Method and system for extracting and removing organic carboxylic acid in wastewater by-product in coal liquefaction process

Abstract

The invention discloses a method and a system for extracting and removing organic carboxylic acid in waste water byproducts in a coal liquefaction process, the method comprises the following steps: taking waste water containing organic carboxylic acid as a byproduct in the coal liquefaction process as a raw material, taking a composite solvent of ketone and ester as an extracting agent, contacting the extracting agent with the raw material to extract the raw material, and standing for layering to obtain an extraction phase and a raffinate phase; wherein the extraction phase contains the organic carboxylic acid and the composite extraction agent, and the raffinate phase contains the wastewater from which the organic carboxylic acid is removed. According to the method, the mixture of high-boiling-point ketone and ester is adopted as the extracting agent, and through multi-stage countercurrent liquid-liquid extraction of the extracting agent and the raw materials, organic carboxylic acid in waste water byproducts in the coal liquefaction process can be effectively removed, and after an extraction phase is separated through a rectifying tower, tower kettle extracting agent effluent can be recycled; and the tower top fraction is rectified to respectively obtain high-purity acetic acid and butyric acid which can be continuously used as reaction raw materials, so that the production cost is further reduced, the method is economical and environment-friendly, and the recycling of acetic acid and butyric acid is realized.

Description

Technical Field

[0001] The invention relates to a method and a system for removing organic carboxylic acids from wastewater, and in particular to a method and a system for removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process by extraction. Background Art

[0002] The aqueous by-products produced in the Fischer-Tropsch synthesis process of coal liquefaction are rich in a large number of organic components such as aldehydes, ketones, alcohols, and acids. Effective resource development of such aqueous by-products can not only extract a considerable number of organic components, but also help to meet wastewater discharge standards, reduce wastewater treatment costs, and promote a fundamental change in resource utilization. A large amount of low-concentration, low-molecular-weight organic carboxylic acid aqueous solutions are produced in the coal liquefaction industry. Low-molecular-weight carboxylic acids, such as acetic acid and butyric acid, occupy an important position in the organic chemical industry. They are not only important organic chemical raw materials, but also common organic solvents. Separating and purifying high-concentration acetic acid, butyric acid and other low-molecular-weight carboxylic acids from a large amount of low-concentration organic carboxylic acid wastewater solutions not only has high economic value, but also can protect the ecological environment well.

[0003] Since butyric acid and water can form a binary azeotropic system, and the binary system of acetic acid and water is difficult to separate due to the similar boiling points between the components and the relative volatility close to 1, it is difficult to separate them by ordinary distillation alone. At present, the main methods for separating acetic acid from aqueous solution include distillation, extraction, esterification, adsorption, crystallization, pervaporation, biodegradation and neutralization.

[0004] The literature (Li Xin, Wang Shaopeng. Recovery of low-concentration acetic acid aqueous solution [J]. Chemical Engineering, 1996, 24(5):43-46.) reported an extraction experiment for the recovery of low-concentration acetic acid, using a trifatty amine-kerosene-n-decyl alcohol system as the extractant. However, the above method cannot recover the extractant and the entrainer, and the process is complicated. It is only suitable for small-scale experiments, and it is difficult to industrialize. The economic efficiency is not ideal.

[0005] Reference (Wang Ming, Yu Lulu, Zhou Lingli, et al. Simulation study on the separation of acetic acid-water mixture by extractive distillation [J]. Journal of Yichun University, 2020, 42(6): 43-47.) Using N-methylpyrrolidone (NMP) as the extractant, the extraction distillation separation of acetic acid and water was simulated. The extraction distillation separation technology used requires multiple condensation, heating and other steps. The operation process is cumbersome and the energy consumption is high. Reference (PENG Y, SHEN Y, HUANG Q, et al. Separation of near-boiling mixtures (acetic acid and water) enhanced by ionic liquid [J]. The Journal of Chemical Thermodynamics, 2023, 187.) Using ionic liquid (IL) 1,2,3-trimethylimidazolium dimethyl phosphate ([TMIM] + [Me2PO4] − ) is used as a distillation azeotropic agent in the water / acetic acid system, but the azeotropic distillation process also has the problem of high energy consumption.

[0006] With the increasing global awareness of environmental protection and effective resource conservation, the treatment of organic wastewater has received more and more attention. Therefore, the efficient removal of organic carboxylic acids in wastewater is particularly important. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a method for extracting and removing organic carboxylic acids from wastewater byproducts in the coal liquefaction process with low energy consumption and good removal effect; A second object of the present invention is to provide a system used in the above method.

[0008] Technical solution: The method for extracting and removing organic carboxylic acids from wastewater byproducts of the coal liquefaction process described in the present invention uses wastewater containing organic carboxylic acids as a byproduct of the coal liquefaction process as a raw material, and a composite solvent of ketones and esters as an extractant. The extractant and the raw material are subjected to multi-stage reverse contact to perform liquid-liquid extraction on the raw material, and after standing and stratification, an extraction phase and a raffinate phase are obtained; wherein the extraction phase contains organic carboxylic acids and the composite extractant, and the raffinate phase contains wastewater with reduced organic carboxylic acid content.

[0009] The raw material and the extractant are in reverse contact for multiple times under certain mass flow ratio and stirring rate conditions, and continuous liquid-liquid extraction is performed on the raw material; after standing and stratification, the organic carboxylic acid content in the raffinate phase is reduced, and the raffinate phase meets the discharge standards after treatment.

[0010] The extraction phase is an organic carboxylic acid and a composite extractant. After distillation treatment in a solvent recovery tower, the solvent effluent at the bottom of the tower can be recycled, and the top fraction can be separated by distillation to obtain high-purity acetic acid and butyric acid, thereby realizing the resource utilization of acetic acid and butyric acid in wastewater.

[0011] The boiling points of the ketone and the ester in the extractant are both 30°C to 100°C higher than the boiling point of butyric acid. The extractant of the present invention uses a mixture of high-boiling-point ketones and esters as a composite extractant. On the one hand, the extractant should be insoluble in water and soluble in organic carboxylic acids, so as to achieve a better separation effect. At the same time, the stability, source and recyclability of the extractant should be taken into account. Through the extraction method of the present invention, the water content in the extraction phase is low, and the organic carboxylic acid content in the raffinate phase water is less than 0.10%.

[0012] Wherein, the mass ratio of ketone to ester in the extractant is 0.1:1~1.0:1.

[0013] Wherein, the mass flow ratio of the extractant to the raw material is 1:1~5:1.

[0014] Wherein, the ketone is a fatty ketone; the ester is an acid ester; preferably, the ketone in the extractant is 1,1,3-trimethylcyclohexenone, and the ester is (3,4-diethyl-6-methyloctyl) ethyl ester.

[0015] The extractant and the raw material are contacted and extracted under stirring conditions, and the stirring rate is 300-1000 rpm.

[0016] The extraction process is carried out in a multi-stage impeller stirring tower, and the extractant and the raw material are stirred by the multi-stage impeller for reverse contact extraction; the number of stirring impellers in the multi-stage impeller stirring tower is 10 to 20.

[0017] The system used in the above method includes a liquid-liquid extraction tower, a solvent recovery tower and a distillation tower; the upper and lower ends of the liquid-liquid extraction tower are respectively provided with a feed port for raw material F and a feed port for extractant S; the liquid-liquid extraction tower is provided with a multi-stage stirring impeller, the top of the tower is provided with an extraction phase static section, the bottom is provided with a raffinate phase static section, the extraction phase static section is provided with an extraction phase overflow port, and the raffinate phase static section is provided with a raffinate phase discharge port; the bottoms of the solvent recovery tower and the distillation tower are respectively connected to reboilers, and the tops are respectively provided with a condenser, a reflux tank and an intermediate storage tank for the top fraction connected in sequence.

[0018] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: The present invention adopts a mixture of high-boiling ketones and esters as an extractant, and after multi-stage countercurrent liquid-liquid extraction with the raw materials, it can not only effectively remove organic carboxylic acids in the wastewater byproducts of the coal liquefaction process, but also the extractant effluent from the bottom of the tower can be recycled after the extraction phase is separated by a distillation tower, and the top fraction is distilled to obtain high-purity acetic acid and butyric acid, which can be used as reaction raw materials, which helps to further reduce production costs, is economical and environmentally friendly, and realizes the resource utilization of acetic acid and butyric acid. (2) The liquid-liquid extraction method of the present invention is carried out at room temperature, with low energy consumption, and no secondary waste solution is discharged during the whole process, which is conducive to promoting the green development of the chemical industry. (3) The liquid-liquid extraction process system of the present invention can not only obtain high-purity organic carboxylic acids, but also the extractant can be recycled, which has great environmental significance and industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the multi-stage countercurrent liquid-liquid extraction process system of the present invention; Figure 2 It is a schematic diagram of the structure of the liquid-liquid extraction tower in the system of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in further detail below.

[0021] Example 1

[0022] Reference Figure 1 The multi-stage countercurrent liquid-liquid extraction process system used in the method for removing organic carboxylic acids from wastewater byproducts in the coal liquefaction process by liquid-liquid extraction of the present invention comprises a liquid-liquid extraction tower 1, a solvent recovery tower 2 and a distillation tower 3.

[0023] like Figure 2 As shown, the upper and lower ends of the liquid-liquid extraction tower 1 are respectively provided with a feed port 1-1 for raw material F and a feed port 1-2 for extractant S, a multi-stage stirring impeller 1-5 is provided in the tower, an extraction phase static section 1-6 is provided above the multi-stage stirring impeller 1-5 in the tower, and a raffinate phase static section 1-7 is provided below; the extraction phase static section 1-6 is provided with an extraction phase overflow port 1-3, and the raffinate phase static section 1-7 is provided with a raffinate phase discharge port 1-4. The extraction phase overflow port 1-3 is connected to the inlet of the solvent recovery tower 2.

[0024] The tops of the solvent recovery tower 2 and the distillation tower 3 of the present invention are respectively connected with a condenser 4, a reflux tank 5, and an intermediate storage tank 6 for the top fraction. Specifically, the top outlet of the solvent recovery tower 2 is connected with the condenser 4, the condenser 4 is connected with the reflux tank 5, and the outlet of the reflux tank 5 is respectively connected with the solvent recovery tower 2 and the intermediate storage tank 6 for the top fraction; the bottom of the solvent recovery tower 2 is provided with a solvent outlet, the solvent outlet is connected with the extractant S feed port 1-2 of the liquid-liquid extraction tower 1, and the solvent outlet also forms a circulation loop with the reboiler 7; the outlet of the intermediate storage tank 6 for the top fraction is connected with the inlet of the distillation tower 3.

[0025] The top outlet of the distillation tower 3 is connected to a condenser 4, which is connected to a reflux tank 5. The outlet of the reflux tank 5 is respectively connected to the distillation tower 3 and the intermediate storage tank 6 for the top fraction. The intermediate storage tank 6 for the top fraction is provided with an outlet for an acetic acid solution. The bottom outlet of the distillation tower 3 forms a circulation loop with a reboiler 7. After the top fraction of the solvent recovery tower 2 enters the distillation tower 3 for separation, a high-purity acetic acid solution can be obtained at the top of the distillation tower 3, and a high-purity butyric acid solution can be obtained at the bottom of the tower.

[0026] The method for removing organic carboxyl groups from wastewater byproducts of coal liquefaction process by multi-stage countercurrent liquid-liquid extraction of the present invention comprises the following steps: The raw material comes from the aqueous byproduct wastewater of the coal liquefaction process, and its composition and physical property data are shown in Table 1. Under room temperature conditions, according to the flow rate of raw material F of 1.0 kg / h and composite extractant S of 3.0 kg / h, raw material F enters from the upper feed port 1-1 of liquid-liquid extraction tower 1, and composite extractant S enters from the lower feed port 1-2 of liquid-liquid extraction tower 1, wherein the ketone in the composite extractant S is 1,1,3-trimethylcyclohexenone, and the ester is (3,4-diethyl-6-methyloctyl) ethyl ester, and the mass ratio of ketone to ester is 0.43:1; the liquid-liquid extraction tower adopts 15-stage stirring blades. The wheel is stirred and mixed for extraction at a rate of 700 rpm. The raw material F and the composite extractant S are in reverse contact in the liquid-liquid extraction tower 1. After standing and stratification, the raffinate is left standing for more than 15 minutes in the raffinate phase standing section 1-6, and the content of organic acid in the raffinate phase water is reduced to less than 0.10%; wherein, the top discharge of T101 tower is: trace water, mixed acid, extraction solvent; the extraction phase flowing out of the overflow port 1-3 at the top of the liquid-liquid extraction tower 1 is distilled in the solvent recovery tower 2 and then taken out from the tower bottom, It can be recycled into the liquid-liquid extraction tower 1 for repeated use, and the extracted phase from the tower bottom can be recycled into the solvent recovery tower for treatment after being reboiled in the reboiler 7; the top fraction of the solvent recovery tower 2 is condensed by the condenser 4 and then enters the reflux tank 5, among which the top discharge of the T102 tower is: trace water and mixed acid; the trace water and mixed acid in the T102 reflux tank 5 are partially extracted and enter the intermediate storage tank 6 of the top fraction, and part of them are refluxed into the solvent recovery tower 2; the fraction coming out of the intermediate storage tank 6 of the top fraction enters the distillation Tower 3 is subjected to distillation. After distillation and separation in distillation tower 3, the acetic acid produced from the top of the tower sequentially enters into condenser 4, reflux tank 5 and intermediate storage tank 6 for the top fraction connected to the distillation tower, wherein the top discharge of tower T103 is: trace water and acetic acid; part of the trace water and acetic acid in reflux tank 5 of T103 are produced and enter intermediate storage tank 6 for the top fraction, and part of them are refluxed into distillation tower 3; a high-purity acetic acid solution is obtained in intermediate storage tank 6 for the top fraction, and the bottom effluent of distillation tower 3 is a high-purity butyric acid solution.

[0027]

[0028] Example 2

[0029] The basic steps are similar to those of Example 1, except that the mass flow ratio of the composite extraction solvent to the raw material, that is, the solvent ratio, is different. The liquid-liquid extraction separation results are shown in Table 2.

[0030]

[0031] It can be seen from Table 2 that with the increase of solvent ratio, the organic acid content in the raffinate phase gradually decreases, and the water content in the extract phase also gradually decreases. When the solvent ratio increases to 3.0:1, the organic acid content in the raffinate phase aqueous solution is 0.070%, which meets the emission standard. Therefore, considering the production cost and other issues, the solvent ratio of 3.0:1 is selected as the optimal solvent ratio.

[0032] Example 3

[0033] The basic steps are similar to those of Example 1, except that the mass ratio of ketone to ester in the solvent composite extractant is different. The liquid-liquid extraction separation results are shown in Table 3.

[0034]

[0035] It can be seen from Table 3 that with the increase of the mass ratio of ketone to ester, the content of organic acid in the raffinate phase becomes lower and lower, while the water content in the extract phase becomes higher and higher. This is because the solubility of water in ketone is higher than that in ester, and the excessive water content in the extract phase affects the difficulty, purity and energy consumption of subsequent organic acid separation. Therefore, the mass ratio of ketone to ester is selected as 3:7, i.e. 0.43:1, which is the optimal ratio of the composite extractant. At this time, the content of organic acid in the raffinate phase water is 0.070%, which meets the emission standard.

[0036] Example 4

[0037] The basic steps are similar to those of Example 1, except that the number of extraction stages is different. The liquid-liquid extraction separation results are shown in Table 4.

[0038]

[0039] It can be seen from Table 4 that with the increase of the number of extraction stages, the organic acid content in the raffinate phase water gradually decreases, and the water content in the extract phase basically does not change. When the number of extraction stages increases to 15, the organic acid content in the raffinate phase water decreases to 0.070%, reaching the emission standard. Since the increase in the number of extraction stages will increase the equipment investment cost, after comprehensive consideration, the extraction stage 15 is selected as the optimal extraction stage.

[0040] Example 5

[0041] The basic steps are similar to those of Example 1, except that the stirring rate is different. The liquid-liquid extraction separation results are shown in Table 5.

[0042]

[0043] It can be seen from Table 5 that with the increase of stirring rate, the content of organic acid in the raffinate phase water gradually decreases. When the stirring rate reaches a certain level, the reduction of organic acid in the raffinate phase water is significantly reduced, and the water content in the extract phase remains basically unchanged. Since the higher the rotation rate, the greater the energy consumption, when the stirring rate reaches 700rpm, the content of organic acid in the raffinate phase water is reduced to 0.070%, reaching the emission standard. Therefore, the optimal stirring rate is 700rpm.

[0044] Comparative Example 1 The basic steps of Comparative Example 1 are the same as those of Example 1, except that the extractant is different. The liquid-liquid extraction separation effect is shown in Table 6.

[0045]

[0046] Compared with the extraction effect of 1,1,3-trimethylcyclohexenone or (3,4-diethyl-6-methyloctyl)ethyl ester as a single solvent in Example 3, the extraction effect of the extractant in Example 3 is significantly better than the extraction effects of the extractants in Comparative Example 1.

Claims

1. A method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process, characterized in that: The method uses wastewater containing organic carboxylic acids produced as a by-product in the coal liquefaction process as raw material, and a composite solvent of ketones and esters as an extractant. The extractant and the raw material are subjected to multi-stage reverse contact to carry out liquid-liquid extraction of the raw material. After standing and stratification, an extraction phase and a raffinate phase are obtained; wherein the extraction phase contains organic carboxylic acids and the composite extractant, and the raffinate phase contains wastewater with reduced organic carboxylic acid content.

2. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: After the extract phase is treated by rectification, the solvent is recycled, and the fraction is separated by rectification to obtain acetic acid and butyric acid.

3. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The boiling points of the ketone and the ester in the extractant are both 30°C to 100°C higher than the boiling point of butyric acid.

4. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The mass ratio of ketone to ester in the extractant is 0.1:1-1.0:

1.

5. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The mass flow ratio of the extractant to the raw material is 1:1 to 5:

1.

6. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The ketone is an aliphatic ketone; and the ester is an acid ester.

7. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The ketone in the extractant is 1,1,3-trimethylcyclohexenone, and the ester is (3,4-diethyl-6-methyloctyl) ethyl ester.

8. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The extractant and the raw material are contacted and extracted under stirring conditions, and the stirring rate is 300-1000 rpm.

9. The method for extracting and removing organic carboxylic acids from wastewater byproducts in a coal liquefaction process according to claim 1, characterized in that: The extractant and the raw material are stirred by a multi-stage impeller for reverse contact extraction; the number of the impeller stages is 10 to 20.

10. A system used in the method according to claim 1, characterized in that: The invention comprises a liquid-liquid extraction tower (1), a solvent recovery tower (2) and a distillation tower (3); the upper and lower ends of the liquid-liquid extraction tower (1) are respectively provided with a raw material F feed port (1-1) and an extractant S feed port (1-2); a multi-stage stirring impeller (1-5) is provided inside the liquid-liquid extraction tower (1); an extraction phase static section (1-6) is provided at the top of the tower; a raffinate phase static section (1-7) is provided at the bottom; the extraction phase static section (1-6) is provided with an extraction phase overflow port (1-3); and the raffinate phase static section (1-7) is provided with a raffinate phase discharge port (1-4); the bottoms of the solvent recovery tower (2) and the distillation tower (3) are respectively connected to a reboiler (7); and the tops are respectively provided with a condenser (4), a reflux tank (5) and a tower top fraction intermediate storage tank (6) which are connected in sequence.

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