Method for purifying ethylene glycol solution, membrane separation device and application of membrane separation device

Abstract

The invention relates to the technical field of ethylene glycol purification, and discloses a purification method of an ethylene glycol solution, a membrane separation device and application of the membrane separation device. The purification method comprises the steps that (1) an ethylene glycol solution is fed for purification treatment, a purification system comprises a membrane separation device composed of a booster pump and a first membrane assembly, and the first membrane assembly at least comprises an I-1 membrane set, an I-2 membrane set and an I-3 membrane set and is used for intercepting ethylene glycol and metal ions; (2) the obtained primary concentrated solution of the purification system is subjected to concentration treatment, a concentration system comprises a membrane separation device composed of a booster pump, a circulating concentration water tank II-1 and a membrane separation assembly II-2 membrane, the II-2 membrane intercepts one or more of monovalent ions, divalent ions and trivalent ions, and purified ethylene glycol clear liquid is obtained. The method is energy-saving and easy to implement, is suitable for purifying the low-concentration ethylene glycol solution, and has a very good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of ethylene glycol purification, and in particular to a method for purifying an ethylene glycol solution, a membrane separation device and applications thereof. Background Art

[0002] Ethylene glycol is also called glycol, EG for short, with the chemical formula (CH2OH)2. Ethylene glycol is a colorless, transparent, viscous liquid with a sweet taste and hygroscopicity. It is the simplest aliphatic diol with the chemical properties of alcohols and can generate 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 polymer compounds such as polyester fibers. In addition, it can also be used as a raw material for medicines and plastics and a high-boiling point solvent for the production of cosmetics and explosives. It can replace glycerin in industrial production. It is soluble in water and can be mixed with water in any proportion. After mixing, the freezing point is significantly reduced due to the change in the vapor pressure of the cooling water. Therefore, it can be used as an automotive antifreeze and aircraft engine refrigerant. Ethylene glycol is a basic organic chemical raw material with a wide range of uses. In addition, ethylene glycol can also be directly used as a solvent in products such as dyes and inks, and as a lubricant for products such as cellophane, fibers and leather.

[0003] There are two main types of ethylene glycol production methods. The first is the process technology of producing ethylene glycol through coal chemical industry: it is divided into direct synthesis method, which uses CO and H2 to directly synthesize ethylene glycol; indirect synthesis method mainly includes formaldehyde carbonylation method, formaldehyde condensation method, and oxalate synthesis method. The second category is the production process using petrochemical route: mainly including ethylene oxide hydration method and ethylene carbonate catalytic method.

[0004] In the process of producing and concentrating ethylene glycol, various metal catalysts are inevitably used, and pipeline transportation and other processes are adopted. During this process, the aqueous solution of ethylene glycol is often mixed with metal ions. Metal ions cannot be separated during the evaporation and concentration process of ethylene glycol, and are impurities that are difficult to remove. Judging from the current use of ethylene glycol recovery systems at home and abroad, for divalent metal ions (such as Ca 2+ Mg 2+ ) is generally removed by forming a precipitate, but the precipitation method has a certain range of requirements for ion concentration. For monovalent salts (such as NaCl), flash evaporation is generally used for removal, and the flash evaporation process requires very high energy consumption. The present invention provides a new method for purifying ethylene glycol aqueous solution that is different from the existing disclosed technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that in the prior art, salt-containing impurities in ethylene glycol aqueous solution are usually purified by azeotropic distillation, but there is a defect that the energy consumption is too high. A purification method for ethylene glycol solution and a membrane separation device and application thereof are provided. The purification method is simple and easy to operate, has low energy consumption, and can effectively remove metal ions in ethylene glycol solution.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for purifying an ethylene glycol solution, wherein the purification method comprises:

[0007] (1) feeding ethylene glycol solution through a purification system for purification treatment, wherein the purification system comprises a membrane separation device composed of a booster pump and a first membrane assembly, the first membrane assembly comprises at least three-stage membrane separation groups, namely, membrane group I-1, membrane group I-2 and membrane group I-3, and the membranes of membrane group I-1, membrane group I-2 and membrane group I-3 are the same or different, and each is a first nanofiltration membrane, and the first nanofiltration membrane intercepts ethylene glycol and metal ions in the ethylene glycol solution; obtaining a first-stage concentrated liquid and a purified liquid of the purification system;

[0008] (2) The primary concentrated liquid of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device composed of a booster pump, a circulating concentrated water tank II-1, and a second membrane assembly, the second membrane assembly includes a membrane separation assembly II-2 membrane, the II-2 membrane is a second nanofiltration membrane, and the second nanofiltration membrane has no retention of ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent ions, divalent ions and trivalent ions, to obtain a clear liquid containing purified ethylene glycol.

[0009] The 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 composed of a booster pump and a first membrane assembly, the first membrane assembly at least includes three-stage membrane separation groups Ⅰ-1 membrane group, Ⅰ-2 membrane group and Ⅰ-3 membrane group; and the concentration system includes a membrane separation device composed of a booster pump, a circulating concentration water tank Ⅱ-1 and a second membrane assembly Ⅱ-2.

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

[0011] Through the above technical scheme, by using nanofiltration membranes with different retention rates for impurities in ethylene glycol solution and adopting a reasonable combination process, the removal and purification of impurities in ethylene glycol solution is achieved, and a high recovery rate is achieved. Compared with the traditional evaporation method for purifying ethylene glycol solution, the method of the present invention is energy-saving and easy to implement, and is suitable for purifying low-concentration ethylene glycol solution. It has very good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0014] Description of Reference Numerals

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

[0016] II-1-circulating concentrated water tank; II-2-membrane separation component II-2 membrane. DETAILED DESCRIPTION

[0017] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

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

[0019] (1) feeding ethylene glycol solution through a purification system for purification treatment, wherein the purification system comprises a membrane separation device composed of a booster pump and a first membrane assembly, the first membrane assembly comprises at least three-stage membrane separation groups, namely, membrane group I-1, membrane group I-2 and membrane group I-3, and the membranes of membrane group I-1, membrane group I-2 and membrane group I-3 are the same or different, and each is a first nanofiltration membrane, and the first nanofiltration membrane intercepts ethylene glycol and metal ions in the ethylene glycol solution; obtaining a first-stage concentrated liquid and a purified liquid of the purification system;

[0020] (2) The primary concentrated liquid of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device composed of a booster pump, a circulating concentrated water tank II-1, and a second membrane assembly, the second membrane assembly includes a membrane separation assembly II-2 membrane, the II-2 membrane is a second nanofiltration membrane, and the second nanofiltration membrane has no retention of ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent ions, divalent ions and trivalent ions, to obtain a clear liquid containing purified ethylene glycol.

[0021] The inventor of the present invention has found that: in the prior art, azeotropic distillation is usually used to purify salt-containing impurities in ethylene glycol aqueous solution, but there is a defect problem of too much energy consumption, especially when the water content in the ethylene glycol solution is high, it is not economical and consumes a lot of energy. Based on this, the inventor of the present invention has found that by using the purification system and the concentration system of the present invention, wherein the purification system and the concentration system are both implemented by a membrane separation device, but the first membrane component used in the purification system intercepts the ethylene glycol and metal ions in the ethylene glycol solution; the first-level concentrated liquid and the purified liquid of the purification system are obtained, preferably, the interception rate of ethylene glycol is 20% or more, and the interception rate of metal ions is 98% or more; the second membrane component of the concentration system has no interception rate for ethylene glycol, and intercepts one or more of monovalent ions, divalent ions and trivalent ions, preferably, the interception rate of high-valent metal ions (divalent ions or trivalent ions) is 98% or more, and the interception rate of monovalent ions is 50% or more; in this way, ethylene glycol can be continuously concentrated. In summary, the present invention uses the first membrane module and the second membrane module to work in combination, which can achieve purification and concentration of ethylene glycol.

[0022] According to the present invention, the clear liquid separated by the Ⅰ-1 membrane group enters the Ⅰ-2 membrane group as feed, and the concentrated liquid of the Ⅰ-1 membrane group serves as the primary concentrated liquid of the purification system; the clear liquid of the Ⅰ-2 membrane group serves as the feed of the Ⅰ-3 membrane group; the concentrated liquid of the Ⅰ-2 membrane group returns to the feed of the Ⅰ-1 membrane group; the clear liquid of the Ⅰ-3 membrane group serves as the purified liquid, and the concentrated liquid of the Ⅰ-3 membrane group returns to the feed of the Ⅰ-1 membrane group.

[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 separation ability for a long time in the environment of ethylene glycol solution, and can have a retention rate of 20% or more for ethylene glycol in the ethylene glycol solution, and a retention rate of greater than 98% or more 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 retention rate for ethylene glycol in the ethylene glycol solution, a retention rate for divalent ions or trivalent ions in the ethylene glycol solution of 98% or more, and a retention rate for monovalent ions in the ethylene glycol solution of 50% or more.

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

[0026] Table I

[0027]

[0028]

[0029] In the present 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 contains ethylene glycol, water and metal salts. In the present 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, and more preferably, the metal is magnesium and / or sodium. In the present invention, the impurities in the ethylene glycol solution that usually need to be treated are not too complicated, usually one or more common salts of magnesium sulfate, sodium chloride and sodium nitrate, so it is only necessary to remove these salt impurities, usually as long as they are salts that can be retained by the membrane.

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

[0034] According to the present invention, the content of the metal salt is 10-10000 mg, preferably 10-5000 mg, relative to 1L of the ethylene glycol solution. In the present invention, the content of the metal salt is not easy to be too high, and the metal salt cannot be separated if the content is too high. The content of the metal salt cannot exceed 1%, that is, the content of the metal salt does not exceed 10000 mg relative to 1L of the ethylene glycol solution.

[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 ≤2Mpa, preferably 0.6-1.5Mpa.

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

[0038] According to the present invention, the single-stage recovery rate is controlled between 60-80%. In the present invention, it should be noted that "single-stage recovery rate" refers to the ratio of the flow rate entering the membrane module to the output of the clear liquid of the membrane module. The recovery rate is controlled to prevent the concentrated liquid flow rate from being too small, resulting in the deposition of pollutants on the membrane module.

[0039] According to the present invention, the purification of ethylene glycol solution first requires the removal of metal ions in the solution. Since the first nanofiltration membrane has a retention rate of only 98% for metal ions, it is necessary to thoroughly remove the metal ions in the ethylene glycol solution through multi-stage filtration. In the present invention, the purification system includes a membrane separation device composed of a booster pump and a first membrane assembly, and the first membrane assembly includes at least three membrane separation groups, namely, a Ⅰ-1 membrane group, a Ⅰ-2 membrane group, and a Ⅰ-3 membrane group.

[0040] Specifically, in the present invention, the purification method comprises:

[0041] In step (1):

[0042] (1-1) feeding the ethylene glycol solution through the membrane group I-1 of the purification system for filtering to obtain a clear solution 1;

[0043] (1-2) filtering the clear liquid 1 through the I-2 membrane group of the purification system to obtain a concentrated liquid 2 and a clear liquid 2;

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

[0045] The concentrated liquid 2 and the concentrated liquid 3 are returned to the I-1 membrane group of the purification system to continue filtering, and the single-stage recovery rate is controlled between 60-80%;

[0046] Wherein, the concentrated liquid of the Ⅰ-1 membrane group is used as the primary concentrated liquid of the purification system;

[0047] In step (2):

[0048] (2-1) The primary concentrated liquid of the purification system is concentrated in a circulating concentrated water tank II-1 and a second membrane assembly in sequence, wherein the membrane of the membrane separation assembly II-2 in the second membrane assembly is a second nanofiltration membrane, and the second nanofiltration membrane has no retention of ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent ions, divalent ions and trivalent ions, to obtain a concentrated liquid and a clear liquid containing purified ethylene glycol;

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

[0050] In the present 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 clear liquid. Membrane separation cannot only intercept impurities, but the concentrated part cannot be thrown away, which will waste a lot of materials. Therefore, the concentrated liquid part needs to be returned for further processing, but if the impurity content is too high, higher than the raw material, it is not necessary.

[0051] When the TDS of the clear liquid after the membrane purification of the membrane separation module II-2 is greater than the TDS of the concentrated liquid after the membrane purification of the purification system I-1, the concentration is stopped and the concentrated liquid is discharged as waste liquid. As above, the purpose is to recover ethylene glycol to the maximum extent, but the concentration can only be concentrated to a certain extent.

[0052] In the present invention, it should be noted that the concentrated solution is a concentrated solution containing impurities, and the clear solution is an ethylene glycol solution without 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 the purification system, Figure 1 As shown, Figure 1 It is a schematic diagram of the process of the purification system in the membrane separation device of the present invention, Figure 1 The purified liquid obtained from I-3 in the present invention is used as the final purified product of the present invention, in step (1):

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

[0056] (1-2) filtering the clear liquid 1 through the I-2 membrane group of the purification system to obtain a concentrated liquid 2 and a clear liquid 2;

[0057] (1-3) filtering the clear liquid 2 through the I-3 module of the purification system to obtain a concentrated liquid 3 and a purified liquid, which is used as the final product of the ethylene glycol purified liquid of the present invention;

[0058] The concentrated liquid 2 and the concentrated liquid 3 are returned to the I-1 membrane group of the purification system to continue filtering.

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

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

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

[0062] The 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 composed of a booster pump and a first membrane assembly, the first membrane assembly at least includes three-stage membrane separation groups Ⅰ-1 membrane group, Ⅰ-2 membrane group and Ⅰ-3 membrane group; and the concentration system includes a membrane separation device composed of a booster pump, a circulating concentration water tank Ⅱ-1 and a second membrane assembly Ⅱ-2.

[0063] According to the present invention, the purification system comprises at least an I-1 membrane group, an I-2 membrane group and an I-3 membrane group which are connected in sequence, and both the I-2 membrane group and the I-3 membrane group have outlets connected to the I-1 membrane group.

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

[0065] According to the present invention, the membrane of the membrane separation component II-2 is provided with a clear liquid outlet and an outlet for returning the concentrated liquid to the circulating concentrated water 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 an ethylene glycol solution.

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

[0068] In the following examples and comparative examples:

[0069] The ion types and contents in the ethylene glycol solution were tested by ion chromatography, and the ion chromatograph used in the present invention was purchased from Swiss Metrohm 940 Professional IC Vario ONE.

[0070] The ethylene glycol content in the solution was determined by the refractometry. Aqueous solutions of ethylene glycol with different concentrations of 0 to 10% were prepared, and their refractive index was determined using a Japanese Atuo refractometer. A relationship line between concentration and refractive index was made. Within this concentration range, the ethylene glycol concentration and the refractive index were linearly related. 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 the present invention, the TDS meter used was purchased from Tokyo Instruments and its model number was TDS530. It should be noted that the TDS value indicates how many milligrams of soluble solids are dissolved in 1 liter of water. It is the abbreviation of total dissolved solids, also known as the total amount of soluble solids.

[0072] During the test embodiment, ion chromatography is first used to test the type and content of ions in the ethylene glycol solution. In view of the fact that ethylene glycol often contains calcium, magnesium, sodium, sulfate, chloride ions, etc. in the normal process, the ion content and ethylene glycol content under common working conditions are usually prepared as the test liquid in the verification embodiment.

[0073] The prepared drugs are magnesium sulfate, sodium chloride and calcium chloride. All three drugs are purchased from Beijing Reagent Factory and are chemically pure.

[0074] Ethylene glycol purchased from J&K is chemically pure.

[0075] The concentration values ​​of each component in the drug preparation are calculated by weighing on a balance and using the weight method.

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

[0077] Example 1

[0078] This embodiment is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

[0079] In the purification system, Figure 1 As shown, in step (1):

[0080] (1-1) filtering the raw material liquid (ethylene glycol solution containing impurities) through the purification system first-level I-1 membrane group to obtain the purification system first-level concentrated liquid and clear liquid 1; wherein the purification system first-level concentrated liquid is sent to the circulating concentrated water tank II-1 for concentration treatment;

[0081] The raw material liquid includes magnesium sulfate and ethylene glycol. The contents of the components in the raw material liquid are shown in Table 1-1, and the purification conditions are also shown in Table 1-1:

[0082] Table 1-1

[0083]

[0084] (1-2) filtering the clear liquid 1 through the secondary I-2 membrane group of the purification system to obtain a concentrated liquid 2 and a clear liquid 2;

[0085] (1-3) The clear liquid 2 is filtered through the third-stage I-3 membrane group of the purification system to obtain a concentrated liquid 3 and a purified liquid, which is used as 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 concentrated liquid 2 and the concentrated liquid 3 are returned to the first-level I-1 membrane group of the purification system to continue filtering;

[0087] Among them, the nanofiltration membranes of the first-level I-1 membrane group of the purification system, the second-level I-2 membrane group of the purification system, and the third-level I-3 membrane group of the purification system are the same, and each is the first membrane component in Table 1-1.

[0088] In a concentration system, Figure 2 As shown, in step (2):

[0089] (2-1) The primary concentrated liquid of the purification system is sequentially concentrated through a circulating concentrated water tank II-1 and a membrane of a 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] Among them, when the TDS in the clear liquid in the membrane of the membrane separation component II-2 is less than the TDS in the first-stage concentrated liquid of the purification system, the concentrated liquid obtained is returned to the circulating concentrated water tank II-1 for further concentration treatment; until the TDS in the clear liquid in the membrane of the membrane separation component II-2 is greater than the TDS in the first-stage concentrated liquid of the purification system, the concentration is stopped, and the clear liquid obtained in the process is combined with the raw liquid as the feed of the first-stage membrane group I-1. The content of each component in the raw liquid and the purification conditions are shown in Table 1-1, the indicators of the discharged concentrated liquid are shown in Table 1-2, and the purified liquid is shown in Table 1-3.

[0091] The energy consumption required for this test is 2.2KWH / ton of water.

[0092] Table 1-2

[0093]

[0094] Table 1-3

[0095]

[0096]

[0097] Example 2

[0098] This embodiment is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

[0099] The ethylene glycol solution is purified by the same purification method as in Example 1, except that the contents of the components in the raw liquid and the purification conditions are shown in Table 2-1, the concentrated liquid obtained after treatment and the concentration conditions are shown in Table 2-2, and the purified liquid is shown in Table 2-3.

[0100] The energy consumption required for this test is 1.7KWH / ton of water.

[0101] Table 2-1

[0102]

[0103] Table 2-2

[0104]

[0105] Table 2-3

[0106]

[0107] Example 3

[0108] This embodiment is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

[0109] The ethylene glycol solution was purified by the same purification method as in Example 1, except that the contents of the components in the raw liquid and the purification conditions are shown in Table 3-1, the concentrated liquid obtained after treatment and the concentration conditions are shown in Table 3-2, and the purified liquid is shown in Table 3-3.

[0110] The energy consumption required for this test is 2.4KWH / ton of water.

[0111] Table 3-1

[0112]

[0113] Table 3-2

[0114]

[0115] Table 3-3

[0116]

[0117] Example 4

[0118] This embodiment is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

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

[0120] The energy consumption required for this test is 2.1KWH / ton of water.

[0121] Table 4-1

[0122]

[0123] Table 4-2

[0124]

[0125] Table 4-3

[0126]

[0127] Example 5

[0128] This embodiment is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

[0129] The ethylene glycol solution was purified by the same purification method as in Example 1, except that the contents of the components in the raw liquid and the purification conditions are shown in Table 5-1, the concentrated liquid obtained after treatment and the concentration conditions are shown in Table 5-2, and the purified liquid is shown in Table 5-3.

[0130] The energy consumption required for this test is 1.8KWH / 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 is intended to illustrate the use of the membrane separation device of the present invention to purify an ethylene glycol solution to obtain a purified ethylene glycol solution.

[0140] The ethylene glycol solution was purified by the same purification method as in Example 1, except that the contents of the components in the raw liquid and the purification conditions are shown in Table 6-1, the concentrated liquid obtained after the treatment and the concentration conditions are shown in Table 6-2, and the purified liquid is shown in Table 6-3.

[0141] The energy consumption required for this test is 2.0KWH / 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] 250ml of aqueous solution containing 2.5%wt ethylene glycol and 130mg / L magnesium sulfate was distilled in a vacuum distillation system under the conditions of -80kpa and 141°C for 30min. The steam was condensed and collected by a condenser and then the ion content and ethylene glycol content in the condensate were tested by ion chromatography. After the test, no magnesium sulfate was detected in the condensate and the ethylene glycol content was 2.5%; however, the evaporation method has high temperature, high energy consumption and high cost.

[0151] Comparative Example 2

[0152] The ethylene glycol solution was purified by 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 this comparative example 2, evaporation can be completed and the recovery rate can reach 100%, but the energy consumption is high due to the evaporation method.

[0154] The contents of the components in the raw liquid and the purification conditions are shown in Table D2-1. The concentrated liquid obtained after the 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] From the above results, it can be seen that the implementation conditions of the method of the present invention for ethylene glycol purification are mild, the metal impurities in the ethylene glycol aqueous solution can be removed at room temperature, and a certain degree of concentration can be achieved, and the recovery rate is high. The energy consumption required in the test process is low. If the processing scale is enlarged, lower energy consumption per ton of water treatment can be obtained. Compared with the traditional evaporation method, it is easier to implement on a large scale and more energy-efficient, and is an advanced method for ethylene glycol purification.

[0163] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for purifying an ethylene glycol solution, characterized in that: The purification method comprises: (1) feeding an ethylene glycol solution through a purification system for purification, wherein the purification system comprises a membrane separation device consisting of a booster pump and a first membrane assembly, wherein the first membrane assembly comprises at least three-stage membrane separation groups, namely, a (Ⅰ-1) membrane group, a (Ⅰ-2) membrane group and a (Ⅰ-3) membrane group, and the membranes of the (Ⅰ-1) membrane group, the (Ⅰ-2) membrane group and the (Ⅰ-3) membrane group are the same or different and are each a first nanofiltration membrane, and the first nanofiltration membrane intercepts ethylene glycol and metal ions in the ethylene glycol solution; obtaining a first-stage concentrated liquid and a purified liquid of the purification system; (2) The primary concentrated liquid of the purification system is concentrated by a concentration system, wherein the concentration system includes a membrane separation device composed of a booster pump, a circulating concentrated water tank (II-1), and a second membrane assembly, the second membrane assembly includes a membrane separation assembly (II-2) membrane, the (II-2) membrane is a second nanofiltration membrane, and the second nanofiltration membrane has no retention of ethylene glycol in the ethylene glycol solution, but retains one or more of monovalent ions, divalent ions and trivalent ions, to obtain a clear liquid containing purified ethylene glycol.

2. The purification method according to claim 1, wherein The clear liquid separated by the membrane group (Ⅰ-1) enters the membrane group (Ⅰ-2) as feed, and the concentrated liquid of the membrane group (Ⅰ-1) serves as the primary concentrated liquid of the purification system; The clear liquid of the membrane group (Ⅰ-2) is used as the feed of the membrane group (Ⅰ-3); the concentrated liquid of the membrane group (Ⅰ-2) is returned to the feed of the membrane group (Ⅰ-1); The clear liquid from the membrane group (I-3) is used as the purified liquid, and the concentrated liquid from the membrane group (I-3) is returned to the feed of the membrane group (I-1).

3. The purification method according to claim 1 or 2, 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, has a rejection rate of 98% or more for divalent ions or trivalent ions in the ethylene glycol solution, and has 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 any one of claims 1 to 4, wherein The concentration of ethylene glycol contained in the ethylene glycol solution is 0.01-10%, preferably 3-10%; Preferably, the content of the metal salt is 10-10000 mg, preferably 10-5000 mg, relative to 1 L of the ethylene glycol solution.

6. The purification method according to claim 5, wherein The ethylene glycol solution comprises ethylene glycol, water and a metal salt; Preferably, the metal salt is selected from one or more of metal sulfates, chlorides, nitrates and phosphates; Preferably, the metal is selected from one or more of iron, aluminum, calcium, magnesium, sodium, lithium, manganese and copper.

7. The purification method according to claim 1 or 6, wherein: The temperature of the ethylene glycol solution is 15-50°C, preferably 15-35°C; And / or, the working pressure of the purification system is ≤2Mpa, preferably 0.6-1.5Mpa; And / or, the working pressure of the concentration system is ≤2.5Mpa, preferably 1-2Mpa.

8. The purification method according to any one of claims 1 to 7, wherein: The single-stage recovery rate is controlled between 60-80%.

9. The purification method according to any one of claims 1 to 8, wherein: The purified liquid is then returned to the purification system for further filtering; and / or, when the TDS of the clear liquid after the membrane purification by the membrane separation module II-2 is less than the TDS of the concentrated liquid after the membrane purification by the purification system I-1, the concentrated liquid is returned to the circulating concentrated water tank (II-1) for further concentration treatment; and / or, when the TDS of the clear liquid after the membrane purification of the membrane separation module II-2 is greater than the TDS of the concentrated liquid after the membrane purification of the purification system I-1, the concentration process is stopped and the concentrated liquid is discharged as waste liquid; TDS refers to the total dissolved solids in the solution.

10. A membrane separation device, characterized in that: The membrane separation device comprises a purification system and a concentration system which are connected in sequence, wherein the purification system comprises a membrane separation device consisting of a booster pump and a first membrane assembly, wherein the first membrane assembly comprises at least three-stage membrane separation groups (Ⅰ-1) membrane group, (Ⅰ-2) membrane group and (Ⅰ-3) membrane group; and the concentration system comprises a membrane separation device consisting of a booster pump, a circulating concentration water tank (Ⅱ-1) and a second membrane assembly, wherein the second membrane assembly comprises a membrane separation assembly (Ⅱ-2) membrane.

11. The membrane separation device according to claim 10, wherein: The (Ⅰ-1) membrane group, (Ⅰ-2) membrane group and (Ⅰ-3) membrane group are connected in sequence, and the (Ⅰ-2) membrane group and (Ⅰ-3) membrane group both have outlets connected to the (Ⅰ-1) membrane group; And / or, the (Ⅰ-1) membrane group is connected to the circulating concentration water tank (Ⅱ-1) in the concentration system and the membrane of the membrane separation assembly (Ⅱ-2) in the second membrane assembly in sequence; And / or, the membrane of the membrane separation component (II-2) is provided with a clear liquid outlet and an outlet for returning the concentrated liquid to the circulating concentrated water tank (II-1).

12. Use of the membrane separation device according to claim 10 or 11 in a method for purifying an ethylene glycol solution.

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