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May 5, 1936. R. B. Ma. CMUN 2,039,653 MANUFACTURE OF THE OXIDE AND THE CHLORIDE OF Filed May 16, 1932

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AORNEYs Patented May 5, 1936 2,039,653

UNITED STATES PATENT OFFICE 2,039,653 MANUFACTURE OF THE OXDE AND THE CHLORIDE OF MAGNESHUM Robert Burns MacMullin, Niagara Falls, N. Y., assignor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia Application May 16, 1932, Serial No. 611,576 4 Claims. (CI. 23-91) This invention relates to improvements in the vaporized annonium chloride over the calcined manufacture of magnesium chloride from dolo dolomite while maintaining the latter at a tem mite and chloride. The complete perature of 300-500° C. in an appropriate retort. process of the invention comprises calcination of An inert gas, nitrogen from the carbonating dolomite to produce a mixture of magnesium and towers used in the ammonia Soda, process for 5 oxides, treatment of this mixture with example, may be passed through the retort to ammonium chloride at elevated temperature to aSSist in carrying out the ammonia and steam and produce a mixture of magnesium and calcium in bringing the reaction substantially to con chlorides, differential conversion of this mixture pletion. The ammonia, so liberated may be re 0 to produce a mixture of magnesium oxide and cal turned to the ammonia, soda, process. The mix 0 cium chloride and treatment of this mixture with ture of magnesium and calcium chlorides thus in the presence of water to pre produced is subjected to a differential conversion cipitate calcium and to produce a solu to convert the magnesium chloride to magnesium tion of magnesium chloride. The invention in oxide without conversion of the calcium chloride. cludes the complete process, improvements in sev This reaction may be effected in the same retort 5 eral of the steps combined in the complete proc in which the oxide mixture was converted to the eSS and certain novel combinations of these stepS. chloride mixture. This differential conversion In Some forms in which the ammonia, Soda, may be effected by passing free oxygen, air Or process is practiced, solid ammonium chloride is other gas mixture including free oxygen through obtained as a by-product. The ammonia Con the retort while maintaining a temperature of 20 tent of this ammonium chloride may be recovered, 400-700° C. in the retort. The reaction may be for re-use in the ammonia, Soda process for ex illustrated as follows: ample, by treatment with lime or magnesia. Calcined dolomite may be used for this treatment, but when used mixtures of magnesium and cal The chlorine evolved may be recovered in any cium chlorides are produced. No practical appropriate manner. This differential conver method for the Separation of the magnesium and sion may also be effected by passing water vapor calcium contents of such mixtures has hitherto or gas mixtures including the same through the been developed. This invention provides an im retort while maintaining a temperature of 400 proved method for producing magnesium chloride 650° C. in the retort. The reaction may be illus 30 Substantially free from calcium compounds from trated as follows: dolonite With annonium chloride which, in con junction with the ammonia, Soda process, affords an advantageous method of recovery of the am The hydrochloric acid evolved may be recovered 3. 5 monia content of the ammonium chloride. in any appropriate manner. The differential In carrying out the complete process of the conversion may also be effected, in this manner, present invention: Dolomite, containing approxi with mixtures of free oxygen or a gas mixture mately equal molecular proportions of magnesium including free oxygen and water vapor to produce carbonate and , is calcined to mixtures of chlorine and hydrochloric acid in pro 40 expel the carbon dioxide, at a temperature ap portions varying in accordance with the propor 40 proximately 1000° C. for example. The calcined tion of free oxygen and water vapor used. The dolomite, a mixture of magnesium and calcium mixture of magnesium oxide and calcium chloride oxides, is subjected to the action of an approxi thus produced is subjected to the action of car mately equivalent amount of ammonium chloride bon dioxide in the presence of water to precipi at a temperature approximating. 300-550° C. to tate calcium carbonate and to form an aqueous liberate ammonia. The reaction may be illus Solution of magnesium chloride. The precipi trated as follows: tated calcium carbonate is separated from the magnesium chloride solution, by filtration for ex ample. This magnesium chloride solution from Which the calcium carbonate has been Separated This reaction may be effected either by mixing may contain Small amounts of magnesium bicar the calcined dolomite with the ammonium chlo bonate and traces of calcium . These ride, dry, at a temperature below 300° C. and are precipitated as the correspond thereafter heating the mixture to 300-500° C. ing by heating the solution to the boil 55 in an appropriate retort or by passing previously ing temperature to expel carbon dioxide and the 55 2,039,658 precipitated carbonates are separated from the both illustrated as carried out in the "retort', the solution, by filtration for example. The sep first of these operations being designated "a" arated magnesium and calcium carbonates are and the Second being designated "b'. - With advantage returned to the reaction in which The invention includes improvements in the the mixture of magnesium oxide and calcium manufacture of magnesium chloride from dolo chloride is converted to magnesium chloride and mite and ammonium chloride. The invention calcium carbonate. Following the separation of also includes improvements in the separation these carbonates, the magnesium chloride may be of the magnesium and calcium contents of mix recovered from the solution in any appropriate tures of magnesium and calcium chlorides, im O manner, by evaporation and crystallization for . . provements in the separation of the magnesium 10 example. The calcium carbonate initially sep and calcium contents of mixtures of magnesium a rated from the Inagnesium chloride Solution pro oxide and calcium chloride, improvements in the duced by conversion of the mixture of magnesium production of magnesium chloride from mixtures oxide and calcium chloride may be washed free of magnesium and calcium chlorides, improve from magnesium compounds and calcined to pro ments in the production of chlorine and ammonia duce a lime of high purity, useful for example in from ammonium chloride, improvements in the the ammonia soda process or in the causticiza recovery of ammonia from ammonium chloride, tion of sodium carbonate. - and improvements in the production of mixtures. In the differential conversion of the magnesium of magnesium oxide and calcium chloride from chloride content of the magnesium chloride-cal dolomite. cium chloride mixture produced by treatment of I claim: . . the mixed oxides with ammonium chloride, the 1. In the production of magnesium chloride temperature should be limited not to exceed about from mixtures of magnesium and calcium chlo 700° C., or better 650° C., to avoid conversion of rides, the improvement which comprises subject the calcium chloride present to . ing the mixture to the action of a reagent selected It is further advantageous to limit this tempera from the group consisting of free oxygen, water ture not to exceed about 620 C. since. above this vapor and gas mixtures including the same at temperature a eutectic tends to form and melt, a temperature of 400-700° C., and subjecting the substantial proportions of both magnesium chlo resulting mixture of magnesium oxide-calcium ride and calcium chloride being present, and thus chloride to the action of carbon dioxide in the : to interfere with the operation. presence of water and separating the precipi It is possible to effect some separation of cal tated calcium carbonate from the Solution of cium chloride and magnesium oxide, from the magnesium chloride thus produced. mixture produced by differential conversion of 2. In the production of magnesium chloride the chloride mixture, by treating the mixture from dolomite and annonium chloride, the in with water to dissolve the calcium chloride and provement which comprises calcining the dolor to leave the magnesium oxide, but the formation mite, subjecting the resulting mixture of mag of insoluble basic magnesium chlorides interferes nesium and calcium oxides to the action of am with this operation. Magnesium chloride, more monium chloride at a temperature of 300-550° C., 40 over, is not obtained as a direct product of this subjecting the resulting mixture of magnesium : operation. By subjecting the magnesium oxide and calcium chlorides to the action of a reagent calcium chloride mixture to the action of carbon selected from the group consisting of free oxygen, dioxide in the presence of water, the formation water vapor and gas mixtures including the same of basic magnesium chlorides is avoided or any at a temperature of 400-700° C., subjecting the formed are decomposed and the magnesium Con resulting mixture of magnesium oxide and cal 4 5 tent of the mixture is converted substantially cium chloride to the action of Carbon dioxide in completely to magnesium chloride. the presence of water and separating the precipi In the conversion of the magnesium oxide tated calcium carbonate from the Solution of calcium chloride mixture to magnesium chloride magnesium chloride thus produced. and calcium carbonate, the amount of water is 3. In the production of mixtures of magnesium advantageously limited to obtain a concentrated Oxide and calcium chloride from dolomite, the solution containing as much as 15-20% of mag improvement which comprises calcining the dolo nesium chloride or more. However, if the amount mite, subjecting the resulting mixture of mag of water used is too limited the slurries produced nesium and calcium oxides to the action of am become difficult to handle. The carbon dioxide monium chloride at a temperature of 300-550°C., 5 used in this conversion may be supplied in high . and subjecting the resulting mixture of mag concentration or in the form of a gas mixture nesium and calcium chlorides to the action of containing a relatively small proportion of car a reagent selected from the group consisting of bon dioxide. Flue gases containing upwards of free oxygen, water vapor and gas mixtures in 12% CO2, for example, are useful in this connec cluding the same at a temperature of 400-700° C. (3 tion. The carbon dioxide expelled in the precipi 4. In the recovery of ammonia and chlorine tation of magnesium and calcium bicarbonates as from ammonium chloride, the improvement carbonates may be recovered and used in the which comprises subjecting ammonium chloride operation. - to the action of a mixture of magnesium and The accompanying drawing illustrates, as a calcium oxides at a temperature of 300-550° C., flow sheet, one embodiment of the combined op and subjecting the resulting mixture of magne eration of the invention. The conversion of the sium and calcium chlorides to the action of a oxide mixture to the chloride mixture With am reagent selected from the group consisting of monium chloride and the subsequent differential free OXygen, Water vapor and gas mixtures in conversion of the chloride mixture to a mixture cluding the same at a temperature of 400-700° C. O of magnesium oxide and calcium chloride are ROBERT BURNS MACMULLIN.