Process for producing ammonium carbonate and sodium carbonate

Abstract

A process for generating (NH4)2CO3 and Na2CO3 within an electrodialysis cell stack by supplying an aqueous solution containing NH4Cl, NaCl, and dissolved CO2 to the base chamber of an electrodialysis cell stack, and obtaining an outlet solution from the base chamber containing (NH4)2CO3 and Na2CO3, wherein the pH of the outlet solution from the base chamber is a maximum of 9.5.

Description

[Technical Field]

[0001] The present invention relates to a process for producing (NH4)2CO3 and Na2CO3 from an aqueous solution containing ammonium chloride, sodium chloride, and dissolved CO2 using an electrodialysis cell stack. [Background technology]

[0002] The primary industrial process for producing synthetic sodium carbonate is the soda ash process, also known as the Solvay process (ammonia-soda process), or, in a modified embodiment, the HOU process. This process involves treating an ammoniacal brine with a carbon dioxide-containing gas. Sodium carbonate is obtained by recovering the sodium bicarbonate precipitate from the solution and calcining it. The mother liquor, obtained by separating the sodium bicarbonate, contains ammonium chloride and sodium chloride. The mother liquor is then reacted with either calcium oxide or calcium hydroxide to obtain ammonia, which is either recycled back into the initial brine solution in the ammonia-soda process, or treated in the HOU process to precipitate solid NH4Cl. Further details on the process of producing sodium carbonate by the ammonia-soda ash process and the production of refined bicarbonate are described in Ullmann's Encyclopedia of Industrial Chemistry ("Sodium carbonate" chapter, Vol. 33, pages 299-317, 2012 edition, Wiley-VCH Verlag GmbH&Co, particularly paragraphs 1.4.1 and 1.4.2).

[0003] Known soda ash processes are known to consume large amounts of energy, particularly for recycling ammonia. Furthermore, there remains a need to improve ammonia recycling and reduce undesirable by-products of the process. Electrolysis of ammonium chloride to recover or produce chlorine, ammonia, or both is disclosed in U.S. Patent No. 2,209,681. In this method, an electrolytic current is passed through an electrolytic cell containing an aqueous electrolyte comprising ammonium chloride and sodium chloride, where the concentration of sodium chloride is at least equal to the concentration of ammonium chloride. This process has several drawbacks and is not currently in use.

[0004] A process for obtaining chemicals from a mother liquor containing ammonium chloride and sodium chloride, obtained after filtering out wastewater from a soda ash process, particularly sodium bicarbonate, is described in Australian Patent No. 96 / 01330. This process separates sodium and ammonium ions from chloride ions and converts the thus separated ions, along with the associated counterions of water dissociation, into sodium hydroxide, ammonium hydroxide, ammonia, and hydrochloric acid, respectively. The separation of sodium and ammonium ions from chloride ions is performed by electrodialysis. The electrodialysis is performed using at least three chambers (see Figure 2 in the above-mentioned document) separated from each other by one monopolar anion-selective membrane and one monopolar cation-selective membrane (each separated from the next chamber by a bipolar membrane). In an alternative embodiment of this disclosure (see Figure 3 in the above-mentioned document), only two chambers, alternately separated by bipolar and cation-selective membranes, are used to obtain one stream containing hydrochloric acid, sodium chloride, and ammonium chloride, and a second stream containing ammonium hydroxide and sodium hydroxide. In the above disclosure, the solution entering the base chamber has had carbon dioxide removed.

[0005] Electrodialysis technology is well-known and is mainly used in electrolysis processes such as drinking water production, seawater desalination, brackish water desalination, industrial wastewater treatment, acid or alkali recovery in the metal plating industry, and food and pharmaceutical processes. The principle of electrodialysis is well described, for example, in Ullmann's Encyclopedia of Industrial Chemistry (2011 edition, Wendt,-VCH Verlag GmbH&Co, Vol.12 pp 273-313, Electrochemistry) or Technique de l'Ingenieur Encyclopedia 2006 edition, (Chapter Electrodialyse, J2840 V1, 2006, pp 1-15 and Technical appendixes pp 1-3).

[0006] SOLVAY International Publication No. 2016 / 055367 describes a process for producing ammonia from a solution containing ammonium chloride (NH4Cl) supplied to at least one base chamber of an electrodialysis cell stack, wherein the base chamber is maintained at a pH of at least 10, preferably in the range of 10.3 to 12.0. Examples of this disclosure show that at least 98.5% of the ammonium chloride (NH4Cl) can be converted to ammonia (NH4OH), and that when the base chamber is maintained at pH 9.8 under the same conditions, the conversion from ammonium chloride to ammonia is reduced to 86.5%.

[0007] When operating the above process, under the above pH conditions, ammonium ions (NH4) + Ammonia leaks from the base chamber through the selective membrane into the acid chamber, and when the acidic solution is then made usable as an acid or discharged into the environment after neutralization, an acidic solution containing ammonium ions, which is harmful to certain applications, is produced. In fact, ammonia is toxic to most aquatic species, and when present in low concentrations, it is difficult and costly to remove by steam, oxidize with photocatalytic technology, or treat by expensive biological processes. [Overview of the project] [Means for solving the problem]

[0008] The inventors have found that ammonia leakage through the electrodialysis membrane of a base chamber supplied with an aqueous solution containing NH4Cl, NaCl, and dissolved CO2 can be strongly reduced or eliminated by maintaining the pH of the base chamber at less than 9.5.

[0009] In particular, the presence of dissolved CO2 can be brought about by carbonating at least a portion of the NH4Cl and NaCl solution upstream of the base chamber with a CO2-containing gas, thereby resulting in a solution containing NH4Cl, NaCl, and dissolved CO2 before the aqueous solution is supplied to the base chamber.

[0010] Accordingly, the present invention relates to a process for generating (NH4)2CO3 and Na2CO3 in an electrodialysis cell stack by supplying an aqueous solution containing NH4Cl, NaCl, and dissolved CO2 to the base chamber of an electrodialysis cell stack and obtaining an outlet solution from the base chamber containing (NH4)2CO3 and Na2CO3, wherein the pH of the outlet solution from the base chamber is a maximum of 9.5.

[0011] The present invention relates to a process for producing sodium carbonate by a soda ash process, and further to a process that includes the step of producing (NH4)2CO3 and Na2CO3 using the above process.

[0012] Electrodialysis refers to an electrochemical process that allows for the extraction of salt ions from one solution to another, at least partially or completely, through an ion-exchange membrane under an electric field. In a preferred form of the present invention, electrodialysis is performed in an electrodialysis cell stack, including the combination of bipolar ion-exchange membranes and anion and / or cationic ion-exchange membranes in a series of adjacent chambers. An anionic membrane is an ion-exchange membrane that is permeable to anions and, ideally, impermeable to cations. A cationic membrane is itself permeable to cations and impermeable to anions. A bipolar membrane is an ion-exchange membrane comprising a cationic surface and an anionic surface. Such membranes can be produced by joining a cationic membrane and an anionic membrane. Bipolar membranes can be produced, for example, by the process described in International Publication No. 01 / 79335 in the name of SOLVAY.

[0013] Within a bipolar film, under the action of a sufficient local electric field, the H of water diffused therein... + and OH - Dissociation into ions occurs, and then ions move to both sides of the membrane. Consequently, acidification occurs in one chamber adjacent to the bipolar membrane, and alkalization occurs in the other adjacent chamber. Continuous bipolar membranes are separated by cationic or anionic monopolar membranes. When an electrodialysis machine has only bipolar membranes and one type of monopolar membrane (cationic or anionic), it is said to have two (types) of chambers. It is preferable that the electrodialysis machine used in the process of the present invention has only bipolar membranes and anionic membranes.

[0014] The chambers located between the anion plane and the anion film of the bipolar membrane constitute the base chambers. These chambers contain OH originating from the bipolar membrane. - Ions are supplied. In the process of the present invention, an aqueous solution containing ammonium chloride, sodium chloride, and dissolved CO2 is supplied to the base chamber. OH supplied from the bipolar membrane - The ions react with the ammonium cation to obtain the desired ammonia and water.

[0015] In the present invention, dissolved CO2 in a solution containing NH4Cl and NaCl, which is supplied to the base chamber at a maximum pH of 9.5, generally exists as bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ). In an aqueous solution, counterions of the bicarbonate ion, which is a cation, such as ammonium (NH4+), sodium (Na + ), and to a lesser extent, hydronium ions (H3O + ) are present.

[0016] A first advantage of the present invention is that the loss of ammonium ions through the membranes of the dialysis cell stack in the base chamber is reduced.

[0017] A second advantage of the present invention related to the first advantage is that the amount of ammonium ions migrating to the adjacent acid chamber is limited, which facilitates making the produced acidic solution valuable while reducing the amount of ammonium impurities in the acidic solution.

[0018] A third advantage of the present invention is that it facilitates the use of the acid generated in the electrodialysis cell stack, reduces the cost of treating the acidic solution after use for removing ammonia, and since ammonia is harmful to natural fish and aquatic flora, when discharging the used acid into rivers and seas after the appropriate treatment, it also reduces the environmental impact on such biological species.

[0019] A fourth advantage of the present invention is to improve the sustainability of the process that produces sodium carbonate by the ammonia-soda ash process by reducing CO2 emissions from fossil fuels. In fact, the present invention makes it possible to partially or completely replace the use of lime (CaO) to regenerate ammonium chloride (NH4Cl) into alkaline ammonia (in the present invention as (NH4)2CO3 or NH4HCO3 if further carbonated) with an electrodialysis process that can use "green electricity" (i.e., generated from solar, wind, geothermal, biogas and low-impact hydroelectric power sources).

[0020] Note: In conventional soda ash processes, lime (CaO) is primarily produced in lime kilns that use fossil carbon sources such as coke to calcine calcium carbonate (limestone).

[0021] A fifth advantage of the present invention, which is a favorable embodiment, is that it does not use a lime kiln to produce ammonium carbonate or sodium carbonate in this process. This makes it possible to avoid such equipment, which is costly to construct and operates at high temperatures, and to reduce associated maintenance costs.

[0022] A sixth advantage of the present invention is to reduce the amount of solid waste liquid from ammonia distillates when lime or lime pulp is used in the distillation process, resulting in some unreacted lime or limestone remaining in the solid waste liquid. In contrast, if the thermal calcination of limestone is replaced with power generation using alkaline and acidic solutions, the limestone can be corroded with the acidic solution, thereby minimizing the amount of unreacted limestone in the final solid waste liquid while generating the necessary carbon dioxide.

[0023] A seventh advantage of the present invention is that it increases the yield in the ammonia soda process using sodium chloride (NaCl) to values ​​exceeding 60-70%, 90%, or 95%. In fact, by using an anion membrane in this process, it is possible to transfer the chloride from NH4Cl and NaCl to an acidic solution (i.e., a solution containing HCl) while retaining sodium ions in the base chamber, and to recycle a portion of the outlet solution into the soda ash process. Thus, the process of the present invention makes it possible to improve the recyclability of raw materials such as sodium chloride or limestone for producing sodium carbonate.

[0024] definition In this specification, the term “ammonia-soda ash process” refers to the process described in the art above as a first or second variation of the Solvay process for producing sodium carbonate (soda ash) by an ammonia process.

[0025] In this specification, the term "electrodialysis" refers to an electrochemical process that allows salt ions to be extracted, at least partially or completely, from one solution to another through an ion-exchange membrane subjected to an electric field.

[0026] In this specification, the term "electrodialysis cell stack" refers to a device capable of performing the electrodialysis process. It generally consists of several cells separated by ion exchange membranes (also called ion permeable selective membranes).

[0027] The term "includes" encompasses "essentially consisting of" and further "consisting of."

[0028] In this specification, the terms “%”, “weight%”, “wt%”, “wt.%”, “weight percent”, or “weight percent” may be used interchangeably unless the term “%” explicitly refers to another physical unit (e.g., “mol%” or “mol.%”, “vol.%” or “vol.%”).

[0029] When the term "approximately" is used before a quantitative value, it corresponds to a variation of ±10% of the nominal quantitative value, unless otherwise specified. [Brief explanation of the drawing]

[0030] [Figure 1] The function of the electrodialysis apparatus in one embodiment of the process of the present invention is schematically shown. [Modes for carrying out the invention]

[0031] Electrodialysis is a technique that involves combining different types of membranes, such as bipolar ion exchange membranes, anion ion exchange membranes, and / or cationic ion exchange membranes, in a series of adjacent chambers. Anionic membranes are ion exchange membranes that are permeable to anions and, ideally, impermeable to cations. Cationic membranes are themselves permeable to cations and impermeable to anions.

[0032] A bipolar film is an ion-exchange film containing a cationic surface and an anionic surface. Such films can be produced by joining a cationic film and an anionic film. Bipolar films can be produced, for example, by the process described in International Publication No. 01 / 79335 under the name of SOLVAY.

[0033] Within a bipolar film, under the action of a sufficient local electric field, the H of water that permeates there... + and OH - Dissociation into ions occurs, and then ions move to both sides of the membrane. Consequently, acidification occurs in one chamber adjacent to the bipolar membrane, while alkalization occurs in the other adjacent chamber.

[0034] Continuous bipolar membranes are separated by cationic or anionic monopolar membranes. When an electrodialysis machine has only bipolar membranes and one type of monopolar membrane (cationic or anionic), it is said to have two (types) chambers. It is preferable that the electrodialysis machine used in the process of the present invention has only bipolar membranes and anionic membranes.

[0035] The chambers located between the anion plane and the anion film of the bipolar membrane constitute the base chambers. These chambers contain OH originating from the bipolar membrane. - Ions are supplied. In the process of the present invention, a solution containing ammonium chloride, sodium chloride, and dissolved CO2 is supplied to the base chamber. OH supplied from the bipolar membrane - Ions are dissolved carbon dioxide (H2CO3) or bicarbonate ions (HCO3) - It reacts with dissolved CO2 present as ammonium carbonate or sodium carbonate.

[0036] The pH inside the base chamber is generally maintained within the desired range by controlling the flow rate of the supply solution and the current density applied to the electrodialysis cell stack, thereby OH - The generation of is induced.

[0037] In this invention, the pH of the outlet solution from the base chamber is at most 9.5, preferably at most 9.0. Generally, the pH of the outlet solution from the base chamber is at least 6.5, preferably at least 7.0.

[0038] The chamber located between the cation plane and the anion film of the bipolar film constitutes an acid chamber. In this chamber, H originating from the bipolar film... + Cl from a base chamber supplied with ions and aqueous solutions containing ammonium chloride and sodium chloride, through an anion membrane - Ions are supplied.

[0039] The present invention also relates to many further embodiments of the processes described below, and any one of the other embodiments can be combined with others, either alone or in combination with several embodiments, unless they are obviously incompatible.

[0040] In one embodiment, the electrodialysis cell stack used in the process of the present invention includes at least four chambers separated from each other by alternating bipolar and anionic membranes. Preferably, each anionic membrane separates the base chamber from the acid chamber.

[0041] However, on an industrial scale, it is preferable that the electrodialysis cell stack includes multiple alternating base chambers and acid chambers separated from each other by multiple alternating bipolar membranes and anionic membranes. For example, the cell stack may consist of a series of acid chambers and base chambers defined by a continuous anionic membrane and bipolar membrane. In such a structure, each anionic membrane or bipolar membrane has one side facing the base chamber and the other side facing the acid chamber.

[0042] The electrodialysis cell stack is sealed on both sides by an electrolyte chamber containing electrode elements and degassing means. The electrode elements are generally made of a corrosion-resistant material such as metal or metal oxide.

[0043] The concentrations of ammonium chloride and sodium chloride, as well as dissolved carbon dioxide, in the supply solution are not particularly limited. However, over-diluting the solution can lead to significant energy consumption required to recover or concentrate the resulting ammonium carbonate or sodium carbonate.

[0044] To avoid reaching the salt saturation limit, a concentrated solution containing ammonium chloride or sodium chloride and / or bicarbonate or ammonium carbonate and bicarbonate or sodium carbonate until saturation is not reached may be preferable.

[0045] Generally, the aqueous solution supplied to the base chamber contains a maximum of 6 moles of NH4 per kilogram of aqueous solution. + Up to 6 moles of Cl per 1 kg- , and up to 3.5 moles of Na per 1 kg + It also contains up to 3.5 moles of dissolved CO2 per kilogram.

[0046] In aqueous solutions supplied to a base chamber, the concentration of chemical species must take ionic neutrality into consideration. That is, the total number of cation species is equal to the total number of anionic species and is expressed by equivalent electron charge.

[0047] The feed solution contains ammonium chloride and sodium chloride, dissolved CO2, and may contain other components such as ammonium bicarbonate and / or sodium bicarbonate. The feed solution is advantageously derived from a filtered solution obtained by separating crude sodium bicarbonate crystals from the mother liquor after exiting a SOLVAY carbonation column.

[0048] In one embodiment, the aqueous solution containing NH4Cl, NaCl, and dissolved CO2 is the mother liquor obtained after filtering sodium bicarbonate (crude sodium bicarbonate) in the soda ash process. Optionally, the mother liquor is pretreated to reduce or adjust the volatile ammonia (NH3) and carbon dioxide (CO2) content.

[0049] In further embodiments, the feed aqueous solution of the base chamber may, advantageously, supplement the dissolved CO2 by injecting carbon dioxide into the mother liquor (i.e., carbonating the mother liquor).

[0050] In a further embodiment, the outlet solution from the base chamber, containing dissolved (NH4)2CO3 and Na2CO3, is carbonated by injecting a gas containing CO2 to produce a carbonate solution or carbonate slurry, and dissolved carbonate ions (CO3) from ammonium carbonate and sodium carbonate. 2- At least a portion of ) is bicarbonate ions (HCO3 -) is converted, and at least a portion of the carbonated solution or slurry is recycled and returned to the base chamber. In this further embodiment, depending on the pH of the outlet aqueous solution from the base compartment and the amount of CO2 injected into the inlet aqueous solution before being introduced into the base compartment, ammonium carbonate ((NH4)2CO3) may exist partially or entirely as ammonium bicarbonate (NH4HCO3). The same applies to sodium carbonate (Na2CO3), which may exist partially or entirely as sodium bicarbonate (NaHCO3) if it is further carbonated with sodium carbonate (Na2CO3) or a gas containing CO2 in the aqueous solution of the base compartment (inlet solution or outlet solution).

[0051] Bicarbonate (HCO3) - ) / carbonic acid (CO3 2- Since the pH of the solution is determined by the ratio of ions, generally, both carbonate or ammonium bicarbonate and carbonate or sodium bicarbonate are present simultaneously in the aqueous solution.

[0052] The concentration of ammonium chloride in the feed aqueous solution of the present invention is not particularly limited. In a preferred embodiment, the feed solution contains at least 2 g / kg, for example, at least 5 g / kg, preferably at least 10 g / kg, more preferably at least 50 g / kg, even more preferably at least 100 g / kg, even more preferably at least 130 g / kg, and even more preferably at least 160 g / kg of ammonium chloride per 1 kg of feed solution.

[0053] The outlet solution from the base chamber generally contains a maximum of 5.0 moles of total ammonia per kg. Advantageously, it contains a maximum of 2.0 moles of total ammonia per kg of outlet solution, more advantageously, a maximum of 1.5 moles, or even more advantageously, a maximum of 1.0 mole of total ammonia. In such embodiments, the total free ammonia is advantageously a maximum of 0.5 moles of free ammonia per kg of outlet solution, or even more advantageously, a maximum of 0.3 moles of free ammonia per kg of outlet solution.

[0054] In further embodiments, an outlet solution from the base chamber containing (NH4)2CO3 and Na2CO3 is introduced into the soda ash process. Optionally, gaseous ammonia is recovered from the outlet liquid of the base chamber before introducing the outlet solution from the base chamber into the soda ash process. Such ammonia recovery can be performed by heating and stripping.

[0055] In further embodiments of the embodiments cited above, the process includes the further step of dissolving sodium chloride in the outlet solution of the base chamber to obtain ammonia brine, and introducing the ammonia brine thus obtained into the soda ash process.

[0056] The separation of crude sodium bicarbonate crystals from their mother liquor is typically performed using a rotary filter, band filter, or centrifuge after exiting a SOLVAY carbonation column. The mother liquor contains ammonium chloride, which needs to be recycled and regenerated into ammonia for reuse in the ammonia-soda ash process.

[0057] The regeneration of the aforementioned ammonium chloride (NH4Cl) into at least some alkaline ammonia such as ammonium carbonate or ammonium bicarbonate can be carried out according to the present invention.

[0058] The concentration of sodium chloride in the feed solution is not particularly limited. In a preferred embodiment, the feed solution may consist of at least 20 g / kg. Generally, the feed solution contains a maximum of 250 g / kg, preferably a maximum of 100 g / kg, of sodium chloride.

[0059] The chamber located between the cation plane and the anion film of the bipolar film constitutes an acid chamber. In this chamber, H originating from the bipolar film... + Ions and Cl that passed through the anion membrane - Ions are supplied. The acid chamber may be supplied with, for example, water or a diluted hydrochloric acid solution, in which case H supplied by the membrane. + Ions and Cl -The ions form hydrochloric acid, which is obtained as the outlet liquid from the acid chamber.

[0060] In further embodiments, the process of the present invention includes, in a further step, recovering the outlet liquid from an acid chamber containing hydrochloric acid.

[0061] The outlet liquid from the acid chamber can be partially recycled back to the inlet of the acid chamber. The remainder of this outlet liquid is removed from the process and corresponds to one of the simultaneous products of the process of the present invention.

[0062] The hydrochloric acid thus produced can be used as is, or it can be concentrated by removing at least some of its water content to produce a concentrated aqueous hydrochloric acid solution. A maximum HCl concentration of 37.5% by weight or more is advantageous for transporting such concentrated acid.

[0063] Hydrochloric acid or concentrated hydrochloric acid can be sold, used in other processes, or reacted with calcium carbonate (limestone) to produce carbon dioxide. This is particularly advantageous because the carbon dioxide gas obtained by such acid attack will have a high concentration, such as at least 80 vol% CO2 or at least 90 vol% or more CO2. This can be achieved by tightening the air inlet of the acid attack apparatus used. In comparison, conventional lime kilns for calcining calcium carbonate produce gas containing approximately 40 vol% CO2. In addition, such a high CO2 concentration provides greater applicability to the use of the associated CO2-containing gas, and further to its use in the soda ash process. This also limits the dimensions of the pipes for transporting such gas and reduces the power required to compress the gas for injection into a bicarbonation column (to produce crude bicarbonate) or into a sodium bicarbonate crystallizer.

[0064] Accordingly, in a further embodiment of the process of the present invention, an aqueous hydrochloric acid solution or concentrated aqueous hydrochloric acid solution from the acid chamber is reacted with limestone to obtain an aqueous solution of carbon dioxide (CO2) and calcium chloride (CaCl2). Optionally, in the above further embodiment, the process includes a further step of recycling the aqueous calcium chloride (CaCl2) solution to the acid chamber at least partially. The carbon dioxide thus obtained can, advantageously, be injected and dissolved in an aqueous solution supplied to the base chamber. This is particularly advantageous because the pH at the outlet of the base chamber can be easily controlled to a maximum of 9.5 or 9.0.

[0065] Alternatively, the carbon dioxide (CO2) obtained above can be injected into at least a portion of the outlet solution from the base chamber (containing (NH4)2CO3 and Na2CO3) to dissolve it, thereby forming dissolved ammonium bicarbonate (NH4HCO3) or dissolved sodium bicarbonate (NaHCO3). The solution thus obtained, containing an aqueous solution with NH4Cl, NaCl, and dissolved CO2, can then be recycled and supplied to the base chamber. This is particularly advantageous in the "supply and discharge" operations of an electrodialysis machine.

[0066] The carbon dioxide (CO2) obtained above can, advantageously, be introduced into the soda ash process along with additional carbon dioxide from external sources, such as a steam generator that optionally uses a carbonicating combustible material, or from other industries such as the cement or glass industry.

[0067] The present invention also relates to a process for producing sodium carbonate by a soda ash process, which then includes the step of producing (NH4)2CO3 and Na2CO3 according to one embodiment of the present invention or one of its optional alternative forms. In fact, the present invention has the advantage of regenerating acidic forms of ammonia, such as ammonium chloride (NH4Cl), into alkaline forms of ammonia, such as ammonium carbonate or ammonium bicarbonate. Such dissolved alkaline ammonium salts can be beneficially recycled in brine upstream of a conventional soda ash process so that they can again absorb acidic carbon dioxide in one or all of the different steps using CO2. In such steps, it is advantageous to introduce an outlet solution from the base chamber or a solution derived from an outlet solution from the base chamber in the ammonia absorption step, or the bicarbonation column washing step, or the crude sodium bicarbonate precipitation step.

[0068] In further embodiments, (NH4)2CO3 and Na2CO3 from or derived from the outlet solution of the base chamber are supplied to the soda ash process before ammonia (NH3) absorption in the NaCl brine, as before step 3 of the chapter “Sodium carbonate” in Ullmann's Encycl. 2012 reported above.

[0069] In further embodiments, (NH4)2CO3 and Na2CO3 from or derived from the outlet solution of the base chamber are supplied to the soda ash process before precipitation of the crude sodium bicarbonate produced on the bicarbonation column (i.e., the “production column”), as before step 4 of the “Sodium carbonate” chapter of Ullmann's Encycl. 2012 reported above, or are supplied directly to the bicarbonation column. Instead of the bicarbonation column, (NH4)2CO3 and Na2CO3 may be supplied before (or into) the sodium bicarbonate crystallizer.

[0070] In this invention, a portion of hydrochloric acid can be used for specific applications different from the acid attack of calcium carbonate that produces carbon dioxide. Hydrochloric acid can be concentrated and sold.

[0071] In the present invention, the CO2 source is advantageously supplemented or entirely supplied by CO2 from other industries that produce CO2 gas, such as the cement industry, glass industry, iron industry, or waste energy industries that burn carbon-containing combustible materials (either fossil combustible materials or non-fossil combustible materials such as waste biomass) or materials of mineral or subsurface origin for the production of soda ash or refined sodium bicarbonate. Advantageously, the CO2 source may originate from or be supplemented by CO2-containing gases, including CO2 capture processes, such as fumes, combustion gases, industrial gases, gas wastewater, or CO2 captured from ambient air or the ocean. The gases may be used as is, or may be used after being re-concentrated in CO2 to reduce their inert components and air content, thereby easing constraints on their transport and increasing their absorption yield.

[0072] In alternative forms, or as a complement to the aforementioned CO2 sources, the recovery of CO2-containing gases from a soda ash process or a purified sodium bicarbonate process, such as fume from a steam generator or carbonation column, constitutes a favorable further embodiment. To facilitate their use in the production of soda ash or purified sodium bicarbonate, the CO2-containing gases can also be re-concentrated in CO2 before use. An example of the technique for such re-concentration is described in SOLVAY International Publication No. 2016 / 102568. Such CO2-containing gases or re-concentrated CO2-containing gases can also be used to provide dissolved CO2 in aqueous solutions containing NH4Cl and NaCl supplied to the base chamber of the electrodialysis cell stack of the present invention.

[0073] In any of the embodiments described above, the hydrochloric acid produced in the acid chamber may be reacted whole or partially with limestone to obtain carbon dioxide. The carbon dioxide may then be used to precipitate crude sodium bicarbonate crystals in a bicarbonation column, or alternatively, the carbon dioxide may then be used to precipitate crude sodium bicarbonate in a sodium bicarbonate crystallizer.

[0074] In this invention, the hydrochloric acid (HCl) concentration in the acid compartment is preferably at least 0.1 mol / L, and more preferably at least 0.5 mol / L. In fact, it has been observed that the more concentrated the hydrochloric acid, the less ammonia diffuses and leaks out within the acid compartment.

[0075] The following examples are intended solely to illustrate the present invention and not to limit the scope of the claimed invention. [Examples]

[0076] Example 1 - Not according to the present invention A mother liquor, obtained after filtering sodium bicarbonate from a soda ash plant and containing ammonium chloride, sodium chloride, and dissolved CO2, was supplied to the base chamber of an electrodialysis cell stack containing bipolar and anionic membranes. The liquid contained 170 g / l ammonium chloride, 70 g / l sodium chloride, 60 g / l ammonium bicarbonate, and 40 g / l sodium bicarbonate as dissolved species. This solution was diluted with deionized water, and different ammonium chloride concentrations reported in the second and third columns of the table below were tested. The temperature inside the electrodialysis cell stack was set to 50°C, and the current was 0-1.5 kA / m². 2 Multiple current densities were applied. The pH of the base chamber was measured at the chamber outlet (i.e., representing the pH inside the chamber) and maintained at the indicated strongly alkaline pH (10.5 and 13.0).

[0077] Leakage of ammonium ions from the base chamber (molar equivalent of ammonium NH4) + The amount of flow (or flux) is expressed and reported in terms of the corresponding surface units of the membrane per unit time, so the total amount of molar equivalent NH4 passing through the anion exchange membrane (anion permeable selective membrane) is expressed as the amount of flow (or flux) and reported in terms of time. + / m 2 (represented as .h) - Through the anion exchange membrane (indicated as AEM) to the first acid chamber, - Through the bipolar membrane (shown as BPM membrane in the table) to the second acid chamber This was measured by the increase in ammonium concentration in each acid chamber.

[0078] Several tests were conducted in small cells to quantify ammonia loss when the pH exceeds 10. The results in the table below show that, in some cases, it is possible to control the loss through the anionic membrane when a high current density is applied. This is not the case for ammonia loss through the bipolar membrane.

[0079] Example 2 - The present invention Example 1 was repeated under the same conditions, except that the pH at the outlet of the base chamber was controlled to 8.0-8.6.

[0080] Low sensitivity ammonia leakage (*) is detected at the same current density of 0-1.5 kA / m³. 2 Even when applied within this range, measurements could be taken in a 10-hour test at equivalent current densities passing through each film.

[0081] (*): The detection limit for ammonia is 0.005 moles of NH3 per kg of solution. To confirm the reliability of the results, the test was performed twice (double test).

[0082] Compared to Table 1 (not according to the present invention, with a high pH of 10-14), ammonia leakage (NH4 + as molar equivalent / h / m 2 It can be confirmed that the value represented by ( ) is more sensitive than the leakage of ammonia at pH levels lower than 9.5 (according to the present invention) as shown in Table 2.

[0083] This demonstrates one of the claimed advantages of the present invention, which is the highly sensitive avoidance and reduction of ammonium ions leaking through the membrane when the pH of the base chamber is controlled to a maximum of 9.5.

[0084] Example 3 - The present invention In this example, the test was conducted in an electrodialysis cell stack containing bipolar and anionic membranes, and supplied with mother liquor obtained after filtering sodium bicarbonate from a soda ash plant, containing ammonium chloride, sodium chloride, and dissolved CO2. The liquid was supplied to the base chamber in a "feed-and-bleed" manner, i.e., the liquid in the base chamber was recirculated within the loop of the electrodialysis machine, the mother liquor was supplied within the recirculated loop, and a portion of the outlet aqueous solution coming out of the base chamber was released to maintain a constant amount of base liquid in the electrodialysis machine. The recirculation loop was carbonated with a gas containing carbon dioxide and then supplied back into the base chamber. The pH of the outlet solution from the base chamber was controlled by adjusting the flow of the carbon dioxide-containing carbon dioxide gas. The salt concentrations in the base chamber are shown in Table 3 below.

[0085] The instrument used to measure the pH of the base outlet solution was a Hamilton probe, calibrated at the start of each test with standard calibration solutions at three pH values ​​(4, 7, and 9).

[0086] To maximize production by adjusting the supply flow without affecting the movement phenomena, the current density applied to each test was changed.

[0087] The test results showed that reducing the pH to below 9.5 (a decrease of 0.7 pH units) reduced leakage by 58%, indicating that the pH within the base compartment has a significant impact on ammonia leakage. The results presented in Table 3 are from samples taken under stabilization conditions (50 hours after the procedure).

[0088] It was also observed that the acid concentration in the acid loop had a sensitive effect on ammonia leakage. Increasing the HCl concentration in the acid compartment from 0.01 M to 2 M reduced the movement of ammonia into the acid compartment by more than 60%.

[0089] This demonstrates one of the claimed advantages of the present invention, which is the sensitive avoidance and reduction of ammonium ions leaking through the membrane when the pH of the base chamber is controlled to a maximum of 9.5, preferably to a maximum of 9.0.

[0090] Table 1

[0091] Table 2

[0092] Table 3

Claims

1. NH ４ Cl, NaCl, dissolved CO ２ An aqueous solution containing is supplied to the base chamber of an electrodialysis cell stack, and by obtaining an outlet solution from the base chamber containing (NH ４ ), ２ CO ３ and Na ２ CO ３ A process for generating (NH ４ ), ２ CO ３ and Na ２ CO ３ within the electrodialysis cell stack, wherein the pH of the outlet solution from the base chamber is at most 9.

5.

2. The process according to claim 1, wherein the pH of the outlet solution from the base chamber is at least 6.5, preferably at least 7.

0.

3. The process according to claim 1 or 2, wherein the base chamber is surrounded between one bipolar membrane and one anion membrane.

4. The process according to any one of claims 1 to 3, wherein the electrodialysis cell stack includes at least four chambers separated from each other by alternating bipolar and anion membranes.

5. The process according to claim 4, wherein each anion membrane separates the base chamber from the acid chamber.

6. The process according to claim 5, further comprising the steps of obtaining an outlet liquid containing an aqueous hydrochloric acid solution from the acid chamber, and optionally concentrating the aqueous hydrochloric acid solution by removing at least a portion of its water content to produce a concentrated aqueous hydrochloric acid solution.

7. NH ４ Cl, NaCl, dissolved CO ２ The aqueous solution containing is a mother liquor obtained after filtering sodium bicarbonate in the soda ash process, and the mother liquor optionally contains volatile ammonia (NH₄). ３ ) and carbon dioxide (CO2) ２ The process according to any one of claims 1 to 6, which can be pre-treated to reduce the following:

8. Dissolution (NH ４ ) ２ CO ３ and Na ２ CO ３ The outlet solution from the base chamber, which includes CO, is used to produce a carbonated liquid or carbonated slurry. ２ Carbonation occurs by injecting a gas containing the ammonium carbonate and sodium carbonate (CO2). ３ ２－ At least a portion of ) is bicarbonate ions (HCO3 ３ － The process according to any one of claims 1 to 7, wherein the carbonation solution or slurry is converted to a base, and at least a portion of the carbonation solution or slurry is recycled and returned to the base chamber.

9. (NH ４ ) ２ CO ３ and Na ２ CO ３ The process according to any one of claims 1 to 8, further comprising the step of introducing the outlet solution from the base chamber, which includes the above, into a soda ash process after optionally recovering gaseous ammonia from the outlet liquid of the base chamber.

10. The process according to any one of claims 7 to 9, further comprising the steps of dissolving sodium chloride in the outlet solution of the base chamber to obtain ammonia brine, and introducing the ammonia brine thus obtained into the soda ash process.

11. The hydrochloric acid aqueous solution or the concentrated hydrochloric acid aqueous solution from the acid chamber is reacted with limestone to produce carbon dioxide (CO2). ２ ) and calcium chloride (CaCl ２ The process according to any one of claims 5 to 10, further comprising the step of obtaining an aqueous solution.

12. The aforementioned acid chamber contains the calcium chloride (CaCl ２ The process according to claim 11, further comprising the step of recycling the aqueous solution at least partially.

13. The process according to claim 10, wherein the carbon dioxide is optionally introduced into the soda ash process together with additional carbon dioxide from an external source.

14. A process for producing sodium carbonate by a soda ash process, according to any one of claims 1 to 13 (NH ４ ) ２ CO ３ and Na ２ CO ３ A process that includes the steps to produce [something].

15. The process according to any one of claims 6 to 14, wherein the hydrochloric acid produced in the acid chamber is reacted with limestone to obtain carbon dioxide.

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