Methods for producing sodium carbonate or sodium bicarbonate

Abstract

Plant for electrically producing sodium carbonate (Na2CO3) comprising: (A) an electrolyzer to electrolyze a sodium chloride (NaCl) aqueous solution into a sodium hydroxide (NaOH) aqueous solution and chlorine (Cl2) or hydrochloric acid (HCl), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period; (B) carbonating means to partially or totally carbonate the sodium hydroxide (NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate aqueous solution; (C) storage means of the sodium hydroxide (NaOH) aqueous solution or of the sodium carbonate aqueous solution; (D) a crystallizer equipment to concentrate the sodium carbonate aqueous solution and to produce sodium carbonate crystals and a mother liquor; (E) separation means to separate the sodium carbonate (Na2CO3) crystals from their mother liquor and recover the sodium carbonate (Na2CO3) crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period..

Description

[0001] METHODS FOR PRODUCING SODIUM CARBONATE OR SODIUM BICARBONATE The present invention relates to a plant for producing sodium carbonate (Na2CO3) and / or optionally sodium bicarbonate (NaHCO3) with reduced fossil carbon dioxide (CO2) emission, by electrolysis 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. 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, or low fossil CO2 footprint electricity such as from nuclear power. More advantageously, carbon dioxide (CO2) used for carbonating partially or totally a sodium hydroxide (NaOH) aqueous solution produced by said plant or process is partly, or totally, biogenic, or from biogenic origin, or not derivingfrom fossil origin. Alternatively, part or the totality of the carbon dioxide (CO2)used for carbonating partially or totally the sodium hydroxide (NaOH) aqueous solution produced by said plant or process is a CO2 recovered from another emitting industries such as a power plant, a glass plant, a cement plant, a pulp or paper plant, etc… to reduce the overall CO2 fossil emissions and increase the circularity of the use of said CO2. 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. Technical field Sodium carbonate (Na2CO3), 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. Sodium bicarbonate (NaHCO3) 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. The ammonia synthetic process, which encompasses 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 (CaCO3) as source of CO2 (or of the carbonate). And both raw materials are constantly generated and replenished by the nature, on a human timescale. 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 (CaCO3), 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. 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 transport, and the exploitable reserves of identified deposits are limited. Availabilities of said identified ore deposits in Turkey represent about 20 to 40 years production, and a few centuries for the Wyoming USA ore deposit. Moreover, the CO2 content of the manufactured sodium carbonate or bicarbonate from such ores, is totally fossil and is freed in the atmosphere when used in the glass or metallurgy industries. This avoid such processes to be sustainable in the long term and meet net zero emission of fossil CO2 and of greenhouse gases to be in line with COP21 commitments. 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. WO 2008 / 031834 (from Solvay) discloses a method for producing sodiumcarbonate, according to which an aqueous sodium chloride solution iselectrolyzed in a membrane-type cell from which an aqueous sodium hydroxidesolution is collected and carbonated by direct contact with carbon dioxide toform a slurry of crystals of anhydrous sodium carbonate. Said disclosure is silenton the use of renewable energy and the problem of its fluctuating availability. Itis also silent on the overall decrease of fossil CO2 footprint of soda ash andsodium bicarbonate production to go to zero emission. Brief description of the invention The present invention relates to a method for producing sodium carbonate(Na2CO3) or sodium bicarbonate (NaHCO3), comprising electrolyzing an aqueous solution of sodium chloride (NaCl) to obtain:- chlorine gas (Cl2) or hydrochloric acid (HCl) and- an aqueous solution comprising sodium hydroxide (NaOH)and carbonating the aqueous solution comprising sodium hydroxide (NaOH) with a gas comprising carbon dioxide (CO2) to produce sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3) or a mixture thereof, wherein at least 25 wt.% of the carbon comprised in the carbon dioxide (CO2) is biogenic.The present invention relates also to a plant for electrically producingsodium carbonate (Na2CO3) comprising:(A) an electrolyzer to electrolyze a sodium chloride (NaCl) aqueous solution intoa sodium hydroxide (NaOH) aqueous solution and chlorine (Cl2), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recovering the sodium carbonate (Na2CO3) crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period. For this, preferably the electrolyzer comprises modulation means of the voltage and / or of the intensity of electrical current supplying the electrolyzer. The present invention relates also to a plant for electrically producingsodium carbonate (Na2CO3) comprising:(A) a set of at least two electrolyzer cellstacks to electrolyze a sodium chloride(NaCl) aqueous solution into an aqueous solution comprising sodium hydroxide (NaOH) and into chlorine (Cl2), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recovering the sodium carbonate (Na2CO3) crystals;and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period. The present invention relates also to the sodium carbonate crystals orbicarbonate crystals obtainable by the above methods or by the above plants of the present invention,- comprising at least 25 wt.% of their carbon content being biogenic carbon,preferably at least 80 wt. % of their carbon content being biogenic carbon; and- preferably comprising at most 20 mg calcium (Ca) and / or at most 20 mgmagnesium (Mg) per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals. Indeed, the inventors have discovered that even with low impurities levelssuch as calcium and magnesium made with the process of said invention, attrition of the obtained sodium carbonate or sodium bicarbonate, is acceptablefor main final uses, such as the glass or detergent manufacturers. It enables themto reduce scopes 1, 2 and 3, emissions of fossil CO2 as defined by theGreenhouse Gas Protocol organization. Moreover, the purity obtained of saidsodium carbonate and bicarbonate, exceeds sensitively the chemical purity incalcium, magnesium, iron, silica, organics, and insoluble, of trona ore orammonia based processes producing them. Moreover, said purity renders themparticularly suited for the increasing demand of the market of ‘battery grade’ soda ash and sodium bicarbonate, associated to the development of electric vehicles for reducing the fossil CO2 emissions of transport activities. The present invention relates also to an electrolysis method of a sodiumchloride solution for producing a sodium carbonate solution in a cathode compartment, and hydrochloric acid in an anode compartment,- said anode compartment comprising a Hydrogen Depolarized Anode (HDA), and- the cathode compartment is fed with an aqueous solution comprising dissolvedcarbon dioxide (CO2) wherein sodium hydroxide is produced and carbonated into sodium carbonate with the dissolved direct carbonation of the caustic soda with the dissolved carbon dioxide (CO2) in the cathodic circuit, in order to produce sodium carbonate The present inventors found surprisingly that storing the intermediate sodium hydroxide or sodium carbonate aqueous solutions represent a higherenergy density per volume or per ton, of equivalent electric energy than knownaccumulators such as classical batteries as lead-acid batteries (25 Wh / kg) or modern lithium-ion batteries (125 Wh / kg). Indeed considering the electric energy needed for electrically producing sodium carbonate from caustic soda needingabout 2000 (+ / - 30%) kWh / t caustic soda and close stoichiometrically for themanufacturing of sodium carbonate, a storage of:- caustic soda at 2 to 8 mol / kg of solution, or of- sodium carbonate aqueous solution at 1 to 3 mol of sodium per kg of solutionrepresents an equivalent storage of electrical energy respectively of about 160 to 640 Wh / kg of solution (160 to 640 kWh / t solution) of NaOH and 160 to 480Wh / kg of solution (160 to 480 kWh / t solution) of Na2CO3.The remaining steps of the manufacture of sodium carbonate orbicarbonate (mainly crystallization and drying) represent a smaller quantity ofthe overall consumed energy, less than about 30%. The invention enables by synergy, running at a stable production rate thecrystallization equipment of sodium carbonate and bicarbonate, and also drying equipment, offering stable particle sizes of sodium carbonate or bicarbonatecrystals needed for end users of said sodium carbonate and bicarbonate products.This avoids also to over-size the volumes and sizes of crystallization and dryingequipment to fit them to the production rate of sodium hydroxide upstream. Thiscompensates for the fluctuating availability of renewable electricity, in particularsolar and / or wind energy, or when the electrical network must be balancedduring peak hours. Indeed, this fluctuation of available energy, and the storagecapacity of said renewable ‘green’ energies, linked to the oversizing ofequipment to fit said fluctuation, are a major problem for industrialdecarbonation. Moreover, the present invention decreases sensitively the need of ‘strategicmaterials’, such as: lithium, nickel, cobalt, cupper, cadmium, molybdenum, dysprosium, gallium, and other rare earths, for storing said renewable fluctuatingenergy in batteries or other storage means. Indeed such ‘strategic materials’ areconsidered world-wide limited Earth resources, and they are not evenlydistributed in all regions. They represent heavy bottlenecks limiting the energytransition rate of the industry, to be done progressively by 2050. Also, their ownextraction, manufacturing, and purification are energy intensive. The investmentcosts in storing said renewable energies are of the same magnitude as theinvestment costs of producing said energy. Definitions For purposes of the present specification, certain terms are intended to have the following meanings. The term electrolysis refers to a technique using electric current to drive a chemical reaction. Generally, in an electrolysis the electric current drives an otherwise non-spontaneous chemical reaction. Such techniques usually use at least one couple of electrodes, named anode and cathode, and whereby respectively a chemical oxidation and a chemical reduction of ions or of neutral molecules occur. The term ‘electrolyzer’ refers to an equipment wherein an electrolysis process is performed or may be performed. It generally comprises several cells or chambers comprising electrodes (anode or cathode) and said cells or chambers are generally delimited by at least one ion exchange membrane (also called ion perm-selective membrane). The term ‘anion-exchange membrane’ (AEM) or ‘anionic membrane’ refers to an ion-exchange membrane that is permeable to anions and, ideally, impermeable to cations. Similarly, in present specification, the term ‘cation- exchange membrane’ (CEM) or ‘cationic membrane’ refers to an ion-exchange membrane that is permeable to cations and, ideally, impermeable to anions. 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 electric field to another solution. In the present specification, the term ‘cellstack’ refers to an equipment wherein an electrolysis or an electrodialysis process may be performed. It generally comprises arrangement of several electrolysis cells or electrodialysis cells or chambers. The expression ‘to operate the crystallizer equipment in a constant production rate’ in the present specification, 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 electrolyzer 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 electrolyzer 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). 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 biogeniccontent of a given product, based on carbon 14 isotope measurement of saidsample. Instrumental error of the method is typically within 0.1-0.5 % (on relative standard deviation). In present specification and described embodiments, the biogenic carbon dioxide may also be advantageously produced by at least one microorganism and / or by at least one biological process. 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’ or ‘decarbonizedenergy’, in complement of the ‘green energy’ listed above, includes heat or cold recovered by heat pumps and nuclear energy. 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, 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). The term "purge” refers to a stream withdrawn from a part of a process to limit impurity concentration in this process. 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. The term "impurity” refers to a compound different from the sodium carbonate and / or the sodium bicarbonate salt to be produced. The term “carbonating” refers to the action of increasing the amount of total carbonate (i.e. carbonate and bicarbonate) of a stream. The term “bicarbonating” refers to the action of increasing the amount of bicarbonate of a stream. The term "comprising" includes "consisting essentially of" and also "consisting of". In the present specification, the terms “%”, “% by weight”, “wt%”, “wt. %”, “weight percentage”, or “percentage by weight” can be used interchangeably, unless the “%” term is explicitly referred to another physical unit (such as for instance “% in mole”, or mol. %”, “% in volume” or “vol. %”, etc...). 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. Detailed description of the invention The present invention relates to a method for producing sodium carbonate(Na2CO3) or sodium bicarbonate (NaHCO3), comprising electrolyzing an aqueous solution of sodium chloride (NaCl) to obtain:- chlorine gas (Cl2) or hydrochloric acid (HCl) and- an aqueous solution comprising sodium hydroxide (NaOH)and carbonating the aqueous solution comprising sodium hydroxide (NaOH) with a gas comprising carbon dioxide (CO2) to produce sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3) or a mixture thereof, wherein at least 25 wt.% of the carbon comprised in the carbon dioxide (CO2) is biogenic. The present invention relates also to a plant for electrically producingsodium carbonate (Na2CO3) comprising:(A) an electrolyzer to electrolyze a sodium chloride (NaCl) aqueous solution intoa sodium hydroxide (NaOH) aqueous solution and chlorine (Cl2), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recovering the sodium carbonate (Na2CO3) crystals; and wherein the plant is further characterized in that the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period. The present invention relates also to a plant for electrically producingsodium carbonate (Na2CO3) comprising:(A) a set of at least two electrolyzer cellstacks to electrolyze a sodium chloride(NaCl) aqueous solution into an aqueous solution comprising sodium hydroxide (NaOH) and into chlorine (Cl2), wherein the electrolyzer cellstack set comprises operation means enabling to stop and start at least one of the electrolyzer cellstacks and so to operate the set of the electrolyzer cellstacks in at least 2 production rates on a given time period by adjusting the number of operating cellstacks;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recover the sodium carbonate (Na2CO3)crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period. The present invention relates also to the sodium carbonate crystals orbicarbonate crystals obtainable by the above methods or by the above plants of the present invention,- comprising at least 25 wt.% of their carbon content being biogenic carbon,preferably at least 80 wt. % of their carbon content being biogenic carbon; and- preferably comprising at most 20 mg calcium (Ca) and / or at most 20 mgmagnesium (Mg) per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals. The present invention relates also to an electrolysis method of a sodiumchloride solution for producing a sodium carbonate solution in a cathode compartment, and hydrochloric acid in an anode compartment,- said anode compartment comprising a Hydrogen Depolarized Anode (HDA),and- the cathode compartment is fed with an aqueous solution comprising dissolvedcarbon dioxide (CO2) wherein sodium hydroxide is produced and carbonated into sodium carbonate with the dissolved direct carbonation of the caustic soda with the dissolved carbon dioxide (CO2) in the cathodic circuit, in order to produce sodium carbonate The present invention relates also to further advantageous embodiments of the method(s) or the plant(s) or product(s) which are described in more details hereafter. Said embodiments are combinable with any one of the other embodiments, isolated or in combination with several embodiments, unless obviously non-compatible. [1]. A method for producing sodium carbonate (Na2CO3) or sodiumbicarbonate (NaHCO3), comprising electrolyzing an aqueous solution of sodium chloride (NaCl) to obtain:- chlorine gas (Cl2) or hydrochloric acid (HCl) and- an aqueous solution comprising sodium hydroxide (NaOH)and carbonating the aqueous solution comprising sodium hydroxide (NaOH) with a gas comprising carbon dioxide (CO2) to produce sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3) or a mixture thereof, wherein at least 25 wt.% of the carbon comprised in the carbon dioxide (CO2) is biogenic. [2]. The method according to [1], wherein at least 80 wt.% or at least 90wt% of the carbon comprised in the carbon dioxide (CO2) is biogenic. [3]. The method according to [1] or [2], wherein the produced sodiumcarbonate (Na2CO3) or sodium bicarbonate (NaHCO3) are in aqueous solution or in a slurry of Na2CO3 crystals or a slurry of NaHCO3 crystals, and mixtures thereof. [4]. The method according to any of [1] to [3] wherein the electrolysis ofthe aqueous sodium chloride solution is operated in an electrolyzer cell, and the electrolyzer cell is a bipolar membrane electrolysis cell or a monopolar membrane cell. Such bipolar membrane electrolysis cell and monopolar membrane electrolysis cell are described for their principles and typicalembodiments in as described in EU - BAT Reference document for theProduction of Chlor-alkali - 2014 – edited by the Joint Research Center Institute- doi:10.2791 / 13138 – §2.4, Chapter 2, pages 24-31.[5]. The method according to [4] wherein the electrolyzer cell comprisesan anode compartment fed with the aqueous sodium chloride solution, which is preferably acidified, and an aqueous sodium chloride depleted solution in sodium chloride is removed from the anode compartment and at least partially resaturated with sodium chloride.[6]. The method according to any of [4] or [5] wherein the electrolyzer cellcomprises ion-exchange membrane(s) more permeable to monovalent ions than multivalent ions. [7]. The method according to any of [1] or [6] wherein the concentration ofthe aqueous solution comprising sodium hydroxide (NaOH) is at least 8 wt%NaOH, preferably at least 12 wt% NaOH. [8]. The method according to any of [1] or [7] wherein the concentration ofthe aqueous solution comprising sodium hydroxide (NaOH) is at most 32 wt% NaOH, preferably at most 30 wt% NaOH. [9]. The method according to any of [1] to [8], wherein a solution ofNa2CO3 is produced, and the solution of Na2CO3 is further processed tocrystallize sodium carbonate crystals selected from the list of: sodiumdecahydrate crystals, sodium carbonate monohydrate crystals, sodium carbonate anhydrous crystals.

[10] . The method according to [9], wherein the Na2CO3 solutioncomprises at most 30 wt% Na2CO3.

[11] . The method according to [9] or

[0010] , wherein the sodium carbonatecrystals are produced by evaporation of water and / or cooling, of the solution of Na2CO3. The evaporation of Na2CO3 solution to remove part of the water is preferably operated in multiple effect crystallizers or in a crystallizer with mechanical recompression of steam.

[12] . The method according to any of [9] to

[0011] , wherein the sodiumcarbonate crystals, are recovered and then dried.

[13] . The method according to any of [1] to

[0012] , wherein a solution ofNa2CO3 is produced, and wherein part of said solution is further carbonated with a gas comprising biogenic carbon dioxide (CO2) to crystallize sodiumbicarbonate crystals comprising partially or totally biogenic CO2, and preferablywherein at least 25 wt% or at least 80wt% of the carbon of the sodium bicarbonate crystals is biogenic.

[14] . The method according to any of [9] to

[0013] wherein part of thesolutions comprising sodium carbonate obtained with, or after, the crystallizationof the sodium decahydrate crystals, or the sodium carbonate monohydrate crystals, or the sodium carbonate anhydrous crystals, or the sodium bicarbonate crystals, is purged to control the sodium chloride (NaCl) content at a concentration of atmost 15 wt% NaCl, preferably at most 6 wt% NaCl, during the crystallization of said sodium carbonate or bicarbonate crystals. Preferably this purge comprising sodium carbonate and sodium chloride is recycled back to purify calcium and / or magnesium in at least part of the sodium chloride solution electrolyzed into sodium hydroxide.

[15] . The method according to any of [1] to

[0014] , wherein the sodiumchloride from the sodium chloride aqueous solution derives from: a solar pond salt, or sea salt, rock-salt, or a dissolved salt from a geological salt cavity, or industrial vacuum crystallized salt, or a residual or a co-product sodium chlorideresulting from another industry, or a sea-water desalination unit.

[0016] . The method according to any of [1] to

[0014] , wherein the electrolyzeof the sodium chloride aqueous solution uses an electrical tension, and said electrical tension is provided with electricity having a reduced fossil CO2 footprint, preferably 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, geothermal electricity, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, or mixtures thereof.

[17] . The method according to any of [1] to

[0016] , wherein carbon dioxide(CO2) used for carbonating at least part of the aqueous outlet solution of the base chamber to obtain a carbonated liquid is from CO2 captured from the air, or deriving from the combustion of fossil carbonaceous combustibles, or deriving from fossil carbon dioxide, or combination thereof.

[18] . The method according to any of [1] to

[0017] , wherein the carbondioxide (CO2) derives partly or totally from fumes or gases 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 a waste-to-energy plant, a pulp plant, a paper plant, an oil refinery, a petro-chemical plant, a coal gasificationplant, a cement plant, a tile manufacturing plant, a brick manufacturing plant, amining process, a mineral processing plant, a lime plant, an ammonia plant, a fertilizer plant, a biochar plant, a biogas plant, or combinations thereof.

[19] . The method according to any of [1] to

[0018] , wherein chlorine iscoproduced with sodium hydroxide, and at least part of the chlorine (Cl2) produced by electrolyzing the aqueous solution of sodium chloride (NaCl) is further burnt with dihydrogen gas (H2) to obtain an HCl gas, which is dissolved in water to obtain an acid HCl solution, and said acid solution is further used toproduce CO2 by acid attack of limestone (CaCO3) or of a rock comprisingcarbonated minerals such as dolomite.

[20] . Plant for electrically producing sodium carbonate (Na2CO3)comprising:(A) an electrolyzer to electrolyze a sodium chloride (NaCl) aqueous solution intoa sodium hydroxide (NaOH) aqueous solution and chlorine (Cl2), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recovering the sodium carbonate (Na2CO3) crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in aconstant production rate in the said time period. For this, preferably, theelectrolyzer comprises modulation means of the voltage and / or of the intensity of electrical current supplying the electrolyzer.

[21] . The plant according to

[0020] , wherein the storage means (C ) of thesodium hydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2CO3) aqueous solution, 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 electrolyze, in the electrolyzer, the sodium chloride (NaCl) intosodium hydroxide (NaOH) per unit volume (m3) of the sodium hydroxide(NaOH) aqueous solution and / or of the sodium carbonate (Na2CO3) aqueoussolution stored in the storage means (C).

[0022] . The plant according to

[0021] , wherein the storage means (C ) of thesodium hydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2CO3) aqueous solution, has an equivalent electrical power storage ability per volume of at least 160 kWh / m3, or at least 240 kWh / / m3, calculated as the electrical power (expressed in kWh) used to electrolyze, in the electrolyzer, thesodium chloride (NaCl) into sodium hydroxide (NaOH) per unit volume (m3) ofthe sodium hydroxide (NaOH) aqueous solution and / or of the sodium carbonate(Na2CO3) aqueous solution stored in the storage means (C).

[0023] . The plant according to any of

[0020] to

[0022] , wherein the electrolyzer(A) uses electricity to electrolyze the sodium chloride (NaCl) 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, geothermal electricity, 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.

[24] . The plant according to any of

[0020] to

[0023] , wherein the at least 2production 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.

[25] . The plant according to any of

[0020] to

[0024] , wherein the at least 2production rates ratio expressed as the ratio of a high production rate to a low production rate is at most 5 or at most 3.

[26] . The plant according to any of

[0020] to

[0025] , wherein the crystallizerequipment (D) to concentrate the sodium carbonate (Na2CO3) aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor, comprises:- an optional (D1) pre-evaporator means such as: a falling film evaporator or aforced circulation evaporator, to remove at least part of the water of the sodium carbonate (Na2CO3) aqueous solution;- (D2) crystallizer means such as a sodium carbonate anhydrous (Na2CO3)crystallizer, or a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or a sodium sesquicarbonate (Na2CO3.NaHCO3.2H2O) crystallizer.

[27] . The plant according to any of

[0020] to

[0026] , wherein the crystallizerequipment (D) further comprises:- an optional (D1) pre-evaporator means, and- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer,- a separation means (E2) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)crystals into a purified sodium carbonate solution,- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with thepurified 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.

[28] . The plant according to any of

[0020] to

[0027] , wherein the crystallizerequipment (D) further comprises:- an optional (D1) pre-evaporator means, and- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with thesodium 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 carbonatemonohydrate crystallizer,- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer fed with thepurged mother liquor from the sodium carbonate monohydrate crystallizer,- a separation means (E’) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)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 (Na2CO3.H2O) crystallizer.

[29] . The plant according to any of

[0020] to

[0028] , wherein the mother liquorfrom 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 ofthe least part of the purged mother liquor, to recycle the at least part of themother liquor to a sodium chloride brine purification module or to the electrolyzer or upfront the electrolyzer to recover at least part of the sodium chloride of the purged mother liquor and to electrolyze it into sodium hydroxide and / or chlorine.

[30] . Sodium carbonate crystals or sodium bicarbonate crystals, obtainableby the method of [1] to

[0019] ,- comprising at least 25 wt.% of its carbon content is biogenic carbon, preferablyat least 80 wt. % of its carbon content is biogenic carbon; and- preferably comprising at most 20 mg calcium (Ca) and / or at most 20 mgmagnesium (Mg) per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals.

[31] . Sodium carbonate crystals or sodium bicarbonate crystals of

[0030] ,wherein at least 95 wt.% or at least 99 wt% of its carbon content is biogenic, or is CO2 captured from the air.

[32] . The sodium carbonate crystals or sodium bicarbonate crystals of

[0030] or

[0031] comprising at most 10 mg iron (Fe), preferably at most 4 mg iron per kilogram of crystals.

[33] . Plant for electrically producing sodium carbonate (Na2CO3)comprising:(A) a set of at least two electrolyzer cellstacks to electrolyze a sodium chloride(NaCl) aqueous solution into an aqueous solution comprising sodium hydroxide (NaOH) and into chlorine (Cl2), wherein the electrolyzer cellstack set comprises operation means enabling to stop and start at least one of the electrolyzer cellstacks and so to operate theset of the electrolyzer cellstacks in at least 2 production rates on a given time period by adjusting the number of operating cellstacks;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recover the sodium carbonate (Na2CO3)crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period.

[34] . The plant according to

[0033] , wherein the electrolyzer cellstacks useelectricity to electrolyze the sodium chloride (NaCl) aqueous solution into the sodium hydroxide (NaOH) aqueous solution and into chlorine (Cl2), and wherein the electricity is at least partly, and preferably totally, a ‘greenelectricity’, or has a reduced fossil CO2 footprint, preferably selected among thegroup 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, geothermal electricity, 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.

[35] . The plant of

[0033] or

[0034] , wherein the plant to produce sodiumcarbonate (Na2CO3) 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.

[36] . The plant of any

[0033] to

[0035] , wherein the set (A) comprisesoperation means:- to modulate the production rate of at least part of the electrolyzer cellstacks bymodulating the intensity of electricity used to electrolyze the sodium chloride (NaCl) aqueous solution; and / or- to switch off and switch on at least part of the electrolyzer cellstacks of the set;to operate the set (A) of electrolyzer cellstacks in the at least 2 production rates on the given time period.

[37] . The plant of any

[0033] to

[0036] , wherein the time period is at least 1hour or at least 10 hours.

[38] . The plant of any

[0033] to

[0037] , wherein the time period is at most 1week or at most 1 day.

[39] . The plant of any

[0033] to

[0038] , wherein the at least 2 production ratesratio expressed as the ratio of a high production rate to a low production rate is at least 1,2 or at least 1,5.

[40] . The plant of any

[0033] to

[0039] , wherein the at least 2 production ratesratio expressed as the ratio of the higher production rate to the lower production rate is at most 5 or at most 3.

[0041] . The plant of any

[0033] to

[0040] , wherein at least part or the totality ofthe electrolyzer cellstacks comprise(s) 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.

[42] . The plant of any

[0033] to

[0041] , wherein at least part or the totality ofthe electrolyzer cellstacks or the set (A), can be, or is, operated in a feed and bleed mode.

[43] . The plant of any

[0033] to

[0042] , wherein the crystallizer equipment (D)to concentrate the sodium carbonate (Na2CO3) aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor, comprises:- an optional (D1) pre-evaporator means such as: a falling film evaporator or aforced circulation evaporator, to remove at least part of the water of the sodium carbonate (Na2CO3) aqueous solution;- (D2) crystallizer means such as a sodium carbonate anhydrous (Na2CO3)crystallizer, or a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or a sodium sesquicarbonate (Na2CO3.NaHCO3.2H2O) crystallizer.

[44] . The plant of any

[0033] to

[0043] , wherein the crystallizer equipment (D)further comprises:- an optional (D1) pre-evaporator means, and- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer,- a separation means (E2) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)crystals into a purified sodium carbonate solution,- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with thepurified 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.

[45] . The plant of any

[0033] to

[0044] , wherein the crystallizer equipment (D)further comprises:- an optional (D1) 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 carbonatemonohydrate crystallizer,- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer fed with thepurged mother liquor from the sodium carbonate monohydrate crystallizer,- a separation means (E’) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)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 (Na2CO3.H2O) crystallizer.

[46] . The plant of any

[0033] to

[0045] , wherein the mother liquor from thecrystallizer 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 thecrystallizer equipment ( (D), (D2), or (D2’) ) and a recycling means of the leastpart of the purged mother liquor, to recycle the at least part of the mother liquor to a sodium chloride brine purification module or to at least one electrolyzer cellstack of the set (A), or upfront of at least one electrolyzer cellstack of the set (A) to recover at least part of the sodium chloride of the purged mother liquor and to electrolyze it into sodium hydroxide and / or into chlorine (Cl2).

[47] . An electrolysis method of a sodium chloride solution for producing asodium carbonate solution in a cathode compartment, and hydrochloric acid in an anode compartment,- said anode compartment comprising a Hydrogen Depolarized Anode (HDA),and- the cathode compartment is fed with an aqueous solution comprising dissolvedcarbon dioxide (CO2) wherein sodium hydroxide is produced and carbonated into sodium carbonate with the dissolved direct carbonation of the caustic soda with the dissolved carbon dioxide (CO2) in the cathodic circuit, in order to produce sodium carbonate

[48] . A method for producing Na2CO3 and HCl from an NaCl aqueoussolution, using an electrolyzer comprising at least a cathode compartment and an anode compartment, characterized in that:- the cathode compartment produces NaOH and dihydrogen (H2), and saidcompartment is fed with an aqueous solution comprising dissolved CO2 whichreacts with NaOH in said compartment to produce the Na2CO3 solution fromwhich dihydrogen (H2) is separated and said Na2CO3 solution is recovered;- the anode compartment comprises a Hydrogen Depolarized Anode (HDA) fedwith at least part of the dihydrogen (H2) produced in the cathode compartment and separated from it, to produce hydrochloric acid which is recovered from theanode compartment, and- the sodium chloride is fed :either in the anode compartment in a configuration of the electrolyzer with 2 compartments: cathode compartment and anode compartment separated by a cation permselect membrane permeable to sodium ions Na+ from the sodium chloride solution to migrate to the cathode compartment; or in a salt compartment placed between the cathode compartment and the anode compartment in a configuration with 3 compartments, and said salt compartment is separated from the cathode compartment with a cation permselect membrane permeable to sodium ions Na+ from the sodium chloride solution to migrate to the cathode compartment, and said salt compartment is separated from the anode compartment with an anion permselect membrane permeable to chloride ions Cl- from the sodiumchloride solution to migrate to the anode compartment.

[49] . The method of

[0047] or

[0048] , wherein at least 25 wt.% of the carbon ofthe dissolved carbon dioxide (CO2) of the aqueous solution feeding the cathode compartment is biogenic.

[50] . The method of

[0049] , wherein at least 40 wt.% of the carbon of thedissolved carbon dioxide (CO2) of the aqueous solution feeding the cathode compartment is biogenic.

[51] . The method of

[0050] , wherein at least 80 wt.% or at least 90 wt.% ofthe carbon of the dissolved carbon dioxide (CO2) of the aqueous solution feeding the cathode compartment is biogenic.

[52] . The method of any of

[0047] to

[0051] , wherein the cation permselectmembrane or the anion permselect membrane is / are more permeable to monovalent ions than multivalent ions.

[0053] . The method of any of

[0047] to

[0052] , wherein the carbon of the solutionof Na2CO3 which is produced comprises at least 25 wt.% or at least 40 wt.% of biogenic carbon.

[54] . The method of

[0053] , wherein the carbon of the solution of Na2CO3which is produced comprises at least 80 wt.% or at least 90 wt.% of biogenic carbon.

[55] . The method of any of

[0047] to

[0054] , wherein the solution of Na2CO3exiting the cathode compartment comprises NaOH and is further carbonated with CO2, preferably with biogenic CO2.

[56] . The method of any of

[0047] to

[0055] , and the solution of Na2CO3 isfurther processed to crystallize sodium carbonate crystals selected from the list of: sodium decahydrate crystals, sodium carbonate monohydrate crystals, sodium carbonate anhydrous crystals.

[57] . The method according to

[0056] , wherein the sodium carbonate crystalsare produced by evaporation of water and / or cooling, of the solution of Na2CO3. The evaporation of Na2CO3 solution to remove part of the water is preferably operated in multiple effect crystallizers or in a crystallizer with mechanical recompression of steam.

[58] . The method of

[0056] or

[0057] , wherein the sodium carbonate crystals,are recovered and then dried.

[59] . The method of any

[0047] to

[0057] , wherein a solution of Na2CO3 isproduced, and wherein part of said solution is further carbonated with a gas comprising biogenic carbon dioxide (CO2) to crystallize sodium bicarbonate crystals comprising partially or totally biogenic CO2.

[60] . The method of any

[0047] to

[0059] , wherein the sodium chloride fromthe sodium chloride aqueous solution derives from: a solar pond salt, or sea salt, rock-salt, or a dissolved salt from a geological salt cavity, or industrial vacuum crystallized salt, or a residual or a co-product sodium chloride resulting from an other industry, or a sea-water desalination unit.

[61] . The method of any

[0047] to

[0060] , wherein the electrolyze of thesodium chloride aqueous solution uses an electrical tension, and said electrical tension is provided with electricity having a reduced fossil CO2 footprint, preferably 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, geothermal electricity, electricity generated by compressed air such as from compressed air stored in underground cavities, nuclear electricity, or mixtures thereof.

[62] . The method of any of

[0047] to

[0061] , wherein carbon dioxide (CO2)used for carbonating at least part of the aqueous outlet solution of the base chamber to obtain a carbonated liquid is from CO2 captured from the air, or deriving from the combustion of fossil carbonaceous combustibles, or deriving from fossil carbon dioxide.

[63] . The method of any of

[0047] to

[0061] , wherein the carbon dioxide (CO2)derives partly or totally from fumes or gases 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 a waste-to-energy plant, a pulp plant, a paper plant, an oil refinery, a petro-chemical plant, a coal gasification 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.

[64] . The method of any of

[0047] to

[0063] , wherein at least part of thechlorine (Cl2) produced by electrolyzing the aqueous solution of sodium chloride (NaCl) is further burnt with dihydrogen gas (H2) to obtain an HCl gas, which is dissolved in water to obtain an acid HCl solution, and said acid solution is further used to produce CO2 by acid attack of limestone (CaCO3) or of a rock comprising carbonated minerals such as dolomite.

[65] . Sodium carbonate crystals or sodium bicarbonate crystals, obtainableby the method of

[0047] to

[0064] ,- comprising at least 25 wt.% of its carbon content being biogenic carbon,preferably at least 80 wt. % of its carbon content is biogenic carbon; and- preferably comprising at most 20 mg calcium (Ca) and / or at most 20 mgmagnesium (Mg) per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals.

[66] . Sodium carbonate crystals or sodium bicarbonate crystals of

[0065] ,wherein at least 95 wt.% or at least 99 wt% of its carbon content is biogenic, or is CO2 captured from the air.

[67] . The sodium carbonate crystals or sodium bicarbonate crystals of

[0065] or

[0066] comprising at most 10 mg iron (Fe), preferably at most 4 mg iron per kilogram of crystals.

[68] . The method according to any method [1] to

[0064] , wherein the sodiumchloride used to produce sodium carbonate is a sodium chloride recovered from the reaction with calcium chloride with a sodium sulfate originated from the list consisting of: sodium sulfate obtained from SOx fumes mitigation, sodiumsulfate from battery recovery or recycling, such as lithium or lead batteries,sodium sulfate originating from manufacturing of CAM (cathode active material) and PCAM (precursor cathode active material) for batteries or production of Li, Co, Mn, Ni, sodium sulfate generated by other industries using sulfuric acid.

[69] . The method according to

[0068] , wherein the calcium chloride isgenerated from carbonated ores such as limestone or dolomite, which are reactedwith hydrochloric acid generated in one of the above-described methods [1] to

[0064] .

[70] . The method according to

[0068] or

[0069] , wherein gypsum iscoproduced from the reaction of sodium sulfate with calcium chloride andrecovered to be further valorized.

Claims

C L A I M S 1. Plant for electrically producing sodium carbonate (Na2CO3)comprising:(A) an electrolyzer to electrolyze a sodium chloride (NaCl) aqueous solution intoa sodium hydroxide (NaOH) aqueous solution and chlorine (Cl2), wherein the electrolyzer comprises operation means enabling the electrolyzer to be operated in at least 2 production rates on a given time period;(B) carbonating means to partially or totally carbonate the sodium hydroxide(NaOH) aqueous solution with a gas comprising carbon dioxide (CO2) into a sodium carbonate (Na2CO3) aqueous solution;(C) storage means of the sodium hydroxide (NaOH) aqueous solution or of thesodium carbonate (Na2CO3) aqueous solution;(D) a crystallizer equipment to concentrate the sodium carbonate (Na2CO3)aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor;(E) separation means to separate the sodium carbonate (Na2CO3) crystals fromtheir mother liquor and recovering the sodium carbonate (Na2CO3) crystals; and wherein the storage means of the sodium hydroxide (NaOH) aqueous solution, or the storage means of the sodium carbonate (Na2CO3) aqueous solution, is of a volume sufficient to operate the crystallizer equipment in a constant production rate in the said time period.

2. The plant of claim 1, wherein the storage means (C) of the sodiumhydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2CO3) aqueous solution, 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 electrolyze, in the electrolyzer, the sodium chloride (NaCl) into sodiumhydroxide (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).

3. The plant of claims 1 or 2, wherein the storage means (C) of the sodiumhydroxide (NaOH) aqueous solution or of the sodium carbonate (Na2CO3) aqueous solution, has an equivalent electrical power storage ability per volumeof at least 160 kWh / m3, or at least 240 kWh / / m3, calculated as the electrical power (expressed in kWh) used to electrolyze, in the electrolyzer, 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).

4. The plant of any preceding claims, wherein the electrolyzer (A) useselectricity to electrolyze the sodium chloride (NaCl) 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, geothermal electricity, 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.

5. The plant of any preceding claims, wherein the at least 2 productionrates 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.

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

7. The plant of any preceding claims, wherein the crystallizer equipment(D) to concentrate the sodium carbonate (Na2CO3) aqueous solution and to produce sodium carbonate (Na2CO3) crystals and a mother liquor, comprises:- an optional (D1) pre-evaporator means such as: a falling film evaporator or aforced circulation evaporator, to remove at least part of the water of the sodium carbonate (Na2CO3) aqueous solution;- (D2) crystallizer means such as a sodium carbonate anhydrous (Na2CO3)crystallizer, or a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer, or a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer, or a sodium sesquicarbonate (Na2CO3.NaHCO3.2H2O) crystallizer.

8. The plant of any preceding claims, wherein the crystallizer equipment(D) further comprises:- an optional (D1) pre-evaporator means, and- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer,- a separation means (E2) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)crystals into a purified sodium carbonate solution,- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with thepurified 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, wherein the crystallizer equipment(D) further comprises:- an optional (D1) pre-evaporator means, and- (D2’) a sodium carbonate monohydrate (Na2CO3.H2O) crystallizer fed with thesodium 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 carbonatemonohydrate crystallizer,- (D2) a sodium carbonate decahydrate (Na2CO3.10H2O) crystallizer fed with thepurged mother liquor from the sodium carbonate monohydrate crystallizer,- a separation means (E’) to separate sodium carbonate decahydrate(Na2CO3.10H2O) crystals from their mother liquor,- a melting device to melt the sodium carbonate decahydrate (Na2CO3.10H2O)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 (Na2CO3.H2O) crystallizer.

10. The plant of any preceding claims, wherein the mother liquor from thecrystallizer 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 thecrystallizer equipment ( (D), (D2), or (D2’) ) and a recycling means of the leastpart of the purged mother liquor, to recycle the at least part of the mother liquorto a sodium chloride brine purification module or to the electrolyzer or upfront the electrolyzer to recover at least part of the sodium chloride of the purged mother liquor and to electrolyze it into sodium hydroxide and / or chlorine.

11. A method for producing sodium carbonate (Na2CO3) or sodiumbicarbonate (NaHCO3), comprising electrolyzing an aqueous solution of sodium chloride (NaCl) to obtain:- chlorine gas (Cl2) or hydrochloric acid (HCl) and- an aqueous solution comprising sodium hydroxide (NaOH)and carbonating the aqueous solution comprising sodium hydroxide (NaOH) with a gas comprising carbon dioxide (CO2) to produce sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3) or a mixture thereof, wherein at least 25 wt.% of the carbon comprised in the carbon dioxide (CO2) is biogenic.

12. The method of the preceding claim, wherein at least 80 wt.% or atleast 90 wt% of the carbon comprised in the carbon dioxide (CO2) is biogenic.

13. The method of claim 11 or 12, wherein the produced sodium carbonate(Na2CO3) or sodium bicarbonate (NaHCO3) are in aqueous solution or in a slurry of Na2CO3 crystals or a slurry of NaHCO3 crystals, and mixtures thereof.

14. The method of any claim 11 to 13, wherein the electrolysis of theaqueous sodium chloride solution is operated in an electrolyzer cell, and the electrolyzer cell is a bipolar membrane electrolysis cell or a monopolar membrane cell.

15. An electrolysis method of a sodium chloride solution for producing asodium carbonate solution in a cathode compartment, and hydrochloric acid in an anode compartment,- said anode compartment comprising a Hydrogen Depolarized Anode (HDA),and- the cathode compartment is fed with an aqueous solution comprising dissolvedcarbon dioxide (CO2) wherein sodium hydroxide is produced and carbonated into sodium carbonate with the dissolved direct carbonation of the caustic soda with the dissolved carbon dioxide (CO2) in the cathodic circuit, in order to produce sodium carbonate.

16. A method for producing Na2CO3 and HCl from an NaCl aqueoussolution, using an electrolyzer comprising at least a cathode compartment and ananode compartment, characterized in that:- the cathode compartment produces NaOH and dihydrogen (H2), and saidcompartment is fed with an aqueous solution comprising dissolved CO2 which reacts with NaOH in said compartment to produce the Na2CO3 solution fromwhich dihydrogen (H2) is separated and said Na2CO3 solution is recovered;- the anode compartment comprises a Hydrogen Depolarized Anode (HDA) fedwith at least part of the dihydrogen (H2) produced in the cathode compartment and separated from it, to produce hydrochloric acid which is recovered from the anode compartment, and- the sodium chloride is fed :either in the anode compartment in a configuration of the electrolyzer with 2 compartments: cathode compartment and anode compartment separated by a cation permselect membrane permeable to sodium ions Na+from the sodium chloride solution to migrate to the cathode compartment; or in a salt compartment placed between the cathode compartment and the anode compartment in a configuration with 3 compartments, and said salt compartment is separated from the cathode compartment with a cation permselect membrane permeable to sodium ions Na+from the sodium chloride solution to migrate to the cathode compartment, and said salt compartment is separated from the anode compartment with an anion permselect membrane permeable to chloride ions Cl- from thesodium chloride solution to migrate to the anode compartment.

17. The method of [claims 15 or 16, wherein at least 25 wt.% of thecarbon of the dissolved carbon dioxide (CO2) of the aqueous solution feeding the cathode compartment is biogenic.

18. The method of the preceding claim, wherein at least 80 wt.% or atleast 90 wt.% of the carbon of the dissolved carbon dioxide (CO2) of the aqueous solution feeding the cathode compartment is biogenic.

19. Sodium carbonate crystals or sodium bicarbonate crystals, obtainableby the method of any preceding claims, or by the plant of any preceding claims,- comprising at least 25 wt.% of their carbon content being biogenic carbon,preferably at least 80 wt. % of their carbon content being biogenic carbon; and- preferably comprising at most 20 mg calcium (Ca) and / or at most 20 mgmagnesium (Mg) per kilogram of crystals, preferably at most 8 mg calcium and / or at most 8 mg magnesium per kilogram of crystals.

20. The sodium carbonate crystals or sodium bicarbonate crystals of thepreceding claim comprising at most 10 mg iron (Fe), preferably at most 4 mg iron per kilogram of crystals.