A system and method for treating wastewater containing organic acids

Abstract

The application provides a treatment system and method for organic acid-containing wastewater. The treatment system provided by the application adopts two-stage electrodialysis devices to remove organic acids in the wastewater comprehensively. The first-stage electrodialysis device is divided into two compartments to remove the organic acids in the organic acid-containing wastewater (for example, Fischer-Tropsch water) and concentrate and reduce the corresponding organic acid salts respectively. The concentrated and reduced organic acid salts are continuously regenerated into corresponding organic acids and organic bases by the second-stage electrodialysis device. The organic bases can be reused in the first-stage electrodialysis device as a medicine source, and the organic acids can be recovered as by-products. The treatment system of the application can not only improve the unit membrane deacidification efficiency of the weak electrolyte of the organic acids, but also remove the organic acids in the organic acid-containing wastewater (for example, Fischer-Tropsch water) efficiently. The whole process does not need additional medicine, and the concentration and recovery of the organic acids can be realized, which has higher economic benefits and environmental protection significance.

Description

Technical Field

[0001] This invention relates to the field of water treatment, and more specifically to a treatment system and method for wastewater containing organic acids. Background Technology

[0002] In current domestic coal indirect liquefaction projects, Fischer-Tropsch synthesis water is a large amount of synthesis water produced simultaneously with the Fischer-Tropsch reaction of syngas to produce synthetic oil. The oil-to-water ratio in Fischer-Tropsch synthesis water is approximately 1:1.2. Therefore, indirect liquefaction projects with a certain production capacity produce a very large amount of Fischer-Tropsch synthesis water. Taking the Fischer-Tropsch synthesis water produced by the Ningxia Coal-to-Oil project of China Energy Investment Corporation as an example, its annual production reaches 5 million tons.

[0003] Fischer-Tropsch synthesis water contains approximately 1% organic acids (including but not limited to formic acid, acetic acid, propionic acid, butyric acid, and valeric acid) and about 5% other oxygen-containing organic compounds (including but not limited to alcohols, aldehydes, and ketones), which accumulates to a considerable amount. Water treatment units are typically installed to purify and recover these oxygen-containing organic compounds.

[0004] To prevent organic acids in Fischer-Tropsch water from directly entering the distillation column and causing corrosion, existing treatment processes use alkali neutralization at the front end to remove acid. This involves adding inorganic alkali to maintain a near-neutral pH for subsequent distillation. However, neutralization is costly, and the organic acid salts produced during neutralization require further hazardous waste disposal at the end.

[0005] Patent CN103435211A discloses a method for removing organic acids and purifying and recovering other oxygen-containing organic compounds from Fischer-Tropsch synthesis water. This invention uses an alkali-addition method to neutralize and deacidify organic acids, and the resulting carboxylates are then removed using resin or membrane methods. Other oxygen-containing organic compounds are separated and recovered using distillation. The alkali-addition method used in this patent is a very traditional and effective method for deacidifying Fischer-Tropsch water. However, this method has drawbacks: the scale of coal indirect liquefaction determines the very large scale of Fischer-Tropsch synthesis water production, resulting in a very high proportion of alkali consumption in the front-end. Furthermore, it inevitably generates impurities such as organic acid salts in the back-end, which are hazardous wastes with considerable disposal costs.

[0006] Patent CN103555543A discloses a method for deacidifying fruit wine using a bipolar membrane, which utilizes OH groups generated by water ionization through the bipolar membrane. - This patent describes a method for neutralizing and reducing the acidity of organic acids in fruit wine without adding other impurities to avoid affecting the quality of the fruit acids. The method uses a bipolar membrane to reduce the acidity of fruit wine online, which is very effective. However, a drawback is that all the fruit acid solutions to be purified must pass through a bipolar membrane electrodialysis device, without a volume reduction process. Furthermore, the investment and operating costs of bipolar membrane electrodialysis are considerable; therefore, economic considerations must be taken into account in practical applications.

[0007] Patent CN1199976C discloses an electrodialysis method for separating sugars and acids from biomass hydrolysates. The patent employs a two-compartment bipolar membrane electrodialysis device composed of a bipolar membrane and an anion exchange membrane to purify sugars in the biomass hydrolysates, remove and recover organic and inorganic acids, and adjust the pH of the biomass hydrolysates to meet the requirements of the next fermentation step. In this patent, the impurity acids are a mixture of organic and inorganic acids. The presence of inorganic acids directly serves as a strong electrolyte in the acid chamber of the electrodialysis process, resulting in better ionic strength and lower energy consumption compared to deacidification of solutions containing only organic acids. This patented technology is not suitable for the removal of weak electrolyte organic acids. Summary of the Invention

[0008] In view of the problems existing in the prior art, one of the objectives of this invention is to provide a treatment system for wastewater containing organic acids. The treatment system provided by this invention employs a two-stage electrodialysis unit to comprehensively remove organic acids from wastewater. The first-stage electrodialysis unit is divided into two compartments to separately deacidify wastewater containing organic acids (e.g., Fischer-Tropsch water) and concentrate and reduce the corresponding organic acid salts. The concentrated and reduced organic acid salts are then continuously regenerated into corresponding organic acids and organic bases through a second-stage electrodialysis unit. The organic bases can be reused in the first-stage electrodialysis unit as a reagent source, and the organic acids can be recovered as byproducts. This treatment system not only improves the unit membrane treatment capacity and deacidification efficiency of organic acid weak electrolytes, enabling efficient removal of organic acids from wastewater containing organic acids (e.g., Fischer-Tropsch water), but also eliminates the need for additional reagents throughout the process. Furthermore, it achieves the concentration and recovery of organic acids, thus possessing certain economic benefits and environmental significance.

[0009] The second objective of this invention is to provide a processing method corresponding to the above-mentioned processing system.

[0010] To achieve one of the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A wastewater treatment system containing organic acids includes a primary electrodialysis unit and a secondary electrodialysis unit, wherein...

[0012] The primary electrodialysis device includes a first cathode plate, a first anode plate, a first cation membrane adjacent to the first cathode plate, a second cation membrane adjacent to the first anode plate, and a first membrane stack consisting of multiple, preferably at least four, first anion membranes disposed between the first cation membrane and the second cation membrane.

[0013] The secondary electrodialysis device includes a second cathode plate, a second anode plate, and a second membrane stack disposed between the second cathode plate and the second anode plate. The second membrane stack includes at least one set of repeating units composed of a first bipolar membrane, a third cation membrane, and a second anion membrane arranged sequentially along the direction from the second cathode plate to the second anode plate, and a second bipolar membrane adjacent to the second anode plate.

[0014] The primary electrodialysis device is provided with a first water inlet, a first alkali inlet, a first water outlet, and a first salt outlet. The secondary electrodialysis device is provided with a second water inlet, a second salt inlet, a second acid outlet, a second salt outlet, and a third alkali outlet. The first salt outlet is connected to the second salt inlet.

[0015] According to the present invention, the number of the first anal membranes can be determined based on the processing scale.

[0016] In this invention, hydroxide ions can be chain-transferred between adjacent water molecules, exhibiting high electromobility, superior to that of organic acid anions. A drawback of primary electrodialysis treatment devices or processes is that, due to the presence of OH groups in the alkali chamber... - The consumption of alkali in the system reduces the alkali concentration, but it will not drop to zero. On the contrary, the concentration of organic acid salts will increase. Direct discharge of low-concentration alkali will cause secondary pollution and waste resources. By combining a secondary electrodialysis unit, the organic acid salts produced by the primary electrodialysis unit or process can be prepared using acid-base methods, effectively reusing the organic acid salts and forming a complete process. One drawback of this process is that low-concentration alkali will be neutralized by hydrogen ions in the secondary electrodialysis, resulting in some waste. However, this loss is negligible compared to the beneficial effects obtained by this invention.

[0017] When a two-stage electrodialysis unit is used alone to treat Fischer-Tropsch syngas water, the salt chamber containing the Fischer-Tropsch syngas water undergoes deacidification under the influence of an electric field, while the alkali chamber receives H2O migrating from the salt chamber. + Neutralization involves the acid chamber receiving organic acid ions migrating from the salt chamber to form organic acids, thus removing the organic acids. However, there are two main drawbacks in actual operation: 1. The weak ionic strength of the Fischer-Tropsch synthesis water in the salt chamber leads to low ion migration efficiency. Simultaneously, the low conductivity of the salt chamber results in excessively high ohmic resistance of the membrane stack itself, making power consumption uneconomical. 2. The OH- ions generated by the bipolar membrane in the alkali chamber... - Instead of fulfilling its alkali-producing value, it was instead affected by the organic acid H that migrated from the salt chamber. + Neutralization does not produce high-value-added products; at the same time, the water produced by neutralization does not effectively contribute migratable ions in the alkali chamber, further increasing the ohmic resistance of the bipolar membrane stack.

[0018] Therefore, the inventors of this application combine a primary electrodialysis device and a secondary electrodialysis device. The two devices complement each other, effectively improving the efficiency of organic acid removal, while also having high economic benefits and environmental value.

[0019] According to the present invention, the first outlet can be connected to the first inlet, thereby realizing the self-circulation of the wastewater to be treated.

[0020] According to the present invention, the first salt outlet can also be connected to the first salt inlet through the setting of a branch, thereby realizing the self-circulation of the alkali solution.

[0021] According to the present invention, in application, it is possible to choose whether to allow the alkali solution to self-circulate or to pass it into a secondary electrodialysis unit for further treatment, depending on actual needs.

[0022] In some preferred embodiments of the present invention, the primary electrodialysis apparatus includes a primary cathode chamber formed between the first cathode plate and the first cation membrane, a primary anode chamber formed between the first anode plate and the second cation membrane, at least one alkali chamber adjacent to the primary cathode chamber, at least one alkali chamber adjacent to the primary anode chamber, and at least one set of alkali chambers and deacidification chambers alternately arranged between the at least one alkali chamber and the at least one alkali chamber.

[0023] The first water inlet is connected to the deacidification chamber, and the first alkali inlet is connected to the alkali chamber.

[0024] In some preferred embodiments of the present invention, the primary electrodialysis apparatus includes a primary cathode chamber formed between the first cathode plate and the first cation membrane, a primary anode chamber formed between the first anode plate and the second cation membrane, one alkali chamber adjacent to the primary cathode chamber, two alkali chambers adjacent to the primary anode chamber, and at least one set of alkali chambers and deacidification chambers alternately arranged between the one alkali chamber and the two alkali chambers.

[0025] The first water inlet is connected to the deacidification chamber, and the first alkali inlet is connected to the alkali chamber.

[0026] In some preferred embodiments of the present invention, the secondary electrodialysis apparatus includes a secondary cathode chamber formed between the second cathode plate and the second membrane stack, a secondary anode chamber formed between the second anode plate and the second membrane stack, and at least one set of alkali chambers, salt chambers, and acid chambers alternately formed between the secondary cathode chamber and the secondary anode chamber.

[0027] The second salt inlet is connected to both the alkali chamber and the salt chamber, and the second water inlet is connected to the acid chamber.

[0028] According to the present invention, the second salt outlet can be connected to the second salt inlet, thereby realizing the self-circulation of the alkali solution.

[0029] In some preferred embodiments of the present invention, the first cation membrane and the second cation membrane are selected from perfluorosulfonic acid membranes.

[0030] In some preferred embodiments of the present invention, the third cation exchange membrane is selected from homogeneous ion exchange membranes.

[0031] In some preferred embodiments of the present invention, the first anion membrane and the second anion membrane are selected from homogeneous ion exchange membranes.

[0032] In some preferred embodiments of the present invention, the first bipolar membrane and the second bipolar membrane are selected from bipolar membranes.

[0033] According to the present invention, the bipolar membrane is a conventional membrane used in the art, and those skilled in the art can select it according to the characteristics of the water to be treated, the treatment volume and other requirements. The present invention does not impose too many restrictions on this.

[0034] According to the present invention, the bipolar membrane may be ASTOM's BP-1E or LANCYTOM's BP-2.

[0035] According to the present invention, both the anode plate and the cathode plate can be conventional products in the field of electrodialysis.

[0036] According to the present invention, the perfluorosulfonic acid membrane and the primary homogeneous ion exchange membrane described herein are all conventional membranes used in the art. Those skilled in the art can select them according to the characteristics of the water to be treated, the treatment capacity and other requirements. The present invention does not impose too many restrictions on this.

[0037] In some preferred embodiments of the present invention, the acid chamber of the secondary electrodialysis device is filled with anion exchange resin and / or cation exchange resin.

[0038] In some preferred embodiments of the present invention, the acid chamber of the secondary electrodialysis device is filled with anion exchange resin and cation exchange resin.

[0039] In some preferred embodiments of the present invention, the filling volume ratio of the anion exchange resin and the cation exchange resin is (1-5):1, preferably (1.5-2):1.

[0040] In some preferred embodiments of the present invention, the acid chamber of the secondary electrodialysis device is filled with gel-type anion exchange resin and gel-type cation exchange resin.

[0041] In some preferred embodiments of the present invention, the filling volume ratio of the gel-type anion exchange resin and the gel-type cation exchange resin is (1-5):1, preferably (1.5-2):1.

[0042] According to the present invention, both the anion exchange resin and the cation exchange resin are conventional resins used in the art, and those skilled in the art can make conventional selections according to actual needs. A preferred embodiment is that the anion exchange resin is selected from one or more resins such as Purolite and Rohm and Haas; and / or the cation exchange resin is selected from one or more resins such as Purolite and Rohm and Haas.

[0043] To achieve the second objective mentioned above, the technical solution adopted by the present invention is as follows:

[0044] A method for treating wastewater containing organic acids using the treatment system described in any of the above embodiments includes:

[0045] S1. Alkali solution is introduced into the first alkali inlet and wastewater containing organic acid is introduced into the first water inlet, thereby obtaining wastewater recovery liquid at the first water outlet and salt recovery liquid at the first salt outlet, so that part of the alkali solution recovery liquid is recycled to the first alkali inlet.

[0046] S2. The remaining portion of the salt-containing recovery solution is introduced into the second salt inlet, and water is introduced into the second water inlet, thereby obtaining an organic acid recovery solution at the second acid outlet, an inorganic salt solution at the second salt outlet, and an alkali solution at the third alkali outlet.

[0047] According to the present invention, in steps S1 and S2, the amount of alkali entering the first inlet and the second salt inlet is determined according to the process concentration requirements.

[0048] In some preferred embodiments of the present invention, the operating parameters of the primary electrodialysis device include: an operating temperature of 5°C to 30°C, and / or an operating voltage of 5V to 100V, and / or a current density of 1mA / cm². 2 ~30mA / cm 2 .

[0049] In some preferred embodiments of the present invention, the operating parameters of the secondary electrodialysis device include: an operating temperature of 5°C to 30°C, and / or an operating voltage of 5V to 100V, and / or a current density of 1mA / cm². 2 ~80mA / cm 2 .

[0050] In some preferred embodiments of the present invention, the alkaline solution is selected from one or more of sodium hydroxide and potassium hydroxide.

[0051] In some preferred embodiments of the present invention, the organic acid in the wastewater contains an organic acid concentration of 0.5 wt% to 5 wt%.

[0052] In some preferred embodiments of the present invention, the flow rates of materials in each level and chamber are the same or different, and each is independently 10L / h to 200L / h.

[0053] In some preferred embodiments of the present invention, the flow rates of any two streams of material in each stage and chamber are controlled to differ from each other by less than 10%, preferably less than 5%.

[0054] In some preferred embodiments of the present invention, the flow rate of materials in each level and chamber is controlled to be the same.

[0055] The beneficial effects of this invention are at least in the following aspects:

[0056] (1) A typical repeating unit in a conventional electrodialysis apparatus consists of one cation exchange membrane, one anion exchange membrane, and two compartments. Its function is to simultaneously concentrate and desalinate the saline solution. However, conventional electrodialysis apparatuses are very inefficient at removing organic acids from Fischer-Tropsch water. Compared to conventional electrodialysis desalination, the current density for removing organic acids from Fischer-Tropsch water is only 10% to 30% of that for inorganic salt removal. Because only ionized components can migrate across the ion exchange membrane under the influence of current during electrodialysis, the main factor affecting the deacidification efficiency of Fischer-Tropsch solution is ionic strength, i.e., the degree of dissociation of organic acids. In this invention, a single-stage electrodialysis apparatus with a specific structure is used for the deacidification of Fischer-Tropsch water. The method involves using OH... - The cations are selectively added to the Fischer-Tropsch water system for neutralization without introducing other cations. OH- is added. - After ionization, H+ in Fischer-Tropsch water + With OH - A stable covalent compound, H₂O, is formed, and a large amount of organic acid anions are released, thereby increasing the dissociation intensity of the organic acid and causing it to migrate out of the desalination chamber as the main current carrier. Therefore, the device or process provided by this invention can effectively improve the organic acid removal efficiency per unit membrane of a primary electrodialysis unit. Specifically, without affecting the acid removal rate, the organic acid removal current density in anion exchange membrane electrodialysis can be increased to more than twice that of conventional electrodialysis.

[0057] (2) The present invention uses a two-stage electrodialysis device with a specific structure for acid-base regeneration of organic acid salts. The repeatable membrane stack of this two-stage electrodialysis device adopts a three-compartment bipolar membrane / anion membrane / cation membrane structure. The acid chamber is filled with ion exchange resin, so that the resin is evenly distributed in the acid chamber, which acts as a salt bridge for organic acid solution to adsorb and transfer ions in the solution, improve the conductivity and ion migration ability of the solution, and effectively reduce the power consumption of the system.

[0058] (3) Organic acids in wastewater are removed by a combination of primary and secondary electrodialysis units. The primary electrodialysis unit consists of two compartments that respectively deacidify Fischer-Tropsch water and concentrate and reduce the corresponding organic acid salts. The concentrated organic acid salts are continuously regenerated into corresponding organic acids and organic bases by the secondary electrodialysis unit. The generated organic bases are used in situ in the primary electrodialysis unit as OH-. - The process involves the efficient removal of organic acids from Fischer-Tropsch water, with the organic acids being recovered as a byproduct. This invention not only efficiently removes organic acids from Fischer-Tropsch water, but also eliminates the need for additional chemical additives.

[0059] (4) Due to the high investment cost of bipolar membranes, another beneficial effect of the first-stage electrodialysis device in this invention is that the organic acid salt wastewater can be reduced to less than 20% of the total water volume before entering the second-stage electrodialysis device, thereby reducing the treatment scale of the second-stage electrodialysis device and further reducing investment and operating costs. Attached Figure Description

[0060] Figure 1 This is an internal configuration diagram of the primary electrodialysis device in Embodiment 1 of the present invention.

[0061] Figure 2 This is an internal configuration diagram of the secondary electrodialysis device in Embodiment 1 of the present invention.

[0062] Figure 3 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0063] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited to the following description.

[0064] In the following embodiments, unless otherwise specified, the first cathode plate is a graphite electrode plate; the first anode plate is a titanium-coated ruthenium-iridium electrode plate (Machnetto electrodialysis electrode plate); the first cation membrane is a perfluorosulfonic acid ion exchange membrane; the second cation membrane is a perfluorinated ion exchange membrane; the first anion membrane is a homogeneous ion exchange membrane; the first bipolar membrane is a conventional bipolar membrane (ASTOM's BP-1E); the second bipolar membrane is the same as the first bipolar membrane; the third cation membrane is a homogeneous ion exchange membrane; and the second anion membrane is a homogeneous ion exchange membrane; the anion exchange resin is a gel-type resin; and the cation exchange resin is a gel-type resin. The electrode plate and membrane dimensions are 75*195mm.

[0065] In the following embodiments, unless otherwise specified, the alkaline solution refers to a 6 wt% sodium hydroxide solution; the organic acid in the Fischer-Tropsch water (i.e., FT water) has a mass concentration of approximately 0.8 wt%, and its specific types and contents are shown in Table 1; the water used in the secondary electrodialysis device refers to deionized water.

[0066] Table 1

[0067]

[0068] Example 1

[0069] The processing system used in this embodiment includes a primary electrodialysis unit and a secondary electrodialysis unit, wherein,

[0070] like Figure 1As shown, the primary electrodialysis device includes a first cathode plate, a first anode plate, a first cation membrane (K) adjacent to the first cathode plate, a second cation membrane (K) adjacent to the first anode plate, and a first membrane stack consisting of 20 first anion membranes (A) disposed between the first cation membrane (K) and the second cation membrane (K). A primary cathode chamber is formed between the first cathode plate and the first cation membrane (K), and a primary anode chamber is formed between the first anode plate and the second cation membrane (K). Twelve primary alkali chambers and nine primary deacidification chambers are formed in the first membrane stack. The distribution of the alkali chambers and deacidification chambers along the direction from the first cathode plate to the first anode plate is as follows: alkali chamber, alkali chamber, deacidification ...

[0071] like Figure 2 As shown, the secondary electrodialysis device includes a second cathode plate, a second anode plate, and a second membrane stack disposed between the second cathode plate and the second anode plate. A secondary cathode chamber is formed between the second cathode plate and the second membrane stack, and a secondary anode chamber is formed between the second anode plate and the second membrane stack. The second membrane stack includes 10 repeating units composed of a first bipolar membrane (BP), a second bipolar membrane (BP), a cation exchange membrane (K), and an anion exchange membrane (A). In each repeating unit, a secondary alkaline chamber is formed between the first bipolar membrane (BP) and the cation exchange membrane (K), a secondary salt chamber is formed between the cation exchange membrane (K) and the anion exchange membrane (A), and a secondary acid chamber is formed between the anion exchange membrane (A) and the second bipolar membrane (BP).

[0072] The primary electrodialysis unit is equipped with a first water inlet, a first alkali inlet, a first water outlet, and a first brine outlet. The secondary electrodialysis unit is equipped with a second water inlet, a second brine inlet, a second acid outlet, a second brine outlet, and a third alkali outlet. The first brine outlet is connected to both the first and second alkali inlets. The first water outlet is connected to the first water inlet. The second alkali outlet is connected to both the first and second alkali inlets.

[0073] The secondary acid chamber is filled with anion exchange resin and cation exchange resin, wherein the volume ratio of anion exchange resin to cation exchange resin is 1.5:1.

[0074] The Fischer-Tropsch water was treated using the above-mentioned treatment system. The mass concentration of organic acids in the Fischer-Tropsch water was approximately 0.8 wt%, and the specific types and contents are shown in Table 1.

[0075] Both the primary and secondary electrodialysis units employ a partial circulation operation mode. A portion of the alkali solution is recirculated from the first salt outlet to the first alkali inlet. A small portion of the primary alkali chamber outlet is bypassed to the secondary salt chamber, serving as overflow of the failed alkali solution from the primary electrodialysis unit and as replenishment of the organic acid salt feed solution for the secondary electrodialysis unit. This solution then enters the secondary salt chamber for acid-base preparation. The alkali solution prepared in the secondary bipolar membrane electrodialysis alkali chamber is bypassed to the inlet of the primary electrodialysis alkali chamber, serving as overflow of the secondary alkali solution and as replenishment of the primary alkali solution.

[0076] Specifically, an alkaline solution is introduced into the primary alkaline chamber of the primary electrodialysis unit, and Fischer-Tropsch water filtered through a 50-mesh security filter is introduced into the primary deacidification chamber of the primary electrodialysis unit, so that the Fischer-Tropsch water circulates within the primary electrodialysis unit, and a portion of the alkaline solution circulates within the primary electrodialysis unit, while the other portion of the alkaline solution enters the secondary electrodialysis unit.

[0077] Deionized water is introduced into the secondary acid chamber of the secondary electrodialysis unit, thereby obtaining alkali recovery solution at the outlet of the secondary alkali chamber, organic acid recovery solution at the outlet of the secondary acid chamber, organic salt recovery solution at the outlet of the secondary salt chamber, and Fischer-Tropsch water recovery solution at the outlet of the primary deacidification chamber, so that the alkali recovery solution is recycled to the primary alkali chamber.

[0078] The operating parameters for controlling the primary electrodialysis unit are: temperature 25℃, current density 20mA / cm³. 2 The operating parameters for the secondary electrodialysis unit are: temperature 25℃, current density 20mA / cm³. 2 The flow rate of materials in each level and chamber is controlled at 40L / h.

[0079] After the system ran for 1 hour, the content of organic acids in the Fischer-Tropsch water recovery solution and the organic acid recovery solution was measured, and the results are shown in Table 2.

[0080] Table 2

[0081] project Fischer Water Fischer-Tropsch water recovery solution Organic acid recovery liquid Formic acid (mg / L) 196 — 490 Acetic acid (mg / L) 6385 638 14368 Propionic acid (mg / L) 1192 145 2618 Butyric acid (mg / L) 457 39 1044 Valeric acid (mg / L) 210 — 525

[0082] According to the data in Table 2, the content of organic acids in the Fischer-Tropsch water recovery solution is about 0.08 wt%. It can be seen that the two-stage electrodialysis system of the present invention can achieve a removal rate of more than 90% of organic acids in Fischer-Tropsch water.

[0083] Example 2

[0084] Example 2 uses the treatment system from Example 1 and treats Fischer-Tropsch water in essentially the same manner as in Example 1, except that the current density of the primary and secondary electrodialysis units is adjusted to 10 mA / cm². 2 The results showed that it took approximately 2 hours of removal to reduce the organic acid content in the Fischer-Tropsch water recovery solution to about 0.08 wt%.

[0085] Example 3

[0086] Example 3 uses the treatment system from Example 1 and treats Fischer-Tropsch water in essentially the same manner as in Example 1, except that the current density of the primary and secondary electrodialysis units is adjusted to 15 mA / cm². 2 The results showed that it took approximately 1.5 hours of removal to reduce the organic acid content in the Fischer-Tropsch water recovery solution to about 0.08 wt%.

[0087] Example 4

[0088] The treatment system used in Example 4 differs from that in Example 1 only in that the number of first anion membranes (A) is 20. This results in the following distribution of the alkali chamber and deacidification chamber along the direction from the first cathode plate to the first anode plate: alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber, deacidification chamber, alkali chamber. Under operating conditions identical to those in Example 1, the results show that it takes approximately 0.5 hours of deacidification to reduce the organic acid content in the Fischer-Tropsch water recovery solution to approximately 0.08 wt%.

[0089] Comparative Example 1

[0090] Comparative Example 1 employs a single-stage electrodialysis process. Specifically, the electrodialysis device used in this process is a conventional two-compartment electrodialysis device with alternating anion and cation membranes. More specifically, this conventional two-compartment electrodialysis device includes a cathode plate, an anode plate, and a membrane stack disposed between the cathode plate and the anode plate. The membrane stack includes 10 repeating units composed of cation and anion membranes to form alternating acid and deacidification chambers within the membrane stack.

[0091] The conventional two-compartment electrodialysis apparatus was used to treat Fischer-Tropsch water. Specifically, the organic acid receiving solution was introduced into the acid chamber at the same flow rate as in Example 1, and the Fischer-Tropsch water filtered through a 50-mesh security filter was introduced into the deacidification chamber at the same flow rate as in Example 1. The operating temperature of the apparatus was the same as in Example 1.

[0092] The results showed that the current density in this conventional two-compartment electrodialysis device was significantly reduced to 2 mA / cm². 2 ~5mA / cm 2 This reduces the amount of Fischer-Tropsch water treated per unit membrane area per unit time.

[0093] Comparative Example 2

[0094] The processing system used in Comparative Example 2 differs from that in Example 1 in that the resin content in the bipolar membrane electrodialysis is adjusted so that there is no resin filling in the secondary electrodialysis.

[0095] The results showed that the current density in the bipolar membrane electrodialysis device was significantly reduced to 10 mA / cm². 2 .

[0096] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A wastewater treatment system containing organic acids, comprising a primary electrodialysis unit and a secondary electrodialysis unit, wherein, The primary electrodialysis device includes a first cathode plate, a first anode plate, a first cation membrane adjacent to the first cathode plate, a second cation membrane adjacent to the first anode plate, and a first membrane stack consisting of at least four first anion membranes disposed between the first cation membrane and the second cation membrane. The secondary electrodialysis device includes a second cathode plate, a second anode plate, and a second membrane stack disposed between the second cathode plate and the second anode plate. The second membrane stack includes at least one set of repeating units composed of a first bipolar membrane, a third cation membrane, and a second anion membrane arranged sequentially along the direction from the second cathode plate to the second anode plate, and a second bipolar membrane adjacent to the second anode plate. The primary electrodialysis device is provided with a first water inlet, a first alkali inlet, a first water outlet, and a first salt outlet. The secondary electrodialysis device is provided with a second water inlet, a second salt inlet, a second acid outlet, a second salt outlet, and a third alkali outlet. The first salt outlet is connected to the second salt inlet.

2. The processing system according to claim 1, characterized in that, The primary electrodialysis apparatus includes a primary cathode chamber formed between the first cathode plate and the first cation membrane, a primary anode chamber formed between the first anode plate and the second cation membrane, at least one alkali chamber adjacent to the primary cathode chamber, at least one alkali chamber adjacent to the primary anode chamber, and at least one set of alkali chambers and deacidification chambers alternately arranged between the at least one alkali chamber adjacent to the primary cathode chamber and the at least one alkali chamber adjacent to the primary anode chamber. The first water inlet is connected to the deacidification chamber, and the first alkali inlet is connected to the alkali chamber.

3. The processing system according to claim 2, characterized in that, The primary electrodialysis device includes a primary cathode chamber formed between the first cathode plate and the first cation membrane, a primary anode chamber formed between the first anode plate and the second cation membrane, one alkali chamber adjacent to the primary cathode chamber, two alkali chambers adjacent to the primary anode chamber, and at least one set of alkali chambers and deacidification chambers alternately arranged between the one alkali chamber and the two alkali chambers.

4. The processing system according to any one of claims 1-3, characterized in that, The secondary electrodialysis apparatus includes a secondary cathode chamber formed between the second cathode plate and the second membrane stack, a secondary anode chamber formed between the second anode plate and the second membrane stack, and at least one set of alkali chambers, salt chambers, and acid chambers alternately formed between the secondary cathode chamber and the secondary anode chamber. The second salt inlet is connected to the salt chamber, and the second water inlet is connected to the acid chamber and the alkali chamber.

5. The processing system according to any one of claims 1-3, characterized in that, The first cation exchange membrane and the second cation exchange membrane are selected from perfluorosulfonic acid membranes; and / or The third cation exchange membrane is selected from homogeneous ion exchange membranes; and / or The first anion exchange membrane and the second anion exchange membrane are selected from homogeneous ion exchange membranes; and / or The first bipolar membrane and the second bipolar membrane are selected from bipolar membranes.

6. The processing system according to any one of claims 1-3, characterized in that, The acid chamber of the secondary electrodialysis device is filled with anion exchange resin and / or cation exchange resin.

7. The processing system according to claim 6, characterized in that, The acid chamber of the secondary electrodialysis device is filled with anion exchange resin and cation exchange resin.

8. The processing system according to claim 7, characterized in that, The filling volume ratio of the anion exchange resin to the cation exchange resin is (1~5):

1.

9. The processing system according to claim 8, characterized in that, The volume ratio of the anion exchange resin to the cation exchange resin is (1.5~2):

1.

10. A method for treating wastewater containing organic acids using the treatment system according to any one of claims 1-9, comprising: S1. Alkali solution is introduced into the first alkali inlet and wastewater containing organic acid is introduced into the first water inlet, thereby obtaining wastewater recovery liquid at the first water outlet and salt recovery liquid at the first salt outlet, and causing part of the salt recovery liquid to be recycled back to the first alkali inlet. S2. The remaining portion of the salt-containing recovery solution is introduced into the second salt inlet, and water is introduced into the second water inlet, thereby obtaining an organic acid recovery solution at the second acid outlet, an inorganic salt solution at the second salt outlet, and an alkali solution at the third alkali outlet.

11. The method according to claim 10, characterized in that, The operating parameters of the primary electrodialysis device include: operating temperature of 5℃~30℃, and / or operating voltage of 5V~100V, and / or current density of 1mA / cm². 2 ~30mA / cm 2 ; and / or The operating parameters of the secondary electrodialysis device include: operating temperature of 5℃~30℃, and / or operating voltage of 5V~100V, and / or current density of 1mA / cm². 2 ~80mA / cm 2 .

12. The method according to claim 10, characterized in that, The alkaline solution is selected from one or more of sodium hydroxide and potassium hydroxide; and / or the organic acid in the wastewater containing organic acid has a mass concentration of 0.5wt% to 5wt%.

13. The method according to claim 10, characterized in that, The flow rates of materials in each level and chamber may be the same or different, and each is independently 10L / h to 200L / h.

14. The method according to claim 13, characterized in that, The flow rates of any two materials in each level and chamber should differ by less than 10%.

15. The method according to claim 14, characterized in that, Control the flow rate of any two materials in each level and chamber to be less than 5% different from each other.

16. The method according to claim 10, characterized in that, Control the flow rate of materials in all levels and chambers to be the same.

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