DE1567922B2 - Process for the production of pure sodium hydrogen carbonate - Google Patents

Description

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It is well known that sodium hydrogen carbonate can be converted into sodium carbonate by means of sodium hydroxide. In the course of the introduction of carbon dioxide or the subsequent carbonization of the electrolyte solution extracted from the cells again from gas mixtures in sodium hydroxide solutions, which contains it, this will become this. The sodium hydroxide-sodium carbonate required for this purpose in excess sodium hydrogen carbonate falls in large-scale quantities in the electro-5. This process has the disadvantage that the lytic recovery of chlorine from sodium chloride from the. Cells withdrawn solution to this back solution, namely in the diaphragm process must be carried out and by changing their NaOH content to about 11 to 14 percent by weight and the electrolysis in the un-amalgam process with 40 to 50 percent by weight more desirable Way can affect. It can also have NaOH content. With the more dilute sodium hydroxide, the production of sodium hydrogen carbonate only in hydroxide solution, considerable amounts of water are introduced into the close technical and local connection with the reaction mixture, in which the electrolysis is carried out. In addition, the electrolysis of the large amount of sodium hydrochloride formed must be modified in such a way that the carbonate remains dissolved. Although this sodium any method passageway to be isolated only to accumulation of a hydrogen carbonate, the 15 4- to 8% ig ^en hydroxide must electrolyzed mother liquors in a further operation at will, while otherwise be evaporated by the amalgam method, a considerable expenditure of energy. one process run a sodium hydroxide - To avoid the evaporation, after the solution with a content of 40 to 50% NaOH Swedish patent specification 88 181 one should be obtained.

Sodium hydroxide obtained in the diaphragm process is also known, solution containing 13% NaOH and 19% NaCl, after which sodium carbonate in anhydrous form or additional sodium chloride is added. The solution obtained as a monohydrate from concentrated sodium hydroxide is carbonized, with the solution of the mercury cells. Sodium chloride-containing solution can be produced with little soluble Na-. For this purpose, a trium hydrogen carbonate precipitates in a carbonization stage and is separated off. 25 Mother liquor with less than 20% NaOH and more The resulting sodium chloride containing more than 6% Na ₂ CO _{3 is} introduced and the sodium filtrate is to be returned to the electrolysis. carbonate formation required amount of CO ₂ gas to-It still contains large amounts of sodium. The carbonized solution is then converted into hydrogen carbonate, which is first given a crystallization stage by adding calcium chloride to sodium chloride and calcium carbonate with 56 to 63 percent by weight of NaOH carbonate must be converted. This leads to sodium carbonate monohydrate or an unfavorable utilization of the carbon dioxide, which is extracted from anhydrous sodium carbonate with an alkali containing more than 63 percent by weight of NaOH originally obtained from limestone by burning and is now only re-thermal. The mother liquor that falls after the carbonate has been separated off and the precipitated calcium carbonate is split up in the sodium hydroxide is then fed back into the carbonization trium hydrogen carbonate production stage.

can. In addition, this method cannot be used without external heat input

avoid that the sodium hydrogen obtained works, the necessary for water evaporation must

carbonate is contaminated by sodium chloride. lent heat through the neutralization and

As such, these disadvantages would have to be offset by the heat of thinning of the sodium hydroxide solution.

a more concentrated pure sodium hydroxide and which inevitably have to be included in the process

solution, such as the amount of water carried in the chlor-alkali, kept as small as possible

electrolysis using the amalgam process. For these reasons it is necessary that

Sodium hydroxide solution. In which a sodium hydroxide solution is used,

Carbonization of such concentrated sodium hy- 45 whose NaOH content is used in the production of sodium

However, hydroxide solutions form very quickly a carbonate monohydrate not below 56% and at the

thick pulp, which as solids sodium hydrogen- manufacture of anhydrous sodium carbonate does not

carbonate, sodium carbonate and mixed crystals both may be below 63%. In addition, the process separates

Compounds in the most varied of combinations - always from, if not sodium carbonate, but-

contains settlements. These crystalline mixtures accept sodium hydrogen carbonate as the end product.

no more carbon dioxide, so that this is already being strived for.

did not form sodium carbonate to sodium hydrogen- Therefore, other possibilities for the

carbonate can react. In addition, the carbonization of sodium hydrogen carbonate under

ization products only with considerable technical turnaround of sodium hydroxide solutions from the

Separate effort from the mother liquor. 55 Sodium chloride electrolysis with a lower NaOH content

These difficulties are supposed to be sought after from the halt.

Swiss Patent 253 010 known method A method for the production of pure can be circumvented in that, in contrast to sodium hydrogen carbonate, by implementing normal operating mode, one from the cells of a sodium hydroxide solution, which in the sodium chloride-sodium chloride electrolysis after the amalgam Ver 60 electrolysis with Sodium hydroxide solution withdrawn from an NaOH content of over 40 hazards is found to be very weight percent, with carbon dioxide or this low concentration found exhaustively with gases containing carbon dioxide. After that the hub is being treated. The sodium hydrogen carbonate, which is deposited in an easily filterable trium hydroxide solution with a form of the process, is obtained and separated from the mother liquor after the separation of solid, which is returned to the mother cells remaining in the electrolysis sodium hydrogen carbonate. The dissolved sodium hydrogen percent contained in the recycled liquor to a NaOH content of 8 to 15 percent by weight mother liquor is diluted, whereupon pure CO ₂ carbonate is introduced into this solution with the gas mixture formed in the cell or a gas mixture containing it

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and the sodium hydrogen carbonate formed trium hydroxide solution in several gas-side downstream:

separates. change-over vessels or in precipitation columns, such as

For the process according to the invention, they should be common in the ammonia-soda process, too

Sodium hydroxide solution can be used, as it is used in carbonizing. The ammonia-soda

the sodium chloride electrolysis after the amalgam- 5 drive well-known circuit of carbonization

Procedure is obtained. This is where sodium vessels fall according to Honigmann's opinion for this too

Hydroxide solutions with concentrations of over carbonization proved to be very suitable. If here-

40 percent by weight of NaOH, directly without with three reaction vessels connected in series

any pretreatment according to the invention to sodium, the carbon dioxide is first in the reaction

hydrogen carbonate can be implemented. io vessel is initiated in which the carbonization is

What is also necessary for the implementation is advanced. The exhaust gas of the first react carbon dioxide is preferably obtained by burning the tion vessel in the second reaction vessel, the calcium carbonate or calcining of sodium, a less carbonized sodium hydroxide solution, hydrogen carbonate. It can also contain CO _a -containing; its exhaust gas in turn is used in the third gas, as is the case when washing out a vessel, in which the fresh sodium hydroxide solution and CO ₂ from gas mixtures required for syntheses or the recirculated sodium hydrogen carbonate seeds are created when carbonaceous substances are burned. saturated mother liquor have been fed. According to Be-Also, _{natural gas containing CO 2} can be used. At the end of the carbonization in the first vessel, mixtures of the various processes in this are also emptied. By switching the gas supply, the resulting gases are suitable for carbonization. 20 the formerly second vessel to the first on the gas side and the gas containing carbon dioxide should be very pure and the formerly second vessel to the first on the gas side and that is therefore switched to the second on the gas side by washing with the formerly third vessel: water, possibly with sodium hydrogen carbon The first vessel is cleaned with fresh sodium sodium solution and, using the electrostatic method, hydroxide solution and saturated sodium hydrogen, in order to fill it with fly ash, acidic components and carbonate solution, and now as a third reaction and aerosols or the like. The carbon dioxide vessel switched. The gas contained in the emptying of the reaction can be high percentage, for example vessels, adhering to the cooling pipes or walls, gas containing 90 ° / ₀ CO ₂ or with inert gases, permanent sodium hydrogen carbonate crystals such as nitrogen and oxygen, if mixed, the process of the process according to the invention cannot be used. 30 away because they are at the beginning of the next procedural step

The process of the invention is dissolved in one of the fresh sodium hydroxide solutions

Carbonizer suitable reaction vessel, for example.

wise in a closed cylindrical, vertical The sodium hydrogen carbonate crystallizes in the upright vessel, carried out with a lower reaction mixture set according to the invention in inlet port for the carbon dioxide-rich and a well-formed crystals, which after the implementation upper outlet port for the low-carbon dioxide easily, for example by decanting and on-gas is provided. This reaction vessel is charged with final centrifugation or filtration, separated sodium hydroxide solution. Can be according to the invention. The moist crystalline is obtained here used for this purpose a sodium hydroxide solution, sat is not washed, but directly with hot within or outside the reaction vessel 40 air entering into a drying apparatus with a Tempemit an originating from a previous operation temperature of about 15O ⁰ C, dried . About mother liquor of sodium bicarbonate overall surprisingly is is saturated in the present invention, is diluted to a solution containing 8 to carbonation of an example 5O ° / _O by weight of soda-.15 percent by weight, preferably 10 to 12 wt liquor without water evaporation of the residual solution which percent, contains sodium hydroxide. Both solutions are mixed 45 yield of dry, pure sodium hydrogen at temperatures of 20 to 3O ⁰ C. carbonate about 95 to 96 ° / ₀ of theory and suspended in saturated sodium bicarbonate solution mainly contains from 8.7 to 10.0 percent by weight of the mixture during cooling of the Reaktionsbei these temperatures set final temperature. In addition, sodium hydrogen carbonate. Thus, a saturated, approximately 9 to 10 part by weight 45 to 55 weight percent sodium 50 percent aqueous sodium hydrogen carbonate solution, hydroxide solution 2.3 to 5.5 parts by weight, preferably as mother liquor, is obtained per Ge. This solution is used in accordance with the invention, 3 to 4 parts by weight, of mother liquor for the preparation of the fresh sodium hydroxide-sodium hydroxide solution to be used according to the invention in part for diluting. The other part may need a solution. In the in the reaction vessel N & N further technical use are fed, more existing 8- to 15gewichtsprozentige Na falls 55 Thus, in the inventive Arbeitstriumhydroxidlösung will be initiated by the way, any evaporation of the adjusting with the sodium mixing temperature CO ₂ in the. hydroxide solution, apart from. During the addition of CO ₂ , the temperature of the reaction mixture rises further from the insignificant amount of moisture and is kept at values of 65 to 70 ° C by cooling the centrifuged or filtered crystallizate. At the end 60 adheres and is removed during the drying process. It is the carbon dioxide absorption is also very advantageous that the reaction mixture is ^{cooled to temperatures of 22 to 28 °} C. after the inventive mixture in order to achieve a re ^; nes sodium, the sodium hydrogen carbonate formed is obtained if possible hydrogen carbonate, which crystallizes below 0.015% completely. The introduction of the carbon sodium chloride and only about 10 ~ ³ ° / ₀ silica dioxide is continued until practically does not contain any alkaline earths and iron oxides 65, provided in KORRO absorption in the reaction mixture occurs more. protected against ionization, for example with VA steel

In order to remove the carbon dioxide as completely as possible, the reaction vessels are clad. That after

use, it has proven to be advantageous to use the sodium produced by the method according to the invention

bicarbonate can easily be used for nutritional or pharmaceutical purposes will.

The following is the implementation of the invention Procedure explained in more detail using an example.

example

Three steel containers with a ^{capacity of 80 m 3} , which are lined with stainless steel to protect against corrosion and equipped with a cooling pipe system and which have inlet and outlet nozzles for liquid and gas, are connected in series on the gas side in the form of a battery. The container 1 is strength sodium hydroxide solution and 38 m ³ mother liquor ^he filled with 7 m ³ 50% in the form of saturated 9.8% sodium bicarbonate solution. As a result of the heat of dilution, the initial temperature rises from 28 ° C to around 42 ° 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 passes through the initially empty container 2 and 3 and escapes into the open. 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. This requires 5.91 carbon dioxide. The hourly throughput is therefore 655 kg of carbon dioxide. After about 3 hours the temperature in the reaction vessel has risen to 62 ° C. Now the container 2, which has previously also been filled with 11% sodium hydroxide solution, is switched into the gas flow. Since now two container fillings have to be supplied with carbon dioxide, the carbon dioxide throughput per hour is doubled, it is therefore 1310 kg. As soon as the temperature in the first container has reached 65 to 70 ° C, the water cooling is activated to keep the temperature at this level. After a further 3 hours, the third vessel filled with sodium hydroxide solution is also switched on and the carbon dioxide throughput is set to the final value of 1965 kg per hour. In the container 1, the temperature is lowered ^{to the end temperature of 28 ° C. towards the end of the process sequence.} The temperature control is carried out accordingly in the other containers.

The sodium hydrogen carbonate suspension completely carbonized and cooled in container 1 after 9 hours is discharged into a receptacle under the pressure of the compressed gas. To When the vessel is emptied, the flow of carbon dioxide is switched over so that the gas now enters the container 2 as the first crossed out on the gas side. The exhaust gas from this container flows into the downstream former Tray 3, which is now switched as Tray 2. From this the residual gas escapes into the open. The crystals the container filling 1 are centrifuged by

ίο the mother liquor separated. The moist crystals have a water content of about 9 percent by weight. The crystals are dried with hot air at an inlet temperature of 150.degree. 10 550 kg of dry sodium hydrogen carbonate are obtained. ^{38 m 3 of} the mother liquor, which is also obtained during centrifugation and is saturated with sodium hydrogen carbonate, is used to dilute a new carbonization batch. The remaining 4650 kg = ~ 4.2 m ³ are removed and introduced into the ammonia-soda process.

The 38 m ^{3 of} sodium hydrogen carbonate solution that is to be used for diluting the next step is returned to the reaction ^{vessel, mixed with 7 m 3 of} sodium hydroxide solution and carbonized again, the exhaust gas from the second container now being fed into this container, which is thus connected as the third on the gas side is initiated. The procedure described is continued so that the vessels are switched over after a three-hour cycle and a vessel is emptied and refilled every 3 hours.

Claims (1)

Claim: Process for the production of pure sodium hydrogen carbonate by reacting sodium hydroxide solution, those in sodium chloride electrolysis with an NaOH content of over 40 percent by weight accrues, with carbon dioxide or gases containing it, characterized in that that the sodium hydroxide solution with a derived from the process and after ■ the separation of solid sodium hydrogen carbonate remaining mother liquor on one Sodium hydroxide content of 8 to 15 percent by weight is diluted, whereupon in this solution pure carbon dioxide or a gas mixture containing this introduced and the sodium hydrogen carbonate formed is separated.