Plant for electrically producing sodium carbonate or bicarbonate

Abstract

Plant for electrically producing sodium carbonate (Na2CO3) comprising: (A) an electrodialyzer cellstack to electrodialyze a sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) solution and into a hydrochloric acid (HCl) solution, wherein the electrodialyzer cellstack comprises operation means enabling the electrodialyzer cellstack to be operated in at least 2 production rates on a given time period; (B) carbonating mean(s) to partially or totally carbonate the NaOH solution with CO2 into a Na2CO3 solution; (C) storage mean(s) of the NaOH solution or of the Na2CO3 solution; (D) a crystallizer equipment to concentrate Na2CO3 solution and to produce Na2CO3 crystals and a mother liquor; and wherein the storage means of the NaOH solution, or of the Na2CO3 solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period and of an equivalent electrical power storage per stored volume of at least 100 kWh / m3 calculated as the electrical power used by the electrodialyzer the NaCl to transform it into NaOH or Na2CO3 stored in the storage means (C).

Description

[0001] Plant for electrically producing sodium carbonate or bicarbonate

[0002] The present invention relates to a plant for producing sodium carbonate (Na2COs) and / or optionally sodium bicarbonate (NaHCCh) with reduced fossil carbon dioxide (CO2) emission, by electrodialysis of sodium chloride. The invention relates also to a process for producing sodium carbonate or bicarbonate. It relates also to sodium carbonate and bicarbonate crystals having a low and / or having ‘net zero’ fossil CO2 footprint.

[0003] Preferably, the said plant or the related method, use an electricity which is partly or totally a ‘green electricity’, or an electricity having a reduced fossil CO2 footprint. Advantageously, this electricity is selected among the group consisting of: hydraulic electricity (hydropower), solar photovoltaic electricity, wind electricity, waste to energy electricity, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from geothermal heat or low fossil CO2 footprint electricity such as from nuclear power.

[0004] More advantageously, the carbon dioxide (CO2) used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution produced by said plant or process is partly, or totally, biogenic, or from biogenic origin, or not deriving from fossil origin.

[0005] The said method enables sensitively a reduction of the CO2 fossil footprint when producing sodium carbonate or bicarbonate, compared to known processes and is a way to achieve net zero emission for such manufacturing and for the obtained products.

[0006] Technical field

[0007] Sodium carbonate (ISfeCCh), or soda ash, is one of the largest volume essential alkali product made worldwide with a total production in 2022 of more than 65 million tons. Sodium carbonate finds major use in the glass, chemicals, detergents industries, non-ferrous metallurgy, and also in the sodium bicarbonate production industry.

[0008] Sodium bicarbonate (NaHCCh) is also an essential chemical produced worldwide finding main uses in food and feed, acidic fumes mitigation, and pharmaceuticals uses.The main processes for manufacturing sodium carbonate production are the ammonia synthetic process (also called the SOLVAY ammonia soda process), the ammonium chloride process, and sodium carbonate or bicarbonate ore-based processes.

[0009] The ammonia synthetic process, which encompass one of its alternatives: the ‘dual process’ or HOU process, is the main one used worldwide (two thirds of the world production). This process consists in treating an ammoniacal brine comprising sodium chloride with a gas containing carbon dioxide. From the solution, sodium bicarbonate precipitates, is recovered and calcined to obtain sodium carbonate. Details of said process and of the production of refined sodium bicarbonate, is described in Ullmann's Encyclopedia of Industrial Chemistry (“Sodium carbonate” chapter, Vol. 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, as starting materials, worldwide abundant raw materials, which are: sodium chloride (NaCl) as source of sodium, and lime stone (CaCOs) as source of CO2 (or of the carbonate). And both raw materials are constantly generated and replenished by the nature, on a human timescale.

[0010] Said sourcing of carbonate in the ammonia soda process may be replaced partially or totally with CO2 from other industries or with biogenic CO2. And limestone (CaCCh), as source of alkalinity when calcined, can be substitute with non-fossil alkalis. One limit of the present ammonia soda process is that it uses thermic energy (9.7 to 13.6 GJ / ton of soda ash), part of it at high temperatures for limestone calcination (above 950°C). This high temperature energy is not easy to substitute with green energy such as fast developing solar photovoltaic or wind electrical power.

[0011] The main present alternative processes to produce sodium carbonate (soda ash) are those using sodium carbonate-containing minerals, such as fossil Trona, which represent one third of the world production of soda ash. The exploited ores related to alkaline volcanism, occur in a limited number of countries: mainly the USA, Turkey, China. The limited number of countries where such ore deposits occur, induces heavy intercontinental transports, and the exploitable reserves of identified deposits are limited. Availabilities of said ore deposits in Turkey represent about 20 to 40 years production, and a few centuries for the Wyoming USA deposit. Moreover, the CO2 content of the manufactured sodium carbonate or bicarbonate from such ores, is totally fossil and is freed in the atmospherewhen used in the glass or metallurgy industries. This avoid such processes to be sustainable in long term and meet net zero emission of fossil CO2 and of greenhouse gasses to be in line with COP21 commitments.

[0012] There is therefore a need to improve sodium carbonate and bicarbonate manufacturing processes so that to be fitted to the use of sustainable green energy and which can integrate non-fossil CO2 sourcing or captured fossil CO2 from other industries to meet at once, or progressively, net zero emissions requirements. Such improved processes should meet the need to massively use green and sustainable energy. Indeed, the International Energy Agency ‘net zero 2023 perspective for year 2050’, forecasts as achievable: 70% of total primary energy supply being renewable energy, about 10% nuclear energy, and less than 10% oil and coal fossil primary energy (compared to 80% of fossil fuels in 2021 including natural gas worldwide), and less than 10% others.

[0013] US6554990 (from Solvay) discloses a process for the manufacture of alkali metal hydroxide such as sodium hydroxide, according to which an electrodialysis cell containing three compartments is used, an aqueous alkali metal halide solution is circulated in a saline compartment of the cell, delimited between an anionic membrane and a cationic membrane, and an alkali metal halide is introduced into an acidic compartment of the cell, delimited between the anionic membrane and a cationic face of a bipolar membrane and an aqueous alkali metal hydroxide solution is extracted from an alkaline compartment of the cell, delimited between the cationic membrane and an anionic face of the bipolar membrane. Though said process induces the production of acid solutions of hydrochloric acid which comprise sodium chloride. This makes it difficult the use of said hydrochloric acid for other uses.

[0014] Brief description of the invention

[0015] The present invention relates to a plant for electrically producing sodium carbonate (ISfeCCh) comprising:

[0016] (A) an electrodialyzer cellstack to electrodialyze a sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and into a hydrochloric acid (HC1) aqueous solution,

[0017] wherein the electrodialyzer cellstack comprises operation means enabling the electrodialyzer cellstack to be operated in at least 2 production rates on a given time period;(B) carbonating mean(s) to partially or totally carbonate the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (ISfeCCh) aqueous solution; (C) storage mean(s) of the sodium hydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2COs) aqueous solution;

[0018] (D) a crystallizer equipment to concentrate the sodium carbonate (Na2COs) aqueous solution and to produce sodium carbonate (Na2COs) crystals and a mother liquor;

[0019] (E) separation mean(s) to separate the sodium carbonate (Na2COs) crystals from their mother liquor and recovering the sodium carbonate (Na2COs) crystals;

[0020] and wherein the plant is further characterized in that the storage means (C) of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2COs) aqueous solution :

[0021] - is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period; and

[0022] - has an equivalent electrical power storage ability per volume of at least 100 kWh / m3 calculated as the electrical power (expressed in kWh) used to electro-dialyze, in the electrodialyzer cellstack, the sodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) of the sodium hydroxide (NaOH) aqueous solution and / or of the sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).

[0023] Alternatively the present plant may be used for producing sodium bicarbonate (NaHCOs), by either adding a crystallization reactor means (D’) to bicarbonate the sodium carbonate aqueous solution from storage mean (C ) and crystallizing sodium bicarbonate crystals.

[0024] The present invention relates also to the sodium carbonate or bicarbonate crystals produced by the plant or the process of the present invention, wherein the carbon dioxide (CO2) in the gas used to partially or totally carbonate the sodium hydroxide (NaOH) aqueous solution is at least partly or is totally biogenic.

[0025] The present inventors found surprisingly, that storing the intermediate sodium hydroxide or sodium carbonate aqueous solutions represent a higher energy density per volume or per ton of equivalent electric energy than known accumulators such as classical batteries as lead-acid batteries (25 Wh / kg) or modern lithium-ion batteries (125 Wh / kg). Indeed considering the electricalenergy needed for electrically producing sodium carbonate from caustic soda needing about 2000 (+ / - 30%) kWh / 1 caustic soda and close stoichiometrically for the manufacturing of sodium carbonate, a storage of caustic soda aqueous solution or of sodium carbonate aqueous solution at 2 to 6 mol or more of alkaline sodium per kg of solution represents an equivalent storage of electrical energy of about 80 to 480 Wh or more / kg of solution. Examples of electrical energy storage equivalent according to alkaline sodium concentration per kg of aqueous solution:

[0026]

[0027] In those concentrations the weight density being close to 1 (1.04 to 1.3 kg / liter of alkaline aqueous solution), the said electrical energy storing weight densities are also close to, or of the same magnitude of order, of the equivalent electrical energy storing volumetric densities expressed in Wh / liter (kWh / 1). And they represent therefore also volumetric electrical energy storing densities close to or higher than lead-acid batteries or than modern lithium-ion batteries.

[0028] The remaining steps of the manufacture of sodium carbonate or bicarbonate (mainly crystallization and drying) represents a minor ratio of the overall consumed energy. The invention enables to run at a stable production rate the crystallization and drying equipment, without over-sizing their volumes and sizes, to compensate the fluctuant availability of the used electricity, in particular when solar or wind energy is used, or when the electrical network has to be balanced during peak-hours. Indeed this fluctuation of available energy is a major problem for industrials processes, and for operators investing in them.Also the present invention avoids and decreases sensitively the need of ‘strategic materials’ (such as lithium, nickel, cobalt, copper, cadmium, molybdenum, dysprosium, gallium, and other rare earths) for storing in batteries or other storing means, said green and low fossil CO2 energy. Indeed such ‘strategic materials’ are considered limited Earth resources, and represent a bottleneck and a limit for the energy transition of the industry to be done progressively by 2050.

[0029] Moreover, the production of sodium carbonate using electrodialysis of sodium chloride solutions into caustic soda (NaOH) and hydrochloric acid (HC1) has an electricity consumption sensitively decreased compared to the production of caustic soda and chlorine by membrane electrolysis of sodium chloride solutions. The decrease of energy consumption is down to about 30% less by electrodialysis compared to electrolysis. This eases decreasing the CO2 footprint for the needed electrical power for producing sodium carbonate / bicarbonate from caustic soda, and to switch to ‘green energy’.

[0030] Moreover the use of electrodialysis of sodium chloride solution into sodium hydroxide with sodium carbonate (in base chamber), gives good synergies with the use of gaseous CO2 from biogenic origin: impurities level requirements in the CO2 gas feeding an electrodialyzer, wherein at least part of the caustic soda (NaOH) is replaced by sodium carbonate with a lower pH, causes less precipitation of divalent and trivalent metal impurities than with sodium hydroxide at same molarity, preserving in this the operation life expectancy of the used membranes in the electrodialyzer. It also decreases the quantity of sodium hydroxide solution and hydrochloric acid, used for purifying the aqueous solution comprising sodium chloride fed in the salt chamber, such as the sodium hydroxide solution and hydrochloric acids used for secondary purification of brine in ion-exchange unit (as described in EU - BAT Reference document for the Production of Chlor-alkali - 2014 - edited by the Joint Research Center Institute - doi: 10.2791 / 13138 - § 2.5 Brine purification, and § 2.5.3.3).

[0031] The invention relates also to a method wherein part of the carbonated liquid obtained from carbonating the outlet solution of the base chamber of the above method is further processed to crystallize sodium carbonate crystals or sodium bicarbonate crystals.

[0032] The invention relates also to sodium carbonate crystals produced with a process using said plant of the invention. The present invention relates also tosodium carbonate crystals in which at least 25% of its carbon content is biogenic carbon, and comprise at most 20 mg calcium or magnesium per kilogram of sodium carbonate crystals. The invention relates also to sodium bicarbonate crystals in which at least 25% of its carbon content is biogenic carbon, and comprise at most 20 mg calcium or magnesium per kilogram of sodium bicarbonate crystals.

[0033] Indeed the inventors have discovered that even with low impurities levels such as calcium and magnesium made with the process of said invention, attrition of the obtained sodium carbonate is acceptable for main final uses and enable them to reduce scopes 1, 2 and 3, emissions of fossil CO2 as defined by the Greenhouse Gas Protocol organization.

[0034] The invention relates also to sodium carbonate crystals or the sodium bicarbonate crystals made according to the present process and in which at least 25% of the used electrical energy for the electrodialyzer is provided with electricity selected from the group consisting of: hydraulic electricity, solar photovoltaic electricity, wind electricity, waste to energy electricity, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, electricity generated from geothermal heat, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, or mixtures thereof.

[0035] Indeed the good synergy of the combination of electrodialysis and sodium carbonate or bicarbonate crystallization presents a surprising optima for decreasing the CO2 fossil footprint and achieve net zero fossil emission for manufacturing sodium carbonate or sodium bicarbonate, while reducing natural resources such as ‘strategic materials’ needed for the plant of the present invention, or for the related process, or for manufacturing said products.

[0036] Definitions

[0037] For purposes of the present specification, certain terms are intended to have the following meanings.

[0038] The term ‘electrodialysis’ refers to an electrochemical process which enables to at least partially or totally extract salt ions from one solution through an ion-exchange membrane subjected to an electrical field to another solution.

[0039] The term ‘electrodialyzer cellstack’ refers to an equipment wherein an electrodialysis process may be performed. It generally comprises several cellsdelimited by ion exchange membranes (also called ion perm-selective membranes).

[0040] The expression ‘to operate the crystallizer equipment in a constant production rate’ intends to mean that the production rate is between + / -10% of a nominal production rate on the given time period considered for the operation of the electrodialyzer cellstack which ‘is operated at the at least 2 production rates on the given time period’ . This variation of the nominal production rate within the ‘given time period’ of the crystallization sector is advantageously less than one third, preferably less than 20% of the bigger ratio of the at least 2 production rates of the electrodialyzer cellstack during the given time period. Generally the ‘given time period’ is daily or at least twice daily (such as solar photovoltaic production day / night, or mornings and evenings peak-hours). It may also be one or several days (for instance when considering wind power variability).

[0041] The term ‘biogenic carbon’ or ‘biogenic carbonate’ in the present specification, is carbon or carbonate whose carbon source was directly in equilibrium with CO2 in the atmosphere. In the present specification the biogenic (also called ‘biobased’) carbon content is measured according to ASTM D6866-22 Standard Test Method for determining the biobased content of solid, liquid, and gaseous samples using Radiocarbon Analysis. Said method provides accurate biobased / biogenic carbon content results: the method uses Isotope Ratio Mass Spectrometry (IRMS) techniques to quantify the biobased or biogenic content of a given product, based on carbon 14 isotope measurement of said sample. Instrumental error of the method is typically within 0.1-0.5 % (on relative standard deviation).

[0042] The term ‘green energy’ also called ‘renewable energy’ refers commonly to energy from renewable natural resources that are replenished on a human timescale. This encompasses solar energy (thermic or photovoltaic electricity energy), wind power, hydropower, bioenergy (derived from biomass (generally from terrestrial of from marine origin), and geothermal energy. In present specification low fossil CO2 footprint energy in complement of the ‘green energy’ listed above, includes heat or cold recovered by heat pumps, and nuclear energy.

[0043] The term ‘green electricity’ also called ‘renewable electricity’ refers commonly to electricity produced from renewable natural resources that are replenished on a human timescale. This encompasses solar electricity (either from thermic origin, or from solar photovoltaic production), wind power,hydropower or hydraulic electricity, marine power, electricity deriving or produced from bioenergy (ie. derived from biomass, and generally from terrestrial of from marine origins), and electricity derived from geothermal energy. In present specification low fossil CO2 footprint electricity in complement of the ‘green energy’ listed above, includes nuclear power (electricity produced from nuclear energy).

[0044] The expression ‘feed and bleed mode’ relates to operating an electrodialyzer cellstack so that an original solution feeds a loop of an aqueous solution feeding a least one chamber of an electrodialyzer cellstack, and said loop of the aqueous solution feeding the at least one chamber collects also at least part of the aqueous solution exiting said chamber, and a bleed is operated on said loop or on the solution exiting the chamber so that the volume of the solution in the loop is controlled to be more or less constant, such as for instance + / -15%. This mode of operation of an electrodialyzer has the interest to operate the electrodialyzer in concentrations range which may be different from the concentrations of the original solution that feeds the loop.

[0045] The term "purge” refers to a stream withdrawn from a part of a process to limit impurity concentration in this process.

[0046] The expression “derived from” for instance “sodium chloride derived from: a solar pond salt or from sea” refers to a sodium chloride stream withdrawn as such from said solar pond or sea, or to a stream that have been subjected to one or several chemical engineering operation downstream the said crystallizer (such as: purifying, concentrating, thermally transforming, decanting, centrifuging, crystallizing, filtering, evaporating, drying, diluting, heating, cooling operations), or that has been mixed with one or more other stream(s), though keeping at least one part of the sodium chloride withdrawn from said solar pond or sea.

[0047] The term "impurity” refers to a compound different from the sodium carbonate and / or the sodium bicarbonate salt to be produced.

[0048] The term “carbonating” refers to the action of increasing the amount of total carbonate (i.e. carbonate and bicarbonate) of a stream.

[0049] The term “bicarbonating” refers to the action of increasing the amount of bicarbonate of a stream.

[0050] The term "comprising" includes "consisting essentially of and also "consisting of.

[0051] In the present specification, the terms “%”, “% by weight”, “wt%”, “wt. %”, “weight percentage”, or “percentage by weight” can be usedinterchangeably, unless the “%” term is explicitly referred to an other physical unit (such as for instance “% in mole”, or mol. %”, “% in volume” or “vol. %”, etc....).

[0052] A plurality of elements includes two or more elements.

[0053] The phrase ‘A and / or B’ refers to the following selections: element A; or element B; or combination of elements A and B (A+B). The phrase ‘A and / or B’ is equivalent to at least one of A and B. The phrase ‘A and / or B’ equates to at least one of A and B.

[0054] The phrase ‘Al, A2, ... and / or An’ with n > 3 includes the following choices: any single element Ai (i= 1, 2, ...n); or any sub-combinations of from two to (n-1) elements chosen from Al, A2, ..., An; or combination of all elements Ai (i=l, 2, ... n). For example, the phrase ‘Al, A2, and / or A3’ refers to the following choices: Al; A2; A3; A1+A2; A1+A3; A2+A3; or A1+A2+A3.

[0055] In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range: excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.

[0056] In the present specification, the description of several successive ranges of values for the same variable also comprises the description of embodiments where the variable is chosen in any other intermediate range included in the successive ranges. Thus, for illustration purpose, when it is stated that "the element X is generally at least 10, advantageously at least 15", the present description also includes another embodiment where a new minimum can be selected between 10 and 15, for example: where "the element X is at least 11", or also where: "the element X is at least 13.74", etc.; 11 or 13.74 being values included between 10 and 15. Also for illustration purpose, when it is indicated that "the element X is generally at most 15, advantageously at most 10", the present description also includes another embodiment where a new maximum can be selected between 10 and 15.

[0057] In the present description, wherein an element or composition is said to be included in and / or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components.For example, when in an embodiment the choice of an element from a group of elements is described, the following embodiments are also explicitly described:

[0058] - the choice of two or more elements from the group,

[0059] - the choice of an element from a subgroup of elements consisting of the group of elements from which one or more elements have been removed.

[0060] The use of the singular ‘a’ or ‘one’ herein includes the plural unless specifically stated otherwise.

[0061] If the term "about" is used before a quantitative value, this corresponds to a variation of ± 10% of the nominal quantitative value, unless otherwise indicated.

[0062] Brief description of the figures

[0063] Figure 1 (Fig. 1) shows schematically the function of an electrodialyzer in one embodiment of the plant and process of the present invention.

[0064] Figure 2 (Fig. 2) shows schematically an equipment for implementing an embodiment of the plant or of the process according to the invention.

[0065] Figure 3 (Fig. 3) shows schematically an equipment for implementing an embodiment of the plant or of the process according to the invention.

[0066] Detailed description of the invention

[0067] Electrodialysis refers to electrochemical processes which enable to extract salt ions from one solution through an ion-exchange membrane subjected to an electrical field to another solution.

[0068] Electrodialysis technologies are known: they are mainly used for electroseparation processes, such as the production of drinkable water, industrial waste water treatments, acid or alkali recovery in metal plating industries, food and pharmaceuticals processes. Electrodialysis principles are well described for instance in Ullmann’s Encyclopedia of Industrial Chemistry (2011 edition, Wiley -VCH Verlag GmbH & Co, Vol. 12 pp 273-313, Electrochemistry), or in Technique de 1’Ingenieur Encyclopedia (2006 edition, Chapter Electrodialyse, J2840 VI, 2006, pp 1-15 and Technical appendixes pp 1-3).

[0069] In a preferred mode of the present invention, the electrodialysis is operated in an electrodialysis cellstack which comprises combining, within a set of adjoining chambers, bipolar ion-exchange membranes with anionic and / or cationic ion-exchange membranes.The anionic membranes are ion-exchange membranes that are permeable to anions and, ideally, impermeable to cations. The cationic membranes are themselves permeable to cations and impermeable to anions. A bipolar membrane is an ion-exchange membrane comprising a cationic face and an anionic face. Such membranes may be produced by joining a cationic membrane and an anionic membrane. The bipolar membrane may for example be produced by the process described in WO 01 / 79335 in the name of Solvay.

[0070] Within the bipolar membrane, under the action of a sufficient local electrical field, the dissociation of the water that has diffused therein, to its H+and OH' ions takes places, which ions then migrate on both sides of this membrane. There is therefore acidification in one of the chambers adjacent to the bipolar membrane and alkalization in the other adjacent chamber. Successive bipolar membranes are separated by cationic or anionic monopolar membranes. When the electrodialyzer only possesses bipolar membranes and one type of monopolar membranes (cationic or anionic), they are said to have two (types of) chambers. The electrodialyzer used in the method of the present invention possesses preferably only bipolar and anionic membranes.

[0071] The chamber located between the anionic face of the bipolar membrane and a cationic membrane constitutes a base chamber. In this chamber there is a supply of OH' ions originating from the bipolar membrane. In the method of the present invention, the base chamber is preferably fed with an aqueous solution comprising sodium carbonate. The OH' ions supplied from the bipolar membrane will provide alkalinity to absorb then acidic carbon dioxide to form a carbonated solution.

[0072] In an advantageous embodiment the electrodialyzer used in present invention comprises at least three chambers one of which is a salt chamber, a second one is a base chamber and a third one is an acid chamber.

[0073] A first advantage of the present invention is the decrease of the need to store fluctuating electricity such as the one produced by solar energy or wind energy (highly variable in a daily period or days period such as photovoltaic electricity or wind power electricity that constitutes and will constitutes major sourcing of renewable electricity by 2050.

[0074] A second advantage of the present invention is the possibility to store electrical energy at an equal or a higher energy density (per unit of volume and / or per unit of weight) and with a lower consumption of ‘strategic materials’ for the industrial use of the manufacture of sodium carbonate or sodiumbicarbonate, in particular for the manufacture of said products with low fossil CO2 footprint.

[0075] A third advantage of the present invention is the reduced electrical energy consumption of the plant to produce sodium carbonate or bicarbonate compared to an equivalent plant wherein an electrolyzer would be used rather than an electrodialyzer, decreasing as such the CO2 footprint related to the electrical energy production, whatever the electrical energy origin, easing as such a nearzero CO2 foot-print of the produced sodium carbonate or bicarbonate.

[0076] A fourth advantage of the present invention is the possibility to use renewable energy or low fossil CO2 footprint energy, replacing high temperature steps of conventional processes (limestone calcination into lime used in both Soda ammonia process and Trona solution mining process using generally coal) and replacing it with electricity having a reduced fossil CO2 footprint, said electricity being preferably selected among the group consisting of: hydraulic electricity, photovoltaic electricity, wind electricity, waste to energy electricity, electricity generated from biogas, electricity generated from biomass combustion, electricity generated from hydrogen combustion, electricity generated from geothermal heat, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, and mixtures thereof. This contributes also to a near-zero CO2 foot-print of the produced sodium carbonate or bicarbonate. This is particularly interesting when said low fossil CO2 footprint energy is used by other consumers (for instance towns’ uses at peak hours for lightning, heating or cooling, or domestic appliances) and is less available temporarily for industrial uses.

[0077] A fifth advantage of the present invention is that the crystallization equipment producing sodium carbonate or bicarbonate crystals is operating at a more constant operation conditions (such as the residence time and the growing rate of the crystals in the crystallizers) inducing more stable particle size distribution of the produced sodium carbonate or bicarbonate crystals. Indeed operating the crystallizer (D) in much higher rate generates a higher quantity of fines crystals that constitute problems for main customers uses, such as glass manufacturers (giving less homogeneity in the mixture fed in glass oven, also dust generation when the mixture is loaded in the oven, melted incrustations on the oven surfaces above the melt, and potential sanitary problems for the workers in said areas). Such problem is much less sensitive or does not occur for industrials producing caustic soda and chlorine: the electrolyzer stack generates aliquid (sodium hydroxide solution) that is quite less impacted than crystallized solids such as sodium carbonate or bicarbonate by production rate.

[0078] A sixth advantage of the present invention is to ease CO2 capture from fumes, or from other industries, or from the atmosphere, as the produced sodium hydroxide is highly reactive to capture said CO2 even at low concentration (with CO2 at concentrations lower than 30% vol. or even lower than 10% vol. on dry gases), or even for capturing efficiently CO2 from Earth atmosphere (a. 420 ppm by volume) and to increase the circularity of CO2 resources by manufacturing sodium carbonate or bicarbonate.

[0079] A seventh advantage of the present invention is when CO2 capture, or CO2 from other industries, are not available locally to be able to use limestone (CaCCh) of low purity at 60 to 85% CaCCh (which is not at all recommended in Ammonia soda process, as mineral impurities of limestone mainly clays and aluminum or iron silicates form with hydrated lime Ca(OH)2 insoluble matters, generating a loss of calcium hydroxide, and heavy incrustations in distillers).

[0080] A eighth advantage of the present invention is to increase by synergy the use of other by-products, such as concentrated brines from desalination discharge from reverse osmosis or from multiple effects evaporation equipment in regions of the world were drinkable water is scarce, and to use it as NaCl raw material for the present method and by so-doing, reducing the stress on existing natural resources.

[0081] A ninth advantage of the present invention is the possibility to process the sodium hydroxide aqueous solution, or the carbonate solution exiting from the base chamber, even if the said sodium hydroxide or carbonate solution comprises traces of sodium chloride generated by the leakage of chlorides ions from the salt chamber to the base chamber through a cationic membrane of the electrodialyzer, as sodium chloride will be then separated during crystallization of sodium carbonate or bicarbonate and will remain in the mother liquor of the crystallizers. Said sodium chloride then purged with part of sodium carbonate can be recycled upfront the brine (NaCl solution) to be used for purifying said brines in impurities such as calcium, before feeding it to the salt chamber, avoiding or reducing sodium carbonate loss and enabling a useful synergy between electrodialyzer sector and the crystallization of sodium carbonate or bicarbonate.

[0082] Therefore, the method of the present invention enables to improve the circularity of the use of raw materials such as sodium chloride or limestone, and optimizes by synergy, a decrease of the CO2 fossil footprint of the manufactureof sodium carbonate or bicarbonate, and a decrease of consumption of ‘strategic materials’, paving the way to net zero emission for sodium carbonate or bicarbonate manufacturing.

[0083] The present invention relates to several advantageous embodiments which are described hereafter as ‘Items’.

[0084] Item 1. Plant for electrically producing sodium carbonate (Na2CO3) comprising:

[0085] (A) an electrodialyzer cellstack to electrodialyze a sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and into a hydrochloric acid (HC1) aqueous solution,

[0086] wherein the electrodialyzer cellstack is operated in at least 2 production rates on a given time period;

[0087] (B) carbonating mean(s) to partially or totally carbonate the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2COs) aqueous solution; (C) storage mean(s) of the sodium hydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2COs) aqueous solution;

[0088] (D) a crystallizer equipment to concentrate the sodium carbonate (Na2COs) aqueous solution and to produce sodium carbonate (Na2COs) crystals and a mother liquor;

[0089] (E) separation mean(s) to separate the sodium carbonate (Na2COs) crystals from their mother liquor and recovering the sodium carbonate (Na2CO3)crystals;

[0090] and wherein the plant is further characterized in that the storage means (C) of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2COs) aqueous solution :

[0091] - is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period; and

[0092] - has an equivalent electrical power storage ability per volume of at least 100 kWh / m3 calculated as the electrical power (expressed in kWh) used to electro-dialyze, in the electrodialyzer cellstack, the sodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) of the sodium hydroxide (NaOH) aqueous solution and / or of the sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).

[0093] Item 2. The plant of item 1, wherein the electrodialyzer (A) uses electricity to electrodialyze the sodium chloride (NaCl) aqueous solution into thesodium hydroxide (NaOH) aqueous solution and into the hydrochloric acid (HC1) aqueous solution,

[0094] and wherein the electricity is at least partly, and preferably totally, a ‘green electricity’ or has a reduced fossil CO2 footprint, preferably selected among the group consisting of: hydraulic electricity, solar photovoltaic electricity, wind electricity, waste to energy electricity including waste heat from geothermal energy, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, electricity generated from geothermal heat, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, electricity from cogeneration of steam and electricity, or mixtures thereof.

[0095] Item 3. The plant of items 1 or 2, wherein the plant to produce sodium carbonate (Na2COs) have at least part of the pieces of equipment (B) to (E) that use electricity and wherein the used electricity is at least partly, and preferably totally, a ‘green electricity’, or has a reduced fossil CO2 footprint, preferably selected among the group consisting of: hydraulic electricity, solar photovoltaic electricity, wind electricity, waste to energy electricity, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, electricity generated from geothermal heat, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, electricity from cogeneration of steam and electricity, or mixtures thereof.

[0096] Item 4. The plant of any preceding items, wherein the at least 2 production rates ratio expressed as the ratio of a high production rate to a low production rate is at least 1,2 or at least 1,5.

[0097] Item 5. The plant of any preceding items, wherein the at least 2 production rates ratio expressed as the ratio of a high production rate to a low production rate is at most 5 or at most 3.

[0098] Item 6. The plant of any preceding items, wherein the said given time period is at least 1 hour, preferably at least 10 hours.

[0099] Item 6’. The plant of any preceding items, wherein the said given time period is at least 6 hours, preferably at least 12 hours.

[0100] Item 7. The plant of any preceding items, wherein the said given time period is at most one week, preferably at most 1 day.Item 8. The plant of any preceding items, wherein the electrodialyzer cellstack (A) to electrodialyze the sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and a hydrochloric acid (HC1) aqueous solution, comprises at least 2 chambers: a base chamber wherein the sodium hydroxide (NaOH) aqueous solution is produced and an acid chamber wherein the hydrochloric acid (HC1) aqueous solution is produced.

[0101] Item 9. The plant of the preceding item, wherein the electrodialyzer cellstack (A) comprises at least 3 chambers: a base chamber, an acid chamber, and a salt chamber wherein the sodium chloride is fed and wherein the sodium ions are permeated to the base chamber through a cation permselective membrane and the chloride ions are permeated to the acid chamber through an anion permselective membrane.

[0102] Item 10. The plant of any preceding items, wherein the electrodialyzer cellstack (A), can be, or is, operated in a feed and bleed mode.

[0103] Item 11. The plant of any preceding items, wherein the crystallizer equipment (D) to concentrate the sodium carbonate (Na2COs) aqueous solution and to produce sodium carbonate (Na2COs) crystals and a mother liquor, comprises:

[0104] - an optional (DI) pre-evaporator means such as: a falling film evaporator or a forced circulation evaporator, to remove at least part of the water of the sodium carbonate (Na2COs) aqueous solution;

[0105] - (D2) crystallizer means such as a sodium carbonate anhydrous (Na2COs) crystallizer, or a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or a sodium sesqui carb onate (Na2CO3.NaHCO3.2H2O) crystallizer.

[0106] Item 12. The plant of any preceding items 1 to 11, wherein the crystallizer equipment (D) further comprises:

[0107] - an optional (DI) pre-evaporator means, and

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

[0109] - a separation means (E2) to separate sodium carbonate decahydrate (Na2CO3. IOH2O) crystals from their mother liquor,

[0110] - a melting device to melt the sodium carbonate decahydrate (Na2CO3. IOH2O) crystals into a purified sodium carbonate solution,

[0111] - (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with the purified sodium carbonate solution to produce (Na2CO3.H2O) crystals and their mother liquor,- (E) a separation means to separate sodium carbonate monohydrate (Na2COs.H2O) crystals from their mother liquor.

[0112] This item 12 embodiment, comprising a sodium carbonate decahydrate crystallizer and then a sodium carbonate monohydrate crystallizer is particularly advantageous when the produced sodium carbonate (Na2COs) aqueous solution comprises high levels of sodium chloride (NaCl), such as at least 1.0 wt.% or at least 1.5 wt.% NaCl. This embodiment enables to reduce the energy consumption of such configuration for concentrating the NaCl impurity and others (Na2SO4, KC1, ...) and reducing sodium carbonate in the final purge compared to a configuration according to the following item 13, comprising a monohydrate crystallizer and then the treatment of the purge of the monohydrate crystallizer in a decahydrate crystallizer.

[0113] Item 13. The plant of any preceding items 1 to 11, wherein the crystallizer equipment (D) further comprises:

[0114] - an optional (DI) pre-evaporator means, and

[0115] - (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with the sodium carbonate solution to produce sodium carbonate monohydrate (Na2CO3.H2O) crystals and their mother liquor,

[0116] - (E) a separation means to separate sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor,

[0117] - a purge means of at least part of the mother liquor from the sodium carbonate monohydrate crystallizer,

[0118] - (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer fed with the purged mother liquor from the sodium carbonate monohydrate crystallizer, - a separation means (E’) to separate sodium carbonate decahydrate (Na2CO3. lOEEO) crystals from their mother liquor,

[0119] - a melting device to melt the sodium carbonate decahydrate (Na2CO3. IOH2O) crystals into a purified sodium carbonate solution,

[0120] - a recycling means of the purified sodium carbonate solution to recycle it to the (D2’) sodium carbonate monohydrate (Na2CO3.H2O) crystallizer.

[0121] This item 13 embodiment, comprising first a sodium carbonate monohydrate crystallizer and then a sodium carbonate decahydrate crystallizer for treating the mono purge, recovering most of the sodium carbonate from the purge, and concentrating the purge in sodium chloride, is particularly advantageous when the produced sodium carbonate (Na2CC>3) aqueous solution out of the electrodialyzer, and feeding the mono crystallizer, comprises lower levels ofsodium chloride (NaCl), such as: at most 1.5 wt.% or even at most 1.0 wt.% NaCl. As this enables to reduce the energy consumption of such configuration compared to a configuration according to the preceding item 12, comprising a deca(hydrate) crystallizer for purifying first the content the sodium carbonate aqueous solution in NaCl (and other impurities cited above), and then a mono(hydrate) crystallizer for crystallizing sodium carbonate crystals, and then the treatment of the purge of the mono crystallizer back in the deca crystallizer, and purging there the sodium chloride and other impurities.

[0122] Item 14. The plant of any 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 means (E) comprises a purge means for purging at least part of the mother liquor from the crystallizer equipment ( (D), (D2), or (D2’) ) and a recycling means of the least part of the purged mother liquor, to recycle the at least part of the mother liquor to a sodium chloride brine purification module or to the EDIA cellstack or upfront the EDIA cellstack to recover at least part of the sodium chloride of the purged mother liquor and to electrolyze it into sodium hydroxide and / or hydrochloric acid.

[0123] Item 15. Process for producing sodium carbonate (Na2COs) crystals or sodium bicarbonate (NaHCCE) crystals from a sodium chloride (NaCl) solution, comprising the following steps :

[0124] (i) optionally pre-treating the sodium chloride (NaCl) solution in removing at least part of impurities selected from the group consisting of: insolubles, calcium, magnesium, heavy metals, fluoride, bromide, iodide, sulfate, organics and combination thereof to obtain an optional pre-treated sodium chloride solution;

[0125] (ii) electro-dialyzing in an electrodialyzer cellstack (A), the sodium chloride solution or the optional pre-treated sodium chloride solution into a sodium hydroxide (NaOH) aqueous solution and into a hydrochloric acid (HC1) aqueous solution, wherein the electrodialyzer cellstack is operated in at least 2 production rates on a given time period;

[0126] (iii) carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2COs) aqueous solution;

[0127] (iv) storing the sodium hydroxide (NaOH) aqueous solution into a storage mean(s) (Cl) before step (iii), and / orstoring the sodium carbonate (Na2COs) aqueous solution into a storage means (C2) after step (iii);

[0128] (v) crystallizing at least part of the sodium carbonate of the sodium carbonate solution into sodium carbonate crystals and a mother liquor in a crystallizer equipment (D);

[0129] (vi) separating the sodium carbonate (ISfeCCh) crystals from the mother liquor in a separation means (E),

[0130] and recovering the sodium carbonate (ISfeCCh) crystals;

[0131] (vii) optionally crystallizing sodium bicarbonate (NaHCCh) crystals by further carbonating the sodium carbonate (ISfeCCh) aqueous solution from step (iii) with a gas comprising CO2 or biogenic CO2 in a crystallizer equipment (D’), so that to produce sodium bicarbonate crystals and their mother liquor, optionally separating the sodium bicarbonate crystals from their mother liquor in a separation means (E’), and recovering the sodium bicarbonate (NaHCCE) crystals;

[0132] and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, and / or the storage means of the sodium carbonate (ISfeCCE) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period, and

[0133] the storage means volume has an equivalent electrical power storage ability per volume of at least 100, preferably at least 200, more preferably 300 kWh / m3 calculated as the electrical power (expressed in kWh) used to electro-dialyze the sodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) of the produced sodium hydroxide (NaOH) aqueous solution and / or of the produced sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).

[0134] Item 16. The process of the preceding item, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution, or the sodium carbonate aqueous solution, is partially or totally biogenic, or is CO2 captured from the air. Advantageously, the carbon dioxide (CO2) may result from concentration or purification processes which increase its CO2 concentration. This may include concentration processes such as: an amine based process, an ammonia based process, a Pressure Swing Absorption (PSA) process, a Temperature Swing Absorption (TSA) process, a cryogenic process, or a membrane process.Item 17. The process of items 15 or 16, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution derives from fumes generated by plants or equipment thereof selected from the group consisting of: a power plant, a glass plant, a steel or sinter plant, a waste plant or waste-to-energy plant, a pulp or paper plant, an oil refinery, a petro-chemical plant, a cement plant, a tile manufacturing plant, a brick manufacturing plant, a mining process, a mineral processing plant, a lime plant, an ammonia plant, a fertilizer plant, a biochar plant, a biogas plant, and combinations thereof.

[0135] Item 18. The process of any of the items 15 to 17, wherein the carbon dioxide (CO2) used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution is generated by acid attack of limestone (CaCOs) with the hydrochloric acid (HC1) aqueous solution generated in the electrodialyzer cell stack at step (ii).

[0136] Item 19. The process of the preceding item, wherein the limestone (CaCOs) is an impure limestone comprising less than 95 wt.% CaCOs, preferably less than 90 wt.% or less than 80 wt.% CaCOs content.

[0137] Item 20. The process of any of the items 15 to 19, wherein the sodium chloride from the sodium chloride aqueous solution derives from: a solar pond salt, or sea salt.

[0138] Item 21. The process of any the items 15 to 20, wherein the sodium chloride derives from: a seawater desalination process, preferably from a reverse osmosis desalination process.

[0139] Item 22. The process of any of the preceding items, wherein the sodium chloride derives from a geological salt cavity, or is an industrial crystallized salt.

[0140] Item 23. The process of any preceding items, wherein the sodium chloride (NaCl) solution is pre-treated at a step (i), and the step (i) comprises pre-treating a brine comprising sodium chloride, water, and impurities selected among: insolubles, soluble calcium and / or soluble magnesium, and optional soluble metals,

[0141] - in a primary purification step (il) wherein sodium carbonate is added, preferably as part of a purge of the crystallizing step (v) comprising sodium carbonate aqueous solution, to precipitate calcium carbonate and remove at least partly soluble calcium from the brine,

[0142] and / or wherein a sodium hydroxide aqueous solution is added, preferably as part of the one produced by the electrodialyzer cell-stack at step (il), or as part of the- 1 -

[0143] sodium carbonate aqueous solution comprising sodium hydroxide of the carbonation step (iii) to precipitate magnesium hydroxide,

[0144] removing the insolubles, the precipitated calcium carbonate and / or the precipitated magnesium hydroxide to obtain a primary pre-treated sodium chloride aqueous solution,

[0145] - an optional super-purification step (i2) wherein the primary pre-treated sodium chloride aqueous solution is treated in an ions-exchange resin to remove further: soluble calcium, soluble magnesium, and soluble metals and for obtaining a secondary pre-treated sodium chloride aqueous solution

[0146] and feeding the electrodialyzer cellstack with the primary or the secondary pretreated sodium chloride aqueous solution at step (ii).

[0147] Item 24. The process of any preceding items wherein the sodium hydroxide (NaOH) aqueous solution from step (ii) or the sodium carbonate (Na2COs) aqueous solution from steps (iii) or (iv) comprises at least 1 or at least 2 mol alkaline Na+ (from NaOH or from Na2CO3) per liter.

[0148] Item 24’. The process of any preceding item wherein the sodium hydroxide (NaOH) aqueous solution from step (ii) or the sodium carbonate (Na2COs) aqueous solution from steps (iii) or (iv) comprises at most 6 or at most 3 mol alkaline Na+ (from NaOH or from Na2CO3) per liter.

[0149] Item 25. The process of any preceding item wherein the electrodialyzer cell stack is operated in feed and bleed mode.

[0150] Item 26. The process of any preceding item wherein the electrodialyzer cell stack is operated at constant + / -15% feed flow rate, preferably at constant + / -5% feed flow rate within the said time period.

[0151] Item 27. The process of any preceding item wherein the electrodialyzer cell stack is operated at a constant temperature value + / -15%, preferably at constant temperature value + / - 5% within the said time period.

[0152] Item 28. The sodium carbonate or bicarbonate crystals produced by the process of any preceding items, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution is at least partly biogenic.

[0153] Item 29. Sodium carbonate crystals or sodium bicarbonate crystals - wherein at least 25 wt.% of its carbon content is biogenic, preferably at least 80 wt. % of its carbon content is biogenic; and

[0154] - and comprising at most 20 mg calcium and / or at most 20 mg magnesium perkilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals.

[0155] Item 30. Sodium carbonate crystals or sodium bicarbonate crystals according to the preceding items:

[0156] - wherein at least 95 wt.% or at least 99 wt% of its carbon content is biogenic, or is CO2 captured from the air.

[0157] Item 31. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the preceding items 28 to 30, comprising at most 10 mg iron (Fe), preferably at most 4 mg iron (Fe) per kilogram of crystals.

[0158] Item 32. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the items 28 to 31 wherein at least 10% in weight of the crystals are above 50 pm, or above 200 pm.

[0159] Item 33. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the items 28 to 32 wherein at mostl0% in weight of the crystals are above 1800 pm, or above 1100 pm

[0160] Item 34. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the items 28 to 33 wherein the medium size in weight (D50) is comprised between 200 and 600 pm, preferably comprised between 300 and 500 pm.

[0161] Item 35. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the items 28 to 33 wherein the crystals have a size fraction passing a 125 pm sieve is less than 8 wt%, preferably less than 4 wt%, more preferably less than 1 wt. %.

[0162] The following examples are intended only to exemplify the invention and are not intended to limit the scope of the claimed invention.

[0163] Examples

[0164] Example 1

[0165] Figure 1 (Fig. 1) shows schematically the function of the electrodialyzer in one embodiment of the process of the present invention, illustrating an advantageous configuration of the electrodialysis cellstack. In this example, the electrodialyzer cellstack comprises a succession of 3 chambers: base chamber, acid chamber, salt chamber.

[0166] An aqueous solution advantageously comprising sodium carbonate is fed into the base chamber, bounded between a cationic permselective membrane and an anionic permselective face of a bipolar membrane.An aqueous solution is fed into the acid chamber, said acid chamber being bounded between a cationic face of the bipolar membrane and an anionic membrane,

[0167] An aqueous solution comprising sodium chloride is fed into the salt chamber, said salt chamber being bounded between one anionic membrane and one cationic membrane,

[0168] In the base chamber sodium hydroxide (NaOH) and in the acid chamber hydrochloric acid (HC1) are generated, by splitting water molecules with the bipolar membrane into hydroxide anions (OH-) in the base chamber and into hydronium cations (H+) in the acid chamber, transferring sodium ions (Na+) to the base chamber through the cation selective membrane and transferring chloride ions (C1-) to the acid chamber through the anionic membrane by using an electrical tension between the salt chamber and the acid chamber,

[0169] An aqueous outlet solution comprising sodium hydroxide and sodium carbonate from the base chamber is removed and cane be used as illustrated in Example 2. An aqueous outlet solution comprising sodium chloride depleted in sodium chloride is removed from the salt chamber, and may be re-concentrated with sodium chloride by dissolving solid sodium chloride with an optional brine purification, or be released in the sea if the initial brine was coming from a desalination unit. As such it avoids concentrating locally the sodium chloride in the sea or in brackish ponds and to limit therefore the environmental impact of such release in the environment. It enables also to valorize part of the sodium chloride exiting said desalination unit in a circular way.

[0170] An aqueous outlet solution comprising hydrochloric acid is removed from the acid chamber, so that to be valorize as mentioned in the above described embodiments.

[0171] Example 2

[0172] Figure 2 (Fig. 2) schematically shows an installation for implementing an advantageous embodiment of the plant or of the process according to the invention. The installation shown schematically in Figure 2 comprises an electrodialysis cellstack (A) [also (1) in the figure], a carbonation tower (B) [also (2) in the figure], a storing mean (C) for the sodium hydroxide and sodium carbonate aqueous solution, an evaporator-crystallizer (D) [also referenced (3) in the figure] and a dryer (4).The electrodialysis cell is a multi-chamber cell type with a combination of cation, anion, and bipolar membranes comprising acid, base and salt compartments. Cells of this type are well known in electrolytic technique and widely used for the industrial production of aqueous solutions of a base and an acid starting from aqueous solutions of the corresponding salt (Ullmann’s Encyclopedia, Sodium Hydroxide, p. 376).

[0173] According to the invention, an aqueous solution of sodium chloride (6) is introduced into the salt compartment of the electrodialysis cell, while a diluted aqueous hydrochloric acid solution (9) and a diluted aqueous solution comprising sodium carbonate and caustic soda (11) are introduced into the acid and base compartments of the cell, respectively. During electrodialysis cell operation, hydrochloric acid and sodium hydroxide are generated in the acid and base compartments, respectively, while sodium chloride is gradually depleted in the salt compartment. An aqueous outlet solution comprising sodium chloride depleted in sodium chloride is extracted from the salt chamber. Simultaneously, an aqueous solution comprising sodium carbonate and sodium hydroxide enriched in sodium hydroxide and a hydrochloric acid solution enriched in hydrochloric acid are extracted from the base and the acid compartment, respectively. The aqueous solution of sodium chloride fed to the electrodialysis cell and the outlet aqueous solution depleted in sodium chloride extracted from the cell constitute a sodium chloride solution loop. The outlet aqueous solution depleted in sodium chloride is partially purged (7). Another aqueous solution of sodium chloride (5) is fed to the loop in order to raise the sodium chloride concentration. Similarly, the aqueous solution of hydrochloric acid fed to the electrodialysis cell and the outlet aqueous solution enriched in hydrochloric acid extracted from the cell constitute a hydrochloric acid solution loop. The outlet aqueous solution enriched in hydrochloric acid is partially purged from the system for downstream use (10). Water (8) is fed to the hydrochloric acid solution loop in order to regulate the hydrochloric acid concentration. In the same way, the aqueous solution comprising sodium carbonate and sodium hydroxide fed to the electrodialysis cell and the outlet aqueous solution comprising sodium carbonate and sodium hydroxide enriched in sodium hydroxide extracted from the cell constitute a sodium hydroxide and sodium carbonate solution loop. A first portion of the outlet aqueous solution comprising sodium carbonate and sodium hydroxide enriched in sodium hydroxide extracted from the cell (12) is recycled in the sodium hydroxideand sodium carbonate solution loop, wherein another portion (13) is sent to a carbonation tower (B) also referenced (2), where a gas comprising carbon dioxide (14) of which 82% of its carbon content is biogenic, generated from a waste to energy unit using waste biomass material, and said CO2 gas is to the carbonation tower to obtain a carbonated liquid, wherein the sodium hydroxide is transformed into sodium carbonate and water. Said carbonated liquid is partly recycled in the sodium hydroxide and sodium carbonate solution loop (15), wherein another portion is sent to a storing tank (C) wherein the sodium carbonate aqueous solution is stored so that the sections (A) and (B) using fluctuating energy as much as available, producing variable flow thereto of carbonated solution more independent from sections (D) and (E) operating then at constant nominal production rate. This enables to decrease investment for delivering a constant sourcing of electricity for sodium carbonate or bicarbonate crystals. Part of the sodium carbonate aqueous solution is sent (17) to an evaporator-crystallizer (D) (also referenced (3) in the figure). In this unit, the slurry is subjected to controlled evaporation to crystallize sodium carbonate. In a further piece of equipment (E ), not represented, the crystals of sodium carbonate (19) and a mother liquor (18) are separated. Sodium carbonate crystals (19) are then sent to a drying unit for final processing, giving dry sodium carbonate crystals as the end product (20).

[0174] The example below serves to illustrate the invention. It refers to Figure 2. During day time an electrodialysis stack (1) with a 3 compartment configuration, consisting of 100 unitary cells with 1 m2surface area, was assembled by alternating bipolar, anionic and cationic membranes at a current density of 1500 A / m2constituted at 40% of green electricity (mainly solar PV and hydropower) for 8 hours. 1.2 t / h of a substantially saturated brine (5), containing, per kg, 250 g of sodium chloride, are fed to the sodium chloride solution loop. Simultaneously, 22 t / h of an aqueous solution of sodium chloride (6) containing, per kg, 155 g of sodium chloride is introduced into the salt compartment of the electrodialysis cell. At the same time, 23 t / h of an aqueous solution comprising sodium carbonate and sodium hydroxide (11) containing per kg, 139 g of sodium carbonate and 45 g sodium hydroxide and 20.4 t / h of an aqueous solution of hydrochloric acid (9) containing per kg, 34 g of hydrochloric acid are fed to the base and acid compartment of the cell, respectively.

[0175] At the outlet of the electrodialysis cell, the following are obtained:

[0176] - 20.9 t / h of depleted or dilute brine, containing per kg, 150 g of sodium chloride;- 20.5 t / h of an enriched hydrochloric acid solution, containing per kg, 40 g of hydrochloric acid;

[0177] - 23.8 t / h of an aqueous solution comprising sodium carbonate and sodium hydroxide containing per kg, 134 g of sodium carbonate and 50 g sodium hydroxide.

[0178] In order to control the concentration of the hydrochloric acid solution, 3.2 t / h of water (8) are fed to the hydrochloric acid solution loop. 3.3 t / h of a hydrochloric acid solution containing, per kg, 40 g of hydrochloric acid (10) are extracted from the hydrochloric acid solution loop. Similarly, 0.15 t / h of depleted or dilute brine, containing, per kg, 150 g of sodium chloride are extracted from the sodium chloride solution loop.

[0179] 20.5 t / h of the outlet aqueous solution comprising sodium carbonate and sodium hydroxide are recycled to sodium hydroxide and sodium carbonate solution loop (12), wherein 3.3 t / h are sent to a carbonation tower (2). Here, 90 kg / h of carbon dioxide (14) are also fed to obtain a carbonated liquid containing, per kg, 180 g of sodium carbonate. 1 t / h of carbonated liquid (16) are stored in a storage tank insulated.

[0180] Part of carbonated liquid (17) is withdrawn from the storage tank C and introduced at a constant flow of 0.8 t / h into the evaporator-crystallizer (3), and where 134 kg / h of sodium carbonate crystals (17) are produced and separated from the mother liquor (18), and sent to a dryer (4) obtaining 128 kg / h of dried sodium carbonate crystals (19).

[0181] The mother liquor (18) is recycled mostly up-front at the evaporator-crystallizer (3) feed, except a part of it which is purged from the crystallizer to control and limit the concentration of soluble impurities (mainly sodium chloride and sulfate) in the mother liquor present in the crystallizer (3) and adjusted according to the specifications content of said impurities to be achieved in the dried sodium carbonate crystals (20).

[0182] Then during 16 hours, the electrodialyzer stack is then powered at a current density of 1000 A / m2which represents a second production rate (low rate) of about two thirds of the first operating rate at 1500 A / m2, producing roughly 0.7 time the caustic of the previous high operating rate due to slight higher current yield representing a ratio of high production rate to low production rate of 1 / 0.7 = a. 1.4. This represents a production flow (16) of 0.7 t / h of sodium carbonate solution feeding the storage tank for 16 hours.The mean value of the high production rate 1.0 t / h during 8 hours and the low production rate 0.7 t / h during 16 hours of the electrodialyzer gives a mean operating of 0.8 t / h on the 24 hours of the given time period (sum of the 8 + 16 hours). Generating therefore during the high operation rate, in 8 hours of the EDIA, an exceeding volume of carbonated solution of 1.0 -0.8 = 0.2 t / h divided by 0.8 t / h = 0.25 excess of the mean feeding rate of the crystallizer that has to be stored in the storage tank (C) during 8 hours and this excess being consumed then during the low operating rate of the EDIA during the 16 hours at a rate of 0.7 t / h. The excess of the storage volume needed corresponds to the 0.25 x 0.8 t / h x 8 hours and represents 1.6 t of sodium carbonate solution to be stored to feed constantly the crystallizer equipment which is reasonable. This results in a constant crystal particles size distribution meeting consumer specifications.

[0183] The purge is recycled at the brine purification sector wherein sodium chloride brine is purified before feeding the electrodialysis cell (1). This enables to valorize the sodium chloride part of the purge and be electrolyzed and so avoiding to be lost. Sodium carbonate and optionally sodium sulfate are also valorized and not lost, as they can be used as precipitating agent of calcium ions (as gypsum and / or calcium carbonate) at the purification sector of the raw brine comprising sodium chloride and its impurities, before being purified and then used in the electrodialysis cell (1) feeding the salt chamber as stream (6). This enables to achieve a sharp decrease in purged brine quantity and to approach a near-zero loss of sodium carbonate in the purged mother liquor from the evaporatorcrystallizer (3) sector.

[0184] Moreover the sodium carbonate produced with the obtained carbonated solution generated in the electrodialyzer is of excellent purity in complement of the good particle size distribution stability and characteristics. The sodium carbonate crystals obtained on the 24 hours’ time period have a calcium (Ca) and a magnesium (Mg) content of less than 20 ppm, an iron content (Fe) of less than 10 mg / kg, with most samples taken every hour having respectively less than 8 ppm regarding calcium, same for magnesium content, and less than 4 ppm for the iron content.

[0185] A manufacturing of sodium bicarbonate crystals from the outlet aqueous solution comprising sodium hydroxide and sodium carbonate would enable to obtain comparable crystal purities with the used carbon dioxide gas, as the occlusion of impurities are similar for sodium carbonate and bicarbonate, withgenerally a favorable impurity split in crystals and mother liquor for sodium bicarbonate compared to sodium carbonate crystals for said impurities.

[0186] The obtained sodium carbonate crystals present surprisingly a good particle size distribution, with less than 10% in weight of the crystals above 1100 pm, a medium particle size in weight (D50) comprised between 480 pm and 620 pm on the 24 hours, with a size fraction passing a 125 pm sieve of less than 1 wt. % for most samples. Moreover the attrition behavior of such sodium carbonate is similar to the one of the soda ammonia process, meeting market requests. The fossil CO2 footprint of said sodium carbonate is reduced when using green electricity of a factor 3 to more than 5 compared to existing soda ammonia process and trona ore process.

[0187] Example 3

[0188] Figure 3 (Fig. 3) schematically shows an advantageous embodiment of the plant or of the process according to the invention.

[0189] Figure 3 schematically shows an installation for implementing a first embodiment of the method according to the invention. The installation shown schematically in Figure 3 comprises an electrodialysis cell 1.

[0190] The electrodialysis cell is a multichamber cell type with a combination of cation, anion, and bipolar membranes comprising acid, base and salt chambers. Cells of this type are well known in electrolytic technique and widely used for the industrial production of aqueous solutions of a base and an acid starting from aqueous solutions of the corresponding salt (Ullmann’s Encyclopedia, Sodium Hydroxide, p. 376).

[0191] According to the invention, an aqueous solution of sodium chloride (6) is introduced into the salt chamber of the electrodialysis cell, while a diluted aqueous hydrochloric acid solution (9) and a diluted aqueous sodium hydroxide solution (11) are introduced into the acid and base chambers of the cell, respectively. During electrodialysis cell operation, hydrochloric acid and sodium hydroxide are generated in the acid and base chambers, respectively, while sodium chloride is gradually depleted in the salt chamber. An aqueous outlet solution comprising sodium chloride depleted in sodium chloride is extracted from the salt chamber (7). Simultaneously, an aqueous sodium hydroxide solution enriched in sodium hydroxide and a hydrochloric acid solution enriched in hydrochloric acid are extracted from the base and the acid chamber, respectively. The aqueous solution of sodium chloride fed to the electrodialysis cell and the outlet aqueous solution depleted in sodium chloride extracted fromthe cell constitute a sodium chloride solution loop. The outlet aqueous solution depleted in sodium chloride is partially purged (7). Another aqueous solution of sodium chloride (5) is fed to the loop in order to raise the sodium chloride concentration. Similarly, the aqueous solution of hydrochloric acid fed to the electrodialysis cell and the outlet aqueous solution enriched in hydrochloric acid extracted from the cell constitute a hydrochloric acid solution loop. The outlet aqueous solution enriched in hydrochloric acid is partially purged from the system for downstream use (10). Water (8) is fed to the hydrochloric acid solution loop in order to regulate the hydrochloric acid concentration. In the same way, the aqueous solution comprising sodium hydroxide fed to the electrodialysis cell and the outlet aqueous solution comprising sodium hydroxide enriched in sodium hydroxide extracted from the cell constitute a sodium hydroxide solution loop. Water (15) is fed to the sodium hydroxide solution loop in order to regulate the sodium hydroxide concentration.

[0192] The example below serves to illustrate the invention. It refers to Figure 1. An electrodialysis stack (1) with a 3-chamber configuration, consisting of 5 unitary cells with 0.02 m2surface area, was assembled by alternating bipolar, anionic and cationic membranes at an initial current density of 500 A / m2. In these conditions, 1.381 / h of a substantially saturated brine (5), containing, per kg, 250 g of sodium chloride, are fed to the sodium chloride solution loop.

[0193] Simultaneously, 1001 / h of an aqueous solution of sodium chloride (6) containing, per kg, 205 g of sodium chloride is introduced into the salt chamber of the electrodialysis cell. At the same time, 1001 / h of a sodium hydroxide solution (11) containing, per kg, 128 g sodium hydroxide and 1001 / h of an aqueous solution of hydrochloric acid (9) containing, per kg, 49 g of hydrochloric acid are fed to the base and acid chamber of the cell, respectively.

[0194] In order to control the concentration of the hydrochloric acid solution, 1.1 1 / h of water (8) are fed to the hydrochloric acid solution loop. 1.51 / h of an enriched hydrochloric acid solution, containing, per kg, 51 g of hydrochloric acid (10) are extracted from the hydrochloric acid solution loop. At the same time, in order to control the concentration of the sodium hydroxide solution, 0.51 1 / h of water (15) are fed to the sodium hydroxide solution loop. 0.5 1 / h of an enriched sodium hydroxide solution containing, per kg, 132 g of sodium hydroxide are extracted from the sodium hydroxide solution loop. Similarly, 0.981 / h of depleted or dilute brine, containing, per kg, 201 g of sodium chloride (14) are extracted from the sodium chloride solution loop. The concentration ofhydrochloric acid, sodium hydroxide and sodium chloride in the respective loops was checked in line by means of conductivity probes placed on streams 7, 9 and 11, giving stable readings of 510, 280 and 460 mS / cm, respectively. Under these process conditions, the power consumption is 1.33 kWh / kg NaOH.

[0195] After 240 minutes, the current density was increased to 1000 A / m2with a ramp of 5 A / min (ie 5 / 0.02 m2= 250 A / m2 / min so in 2 minutes time the increase of 500 to 1000 A / m2operating condition). In these conditions, 3 1 / h of a substantially saturated brine (5), containing, per kg, 250 g of sodium chloride, are fed to the sodium chloride solution loop. Simultaneously, 1001 / h of an aqueous solution of sodium chloride (6) containing, per kg, 210 g of sodium chloride is introduced into the salt chamber of the electrodialysis cell. At the same time, 1001 / h of a sodium hydroxide solution (11) containing, per kg, 126 g sodium hydroxide and 1001 / h of an aqueous solution of hydrochloric acid (9) containing, per kg, 48 g of hydrochloric acid are fed to the base and acid chamber of the cell, respectively.

[0196] In order to control the concentration of the hydrochloric acid solution, 2.0 1 / h of water (8) are fed to the hydrochloric acid solution loop. 2.71 / h of an enriched hydrochloric acid solution, containing, per kg, 51 g of hydrochloric acid (10) are extracted from the hydrochloric acid solution loop. At the same time, in order to control the concentration of the sodium hydroxide solution, 0.91 1 / h of water (15) are fed to the sodium hydroxide solution loop. 0.91 / h of an enriched sodium hydroxide solution containing, per kg, 132 g of sodium hydroxide are extracted from the sodium hydroxide solution loop. Similarly, 2.1 1 / h of depleted or dilute brine, containing, per kg, 206 g of sodium chloride (14) are extracted from the sodium chloride solution loop. The water flowrates were adjusted so that the conductivity values measured in the increased current density matched those found at lower current density within a range of + / - 10 % of the nominal value previously measured, implying that the concentration of hydrochloric acid, sodium hydroxide and sodium chloride was kept stable. Under the new process conditions, the power consumption was 2.04 kWh / kg NaOH.

[0197] After 120 minutes, the current density was decreased again to 500 A / m2.

[0198] The water flowrates were again adjusted so that the conductivity values measured in the decreased current density matched those found previously within a range of + / - 10 % of the nominal value previously measured, implying that the concentration of hydrochloric acid, sodium hydroxide and sodium chloride was kept stable. Under these process conditions, the power consumption is 1.36kWh / kg NaOH, confirming therefore the reversibility of the process under current density modulation conditions, and showing a non-linearity of current intensity versus the produced chemicals.

[0199] Alternatively, to the on-line conductivity measurements, a check with periodical chemical analysis showed in the above conditions a good stability (+ / -10%) of the chemical concentrations of the produced chemicals in the outlets of the base and acid chambers. Showing therefore that the control of the water fed in the loops of the base and acid chambers, during the feed and bleed operation, enables to compensate for the electrical currents variations so that to set stable operating conditions of each chambers (base or acid) of the electrodialyzer.

[0200] This enables in the subsequent steps of the process to obtain stable base and acid solutions compositions in caustic soda and / or sodium carbonate (in base chamber), and in hydrochloric acid (in acid chamber) even with a fluctuating electrical power of the electrodialyzer cellstack.

[0201] Without a water introduction compensation in the feed and bleed operation, controlled based on conductivity or chemical concentration measurements, the concentrations fluctuations of the produced chemicals in base and acid chambers, leads to variations that are strongly non linear compared the current intensity fluctuations, avoiding stable electrodialysis operation for the produced chemicals, forcing to stop part of the electrodialyzers cells and put them in standby when electrical power availability decreases or to restart them when electrical power availability increases.

Claims

1. - 33 -C L A IM S1. Plant for electrically producing sodium carbonate (Na2CO3) comprising:(A) an electrodialyzer cellstack to electrodialyze a sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and into a hydrochloric acid (HC1) aqueous solution,wherein the electrodialyzer cellstack comprises operation means enabling the electrodialyzer cellstack to be operated in at least 2 production rates on a given time period;(B) carbonating mean(s) to partially or totally carbonate the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2COs) aqueous solution;(C) storage mean(s) of the sodium hydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2COs) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2COs) aqueous solution and to produce sodium carbonate (Na2COs) crystals and a mother liquor;(E) separation mean(s) to separate the sodium carbonate (Na2COs) crystals from their mother liquor and recovering the sodium carbonate (Na2COs) crystals; and wherein the plant is further characterized in that the storage means (C) of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2COs) aqueous solution :- is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period; and- has an equivalent electrical power storage ability per volume of at least 100 kWh / m3 calculated as the electrical power (expressed in kWh) used to electrodialyze, in the electrodialyzer cellstack, the sodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) of the sodium hydroxide (NaOH) aqueous solution and / or of the sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).- 34 -2. The plant of claim 1 wherein the storage means (C) has an equivalent electrical power storage ability per volume of at least 150 kWh / m3, preferably at least 300 kWh / m3 expressed per unit volume (m3) of the sodium hydroxide (NaOH) aqueous solution and / or of the sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).

3. The plant of any preceding claims, wherein the electrodialyzer cellstack (A) to electrodialyze the sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and a hydrochloric acid (HC1) aqueous solution, comprises at least 2 chambers: a base chamber wherein the sodium hydroxide (NaOH) aqueous solution is produced and an acid chamber wherein the hydrochloric acid (HC1) aqueous solution is produced.

4. The plant of the preceding claim further comprising :(Al) a water or a diluted aqueous solution feeding means, hydraulicly connected to, or upfront to, the base chamber; and(A2) a control system able to act on the water or on the diluted aqueous solution flowrate to control the sodium hydroxide concentration of the sodium hydroxide aqueous solution exiting the base chamber at a value of at most + / -15%, preferably + / - 5%, of a nominal value so that to be able to compensate the variation of the at least 2 production rates on the given time period.

5. The plant of any preceding claims, wherein the electrodialyzer cellstack (A) comprises at least 3 chambers: a base chamber, an acid chamber, and a salt chamber wherein the sodium chloride is fed and wherein the sodium ions are permeated to the base chamber through a cation permselective membrane and the chloride ions are permeated to the acid chamber through an anion permselective membrane.

6. The plant of the preceding claim further comprising :(A3) a water or a diluted aqueous solution feeding means, hydraulicly connected to, or upfront to, the acid chamber; and(A4) a control system able to act on the water or on the diluted aqueous solution flowrate to control the hydrochloric acid (HC1) concentration of the hydrochloric acid aqueous solution exiting the acid chamber at a value of at most + / -15%, preferably + / - 5%, of a nominal value so that to be able to compensate the variation of the at least 2 production rates on the given time period.

7. The plant of any preceding claims, wherein the crystallizer equipment (D) to concentrate the sodium carbonate (ISfeCCh) aqueous solution and to produce sodium carbonate (ISfeCCh) crystals and a mother liquor, comprises: - an optional (DI) pre-evaporator means such as: a falling film evaporator or a forced circulation evaporator, to remove at least part of the water of the sodium carbonate (ISfeCCh) aqueous solution;- (D2) crystallizer means such as a sodium carbonate anhydrous (ISfeCCh) crystallizer, or a sodium carbonate monohydrate (JSfeCCh.H^O) crystallizer, or a sodium carbonate decahydrate (ISfeCCh.lOTbO) crystallizer, or a sodium sesqui carb onate (Na2CO3.NaHCO3.2H2O) crystallizer.

8. The plant of any preceding claims 1 to 7, wherein the crystallizer equipment (D) further comprises:- an optional (DI) pre-evaporator means, and- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer,- a separation means (E2) to separate sodium carbonate decahydrate (Na2CO3. IOH2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3. IOH2O) crystals into a purified sodium carbonate solution,- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with the purified sodium carbonate solution to produce (Na2CO3.H2O) crystals and their mother liquor,- (E) a separation means to separate sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor.

9. The plant of any preceding claims 1 to 7, wherein the crystallizer equipment (D) further comprises:- an optional (DI) pre-evaporator means, and- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with the sodium carbonate solution to produce sodium carbonate monohydrate (Na2CO3.H2O) crystals and their mother liquor,- (E) a separation means to separate sodium carbonate monohydrate (Na2CO3.H2O) crystals from their mother liquor,- a purge means of at least part of the mother liquor from the sodium carbonate monohydrate crystallizer,- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer fed with the purged mother liquor from the sodium carbonate monohydrate crystallizer,- a separation means (E’) to separate sodium carbonate decahydrate (Na2COs. IOH2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (ISfeCCh. IOH2O) crystals into a purified sodium carbonate solution,- a recycling means of the purified sodium carbonate solution to recycle it to the (D2’) sodium carbonate monohydrate (ISfeCCh.EEO) crystallizer.

10. The plant of any preceding claims, wherein the mother liquor from the crystallizer equipment comprises dissolved sodium carbonate and dissolved sodium chloride, and the crystallizer equipment (D) or the separation means (E) comprises a purge means for purging at least part of the mother liquor from the crystallizer equipment ( (D), (D2), or (D2’) ) and a recycling means of the least part of the purged mother liquor, to recycle the at least part of the mother liquor to a sodium chloride brine purification module or to the EDIA cellstack or upfront the EDIA cellstack to recover at least part of the sodium chloride of the purged mother liquor and to electrolyze it into sodium hydroxide and / or hydrochloric acid.

11. Process for producing sodium carbonate (ISfeCCE) crystals or sodium bicarbonate (NaHCCh) crystals from a sodium chloride (NaCl) solution, comprising the following steps :(i) optionally pre-treating the sodium chloride (NaCl) solution in removing at least part of impurities selected from the group consisting of: insolubles, calcium, magnesium, heavy metals, fluoride, bromide, iodide, sulfate, organics and combination thereof to obtain an optional pre-treated sodium chloride solution;(ii) electro-dialyzing in an electrodialyzer cellstack (A), the sodium chloride solution or the optional pre-treated sodium chloride solution into a sodium hydroxide (NaOH) aqueous solution and into a hydrochloric acid (HC1) aqueous solution, wherein the electrodialyzer cellstack is operated in at least 2 production rates on a given time period;(iii) carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2COs) aqueous solution;- 37 -(iv) storing the sodium hydroxide (NaOH) aqueous solution into a storage mean(s) (Cl) before step (iii), and / orstoring the sodium carbonate (ISfeCCh) aqueous solution into a storage means (C2) after step (iii);(v) crystallizing at least part of the sodium carbonate of the sodium carbonate solution into sodium carbonate crystals and a mother liquor in a crystallizer equipment (D);(vi) separating the sodium carbonate (Na2COs) crystals from the mother liquor in a separation means (E),and recovering the sodium carbonate (ISfeCCh) crystals;(vii) optionally crystallizing sodium bicarbonate (NaHCCh) crystals by further carbonating the sodium carbonate (ISfeCCh) aqueous solution from step (iii) with a gas comprising CO2 or biogenic CO2 in a crystallizer equipment (D’), so that to produce sodium bicarbonate crystals and their mother liquor, optionally separating the sodium bicarbonate crystals from their mother liquor in a separation means (E’), and recovering the sodium bicarbonate (NaHCCh) crystals;and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, and / or the storage means of the sodium carbonate (Na2COs) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period, andthe storage means volume has an equivalent electrical power storage ability per volume of at least 100, preferably at least 200, more preferably 300 kWh / m3 calculated as the electrical power (expressed in kWh) used to electro-dialyze the sodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) of the produced sodium hydroxide (NaOH) aqueous solution and / or of the produced sodium carbonate (Na2CO3) aqueous solution stored in the storage means (C).

12. The process of the preceding claim wherein the electrodialyzer cell stack is operated in feed and bleed mode.

13. The process of any preceding claim wherein the electrodialyzer cell stack is operated at constant + / -15% feed flow rate, preferably at constant + / -5% feed flow rate within the said time period.- 38 -14. The process of any preceding claims wherein the electrodialyzer cell stack is operated at a constant temperature value + / -15%, preferably at constant temperature value + / - 5% within the said time period.

15. The process of the preceding claims, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution is biogenic, or is not deriving from fossil carbon or not deriving from fossil carbon dioxide, or is CO2 captured from the air.

16. The process of any preceding claims, wherein the electrodialyzer (A) uses electricity to electrodialyze the sodium chloride (NaCl) aqueous solution into the sodium hydroxide (NaOH) aqueous solution and into the hydrochloric acid (HC1) aqueous solution,and wherein the electricity is at least partly, and preferably totally, a ‘green electricity’ or has a reduced fossil CO2 footprint, preferably selected among the group consisting of: hydraulic electricity, solar photovoltaic electricity, wind electricity, waste to energy electricity, electricity generated from biomass combustion, electricity generated from biogas combustion, electricity generated from hydrogen combustion, electricity generated from geothermal heat, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, electricity from cogeneration of steam and electricity, or mixtures thereof.

17. The process of any preceding claims, wherein the at least 2 production rates ratio expressed as the ratio of a high production rate to a low production rate is at least 1,2 or at least 1,5.

18. The process of any preceding claims, wherein the at least 2 production rates ratio expressed as the ratio of a high production rate to a low production rate is at most 5 or at most 3.

19. The process of any claim 11 to 18, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution derives from fumes generated by plants or equipment thereof selected from the group consisting of: a power plant, a glass plant, a steel or sinter plant, a waste plant or waste-to-energy plant, a pulp or paper plant, an oil refinery, a petro-chemical plant, a cement plant, a tile manufacturing plant, a brick manufacturing plant, a mining process, a mineral processing plant, a lime- 39 -plant, an ammonia plant, a fertilizer plant, a biochar plant, a biogas plant, and combinations thereof.

20. The process of any preceding claims, wherein the sodium chloride from the sodium chloride aqueous solution derives from: a solar pond salt, or sea salt.

21. The process of any preceding claims, wherein the sodium chloride derives from: a seawater desalination process, preferably from a reverse osmosis desalination process.

22. The process of any of the preceding claims, wherein the sodium chloride derives from a geological salt cavity, or is an industrial crystallized salt.

23. The sodium carbonate or bicarbonate crystals produced by the process of any preceding claims, wherein the carbon dioxide (CO2) in the gas used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution is at least partly biogenic.

24. Sodium carbonate crystals or sodium bicarbonate crystals:- wherein at least 25 wt.% of its carbon content is biogenic, preferably at least 80 wt. % of its carbon content is biogenic; and- comprising at most 20 mg calcium and / or at most 20 mg magnesium per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals.

25. Sodium carbonate crystals or sodium bicarbonate crystals according to one of the preceding claims:- wherein at least 95 wt.% or at least 99 wt% of its carbon content is biogenic, or is CO2 captured from the air.

26. Sodium carbonate crystals or sodium bicarbonate crystals according to the preceding claim comprising at most 10 mg iron (Fe), preferably at most 4 mg iron (Fe) per kilogram of crystals.

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