Method for separating carbon dioxide

Abstract

The present invention relates to a method for separating carbon dioxide in the form of carbonates.

Description

[0001] Process for the capture of carbon dioxide

[0002] The present invention relates to the technical field of carbon dioxide capture and the technical field of recycling or reuse.

[0003] In particular, the present invention relates to a process for the separation of carbon dioxide from aqueous solution.

[0004] It has long been known that carbon dioxide in aqueous solution exists in equilibrium with the unstable carbonic acid "H2CO3" and its corresponding bases hydrogen carbonate (HCO3) and carbonate (CO3 2 ) stands.

[0005] H2O + HCO3- - H3O + + CO3 2 -

[0006] (2)

[0007] By introducing carbon dioxide into basic solutions, the equilibrium can be shifted towards the carbonates.

[0008] Basic carbonate-containing solutions can precipitate the ions of mono-, di- or trivalent metals in the form of basic salts, particularly in the form of hydroxides, oxides, carbonates or mixed salts.

[0009] In particular, the carbonates form with a variety of divalent metal ions, such as Ca 2+ , Fe 2+ or Mn 2+ , poorly soluble carbonates.

[0010] Carbonates occur naturally and are used for a wide variety of applications. The most commonly used carbonate in industry, especially in the construction sector, is calcium carbonate (CaCO3), which is the main component of fossil limestone. Due to its numerous applications, the global demand for calcium carbonate is very high. In 2010, 6,000 Mt of limestone were mined. Other carbonates, such as iron carbonate, are used in the steel industry. However, for some applications, such as paper production, fossil carbonates do not have sufficient qualities, for example, in terms of purity or particle morphology. For these applications, calcium carbonate is produced synthetically.

[0011] Synthetic calcium carbonate is currently primarily produced from fossil limestone and carbon dioxide. The carbon dioxide used often comes from flue gases and is bound during calcium carbonate synthesis. Synthetic calcium carbonate is obtained by heating calcium carbonate, thus converting it to calcium oxide, known as quicklime. The subsequent addition of water produces calcium hydroxide (Ca(OH)2), also known as slaked lime. Synthetic calcium carbonate can then be obtained from solutions or suspensions of calcium hydroxide by introducing carbon dioxide, particularly from flue gases.

[0012] However, the conversion of limestone into the calcium hydroxide required for the precipitation reaction produces significantly more carbon dioxide than is bound in the calcium carbonate, because the carbon dioxide bound in the limestone is expelled from the limestone, and the high temperatures required for this are usually achieved through combustion processes. The disadvantages of this process are therefore the use of fossil limestone and the release of carbon dioxide into the atmosphere.

[0013] In order to avoid the use of fossil limestone for the production of calcium carbonate, research and work are being carried out on the recovery of calcium, especially dissolved calcium ions, from calcium-rich waste.

[0014] Over the years, several publications have been published, particularly on various extraction agents for the extraction of calcium and calcium ions. These publications tested suitable extraction agents at different concentrations for their efficiency in extracting calcium from calcium-rich waste. The results showed that the acids acetic acid (CH3COOH), nitric acid (HNO3), and propanoic acid (C2H5COOH), as well as the ammonium salts ammonium chloride (NH4Cl), ammonium acetate (CH3COONH4), and ammonium nitrate (NH4NO3) have an efficiency of over 50% in dissolving calcium from calcium-rich waste. In particular, the aforementioned acids and ammonium salts have an efficiency of over 80% in dissolving calcium from calcium-containing waste at a concentration of 0.5 mol / l.

[0015] Extraction efficiency can be determined by first determining the calcium content of the solid to be extracted and, after extraction, by measuring the calcium content in the extract, for example, by inductively coupled plasma optical emission spectroscopy (ICP-OES). The choice of extraction agent is important not only for extraction efficiency but also for selectivity: For example, the solubility or extraction capacity for various metal compounds often depends on both the pH value and the base corresponding to the free acid.

[0016] Another problem that arises during the extraction of metal ions, especially calcium ions, is to convert the cation-rich, especially calcium-rich, extracts back into solids, which represent raw materials for industrial processes.

[0017] Carbonates are not stable in acidic conditions, but rather react, releasing CO2, to form metal compounds of the anions corresponding to the free acids. In the case of acetic acid, for example, acetates are usually highly soluble. Especially when using acetic acid as an extraction agent, which generally exhibits very good reactivity, high carbonate yields can only be achieved if uneconomically high amounts of a strong base are used, which keeps the pH permanently in the basic range.

[0018] For example, if carbon dioxide is introduced into a calcium-rich extract with a pH in the slightly acidic or neutral range, the pH will shift increasingly toward the acidic range due to carbonate precipitation, as protons or hydronium ions are released during this process. However, this is unfavorable for the precipitation of carbonates.

[0019] Therefore, other extraction agents, particularly ammonium salts, are predominantly used to develop processes for the synthesis of calcium carbonate from waste materials. A patented process for the production of calcium carbonate from waste materials is the so-called Slag2PCC process, which is described in EP 2 294 233 B1. The individual reaction steps for the production process are explained below:

[0020] Calcium is extracted from slag using ammonium chloride. This produces highly soluble calcium chloride and ammonium hydroxide.

[0021] In the next step, the extract is filtered and then transferred to a second reactor. The ammonium hydroxide present reacts with carbon dioxide to form ammonium carbonate (NH^CO3).

[0022] 2 NH4OH + CO2 ^===== (NH4)2CO3(aq) + H2O(|) (4)

[0023] The ammonium chloride is regenerated to calcium carbonate by the reaction of ammonium carbonate with calcium chloride and can be reused in the process.

[0024] (NH4)2CC>3( aq ) + CaCl2( aq ) - CaCO 3(S ) + 2 NH4Cl( aq )

[0025] The described procedure results in a high-quality product, but has the disadvantage that the ammonium salt used has a lower extraction efficiency than other extraction agents, such as acetic acid. Furthermore, ammonium chloride has the further disadvantage of being too corrosive for long-term use in industrial plants.

[0026] Furthermore, it has long been known in the art to separate carbon dioxide from exhaust gases by absorption by aqueous amine solutions. Primary, secondary, or tertiary amines are used for this purpose, which interact with carbon dioxide in various ways.

[0027] While primary and secondary amines react with carbon dioxide to form carbamates, the use of tertiary amines results in the formation of bicarbonates and carbonates (cf. Hagewiesche 1995, Chemical Engineering Science, Vol. 50, No. 7, pp. 1071-1079, (CO2 absorption in amines)). One of the most commonly used amines for carbon dioxide absorption is monoethanolamine, a primary amine that is very inexpensive and has a high carbon dioxide absorption capacity.

[0028] The disadvantage of this method, also known as "amine scrubbing," of binding carbon dioxide using amine solutions is, firstly, that the removal of carbon dioxide from exhaust gases using amines is relatively energy-intensive. For example, the carbamate formation that occurs with primary and secondary amines leads to significant heat generation, so that the subsequent release of the carbon dioxide, i.e., the so-called desorption, requires a relatively high energy input. Secondly, this energy input occurs by heating the amine solution, which often leads to thermal degradation of the amine.

[0029] This results in the high costs and high energy consumption for carbon dioxide separation from exhaust gases using amine scrubbing.

[0030] Islam (Islam 2010; Engineering e-Transaction (ISSN 1823-6379), Vol. 5, No. 2, December 2010, pp. 97-109, online at http: / / ejum.fsktm.um.edu.my (amine degradation)) reports extensively on the degradation of amines. This degradation not only reduces the proportion of active amines, but also negatively impacts the system through foaming processes, foam formation, and corrosion.

[0031] To address these disadvantages, various approaches have been developed:

[0032] For example, EP 2 740 572 A1 discloses a method by which the change in the composition of the amine solution during operation can be minimized.

[0033] Furthermore, EP 3 221 030 A1 concerns the energetic optimization of carbon dioxide release from the amine solution.

[0034] In addition, optimized amines are often used, such as in EP 3 378 550 A1, in which the amine is used in solid form. WO 2015 / 190936 A1 describes the use of a mixture of an amine and an amino acid salt.

[0035] In CA 3 027 122 A1 and a review article by Puxty (Puxty 2019; Environmental Science and Technology, 01 Aug 2019, 43(16):6427-6433, DOI: 10.1021 / es901376a (Absorption Performance of Various Amines)), various amines are investigated for their possible applications.

[0036] As a result, the state of the art still lacks a simple process that allows for the capture of carbon dioxide, particularly from flue gases, and for the sustainable use of the substances or chemicals used in this process in a circular process.

[0037] Furthermore, the state of the art also lacks a simple and energy-efficient process for obtaining high-quality metal compounds from residual materials.

[0038] In particular, the state of the art still lacks a sustainable process for the production of calcium carbonates that is sustainable and energy-efficient.

[0039] The object of the present invention is to avoid, or at least mitigate, the disadvantages associated with the prior art described above.

[0040] In particular, it is an object of the present invention to provide an efficient, sustainable process for producing a variety of metal compounds, in particular calcium carbonate, which are suitable as raw materials for industrial processes, wherein the metal compounds can be obtained in high purity.

[0041] Furthermore, it is an object of the present invention to provide an efficient, sustainable process for the production of synthetic calcium carbonate, wherein the chemicals and substances used can ideally be reused. A further object of the present invention is to provide a process for the efficient and low-energy capture of carbon dioxide, particularly from flue gases, wherein the substances and chemicals used can also be reused.

[0042] The present invention, according to a first aspect of the present invention, provides a method for separating carbon dioxide according to claim 1; further advantageous embodiments of this aspect of the invention are the subject of the relevant subclaims.

[0043] It goes without saying that special configurations, in particular special embodiments or the like, mentioned below, which are only described in connection with one aspect of the invention, also apply to the other aspects of the invention without this requiring express mention.

[0044] Furthermore, with all relative or percentage quantities, especially those based on weight, mentioned below, it should be noted that, within the scope of the present invention, these must be selected by the person skilled in the art in such a way that the sum of the ingredients, additives, auxiliaries, or the like always results in 100% or 100% by weight. However, this is self-evident to the person skilled in the art.

[0045] In addition, all parameter specifications or similar mentioned below can in principle be determined or ascertained using standardized or explicitly specified determination methods or methods that are familiar to the person skilled in the art.

[0046] Having said this, the subject matter of the present invention will be explained in more detail below.

[0047] The present invention - according to a first aspect of the present invention - thus relates to a process for the separation of carbon dioxide in the form of basic metal salts, in particular carbonates, preferably calcium carbonate, wherein a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide, a second acidic aqueous solution containing at least one acid is admixed with metal ions, in particular calcium ions, the first basic aqueous solution and the second aqueous solution are then mixed to obtain a reaction solution from which basic metal salts, in particular carbonates, preferably calcium carbonate, are precipitated, and the amine and / or the acid are separated from the reaction solution.

[0048] In this context, it is particularly possible for the acid and / or the amine, preferably the acid and the amine, to be separated from the reaction solution after the precipitation of the metal salts. However, it is equally possible for the acid to be separated from the second solution before mixing the first basic solution and the second solution, and for the amine to be separated from the reaction solution after the precipitation of the metal salts.

[0049] Within the scope of the process according to the invention, it is particularly possible to use both the amine and the acid in circulating processes and thus to provide a highly efficient and sustainable process for the production of basic metal salts, preferably calcium carbonate, which, moreover, has a positive CO2 balance, ie in the course of which more carbon dioxide is bound than is released.

[0050] The present invention, according to a preferred embodiment, therefore relates to a process for the separation of carbon dioxide in the form of basic metal salts, in particular carbonates, preferably calcium carbonate, wherein a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide, a second acidic aqueous solution containing at least one acid is admixed with metal ions, in particular calcium ions, the first basic aqueous solution and the second aqueous solution are subsequently mixed to obtain a reaction solution from which basic metal salts, in particular carbonates, preferably calcium carbonate, are precipitated, and the amine and / or the acid are separated from the reaction solution, wherein the amine and the acid are recovered and subsequently used to prepare the first basic solution containing at least one tertiary amine and the second acidic solution,containing at least one acid,

[0051] The most economically significant application to date is the possibility of extracting synthetic calcium carbonate from construction waste or slag. However, the process is applicable to virtually any metal that forms sparingly soluble salts in alkaline media in the presence of carbonate or hydroxide ions, particularly carbonates, oxides, hydroxides, or their mixed salts. Precipitation as carbonate is preferred, as the carbonates can usually be precipitated with a defined composition. The individual metals can then be (re)covered in high purity, especially through fractional precipitation.

[0052] The process according to the invention is primarily driven by the chemical reactions taking place, in particular acid-base reactions and precipitation reactions, so that an external energy supply - if at all - is only required to a small extent and the process can preferably be carried out at room temperature.

[0053] The process according to the invention makes it possible, in particular, to use mineral, preferably calcium-containing, residues, especially construction rubble or slag, such as those generated during iron production, as valuable materials for the extraction of raw materials and products, especially high-purity, synthetic calcium carbonate. The required carbon dioxide preferably originates from flue gases and can thus help significantly improve the CO2 balance of necessary industrial combustion processes, such as in kilns in the cement industry.

[0054] The process according to the invention thus enables the production of basic metal salts, preferably carbonates, from non-fossil sources. The cations, particularly calcium ions, extracted from construction waste, for example, react in a CO2-laden amine solution to form basic salts, particularly carbonates, which can thus be obtained in high quality with moderate energy consumption.

[0055] The conventional production of high-quality carbonates, especially calcium carbonates, as well as the desorption of CO2-laden amine solutions, is energy-intensive. In contrast, the process according to the invention enables the production of carbonates under ambient conditions with parallel desorption of carbon dioxide from amine solutions. After desorption of the amine solution, the CO2 in the present invention does not require the laborious storage required in other processes, but is obtained as a basic salt, preferably as a carbonate in crystalline form.

[0056] Especially in the synthesis of calcium carbonate, it is possible to produce calcium carbonate in specific modifications depending on the process parameters such as pressure and temperature. When precipitation occurs under

[0057] In the context of the present invention, the modification vaterite is preferably precipitated under ambient conditions, which can be easily converted into calcite.

[0058] It is known that vaterite precipitates from aqueous, highly supersaturated solutions, and that amorphous calcium carbonate transforms into vaterite in the presence of acetic acid. The calcium carbonate modification can be influenced, in particular, by the conditions during the loading of the amine with carbon dioxide. For example, calcite can also be selectively obtained in addition to vaterite.

[0059] The purity of the obtained basic salts, in particular carbonates, preferably calcium carbonate, can be specifically adjusted, in particular, for example, by separating the individual metal cations, which form poorly soluble basic salts, separately by means of fractional precipitation.

[0060] Depending on the waste materials used, the unextracted components can be further recycled. This allows increasingly scarce sand to be recovered from concrete or sand-lime quarry.

[0061] The process according to the invention increases the economic efficiency of CO2 capture from flue gases or the atmosphere. In contrast to the prior art, the desorption of carbon dioxide is not thermal, but rather by reaction with salt-forming, particularly carbonate-forming cations, preferably calcium carbonate. This produces high-quality salts, particularly carbonates, preferably calcium carbonate.

[0062] In particular, it also enables the separation of calcium and other components, such as sand, which can be recycled for the production of various building materials, from construction waste, especially concrete rubble. Recovery and processing of the amine and an aqueous acid are possible, particularly using distillation processes, so that the required reactants can always be recovered and reused.

[0063] As previously stated, in the present invention, metal salts, preferably calcium carbonates, are obtained from residues, with the precipitation step being carried out by the desorption of CCh-laden amines. This has two advantages: Firstly, the energy required for the desorption of CO2-laden amines, which in many cases makes amine scrubbing uneconomical, is reduced. Secondly, this procedure enables the use of acids with maximum extraction efficiency, since neutralization takes place via the amine, which, unlike alkalis, especially sodium hydroxide, can be recovered after the precipitation reaction.

[0064] In the context of the present invention, an acid is understood to mean in particular a Brönsted acid, ie a substance which has a proton (H +). The term "acid" therefore includes not only compounds expressly designated as acids, but also, for example, acidic cations, in particular ammonium ions, such as NH 2 . In the context of the present invention, a base is understood to mean a Brønsted base, ie a compound capable of donating a proton (H + ) to record.

[0065] For the purposes of the present invention, a basic salt is understood to mean a salt that has a basic pH when dissolved in water, or whose anion(s) have a basic pH in aqueous solution. The anions are typically the corresponding bases of weak acids. For the purposes of the present invention, basic salts include, in particular, carbonates, oxides, hydroxides, and mixed salts, such as oxide hydroxides.

[0066] As already stated above, in the context of the present invention, tertiary amines are used in an aqueous solution, in particular for preparing a basic aqueous solution.

[0067] The use of tertiary amines allows for the full benefits of the process according to the invention. When a tertiary amine is used, the CO2 reacts directly with the water to form bicarbonates, which, in a further reaction, usually involving the use of energy, form carbonates.

[0068] (6) (7)

[0069] Since the use of a tertiary amine does not lead to carbamate formation, but only a proton is added to the amine, the regeneration of the amine does not require a large input of energy. When using primary and secondary amines, CCh separation using an amine solution is normally an energetically intensive process due to the energy required to release the CO2 from the formed carbamates. The use of a tertiary amine for CCh absorption directly leads to the formation of bicarbonate and carbonate in the solution. If the CCh-laden amine solution is added directly to a cation-rich extract, especially an acidic, preferably acetic acid, cation-rich extract, this leads to the direct precipitation of carbonates, especially calcium carbonate, i.e. the absorbed carbon dioxide is released from the amine solution and the carbonate is bound to the cations.Thus, the release of CO2 from amines is possible without any energetic expenditure.

[0070] In the context of the present invention, it has proven particularly useful if the amine is selected from the group of tertiary amines with C1 to C10 residues and polyamines. Preferably, the amine can be selected from tertiary amines with C1 to C5 residues, preferably C1 to C6 residues, more preferably C1 to C3 residues. Furthermore, it is possible for the aforementioned amines to be functionalized with functional groups, in particular hydroxyl groups, nitro groups, thiol groups, ether groups, etc., preferably hydroxyl groups.

[0071] It is also possible for the amine to be selected from tertiary aliphatic amines with C1 to C2 residues, tertiary aromatic amines, polyamines, and mixtures thereof, preferably tertiary aliphatic amines with C1 to C2 residues, preferably tertiary aliphatic amines with C1 to C3 residues. Furthermore, within the scope of the present invention, it can also be provided that the aforementioned amines are functionalized with functional groups, in particular alcohol functions, nitro functions, or thiol functions, or that they contain aliphatic and aromatic residues in one molecule.

[0072] Particularly good results are obtained in the present invention when the amine is selected from trimethylamine, triethylamine, triethanolamine, dimethylethanolamine, and mixtures thereof. In this context, it is preferred if the amine is triethanolamine. Triethanolamine is available inexpensively in large quantities and is not harmful to health.

[0073] The content of tertiary amines in the first basic solution, especially before loading or addition of carbon dioxide, can vary widely. However, it has proven advantageous to use concentrated solutions of the amine. Within the scope of the present invention, it is particularly provided that, to prepare the first basic solution, water and the tertiary amine are mixed with an amine content of up to 70 vol.%, preferably up to 60 vol.%, preferably up to 55 vol.%, based on the total volume of water and amines.

[0074] Likewise, it can be provided within the scope of the present invention that, to prepare the first basic solution, the tertiary amine and water are mixed with a proportion of amine in the range from 10 to 70 vol.%, in particular 10 to 65 vol.%, preferably 30 to 60 vol.%, more preferably 40 to 55 vol.%, based on the total volume of water and amines.

[0075] As for the pH of the first basic aqueous solution, this can naturally vary within wide ranges. However, it has proven advantageous for the first basic aqueous solution, containing at least one amine and optionally carbon dioxide, to have a pH greater than 8, preferably a pH in the range of 8 to 10, preferably in the range of 8 to 9. At pH values ​​in the aforementioned ranges, in particular, efficient absorption of carbon dioxide in aqueous solution is achieved, as well as sufficient neutralization of acids during the precipitation reaction to obtain stable basic salts, especially carbonates.

[0076] Within the scope of the present invention, it is particularly provided that the first basic aqueous solution contains the CO2 in dissolved form as well as in the form of bicarbonates and carbonates. Upon introduction of CO2 into the first basic aqueous solution containing at least one amine, the carbon dioxide is initially dissolved and then reacts via the unstable carbonic acid to form bicarbonate and carbonate. Due to the basic nature of the amines, which can each bind one proton per molecule, the equilibrium lies largely on the side of the bicarbonates and carbonates, so that large amounts of carbon dioxide can be absorbed by the basic amine solution.

[0077] As far as the pressure at which the first basic aqueous solution is admixed with the carbon dioxide is concerned, this can also vary within a wide range, in particular from ambient pressure to high overpressures. In the context of the present invention, it is preferred if the first basic aqueous solution, containing at least one amine, is admixed with the carbon dioxide under pressure, in particular an overpressure of up to 8 bar, in particular up to 2 bar, preferably up to 1.5 bar, more preferably up to 1 bar. It can also be provided that the first basic aqueous solution, containing at least one amine, is admixed with the carbon dioxide under an overpressure in the range from 0.01 to 8 bar, in particular 0.02 to 2 bar, preferably 0.05 to 1.5 bar, more preferably 0.1 to 1 bar. An increased pressure enables a significantly more rapid absorption of the carbon dioxide.Furthermore, a slight overpressure is often present, particularly in industrial flue gas streams. In the context of the present invention, overpressure is understood to mean a pressure that is higher than the ambient pressure.

[0078] As already explained above, the carbon dioxide used in the present invention preferably originates from an industrial process. Particularly good results are obtained if the carbon dioxide also originates from a flue gas stream or from cement clinker production. Both flue gases and cement clinker production produce large amounts of carbon dioxide, which should not be released into the environment if possible. The process according to the invention now makes it possible to efficiently bind such flue gas streams or the carbon dioxide produced during lime burning. In the present invention, good results are obtained if the acid is selected from the group of organic acids, inorganic acids, ammonium compounds, and mixtures thereof.

[0079] Particularly good results are obtained in this context when the acid is selected from mineral acids, in particular hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, phosphonic acid, carboxylic acids, sulfonic acids, organic phosphonic acids (RP(O)(OH)2) and mixtures thereof. Furthermore, it is further preferred if the acid is selected from hydrochloric acid, sulfuric acid, nitric acid, carboxylic acids, sulfonic acids and mixtures thereof. Particularly good results are obtained when the acid is selected from the group consisting of nitric acid, carboxylic acids, sulfonic acids and mixtures thereof. The acid is most preferably a carboxylic acid.

[0080] Carboxylic acids are particularly suitable in the context of the present invention because, on the one hand, they have a good extraction capacity for a large number of metal compounds and form soluble salts with the metal ions, and, on the other hand, their corresponding bases are still so strong that they can be neutralized by an amine solution to such an extent that stable basic salts, in particular carbonates, can be precipitated.

[0081] In the context of the present invention, best results are obtained when the acid is selected from the group consisting of acetic acid, propanoic acid, butanoic acid, and mixtures thereof. In the context of the present invention, it is particularly preferred if the acid is acetic acid. Acetic acid has excellent chemical and physical properties for both extraction and precipitation and is also a readily available chemical commodity.

[0082] Acetic acid is also preferred as an extraction agent because it has a high extraction efficiency and forms calcium acetate with the extracted calcium ions, which is highly soluble in water.

[0083] If the solutions of the CO2-loaded amine and the extract are now combined, calcium carbonate is deposited according to the following equation:

[0084] The amine is regenerated directly here without additional energy expenditure. By separating the calcium carbonate, the equilibrium is shifted toward the product side, thus forcing the CCH deposition in the form of carbonate. Furthermore, the acetic acid can be recovered automatically, enabling a process in which the reactants can be used in a cyclic process. The acid, especially acetic acid, can also be separated before precipitation, for example, by electrodialysis. This is advantageous in some cases and can positively influence the recovery of the amine.

[0085] As for the amount of acid that the second acidic aqueous solution can contain, this can vary widely, but the proportion should not be too high, otherwise the formation of stable carbonates is difficult.

[0086] In the context of the present invention, it has proven useful if the second acidic aqueous solution contains the acid in amounts of up to 8 mol / l, in particular up to 7 mol / l, preferably up to 6 mol / l, more preferably up to 5 mol / l, based on the second solution.

[0087] Likewise, particularly good results are obtained within the scope of the present invention when the second acidic aqueous solution contains the acid in amounts of 0.1 to 8 mol / l, in particular 0.2 to 7 mol / l, preferably 0.5 to 6 mol / l, more preferably 1 to 5 mol / l, based on the second solution. With acid concentrations in the aforementioned ranges, on the one hand, a good extraction of metal ions, in particular calcium ions, can be achieved; on the other hand, it is still readily possible to neutralize the solutions by adding the amine solution to such an extent that stable carbonates can be obtained.

[0088] Furthermore, it has proven useful within the scope of the present invention if the second aqueous solution, which contains at least one acid, has a pH value in or close to the neutral range after addition of the metal ions or after execution of the extraction. Particularly good results are obtained in this context if the second aqueous solution, which contains at least one acid, has a pH value in the range of not less than 5, preferably not less than 6, after addition of the metal ions or after execution of the extraction. Likewise, it is preferred within the scope of the present invention if the second aqueous solution, which contains at least one acid, has a pH value in the range of 5 to 8.5, in particular 6 to 8, after addition of the metal ions or after execution of the extraction.At the aforementioned pH values, quantitative precipitation of carbonates and other poorly soluble basic salts is readily possible when the first basic aqueous solution and the second aqueous solution are mixed. A change in the pH of the second aqueous solution to the neutral range can occur, in particular, when basic metal salts, such as oxides, hydroxides, carbonates, or phosphates, react with the acid of the second aqueous solution.

[0089] When, within the scope of the present invention, a solution is admixed with metal ions, this means that a soluble metal compound, which decomposes into metal cations and corresponding anions in the presence of water, is added to the solution or—which is preferred according to the invention—the second aqueous solution containing at least one acid is admixed with a substance or mixture of substances to be extracted, and the aqueous solution dissolves metal salts from the substance or mixture of substances to be extracted. The extraction can be carried out in such a way that readily soluble metallic compounds are simply dissolved out of the substance or mixture of substances to be extracted, or by, for example, dissolving basic salts, in particular oxides, hydroxides, or carbonates, by reaction with the acid, and readily soluble metal compounds of the base corresponding to the free acid are formed.

[0090] Typically, within the scope of the present invention, the second aqueous solution is admixed or enriched with metal ions, in particular calcium ions, by extraction. Particularly good results are obtained in this context when the second acidic solution is admixed or enriched with metal ions, in particular calcium ions, by extraction of an inorganic residue, in particular a mineral or metallic residue, preferably a mineral residue. Within the scope of the present invention, a residue is understood to mean, in particular, a by-product or waste product arising in an industrial process. Particularly good results are obtained within the scope of the present invention when the inorganic residue, in particular the mineral residue, is selected from the group of construction rubble, slag, and mixtures thereof.If slag is used in the context of the present invention, it has proven advantageous to use so-called LD slag or converter slag.

[0091] Furthermore, within the scope of the present invention, the amount of second aqueous solution containing at least one acid can vary widely in relation to the substance to be extracted, in particular inorganic residue. However, it has proven useful to use a molar amount of acid of up to 100 mol, in particular 80 mol, preferably 60 mol, and more preferably 50 mol, per kilogram of substance to be extracted, in particular inorganic residue. Likewise, it can be provided that a molar amount of acid in the range of 10 to 80 mol, in particular 20 to 70 mol, in particular 30 to 60 mol, and more preferably 30 to 50 mol, is used per kilogram of solid to be extracted, in particular inorganic residue.

[0092] Furthermore, within the scope of the present invention, it is preferably provided that the extraction is carried out at ambient temperature or at a slightly elevated temperature. Particularly good results are obtained within the scope of the present invention when the extraction is carried out at a temperature in the range of 10 to 40°C, in particular 15 to 30°C, preferably 20 to 30°C.

[0093] Surprisingly, it has been found that only very short extraction times are required for the extraction, especially of construction waste or blast furnace slag.

[0094] In the context of the present invention, it is particularly preferred if the extraction time is up to 2 hours, preferably up to 1.5 hours, preferably up to 1 hour. Likewise, particularly good results are obtained if the extraction time is in the range from 10 minutes to 2 hours, in particular 15 minutes to 1.5 hours, preferably 0.5 hours to 1 hour. Preferably, the inorganic, in particular mineral, preferably calcium-rich, residue is comminuted, in particular ground, before extraction, in particular before mixing with the second aqueous solution containing at least one acid.

[0095] Particularly when the second acidic aqueous solution is enriched or enriched with metal ions by extraction, when using residual materials such as construction rubble or slag, not only calcium ions are extracted from the residues, but also other ions present in the form of acid-soluble compounds. These residues, especially mineral residues, are complex mixtures of substances containing a multitude of metal ions.

[0096] The metal ions are usually ions of metals selected from the group of monovalent metals, divalent metals, trivalent metals, and their mixtures, especially monovalent metals, divalent metals, and their mixtures. These metals often form sparingly soluble basic salts.

[0097] In the context of the present invention, it is preferred if the metal ions are ions of metals selected from the group of alkali metals, alkaline earth metals, metals of the iron group (group 8), manganese, zinc, and mixtures thereof, in particular selected from the group of lithium, magnesium, calcium, strontium, barium, iron, manganese, zinc, and mixtures thereof, preferably selected from the group of lithium, calcium, iron, manganese, and mixtures thereof. The ions are preferably calcium ions.

[0098] The aforementioned metal ions all form sparingly soluble basic salts, preferably carbonates, and can also be precipitated upon addition of the amine-containing carbon dioxide solution. Furthermore, within the scope of the present invention, it is possible to precipitate metal ions that form sparingly soluble carbonates, oxides, or hydroxides under the given conditions.

[0099] Within the scope of the present invention, it is typically provided that the metal ions are precipitated from the reaction solution upon mixing the first basic solution and the second aqueous solution, in particular in the form of their oxides, hydroxides, carbonates, or mixtures thereof. Within the scope of the present invention, however, it is preferred if the metal ions are precipitated from the reaction solution in the form of their carbonates upon mixing the first basic aqueous solution and the second aqueous solution. The targeted precipitation of carbonates has the advantage that they usually have a specific stoichiometry, whereas the precipitation of oxides or hydroxides often yields a multitude of slightly different products, in particular water-containing oxides, hydroxides, or oxide hydroxides, depending on the precise reaction conditions. Furthermore, the precipitation of carbonates also enables the permanent binding of carbon dioxide.

[0100] According to a preferred embodiment of the present invention, the metal ions contained in the second aqueous solution are fractionally precipitated.

[0101] Since the basic salts, especially carbonates, of the above-mentioned metal ions are sparingly soluble but have very different solubility products, it is possible to fractionally precipitate the respective salts, especially metal carbonates, but also hydroxides or oxides, and to obtain highly pure products in each case. Fractional precipitation can be achieved in particular by gradually mixing the first basic aqueous solution and the second aqueous solution. This can be done either by successively adding smaller amounts of the second aqueous solution, which optionally contains at least one acid, to the first basic aqueous solution, so that the metal ion concentration increases gradually and the carbonates with the smallest solubility product precipitate first. However, a successive addition of the first basic aqueous solution to the second aqueous solution is also possible.

[0102] For extracts containing different cations, the addition of a specific amount of carbon dioxide-loaded amines, i.e., the first basic aqueous solution, allows various basic salts, especially carbonates, to be successively precipitated and mechanically separated. This allows the production of pure products from extracts containing different cations.

[0103] The purity of the salts, especially the carbonates, can be controlled by adjusting the mixing ratio between the cation-rich extract, i.e., the second aqueous solution, and the CCh-loaded amine solution, i.e., the first basic aqueous solution. For a second aqueous solution containing both Fe 2+ - and Ca 2+ions, the iron carbonate is precipitated first, followed by the calcium carbonate. This is due to the different solubilities of the various carbonates. The solubilities of common carbonates at 20 °C are as follows: Ca(HCO3)2»CaCO3>MnCO3>MgCO3>Fe(CO3)2. Fractional precipitation allows the respective metal carbonates to be obtained in high purity.

[0104] Within the scope of the present invention, it is preferably provided that, following precipitation, the precipitated metal salts are separated from the reaction solution. In a fractional precipitation, the respective precipitated fractions are preferably separated individually from the reaction solution. The metal salts, in particular carbonates, are then prepared or used for further processing.

[0105] According to the invention, it is generally provided that the acid and the amine are recovered or reprocessed.

[0106] Within the scope of the present invention, it is also usually provided that following the precipitation of the metal ions, in particular calcium ions, the amine and / or the acid are recovered or processed.

[0107] According to a preferred embodiment, it is provided that following the precipitation of the metal ions, in particular calcium ions, the amine and the acid are recovered or processed.

[0108] According to a further preferred embodiment, however, it is provided that following the extraction of the metal ions, in particular calcium ions, and preferably before the precipitation of the metal ions, in particular calcium ions, the acid is recovered or processed and that following the precipitation of the metal ions, in particular calcium ions, the amine is recovered or processed.

[0109] A special feature of the process according to the invention is that, specifically through the combination of tertiary amines and acids, in particular carboxylic acids, it is possible to use both the amine and the acid in a single cycle, replacing only minor unavoidable losses in each case. However, the entire process is very low in loss, i.e., the acids and amines used can be recovered from the reaction solution in high purity and almost quantitatively. Within the scope of the present invention, it is therefore preferably provided that, following the precipitation of the metal ions, both the amine and the acid are recovered or processed.

[0110] As previously stated, it may be provided that the acid is separated from the reaction solution after the precipitation of the metal ions or is separated from the second solution after the extraction and preferably before the precipitation of the metal ions.

[0111] Separating the acid prior to precipitation of the metal ions can be advantageous to enable a simpler and better separation of the amine and acid, allowing the amine and acid to be recovered or reprocessed more easily and in higher yields. If the acid is separated from the second solution after extraction of the metal ions, this can be achieved, for example, by electrodialysis.

[0112] In general, the amine and / or the acid can be separated and recovered or processed separately from the reaction solution by electrodialysis, ie after precipitation of the metal ions, or at another time in the process according to the invention.

[0113] Within the scope of the present invention, it can also be provided that the acid is separated from the reaction solution, in particular recovered, by distillation. Typically, it is provided that the acid is recovered in the form of an aqueous solution, for example in the form of a 40% acid in the case of acetic acid. This acid can then be further processed, in particular purified, and / or diluted to the desired concentration. According to a preferred embodiment of the present invention, it is provided that the acid separated from the reaction solution, in particular in the form of an aqueous solution, is used to prepare the second acidic aqueous solution containing at least one acid.According to this embodiment of the invention, the acid is preferably separated from the reaction solution by first removing water from the reaction solution, in particular by distillation, and then removing the acid.

[0114] Likewise, within the scope of the present invention, it can be provided that the amine is separated from the reaction solution and, in particular, recovered. In this context, it is preferably provided that all more volatile constituents are first separated from the reaction solution. The amine can then be separated, preferably by distillation, from particularly less volatile residues and, if appropriate, further processed, in particular purified. Likewise, it can be provided that the amine is separated from the reaction solution by electrodialysis and recovered or processed. Within the scope of the present invention, it is preferably provided that the amine separated, in particular recovered, from the reaction solution is used to prepare the first basic aqueous solution containing at least one amine.

[0115] The separation or recovery of the used acid and amine is preferably carried out by electrodialysis. In electrodialysis, ions are transported through semipermeable or bipolar membranes under the influence of an electrochemical potential gradient. This allows ions to be separated from aqueous solutions without the addition of external energy, such as heat energy (problem: degradation of the amine). This can be particularly advantageous when using heat-sensitive amines, which are thermally decomposed.

[0116] According to a preferred embodiment of the present invention, it is provided that

[0117] (i) in a first process step, a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide,

[0118] (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with metal ions, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with, in particular mixing with, at least one mineral, in particular calcium-containing, residue, so that a second solution containing metal ions, in particular calcium ions, is obtained, wherein the acid is subsequently separated, in particular recovered,

[0119] (iii) in a subsequent third process step, the first basic aqueous solution containing at least one tertiary amine and carbon dioxide and the second aqueous solution containing metal ions, in particular calcium ions, are mixed so that a reaction solution is obtained and basic metal salts, in particular calcium carbonate, are precipitated from the reaction solution,

[0120] (iv) in a fourth process step following the third process step (iii), the metal salts, in particular the calcium carbonate, are separated from the reaction solution, and

[0121] (v) in a fifth process step following the fourth process step (iv), the amine is separated from the reaction solution, in particular is recovered.

[0122] For this particular preferred embodiment of the present invention, all features, characteristics, advantages and preferred embodiments described above apply accordingly.

[0123] According to a further preferred embodiment of the present invention, it is provided that

[0124] (i) in a first process step, a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide,

[0125] (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with metal ions, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with, in particular mixing it with, at least one mineral, in particular calcium-containing, residue,

[0126] (iii) in a subsequent third process step, the first basic aqueous solution containing at least one tertiary amine and carbon dioxide and the second aqueous solution containing at least one acid and metal ions, in particular calcium ions, are mixed so that a reaction solution is obtained and basic metal salts, in particular calcium carbonate, are precipitated from the reaction solution,

[0127] (iv) in a fourth process step following the third process step (iii), the metal salts, in particular the calcium carbonate, are separated from the reaction solution, and

[0128] (v) in a fifth process step following the fourth process step (iv), the amine and the acid are separated from the reaction solution, in particular recovered.

[0129] For this particular preferred embodiment of the present invention, all features, characteristics, advantages and preferred embodiments described above apply accordingly.

[0130] Furthermore, within the scope of the present invention, it is always possible for the first process step (i) and the second process step (ii) to be carried out in parallel or at different times. It is also possible to carry out the first process step (i) and the second process step (ii) at different locations and to combine the resulting solutions to form the reaction solution at one of the locations or at a third location.

[0131] Furthermore, in the second process step (ii) it can also be provided that after a time has elapsed in which the second solution containing at least one acid is brought into contact with a mineral, in particular calcium-containing, residue, undissolved residue is separated from the solution, in particular by means of filtration, and the extract containing at least one acid and metal ions, in particular calcium ions, with optionally further metal ions, is used further.

[0132] Furthermore, within the scope of the present invention, it can be provided that in the third process step (iii), the first basic aqueous solution and the second aqueous solution are gradually mixed with one another, thus enabling fractional precipitation of various basic metal salts, in particular calcium carbonate, and other basic salts, in particular metal carbonates. Furthermore, it is possible for the acid in process step (ii) and the amine in process step (v) to be separated, in particular recovered or reprocessed, by means of electrodialysis.

[0133] Furthermore, within the scope of the present invention, it can preferably be provided that, in the fifth process step (v), the amine or the amine and the acid are separated from the reaction solution by distillation. This is preferably done by first distilling off the acid, preferably in the form of an aqueous solution, and then separating off the amine, in particular by distillation. However, the amine and acid are preferably separated, in particular recovered or reprocessed, by electrodialysis.

[0134] According to a preferred embodiment of the present invention, the process according to the invention is a process for the separation of carbon dioxide in the form of calcium carbonate, wherein a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide, a second aqueous solution containing at least one acid is admixed with calcium, in particular calcium ions, the first basic aqueous solution and the second aqueous solution are then mixed to obtain a reaction solution from which calcium carbonate is precipitated, and the amine and / or the acid are separated from the reaction solution.

[0135] For this particular and preferred embodiment of the present invention, all the aforementioned advantages, features and special embodiments apply accordingly, which will, however, be readily apparent to a person skilled in the art.

[0136] Typically, within the scope of this preferred embodiment of the present invention, further metal ions are added to the second aqueous solution. In particular, when the second aqueous solution is enriched or enriched with calcium ions by means of extraction, when using residual materials such as construction rubble or slag, not only calcium ions are extracted from the residual materials, but also other ions that are present in the form of acid-soluble compounds. The residual materials, in particular mineral residual materials, are complex mixtures of substances that contain a large number of metal ions. The further ions can be ions of metals selected from the group of alkali metals, alkaline earth metals, metals of the iron group (group 8), manganese, zinc, and mixtures thereof.In particular, it can be provided that the further metal ions are ions of metals selected from the group of lithium, magnesium, strontium, barium, iron, manganese, zinc and mixtures thereof.

[0137] Most preferably, the other metal ions are ions of metals selected from the group of lithium, iron, manganese and mixtures thereof.

[0138] According to a preferred embodiment of this embodiment of the present invention, it is provided that

[0139] (i) in a first process step, a first basic aqueous solution containing at least one amine is carbonated,

[0140] (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with calcium, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with at least one calcium-containing residue, in particular by mixing it, so that a second solution containing metal ions, in particular calcium ions, is obtained, wherein the acid is subsequently separated, in particular recovered,

[0141] (iii) in a subsequent third process step, the first basic aqueous solution containing at least one amine and carbon dioxide and the second aqueous solution containing calcium ions are mixed to obtain a reaction solution and precipitate calcium carbonate from the reaction solution,

[0142] (iv) in a fourth process step following the third process step (iii), the calcium carbonate is separated from the reaction solution, and

[0143] (v) in a fifth process step following the fourth process step (iv), the amine is separated from the reaction solution, in particular is recovered.

[0144] According to a further embodiment of this embodiment of the present invention, it is provided that (i) in a first process step, a first basic aqueous solution containing at least one amine is carbonated,

[0145] (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with calcium, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with, in particular mixing it with, at least one calcium-containing residue,

[0146] (iii) in a subsequent third process step, the first basic aqueous solution containing at least one amine and carbon dioxide and the second acidic aqueous solution containing at least one acid and calcium ions are mixed to obtain a reaction solution and precipitate calcium carbonate from the reaction solution,

[0147] (iv) in a fourth process step following the third process step (iii), the calcium carbonate is separated from the reaction solution, and

[0148] (v) in a fifth process step following the fourth process step (iv), the amine and the acid are separated from the reaction solution, in particular recovered.

[0149] Ca 2+ (aq) + CH3COO- (aq) + HCO 3-(aq) + [HNR3] + (aq) R3N (aq) + CH3COOH (aq) + CaCO 3(s)

[0150] 0)

[0151] The subject matter of the present invention is explained in more detail below with reference to the figures, using preferred embodiments in a non-limiting manner.

[0152] It shows

[0153] Fig. 1 is a schematic representation of an embodiment of the method according to the invention and

[0154] Fig. 2 shows a further schematic representation of an embodiment of the process according to the invention. The preferred embodiment of the process according to the invention shown in Fig. 1 has two cycle processes, namely an amine cycle 1 and an acid cycle 2, in particular an acetic acid cycle. By using the amine and the acid in cycle processes, the process according to the invention can be carried out sustainably, in particular in a resource-saving and energy-efficient manner, as well as cost-effectively.

[0155] In the amine circuit 1, a tertiary amine, in particular triethanolamine, in aqueous solution 3 is mixed with preferably gaseous CO24. Due to the presence of the amine, the aqueous amine-containing solution 3 is basic and can absorb large amounts of carbon dioxide 4. The amine-containing aqueous solution 3 preferably has a pH in the range from 8 to 10, preferably 8 to 9. The amine can be added to the amine-containing solution 3 in amounts of up to 70 vol.%, in particular 65 vol.%, preferably 60 vol.%, more preferably 55 vol.%, based on the amount of amine and water. The aqueous amine solution 3 is mixed with the gaseous CO2 4 by absorption 5, in particular in a reactor. The aqueous amine solution 3 is preferably mixed with the preferably gaseous carbon dioxide at an excess pressure.By the absorption 5 of the gaseous carbon dioxide 4 by the first basic aqueous amine-containing solution 3, a basic carbonate-containing solution 6 is obtained.

[0156] In the acid circuit 2, in particular the acetic acid circuit, a second acidic aqueous solution 7 containing at least one acid is preferably mixed with mineral residues 8, in particular calcium-containing residues such as LD slag. The mineral solid 8 is typically comminuted, in particular ground, in this case. The acid is preferably selected from the group consisting of mineral acids, carboxylic acids, sulfonic acids, phosphonic acids, and mixtures thereof. Particularly good results are obtained when the acid is selected from the group consisting of acetic acid, propanoic acid, butanoic acid, and mixtures thereof. Within the scope of the present invention, it is particularly preferred if the acid is acetic acid.The aqueous solution 7, which contains at least one acid, typically contains the acid in amounts of 0.1 to 5 mol / l, in particular 0.2 to 4 mol / l, preferably 0.5 to 3 mol / l, more preferably 0.2 to 7 mol / l, more preferably 0.5 to 6 mol / l, more preferably 1 to 5 mol / l, based on the second aqueous solution 7. Furthermore, it has proven useful within the scope of the present invention to use an amount of acid in the range of 10 to 80 mol, in particular 20 to 70 mol, more particularly 30 to 60 mol, preferably 30 to 50 mol, per kilogram of mineral residue. The mineral residue 8 is preferably a complex mixture of a wide variety of substances, in particular also salts or oxides of metals. The mineral residue 8 is preferably a calcium-containing residue.By adding the mineral, in particular calcium-containing, residue 8 to the aqueous acidic solution 7, an extraction 9 takes place, in which metal ions, in particular calcium ions, are dissolved from the mineral solid 8.

[0157] The extraction typically takes place over a period of 10 minutes to 2 hours, preferably 15 minutes to 1.5 hours, preferably 0.5 minutes to 1 hour. Furthermore, the extraction preferably takes place at ambient temperature, in particular in the temperature range of 15 to 40°C, preferably 20 to 30°C. The process according to the invention proceeds solely through the driving force of the underlying chemical reactions. An external supply of energy is not necessary—at least up to this point in the process.

[0158] After completion of the extraction 9, ie the time in which the second acidic solution 7 acts on the mineral residue 8, preferably undissolved solid 10 is separated from the solution, in particular by means of filtration.

[0159] The undissolved solid 10 is, particularly when using construction rubble, sand or other aggregates, which in turn can be used to produce building materials.

[0160] The extraction 9 produces a solution 11 containing metal ions. The metal ion-containing solution 11 preferably contains calcium ions and other metal ions. The carbonate-containing basic solution 6 and the metal ion-containing solution 11 are then mixed to form a reaction solution and a precipitation 12 takes place, in which basic metal salts, such as metal hydroxides, metal oxides or metal oxide hydroxides or carbonates, are precipitated. The precipitated basic metal salts are preferably carbonates, preferably calcium carbonate 13. As explained above, it is preferred within the scope of the present invention if the metals whose ions are precipitated comprise calcium. The metals are preferably metals selected from the group consisting of lithium, barium, strontium, calcium, magnesium, iron, zinc, and manganese.The metals are preferably selected from the group consisting of lithium, calcium, iron, manganese, and mixtures thereof. The metals or metal ions are preferably separated in the form of their carbonates, since carbonates in particular usually have a fixed stoichiometry.

[0161] The mixing of the basic carbonate-containing solution 6 and the metal ion-containing solution 11 can also be carried out stepwise or successively to achieve fractional precipitation of the various metal ions. For example, the procedure can be such that successively smaller amounts of the metal ion-containing solution 11 are added to the basic carbonate-containing solution 6, whereby the metal carbonates and, if appropriate, other basic, sparingly soluble salts successively precipitate according to their solubility product. The individual metal salts are then removed from the reaction solution, so that metal salts of high purity can be obtained. A reverse procedure, in which the carbonate-containing solution 6 is successively added to the metal ion-containing solution 11, is also possible.

[0162] After the precipitation 12 is complete, the basic metal salts formed, in particular the calcium carbonate 13 formed, are removed from the process, in particular by filtration from the reaction solution. In the case of fractional precipitation of several different metal ions, the individual fractions are preferably removed from the process separately, in particular from the reaction solution.

[0163] The remaining reaction solution is then fed to recycling 14. In particular, the amine and the acid are recovered or processed. The amine and the acid can be separated, recovered, or processed, particularly by electrodialysis or distillation.

[0164] If a distillative separation is intended, excess water is preferably first removed by distillation, followed by the acid, preferably acetic acid, being separated by distillation, in particular to obtain an aqueous solution of the acid, which in turn is used to prepare the second acidic solution 7, which contains at least one acid. Typically, the amine remains, which is preferably separated from low-volatility residues by distillation and, optionally after further purification, is used to prepare the first basic amine solution 3.

[0165] Fig. 2 shows another preferred embodiment of the present invention. In this embodiment, the precipitation 12 of the metal salts is not part of the acid cycle 2.

[0166] Rather, the acid is removed from the second solution containing metal ions and at least one acid following extraction 9. Preferably, the second solution containing metal ions and at least one acid obtained after extraction 9 is fed to a recycling 15, whereby an acid-containing solution 7 is separated and the acid can be recovered or processed. The remaining metal ion-containing solution 11 is then fed to the precipitation 12. If the acid is separated following extraction 9, the acid is typically separated by electrodialysis.

[0167] Apart from this difference in the separation, recovery, or processing of the acid, the previously described advantages, special features, and characteristics apply accordingly to the embodiment. In particular, the amine is separated in a recycling process 14 following precipitation 12 and used to produce the basic solution 3.

[0168] The subject matter of the present invention is illustrated below in a non-limiting manner by the exemplary embodiments.

[0169] Examples of implementation

[0170] The method according to the invention is explained below using the individual process steps:

[0171] Step 1 : Loading of triethanolamine (TEA) in the autoclave

[0172] The loading of the tertiary amine in an aqueous solution is carried out in a high-pressure stirred tank with a free volume of approximately 550 ml. To prepare the aqueous amine-containing solution, triethanolamine and water are mixed in a proportion of 50 vol% each. The process temperature is T = 25°C, as the solubility of carbon dioxide decreases with increasing temperature. The process pressure was maintained at 5 bar. The solution was stirred throughout the entire test period.

[0173] Step 2: Extraction of calcium from LD slag using acetic acid

[0174] During the extraction process step, the various cations in the slag are extracted using acetic acid. In an initial series of experiments, an LD slag with a calcium content of 0.3 g per 1 g of slag is used. Acetic acid serves as the extraction agent. To analyze the influence of acetic acid concentration on extraction efficiency, various concentrations between 0.5 mol / l and 1.75 mol / l are prepared in aqueous solution. The solid / liquid ratio is 120 g / l in each case. The suspension of extraction agent and solid is rotated in an overhead shaker for 1 h. In a subsequent step, the extract is mechanically separated.

[0175] The studies show that the extraction efficiency is 30% at a concentration of 0.5 mol / l and increases with increasing concentration to approximately 70% at 1.5 mol / l. Concentrations of 1.75 mol / l and higher led to increased Si gel formation, making mechanical separation of the extract impossible. The optimum for the slag used is a solid / liquid ratio of 120 g / L, thus an acetic acid concentration of 1.5 mol / l. Step 3: Precipitation of calcium carbonate with loaded triethanolamine.

[0176] In the following example, the prepared calcium acetic acid extract is brought into contact with the CO2-laden amine solution using a stir plate. In this way, the CO2 is bound during precipitation primarily in the form of calcium carbonate (CaCO3). In a subsequent process step, the solid is mechanically separated, dried, and comminuted.

[0177] A qualitative visual assessment of the samples indicates that the purity of the CaCO3 increases with increasing loading time of the amine-containing solution with carbon dioxide. This assumption was confirmed by X-ray fluorescence analysis (XRF) of the various powders (see Table 1), where the values ​​are given in mass percent. By increasing the loading time from 15 minutes to 60 minutes, for example, the purity of the calcium can be increased from 93% to 96%. At the same time, the mass fraction of other cations decreases with increasing loading time. Due to this fact, iron cations can be specifically separated, for example, in a first precipitation step.

[0178] Table 1 : Purity of the precipitated calcium carbonate depending on the loading time of the amine solution with carbon dioxide

[0179] By further analysis with the X-ray diffractometer and scanning electron microscope, the modification of CaCO can be determined as vaterite.

[0180] Step 4: Preparation of the amine and acid The preparation of the amine and acid is carried out by distillation.

[0181] List of reference symbols:

[0182] 1 Amine cycle 9 Extraction

[0183] 2 Acid cycle 10 Undissolved solid 3 Aqueous amine solution 11 Metal ion-containing solution

[0184] 4 Carbon dioxide 12 Precipitation

[0185] 5 Absorption 15 13 Calcium carbonate

[0186] 6 Carbonate-containing solution 14 Recycling

[0187] 7 Acidic solution 15 Recycling 8 Mineral residue

Claims

Patent claims:

1. A process for the separation of carbon dioxide in the form of basic salts, in particular carbonates, preferably calcium carbonate, characterized in that a first basic aqueous solution containing at least one tertiary amine is admixed with carbon dioxide, a second acidic aqueous solution containing at least one acid is admixed with metal ions, preferably calcium ions, the first basic aqueous solution and the second aqueous solution are then mixed to obtain a reaction solution from which basic metal salts, in particular carbonates, preferably calcium carbonate, are precipitated, and the amine and / or the acid are separated from the reaction solution.

2. Process according to claim 1, characterized in that the amine is a tertiary amine selected from the group of tertiary aliphatic amines having Ci to Ce radicals, tertiary aromatic amines, polyamines and mixtures thereof, in particular tertiary aliphatic amines having Ci to Ce radicals.

3. Process according to claim 1 or 2, characterized in that the first basic aqueous solution containing at least one amine and optionally carbon dioxide has a pH greater than 8, preferably a pH in the range from 8 to 10, preferably in the range from 8 to 9.

4. Process according to one of the preceding claims, characterized in that the acid is selected from the group of organic acids, inorganic acids, ammonium compounds and mixtures thereof.

5. The method according to claim 4, characterized in that the acid is selected from mineral acids, in particular hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, phosphonic acid, carboxylic acids, sulfonic acids, organic phosphonic acids and mixtures thereof, preferably hydrochloric acid, sulfuric acid, nitric acid, carboxylic acids, sulfonic acids and mixtures thereof, preferably nitric acid, carboxylic acids, sulfonic acids and mixtures thereof, particularly preferably carboxylic acids.

6. Process according to claim 4 or 5, characterized in that the acid is selected from the group of acetic acid, propanoic acid, butanoic acid and mixtures thereof, preferably acetic acid.

7. The method according to any one of the preceding claims, characterized in that the second solution comprises the acid in amounts of up to 8 mol / l, in particular up to 7 mol / l, preferably up to 5 mol / l, more preferably up to 5 mol / l, based on the second solution, and / or that the second solution comprises the acid in amounts of 0.1 to 8 mol / l, in particular 0.2 to 7 mol / l, preferably 0.5 to 6 mol / l, more preferably 1 to 5 mol / l, based on the second solution.

8. Process according to one of the preceding claims, characterized in that the second acidic solution is treated with metal ions, preferably calcium ions, by extraction.

9. The method according to claim 8, characterized in that the second acidic solution is admixed with the metal ions, preferably calcium ions, by extraction of an inorganic residue, in particular a mineral or metallic residue, preferably a mineral residue.

10. The method according to claim 9, characterized in that the inorganic residue, in particular mineral residue, is selected from the group of construction rubble, slag and mixtures thereof. 11 . Method according to one of the preceding claims, characterized in that the metal ions are ions of metals selected from the group of monovalent metals, divalent metals, trivalent metals and mixtures thereof, in particular monovalent metals, divalent metals and mixtures thereof.

12. The method according to claim 11, characterized in that the metal ions are ions of metals selected from the group of alkali metals, alkaline earth metals, metals of the iron group, manganese, zinc and mixtures thereof, in particular lithium, magnesium, calcium, strontium, barium, iron, manganese, Zinc and mixtures thereof, preferably lithium, calcium, iron, manganese and mixtures thereof, preferably calcium.

13. The method according to claim 11 or 12, characterized in that the metal ions are precipitated from the reaction solution during mixing of the first basic solution and the second aqueous solution, in particular in the form of their oxides, hydroxides, carbonates and mixtures thereof, preferably in the form of their carbonates.

14. The method according to claim 13, characterized in that the metal ions contained in the second aqueous solution are fractionally precipitated.

15. A process according to any one of the preceding claims, characterized in that following the precipitation of the metal ions, the amine and / or the acid are recovered or processed.

16. Process according to one of the preceding claims, characterized in that the acid, in particular after removal of excess water, is separated from the reaction solution by distillation, in particular recovered, preferably in the form of an aqueous solution.

17. Process according to one of the preceding claims, characterized in that the amine is recovered by separating all other components.

18. Method according to one of the preceding claims, characterized in that (i) in a first process step, a first basic aqueous solution containing at least one amine is admixed with carbon dioxide, (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with metal ions, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with, in particular mixing it with, at least one mineral, in particular calcium-containing, residue, (iii) in a subsequent third process step, the first basic aqueous solution containing at least one amine and carbon dioxide and the second aqueous solution containing at least one acid and metal ions, preferably calcium ions, are mixed so that a reaction solution is obtained and basic salts, in particular carbonates, preferably calcium carbonate, are precipitated from the reaction solution, (iv) in a fourth process step following the third process step (iii), the basic metal salts, in particular carbonates, preferably calcium carbonate, are separated from the reaction solution, (v) in a fifth process step following the fourth process step (iv), the amine and the acid are separated from the reaction solution, in particular recovered.

19. Method according to one of claims 1 to 15, characterized in that (i) in a first process step, a first basic aqueous solution containing at least one amine is admixed with carbon dioxide, (ii) in a second process step, a second acidic aqueous solution containing at least one acid is mixed with metal ions, in particular calcium ions, preferably by bringing the second acidic aqueous solution containing at least one acid into contact with, in particular mixing with, at least one mineral, in particular calcium-containing, residue, so that a second solution containing metal ions, in particular calcium ions, is obtained, wherein the acid is subsequently separated, in particular recovered, (iii) in a subsequent third process step, the first basic aqueous solution containing at least one amine and carbon dioxide and the second aqueous solution containing at least metal ions, preferably calcium ions, are mixed so that a reaction solution is obtained and basic salts, in particular carbonates, preferably calcium carbonate, are precipitated from the reaction solution, (iv) in a fourth process step following the third process step (iii), the basic metal salts, in particular carbonates, preferably calcium carbonate, are separated from the reaction solution, (v) in a fifth process step following the fourth process step (iv), the amine is separated from the reaction solution, in particular is recovered.

Images