CN1425090A - Method for extracting or recovering carboxylic acid from waste liquid of pulp production - Google Patents

Abstract

A method of recovering and/or isolating carboxylic acids from pulp production effluents, which contain carboxylic acids, lignin, water and sometimes complex carbohydrates, furfural and soluble sugars. In this method, the waste liquid is extracted with an extractant selected from the following group of compounds: ethers, saturated and unsaturated hydrocarbons, alcohols, alkyl esters and aryl esters, alkyl and aryl amines, cyclic and/or unsaturated alkyl ketones and methyl isobutyl ketone, methyl butanone, methyl acetone, alkyl chain monocarboxylic Acids, alkyl and aryl amides, aromatic compounds, aldehydes.

Description

Method for extracting or recovering carboxylic acid from waste liquid of pulp production

The invention relates to a method for producing or recovering carboxylic acid from waste liquid of pulp production.

According to the prior art, there are various environmentally friendly processes for the manufacture of pulp from cellulose-containing raw materials, which use dissociative solutions containing carboxylic acids:

"Natural Pulp Manufacturing Process" and Milox-Methods described in WO 96/35013 [Series "Renewable Raw Materials" Volume 8, "Environmentally Friendly Wood Dissociation Processes", Agricultural Press, LLC, Münster (1997)], the cleavage was performed using peroxyformic acid, which was produced from aqueous formic acid and hydrogen peroxide.

• In the Formacell-method, the dissociation is performed using acetic acid to which 5% to 10% formic acid is added; in the Acetosolv-method, the dissociation is performed using acetic acid with a small hydrochloric acid component.

• The applicant describes in DE 100 57 878.0 a new process for the production of pulp using lignocellulose-containing raw materials, in which carboxylic acids are added. According to this method, the starting material is dissociated in an at least binary solvent mixture. This solvent mixture comprises at least one first solvent A and one second solvent B. Solvent A is selected from the group of aliphatic organic monofunctional or polyfunctional carboxylic acids, hydroxycarboxylic acids or derivatives of carboxylic acids, especially carboxylic acid esters or carboxylic acid anhydrides. Solvent B is a bipolar, non-proton-donating solvent with a boiling point between 80°C and 250°C and a refractive index n _D ²⁰ in the range of 1.33 to 1.55, or a solvent selected from the following group Solvents: alkylene glycols, oligoalkylene glycols and polyalkylene glycols.

In this method, the following compounds are preferably used as solvent A: formic acid, acetic acid, propionic acid, butyric acid, tartaric acid, citric acid, oxalic acid, malonic acid and acetic anhydride; preferably the following compounds are used as solvent B Use: cyclohexanone, cyclohexanol, acetonitrile, nitromethane, dimethyl sulfoxide, xylene, dimethylformamide, hexanol, toluene, butyl acetate, dimethylacetamide, HMPT, cyclopentyl Ketone, cyclopentanol, diethylene glycol, triethylene glycol, tetraethylene glycol, (PEG200), PEG400 and/or PEG600.

As carboxylic acid, formic acid and/or acetic acid are particularly preferably used.

• The Acetocell-method, which, although unsuccessful, proposes the use of acetic acid for the dissociation under conditions of high pressure and temperature.

When cellulose-containing raw materials are dissociated in various carboxylic acids, lignin is also dissociated. In addition, during this dissociation process, cellulose will also be decomposed to a certain extent, becoming complex carbohydrates and soluble sugars.

Due to the difference of the added cellulose-containing raw materials, acetic acid with different content ratios will also appear during the dissociation process. For example, according to the method of dissociation using formic acid described in WO 96/35013, if wood is added as a raw material containing cellulose, then under the conditions of this dissociation, the produced acetic acid can reach 5%; As a raw material containing cellulose, only about 0.04% to 0.5% of acetic acid is produced.

After dissociation, lignin will also be partially decomposed and/or transformed into various derivatives, so that the cellulose production waste liquid also contains lignin decomposition products, such as coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, their Derivatives such as syringaldehyde or guaiac, syringol, guaiacol, short-chain concentrates such as esters, ethers or hemiacetals, and decomposition products containing lignocellulosic raw materials, such as sugars and sugars Decomposition. Each of these substances exists in different content ratios.

During the dissociation process, lignin containing double bonds, carbonyl groups, and carboxyl groups is generated, and derivatives such as vanillin, syringaldehyde, syringyl alcohol, vanillic acid, syringic acid, 4-hydroxy-benzoic acid, acetylvanillin, Acetosyringone and dihydroconiferyl alcohol.

The types and proportions of lignin derivatives and decomposition products in waste liquid depend on the different dissociation methods and reaction processes used. Conditions that promote the formation of decomposition products include high temperature, high acidity, oxidizing agents (eg, H ₂ O ₂ , O ₂ , O ₃ , peracids), long dissociation times, and chemical additives.

Thus, the waste liquid from cellulose production is a highly complex mixture, and not only the types of compounds contained in the waste liquid, but also their respective concentrations vary greatly depending on the cellulose-containing raw materials used. For example, according to the "Natural Pulp Manufacturing Process" described in WO 96/35013, its waste liquid can contain the following components: about 67% formic acid, about 29% water, about 3-4% lignin, about 0.04-0.5 % acetic acid and at least 0.26% furfural. In addition, the waste liquid also contains lignin derivatives, lignin decomposition products, complex carbohydrates and soluble sugars.

Naturally, for ecological reasons, in order to reduce waste liquid pollution, and also for cost reasons, it is desirable to recover quantitatively the carboxylic acids used as solvents as much as possible so that they can be reused in the production process.

Therefore, for the above-mentioned various production methods that use cellulose-containing raw materials to produce pulp, which are environmentally friendly, but especially contain carboxylic acids in the dissociated waste liquid, there are also various suggestions, and try to treat various carboxylic acids. Acid compounds are recycled. Nevertheless, in all known methods of recovering carboxylic acids, due to the high complexity of the composition of the waste liquid and its chemical aspects, strong changes in quality and quantity, not only undesirable , side reactions (e.g. concentration reactions, tarring) that hinder further processing of the product (e.g. lignin), and/or these recovery methods require high energy consumption, the loss of carboxylic acid is too high, or the recovered carboxylic acid acid, its purity is not ideal.

In WO 96/35013, for its "Natural Pulp Manufacturing Process", a simple distillation process is proposed for recovering the added formic acid after the pulp is separated. Using this method, the recovery of formic acid can generally exceed 95%. The rest, according to the prior art, can only be left with the lignin. After formic acid is recycled by distillation, the distillation residue, which contains lignin and higher carboxylic acids, is discharged into water. Lignin can be precipitated in water and separated from other residual components.

However, because the distillation method uses aqueous formic acid solution, the most obtained can only be an azeotropic mixture (77.6% aqueous solution of formic acid) instead of pure formic acid without pressurization.

In addition, this known method has the disadvantage that, under the temperature conditions required for distillation, the lignin gradually becomes concentrated and tarred (formation of a dark brown, tarry, porridge-like mass), So that it is no longer possible to further process the lignin therein.

A further disadvantage of the recovery of formic acid by distillation is that the distillation requires an increase in temperature to a maximum of 107°C, which requires additional energy consumption.

This method also fails to separate the acetic acid produced during the dissociation.

- For the Milox process, for the separation of formic acid, the above-mentioned distillation process with disadvantages is likewise proposed.

- For the Formacell-method, in order to recover the chemicals, the waste liquid containing acetic acid and formic acid is distilled and concentrated and spray-dried according to the recommendation on page 142 of "Renewable raw materials" to obtain acetic acid and formic acid in a diluted state, The state of dilution is determined by the moisture contained in the wood raw material used.

Using this method, a formic acid/acetic acid/water mixture of variable composition can be obtained. Spray drying is expensive and requires high energy consumption. The diluted acid mixture is put into distillation equipment and processed into hydrochloric acid which can be reused. Waste liquid powder containing lignin and hemicellulose can be burned for energy utilization.

In addition, DE 36 26 968 A1 also describes a method for the extraction of carboxylic acids from dilute aqueous solutions. In this method, sec-butyl-di-n-octyl-phosphine oxide is used as extractant.

Likewise, a method for the extraction of carboxylic acids from aqueous solutions is described in U.S. Patent 38 16 524. The carboxylic acid content in the solution is up to 2% by weight. In this method, trialkylphosphine oxides are used as extractants.

According to the description of U.S. Patent 2 714 118, for the black waste generated by a neutral or alkaline solution in the pulp production process, especially in the process of using machinery or sodium bicarbonate to dissociate For the liquid, the solid content in the waste liquid must be concentrated to at least 25% solid content ratio, and acidified with sulfuric acid with a concentration of 95%, and then the acetic acid can be extracted with methyl ethyl ketone. According to this patent document, the extraction of carboxylic acids should be good due to the salt effect of the solid content contained in the concentrated and acidified liquid.

Document DE 36 26 968 A1 describes a method for extracting the chemical constituents of lignocellulose-containing raw materials decomposed by the steam explosion method. Dichloromethane was added during the extraction. However, in the method of extraction using the steam explosion method, no waste liquid is generated.

According to the description of "Papermaking" magazine, 1995, volume 5, page 231, 3/04, wood can be dissociated in haloacetic acid without adding sulfuric acid, and then use ketones, esters or cyclic ethers to convert the fiber material Excess acid was washed out.

The object of the present invention is to improve the method for obtaining or recovering carboxylic acid from the waste liquid containing a large amount of lignin produced in the cellulose production process, and to propose an environmentally friendly method for preparing carboxylic acid.

It was a surprising discovery that the recovery of added carboxylic acids and the separation of newly produced carboxylic acids, especially acetic acid, from aqueous dissociation solutions can be carried out in an almost quantitative manner, and in this way to The environment is friendly and no adverse side effects will occur. This preparation/recovery process adopts the method of extraction. The extractant used is selected from the following group of compounds: ethers, saturated and unsaturated hydrocarbons, alcohols, alkyl esters, aryl esters, alkylamines, arylamines, specific Alkyl ketones, alkyl chain monocarboxylic acids, alkyl amides, aryl amides, aromatics and aldehydes.

Based on ecological reasons and considering the compatibility of the process itself, the extractant added in the method of the present invention preferably does not contain any halogen and/or sulfur and/or phosphorus. The various extractants known so far contain these elements.

Furthermore, the carboxylic acid added in the dissociation process preferably also does not contain any halogen and/or sulfur and/or phosphorus compounds. According to the method of the present invention, these carboxylic acids can be recovered.

The following compounds can be used as suitable extractants: Alkyl ethers, above all symmetrical ones, especially diisopropyl ether (DIPE) and di-tert-butyl ether, but also asymmetrical alkyl ethers such as methyl - tert-butyl ether, and cyclic ethers, such as dioxane, or 4,4-dimethyl-1,3-dioxane.

In particular, diisopropyl ether (DIPE) is preferred as the extraction agent. Its boiling point is 68°C, which is sufficiently different from the boiling point temperature of formic acid and higher carboxylic acids. Therefore, from formic acid/diisopropyl ether-extraction Diisopropyl ether can be easily distilled out from the substance, and it can be introduced into the dissociation solution again to participate in the next extraction process. Diisopropyl ether is a waste product from the chemical industry and is relatively cheap. If diisopropyl ether is used as the extractant, a protective gas is also required. The specific gravity of diisopropyl ether is smaller than that of the dissociation solution, so it is best to take out the extraction phase from the upper part of the extraction reaction column.

When diisopropyl ether is used as the extractant, the extraction process is carried out at a temperature of about 60°C. Under this temperature condition, lignin will not undergo any thermal denaturation. Therefore, when diisopropyl ether is used as the extractant, after the extraction process, the lignin remaining in the extraction raffinate and separated out can still be dissolved in acetone. This indicated that lignin did not undergo any structural changes during the extraction process. The separated lignin can be further processed and utilized.

In addition, as extractant, the following compounds can also be used: saturated or unsaturated hydrocarbons, such as heptane or 4-methyl-3-pentene; saturated and/or unsaturated cyclic alcohols, these Alcohols containing at least five carbon atoms, preferably at least six carbon atoms, particularly preferably at least seven carbon atoms, such as 4-methyl-2-olpentyl; alkyl and aryl esters, such as acetate, Propionates, formates, butyrates, terephthalates or benzoates. Among acetates, for example ethyl, normal or isomeric propyl, butyl, pentyl, hexyl and cyclohexyl esters can be used, among propionates ethyl and propyl esters can be used, in Among formic acid esters, propyl ester and isopropyl ester can be used. Likewise, butanediol dicarboxylate can also be used as formate.

Among the butyrates, for example, methyl and ethyl esters can be used, among the terephthalates, diethyl terephthalate can be used, and among the benzoates, ethyl esters can be used.

Suitable as alkylamines and aromatic amine extractants are, for example, tri-n-octylamine and tri-n-decylamine.

Among the cyclic alkanones, cyclohexanone and cyclopentanone are preferred. There are also unsaturated alkyl ketones, methyl isobutyl ketone, methyl acryl ketone, and methyl butanone, which can also be used as extraction agents. Among the alkyl-chain monocarboxylic acids, not only straight-chain but also branched-chain carboxylic acids can be selected. The selected alkyl chain carboxylic acids preferably contain at least six carbon atoms.

Additionally, suitable alkylamides and arylamides which may be used are salicylamides containing N-heterocycles. Suitable aromatic compounds are toluene and xylene. A suitable example of aldehydes is furfural.

It is likewise possible to use mixtures of various solvents as extraction agents.

The method of the invention is especially suitable for recovering carboxylic acid from the waste liquid of the acid dissociation process.

The effluent used for the extraction process preferably does not contain any solid matter.

Using the extraction agent in the method of the present invention, the process of producing carboxylic acid from the dissociation solution is preferably carried out continuously in a circulating countercurrent mode. In order to promote the material exchange between the interfaces of different phases, it is best to make the extractant in the form of droplets, that is, to pass through the extraction solution with a large surface area. Carboxylic acids tend to accumulate in the extractant of the invention due to the favorable partition coefficient. The extractant can be regenerated by distillation.

For most extractants, especially diisopropyl ether which is preferred, the boiling point of the carboxylic acid is generally much higher than that of the extractant, so by distillation, most of the extractant will be extracted from the extraction phase. , while the carboxylic acid remains in the bottoms of the distillation. The carboxylic acids, especially formic acid and acetic acid, can then be separated from the raffinate by distillation. The isolated formic acid is an aqueous solution with a concentration of up to 99%, which is much higher than that in its boiling mixture.

The carboxylic acids are also purified by distillation, separating them from the lignin which is sometimes carried over during the extraction process.

As the extraction increases, the water content in the dissociation solution increases, so that the lignin is gradually precipitated and separated.

According to the method of the present invention, in the waste liquid that carries out extraction, generally should contain the carboxylic acid of 10% by weight at least, contain the carboxylic acid of 20% by weight at least then better, contain the carboxylic acid of 40% by weight at least for the best.

If diisopropyl ether (DIPE) is used as the extractant and the method is carried out in the most preferred mode described below, the formic acid ratio recovered can reach at least 99%.

An important advantage of the method of the present invention is that the extraction process of the dissociation solution is carried out at a temperature much lower than that of the distillation process, so that no undesirable thermal denaturation of the lignin occurs as in the distillation process (Structural changes due to concentration reactions and tarring).

According to the method of the present invention, the concentration of formic acid that can be recovered is far higher than the concentration of formic acid that can be recovered according to known distillation methods. If instead of formic acid obtained according to the hitherto distillation process in the "Natural Pulp Manufacturing Process" (see WO96/35013), a recycled formic acid/water azeotrope is used as solvent, the If the recycled high-concentration formic acid obtained by the method is used as a solvent, the kappa value of the produced pulp will be lower under the condition that other conditions remain unchanged.

In the process of "natural pulp manufacturing method", according to the circulation method of the present invention, high-concentration formic acid can be added, so that, on the one hand, the whole dissociation process can be accelerated, and on the other hand, due to the lower kappa value can be obtained , so it will make the subsequent bleaching process easier. The bleaching process is necessary in many cases. The high concentration of formic acid added to the dissociation process does not have any negative effect on the quality of the cellulose, such as shortening its chain length or compromising its tear strength.

It is even possible to improve and speed up the entire pulp production process by adding carboxylic acids recovered by the extraction process according to the invention.

In addition to producing and recovering carboxylic acids from dissociation solutions containing dissolved lignin, it is also possible to first further separate lignin from dissociation solutions and then dissociate at least lignin-containing The solution uses the extraction process of the present invention. In this case, to separate the lignin in the dissociation solution, permeation membrane process, ultrafiltration process or vacuum evaporation process can be used.

If it is necessary to allow lignin to remain in the extraction raffinate and gradually precipitate out as the proportion of water in the dissociation solution increases, then the used extraction agent should be a solvent that does not dissolve lignin.

If it is necessary to dissolve the dissociated lignin in a suitable solvent for further processing, it is necessary to choose an extractant that can dissolve not only carboxylic acid but also lignin. Then the lignin is extracted together with the carboxylic acid, and then separated from the extractant, so that the lignin dissolved in a higher concentration of carboxylic acid can be processed in the next step. In this case, after further processing of the dissolved lignin, the carboxylic acid can be recovered and reintroduced as a solvent into the pulp production process.

Another preferred way of carrying out the method according to the invention is to use only solvent B itself as the extractive solution in a dissociation solution using carboxylic acids and according to DE 100 57 878.0, at least also using another solvent B. agent. According to DE 100 57 878.0, the following compounds can be used as additional solvent B: cyclohexanone, cyclohexanol, acetonitrile, nitromethane, dimethylsulfoxide, xylene, dimethylformamide, hexanol , toluene, butyl acetate, dimethylacetamide, HMPT, cyclopentanone, cyclopentanol, diethylene glycol, triethylene glycol, tetraethylene glycol, (PEG200), PEG400 and/or PEG600.

Some compounds can be used not only as additional solvent B, but also as extractants, such as alcohols, ketones, aromatics, esters and amides, especially cyclohexanone, cyclopentanone, butyl acetate, toluene and xylene.

In this method, if the solvent B and the compound used to extract carboxylic acid from the waste liquid are the same, the compatibility and separation technology of the process will be significantly improved, and the storage work of chemicals and the entire process flow can be improved. simplify.

The invention is further described below with the aid of an example of a preferred embodiment. as the picture shows:

Fig. 1 uses diisopropyl ether (DIPE) as the schematic diagram of the inventive method of extraction agent (the specific gravity of extraction agent is less than the specific gravity of waste liquid).

The pulp production waste liquid is located in the extraction reaction column 11 .

In the pulp production carried out according to the "natural pulp manufacturing method", the waste liquid contains about 67% formic acid (F), 29% water (W), 3-4% lignin (L), 0.04- 0.5% acetic acid (A), at least 0.26% furfural and soluble sugars and complex carbohydrates.

The extractant, preferably diisopropyl ether (DIPE), is introduced into the waste liquid extraction reaction column 11 through the pipeline 19 in a countercurrent manner from the bottom, and makes it pass through the waste liquid (F, A, W, L), during this process, mainly carboxylic acids (F, A) enter the extractive phase. There is also a small amount of colloidally dissolved lignin entering the organic phase.

The extractant passes through the waste liquid in the form of micro-droplets, so as to ensure better material exchange between the interfaces of different phases by enlarging the surface area.

When using DIPE as the extraction agent, the specific gravity of the extraction phase containing carboxylic acid, especially formic acid (F), acetic acid (A) and trace lignin (L) and the extraction agent DIPE is Small, and separated in the upper part of the extraction reaction column 11, then through the pipeline 12, it is introduced into the distillation equipment 13 of the extractant.

In the distillation column 13, the extractant DIPE is distilled from the extract under mild conditions (temperature about 70° C.). Extracts are introduced and combined from line 12 and line 21. Then, the diisopropyl ether recovered by distillation is introduced into the reaction column 11 again for re-extraction, or it is first introduced into the clarification tank 34 for better three-phase separation.

As the extraction process continues in the waste liquid reaction column 11, due to the continuous decrease of the concentration of organic compounds, the proportion of water in the waste liquid continues to rise. In this way, the dissolved lignin will be gradually separated out. The raffinate after extraction, which contains water (W), lignin (L) and carboxylic acid (F, A) residues, is led out from the extraction reaction column 11 through the pipeline 15 . The lignin is then separated in the clarifier 34, and the wet lignin is also dried in the drying plant 17 for its further use. The moisture W produced in the drying process in the lignin drying equipment 17 is introduced into the second distillation equipment 33 of the extractant through the pipeline 23, so as to recover the residual trace extractant.

In the clarification device 34, the extraction raffinate is subjected to three-phase separation: one is an organic phase (F, A, DIPE), one is an aqueous phase, and the other is a solid phase (L). Via line 20, the extract phase from clarification unit 34 contains traces of DIPE as well as formic and acetic acids. This extraction phase can use cock 18 to enter the waste liquid extraction reaction column 11 (pipeline 19), and re-extract, or enter the distillation reaction column 13 through the delivery pipeline 21, so that the diisopropyl ether therein can be further separated And produce carboxylic acid.

The aqueous phase drawn from the clarification device 34, containing soluble sugars and traces of DIPE, is also introduced into the second DIPE-distillation device 33 through the pipeline 24, so that the extraction agent is recovered almost quantitatively.

When diisopropyl ether is used as the extractant, the extraction temperature condition is about 60°C.

When diisopropyl ether is used as the extractant, for each unit volume of dissociation solution, it is best to use one to three unit volumes of diisopropyl ether for 1 to 8 hours for cyclic extraction, the extraction conditions The preferred temperature range is 30 to 67°C, preferably between 50 and 60°C, and most preferably about 60°C.

The best implementation mode of the method described in Fig. 1 can of course be changed according to factors such as the extraction agent input, the desired extraction rate, etc., for example, different technological processes can be used.

Claims (14)

1. A method for recovering and/or separating carboxylic acids from waste liquids from pulp production, which contain carboxylic acids, lignin and water, and sometimes complex carbohydrates, furfural and soluble sugars, Its characteristics are: The waste liquid is extracted using an extractant selected from the following group of compounds: ethers, saturated and unsaturated hydrocarbons, Alcohols, Alkyl and aryl esters, Alkylamines and arylamines, Cyclic and/or unsaturated alkanones and methyl isobutyl ketone, methyl butanone, methyl acetone, Alkyl chain monocarboxylic acids, Alkylamides and arylamides, aromatic compounds, Aldehydes. 2. according to the described method of claim 1, it is characterized in that: ether is a kind of alkyl ether, preferably a kind of symmetrical alkyl ether, especially diisopropyl ether or di-tert-butyl ether, or a kind of non- Symmetrical alkyl ethers, such as methyl-tert-butyl ether, or a cyclic ether, especially dioxane, or 4,4-dimethyl-1,3-dioxane. 3. according to the described method of claim 1, it is characterized in that: Saturated or unsaturated hydrocarbons are preferably heptane or 4-methyl-3-pentene, The preferred alcohol is 4-methyl-2-pentanol, Alkyl and aryl esters are preferably acetates, propionates, formates, butyrates, terephthalates or benzoates, Alkyl and aryl amines are preferably tri-n-octylamine or tri-n-decylamine, Cyclic alkyl ketones are preferably cyclohexanone and cyclopentanone, Alkyl chain monocarboxylic acids are preferably linear or branched carboxylic acids having at least 6 carbon atoms, Alkyl and aryl amides are preferably salicylamides with N-heterocycles, Aromatic compounds are preferably toluene or xylene, The preferred aldehyde is furfural. 4. According to the method described in one of claims 1 to 3, it is characterized in that: the extraction is carried out in countercurrent mode, and the extraction agent is preferably passed through the waste liquid in the form of droplets. 5. According to the method described in one of claims 1 to 4, it is characterized in that: the extraction agent is regenerated by distillation. 6. The method as claimed in claim 2, characterized in that the extraction with diisopropyl ether is carried out at a temperature in the range of 30 to 67°C, preferably between 50 and 60°C, in particular around 60°C. 7. According to the method described in claim 2 or 6, it is characterized in that: for the dissociation solution of each unit volume, use one to three unit volumes of diisopropyl ether, carry out circulation extraction by 1 to 8 hours. 8. According to the method described in one of claims 1 to 7, it is characterized in that: the carboxylic acid in the waste liquid is formic acid and/or acetic acid, or contains formic acid and/or acetic acid. 9. According to the described method of one of claims 1 to 8, it is characterized in that: the waste liquid contains at least 10% by weight of carboxylic acid, more preferably at least 20% by weight of carboxylic acid, at least 40% by weight of carboxylic acid Sour is best. 10. According to the described method of one of claims 1 to 9, it is characterized in that: no halogen and/or phosphorus and/or sulfur are contained in the extractant. 11. The method as claimed in one of claims 1 to 10, characterized in that the waste liquor from which the extraction is carried out is substantially free of solid matter. 12. The method for recovering formic acid as described in any one of claims 1 to 11. 13. Process for recovering acetic acid as described in any one of claims 1 to 12. 14. According to the method for producing or reclaiming carboxylic acid from the waste liquid produced in the pulp production process according to one of claims 1 to 13, wherein, one or more of the following compounds are added in the dissociation solution : Formic acid, acetic acid, cyclohexanone, cyclohexanol, acetonitrile, nitromethane, dimethyl sulfoxide, xylene, dimethylacetamide, HMPT, cyclopentanone, cyclopentanol, diethylene glycol, triethylene glycol alcohol, tetraethylene glycol, (PEG200), PEG400 and/or PEG600.