Apparatus for electrically producing sodium carbonate or sodium bicarbonate

Abstract

An apparatus for the electroproduction of sodium carbonate (Na2CO3), the apparatus comprising: (A) a set of at least two stacks of electrodialyzer units to electrodialyze a sodium chloride (NaCl) solution into a sodium hydroxide (NaOH) solution and hydrochloric acid (HCl), where the set of stacks of electrodialyzer units operates at at least 2 production rates over a given period of time; (B) one or more carbonating means for partially or completely carbonating the NaOH solution with CO2 into a Na2CO3 solution; (C) one or more storage devices of the NaOH solution or the Na2CO3 solution; (D) crystallizer equipment, which is used for concentrating the Na2CO3 solution and producing sodium carbonate Na2CO3 crystals and mother liquor; (E) one or more separation devices for separating the Na2CO3 crystals from the mother liquor of the Na2CO3 crystals and recovering the Na2CO3 crystals; and wherein the storage means of the NaOH solution or the Na2CO3 solution has a volume sufficient to operate the crystallizer equipment at a constant production rate over said period of time.

Description

[0001] The present invention relates to an apparatus for producing sodium carbonate (Na2CC>3) and / or optionally sodium bicarbonate (NaHC03) with reduced fossil carbon dioxide (CO2) emissions by electrodialysis of sodium chloride. The present invention also relates to a method for producing sodium carbonate or sodium bicarbonate. The present invention also relates to sodium carbonate and sodium bicarbonate crystals having a low and / or a 'net zero' fossil CO2 footprint.

[0002] Preferably, the apparatus or related method uses electricity that is partially or entirely 'green', or that has a reduced fossil CO2 footprint. Advantageously, this electricity is selected from the group consisting of: hydroelectric power (hydroelectricity), solar photovoltaic power, wind power, waste-to-energy power, power generated from biomass combustion, power generated from biogas combustion, or low fossil CO2 footprint power such as from nuclear electricity.

[0003] More advantageously, the carbon dioxide (CO2) used to partially or entirely carbonate the aqueous sodium hydroxide (NaOH) solution produced by the apparatus or method is partially or entirely of biological origin, or from a biological origin source, or is not derived from a fossil origin.

[0004] The method enables a sensitive reduction of the CO2 fossil footprint when producing sodium carbonate or sodium bicarbonate, compared to known methods, and is a way to achieve net zero emissions for such manufacturing and the obtained products. TECHNICAL FIELD

[0005] Sodium carbonate (Na2CC>3) or soda ash is one of the largest quantities of basic alkali products manufactured worldwide, with a total production in 2022 of more than 65 million tons. The main uses of sodium carbonate are in the glass, chemicals, detergent industry, non-ferrous metallurgy, and also in the sodium bicarbonate production industry.

[0006] Sodium bicarbonate (NaHC03) is also a basic chemical produced worldwide, mainly for food and feed, acid fume abatement, and pharmaceutical uses.

[0007] The main methods for manufacturing sodium carbonate production are the ammonia synthesis method (also known as the SOLVAY ammonia soda process), the ammonium chloride method, and methods based on sodium carbonate or sodium bicarbonate ores.

[0008] The ammonia synthesis process (encompassing one of its alternatives: the 'double process' or the HOU process) is the main process used worldwide (two-thirds of the world production). It consists in treating an aqueous ammonia salt containing sodium chloride with a gas containing carbon dioxide. Sodium bicarbonate precipitates from this solution, which is recovered and calcined to obtain sodium carbonate. Details of the process and production of refined sodium bicarbonate are described in Ullmann's Encyclopedia of Industrial Chemistry ["Sodium Carbonate" chapter, volume 33, pages 299-317, 2012 edition, Wiley-VCH Verlag GmbH & Co., paragraphs 1.4.1 and 1.4.2]. One major advantage of the ammonia-soda process is that it uses abundant raw materials in the world as starting materials, which are: sodium chloride (NaCI) as a source of sodium, and limestone (CaC03) as a source of CO2 (or carbonate). Moreover, on the human timescale, these two raw materials are constantly generated and replenished by nature.

[0009] The source of carbonate in the ammonia-soda process can be partially or totally replaced with CO2 from other industries or with biogenic CO2. Moreover, limestone (CaC03) as a source of alkalinity at calcination can be replaced with non-fossil alkalis. One limitation of the ammonia-soda process at present is that it uses thermal energy (9.7 to 13.6 GJ / ton of soda ash), part of which is used at high temperature for limestone calcination (above 950°C). This high-temperature energy source is not easily replaced by green energy such as rapidly developing solar photovoltaic or wind power.

[0010] The main alternative to the production of sodium carbonate (soda ash) at present is those using minerals containing sodium carbonate (such as fossil trona), which represent one-third of the world's soda ash production. The mined ores, associated with alkaline volcanic activity, exist in a limited number of countries: mainly the United States, Turkey, China. The limited number of countries where such deposits exist leads to heavy intercontinental transport, and the limited exploitable reserves of the deposits that have been identified. The available quantities of the deposits in Turkey represent about 20 to 40 years of production, while for the Wyoming deposits in the United States it is several centuries. In addition, the CO2 content of the sodium carbonate or sodium bicarbonate manufactured from such ores is entirely fossil and is released into the atmosphere when used in the glass or metallurgical industry. This makes such a process unsustainable in the long term and unable to achieve net zero emissions of fossil CO2 and greenhouse gases to comply with the COP21 commitments.

[0011] Therefore, there is a need to improve the manufacturing methods of sodium carbonate and sodium bicarbonate to make them suitable for the use of sustainable green energy and to integrate non-fossil CO2 sources or fossil CO2 captured from other industries to meet net-zero emission requirements immediately or gradually. Such improved methods should meet the needs of large-scale use of green and sustainable energy. In fact, the International Energy Agency's 'Net Zero 2023 Outlook 2050' projects the following to be achievable: 70% of total primary energy supply from renewable sources, approximately 10% from nuclear power, less than 10% from oil and coal fossil primary energy sources (compared to 80% globally in 2021 from fossil fuels, including natural gas), and less than 10% from other energy sources.

[0012] US Patent 6554990 (from Solvay) discloses a method for producing alkali metal hydroxides (such as sodium hydroxide). According to this method, an aqueous solution of an alkali metal halide is circulated in a saline chamber defined between an anion exchange membrane and a cation exchange membrane within the unit using a three-chamber electrodialysis unit. The alkali metal halide is then introduced into an acidic chamber defined between the cation exchange membrane and the cation exchange membrane of the unit, and the aqueous solution of the alkali metal hydroxide is extracted from an alkaline chamber defined between the anion exchange membrane and the anion exchange membrane of the unit. However, this method results in an acidic solution containing hydrochloric acid, which makes the hydrochloric acid unsuitable for other uses. Summary of the Invention

[0013] This invention relates to an apparatus for electro-generating sodium carbonate (Na2CO3), comprising:

[0014] (A) An assembly of at least two electrodialysis unit stacks for electrodialysis of an aqueous sodium chloride (NaCl) solution into an aqueous sodium hydroxide (NaOH) solution and an aqueous hydrochloric acid (HCl) solution.

[0015] The electrodialysis unit stack assembly operates at at least two production rates within a given time period;

[0016] (B) One or more carbonate devices for partially or completely carbonated the aqueous sodium hydroxide (NaOH) solution into an aqueous sodium carbonate (Na2CO3) solution using a gas containing carbon dioxide (CO2);

[0017] (C) One or more storage devices for the aqueous solution of sodium hydroxide (NaOH) or the aqueous solution of sodium carbonate (Na2CO3);

[0018] (D) Crystallizer equipment for concentrating the sodium carbonate (Na2CO3) aqueous solution and producing sodium carbonate (Na2CO3) crystals and mother liquor;

[0019] (E) One or more separation devices for separating and recovering sodium carbonate (Na2CO3) crystals from their mother liquor;

[0020] Furthermore, the storage device for the sodium hydroxide (NaOH) aqueous solution or the storage device for the sodium carbonate (Na2CO3) aqueous solution has a volume sufficient to operate the crystallizer equipment at a constant production rate during the said time period.

[0021] Alternatively, the apparatus of the present invention can be used to produce sodium bicarbonate (NaHCO3), which is carried out by adding a crystallization reactor device (D') to bicarbonate the sodium carbonate aqueous solution from the storage device (C) and to crystallize sodium bicarbonate crystals.

[0022] The present invention also relates to sodium carbonate or sodium bicarbonate crystals produced by the apparatus or method of the present invention, wherein the carbon dioxide (CO2) in the gas used to partially or completely carbonate the aqueous sodium hydroxide (NaOH) solution is at least partially or entirely of biological origin.

[0023] The inventors of this invention have unexpectedly discovered that storing intermediate sodium hydroxide or sodium carbonate aqueous solutions represents a higher energy density per volume or per ton of equivalent electrical energy than known energy storage devices (such as classic batteries as lead-acid batteries (25 Wh / kg) or modern lithium-ion batteries (125 Wh / kg)). In fact, considering that the electrical energy required to electrogenerate sodium carbonate from caustic soda requires approximately 2000 (+ / - 30%) kWh / t of caustic soda and is stoichiometrically close to the production of sodium carbonate, storing caustic soda or sodium carbonate aqueous solutions at 1 to 3 mol / kg of alkaline sodium represents an equivalent electrical energy storage of approximately 160 to 480 Wh / kg of solution.

[0024] The remaining steps in the production of sodium carbonate or sodium bicarbonate (primarily crystallization and drying) represent a small percentage of the total energy consumption. This invention enables crystallization and drying equipment to operate at a stable production rate without becoming excessively large or bulky, compensating for fluctuating electricity availability, particularly when using solar or wind power, or when the power grid must be balanced during peak periods. Indeed, such fluctuations in available energy are a major problem for industrial processes and for the operators who invest in them.

[0025] This invention also avoids and succinctly reduces the need for 'strategic materials' (such as lithium, nickel, cobalt, copper, cadmium, molybdenum, dysprosium, gallium, and other rare earth elements) used to store the aforementioned green and low-fossil CO2 energy in batteries or other storage devices. In fact, such 'strategic materials' are considered finite Earth resources and represent a bottleneck and limitation to the energy transition that the industry aims to achieve by 2050.

[0026] Furthermore, compared to membrane electrolysis of sodium chloride solution to produce caustic soda and chlorine, using electrodialysis to convert sodium chloride solution into caustic soda (NaOH) and hydrochloric acid (HCl) to produce sodium carbonate offers a significantly reduced energy consumption. Energy consumption is reduced by as little as approximately 30% compared to electrolysis. This readily reduces the CO2 footprint of the electrical power required to produce sodium carbonate / sodium bicarbonate from caustic soda and facilitates a switch to 'green energy'.

[0027] Furthermore, the use of electrodialysis to convert sodium chloride solution into sodium hydroxide and sodium carbonate (in the alkali chamber) synergizes well with the use of gaseous CO2 from a biological source: the impurity levels in the CO2 gas fed to the electrodialysis unit require that at least a portion of the caustic soda (NaOH) be replaced by sodium carbonate with a lower pH, resulting in less precipitation of divalent and trivalent metal impurities compared to sodium hydroxide of the same molar concentration, thereby maintaining the expected operating life of the membrane used in the electrodialysis unit. It also reduces the amount of sodium hydroxide and hydrochloric acid used to purify the sodium chloride-containing aqueous solution fed into the brine chamber, as is used for secondary purification of brine in the ion exchange unit (as described in EU - BAT Reference for Chlor-Alkali Production - 2014 - edited by Joint Research Center Institute - doi: 10.2791 / 13138 – 2.5 Salt water purification and (2.5.3.3).

[0028] The present invention also relates to a method in which a portion of the carbonated liquid obtained from the outlet solution of the alkali chamber of the above-described carbonated method is further processed to crystallize sodium carbonate crystals or sodium bicarbonate crystals.

[0029] The present invention also relates to sodium carbonate crystals produced by a method using the apparatus described herein. The present invention further relates to sodium carbonate crystals wherein at least 25% of their carbon content is bio-derived carbon, and these crystals contain at most 20 mg of calcium or magnesium per kilogram of sodium carbonate crystals. The present invention also relates to sodium bicarbonate crystals wherein at least 25% of their carbon content is bio-derived carbon, and these crystals contain at most 20 mg of calcium or magnesium per kilogram of sodium bicarbonate crystals.

[0030] In fact, the inventors have discovered that even with low levels of impurities (such as calcium and magnesium) produced using the methods of the invention, the resulting sodium carbonate has an acceptable level of wear for its primary end use and enables it to reduce fossil CO2 emissions as defined in ranges 1, 2, and 3 by the Greenhouse Gas Protocol organization.

[0031] The present invention also relates to sodium carbonate crystals or sodium bicarbonate crystals manufactured according to the method of the present invention, wherein at least 25% of the electrical energy used by the electrodialysis unit is provided by electricity selected from the group consisting of: hydroelectric power, solar photovoltaic power, wind power, waste-to-energy power, electricity generated by biomass combustion, electricity generated by biogas combustion, electricity generated by hydrogen combustion, geothermal power, electricity generated by compressed air (such as compressed air stored in underground cavities), nuclear power, or mixtures thereof.

[0032] In fact, the excellent synergy between electrodialysis and sodium carbonate or sodium bicarbonate crystallization presents unexpectedly optimal results for reducing the CO2 fossil footprint of sodium carbonate or sodium bicarbonate production and achieving net-zero fossil emissions, while simultaneously reducing the natural resources such as 'strategic materials' required for the equipment or related methods of this invention or for manufacturing the product.

[0033] definition

[0034] For the purposes of this specification, certain terms are intended to have the following meanings.

[0035] The term 'electrodialysis' refers to the electrochemical process that enables the extraction of salt ions from one solution to another, at least partially or completely, through an ion-exchange membrane placed under an electric field.

[0036] The term 'electrodialysis unit stack' refers to an apparatus in which an electrodialysis process can be performed. It typically consists of several cells defined by ion exchange membranes (also known as ion-selective permeable membranes).

[0037] The statement 'operating the crystallizer equipment at a constant production rate' is intended to mean that, considering the operation of an electrodialysis unit stack 'operating at least two production rates within a given time period,' the production rate is between + / - 10% of the nominal production rate. This variation in the nominal production rate within the 'given time period' of the crystallization section is advantageously less than one-third, preferably less than 20%, of the larger of the at least two production rates of the electrodialysis unit stack during the given time period. Typically, the 'given time period' is once a day or at least twice a day (e.g., solar photovoltaic day / night, or morning and evening peak periods). It can also be a day or several days (e.g., when considering the variability of wind power).

[0038] In this specification, the terms 'bio-derived carbon' or 'bio-derived carbonate' refer to carbon or carbonate whose carbon source is directly in equilibrium with atmospheric CO2. In this specification, bio-derived (also referred to as 'bio-based') carbon content is measured according to the standard test method of ASTM D6866-22 for determining the bio-based content of solid, liquid, and gaseous samples using radiocarbon analysis. This method provides accurate bio-based / bio-derived carbon content results: it uses isotope ratio mass spectrometry (IRMS) to quantify the bio-based or bio-derived content of a given product based on carbon-14 isotope measurements of the sample. Instrumental errors of the method are typically within 0.1%–0.5% (relative standard deviation).

[0039] The term 'green energy,' also known as 'renewable energy,' generally refers to energy derived from renewable natural resources that are replenished on a human timescale. This encompasses solar energy (thermal or photovoltaic power), wind power, hydropower, bioenergy (derived from biomass, typically from terrestrial or marine sources), and geothermal energy. In this specification, in addition to the 'green energy' listed above, low-fossil CO2 footprint energy includes heat or cold recovered through heat pumps and nuclear energy.

[0040] The term 'green electricity,' also known as 'renewable electricity,' generally refers to electricity generated from renewable natural resources that are replenished on a human timescale. This encompasses solar power (from heat sources or from solar photovoltaic power generation), wind power, hydroelectric power, ocean power, electricity derived from or generated by bioenergy (i.e., derived from biomass and typically from terrestrial or marine sources), and electricity derived from geothermal energy. In this specification, in addition to the 'green energy' listed above, low-fossil CO2 footprint electricity includes nuclear power (electricity produced by nuclear energy).

[0041] The description of 'feed and discharge mode' relates to operating an electrodialysis unit stack such that the raw solution is fed into an aqueous solution loop into at least one chamber of the electrodialysis unit stack, and said loop, which is fed into the aqueous solution into at least one chamber, also collects at least a portion of the aqueous solution leaving said chamber. Discharge is operated either for the loop or for the solution leaving the chamber, such that the solution volume in the loop is controlled to be more or less constant, for example, like + / - 15%. This operating mode of the electrodialysis unit has the advantage of operating the electrodialysis unit within a concentration range that may differ from the concentration of the raw solution fed into the loop.

[0042] The term "cleaning fluid" refers to a stream drawn from a portion of a method to limit the concentration of impurities in that method.

[0043] The expression "derives from", for example, " derived fromThe following definition of sodium chloride: "solar pool salt or from the sea" refers to a stream of sodium chloride extracted directly from the solar pool or the sea, or a stream that has undergone one or more chemical engineering operations (such as purification, concentration, thermal conversion, decantation, centrifugation, crystallization, filtration, evaporation, drying, dilution, heating, or cooling) downstream of the crystallizer, or a stream that has been mixed with one or more other streams but still retains at least a portion of the sodium chloride extracted from the solar pool or the sea.

[0044] The term "impurity" refers to a compound that is different from the sodium carbonate and / or sodium bicarbonate salts that are to be produced.

[0045] The term "carbonation" refers to the effect of increasing the total amount of carbonate (i.e., carbonate and bicarbonate) in a stream.

[0046] The term "bicarbonation" refers to the effect of increasing the amount of bicarbonate in a stream.

[0047] The term "comprising" includes both "consistent with" and "comprises from".

[0048] In this specification, the terms “%”, “weight%”, “wt%”, “wt.%”, “weight percentage” or “percentage by weight” are used interchangeably unless the “%” term explicitly refers to another physical unit (such as “mole%” or “mol.%”, “vol.%”, etc.).

[0049] Multiple elements include two or more elements.

[0050] The phrase 'A and / or B' refers to the following choice: element A; or element B; or a combination of elements A and B (A+B). The phrase 'A and / or B' is equivalent to at least one of A and B.

[0051] The phrase 'A1, A2, ... and / or An' (where n ≥ 3) includes the following choices: any single element Ai (i = 1, 2, ..., n); or any sub-combination of two to (n-1) elements selected from A1, A2, ..., An; or a combination of all elements Ai (i = 1, 2, ..., n). For example, the phrase 'A1, A2, and / or A3' refers to the following choices: A1; A2; A3; A1 + A2; A1 + A3; A2 + A3; or A1 + A2 + A3.

[0052] In this specification, the description of a series of values ​​for a variable defined by a lower limit, or an upper limit, or by both a lower limit and an upper limit also includes embodiments in which the variable is selected correspondingly within that range of values: excluding the lower limit, or excluding the upper limit, or excluding both the lower limit and the upper limit.

[0053] In this specification, the description of several consecutive ranges of values ​​for the same variable also includes descriptions of embodiments in which the variable is selected from any other intermediate ranges included in these consecutive ranges. Thus, for illustrative purposes, when stating "Element X is typically at least 10, advantageously at least 15," this specification also includes another embodiment in which a new minimum value can be selected between 10 and 15, for example: where "Element X is at least 11," or additionally where "Element X is at least 13.74," etc.; 11 or 13.74 are values ​​included between 10 and 15. Also for illustrative purposes, when indicating "Element X is typically at most 15, advantageously at most 10," this specification also includes another embodiment in which a new maximum value can be selected between 10 and 15.

[0054] In this specification, where an element or component is referred to as being included in and / or selected from a list of enumerated elements or components, it should be understood that in the relevant embodiments explicitly considered herein, the element or component may also be any one of these individually enumerated elements or components, or may also be a group consisting of any two or more of these explicitly listed elements or components.

[0055] For example, when the selection of elements from a set of elements is described in the embodiments, the following embodiments are also explicitly described:

[0056] - Select two or more elements from this group.

[0057] - Select features from a subgroup of features that has had one or more features removed from it.

[0058] The singular 'a' or 'one' used in this article includes the plural unless otherwise expressly indicated.

[0059] If the term “about” is used before a numerical value, it corresponds to a variation of ±10% of the nominal value, unless otherwise indicated. Attached Figure Description

[0060] Figure 1 (Fig. 1) schematically illustrates the function of an electrodialysis unit in one embodiment of the device and method of the present invention.

[0061] Figure 2(Fig. 2) schematically illustrates an apparatus for implementing an embodiment of the device according to the invention. Detailed Implementation

[0062] Electrodialysis is an electrochemical process that uses an ion-exchange membrane placed under an electric field to extract salt ions from one solution to another.

[0063] Electrodialysis techniques are known: they are primarily used in electro-separation methods, such as drinking water production, industrial wastewater treatment, acid or alkali recovery in the metal plating industry, and food and pharmaceutical processes. The principles of electrodialysis are detailed in, for example, Ullmann's Encyclopedia of Industrial Chemistry (2011 edition, Wiley-VCH Verlag GmbH & Co., Vol. 12, pp. 273-313, Electrochemistry) or the Technique de l'Ingénieur Encyclopedia (2006 edition, Electrodialysis chapter, J2840 V1, 2006, pp. 1-15 and Technical Appendix pp. 1-3).

[0064] In a preferred embodiment of the invention, electrodialysis is operated in an electrodialysis unit stack comprising combining bipolar ion exchange membranes with anion and / or cation exchange membranes in a set of adjacent chambers.

[0065] Anion exchange membranes are ion exchange membranes that are permeable to anions and ideally impermeable to cations. Cation exchange membranes are permeable to cations and impermeable to anions. Bipolar membranes are ion exchange membranes comprising both a cation-side and an anion-side. Such membranes can be produced by combining cation-side and anion-side membranes. Bipolar membranes can be produced, for example, by the method described in WO 01 / 79335 under the name of Solvay.

[0066] Within the bipolar membrane, under the influence of a sufficient local electric field, the water that has diffused into it dissociates into its H+. + and OH - Ions then migrate across the membrane. Thus, acidification occurs in one of the chambers adjacent to the bipolar membrane and alkalization occurs in the other adjacent chamber. The sequential bipolar membranes are separated by cation or anion unipolar membranes. When the electrodialysis unit has only a bipolar membrane and one type of unipolar membrane (cation or anion), it is claimed to have two (types) of chambers. The electrodialysis unit used in the method of the present invention preferably has only a bipolar membrane and anion membrane.

[0067] The chamber located between the anion exchange side of the bipolar membrane and the cation exchange side constitutes the alkali chamber. OH- ions originating from the bipolar membrane are present in this chamber. - Supply of ions. In the method of the present invention, preferably, an aqueous solution containing sodium carbonate is fed into the alkali chamber. OH- is supplied from the bipolar membrane. - The ions will provide alkalinity to absorb acidic carbon dioxide, thus forming a carbonated solution.

[0068] In an advantageous embodiment, the electrodialysis apparatus used in the present invention comprises at least three chambers, one of which is a salt chamber, the second chamber is an alkali chamber, and the third chamber is an acid chamber.

[0069] The first advantage of this invention is that it reduces the need for storing fluctuating electricity, such as electricity generated by solar or wind power (which is highly variable over daily or multi-day periods, such as photovoltaic or wind power, which constitute and will constitute a major source of renewable electricity by 2050).

[0070] A second advantage of the invention is the possibility of storing electrical energy at a higher energy density (per unit volume and / or per unit weight) and for industrial use in the manufacture of sodium carbonate or sodium bicarbonate with lower 'strategic material' consumption, particularly for the manufacture of said products with a low fossil CO2 footprint.

[0071] A third advantage of the invention is that, compared to an equivalent device that uses an electrolyzer instead of an electrodialysis unit, the energy consumption for producing sodium carbonate or sodium bicarbonate is reduced, thus reducing the CO2 footprint associated with energy production regardless of the energy source, thereby making it easier to achieve a near-zero CO2 footprint for the produced sodium carbonate or sodium bicarbonate.

[0072] A fourth advantage of this invention is the possibility of using renewable energy or low-fossil CO2 footprint energy to replace the high-temperature steps of conventional methods (typically using coal to calcine limestone into lime used in both the alkaline ammonia process and the natural alkali solution mining method) and to replace it with electricity having a reduced fossil CO2 footprint, preferably selected from the group consisting of: hydroelectric power, photovoltaic power, wind power, waste-to-energy power, power generated from biogas, power generated from biomass combustion, power generated from hydrogen combustion, geothermal power, power generated from compressed air (such as compressed air stored from underground cavities), nuclear power, and mixtures thereof. This also contributes to a near-zero CO2 footprint of the produced sodium carbonate or sodium bicarbonate. This is particularly attractive when the low-fossil CO2 footprint energy is used by other consumers (e.g., in towns during peak hours for lightning, heating or cooling, or household appliances) and when industrial use is temporarily less frequent.

[0073] A fifth advantage of this invention is that the crystallization equipment for producing sodium carbonate or sodium bicarbonate crystals operates under more constant operating conditions, such as the residence time and growth rate of the crystals in the crystallizer, resulting in a more stable particle size distribution of the produced sodium carbonate or sodium bicarbonate crystals. In fact, operating the crystallizer (D) at a much higher rate produces a much higher quantity of fine crystals, which poses a problem for major customers, such as glass manufacturers (leading to lower uniformity of the mixture fed into the glass oven, dust generation when the mixture is loaded into the oven, melt scaling on the oven surface above the melt, and potential hygiene problems for workers in the area). For industries producing caustic soda and chlorine, this problem is less acute or does not occur: the electrolyzer stack produces a liquid (sodium hydroxide solution) that is much less affected by the production rate than crystalline solids (such as sodium carbonate or sodium bicarbonate).

[0074] The sixth advantage of the invention is that it is easy to capture CO2 from smoke, or from other industries, or from the atmosphere, because the resulting sodium hydroxide is highly reactive and can capture said CO2 even at low concentrations (wherein the CO2 concentration is less than 30% vol. or even less than 10% vol. based on dry gas), or even to efficiently capture CO2 from the Earth's atmosphere (about 420 ppm by volume) and increase the recycling of CO2 resources by producing sodium carbonate or sodium bicarbonate.

[0075] The seventh advantage of this invention is that it can use low-purity limestone (CaCO3) with 60% to 85% CaCO3 when CO2 capture or CO2 from other industries is not available locally (this is not recommended at all in the ammonia-soda process because the mineral impurities in limestone, mainly clay and aluminum silicate or iron silicate, form insoluble substances with hydrated lime Ca(OH)2, which causes loss of calcium hydroxide and severe scaling in the distiller).

[0076] The eighth advantage of the invention is that by synergistically increasing the use of other byproducts (such as concentrated brine from reverse osmosis or from multi-effect evaporation equipment in areas of the world where drinking water is scarce) and using them as NaCl raw materials for the method of the invention, the pressure on existing natural resources is reduced.

[0077] A ninth advantage of the invention is the possibility of processing the aqueous sodium hydroxide or sodium carbonate solution exiting the alkali chamber, even if the sodium hydroxide or sodium carbonate solution contains trace amounts of sodium chloride generated by chloride ions leaking from the salt chamber to the alkali chamber through the cation exchange membrane of the electrodialysis unit. This is because the sodium chloride will then separate during the crystallization of sodium carbonate or sodium bicarbonate and remain in the mother liquor of the crystallizer. The sodium chloride, then washed with a portion of the sodium carbonate, can then be recycled to the brine (NaCl solution) front end for purifying impurities (such as calcium) in the brine before feeding it into the salt chamber, avoiding or reducing sodium carbonate loss and enabling a useful synergy between the electrodialysis unit and the crystallization of sodium carbonate or sodium bicarbonate.

[0078] Therefore, the method of the present invention enables the improvement of the circularity of the use of raw materials (such as sodium chloride or limestone) and, through synergistic optimization of the reduction of the CO2 fossil footprint of sodium carbonate or sodium bicarbonate production and the reduction of 'strategic material' consumption, paves the way for net-zero emissions in the production of sodium carbonate or sodium bicarbonate.

[0079] The present invention relates to several advantageous embodiments, which are described below as 'projects'.

[0080] Project 1. An apparatus for electrogenerating sodium carbonate (Na2CO3), the apparatus comprising:

[0081] (A) An assembly of at least two electrodialysis unit stacks for electrodialysis of an aqueous sodium chloride (NaCl) solution into an aqueous sodium hydroxide (NaOH) solution and an aqueous hydrochloric acid (HCl) solution.

[0082] The electrodialysis unit stack assembly operates at at least two production rates within a given time period;

[0083] (B) One or more carbonate devices for partially or completely carbonated the aqueous sodium hydroxide (NaOH) solution into an aqueous sodium carbonate (Na2CO3) solution using a gas containing carbon dioxide (CO2);

[0084] (C) One or more storage devices for the aqueous solution of sodium hydroxide (NaOH) or the aqueous solution of sodium carbonate (Na2CO3);

[0085] (D) Crystallizer equipment for concentrating the sodium carbonate (Na2CO3) aqueous solution and producing sodium carbonate (Na2CO3) crystals and mother liquor;

[0086] (E) One or more separation devices for separating and recovering sodium carbonate (Na2CO3) crystals from their mother liquor;

[0087] Furthermore, the storage device for the sodium hydroxide (NaOH) aqueous solution or the storage device for the sodium carbonate (Na2CO3) aqueous solution has a volume sufficient to operate the crystallizer equipment at a constant production rate during the said time period.

[0088] Project 2. The equipment as described in Project 1, wherein the electrodialysis unit stack uses electricity to electrodialyze the sodium chloride (NaCl) aqueous solution into the sodium hydroxide (NaOH) aqueous solution and the hydrochloric acid (HCl) aqueous solution.

[0089] And wherein the electricity is at least partially and preferably entirely 'green electricity' or has a reduced fossil CO2 footprint, and the electricity is preferably selected from the group consisting of: hydroelectric power, solar photovoltaic power, wind power, waste-to-energy power, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, geothermal power, electricity generated from compressed air—such as compressed air stored in underground cavities—nuclear power, electricity from combined heat and power (CHP) of steam and electricity, or mixtures thereof.

[0090] Project 3. The equipment as described in Project 1 or 2, wherein the equipment for producing sodium carbonate (Na2CO3) has at least a portion of multiple units (B) to (E) that use electricity, and wherein the electricity used is at least partially and preferably entirely 'green electricity' or has a reduced fossil CO2 footprint, the electricity preferably being selected from the group consisting of: hydroelectric power, solar photovoltaic power, wind power, waste-to-energy power, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, geothermal power, electricity generated from compressed air (such as compressed air stored in underground cavities), nuclear power, electricity from combined heat and power (CHP) of steam and electricity, or mixtures thereof.

[0091] Item 4. The equipment as described in any of the preceding items, wherein group (A) includes operating means:

[0092] - To regulate the production rate of at least a portion of the electrodialysis unit stack by adjusting the electrical intensity used for electrodialysis of an aqueous sodium chloride (NaCl) solution; and / or

[0093] - At least a portion of the electrodialysis unit stack of the group is used to close and open the group;

[0094] A group (A) of electrodialysis unit stacks operating at at least two production rates within a given time period.

[0095] Item 5. The equipment as described in any of the preceding items, wherein the time period is at least 1 hour or at least 10 hours.

[0096] Item 6. The equipment as described in any of the preceding items, wherein the time period is at least 6 hours or at least 12 hours.

[0097] Item 7. The equipment as described in any of the preceding items, wherein the time period is at most one hour or at most one day.

[0098] Item 8. The equipment as described in any of the preceding items, wherein the ratio of the at least two production rates, expressed as a ratio of high production rate to low production rate, is at least 1.2 or at least 1.5.

[0099] Item 9. The equipment as described in any of the preceding items, wherein the ratio of the at least two production rates, expressed as a ratio of the higher production rate to the lower production rate, is at most 5 or at most 3.

[0100] Item 10. The apparatus of any of the preceding items, wherein at least part or all of the electrodialysis unit stack of the group (A) for electrodialysis of the aqueous sodium chloride (NaCl) solution into an aqueous sodium hydroxide (NaOH) solution and an aqueous hydrochloric acid (HCl) solution comprises at least two chambers: an alkaline chamber for producing the aqueous sodium hydroxide (NaOH) solution and an acid chamber for producing the aqueous hydrochloric acid (HCl) solution.

[0101] Item 11. The apparatus as described in the preceding item, wherein at least a portion or all of the electrodialysis unit stack comprises at least three chambers: an alkali chamber, an acid chamber, and a salt chamber, wherein the sodium chloride is fed, and wherein sodium ions permeate into the alkali chamber through a cation-selective permeation membrane, and chloride ions permeate into the acid chamber through an anion-selective permeation membrane.

[0102] Item 12. The device as described in any of the preceding items, wherein at least part or all of the electrodialysis unit stack or the group (A) can operate in a feed and discharge mode.

[0103] Item 13. The apparatus as described in any of the preceding items, wherein the crystallizer equipment (D) for concentrating the sodium carbonate (Na2CO3) aqueous solution and producing sodium carbonate (Na2CO3) crystals and mother liquor comprises:

[0104] - Optional (D1) pre-evaporator device, such as a falling film evaporator or a forced circulation evaporator, for removing at least a portion of the water from the sodium carbonate (Na2CO3) aqueous solution;

[0105] - (D2) Crystallizer devices, such as anhydrous sodium carbonate (Na2CO3) crystallizer, or sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or sesquicarbonate (Na2CO3.NaHCO3.2H2O) crystallizer.

[0106] Item 14. The apparatus as described in any of the preceding items 1 to 12, wherein the crystallizer apparatus (D) further comprises:

[0107] - Optional (D1) pre-evaporator devices, and

[0108] - (D2) Sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer,

[0109] - Separation device (E2) for separating sodium carbonate decahydrate (Na2CO3.10H2O) crystals from their mother liquor.

[0110] - A melting apparatus used to melt these sodium carbonate decahydrate (Na₂CO₃·10H₂O) crystals into a purified sodium carbonate solution.

[0111] - (D2') Sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, which feeds purified sodium carbonate solution to produce (Na2CO3.H2O) crystals and its mother liquor.

[0112] - (E) Separation device for separating sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor.

[0113] The embodiment of this project, comprising a sodium carbonate decahydrate crystallizer and then a sodium carbonate monohydrate crystallizer, is particularly advantageous when the produced sodium carbonate (Na2CO3) aqueous solution contains a high level of sodium chloride (NaCl) (e.g., at least 1.0 wt.% or at least 1.5 wt.% NaCl). Compared to the configuration according to project 13, which includes a monohydrate crystallizer and then treats the cleaning solution of the monohydrate crystallizer in a decahydrate crystallizer, this embodiment enables a reduction in the energy consumption of such a configuration for concentrating NaCl impurities and others (Na2SO4, KCl, ...) and reducing sodium carbonate in the final cleaning solution.

[0114] Item 15. The apparatus as described in any of the preceding items 1 to 13, wherein the crystallizer apparatus (D) further comprises:

[0115] - Optional (D1) pre-evaporator devices, and

[0116] - (D2') Sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, which is fed with sodium carbonate solution to produce sodium carbonate monohydrate (Na2CO3.H2O) crystals and its mother liquor.

[0117] - (E) Separation device for separating sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor.

[0118] - A cleaning device for at least a portion of the mother liquor from the sodium carbonate monohydrate crystallizer.

[0119] - (D2) Sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, whose feed comes from the cleaned mother liquor of the sodium carbonate monohydrate crystallizer.

[0120] - Separation device (E') used to separate sodium carbonate decahydrate (Na2CO3.10H2O) crystals from their mother liquor.

[0121] - A melting apparatus used to melt these sodium carbonate decahydrate (Na₂CO₃·10H₂O) crystals into a purified sodium carbonate solution.

[0122] - The purified sodium carbonate solution is recycled to the (D2') sodium carbonate monohydrate (Na2CO3.H2O) crystallizer.

[0123] When the sodium carbonate (Na2CO3) aqueous solution produced from the electrodialysis unit and fed into a monohydrate crystallizer contains a low level of sodium chloride (NaCl) (e.g., up to 1.5 wt.% or even up to 1.0 wt.% NaCl), embodiment 13 of this project is particularly advantageous because it first includes a sodium carbonate monohydrate crystallizer and then a sodium carbonate decahydrate crystallizer for treating the monohydrate washing solution, recovering most of the sodium carbonate from the washing solution, and concentrating the sodium chloride in the washing solution. This is because it enables a reduction in energy consumption compared to the configuration according to embodiment 12 above, which includes a decahydrate crystallizer for first purifying the NaCl contents (and other impurities listed above) in the sodium carbonate aqueous solution, and then a monohydrate crystallizer for crystallizing sodium carbonate crystals, and then treating the washing solution of the monohydrate crystallizer in the decahydrate crystallizer and washing away sodium chloride and other impurities there.

[0124] Item 16. The apparatus of any of the preceding items, wherein the mother liquor from the crystallizer equipment comprises dissolved sodium carbonate and dissolved sodium chloride, and the crystallizer equipment (D) or the separation device (E) includes a cleaning device for cleaning at least a portion of the mother liquor from the crystallizer equipment ((D), (D2) or (D2')) and a recycling device for at least a portion of the cleaned mother liquor, for recycling at least a portion of the mother liquor to a sodium chloride brine purification module or to at least one electrodialysis unit stack of group (A) or the front end of at least one electrodialysis unit stack of group (A) to recover at least a portion of the sodium chloride from the cleaned mother liquor and electrolyze it into sodium hydroxide and / or hydrochloric acid.

[0125] Item 17. A method for producing sodium carbonate (Na₂CO₃) crystals or sodium bicarbonate (NaHCO₃) crystals from sodium chloride (NaCl) solution.

[0126] The method includes the following steps:

[0127] (i) Optionally, the sodium chloride (NaCl) solution may be pretreated to remove at least a portion of impurities selected from the group consisting of: insoluble matter, calcium, magnesium, heavy metals, fluorides, bromides, iodides, sulfates, organic matter, and combinations thereof, to obtain an optional pretreated sodium chloride solution;

[0128] (ii) In a group (A) of at least two electrodialysis unit stacks, the sodium chloride solution or optionally a pretreated sodium chloride solution is electrodialyzed into an aqueous solution of sodium hydroxide (NaOH) and an aqueous solution of hydrochloric acid (HCl), wherein the group of electrodialysis unit stacks operates at at least two production rates within a given time period by closing and opening at least a portion of the electrodialysis unit stack during a given time period.

[0129] (iii) The sodium hydroxide (NaOH) aqueous solution is partially or completely carbonated into a sodium carbonate (Na2CO3) aqueous solution using a gas containing carbon dioxide (CO2);

[0130] (iv) Prior to step (iii), the aqueous sodium hydroxide (NaOH) solution is stored in one or more storage devices (C1), and / or

[0131] After step (iii), the sodium carbonate (Na2CO3) aqueous solution is stored in storage device (C2);

[0132] (v) In the crystallizer equipment (D), at least a portion of the sodium carbonate in the sodium carbonate solution is crystallized into sodium carbonate crystals and mother liquor.

[0133] (vi) In the separation device (E), these sodium carbonate (Na2CO3) crystals are separated from the mother liquor.

[0134] And these sodium carbonate (Na2CO3) crystals are recovered;

[0135] (vii) Optionally, sodium bicarbonate (NaHCO3) crystals are crystallized by further carbonated in a crystallizer apparatus (D') with a gas containing CO2 or bio-derived CO2, thereby producing sodium bicarbonate crystals and their mother liquor. Optionally, these sodium bicarbonate crystals are separated from their mother liquor in a separation device (E') and the sodium bicarbonate (NaHCO3) crystals are recovered.

[0136] Furthermore, the storage device for the sodium hydroxide (NaOH) aqueous solution and / or the storage device for the sodium carbonate (Na2CO3) aqueous solution has a volume sufficient to operate the crystallizer equipment at a constant production rate during the said time period.

[0137] Project 18. The method as described in the preceding project, wherein the carbon dioxide (CO2) in the gas used to partially or completely carbonate the aqueous sodium hydroxide (NaOH) solution originates from a biological source not derived from fossil carbon or carbon dioxide, or from CO2 captured from the air.

[0138] Project 19. The method of any of the preceding projects, wherein the carbon dioxide (CO2) in the gas used for partially or completely carbonated the aqueous sodium hydroxide (NaOH) solution or the aqueous sodium carbonate solution is partially or entirely of biological origin or is CO2 captured from the air. Advantageously, the carbon dioxide (CO2) can be generated by a concentration or purification process that increases its CO2 concentration. This may include concentration methods such as: amine-based methods, ammonia-based methods, pressure swing adsorption (PSA) methods, temperature swing adsorption (TSA) methods, cryogenic methods, or membrane methods.

[0139] Item 20. The method as described in Item 16 or 17, wherein the source of the carbon dioxide (CO2) in the gas used to partially or completely carbonate the aqueous sodium hydroxide (NaOH) solution is a fume generated by a plant or its equipment selected from the group consisting of: power plants, glass plants, steel or sintering plants, waste plants or waste-to-energy plants, pulp or paper mills, oil refineries, petrochemical plants, cement plants, tile manufacturing plants, brick manufacturing plants, mining processes, mineral processing plants, lime plants, ammonia plants, fertilizer plants, biochar plants, biogas plants, and combinations thereof.

[0140] Item 21. The method of any one of items 16 to 18, wherein the carbon dioxide (CO2) used for partially or completely carbonated in the sodium hydroxide (NaOH) aqueous solution is generated by acid etching of limestone (CaCO3) with an aqueous solution of hydrochloric acid (HCl) generated in group (A) of the electrodialysis unit stack in step (ii).

[0141] Item 22. The method as described in the preceding item, wherein the limestone (CaCO3) is an impure limestone containing less than 95 wt.% CaCO3, preferably less than 90 wt.% or less than 80 wt.% CaCO3.

[0142] Item 23. The method of any one of items 16 to 20, wherein the sodium chloride from the aqueous sodium chloride solution is derived from: solar pool salt or sea salt.

[0143] Item 24. The method of any one of items 16 to 21, wherein the sodium chloride is derived from: a seawater desalination method, preferably a reverse osmosis desalination method.

[0144] Item 25. The method of any of the preceding items, wherein the sodium chloride is derived from geological salt cavities or industrial crystallized salt.

[0145] Item 26. The method of any of the preceding items, wherein the sodium chloride (NaCl) solution is pretreated in step (i), and step (i) includes pretreating a brine containing sodium chloride, water, and impurities selected from: insoluble matter, soluble calcium and / or soluble magnesium, and optionally soluble metals, in the following steps.

[0146] - A purification step (i1) in which sodium carbonate is added, preferably as part of the washing solution containing an aqueous solution of sodium carbonate in the crystallization step (v), to precipitate calcium carbonate and at least partially remove soluble calcium from the brine.

[0147] And / or the addition of an aqueous sodium hydroxide solution, preferably as part of the aqueous sodium hydroxide solution produced by group (A) of the electrodialysis unit stack in step (ii), or as part of the aqueous sodium carbonate solution containing sodium hydroxide in the carbonation step (iii) to precipitate magnesium hydroxide.

[0148] These insoluble substances, precipitated calcium carbonate, and / or precipitated magnesium hydroxide are removed to obtain a pretreated sodium chloride aqueous solution.

[0149] - An optional ultrapurification step (i2) wherein the primary pretreated sodium chloride aqueous solution is treated in an ion exchange resin to further remove soluble calcium, soluble magnesium, and soluble metals, and to obtain a secondary pretreated sodium chloride aqueous solution.

[0150] In step (ii), the sodium chloride aqueous solution of the primary or secondary pretreatment is fed into the group (A) of the electrodialysis unit stack.

[0151] Item 27. The method of any of the preceding items, wherein the aqueous sodium hydroxide (NaOH) solution from step (ii) or the aqueous sodium carbonate (Na2CO3) solution from step (iii) or (iv) contains at least 1 mol of alkaline Na+ per liter (from NaOH or from Na2CO3), and preferably contains at most 3 mol of alkaline Na+ per liter.

[0152] Item 28. A sodium carbonate or sodium bicarbonate crystal produced by the method described in any of the preceding items, wherein the carbon dioxide (CO2) in the gas used to partially or completely carbonate the aqueous sodium hydroxide (NaOH) solution is at least partially biologically derived, or from a biological source not derived from fossil carbon or not derived from fossil carbon dioxide, or CO2 captured from the air.

[0153] Item 29. A sodium carbonate crystal or sodium bicarbonate crystal,

[0154] - Wherein at least 25 wt.% of its carbon content is of biological origin, preferably at least 80 wt.% of its carbon content is of biological origin; and

[0155] - and it contains up to 20 mg of calcium and / or up to 20 mg of magnesium per kilogram of crystals, preferably up to 8 mg of calcium and / or up to 8 mg of magnesium per kilogram of crystals.

[0156] Item 30. Sodium carbonate crystals or sodium bicarbonate crystals as described in the preceding item:

[0157] - Wherein at least 95 wt.% or at least 99 wt% of its carbon content is of biological origin or is CO2 captured from the air.

[0158] Item 31. Sodium carbonate crystals or sodium bicarbonate crystals as described in any one of Items 25 to 27 above, comprising up to 10 mg of iron (Fe) per kilogram of crystals, preferably up to 4 mg of iron (Fe).

[0159] Item 32. Sodium carbonate crystals or sodium bicarbonate crystals as described in any one of Items 25 to 28, wherein at least 10% by weight of such crystals exceeds 50 µm or exceeds 200 µm.

[0160] Item 33. Sodium carbonate crystals or sodium bicarbonate crystals as described in any one of Items 25 to 29, wherein up to 10% by weight of such crystals exceeds 1800 µm or exceeds 1100 µm.

[0161] Item 34. Sodium carbonate crystals or sodium bicarbonate crystals as described in any one of Items 25 to 30, wherein the intermediate size (D50) by weight is between 200 and 600 µm, preferably between 300 and 500 µm.

[0162] Item 35. Sodium carbonate crystals or sodium bicarbonate crystals as described in any one of items 25 to 31, wherein the crystals having a particle size fraction passing through a 125µm sieve are less than 8 wt%, preferably less than 4 wt%, and more preferably less than 1 wt.

[0163] The following examples are intended to illustrate the invention only and are not intended to limit the scope of the claimed invention. Example

[0164] Example 1

[0165] Figure 1 (Fig. 1) schematically illustrates the function of an electrodialysis unit in one embodiment of the method of the present invention, illustrating an advantageous configuration of the electrodialysis unit stack. In this example, the electrodialysis unit stack comprises three consecutive chambers: an alkali chamber, an acid chamber, and a salt chamber.

[0166] An aqueous solution containing sodium carbonate is advantageously fed into an alkaline chamber defined between a cation-selective permeable membrane and an anion-selective permeable surface of a bipolar membrane.

[0167] An aqueous solution is fed into the acid chamber, which is defined between the cation side of the bipolar membrane and the anion side of the bipolar membrane.

[0168] An aqueous solution containing sodium chloride is fed into a salt chamber, which is defined between an anion exchange membrane and a cation exchange membrane.

[0169] The formation of sodium hydroxide (NaOH) in the alkaline chamber and hydrochloric acid (HCl) in the acid chamber is achieved by the following: water molecules are split into hydroxide anions (OH-) in the alkaline chamber and into hydrated hydrogen cations (H+) in the acid chamber using a bipolar membrane; sodium ions (Na+) are transferred to the alkaline chamber through a cation-selective membrane; and chloride ions (Cl-) are transferred to the acid chamber through an anion exchange membrane using the voltage between the salt and acid chambers.

[0170] The effluent aqueous solution containing sodium hydroxide and sodium carbonate is removed from the alkali chamber and can be used as shown in Example 2. The sodium chloride-depleted effluent aqueous solution containing sodium chloride is removed from the salt chamber, and the sodium chloride can be reconcentrated by dissolving solid sodium chloride and optionally purifying the brine, or released into the sea if the initial brine comes from the desalination unit. Therefore, it avoids the local concentration of sodium chloride in the sea or in the brine pool, and thus limits the environmental impact of such release. It also makes it possible to circulate a portion of the sodium chloride leaving the desalination unit for added value.

[0171] The aqueous solution containing hydrochloric acid is removed from the acid chamber, thereby increasing the added value as mentioned in the above embodiments.

[0172] Example 2

[0173] Figure 2 (Fig. 2) schematically illustrates the setup for implementing an advantageous embodiment of the apparatus or method according to the invention. Figure 2The setup schematically shown includes a group of electrodialysis stacks (A) [represented by electrodialysis unit (1)], a carbonate tower (B) [or (2) in the figure], a storage device for sodium hydroxide and sodium carbonate aqueous solutions (C), an evaporator-crystallizer (D) [also labeled (3) in the figure], and a dryer (4).

[0174] An electrodialysis unit is a multi-compartment unit type comprising acid, alkali, and salt chambers, with a combination of cation, anion, and bipolar membranes. This type of unit is well-known in electrolysis technology and is widely used in the industrial production of aqueous solutions of alkalis and acids from aqueous solutions of the corresponding salts (Ullmann's Encyclopedia, Sodium Hydroxide, p. 376).

[0175] According to the present invention, an aqueous sodium chloride solution (6) is introduced into the salt chamber of the electrodialysis unit, while a diluted aqueous hydrochloric acid solution (9) and a diluted aqueous solution (11) containing sodium carbonate and caustic soda are introduced into the acid chamber and alkali chamber of the unit, respectively. During the operation of the electrodialysis unit, hydrochloric acid and sodium hydroxide are generated in the acid chamber and alkali chamber, respectively, while sodium chloride is gradually depleted in the salt chamber. The sodium chloride depleted outlet aqueous solution containing sodium chloride is extracted from the salt chamber. At the same time, an aqueous solution rich in sodium hydroxide containing sodium carbonate and sodium hydroxide and an aqueous solution rich in hydrochloric acid are extracted from the alkali chamber and acid chamber, respectively. The aqueous sodium chloride solution fed into the electrodialysis unit and the sodium chloride depleted outlet aqueous solution extracted from the unit constitute a sodium chloride solution loop. The sodium chloride depleted outlet aqueous solution is partially washed (7). Another aqueous sodium chloride solution (5) is fed into the loop to increase the sodium chloride concentration. Similarly, the aqueous hydrochloric acid solution fed into the electrodialysis unit and the hydrochloric acid-rich outlet aqueous solution extracted from the unit constitute a hydrochloric acid solution loop. The hydrochloric acid-rich effluent from the system is partially washed for downstream use (10). Water (8) is fed into the hydrochloric acid solution loop to adjust the hydrochloric acid concentration. In the same manner, the aqueous solution containing sodium carbonate and sodium hydroxide fed into the electrodialysis unit and the sodium hydroxide-rich effluent containing sodium carbonate and sodium hydroxide extracted from the unit constitute the sodium hydroxide and sodium carbonate solution loop. A first portion (12) of the sodium hydroxide-rich effluent containing sodium carbonate and sodium hydroxide extracted from the unit is recycled in the sodium hydroxide and sodium carbonate solution loop, while another portion (13) is sent to the carbonation tower (B) (also labeled (2)), and a gas containing carbon dioxide (14) (of which 82% of its carbon content is bio-derived) is generated from the waste-to-energy unit using waste biomass materials, and the CO2 gas is sent to the carbonation tower to obtain a carbonation liquid, in which sodium hydroxide is converted into sodium carbonate and water. The carbonated liquid is partially recycled in a sodium hydroxide and sodium carbonate solution loop (15), with another portion sent to a storage tank (C) where an aqueous sodium carbonate solution is stored. This allows sections (A) and (B) to utilize as much fluctuating energy as possible, making them more independent of sections (D) and (E) in producing variable flow rates of carbonated solution, thereby enabling sections (D) and (E) to operate at a constant nominal production rate. This allows for a reduction in the investment required to provide a constant power source for sodium carbonate or sodium bicarbonate crystals. A portion of the aqueous sodium carbonate solution is sent (17) to an evaporator-crystallizer (D) (also labeled (3) in the figure). In this unit, the slurry is subjected to controlled evaporation to crystallize sodium carbonate. In another unit (E) (not shown), sodium carbonate crystals (19) and mother liquor (18) are separated. The sodium carbonate crystals (19) are then sent to a drying unit for final processing, yielding dried sodium carbonate crystals as the final product (20).

[0176] The following examples illustrate the present invention. It refers to... Figure 2 During the daytime, a group of 10 electrodialysis stacks (1) with a 3-chamber configuration, consisting of bipolar membranes, anion exchange membranes, and cation exchange membranes, is constructed by alternating the assembly of bipolar membranes, anion exchange membranes, and cation exchange membranes (each of the 10 stacks comprises 10 membranes with a surface area of ​​1 m²). 2 A single unit (i.e., a total of 100 units, each unit comprising 3 rooms) at 1500 A / m 2 The system operated for 8 hours at a current density (40% of which was green electricity, mainly solar PV and hydropower). 1.2 t / h of substantially saturated brine (5) (containing 250 g sodium chloride per kg) was fed into the sodium chloride solution loop. Simultaneously, 22 t / h of a sodium chloride aqueous solution (6) (containing 155 g sodium chloride per kg) was introduced into the salt chamber of the electrodialysis unit. Meanwhile, 23 t / h of an aqueous solution containing sodium carbonate and sodium hydroxide (11) (containing 139 g sodium carbonate and 45 g sodium hydroxide per kg) and 20.4 t / h of a hydrochloric acid aqueous solution (9) (containing 34 g hydrochloric acid per kg) were fed into the alkali and acid chambers of the unit, respectively.

[0177] At the outlet of the electrodialysis unit, the following items were obtained:

[0178] -20.9 t / h of depleted or dilute brine, each kg containing 150 g of sodium chloride;

[0179] -20.5 t / h of hydrochloric acid-rich solution, each kg containing 40 g of hydrochloric acid;

[0180] -23.8 t / h of aqueous solution containing sodium carbonate and sodium hydroxide, with 134 g sodium carbonate and 50 g sodium hydroxide per kg.

[0181] To control the concentration of the hydrochloric acid solution, 3.2 t / h of water (8) was fed into the hydrochloric acid solution loop. 3.3 t / h of hydrochloric acid solution was extracted from the hydrochloric acid solution loop, containing 40 g of hydrochloric acid per kg (10). Similarly, 0.15 t / h of depleted or dilute brine was extracted from the sodium chloride solution loop, containing 150 g of sodium chloride per kg.

[0182] A 20.5 t / h outlet aqueous solution containing sodium carbonate and sodium hydroxide is recycled to the sodium hydroxide and sodium carbonate solution loop (12), of which 3.3 t / h is sent to the carbonation tower (2). Here, 90 kg / h of carbon dioxide (14) is also fed to obtain a carbonation liquid containing 180 g of sodium carbonate per kg. 1 t / h of the carbonation liquid (16) is stored in an insulated tank.

[0183] A portion (17) of the carbonated liquid is drawn from the storage tank (C) and introduced into the evaporator-crystallizer (3) at a constant flow rate of 0.8 t / h, where 134 kg / h of sodium carbonate crystals (17) are produced and separated from the mother liquor (18) and sent to the dryer (4) to obtain 128 kg / h of dried sodium carbonate crystals (19).

[0184] The mother liquor (18) is mainly recycled at the front end of the evaporator-crystallizer (3) feed, except for the following: it is washed out from the crystallizer to control and limit the concentration of soluble impurities (mainly sodium chloride and sodium sulfate) in the mother liquor present in the crystallizer (3) and adjusted according to the specification content of said impurities to be achieved in the dried sodium carbonate crystals (20).

[0185] Then, during the 16-hour period, three electrodialysis cell stacks were stopped (and their corresponding chambers were flushed), while the other seven electrodialysis cell stacks continued to operate at 1500 A / m. 2 Operating at a current density that represents the second production rate (low rate), producing approximately 0.7 times the caustic soda of the previous high operating rate, and representing a ratio of 1 / 0.7 = approximately 1.4 between the high and low production rates. This represents a production stream (16) of sodium carbonate solution fed into the storage tank at a rate of 0.7 t / h for 16 hours.

[0186] The average of the high production rate of 1.0 t / h during the 8-hour period and the low production rate of 0.7 t / h during the 16-hour period of the electrodialysis unit gives an average operating rate of 0.8 t / h over a given 24-hour period (the sum of 8 + 16 hours). Therefore, during the high operating rate period, an excess volume of carbonated solution of 1.0 - 0.8 = 0.2 t / h is generated during the 8-hour period of EDIA. Dividing this by 0.8 t / h = 0.25, this exceeds the average feed rate of the crystallizer and must be stored in the storage tank (C) during the 8-hour period. This excess is then consumed at a rate of 0.7 t / h during the 16-hour period of EDIA's low operating rate. The excess volume of the required storage corresponds to 0.25 × 0.8 t / h × 8 hours and represents 1.6 t of sodium carbonate solution to be stored, which is reasonable for a constant feed to the crystallizer equipment. This produces a constant crystal particle size distribution that meets consumer specifications.

[0187] The cleaning solution is recycled in the brine purification section, where the sodium chloride brine is purified before being fed to the electrodialysis unit (1). This allows the sodium chloride portion of the cleaning solution to be enriched and electrolyzed, and thus avoids loss. Sodium carbonate and optionally sodium sulfate are also enriched without loss, as they can be used as precipitants for calcium ions (as gypsum and / or calcium carbonate) in the purification section of the raw brine containing sodium chloride and its impurities before purification, and then used in the electrodialysis unit (1) as feed to the salt chamber as stream (6). This allows for a sharp reduction in the amount of brine to be cleaned and near-zero loss of sodium carbonate in the cleaned mother liquor from the evaporator-crystallizer (3) section.

[0188] Furthermore, the sodium carbonate produced using the carbonated solution obtained in the electrodialysis unit exhibits excellent purity, complementing its good particle size distribution stability and characteristics. Sodium carbonate crystals obtained over a 24-hour period have calcium (Ca) and magnesium (Mg) content less than 20 ppm and iron (Fe) content less than 10 mg / kg, with most samples taken per hour having calcium content less than 8 ppm, the same magnesium content, and iron content less than 4 ppm, respectively.

[0189] Sodium bicarbonate crystals can be produced from an aqueous solution containing sodium hydroxide and sodium carbonate, achieving crystal purity comparable to that obtained using carbon dioxide gas, because the inclusion of impurities is similar for both sodium carbonate and sodium bicarbonate, and the distribution of impurities in the crystals and mother liquor is generally more favorable for sodium bicarbonate than for sodium carbonate crystals.

[0190] The obtained sodium carbonate crystals unexpectedly exhibited a favorable particle size distribution, with less than 10% by weight exceeding 1100 µm. Medium-sized particles (D50) by weight were distributed between 480 µm and 620 µm over 24 hours, with the particle size fraction passing through a 125 µm sieve less than 1 wt.% for most samples. Furthermore, the abrasion behavior of this sodium carbonate was similar to that of the alkali ammonia process, meeting market requirements. Compared to existing alkali ammonia and natural alkali ore processes, the fossil CO2 footprint of the sodium carbonate was reduced by 3 to at least 5 times when using green electricity.

Claims

1. An apparatus for electrogenerating sodium carbonate (Na2CO3), the apparatus comprising: (A) An assembly of at least two electrodialysis unit stacks for electrodialysis of an aqueous sodium chloride (NaCl) solution into an aqueous sodium hydroxide (NaOH) solution and an aqueous hydrochloric acid (HCl) solution. The electrodialysis unit stack assembly operates at at least two production rates within a given time period; (B) One or more carbonate devices for partially or completely carbonated the aqueous sodium hydroxide (NaOH) solution into an aqueous sodium carbonate (Na2CO3) solution using a gas containing carbon dioxide (CO2); (C) One or more storage devices for the aqueous solution of sodium hydroxide (NaOH) or the aqueous solution of sodium carbonate (Na2CO3); (D) Crystallizer equipment for concentrating the sodium carbonate (Na2CO3) aqueous solution and producing sodium carbonate (Na2CO3) crystals and mother liquor; (E) One or more separation devices for separating and recovering sodium carbonate (Na2CO3) crystals from their mother liquor; Furthermore, the storage device for the sodium hydroxide (NaOH) aqueous solution or the storage device for the sodium carbonate (Na2CO3) aqueous solution has a volume sufficient to operate the crystallizer equipment at a constant production rate during the said time period.

2. The device as claimed in claim 1, wherein, The electrodialysis unit stack uses electricity to electrodialyze an aqueous solution of sodium chloride (NaCl) into an aqueous solution of sodium hydroxide (NaOH) and an aqueous solution of hydrochloric acid (HCl). And wherein the electricity is at least partially and preferably entirely 'green electricity' or has a reduced fossil CO2 footprint, and the electricity is preferably selected from the group consisting of: hydroelectric power, solar photovoltaic power, wind power, waste-to-energy power, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, geothermal power, electricity generated from compressed air—such as compressed air stored in underground cavities—nuclear power, electricity from combined heat and power (CHP) of steam and electricity, or mixtures thereof.

3. The device as described in claim 1 or 2, wherein, The equipment for producing sodium carbonate (Na2CO3) has at least a portion of multiple units (B) to (E) that use electricity, and the electricity used therein is at least partially and preferably entirely 'green electricity', or has a reduced fossil CO2 footprint.

4. The device as described in any of the preceding claims, wherein, This group (A) includes operating devices: - To regulate the production rate of at least a portion of the electrodialysis unit stack by adjusting the electrical intensity used for electrodialysis of the sodium chloride (NaCl) aqueous solution; and / or - Used to close and open at least a portion of the stack of electrodialysis unit bodies in this group; The group (A) of electrodialysis unit stacks operating at at least two production rates within a given time period.

5. The device as claimed in any of the preceding claims, wherein, This time period is at least 1 hour or at least 10 hours.

6. The device as claimed in any of the preceding claims, wherein, This time period is at most one week or at most one day.

7. The device as claimed in any of the preceding claims, wherein, The ratio of the at least two production rates, expressed as the ratio of high production rate to low production rate, is at least 1.2 or at least 1.

5.

8. The device as claimed in any of the preceding claims, wherein, The ratio of at least two production rates, expressed as the ratio of the higher production rate to the lower production rate, is at most 5 or at most 3.

9. The device as claimed in any of the preceding claims, wherein, The electrodialysis unit stack includes at least three chambers: an alkali chamber, an acid chamber, and a salt chamber, wherein the sodium chloride is fed, and wherein sodium ions permeate into the alkali chamber through a cation-selective permeation membrane, and chloride ions permeate into the acid chamber through an anion-selective permeation membrane.

10. The device as claimed in any of the preceding claims, wherein, The electrodialysis unit stack or at least part or all of the group (A) can operate in feed and discharge mode.

11. The device as claimed in any of the preceding claims, wherein, The crystallizer equipment (D) used to concentrate the sodium carbonate (Na2CO3) aqueous solution and produce sodium carbonate (Na2CO3) crystals and mother liquor includes: - Optional (D1) pre-evaporator device, such as a falling film evaporator or a forced circulation evaporator, for removing at least a portion of the water from the sodium carbonate (Na2CO3) aqueous solution; - (D2) Crystallizer devices, such as anhydrous sodium carbonate (Na2CO3) crystallizer, or sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or sesquicarbonate (Na2CO3.NaHCO3.2H2O) crystallizer.

12. The device as described in any one of claims 1 to 11, wherein, The crystallizer equipment (D) further includes: - Optional (D1) pre-evaporator devices, and - (D2) Sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, - Separation device (E2) for separating sodium carbonate decahydrate (Na2CO3.10H2O) crystals from their mother liquor. - A melting apparatus used to melt these sodium carbonate decahydrate (Na₂CO₃·10H₂O) crystals into a purified sodium carbonate solution. - (D2') Sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, which feeds purified sodium carbonate solution to produce (Na2CO3.H2O) crystals and its mother liquor. - (E) Separation device for separating sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor.

13. The device as described in any one of claims 1 to 11, wherein, The crystallizer equipment (D) further includes: - Optional (D1) pre-evaporator devices, and - (D2') Sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, which is fed with sodium carbonate solution to produce sodium carbonate monohydrate (Na2CO3.H2O) crystals and its mother liquor. - (E) Separation device for separating sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor. - A cleaning device for at least a portion of the mother liquor from the sodium carbonate monohydrate crystallizer. - (D2) Sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, whose feed comes from the cleaned mother liquor of the sodium carbonate monohydrate crystallizer. - Separation device (E') used to separate sodium carbonate decahydrate (Na2CO3.10H2O) crystals from their mother liquor. - A melting apparatus used to melt these sodium carbonate decahydrate (Na₂CO₃·10H₂O) crystals into a purified sodium carbonate solution. - The purified sodium carbonate solution is recycled to the (D2') sodium carbonate monohydrate (Na2CO3.H2O) crystallizer.

14. The device as claimed in any of the preceding claims, wherein, The mother liquor from the crystallizer equipment contains dissolved sodium carbonate and dissolved sodium chloride, and the crystallizer equipment (D) or the separation device (E) includes a cleaning device for cleaning at least a portion of the mother liquor from the crystallizer equipment ((D), (D2) or (D2')) and a recycling device for at least a portion of the cleaned mother liquor, for recycling at least a portion of the mother liquor to a sodium chloride brine purification module or to at least one electrodialysis unit stack of the group (A) or the front end of at least one electrodialysis unit stack of the group (A) to recover at least a portion of the sodium chloride from the cleaned mother liquor and electrolyze it into sodium hydroxide and / or hydrochloric acid.

15. A method for producing sodium carbonate (Na₂CO₃) crystals or sodium bicarbonate (NaHCO₃) crystals from sodium chloride (NaCl) solution, The method includes the following steps: (i) Optionally, the sodium chloride (NaCl) solution may be pretreated to remove at least a portion of impurities selected from the group consisting of: insoluble matter, calcium, magnesium, heavy metals, fluorides, bromides, iodides, sulfates, organic matter, and combinations thereof, to obtain an optional pretreated sodium chloride solution; (ii) In a group (A) of at least two electrodialysis unit stacks, the sodium chloride solution or the optional pretreated sodium chloride solution is electrodialyzed into an aqueous solution of sodium hydroxide (NaOH) and an aqueous solution of hydrochloric acid (HCl), wherein the group of electrodialysis unit stacks operates at at least two production rates within a given time period by closing and opening at least a portion of the electrodialysis unit stack during a given time period; (iii) The sodium hydroxide (NaOH) aqueous solution is partially or completely carbonated into a sodium carbonate (Na2CO3) aqueous solution using a gas containing carbon dioxide (CO2); (iv) Prior to step (iii), the aqueous sodium hydroxide (NaOH) solution is stored in one or more storage devices (C1), and / or After step (iii), the sodium carbonate (Na2CO3) aqueous solution is stored in storage device (C2); (v) In the crystallizer equipment (D), at least a portion of the sodium carbonate in the sodium carbonate solution is crystallized into sodium carbonate crystals and mother liquor. (vi) In the separation device (E), these sodium carbonate (Na2CO3) crystals are separated from the mother liquor. And these sodium carbonate (Na2CO3) crystals are recovered; (vii) Optionally, sodium bicarbonate (NaHCO3) crystals are crystallized by further carbonated in a crystallizer apparatus (D') with a gas containing CO2 or bio-derived CO2, thereby producing sodium bicarbonate crystals and their mother liquor. Optionally, these sodium bicarbonate crystals are separated from their mother liquor in a separation device (E') and the sodium bicarbonate (NaHCO3) crystals are recovered. Furthermore, the storage device for the sodium hydroxide (NaOH) aqueous solution and / or the storage device for the sodium carbonate (Na2CO3) aqueous solution has a volume sufficient to operate the crystallizer equipment at a constant production rate during the said time period.

16. The method as claimed in the preceding claim, wherein, The carbon dioxide (CO2) in the gas used to partially or completely carbonate the sodium hydroxide (NaOH) aqueous solution comes from a biological source that is not derived from fossil carbon or carbon dioxide, or from CO2 captured from the air.

17. The method of claim 15 or 16, wherein, The source of the carbon dioxide (CO2) in the gas used for partially or completely carbonated sodium hydroxide (NaOH) aqueous solution is the fumes generated by a plant or its equipment selected from the group consisting of: power plants, glass plants, steel or sintering plants, waste plants or waste-to-energy plants, pulp or paper mills, oil refineries, petrochemical plants, cement plants, tile manufacturing plants, brick manufacturing plants, mining processes, mineral processing plants, lime plants, ammonia plants, fertilizer plants, biochar plants, biogas plants, and combinations thereof.

18. The method according to any one of claims 15 to 17, wherein, The carbon dioxide (CO2) used to partially or completely carbonate the sodium hydroxide (NaOH) aqueous solution is generated by acid etching of limestone (CaCO3) with an aqueous solution of hydrochloric acid (HCl) generated in group (A) of the electrodialysis unit stack in step (ii).

19. A sodium carbonate or sodium bicarbonate crystal, produced by the method as described in any of the preceding claims, wherein, The carbon dioxide (CO2) in the gas used to partially or completely carbonate the aqueous sodium hydroxide (NaOH) solution is at least partially biologically derived, or from a biological source not derived from fossil carbon or carbon dioxide, or CO2 captured from the air.

20. A sodium carbonate crystal or sodium bicarbonate crystal, - Wherein at least 25 wt.% of its carbon content is of biological origin, preferably at least 80 wt.% of its carbon content is of biological origin; and - and it contains up to 20 mg of calcium and / or up to 20 mg of magnesium per kilogram of crystals, preferably up to 8 mg of calcium and / or up to 8 mg of magnesium per kilogram of crystals.

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