carbon dioxide at a urea-forming tem the gas strips from the product ammonia and perature, passing the resulting product contain carbon dioxide, said inert gas being one which ing urea, ammonia, and carbon dioxide in contact is not condensed at temperatures at which gase with an inert gas substantially free from am OuS ammonia, and carbon dioxide combine to monia and carbon dioxide at a temperature, be form ammonium carbonate-carbamate, passing O 10 low the boiling point of said product, at which the resulting mixture of gases in contact with an the gas strips from the product ammonia and aqueous liquor at a temperature at which both carbon dioxide, said inert gas being one which is the annonia and carbon dioxide are absorbed in not condensed at temperatures at which gaseous the liquor to form an ammonium carbamate-car ammonia, and carbon dioxide combine to form bonate material, separating the resulting solu 5 5 ammonium carbonate-carbamate, and cooling tion from the inert gas and treating the thus the resulting gaseous mixture containing am Separated solution to convert its ammonia con monia and carbon dioxide to recover an ammo tent into an ammonium salt of the group consist nium carbamate-carbonate material therefrom. ing of ammonium sulfate, ammonium nitrate, 15 The process for the production of urea and ammonium chloride and ammonium phosphate. 20 an ammonium salt which comprises heating am CHARLES K, LAWRENCE. monia, and carbon dioxide at a urea-forming HERMAN A. BEEKHUIS, JR.