Method for obtaining sodium bicarbonate

Abstract

A method for obtaining sodium bicarbonate consists of filling a closed column tank with carbon dioxide and introducing a dispersed sodium hydroxide solution in form of mist having a concentration of 30-50% by weight from the top of the column tank and contacting it with carbon dioxide replenished from a gas tank at atmospheric pressure. At the top of the column tank, on its side, ethylene glycol is continuously fed in an excess of 1:10 - 1:14 calculated as pure sodium hydroxide using a column with a permeable inert filling. The resulting slurry of sodium bicarbonate in ethylene glycol, and located at the bottom of the tank is stirred using a slow-rotating horizontal paddle mixer and moved towards the lower outlet located near the bottom of the column tank, then the sodium bicarbonate crystals are drained and purified by rinsing with methanol. The glycol-water filtrate is discharged to a distillation apparatus, where part of the water is distilled off, and the rest of the water with glycol is returned to the reaction, whereby the gaseous products and the liquid droplets entrained by them, escaping through the upper outlet of the column tank located at the top of the column tank, are passed through a column with a permeable inert filling, which is used to supply ethylene glycol, and the condensed liquid is returned to the column tank.

Description

[0001] Method for obtaining sodium bicarbonate

[0002] TECHNICAL FIELD

[0003] The invention relates to a method for obtaining sodium bicarbonate for non-medical purposes.

[0004] BACKGROUD OF THE INVENTION

[0005] Sodium bicarbonate for non-medical purposes is primarily produced using the Solvay process. The Solvay process is a method for obtaining sodium bicarbonate, which is then converted into sodium carbonate, developed in the 1860s by Ernest Solvay. This process involves a series of chemical reactions:

[0006] NaCI + NH3+ CO2+ H2O -> NaHCO3+ NH4CI

[0007] 2NaHCO3-> Na2CO3+ CO2+ H2O

[0008] The process of producing ammonium carbonate consists of the following main processes and operations: preparation of brine, saturation of brine with ammonia to obtain ammonium brine solution, calcination of limestone to produce the quicklime with simultaneous production of CO2- containing gases, saturation of ammonium brine solution with CO2 (carbonation), separation of NaHCO3crystals from the mother liquor, drying of moist NaHCO3and its thermal decomposition (calcination), regeneration of NH3from the mother liquor by mixing with limewater (milk of lime) and heating.

[0009] Brine preparation

[0010] Natural brines are used, which are saturated with salt, if necessary. Most often, brines produced by leaching salt deposits with water are used. Such brines contain impurities in the form of salts of Mg, Ca, K, etc.. In order to separate the impurities, the brine undergoes a process analogous to the chemical method of water softening. The precipitating CaCOs and MgfOH residues are separated in settling tanks.

[0011] Saturation of brine with ammonia

[0012] NH3 dissolves in brine very well with a significant thermal effect. As the concentration of ammonia increases, the volume of brine increases. Since the solubility of salt in ammonia water decreases, in order to prevent the precipitation of crystals, brine that is not completely saturated (approximately 310 g of NaCI per 1 L) is used. NH3 brine is saturated using tall absorption towers filled with coke or plate columns.

[0013] Calcination of limestone

[0014] Quicklime is obtained in the same way as in the production of binding materials, i.e., in the process of limestone calcination.

[0015] Saturation of ammonia brine with CO2 (carbonation)

[0016] Ammonium brine containing a certain amount of CO2 in a bound state is saturated with CO2 in countercurrent carbonation columns. These are plate-type columns. In the lower part, the plates are separated by tube coolers. Due to the deposition of NaHCOs crystals after several dozen hours of operation, the carbonation column becomes clogged and the process must be stopped for cleaning. For this reason, carbonation columns are connected in batteries of 4-7 units and are sequentially rinsed by passing the entire amount of brine through them, which is then directed to the remaining columns.

[0017] At the same time, to improve the rinsing effect, a certain amount of gas from lime kilns is introduced into the column, allowing for preliminary carbonation of the brine in the rinsed column. CO2-containing gases come from two sources: approximately 40% from limestone calcination and 60% from NaHCOs decomposition. Gases poorer in CO2 are introduced halfway up the column, while more concentrated gases are introduced from the bottom of the column. The liquid column pressure at the bottom of the column is 0.3 MPa, which has a positive effect on the carbonization process.

[0018] Separation of NaHCOs crystals from the mother liquor

[0019] A slurry of NaHCOs crystals in mother liquor (known as milk of sodium bicarbonate) flows out of the carbonization columns. The crystals are separated from the liquid by filtration on rotary filters or by centrifugation in continuous flow centrifuges. Wet NaHCOs tends to stick to heating pipes. In order to obtain NaHCOs, the process must be terminated at this stage.

[0020] The Solvay process is a multi-step process. The raw materials used, such as brine, are contaminated with salts of Mg, Ca, K, etc.. In addition, large amounts of water are used in the process, which must be evaporated at the end of the process to precipitate NaHCOs. This is an energy-intensive process. Furthermore, during concentration, the aqueous solution of NaHCOs forms a thick slurry created by the dispersion of crystals in a saturated solution. Crystallization from such a slurry is difficult.

[0021] Methods and devices for crystallizing NaHCC are known.

[0022] Polish patent PL 171239 Bl discloses a method for crystallizing sodium carbonate monohydrate, according to said method a slurry of sodium carbonate monohydrate crystals in a saturated aqueous solution of sodium carbonate monohydrate is introduced into a crystallization chamber, it is circulated in the crystallization chamber and anhydrous sodium carbonate is introduced into the crystallization chamber through a pipe passing through the cover of the crystallization chamber. A thin layer of water is introduced onto the outer surface of the wall of the extension of the pipe supplying anhydrous sodium carbonate.

[0023] According to Polish patent PL 175923 Bl, an aqueous potassium bicarbonate solution is fed to the crystallizer at an elevated temperature T 1 in the range of 40°C - 90°C, at atmospheric pressure and at a potassium bicarbonate concentration of 1-5% by weight, below the saturation point of the solution at temperature Tl, into a slurry of potassium bicarbonate crystals in crystallizer, wherein the slurry contains 10-30% by weight of solid potassium bicarbonate crystals with a desired, predetermined particle size distribution, at a slurry temperature T2 from 10 to 70°C lower than the temperature Tl and lower than the saturation temperature of the introduced solution, and the concentration of potassium bicarbonate in the introduced solution and temperatures Tl and T2 are selected so that the liquid phase of the slurry is supersaturated, but the degree of supersaturation is maintained at a level at which the size of the potassium bicarbonate crystals in the slurry increases, while the number of crystallization nuclei formed is small, wherein the potassium bicarbonate solution is introduced into the slurry at a rate of 1 / 30 to 1 / 600 of the slurry volume per minute, maintaining the residence time in the crystallizer in the range of 0.5 to 10 hours, and the potassium bicarbonate slurry in the crystallizer is gently stirred so as to suspend the solid potassium bicarbonate without foaming the slurry and to avoid the formation of a large number of crystallization nuclei, and then the crystals of the product are separated and recovered from the slurry.

[0024] Methods for obtaining NaHCCh in a reaction of an aqueous solution containing alkali metal ions with carbon dioxide are also known.

[0025] PL / EP 1783100 discloses a process for producing alkali metal hydrogencarbonate, wherein said process comprises reacting an aqueous solution containing alkali metal ions with carbon dioxide in a crystallizer to precipitate crystals of an alkali metal hydrogencarbonate. The process consists in that a part of a slurry containing the above crystals in the above aqueous solution, is withdrawn from the above crystallizer and, after a part of the above crystals is dissolved, where the large crystals are dissolved a little, it is returned to the above crystallization device, and at the same time, part of the said crystals contained in the slurry is dissolved by adjusting the pressure of the slurry while withdrawing from the crystallizer to be lower than the pressure of the said slurry withdrawn from the crystallizer below the pressure value in the said crystallizer.

[0026] PL / EP 2558185 discloses a method for scrubbing CO2 from industrial gas streams through a cyclic pressurized carbonatation reactor, carbonator, to produce high purity carbonates / bicarbonates, and pure CO2 stream, wherein the said carbonator comprises a steel tank with mixer and cooled double walls, a heat exchangerthat coolsthe carbonator, a coolant volume, a cooled surface area, an impeller that disperses the gas, preferably three baffles that extend through almost all of the working volume of the said tank, motors with variable speed drives, and the shaft seal is preferably of a double mechanical type with cooling, and wherein an industrial gas stream containing CO2 is supplied to the carbonator and bubbled to react with soluble hydroxide and a saturated mixture of carbonates / bicarbonates to produce high-purity carbonate / bicarbonate precipitates in a slurry. The impeller is mounted on a hollow shaft drawing gas from the gas-filled space at the top of the reactor.

[0027] In this second group of methods for producing NaHCOs, the reaction is carried out by passing CO2 through an aqueous solution of NaOH, which causes the need for the evaporation of a significant amount of water, and the resulting saturated liquid slurry is difficult to further crystallize because it has a gelatinous form.

[0028] The well-known Solvay method is a multi-step process. The raw materials used in this process, such as brine, are contaminated with Mg, Ca, K, etc. In addition, large amounts of water are used in the process, which must be evaporated at the end of the process to precipitate NaHCOs. This is an energy-intensive process. Analogously, in the method comprising reaction NaOH with CO2, there is a serious problem associated with the crystallization of NaHCOs from an aqueous solution.

[0029] DISCLOSURE OF THE INVENTION

[0030] The invention relates to obtaining high-purity sodium bicarbonate NaHCOs in a reaction of NaOH with CO2 in a simple, highly efficient manner that is devoid of the problems associated with NaHCOs crystallization.

[0031] The method for obtaining sodium bicarbonate consists in filling a closed column tank with carbon dioxide and introducing a sodium hydroxide solution having a concentration of 30-50% by weight in the form of droplets, preferably dispersed into a mist, from the top of the column tank, and it is brought into contact with carbon dioxide replenished from a gas tank at atmospheric pressure. At the top of the column tank, from its side, ethylene glycol is continuously fed in an excess of 1:10 - 1:14 calculated as pure sodium hydroxide using a column with a permeable inert filling. The sodium bicarbonate slurry in ethylene glycol located at the bottom of the tank is stirred with a slow-rotating horizontal paddle mixer and moved towards the lower outlet located near the bottom of the column tank. The sodium bicarbonate crystals are then drained and purified by rinsing with methanol to remove glycol residues. The glycol-water filtrate is discharged to a distillation apparatus, where part of the water is distilled off and the rest of the water with glycol is returned to the reaction. The gaseous products containing entrained liquid droplets escaping through the upper outlet of the column tank, located at the top of the column tank, are passed through a column with a permeable inert filling, which is fed with ethylene glycol, and the condensed liquid is returned to the column tank.

[0032] The sodium hydroxide fed reacts with carbon dioxide. During the course of the reaction carbon dioxide is automatically replenished from the wet gas tank in accordance with the principle of pressure equalization. The more sodium hydroxide solution is fed from the top of the column tank, the more carbon dioxide is automatically supplied to the column tank from the gas tank. For the reaction to proceed correctly and effectively, it is necessary to feed sodium hydroxide in the form of droplets, preferably mist. The exothermic reaction produces sodium bicarbonate, and the heat released causes some of the water from the raw material, i.e., the sodium hydroxide solution, to evaporate. Because the reaction takes place in the volume of the droplets, a significant amount of water evaporates. The remaining concentrated sodium bicarbonate solution, as a heavy liquid, sinks to the bottom of the tank, where ethylene glycol is located. When the glycol and concentrated sodium bicarbonate come into contact, sodium bicarbonate crystals grow and continue to crystallize fast. The slurry of precipitating sodium bicarbonate crystals is slowly mixed by moving it towards the outlet located at the bottom of the column tank, and then they are filtered and purified by rinsing with methanol to remove glycol residues. The glycol-water filtrate (glycol with water) is discharged to a distillation apparatus where part of the water is distilled off and the rest of the water with glycol is returned to the reaction.

[0033] Water and excess of carbon dioxide are removed by a rectification column that serves as a glycol feeder and at the same time protects against the escape of accidental contaminants.

[0034] The method according to the invention allows forthe elimination of complex and energy-intensive processes while obtaining pure sodium bicarbonate with high efficiency.

[0035] BRIEF DESCRIPTION OF THE FIGURES

[0036] The subject of the invention is illustrated in the figure, which shows an example of a sodium bicarbonate production plant.

[0037] EMBODIMENT OF THE INVENTION

[0038] The closed column tank consists of a vertical pipe 1 with a length of 3 m and a diameter of 500 mm, terminated at the bottom by a horizontal pipe 2 with a length of 1 m and a diameter of 500 mm, which is equipped with a horizontal paddle mixer 3. At the bottom of the column tank A there is a carbon dioxide inlet 4.

[0039] The vertical pipe 1 is covered from above with a tight bottom plate with a sprayer 5 mounted in the middle thereof, into which an aqueous solution of sodium hydroxide is forced from the outside, spraying it inside the vertical pipe 1. Vertical pipe 1 is equipped with an upper outlet 6 for excess gas located at the top on its side, which discharges the gas into a annular vertical rectification column 7 with rings. Ethylene glycol is fed from the top of the annular vertical rectification column 7, which also serves to flush out micro-amounts of impurities carried by redundant carbon dioxide.

[0040] The apparatus is equipped with a wet gas tank 8 for feeding carbon dioxide. At the bottom of the horizontal pipe 2, there is a lower outlet 9 for the post-reaction slurry, which feeds the mixture to a filtration apparatus where the sodium bicarbonate sediment is separated from the effluent transferred for regeneration. The regenerated solvents are reused for the reaction. A 30% NaOH solution in the amount of 15.874 kg and 55 kg of ethylene glycol were used, which is 11.5 times the excess in terms of pure NaOH. 9.838 kg of NaHCOs was obtained.

[0041] The closed column tank A was filled with carbon dioxide at atmospheric pressure. Sodium hydroxide was fed in the form of a mist from the top of vertical pipe 1. During course of the reaction, carbon dioxide was automatically replenished from wet gas tank 8 according to the principle of pressure equalization. The more sodium hydroxide solution is fed from the top of column tank 1, the more carbon dioxide is automatically supplied to column tank 1 from wet gas tank 8. The exothermic reaction produces sodium bicarbonate, and the heat released causes some of the water from the raw material, i.e., the sodium hydroxide solution, to evaporate. Because the reaction takes place in the volume of the droplet, a significant amount of water evaporates. The remaining concentrated sodium bicarbonate solution, as a heavy liquid, sinks to the bottom of column tank 1, where ethylene glycol is located. At the moment when the glycol and concentrated sodium bicarbonate come into contact, sodium bicarbonate crystals grow and continue to crystallize fast. The slurry of precipitating sodium bicarbonate crystals is slowly mixed by moving it towards the lower outlet 9 located at the bottom of column tank 1, and then drained and purified by rinsing with methanol to remove glycol residues. The glycol-water filtrate (glycol with water) is discharged to a distillation apparatus, where part of the water is distilled off and the rest of the water with glycol is returned to the reaction. Water and excess of carbon dioxide are removed by a rectification column 7 filled with Raschig glass rings, which serves as an ethylene glycol feeder and at the same time protects against the escape of accidental contaminants.

[0042] The yield of the first batch is 98.38% due to filtration losses. In subsequent batches, due to the return of the ethylene glycol solution containing a small amount of dissolved NaHCOs from the first batch to the reaction, the yield is 100%. The product had a purity of 99.99%. Due to the fact that the decomposition of sodium bicarbonate begins at a temperature below the melting point and, when heated above 50°C, carbon dioxide begins to be released until complete decomposition at 270°C, the decomposition temperature was measured. The temperature of complete decomposition was measured as being 270°C.

[0043] LIST OF REFERENCES

[0044] 1 - column tank

[0045] 2- horizontal pipe

[0046] 3 - paddle mixer

[0047] 4 - carbon dioxide inlet - sprayer - upper outlet - rectification column- gas tank - lower outlet

Claims

CLAIMS1. A method for obtaining sodium bicarbonate in a reaction of sodium hydroxide with carbon dioxide, filtering the resulting crystals and optionally purifying said crystals, wherein said method is characterized in that a closed column tank is filled with carbon dioxide and a solution of sodium hydroxide, dispersed in form of droplets and having a concentration of 30 - 50% by weight is introduced from the top of the column tank and brought into contact with carbon dioxide replenished from a gas tank at atmospheric pressure, wherein at the top of the column tank, from its side, ethylene glycol is continuously fed in an excess of 1:10 - 1:14 ratio, calculated as pure sodium hydroxide, using a column with a permeable inert filling, and the resulting slurry of sodium bicarbonate in ethylene glycol located at the bottom of the tank is stirred using a slow-speed rotating horizontal paddle mixer and moved towards the lower outlet, located near the bottom of the column tank, then the sodium bicarbonate crystals are drained and purified by rinsing with methanol, and further the glycol-water filtrate is discharged to a distillation apparatus, where part of the water is distilled off, and the rest of the water with glycol is returned to the reaction, whereby the gaseous products and the liquid droplets entrained by them, escaping through the upper outlet of the column tank located at the top of the column tank, are passed through a column with a permeable inert filling, which is fed with ethylene glycol, and the condensed liquid is returned to the column tank.

2. The method according to claim 1, wherein the sodium hydroxide solution is fed in the form of a mist.

3. The method according to claim 1, wherein the inert permeable filling of the column through which ethylene glycol is fed are glass rings.

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