A process and plant for separating a target acid from a crude composition containing the target acid and at least one other acid

Abstract

The present invention relates to a process for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound, wherein the process comprises the steps of: a) subjecting the crude composition to a first liquid-liquid extraction with a first extracting agent in an extraction column so as to obtain a raffinate composition being enriched in the at least one non-acid compound and an extract composition containing the first extracting agent, the target acid and the at least one other acid, and b) subjecting the extract composition obtained in step a) to a second liquid-liquid extraction with a washing solution as second extracting agent in an extraction column so as to obtain an extract composition being enriched in the at least one other acid and a raffinate composition containing the first extracting agent and the target acid, wherein the washing solution is a mixture containing the target acid and water.

Description

[0001] Sulzer Management AG S13776PEP

[0002] A process and plant for separating a target acid from a crude composition containing the target acid and at least one other acid

[0003] The present invention relates to a process and to a plant for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound.

[0004] For ecological reasons and in order to reduce the consumption of fossil resources, the chemical industry is eager to replace petrochemical processes with biological processes using bacteria, such as fermentation processes, or reactions or syntheses, respectively, using renewable raw materials. Prominent examples for respective biological processes are the production of acids, in particular organic acids, such as acrylic acid, lactic acid and many others, by fermentation. However, the known fermentation processes for producing acids, likewise to syntheses from renewable raw materials, often produces minor, but significant amounts of byproducts in the form of other acids than the target acid. Often, these minority acids have similar or even nearly identical chemical properties to the target acid, which makes it challenging to separate the minority acids effectively from the target acid. However, such a removal of the minority acids from the target acid is essential in order to achieve a sufficiently high quality and purity of the final product.

[0005] A common technique used to separate a mixture of several organic acids is distillation, which allows to separate volatile organic compounds based on their different boiling points. During the distillation, the mixture to be separated is heated, which causes that compounds with lower boiling points vaporize and rise to the top of the distillation column, where they are withdrawn as overhead stream, condensed and are then further processed according to the need. In contrast thereto, compounds with higher boiling points do not vaporize, but remain as liquid andflow down the distillation column to the bottom of the distillation column, where they are removed as bottom stream and are then further processed according to the need. However, distillation is not applicable to separate different acids having a similar boiling point. A prominent example of a mixture containing different acids having a very close boiling point is a mixture obtained by fermentation and containing acrylic acid having a boiling point of 141 ,0°C and propionic acid having a boiling point of 141.17°C.

[0006] Other possible separation techniques than distillation are extraction and ion exchange chromatography. However, both techniques are connected with high operational costs if used to separate acid mixtures, because the known extraction processes require large amounts of extractive agent require the separation of large amounts of extracting agent from the product after the extraction and / or requiring the use of expensive extracting agents, whereas ion exchange chromatography methods are expensive, because they necessitate regular maintenance and regeneration of the ion exchange resin.

[0007] In view of this, the object underlying the present invention is to provide a process and a plant for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound, in particular at least one other acid having very similar physical properties, such as boiling point, to the physical properties of the target acid, wherein the process efficiently separates the target acid from the mixture containing the target acid and at least one further acid, wherein the process is characterized by low operational costs and the plant required for performing the process is characterized by low capital expenditures.

[0008] In accordance with the present invention, this object is satisfied by providing a process for separating a target acid from a crude composition containing the targetacid, at least one other acid and at least one non-acid compound, wherein the process comprises the steps of:

[0009] a) subjecting the crude composition to a first liquid-liquid extraction with a first extracting agent in an extraction column so as to obtain a raffinate composition being enriched in the at least one non-acid compound and an extract composition containing the first extracting agent, the target acid and the at least one other acid, and

[0010] b) subjecting the extract composition obtained in step a) to a second liquidliquid extraction with a washing solution as second extracting agent in an extraction column so as to obtain an extract composition being enriched in the at least one other acid and a raffinate composition containing the first extracting agent and the target acid, wherein the washing solution is a mixture containing the target acid and water.

[0011] By performing the separation of the target acid, such as acrylic acid, from a crude composition containing the target acid, at least one other acid, such as propionic acid, and at least one non-acid compound, such as water, in two subsequent liquid-liquid extraction steps, wherein the second liquid-liquid extraction step is performed with a mixture containing the target acid and water as second extracting agent or as washing solution, respectively, in the first step all acids being contained in the crude, such as acrylic acid and propionic acid, are separated together with the first extracting agent as extract composition from the at least one non-acid compound, such as water, which remains as raffinate composition, whereas in the second liquid-liquid extraction step the one or more other acids are extracted by the washing solution from the extract composition obtained in the first liquid-liquid extraction step, so that in the second liquid-liquid extraction step a raffinate composition containing the target acid and the first extracting agent, but no or, if at all, very low amounts of the other acid(s) is obtained. The target acid may then be easily separated from the first extracting agent used in the first liquid-liquid extraction step, so that very pure target acid is obtained, which has a purity degree beingsufficient to be used for challenging products, such as in pharmaceuticals or specialty chemicals. In turn, the first extracting agent may be recycled to the first liquid-liquid extraction step. Because the second extracting agent or washing solution, respectively, used in the second liquid-liquid extraction step is a mixture of water and the target acid, the latter of which may be removed as portion from the pure target acid, the process is characterized by low operational costs and low capital expenditures, since no expensive extracting agent needs to be used for the second liquid-liquid extraction step, but only a portion of the target acid being produced during the process. Thus, both, the first extracting agent used in the first liquid-liquid extraction step as well as the washing solution used as second extracting agent in the second liquid-liquid extraction step may be easily recycled so that the process in accordance with the present invention allows to reduce the amount of waste and thus to minimize the environmental impact of the process. All in all, the process in accordance with the present invention efficiently separates a target acid from a mixture containing the target acid and one or more further acids, in particular other acids having very similar physical properties, such as boiling point, to the physical properties of the target acid, wherein the process is characterized by low operational costs and the plant required for performing the process is characterized by low capital expenditures.

[0012] As indicated above, the process of the present invention allows to recycle process streams so as to minimize the amount of waste and thus the environmental impact of the process. Therefore, it is particularly preferred that the raffinate composition obtained in step b) is subjected in a separation step c) to a separation method so as to separate the raffinate composition into the first extracting agent and into a crude target acid composition. While the first extracting agent is recycled to step a), either i) a portion of the crude target acid composition obtained in the separation step c) is mixed with water to obtain the washing solution, which is used in step b), or ii) the crude target acid composition obtained in the separation step c) is purified in a purification step d) so as to obtain pure target acid, wherein a por-tion of the pure target acid is mixed with water to obtain the washing solution, which is used in step b). Thereby not only the first extracting agent, but also the washing solution or second extracting agent, respectively, is led in a circle so that no or, if at all, minimal amounts of first extracting agent have to be added to compensate possible losses.

[0013] The present invention is not particularly limited concerning the ingredients and amount of ingredients of the crude composition as long as the crude composition contains the target acid, the at least one other acid and the at least one non-acid compound. Preferably, the concentration of the target acid in the crude composition is higher than the concentration of the at least one other acid and of the at least one non-acid compound. The present invention is in particular suitable to process an aqueous crude composition, which contains the target acid, the at least one other acid and water. Such a crude composition is typically the result of a fermentation process or of a chemical synthesis. More preferably, the crude composition contains, based on 100% by weight of the crude composition, 30 to 80% by weight of the target acid and less than 10% by weight of all of the at least one other acid, with the remainder to 100% by weight being the at least one non-acid compound, such as in particular water, optionally together with one or more impurities.

[0014] Also concerning the chemical nature of the target acid, the present invention is not particularly restricted. Good results are in particular obtained, when the target acid is an acid containing at least two acidic groups or containing at least one acidic group plus at least one polar component. Suitable example of the at least one polar component are those being selected from the group consisting of cyclic rings, C=C double bonds, amino groups, halogens nitro group, hydroxyl groups and arbitrary combinations of two or more thereof. Suitable examples for cyclic rings are aromatic cycles, polyaromatic cycles, oxygen-containing cycles, sulfur-containing cycles and nitrogen-containing cycles, whereas suitable examples forhalogens are fluorine, chlorine, bromine and iodine. In turn, suitable examples for acidic group are those being selected from the group consisting of carboxylic groups, sulphonic groups, phosphoric groups and arbitrary combinations of two or more thereof. Particular good results are in obtained, when the target acid is selected from the group consisting of acrylic acid, methacrylic acid, succinic acid, lactic acid, maleic acid, furoic acid, terephthalic acid and furan dicarboxylic acid.

[0015] Preferably, the other acid is an acid having a similar boiling temperature as the target acid, wherein the other acid preferably contains one or more different polar components as the target acid or no polar component at all. Suitable examples for the at least one other acid are acetic acid, propionic acid and butyric acid.

[0016] Preferred combinations of target acid and other acid, as they are typically contained in a fermentation process or other synthesis are i) acrylic acid and propionic acid, ii) methacrylic acid and propionic acid, iii) succinic acid and acetic acid and / or butyric acid, iv) lactic acid and acetic acid as well as v) acrylic acid and acetic acid.

[0017] Further preferred are combinations of target acid and other acid, which are typically contained in an effluent of chemical process. For instance, these acids can be the products of a specific chemical reaction in such a chemical process. In such chemical process, one acid can be the feedstock and the other acid may be the product of the reaction. Alternatively, one acid is the target product of the reaction and the other acid is the by-production of the reaction.

[0018] The first extracting agent, which has the task to separate substantially all acids contained in the crude composition by liquid-liquid extraction from the at least one non-acid compound, may be virtually any solvent, such as water, an ionic liquid or an organic solvent. The first extracting agent may be one solvent or a mixture of two or more solvents. Examples for an ionic liquid are imidazolium-based compounds, quaternary ammonium based ionic liquid and arbitrary combinations oftwo or more of the aforementioned ionic liquids. Good results are in particular obtained, when the first extracting agent is an organic solvent, such as one being selected from the group consisting of C6-C9-aromatic compounds, alcohols, ketones, ethers, cyclic carbonates and arbitrary combinations of two or more of the aforementioned solvents. Particular suitable examples for specific organic solvents are those being selected from the group consisting of acetone, tetrahydrofuran, methanol, benzene, toluene, xylol, methyl-tert-butylether, methyl isobutyl ketone and arbitrary combinations of two or more of the aforementioned solvents.

[0019] In a further development of the idea of the present invention, it is suggested that the first liquid-liquid extraction step a) is performed with a volume ratio of the first extracting agent to the crude composition of 3:1 to 1 :10 and preferably of 1 :2 to 1:5.

[0020] Moreover, it is preferred that the first liquid-liquid extraction step a) is performed at a temperature of at most 50°C and more preferably at ambient temperature. This minimizes potential thermal stress to the involved compounds.

[0021] The first liquid-liquid extraction step a) separates acid compounds from non-acid compounds. More specifically, the first liquid-liquid extraction step a) separates the crude composition into a raffinate composition and into an extract composition, wherein the extract composition contains the first extracting agent and all acid compounds, whereas the raffinate composition is enriched in the non-acid compounds. Preferably, the raffinate composition obtained in step a) contains less than 3.0% by weight and preferably less than 1.0% by weight of the target acid.

[0022] In accordance with the present invention, the second extracting agent or washing solution, respectively, is a mixture of the target acid and water. The optimal concentration of the target acid in the washing solution depends on the concentration of the target acid in the crude composition. Good results are in particular obtained,when the washing solution contains the target acid in a concentration of 80 to 120%, more preferably of 90 to 110%, yet more preferably of 95 to 105% and most preferably of about 100% of the concentration of the target acid in the crude composition. For example, if the crude composition contains 60% by weight of the target acid, the washing solution preferably has a concentration of the target acid of 48 to 72% by weight, more preferably of 54 to 66%, yet more preferably of 57 to 63% and most preferably of about 60%.

[0023] In accordance with a further preferred embodiment of the present invention, the washing solution consists or at least essentially consists of the target acid and water. Therefore, it is preferred that the sum of the concentrations of the target acid and water in the washing solution is at least 90% by weight, preferably at least 95% by weight, more preferably at least 99% by weight and most preferably about 100% by weight.

[0024] A good separation efficiency in the second liquid-liquid extraction step is in particular obtained, when the second liquid-liquid extraction step b) is performed with a volume ratio of washing solution to extract composition of 1 :10 to 1 :100 and more preferably of 1 :20 to 1 :50.

[0025] Moreover, it is preferred that the second liquid-liquid extraction step a) is performed at a temperature of at most 50°C and more preferably at ambient temperature. This minimizes potential thermal stress to the involved compounds.

[0026] The present invention is not particularly limited concerning the device, in which the first liquid-liquid extraction step a) and the second liquid-liquid extraction step b) are performed. Good results are in particular obtained, when the first liquid-liquid extraction step a) is performed in an agitated extraction column and / or in a mixer settler and when the second liquid-liquid extraction step b) is performed in an agitated extraction column and / or in a mixer settler.In accordance with a first particularly preferred embodiment of the present invention, each of the first liquid-liquid extraction step a) and of the second liquid-liquid extraction step b) is performed in a separate agitated extraction column and preferably in an agitated counter-current extraction column. Performing the liquidliquid extraction steps in an agitated extraction column and in particular in an agitated counter-current extraction column leads to an increased efficiency of the respective liquid-liquid extraction, thus allowing to minimize the amount of extracting agent being necessary for the respective liquid-liquid extraction step.

[0027] Alternatively, each of the liquid-liquid extraction in step a) and of the liquid-liquid extraction in step b) may be performed in a separate agitated co-current extraction column.

[0028] Agitated extraction column means that the mixture to be extracted and the extracting agent are mixed in the extraction column by an agitator. Good results are for example obtained, when the agitated extraction column comprises one or more rotating shafts, each of which comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators. For instance, the agitated extraction column comprises two or more compartments, which are separated from each other by static partition plates, wherein at least some and preferably all of the compartments comprise a rotating shaft comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators.

[0029] In accordance with another preferred embodiment of the present invention, the liquid-liquid extraction in step a) and the liquid-liquid extraction in step b) are performed in the same agitated extraction column. For instance, the extraction col-umn is separated in its middle into an upper part and into a lower part, whereas the upper and lower parts act independently from each other, i.e. each of which comprises a separate inlet for an extracting agent, an inlet for composition to be extracted, an outlet for raffinate composition and an outlet for extract composition.

[0030] In accordance with another preferred embodiment of the present invention, each of the first liquid-liquid extraction step a) and of the second liquid-liquid extraction step b) is performed in a separate mixer settler and preferably in a counter-current mixer settler.

[0031] Alternatively, each of the liquid-liquid extraction in step a) and of the liquid-liquid extraction in step b) may be performed in a separate co-current mixer settler.

[0032] The extract composition obtained in the second liquid-liquid extraction step is preferably recycled into the first liquid-liquid extraction step.

[0033] In a further development of the idea of the present invention, it is proposed that the raffinate composition obtained in step b), which contains the first extracting agent and the target acid, is separated in a separation step c) into its components, i.e. into the first extracting agent and into the target acid. More preferably, the raffinate composition obtained in step b) is subjected in the separation step c) to a distillation step so as to separate the raffinate composition into the first extracting agent and into a crude target acid composition. It is preferred that the first extracting agent is then recycled into step a).

[0034] Preferably, the first extracting agent obtained in the separation step c) contains less than 0.5% by weight and more preferably less than 0.02% by weight of the target acid. Thereby extracting agent is obtained, which is pure enough to be recycled as first extracting agent into step a).Furthermore, it is preferred that the crude target acid composition obtained in the separation step c) has a concentration of the target acid of 80 to 98% by weight and more preferably of 98.0% by weight or more.

[0035] In accordance with a particularly preferred embodiment of the present invention, a portion of the crude target acid composition obtained in the separation step c) is mixed with water so as to obtain the washing solution, which is used in the second liquid-liquid extraction step b), whereas the remaining portion of the crude target acid composition is withdrawn from the process as product.

[0036] In accordance with an alternative, particularly preferred embodiment of the present invention, the crude target acid composition obtained in the separation step c) is purified in a purification step d) so as to obtain pure target acid, wherein a portion of the pure target acid is mixed with water so as to obtain the washing solution, which is used in the second liquid-liquid extraction step b), whereas the remaining portion of the pure target acid composition is withdrawn from the process as product.

[0037] Preferably, the purification step d) comprises at least one step of a purification method being selected from the group consisting of crystallization, distillation, membrane-based methods, chromatography and arbitrary combinations of two or more of the aforementioned purification methods.

[0038] Good results are in particular obtained, when the crude target acid composition obtained in the separation step c) is purified in the purification step d) in one or more crystallization steps, such as in one to five subsequent crystallization stages. Each of the crystallization steps may be a suspension crystallization step, a static crystallization step or a falling film crystallization step.Preferably, the pure target acid obtained in the purification step d) contains at least 98% by weight, more preferably at least 99% by weight, still more preferably at least 99.5% by weight and most preferably at least 99.9% by weight of the target acid.

[0039] The process of the present invention is not only suitable for separating the target acid contained in the crude composition from one other acid, but in particular also for separating the target acid contained in the crude composition from two or more other acids. In this case, steps a) and b) may be repeated for each of the other acids exceeding two, so as to separate the crude composition comprising two or more different other acids into a separate fraction for each of the two or more different other acids.

[0040] In accordance with a further aspect, the present invention relates to a plant for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound, wherein the plant comprises:

[0041] a) a first liquid-liquid extraction unit comprising an inlet line for crude composition, an inlet line for the first extracting agent, an outlet line for a raffinate composition and an outlet line for an extract composition,

[0042] b) a second liquid-liquid extraction unit comprising an inlet line being connected with the outlet line for an extract composition of the first liquid-liquid extraction unit, an inlet line for washing solution, an outlet line for a raffinate composition and an outlet line for an extract composition,

[0043] c) optionally an extracting agent recovery unit comprising an inlet line being connected with the outlet line for raffinate composition of the second liquidliquid extraction unit, an outlet line for the first extracting agent being connected with the inlet line for the first extracting agent of the first liquid-liquid extraction unit and an outlet line for target acid, wherein the outlet line fortarget acid is directly or indirectly via a purification unit connected with the inlet line for washing solution of the second liquid-liquid extraction unit.

[0044] Good results are in particular achieved, when each of the first liquid-liquid extraction unit and of the second liquid-liquid extraction unit is an agitated extraction column or a mixer settler and more preferably a counter-current mixer settler or an agitated counter-current extraction column.

[0045] Preferably, the extracting agent recovery unit comprises a distillation column and more preferably consists of a distillation column.

[0046] Furthermore, it is preferred that the outlet line for extract composition obtained in the second liquid-liquid extraction step is connected with an inlet line of the first liquid-liquid extraction unit.

[0047] In a further development of the idea of the present invention, it is proposed that the outlet line for target acid is split into a product removal line and into a recycle line, wherein the recycle line is connected with the inlet line for washing solution of the second liquid-liquid extraction unit. Preferably, a water inlet line leads into the recycle line, before the combined line is combined with the inlet line for washing solution of the second liquid-liquid extraction unit.

[0048] In accordance with an alternative, particularly preferred embodiment of the present invention, the outlet line for target acid is connected with the inlet line of a purification unit, which further comprises an outlet line for pure target acid, wherein the outlet line for pure target acid is split into a product removal line and into a recycle line, wherein the recycle line is connected with the inlet line for washing solution of the second liquid-liquid extraction unit. Also in this embodiment, it is preferred that a water inlet line leads into the recycle line, before the combined line is combined with the inlet line for washing solution of the second liquid-liquid extraction unit.Good results are in particular achieved, when the purification unit comprises at least one of a crystallizer, a distillation column, a membrane-based purification unit and a chromatography purification unit.

[0049] Subsequently, the present invention is described by means of an illustrative, but not limiting figure, wherein:

[0050] Fig. 1 is a schematic view of a plant for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound in accordance with one embodiment of the present invention.

[0051] The plant 10 shown in figure 1 comprises a first liquid-liquid extraction unit 12 being an agitated extraction column, a second liquid-liquid extraction unit 14 being an agitated extraction column, an extracting agent recovery unit 16 being a distillation column as well as a purification unit 18 being a crystallizer. More specifically, the first liquid-liquid extraction unit 12 comprises an inlet line 20 for crude composition, an inlet line 22 for the first extracting agent, an outlet line 24 for a raffinate composition and an outlet line 26 for an extract composition, whereas the second liquid-liquid extraction unit 14 comprises an inlet line being connected with the outlet line 26 for extract composition of the first liquid-liquid extraction unit 12, an inlet line 28 for washing solution, an outlet line 30 for a raffinate composition and an outlet line 32 for an extract composition. The outlet line 32 for extract composition of the second liquid-liquid extraction unit 14 is connected with a further inlet line of the first liquid-liquid extraction unit 12. In addition, the extracting agent recovery unit 16 comprises an inlet line being connected with the outlet line 30 for raffinate composition of the second liquid-liquid extraction unit 14, an outlet line for extracting agent being connected with the inlet line 22 for the first extracting agent of the first liquid-liquid extraction unit 12 and an outlet line 34 for target acid. Inturn, the outlet line 34 for target acid is connected with an inlet line of the purification unit 18, which further comprises an outlet line 36 for pure target acid, which is split into a removal line 38 for pure target acid and a recycle line 40, which combines with an inlet line 42 for water so as to result in the inlet line 28 for washing solution of the second liquid-liquid extraction unit 14.

[0052] During the operation of the plant 10, a crude composition containing the target acid, at least one other acid and at least one non-acid compound, such as acrylic acid as target acid, propionic acid as further acid and water as non-acid compound, is fed via inlet line 20 into the first liquid-liquid extraction unit 12 and is extracted therein with the first extracting agent being fed into the first liquid-liquid extraction unit 12 via the inlet line 22 into a raffinate composition mainly comprising water and traces of acrylic acid and propionic acid and into an extract composition mainly containing the first extracting agent, acrylic acid and propionic acid. While the raffinate composition is withdrawn from the first liquid-liquid extraction unit 12 via outlet line 24, the extract composition is withdrawn from the first liquidliquid extraction unit 12 via the outlet line 26 and is led into the second liquid-liquid extraction unit 14, in which it is extracted with the washing solution being fed into the second liquid-liquid extraction unit 14 via the inlet line 28 into a raffinate composition mainly comprising the first extracting agent and acrylic acid and into an extract composition mainly containing acrylic acid, water and propionic acid. While the extract composition is withdrawn from the second liquid-liquid extraction unit 14 via the outlet line 32 and led into the first liquid-liquid extraction unit 12, the raffinate composition is withdrawn from the second liquid-liquid extraction unit 14 via the outlet line 30 and is fed into the extracting agent recovery unit 16. The raffinate composition being withdrawn from the second liquid-liquid extraction unit 14 is distilled in the distillation column of the extracting agent recovery unit 16 and separated therein into the first extracting agent, which is withdrawn from the extracting agent recovery unit 16 and recycled into the first liquid-liquid extraction unit 12 via line 22, and into a (crude) target acid composition, which is withdrawnfrom the extracting agent recovery unit 16 and led via line 34 into the purification unit 18. The pure target acid being obtained in the purification unit 18 is withdrawn therefrom via the outlet line 36, from which a portion of the pure target acid is split off via the outlet line 38 and is removed from the plant 10, whereas the remaining portion of the pure target acid is led via line 40, mixed with water being led into this line via inlet line 42 and then recycled via the line 28 into the second liquid-liquid extraction unit 14.Reference numerals

[0053] 10 Plant

[0054] 12 First liquid-liquid extraction unit

[0055] 14 Second liquid-liquid extraction unit

[0056] 16 Extracting agent recovery unit

[0057] 18 Purification unit

[0058] 20 Inlet line for crude composition

[0059] 22 Inlet line for the first extracting agent

[0060] 24 Outlet line for a raffinate composition of the first liquid-liquid extraction unit

[0061] 26 Outlet line for an extract composition of the first liquid-liquid extraction unit

[0062] 28 Inlet line for washing solution

[0063] 30 Outlet line for a raffinate composition of the second liquid-liquid extraction unit

[0064] 32 Outlet line for an extract composition of the second liquid-liquid extraction unit

[0065] 34 Outlet line for target acid

[0066] 36 Outlet line for pure target acid

[0067] 38 Removal line for pure target acid

[0068] 40 Recycle line

[0069] 42 Inlet line for water

Claims

Claims:

1. A process for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound, wherein the process comprises the steps of:a) subjecting the crude composition to a first liquid-liquid extraction with a first extracting agent in an extraction column so as to obtain a raffinate composition being enriched in the at least one non-acid compound and an extract composition containing the first extracting agent, the target acid and the at least one other acid, andb) subjecting the extract composition obtained in step a) to a second liquid-liquid extraction with a washing solution as second extracting agent in an extraction column so as to obtain an extract composition being enriched in the at least one other acid and a raffinate composition containing the first extracting agent and the target acid, wherein the washing solution is a mixture containing the target acid and water.

2. The process in accordance with claim 1 , wherein the raffinate composition obtained in step b) is subjected in a separation step c) to a separation step so as to obtain the first extracting agent and a crude target acid composition, wherein the first extracting agent is recycled to step a), and wherein i) a portion of the crude target acid composition obtained in the separation step c) is mixed with water to obtain the washing solution, which is used in step b), or ii) the crude target acid composition obtained in the separation step c) is purified in a purification step d) so as to obtain pure target acid, wherein a portion of the pure target acid is mixed with water to obtain the washing solution, which is used in step b).

3. The process in accordance with claim 1 or 2, wherein the crude composition is an aqueous crude composition, which contains the target acid, the atleast one other acid and water, wherein preferably the crude composition contains, based on 100% by weight of the crude composition, 30 to 80% by weight of the target acid and less than 10% by weight of all of the at least one other acid.

4. The process in accordance with any of the preceding claims, wherein the target acid is an acid containing at least two acidic groups or containing at least one acidic group plus at least one polar component, wherein the at least one polar component is preferably selected from the group consisting of cyclic rings, C=C double bonds, amino groups, halogens nitro group, hydroxyl groups and arbitrary combinations of two or more thereof.

5. The process in accordance with claim 4, wherein the target acid is selected from the group consisting of acrylic acid, methacrylic acid, succinic acid, lactic acid, maleic acid, furoic acid, terephthalic acid and furan dicarboxylic acid.

6. The process in accordance with any of the preceding claims, wherein the first extracting agent is water, an ionic liquid or an organic solvent preferably an organic solvent being selected from the group consisting C6-C9-aromatic compounds, alcohols, ketones, ethers, cyclic carbonates and arbitrary combinations of two or more of the aforementioned solvents, and more preferably an organic solvent being selected from the group consisting of acetone, tetrahydrofuran, methanol, benzene, toluene, xylol, methyl-tert- butylether, methyl isobutyl ketone and arbitrary combinations of two or more of the aforementioned solvents.

7. The process in accordance with any of the preceding claims, wherein the washing solution contains the target acid in a concentration of 80 to 120%,preferably of 90 to 110% and more preferably of 95 to 105% of the concentration of the target acid in the crude composition.

8. The process in accordance with any of the preceding claims, wherein the first liquid-liquid extraction step a) and the second liquid-liquid extraction step b) are performed in the same agitated extraction column.

9. The process in accordance with any of claims, wherein the raffinate composition obtained in step b) is subjected in a separation step c) to a distillation step so as to separate the raffinate composition into the first extracting agent and into a crude target acid composition, wherein preferably the first extracting agent is recycled into step a), and wherein a portion of the crude target acid composition obtained in the separation step c) is mixed with water so as to obtain the washing solution, which is used in the second liquidliquid extraction step b), whereas the remaining portion of the crude target acid composition is withdrawn from the process as product.

10. The process in accordance with claim 2 or 9, wherein the crude target acid composition obtained in the separation step c) is purified in a purification step d) so as to obtain pure target acid, wherein a portion of the pure target acid is mixed with water so as to obtain the washing solution, which is used in the second liquid-liquid extraction step b), whereas the remaining portion of the pure target acid composition is withdrawn from the process as product, wherein the pure target acid obtained in the purification step d) contains at least 98% by weight, preferably at least 99% by weight, more preferably at least 99.5% by weight and most preferably at least 99.9% by weight of the target acid.

11. A plant for separating a target acid from a crude composition containing the target acid, at least one other acid and at least one non-acid compound, wherein the plant comprises:a) a first liquid-liquid extraction unit comprising an inlet line for crude composition, an inlet line for the first extracting agent, an outlet line for a raffinate composition and an outlet line for an extract composition, b) a second liquid-liquid extraction unit comprising an inlet line being connected with the outlet line for an extract composition of the first liquid-liquid extraction unit, an inlet line for washing solution, an outlet line for a raffinate composition and an outlet line for an extract composition,c) optionally an extracting agent recovery unit comprising an inlet line being connected with the outlet line for raffinate composition of the second liquid-liquid extraction unit, an outlet line for the first extracting agent being connected with the inlet line for the first extracting agent of the first liquid-liquid extraction unit and an outlet line for target acid, wherein the outlet line for target acid is directly or indirectly via a purification unit connected with the inlet line for washing solution of the second liquid-liquid extraction unit.

12. The plant in accordance with claim 11 , wherein each of the first liquid-liquid extraction unit and of the second liquid-liquid extraction unit is an agitated extraction column or a mixer settler and preferably a counter-current mixer settler or an agitated counter-current extraction column.

13. The plant in accordance with claim 11 or 12, wherein the outlet line for extract composition of the second liquid-liquid extraction unit is connected with an inlet line of the first liquid-liquid extraction unit.

14. The plant in accordance with any of claims 11 to 13, wherein the outlet line for target acid is split into a product removal line and into a recycle line, wherein the recycle line is connected with the inlet line for washing solution of the second liquid-liquid extraction unit.

15. The plant in accordance with any of claims 11 to 14, wherein the outlet line for target acid is connected with the inlet line of a purification unit, which further comprises an outlet line for pure target acid, wherein the outlet line for pure target acid is split into a product removal line and into a recycle line, wherein the recycle line is connected with the inlet line for washing solution of the second liquid-liquid extraction unit, wherein the purification unit comprises at least one of a crystallizer, a distillation column, a membrane-based purification unit and a chromatography purification unit.

Images