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Cqmcogw MOQIQE Sept. 29, 1970 H. FURKERT 3,531,240 PROCESS FOR THE PRODUCTION OF SODIUM BICARBONATE AND SODA ASH Filed Feb. 13, 1968 wow NIO MOQIQEcQmcmogW 5.93%@812| EouBEqloz //////V///// mvmrron m: BERT run mu m! Z é, - {a _ ATTORNEY 3,531,240 United States Patent O ' C6 Patented Sept. 29, 1970 1 2 equivalent to the sodium hydroxide solution. This proc 3,531,240 ess is restricted to a combination with an ammonia soda PROCESS FOR THE PRODUCTION OF SODIUM ash process because the considerable amount of sodium BICARBONATE AND SODA ASH Herbert Furkert, Starenweg, Germany, assignor to Che bicarbonate required is generally available only in a soda miebau Dr. A. Zieren GmbH '& Co., KG, Cologne, ash plant. Braunsteld, Germany Filed Feb. 13, 1968, Ser. No. 705,192 SUMMARY OF THE INVENTION Claims priority, application Germany, Feb. 24, 1967, It is therefore an object of the present invention to C 41,606 avoid the above-mentioned disadvantages of the direct Int. Cl. C01d 7/00, 7/12 10 soda precipitation by producing soda ash from sodium US. Cl. 23-63 10 Claims amalgam, carbon dioxide and Water. The production of chlorine by electrolysis in a mer ABSTRACT OF THE DISCLOSURE cury cathode type of alkali chlorine cell has achieved increased economic importance without any correspond A process for the preparation of sodium carbonate ing increase in utility of the sodium hydroxide made comprising: (a) reacting sodium amalgam produced by available thereby. It has therefore become a practice to mercury cathode cells of the chlorine process with an convert the sodium hydroxide solution into soda ash, aqueous sodium bicarbonate solution to form a solution which is more readily sold than the sodium hydroxide containing sodium carbonate and sodium hydroxide; (b) solution. treating the sodium carbonate and sodium hydroxide so 20 In the mercury cathode type of alkali chlorine cell, lution with carbon dioxide to form sodium bicarbonate; continuously fed brine is partly decomposed in one com (c) separating solid sodium bicarbonate and a sodium bi partment (called the electrolyzer) between a graphite carbonate containing mother liquor; (d) recirculating the anode and a moving mercury cathode, forming chlorine sodium bicarbonate containing mother liquor to react with gas at the anode and sodium amalgam at the cathode. the sodium amalgam; and (e) calcining the separated so The sodium amalgam ?ows continuously to a second dium bicarbonate to produce sodium carbonate. compartment, called the amalgam decomposer, where it becomes the anode to a short circuited iron or graph~ ite cathode in an electrolyte of sodium hydroxide solu BACKGROUND OF THE INVENTION tion. Puri?ed water is fed to the decomposer, generally The ?eld of the invention is alkali metal carbonate 30 countercurernt to the sodium amalgam; hydrogen gas is generally and the chemical processes for the preparation formed, and the electrolyte increases in sodium hydrox of sodium carbonates particularly. ide content. A solution containing from 30-70% sodium The state of the prior art may be ascertained by ref hydroxide at high purity over?ows from the decomposer. erence to Kirk-Othmer, “Encyclopedia of Chemical Tech The denuded mercury is collected in a small reservoir nology,” 2nd ed., vol. 1 (1963) under the sections “Mer and recycled continuously to the main cell by a cen cury Cathode Cells,” pages 688-698, “Sodium Carbon trifugal pump mounted on each cell. In usual practice, ate,” pages 707-740, and “Sodium Hydroxide,” pages the amalgam leaves the electrolyzer containing 0.2% so 740-758. Examples of the mercury cathode cells used to dium by weight and is returned with less than 0.02% sodium by Weight. produce the sodium amalgam starting materials of the 40 present invention are disclosed in Kirk-Othmer, “Ency According to the present invention the sodium amal clopedia of Chemical Technology,” 1st ed., vol. 1 (1947), gam is treated with an aqueous sodium bicarbonate so pages 375-377. The method and apparatus for carrying lution to form a solution containing sodium carbonate out centrifugal ?ltration is set forth in Kirk-Othmer, “En and sodium hydroxide. The resulting solution is treated cyclopedia of Chemical Technology,” 2nd ed., vol. 4 with carbon dioxide and the sodium bicarbonate formed (1964), pages 732-734 and 748-755. The methods of is separated by ?ltration into a sodium bicarbonate cake converting sodium hydroxide produced by the mercury and sodium bicarbonate containing mother liquor. The cathode cells of the chlorine process into carbonates by sodium bicarbonate containing mother liquor is recir— treatment with gaseous carbon dioxide or sodium bicar culated for reuse with the sodium amalgam. The sodium bonate and sodium carbonate are disclosed in the Ger ‘bicarbonate cake is calcined to soda ash to produce the man Patent 1,141,627 and the German Auslegeschrift end product. 1,232,936, respectviely. Contrary to the prior art processes, the sodium amal The carbonation of sodium hydroxide solution result gam is not reacted with water but with sodium bicar ing from the mercury cathode cells of the chlorine proc bonate solution. The sodium bicarbonate solution is ob ess with gaseous carbon dioxide to form Na2CO3-H2O 55 tained after precipitation and separation of the sodium is known. The disadvantage with this process is that the bicarbonate by centrifuging 0r ?ltering as a centrifuge solution remaining after the precipitate has been sepa product or a ?ltrate. Substantially all of the water nec rated contains a considerable amount of soda. This prod essary for reacting with the sodium amalgam is con uct must be obtained by evaporating the solution and a tinuously recycled through the plant and only the amount considerable number of difficulties are inherent therein. of water removed with the sodium bicarbonate cake The solubility of Na2CO3 decreases with increasing tem must be replaced. perature so that encrustations are formed on the heat The process of the present invention is based on the exchange surfaces of the evaporator whereby the effi observation that a sodium bicarbonate containing ?l ciency of the evaporator is impaired and the process is trate can be reacted without dit?culty with sodium made uneconomical. 65 amalgam, whereas an Na2CO3 containing ?ltrate forms It is also conventional to carbonate the sodium hy a precipitate during the reaction with the sodium droxide solution so that all the water contained in the amalgam. It is very di?icult to separate these Na2CO3 sodium hydroxide solution is bound as water of hydra precipitates from the denuded mercury. As compared tion. By this process the expensive separation of water to the Na2CO3 precipitation the precipitation with so by centrifuging, ?ltering or evaporation is avoided. So 70 dium bicarbonate has the particular advantage that the dium bicarbonate and sodium carbonate are employed amalgam can be reacted with the mother liquor remain for carbonating the sodium hydroxide solution in amounts ing after separation of the precipitte in a simple manner, 3,531,240 3 A. e.g. by centrifuging or ?ltering. Consequently, a special vides that the carbon dioxide formed during calcination step for recovering the NaHCO3 still present in the solu of the sodium bicarbonate is reused during the pre tion is unnecessary. cipitation thereof. Sodium bicarbonate obtained after BRIEF DESCRIPTION OF THE DRAWING separation of the mother liquor is calcinated in the con ventional manner, for example in a rotating calciner, at The process of the present invention is illustrated by about 180—200° C. Carbon dioxide and water are pro the ?owsheet shown in the drawing. In the drawing, so duced in addition to the anhydrous soda ash. The car dium amalgam is treated with sodium bicarbonate solu bon dioxide after compression is reused for the car tion in decomposer 1. The reaction products of decom bonation step and is supplemented from the outside by poser 1 are circulated to carbonating tower 2 for treat 10 supplying an amount of carbon dioxide equal to the ment with carbon dioxide and the sodium bicarbonate amount of carbon dioxide withdrawn with the soda ash suspension resulting therefrom is separated in centrifugal product. ?lter 3 into a sodium bicarbonate cake and a mother When soda ash is produced from sodium, 1 mole of liquor. The sodium bicarbonate cake is removed from water is consumed per mole of soda ash. In order to the centrifugal ?lter and calcined in rotating calciner maintain the amount of cycle water constant, the amount 5 to produce the soda ash. The sodium bicarbonate of water used is supplemented and added to the sodium mother liquor solution separated from the centrifugal bicarbonate solution before the amalgam reaction step. ?lter 3 is fed to collecting vessel 4 from which it is Without further elaboration, it is believed that one returned to the amalgam decomposer. The carbon di skilled in the art can, using the preceding description, oxide by-product of rotating calciner 5 is puri?ed in a 20 utilize the present invention to its fullest extent. The cooler 6 and compressed in compressor 7 for return to following preferred speci?c embodiments are, therefor, the precipitating vessel 2. The water condenser in cooler to be considered as merely illustrative, and not limitative 6 is recycled to the decomposer 1 and can be used for of the remainder of the speci?cation and claims in any amalgam decomposition instead of fresh water. way whatsoever. DETAILED DISCUSSION OF THE INVENTION 25 The invention is further explained with reference to a speci?c example in conjunction with the appended ?ow According to a preferred embodiment of the present sheet. invention, an amalgam containing at most 15 kg. of sodium is reacted with a solution containing at most Example about 11 kg.
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