DE1567922A1 - Process for the production of sodium hydrogen carbonate - Google Patents

Description

Chemical factory Kalk 5 Köln-Kalk, £ 8.8.1967 G. m. B. H. C 6 L / N; CPK 255

Process for the production of sodium hydrogen

carbonate

As is known, sodium hydrogen carbonate can be obtained by introducing carbon dioxide or gas mixtures containing it into sodium hydroxide solutions. The sodium hydroxide solution required for this is obtained in large-scale technical quantities in the electrolytic production of chlorine from sodium chloride solution, namely in the diaphragm process with about 11 to 14 percent by weight of NaOH content and in the amalgam process with 40 to 50 percent by weight of NaOH content. With the more dilute sodium hydroxide solution, considerable amounts of water are introduced into the reaction mixture, in which a correspondingly large amount of the sodium hydrogen carbonate formed remains dissolved. If this sodium hydrogen carbonate is also to be isolated, the mother liquors must be evaporated in a further operation with considerable expenditure of energy. In order to avoid evaporation, according to Swedish patent specification 88 181, further sodium chloride is to be added to a sodium hydroxide solution obtained by the diaphragm process and containing 13% NaOH and 19 % NaCl. The solution obtained in this way is carbonized, whereby the sodium hydrogen carbonate, which is sparingly soluble in the sodium chloride-containing solution, precipitates and is separated off. The resulting piltrate containing sodium chloride should be fed back into the electrolysis. However, it still contains such large amounts of sodium hydrogen carbonate that this can be first obtained by adding calcium chloride to sodium chloride

90-9 827/1 3U

and calcium carbonate must be converted. That leads to an unfavorable use of carbon dioxide, which was originally obtained from limestone by burning and now only after renewed thermal splitting of the precipitated calcium carbonate of the sodium bicarbonate division can be fed. In addition, it is unavoidable in this process that the obtained Sodium hydrogen carbonate is contaminated with sodium chloride.

In itself, these disadvantages would have to be achieved through the use of a concentrated pure sodium hydroxide solution, such as that used in chlor-alkali electrolysis Have the sodium hydroxide solution resulting from the amalgam process removed. So more concentrated during carbonization Sodium hydroxide solutions, however, form a thick paste very quickly, the solids of which are sodium hydrogen carbonate, Contains sodium carbonate and mixed crystals of both compounds in a wide variety of compositions. These crystalline mixtures no longer take up carbon dioxide, so that the sodium carbonate already formed does not can react to sodium hydrogen carbonate. In addition, the carbonation products are only under considerable technical Separate effort from the mother liquor.

These difficulties are to be circumvented according to the method known from Swiss Patent 253 010 in that, in contrast to normal operation, a sodium hydroxide solution of very low concentration withdrawn from the cells of a sodium chloride electrolysis by the amalgam process is treated exhaustively with carbon dioxide. The sodium hydrogen carbonate, which separates out in a readily filterable form, is separated from the mother liquor, which is returned to the electrolysis cells. The friable sodium hydrogen carbonate contained in the returned mother liquor reacts with the sodium hydroxide formed in the cell to form sodium carbonate. In the course of the subsequent carbonization of the electrolyte again withdrawn from the cells

BATHROOM, ORIGINAL

solution, this »sodium carbonate is converted into sodium hydrogen carbonate. This process has the disadvantage that the solution withdrawn from the cells must be fed back to them and, by changing its composition, it can influence the course of the electrolysis in an undesirable manner. In addition, the production of Matriunhydrogencarhonats can only be carried out in close technical and local context with the electrolysis. In addition, the electrolysis must be modified in such a way that with each pass of the process electrolysis is only carried out until a 4 to 8 strength sodium hydroxide solution is obtained, while otherwise a sodium hydroxide solution with a content of 40 to 50 % NaOH is obtained in one pass according to the amalgam process will.

It was therefore looked for other »technically more favorable ways of producing sodium hydrogen carbonate.

Ss was a process for the production of pure sodium bicarbonate by the reaction of sodium hydroxide solution, which in the sodium chloride electrolysis with a NaOH content of over 40 percent by weight accrues «with Carbon dioxide or gases containing it found. Thereafter, the sodium hydroxide solution with a derived from the process and .after the separation of solid Sodium hydrogen carbonate remaining mother liquor diluted to an NaOH content of 8 to 15 percent by weight « whereupon pure COg or a gas mixture containing this is introduced into this solution and the sodium hydrogen carbonate formed is separated off.

A sodium hydroxide solution is to be used for the method according to the invention, as obtained in sodium carbonate electrolysis using the amalgam method will. Sodium hydroxide solutions with concentrations of over 40 percent by weight of NaOH are obtained here

directly without any pretreatment according to the invention Sodium hydrogen carbonate can be implemented.

The carbon dioxide also necessary for the reaction is preferably obtained by burning calcium carbonate or calcining sodium hydrogen carbonate. Aas containing COg can also be used, as occurs when COg is washed out of gas mixtures required for syntheses or when carbonaceous substances are burned. Natural gas containing CO ₂ can also be used. Mixtures of the oases produced in the various processes are also suitable for carbonization. The oasis containing carbon dioxide is said to be very zein and is therefore cleaned of acidic fly dust before it is used by washing it with water, if necessary with sodium hydrogen carbonate solution and using the electrostatic process To free components and aerosols or the like. The carbon dioxide-containing Oas can be used as a high-percentage gas, for example 90% COg-containing gas, or mixed with inert gases such as nitrogen and oxygen.

The process according to the invention is carried out in a reaction vessel suitable as a carbonizer, for example in a closed, cylindrical, upright vessel, which is provided with a lower inlet port for the carbon dioxide-rich and an upper outlet port for the carbon dioxide-rich oas.This reaction vessel is charged with sodium hydroxide solution. According to the invention, a sodium hydroxide solution is used for this purpose, which is diluted inside or outside this reaction vessel with a mother liquor from an earlier operation that is saturated in sodium hydrogen carbonate to form a solution which contains 8 to 15 percent by weight, preferably 10 to 12 percent by weight, sodium hydroxide. Both solutions are mixed at temperatures from 20 to 30 ^{° C.} Saturated sodium hydrogen carbonate

909827 / 13H - 5 -

BATH ORIGINAL

■ ■> 5 - - ■■ .: ■■ - ■■ -.-- ^ · ■ ■

At these temperatures, the solution contains 8.7 to 0.0 percent by weight of sodium hydrogen carbonate. Thus, 45 to 55 percent by weight of sodium hydroxide solution, 2.3 to 5 »5 parts by weight, preferably 3 to 4 parts by weight, of mother liquor are required for the production of the sodium hydroxide solution to be used according to the invention _{At the temperature set by the mixture, CO 2 is} introduced into the 8 to 15 percent by weight sodium hydroxide solution now present in the reaction vessel. During the addition of COg, the temperature of the rises. Reaction mixture continues and is geJb to values of 65 to 70 ^{0 C by cooling.} old. At the end of the carbon dioxide absorption, the Reaktionsgemisoh at temperatures of 22 to 28 ⁰ C is cooled "to the formed Natrlumhydrogencarbonat as completely as possible to crystallize. The introduction of the carbon dioxide is continued until there is practically no more absorption in the reaction mixture.

In order to use the carbon dioxide as completely as possible « It has been found to be advantageous to switch the sodium hydroxide solution in several gas sides one behind the other Vessels or in precipitation columns, as are customary in the ammonia-soda process, to be carbonized. The ones from the Ammonia-soda process known circuit of carbon! - sizing vessels after Honigmann has also chosen for this Carbonization proved to be very suitable. Venn here three reaction vessels are connected in series the carbon dioxide is first introduced into the reaction vessel in which the carbonization has progressed furthest. The exhaust gas from the first reaction vessel arrives into the second reaction vessel containing a less carbonated sodium hydroxide solution; its exhaust gas in turn arrives in the third .Vessel, in which the fresh Sodium hydroxide solution and the recycled; ^ Sodium hydrogen carbonate saturated mother liquor has been fed

- 6 90982 7/1 31 A

BATH ORIGINAL

are. After completion of the carbonization in the first vessel this is emptied. By switching the gas supply, the formerly second vessel becomes the gaaeeltig first and the formerly second vessel becomes the gaaeeltig first and the formerly third vessel to the gas side second »The formerly first vessel is filled with fresh sodium hydroxide solution and saturated sodium hydrogen carbonate solution and now as a third reaction vessel switched. The sodium hydrogen carbonate that remains on the cooling tubes or winches when the reaction vessels are emptied all disrupt the process of the inventive method Iceinesweg, since they too The fresh sodium hydroxide solution must be dissolved at the beginning of the next procedure.

The sodium hydrogen carbonate crystallizes in the reaction mixture set according to the invention in well-formed crystals which can be easily separated after the reaction, for example by decanting and subsequent centrifugation or filtration. The moist crystals obtained in this way are not washed, but are dried directly with hot air which enters a drying device at a temperature of about 150.degree. Surprisingly, in the carbonization of, for example, 50% sodium hydroxide solution according to the invention without water evaporation of the residual solution, the yield of dried, pure sodium hydrogen carbonate is about 95 to 96 % of theory and depends primarily on the final temperature set when the reaction mixture was cooled. In addition, a saturated, approximately 9 to 10 percent by weight aqueous sodium hydrogen carbonate solution is obtained as mother liquor. According to the invention, this solution is partly used to dilute the fresh sodium hydroxide solution. The other part can be used for further technical purposes

be, for example, according to patent »

(Patent application .. <,. * ·. ···) into the ammonia-soda process

be introduced. Demnaoh falls in the

909827/1314

In accordance with the procedure, any evaporation of the water introduced with the sodium hydroxide solution, apart from the insignificant amount of moisture that adheres to the centrifuged or filtered crystals and is removed during the troubling process. £ s continues to be very advantageous in that a pure Natriumhydrogenoarbonat obtained after erfindungsgemäBen-step process, the below 0.015% sodium chloride and only about 1O ^-% silica, * contains alkaline earths and iron oxides, provided in korroslozisgesohUtzten, for example with VA-steel-lined, ReaktionsgefäJ3en is being worked on. The sodium bicarbonate produced by the process according to the invention can readily be used for nutritional or pharmaceutical purposes.

In the following mtru di © BurchfUhrimg the procedure to © iEiiQpj Ballspiel explained in more detail

Be i β ρ i e 1

Three steel containers with a content of 80 nr, which are lined with stainless steel to protect against corrosion and equipped with a cooling pipe system and have inlet and outlet nozzles for liquid and gas, are completely in line with one another. The container 1 is filled with 7 nr 50 pilgrim sodium hydroxide solution and 38 ar mother liquor in the form of a saturated 9.8 liter sodium hydrogen carbonate solution. As a result of the dilution "- the initial heat temperature rises from 28 ° C to approximately 42 ⁰ C. The gas containing 55% CO ₂ and 45 % inert gas, which has been cleaned by washing with water, sodium hydrogen carbonate solution and electrostatically, is now introduced. The exhaust gas from container 1

90 98 27/13 14
BUILDING

crosses through the first empty containers 2 and 3 and arrives at the price. The supply of carbon dioxide per hour is regulated in such a way that the complete carbonization of the sodium hydroxide fed in takes about 9 hours. 5.9 tons of carbon dioxide are used for this. The hourly throughput is thus $ 55 leg of carbon dioxide. NaOH about 3 hours, the temperature in de "reaction vessel ·· increased to 68 ⁰ C. Now the container 2, which was previously also an old matric oxide solution, is switched into the gas flow.Since two container fillings are now to be supplied with carbon oxide, the throughput of carbon oxide per hour is doubled, so it amounts to 1 JIO kg. As soon as the temperature in the first container has risen to 65 to 708c, the water cooling is put into operation to keep the temperature at this level.After three more hours, the third old Hatriuahydroxldlösung is also filled in OefMS and the carbon dioxide throughput to the final value of 1,965 kg per hour is set · Ia container 1 is the. Temperature lowered ^{to the end temperature of 28 0} C towards the end of the process sequence. In the other containers, the temperature control is carried out accordingly «

The sodium hydrogen carbonate suspension, which has been completely carbonized and cooled in container 1 after 9 hours, is drained into a receiving container under the pressure of the compressed oasis. After emptying the vessel, the flow of carbon dioxide is switched over, so that the Qas now passes through container 2 as the first on the gas side. The exhaust gas from this container flows into the closed former container Op-> which is now switched as container 2 · From this the residual gas escapes into the open. The crystals of the container filling 1 are separated from the mother liquor by centrifugation. The hot crystals have a water content of about 9 percent by weight. The crystals are dried with hot air at an inlet temperature of 15O ⁰ C. 10 550 kg of dry sodium hydrogen carbonate are obtained. From the centrifugation also

909827/1314

BAD ORIGINAL, " ⁹ ~

^: "ÖfAlleodea Hufet" rlauie "j, who at lfAfcrluai ^ drugiiarboo * t saturated iit _s " earth 38 a? used to dilute a new obaia egg n ** t. The remaining 4 650 kg «^ 4,2 v ^ are entnoieaea and Into the Aenoniak-fioda-Verfmhrea · introduced *

Bie 2 & w? M * triuahydros "no * rtoonflit solutions, which are to be used for the dilution of the next work steps, are fed back into the definition path xi" dt? sr M * - Teraisoht unä re-esrbonized ₉ where the

Exhaust gas from the second container now into this container « which is connected to the third party on the gas side and every hour a vessel is emptied and is filled again.

909827/1314
BATH ? ^D;

Claims (1)

Claim ▼ experience ssur production of pure carbonate by using clay watriuafcgrdroxidl8 »uag, dl · IMi der Hetriuechloridelektrolyee« dt «la» »IaOH-content of over 40 Gewiohtsprosent accrues« with carbon dioxide or dl · ·· »« containing Oa — n, dmdurefc * marked in gel. that the matrix hydroxide "with a mother liquor which camouflages from the process" and which remains after the separation of τοη solid hydrogen carbonate is diluted to a matrix hydroxide content of 8 to 15 percent, whereupon carbon dioxide or a mixture of carbon dioxide formed in this solution is introduced and "gas mixture" is introduced Hatriuenydrogencarbonat is separated. 90 9 8 27/131 h BATH ORIGINAL