Method for purifying ethylene glycol solution and membrane separation device and application thereof

Abstract

This invention relates to the field of ethylene glycol purification technology, and discloses a method for purifying ethylene glycol solutions, a membrane separation device, and its application. The purification method includes: (1) purifying the ethylene glycol solution feed, wherein the purification system includes a membrane separation device consisting of a booster pump and a first membrane module, the first membrane module including at least membrane groups I-1, I-2, and I-3, for retaining ethylene glycol and metal ions; (2) concentrating the obtained primary concentrate from the purification system, wherein the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1, and a membrane separation component II-2, wherein membrane II-2 retains one or more of monovalent, divalent, and trivalent ions, to obtain purified ethylene glycol solution. This method is energy-saving and easy to implement, suitable for purifying low-concentration ethylene glycol solutions, and has very good industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of ethylene glycol purification technology, specifically to a method for purifying ethylene glycol solutions, a membrane separation device, and its application. Background Technology

[0002] Ethylene glycol, also known as glycol, abbreviated as EG, with the chemical formula (CH2OH)2, is a colorless, transparent, viscous liquid with a sweet taste and hygroscopic properties. It is the simplest aliphatic diol, possessing the chemical properties of alcohols and capable of forming ethers, esters, aldehydes, and acids. Therefore, it can be used as a raw material for the production of polyester resins, alkyd resins, and polyester fibers, and can be used to synthesize high molecular weight compounds such as polyester fibers. Furthermore, it can be used as a raw material for pharmaceuticals and plastics, as well as a high-boiling-point solvent in the production of cosmetics and explosives. In industrial production, it can replace glycerin. It is soluble in water and miscible with water in any proportion. After mixing, the freezing point is significantly lowered due to the change in the vapor pressure of the cooling water, thus it can be used as an antifreeze in automobiles and a refrigerant in aircraft engines. Ethylene glycol is a basic organic chemical raw material with a wide range of applications. In addition, ethylene glycol can also be used directly as a solvent in dyes, inks, and other products, as well as as a lubricant in products such as cellophane, fibers, and leather.

[0003] Ethylene glycol production methods mainly fall into two categories. The first category involves coal chemical routes, including direct synthesis (using CO and H2 to directly synthesize ethylene glycol) and indirect synthesis (formaldehyde carbonylation, formaldehyde condensation, and oxalate ester synthesis). The second category utilizes petrochemical processes, primarily including ethylene oxide hydration and ethylene carbonate catalytic processes.

[0004] In the production and concentration of ethylene glycol, various metal catalysts are inevitably used, and pipeline transportation is employed. During this process, metal ions frequently become contaminated in the aqueous solution of ethylene glycol. These metal ions cannot be separated during the evaporation and concentration of ethylene glycol, making them a difficult-to-remove impurity. Based on the current usage of ethylene glycol recovery systems both domestically and internationally, for divalent metal ions (such as Ca²⁺)... 2+ Mg 2+ Common methods for removing ethylene glycol (such as NaCl) involve precipitation, but precipitation methods have certain requirements regarding ion concentration. For monovalent salts (such as NaCl), flash evaporation is commonly used, but this process requires very high energy consumption. This invention provides a novel method for purifying ethylene glycol aqueous solutions, different from existing publicly available technologies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies that typically use azeotropic distillation to purify salt-containing impurities in ethylene glycol aqueous solutions, which has the drawback of excessive energy consumption. This invention provides a purification method for ethylene glycol solutions, a membrane separation device, and its application. This purification method is simple, easy to implement, and has low energy consumption, and it can effectively remove metal ions from ethylene glycol solutions.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for purifying an ethylene glycol solution, wherein the purification method includes:

[0007] (1) The ethylene glycol solution is fed into a purification system for purification treatment. The purification system includes a membrane separation device consisting of a booster pump and a first membrane module. The first membrane module includes at least three-stage membrane separation groups: membrane group I-1, membrane group I-2, and membrane group I-3. The membranes of membrane groups I-1, I-2, and I-3 may be the same or different, and each is a first nanofiltration membrane. The first nanofiltration membrane retains ethylene glycol and metal ions in the ethylene glycol solution. The first-stage concentrate and purified solution of the purification system are obtained.

[0008] (2) The first-stage concentrate of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1, and a second membrane module. The second membrane module includes a membrane separation component II-2 membrane, which is a second nanofiltration membrane. The second nanofiltration membrane does not retain ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent, divalent, and trivalent ions to obtain a clear liquid containing purified ethylene glycol.

[0009] A second aspect of the present invention provides a membrane separation device, wherein the membrane separation device includes a purification system and a concentration system connected in sequence, wherein the purification system includes a membrane separation device consisting of a booster pump and a first membrane module, the first membrane module including at least three-stage membrane separation groups I-1, I-2 and I-3; and the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1 and a second membrane module II-2.

[0010] A third aspect of the present invention provides an application of the aforementioned membrane separation device in a method for purifying ethylene glycol solutions.

[0011] The above technical solution, employing nanofiltration membranes with different rejection rates for impurities in ethylene glycol solutions and a rational combination of processes, achieves the removal and purification of impurities in ethylene glycol solutions with a high recovery rate. Compared to traditional evaporation methods for purifying ethylene glycol solutions, the method of this invention is energy-saving, easy to implement, and suitable for purifying low-concentration ethylene glycol solutions. It has excellent prospects for industrial application. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the purification system in the membrane separation device of the present invention;

[0013] Figure 2 This is a schematic diagram of the concentration system in the membrane separation device of the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] I-1-I-1 membrane group; I-2-I-2 membrane group; I-3-I-3 membrane group;

[0016] II-1 - Circulating concentrate tank; II-2 - Membrane separation component II-2 membrane. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] As mentioned above, the first aspect of the present invention provides a method for purifying an ethylene glycol solution, wherein the purification method includes:

[0019] (1) The ethylene glycol solution is fed into a purification system for purification treatment. The purification system includes a membrane separation device consisting of a booster pump and a first membrane module. The first membrane module includes at least three-stage membrane separation groups: membrane group I-1, membrane group I-2, and membrane group I-3. The membranes of membrane groups I-1, I-2, and I-3 may be the same or different, and each is a first nanofiltration membrane. The first nanofiltration membrane retains ethylene glycol and metal ions in the ethylene glycol solution. The first-stage concentrate and purified solution of the purification system are obtained.

[0020] (2) The first-stage concentrate of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1, and a second membrane module. The second membrane module includes a membrane separation component II-2 membrane, which is a second nanofiltration membrane. The second nanofiltration membrane does not retain ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent, divalent, and trivalent ions to obtain a clear liquid containing purified ethylene glycol.

[0021] The inventors of this invention discovered that existing technologies for purifying salt-containing impurities in ethylene glycol aqueous solutions typically employ azeotropic distillation, which suffers from excessive energy consumption, especially when the water content in the ethylene glycol solution is high, making it uneconomical and energy-intensive. Based on this, the inventors of this invention discovered that by employing the purification and concentration systems of this invention, both systems utilize membrane separation devices. Specifically, the first membrane module in the purification system retains ethylene glycol and metal ions in the ethylene glycol solution, yielding a primary concentrate and a purified solution. Preferably, this concentrate has a rejection rate of 20% or higher for ethylene glycol and a rejection rate of 98% or higher for metal ions. The second membrane module in the concentration system has no rejection rate for ethylene glycol but retains one or more of monovalent, divalent, and trivalent ions. Preferably, it has a rejection rate of 98% or higher for high-valent metal ions (divalent or trivalent ions) and a rejection rate of 50% or higher for monovalent ions. This allows for the continuous concentration of ethylene glycol. In summary, this invention employs a combination of two membrane modules, a first membrane module and a second membrane module, to achieve the purification and concentration of ethylene glycol.

[0022] According to the present invention, the clarified liquid separated by membrane group I-1 enters membrane group I-2 as feed, and the concentrate of membrane group I-1 is used as the first-stage concentrate of the purification system; the clarified liquid of membrane group I-2 is used as feed of membrane group I-3; the concentrate of membrane group I-2 is returned to the feed of membrane group I-1; the clarified liquid of membrane group I-3 is used as purified liquid, and the concentrate of membrane group I-3 is returned to the feed of membrane group I-1.

[0023] According to the present invention, the first nanofiltration membrane is an organic solvent resistant nanofiltration membrane; the first nanofiltration membrane is selected from one or more of HTRO01-8040, HTRO02-8040, HTRO01-4040 and HTRO02-4040; in the present invention, the first nanofiltration membrane can maintain its separation capability for a long time in the environment of ethylene glycol solution, and can have a rejection rate of 20% or more for ethylene glycol in the ethylene glycol solution, and a rejection rate of more than 98% for metal ions in the ethylene glycol solution.

[0024] According to the present invention, the second nanofiltration membrane is selected from one or more of HTNF01-8040, HTNF02-8040, HTNF01-4040 and HTNF02-4040; in the present invention, the second nanofiltration membrane has no rejection rate for ethylene glycol in the ethylene glycol solution, a rejection rate of 98% or more for divalent or trivalent ions in the ethylene glycol solution, and a rejection rate of 50% or more for monovalent ions in the ethylene glycol solution.

[0025] In this invention, the parameters of the first nanofiltration membrane are shown in Table I.

[0026] Table I

[0027]

[0028]

[0029] In this invention, the parameters of the second nanofiltration membrane are shown in Table II.

[0030] Table II

[0031]

[0032] According to the present invention, the ethylene glycol solution is an aqueous solution of ethylene glycol containing metal ion impurities. Specifically, the ethylene glycol solution comprises ethylene glycol, water, and a metal salt. In this invention, the purpose of purification is to remove these metal salt impurities. Preferably, the metal salt is selected from one or more of metal sulfates, chlorides, nitrates, and phosphates. More preferably, the metal is selected from one or more of iron, aluminum, calcium, magnesium, sodium, lithium, manganese, and copper. Even more preferably, the metal is magnesium and / or sodium. In this invention, the impurities in the ethylene glycol solution that need to be treated are usually not too complex, typically being one or more common salts of magnesium sulfate, sodium chloride, and sodium nitrate. Therefore, it is only necessary to remove these salt impurities, usually only salts that can be retained by the membrane.

[0033] According to the present invention, the concentration of ethylene glycol in the ethylene glycol solution is 0.01-10%, preferably 3-10%.

[0034] According to the present invention, the content of the metal salt relative to 1L of the ethylene glycol solution is 10-10000mg, preferably 10-5000mg. In the present invention, the content of the metal salt should not be too high, as this would prevent separation. The content of the metal salt should not exceed 1%, that is, relative to 1L of the ethylene glycol solution, the content of the metal salt should not exceed 10000mg.

[0035] According to the present invention, the temperature of the ethylene glycol solution is 15-50°C, preferably 15-35°C.

[0036] According to the present invention, the working pressure of the purification system is ≤2 MPa, preferably 0.6-1.5 MPa.

[0037] According to the present invention, the working pressure of the concentration system is ≤2.5 MPa, preferably 1-2 MPa.

[0038] According to the present invention, the single-stage recovery rate is controlled between 60% and 80%. It should be noted that "single-stage recovery rate" refers to the ratio of the flow rate entering the membrane module to the amount of clarified liquid exiting the membrane module. Controlling the recovery rate is to prevent the concentrate flow rate from being too low, which could lead to the deposition of contaminants on the membrane module.

[0039] According to the present invention, the purification of ethylene glycol solution first requires the removal of metal ions from the solution. Since the first nanofiltration membrane has a metal ion rejection rate of only 98%, multi-stage filtration is required to thoroughly remove metal ions from the ethylene glycol solution. In the present invention, the purification system includes a membrane separation device consisting of a booster pump and a first membrane module, wherein the first membrane module includes at least three-stage membrane separation groups: membrane group I-1, membrane group I-2, and membrane group I-3.

[0040] Specifically, in this invention, the purification method includes:

[0041] In step (1):

[0042] (1-1) The ethylene glycol solution is fed through the I-1 membrane module of the purification system for filtration to obtain clear liquid 1;

[0043] (1-2) The clear liquid 1 is filtered through the I-2 membrane module of the purification system to obtain concentrated liquid 2 and clear liquid 2;

[0044] (1-3) The clear liquid 2 is filtered through the I-3 membrane group of the purification system to obtain concentrated liquid 3 and purified liquid;

[0045] The concentrate 2 and the concentrate 3 are returned to the I-1 membrane module of the purification system for further filtration, with the single-stage recovery rate controlled between 60-80%.

[0046] The concentrate from membrane module I-1 serves as the primary concentrate for the purification system.

[0047] In step (2):

[0048] (2-1) The first-stage concentrate of the purification system is sequentially concentrated through the circulating concentration tank II-1 and the second membrane module. The membrane separation component II-2 in the second membrane module is a second nanofiltration membrane. The second nanofiltration membrane does not retain ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent, divalent, and trivalent ions to obtain a concentrate and a clear liquid containing purified ethylene glycol.

[0049] (2-2) When the TDS in the clarified liquid after purification by the membrane separation component II-2 is less than the TDS in the concentrated liquid after purification by the membrane purification system I-1, the obtained concentrated liquid is returned to the circulating concentrated water tank II-1 for further concentration treatment; wherein, TDS represents the total dissolved solids in the solution;

[0050] In this invention, it should be noted that the membrane separation device has one inlet and two outlets: one for the concentrate and the other for the filtered liquid. Membrane separation cannot simply retain impurities, but it also cannot discard the concentrated portion, as this would waste a lot of material. Therefore, the concentrated portion needs to be returned for further processing. However, if the impurity content is too high, exceeding that of the raw material, it is unnecessary to return it.

[0051] Concentration is stopped when the TDS in the clarified liquid after purification by the membrane separation component II-2 is greater than the TDS in the concentrated liquid after purification by the membrane purification system I-1, and the concentrated liquid is discharged as waste liquid. Similarly, this is to maximize the recovery of ethylene glycol, but concentration can only be achieved to a certain extent.

[0052] In this invention, it should be noted that the concentrate contains impurities, and the clear liquid is an ethylene glycol solution free of impurities.

[0053] According to a preferred embodiment of the present invention, a method for purifying an ethylene glycol solution includes two systems: a purification system and a concentration system.

[0054] In purification systems, such as Figure 1 As shown, Figure 1 This is a schematic diagram of the purification system in the membrane separation device of the present invention. Figure 1 The purified solution obtained from I-3 is used as the final purified product of this invention. In step (1):

[0055] (1-1) The raw material liquid (ethylene glycol solution containing impurities) is filtered through the I-1 membrane module of the purification system to obtain the first-stage concentrated liquid and clear liquid 1 of the purification system; wherein, the first-stage concentrated liquid of the purification system is sent to the circulating concentrated water tank II-1 for concentration treatment.

[0056] (1-2) The clear liquid 1 is filtered through the I-2 membrane module of the purification system to obtain concentrated liquid 2 and clear liquid 2;

[0057] (1-3) The clear liquid 2 is filtered through the I-3 module of the purification system to obtain concentrated liquid 3 and purified liquid. The purified liquid is the final product of the ethylene glycol purified liquid of the present invention.

[0058] The concentrate 2 and the concentrate 3 are returned to the I-1 membrane module of the purification system for further filtration.

[0059] In concentration systems, such as Figure 2 As shown, Figure 2 This is a schematic diagram of the concentration system in the membrane separation device of the present invention. Figure 2 The supernatant obtained from II-2 and Figure 1 The raw material liquids are combined and used as feed I-1 to fully utilize and improve the recovery rate; in step (2):

[0060] (2-1) The first-stage concentrate of the purification system is sequentially concentrated by a membrane separation device consisting of a booster pump, a circulating concentrate tank II-1, and a second membrane module, wherein the second membrane module includes a membrane separation module II-2 membrane, to obtain a concentrate and a clear liquid containing purified ethylene glycol.

[0061] (2-2) When the TDS in the clarified liquid after purification by the membrane separation component II-2 is less than the TDS in the concentrated liquid after purification by the membrane purification system I-1, the obtained concentrated liquid is returned to the circulating concentration tank (II-1) for further concentration treatment; until the TDS in the clarified liquid after purification by the membrane separation component II-2 is greater than the TDS in the concentrated liquid after purification by the membrane purification system I-1, the concentration treatment is stopped, and the concentrated liquid is discharged as waste liquid; and the obtained clarified liquid is reused as feed for the first membrane group I-1 to continue to participate in separation.

[0062] A second aspect of the present invention provides a membrane separation device, wherein the membrane separation device includes a purification system and a concentration system connected in sequence, wherein the purification system includes a membrane separation device consisting of a booster pump and a first membrane module, the first membrane module including at least three-stage membrane separation groups I-1, I-2 and I-3; and the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1 and a second membrane module II-2.

[0063] According to the present invention, the purification system includes at least membrane group I-1, membrane group I-2 and membrane group I-3 connected in sequence, and each of membrane group I-2 and membrane group I-3 has an outlet connected to membrane group I-1.

[0064] According to the present invention, the I-1 membrane assembly is sequentially connected to the circulating concentration tank II-1 in the concentration system and the membrane separation assembly II-2 in the second membrane assembly.

[0065] According to the present invention, the membrane separation assembly II-2 is provided with a clear liquid outlet and an outlet for returning the concentrate to the circulating concentrate tank II-1.

[0066] A third aspect of the present invention provides an application of the aforementioned membrane separation device in a method for purifying ethylene glycol solutions.

[0067] The present invention will be described in detail below through embodiments.

[0068] In the following examples and comparative examples:

[0069] The types and contents of ions in the ethylene glycol solution were determined by ion chromatography. The ion chromatograph used in this invention was purchased from Metrohm 940 Professional IC Vario ONE in Switzerland.

[0070] The ethylene glycol content in the solution was determined by refractive index method. Ethylene glycol aqueous solutions with different concentrations from 0% to 10% were prepared, and their refractive index was measured using a Japanese AT&T refractometer. A linear relationship between concentration and refractive index was constructed. Within this concentration range, the ethylene glycol concentration and refractive index showed a linear relationship. The concentration content was then calculated based on the refractive index value of the test sample.

[0071] The TDS of the ethylene glycol solution was tested using a TDS meter. In this invention, the TDS meter used was purchased from Tokyo Instruments, model TDS530. It should be noted that the TDS value indicates how many milligrams of dissolved solids are dissolved in 1 liter of water. It is an abbreviation for total dissolved solids, also known as total dissolved solids.

[0072] In the experimental examples, ion chromatography was first used to test the types and contents of ions in the ethylene glycol solution. Since ethylene glycol often contains calcium, magnesium, sodium, sulfate, chloride, etc. in normal processes, the test liquid is usually prepared with ion content and ethylene glycol content under common operating conditions in the verification examples.

[0073] The reagents used in the preparation were magnesium sulfate, sodium chloride, and calcium chloride. All three reagents were purchased from a reagent factory in Beijing and were chemically pure.

[0074] Ethylene glycol was purchased from Bailingwei and is chemically pure.

[0075] The concentration values ​​of each component in the drug preparation were obtained by weighing using a balance and calculating by gravimetric method.

[0076] The amount of purified liquid obtained from each experiment and the amount of electricity consumed are calculated as (kWh / ton of water) as the energy consumption required for this separation.

[0077] Example 1

[0078] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0079] In purification systems, such as Figure 1 As shown, in step (1):

[0080] (1-1) The raw material liquid (ethylene glycol solution containing impurities) is filtered through the first stage I-1 membrane module of the purification system to obtain the first stage concentrate and clear liquid 1 of the purification system; wherein, the first stage concentrate of the purification system is sent to the circulating concentration tank II-1 for concentration treatment.

[0081] The feed solution includes magnesium sulfate and ethylene glycol. The content of each component in the feed solution is shown in Table 1-1, as are the purification conditions.

[0082] Table 1-1

[0083]

[0084] (1-2) The clear liquid 1 is filtered through the secondary I-2 membrane module of the purification system to obtain concentrated liquid 2 and clear liquid 2;

[0085] (1-3) The clear liquid 2 is filtered through the three-stage I-3 membrane group of the purification system to obtain concentrated liquid 3 and purified liquid. The purified liquid is the final product of the ethylene glycol purified liquid of the present invention. The components of the obtained purified liquid are shown in Table 1-3.

[0086] The concentrate 2 and the concentrate 3 are returned to the first-stage I-1 membrane module of the purification system for further filtration.

[0087] The nanofiltration membranes of the first-stage I-1 membrane module, the second-stage I-2 membrane module, and the third-stage I-3 membrane module of the purification system are the same, and each is the first membrane module in Table 1-1.

[0088] In concentration systems, such as Figure 2 As shown, in step (2):

[0089] (2-1) The primary concentrate of the purification system is sequentially concentrated through the circulating concentration tank II-1 and the membrane separation component II-2, wherein the membrane separation component II-2 has a built-in nanofiltration membrane system, and the nanofiltration membrane is the second membrane component.

[0090] Specifically, when the TDS in the clarified liquid of membrane separation component II-2 is lower than the TDS in the primary concentrate of the purification system, the resulting concentrate is returned to the circulating concentration tank II-1 for further concentration. Concentration is stopped when the TDS in the clarified liquid of membrane separation component II-2 is greater than the TDS in the primary concentrate of the purification system. The clarified liquid obtained during this process is combined with the feed liquid and used as the feed for the first-stage membrane group I-1. The content of each component in the feed liquid and the purification conditions are shown in Table 1-1. The indicators of the discharged concentrate are shown in Table 1-2, and the purified liquid is shown in Table 1-3.

[0091] The energy required for this experiment is 2.2 kWh / ton of water.

[0092] Table 1-2

[0093]

[0094] Table 1-3

[0095]

[0096]

[0097] Example 2

[0098] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0099] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the content of each component in the raw material solution and the purification conditions are shown in Table 2-1, the concentrated solution obtained after treatment and the concentration conditions are shown in Table 2-2, and the purified solution is shown in Table 2-3.

[0100] The energy required for this experiment is 1.7 kWh / ton of water.

[0101] Table 2-1

[0102]

[0103] Table 2-2

[0104]

[0105] Table 2-3

[0106]

[0107] Example 3

[0108] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0109] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the content of each component in the raw material solution and the purification conditions are shown in Table 3-1, the concentrated solution obtained after processing and the concentration conditions are shown in Table 3-2, and the purified solution is shown in Table 3-3.

[0110] The energy required for this experiment is 2.4 kWh / ton of water.

[0111] Table 3-1

[0112]

[0113] Table 3-2

[0114]

[0115] Table 3-3

[0116]

[0117] Example 4

[0118] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0119] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the content of each component in the raw material solution and the purification conditions are shown in Table 4-1, the concentrated solution obtained after treatment and the concentration conditions are shown in Table 4-2, and the purified solution is shown in Table 4-3.

[0120] The energy required for this experiment is 2.1 kWh / ton of water.

[0121] Table 4-1

[0122]

[0123] Table 4-2

[0124]

[0125] Table 4-3

[0126]

[0127] Example 5

[0128] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0129] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the content of each component in the raw material solution and the purification conditions are shown in Table 5-1, the concentrated solution obtained after processing and the concentration conditions are shown in Table 5-2, and the purified solution is shown in Table 5-3.

[0130] The energy required for this experiment is 1.8 kWh / ton of water.

[0131] Table 5-1

[0132]

[0133] Table 5-2

[0134]

[0135]

[0136] Table 5-3

[0137]

[0138] Example 6

[0139] This embodiment illustrates the purification of an ethylene glycol solution using the membrane separation device of the present invention, resulting in a purified ethylene glycol solution.

[0140] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the content of each component in the raw material solution and the purification conditions are shown in Table 6-1, the concentrated solution obtained after processing and the concentration conditions are shown in Table 6-2, and the purified solution is shown in Table 6-3.

[0141] The energy required for this experiment is 2.0 kWh / ton of water.

[0142] Table 6-1

[0143]

[0144] Table 6-2

[0145]

[0146] Table 6-3

[0147]

[0148] Comparative Example 1

[0149] Comparative Example 1 uses evaporation to purify ethylene glycol, specifically:

[0150] 250 ml of an aqueous solution containing 2.5% wt ethylene glycol and 130 mg / L magnesium sulfate was distilled under reduced pressure at -80 kPa and 141 °C for 30 min. The vapor was collected by condensation and analyzed by ion chromatography to determine the ion and ethylene glycol content in the condensate. The results showed that magnesium sulfate was undetectable in the condensate, and the ethylene glycol content was 2.5%. However, the evaporation method involved high temperature, high energy consumption, and high cost.

[0151] Comparative Example 2

[0152] The ethylene glycol solution was purified using the same purification method as in Example 1, except that the salt content in the raw material solution was higher than that in Example 1.

[0153] In Comparative Example 2, evaporation can be completed and the recovery rate can reach 100%. However, the evaporation method is energy-intensive.

[0154] The content of each component in the raw material liquid and the purification conditions are shown in Table D2-1. The concentrated liquid obtained after treatment and the concentration conditions are shown in Table D2-2. The purified liquid is shown in Table D2-3.

[0155] Table D2-1

[0156]

[0157] Table D2-2

[0158]

[0159] Table D2-3

[0160]

[0161]

[0162] The results above demonstrate that the method of this invention for ethylene glycol purification operates under mild conditions, achieving the removal of metal impurities from aqueous ethylene glycol solutions at room temperature, while also achieving a certain degree of concentration and a high recovery rate. The energy consumption required during the experimental process is low, and further scaling up the treatment scale can result in even lower energy consumption per ton of water treated. Compared to traditional evaporation methods, it is easier to implement on a large scale, more energy-efficient, and represents an advanced method for ethylene glycol purification.

[0163] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying an ethylene glycol solution, characterized in that, The purification method includes: (1) The ethylene glycol solution is fed into a purification system for purification treatment. The purification system includes a membrane separation device consisting of a booster pump and a first membrane module. The first membrane module includes at least three-stage membrane separation groups: membrane group I-1, membrane group I-2, and membrane group I-3. The membranes of membrane group I-1, membrane group I-2, and membrane group I-3 may be the same or different, and each is a first nanofiltration membrane. The first nanofiltration membrane retains ethylene glycol and metal ions in the ethylene glycol solution. The first-stage concentrate and purified solution of the purification system are obtained. (2) The first-stage concentrate of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device consisting of a booster pump, a circulating concentration tank II-1, and a second membrane module. The second membrane module includes a membrane separation component II-2 membrane, which is a second nanofiltration membrane. The second nanofiltration membrane does not retain ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent, divalent, and trivalent ions to obtain a clear liquid containing purified ethylene glycol.

2. The purification method according to claim 1, wherein, The clarified liquid separated by membrane module I-1 enters membrane module I-2 as feed, and the concentrate from membrane module I-1 is used as the primary concentrate of the purification system. The supernatant from membrane module I-2 is used as the feed for membrane module I-3; the concentrate from membrane module I-2 is returned to the feed for membrane module I-1. The supernatant from membrane module I-3 is used as the purification solution, and the concentrate from membrane module I-3 is returned to the feed of membrane module I-1.

3. The purification method according to claim 1, wherein, The first nanofiltration membrane has a rejection rate of 20% or more for ethylene glycol in the ethylene glycol solution and a rejection rate of 98% or more for metal ions in the ethylene glycol solution; And / or, the second nanofiltration membrane has no rejection rate for ethylene glycol in the ethylene glycol solution, a rejection rate of 98% or more for divalent or trivalent ions in the ethylene glycol solution, and a rejection rate of 50% or more for monovalent ions in the ethylene glycol solution.

4. The purification method according to claim 1 or 3, wherein, The first nanofiltration membrane is selected from one or more of HTRO01-8040, HTRO02-8040, HTRO01-4040, and HTRO02-4040; And / or, the second nanofiltration membrane is selected from one or more of HTNF01-8040, HTNF02-8040, HTNF01-4040 and HTNF02-4040.

5. The purification method according to claim 1 or 3, wherein, The concentration of ethylene glycol in the ethylene glycol solution is 0.01-10%.

6. The purification method according to claim 5, wherein, The ethylene glycol solution contains 3-10% ethylene glycol.

7. The purification method according to claim 1 or 3, wherein, The content of the metal ions is 10-10000 mg relative to 1 L of the ethylene glycol solution.

8. The purification method according to claim 7, wherein, The content of the metal ions is 10-5000 mg relative to 1 L of the ethylene glycol solution.

9. The purification method according to claim 1 or 3, wherein, The ethylene glycol solution contains ethylene glycol, water, and a metal salt.

10. The purification method according to claim 9, wherein, The metal salt is selected from one or more of the following: sulfates, chlorides, nitrates, and phosphates of metals.

11. The purification method according to claim 10, wherein, The metal is selected from one or more of iron, aluminum, calcium, magnesium, sodium, lithium, manganese, and copper.

12. The purification method according to claim 1, wherein, The temperature of the ethylene glycol solution is 15-50℃; And / or, the operating pressure of the purification system is ≤2 MPa; And / or, the operating pressure of the concentration system is ≤2.5 MPa.

13. The purification method according to claim 12, wherein, The temperature of the ethylene glycol solution is 15-35℃; And / or, the working pressure of the purification system is 0.6-1.5 MPa; And / or, the operating pressure of the concentration system is 1-2 MPa.

14. The purification method according to claim 1, wherein, The single-stage recovery rate is controlled between 60% and 80%.

15. The purification method according to claim 1, wherein, The purified liquid is then returned to the purification system for further filtration. And / or, when the TDS in the clarified liquid after purification by the membrane separation component II-2 is less than the TDS in the concentrated liquid after purification by the membrane purification system I-1, the obtained concentrated liquid is returned to the circulating concentrated water tank II-1 for further concentration treatment; And / or, when the TDS in the clarified liquid after purification by the membrane separation component II-2 is greater than the TDS in the concentrated liquid after purification by the membrane purification system I-1, the concentration process is stopped and the concentrated liquid is discharged as waste liquid. TDS represents the total amount of solids dissolved in the solution.

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