Method for dehydrating ethylene glycol feed liquid with high conductivity

Abstract

The invention relates to the field of pervaporation dehydration, in particular to a method for dehydrating ethylene glycol feed liquid with high conductivity. The SSZ-13 molecular sieve membrane with a high silica-alumina ratio is adopted as a key membrane material, good stability can be kept in pervaporation dehydration of ethylene glycol feed liquid with the conductivity of 50-2000 [mu] S / cm, and the dehydration capacity of the membrane material on ethylene glycol dehydration is further improved by modifying the membrane material.

Description

Technical Field

[0001] This invention relates to the field of pervaporation dehydration, and more specifically to a method for dehydrating ethylene glycol feed with high electrical conductivity. Background Technology

[0002] Ethylene glycol (EG), an indispensable basic raw material in the chemical industry, has a wide range of applications covering key industries such as antifreeze, polyester fibers, unsaturated polyester resins, surfactants, natural gas field hydrate inhibitors, and pharmaceutical intermediates. In the production and storage of EG, precise control of moisture content is a core element to ensure stable product quality and meet application performance standards. Currently, EG dehydration mainly relies on traditional processes such as distillation and vacuum dehydration. However, these methods have significant limitations: the distillation process requires multi-stage evaporation-condensation cycles due to the azeotropic properties of EG and water, resulting in a high proportion of energy consumption in production costs; while vacuum dehydration can lower the operating temperature, the energy loss due to continuous vacuuming and the problem of thermosensitive degradation of EG at high temperatures remain unresolved; more importantly, both methods are based on phase change separation mechanisms, leading to high equipment investment costs.

[0003] Against this backdrop, membrane separation technology, with its advantages of non-phase change, low energy consumption, and ease of operation, has gradually become a research hotspot in the field of ethylene glycol dehydration. Currently, publicly available membrane materials include polymer membranes such as PVA membranes, polyphenylene ether membranes, PPO, and chitosan membranes, as well as inorganic membranes such as NaA-type zeolite membranes and ZSM-5 molecular sieve membranes. Among them, molecular sieve membranes are considered the most promising dehydration material for industrial applications due to their regular microporous structure, which highly matches the diameter of ethylene glycol molecules, and their excellent thermal and chemical stability.

[0004] However, existing molecular sieve membrane dehydration technologies are mainly developed for ideal feed systems. In actual industrial scenarios (such as the purification of ethylene glycol from produced water in permeable natural gas fields), the feed often contains a large number of cations, leading to a significant increase in conductivity. When such high-conductivity feed directly contacts the molecular sieve membrane, the cations exchange with compensating cations in the membrane surface framework, disrupting the integrity of the membrane's crystal structure, causing pore collapse and a decrease in permeate flux. This severely restricts the long-term stability and dehydration efficiency of the molecular sieve membrane in complex industrial feeds. Therefore, the feed needs to be pre-treated with ion exchange to remove salts before pervaporation dehydration of ethylene glycol. However, ethylene glycol can tolerate the presence of cations when it is recycled. Therefore, developing suitable molecular sieve membrane materials for efficient dehydration of high-conductivity industrial ethylene glycol feeds has become a key requirement for overcoming existing process bottlenecks and promoting the green upgrading of the ethylene glycol industry.

[0005] Based on this, the inventors discovered that SSZ-13 with a high silicon-to-aluminum ratio is well-suited for the dehydration of high-conductivity ethylene glycol and exhibits good stability. However, for SSZ-13, the higher the silicon-to-aluminum ratio, the lower the yield of qualified membrane materials that can adapt to ethylene glycol dehydration during membrane preparation. Conversely, a low silicon-to-aluminum ratio in SSZ-13 inevitably leads to unsatisfactory stability. Therefore, how to modify SSZ-13 molecular sieve membranes with relatively low silicon-to-aluminum ratios to further meet the requirements for efficient dehydration of high-conductivity industrial ethylene glycol solutions is an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned issues, this invention employs SSZ-13 molecular sieve membranes with a high silicon-to-aluminum ratio as the key membrane material. These membranes maintain good stability during the pervaporation and dehydration of ethylene glycol solutions with conductivity ranging from 50 to 2000 μS / cm. Furthermore, the dehydration capacity of the membrane material for ethylene glycol dehydration is further enhanced through modification of the membrane material.

[0007] Specifically, the present invention provides a method for dehydrating a high-conductivity ethylene glycol solution, wherein the high-conductivity ethylene glycol solution is directly passed through an SSZ-13 molecular sieve membrane for pervaporation dehydration without any pretreatment to reduce conductivity, wherein the conductivity of the ethylene glycol solution is ≥50μS / cm and ≤2000μS / cm.

[0008] As a preferred embodiment, the silicon-to-aluminum ratio of the SSZ-13 molecular sieve membrane is ≥5.

[0009] As a preferred embodiment, the pH of the ethylene glycol solution is 3-7.5.

[0010] As a preferred approach, the pretreatment measures for reducing conductivity include one or more combinations of ion exchange, chemical neutralization, and adsorption.

[0011] As a preferred embodiment, the SSZ-13 molecular sieve membrane is an unmodified molecular sieve membrane or a modified molecular sieve membrane, wherein the unmodified molecular sieve membrane has a silicon-to-aluminum ratio greater than 15.

[0012] As a preferred method, the SSZ-13 molecular sieve membrane is prepared by in-situ growth, secondary growth or dry gel conversion.

[0013] As a preferred embodiment, the modified molecular sieve membrane is an in-situ loaded MOF layer on the surface of an SSZ-13 molecular sieve membrane, wherein the MOF is UiO-66 and the MOF layer is not selective for ethylene glycol dehydration.

[0014] As a preferred embodiment, the in-situ supported MOF layer is prepared by immersing the SSZ-13 molecular sieve membrane in a synthesis solution containing zirconium salt, ligand and solvent and reacting for 3-12 hours, preferably 3-9 hours, and more preferably 4-6 hours.

[0015] As a preferred method, when the conductivity of the ethylene glycol solution is greater than 2000 μS / cm, the conductivity of the ethylene glycol solution is first reduced to ≤2000 μS / cm before the ethylene glycol solution is passed into the SSZ-13 molecular sieve membrane for pervaporation and dehydration.

[0016] Compared with the prior art, the present invention has the following technical advantages: First, this invention uses SSZ-13 molecular sieve membrane with a high silicon-to-aluminum ratio (silicon-to-aluminum ratio ≥5) as the key membrane material. In the application of pervaporation and dehydration of ethylene glycol feed solution with conductivity of 50-2000 μS / cm at room temperature, it can maintain good stability while ensuring good permeation performance. After 6 days of stable operation, the selectivity of the membrane can still be maintained at more than 90%.

[0017] Secondly, in response to the problem of low yield of SSZ-13 molecular sieve membranes with high silicon-to-aluminum ratio, this invention selects to modify the surface of membranes with silicon-to-aluminum ratio ≥5 and ≤15 by loading UIO-66. The short-term loading of UIO-66 does not improve the hydrophilicity of the membrane surface of SSZ-13 as a protective layer while avoiding ion exchange.

[0018] In addition, for ethylene glycol solutions with higher conductivity, this invention can combine the membrane separation process of SSZ-13 molecular sieve membrane with ion exchange pretreatment to reduce conductivity, thereby meeting more application needs. Attached Figure Description

[0019] Figure 1 The image shows a surface SEM image of the SSZ-13 molecular sieve membrane used in Example 1. Figure 2 The image shows a surface SEM image of the SSZ-13 molecular sieve membrane used in Example 2 after loading a MOF layer onto the surface. Detailed Implementation

[0020] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the essence of the invention are all within the scope of the present invention.

[0021] Example 1 Example 1 uses an SSZ-13 molecular sieve membrane with a silicon-to-alumina ratio of 30.4 (prepared using a secondary growth method, with a tubular alumina support; electron micrograph of the membrane surface is shown below). Figure 1As shown, molecular sieve membranes are used as key membrane materials and are filled into membrane modules.

[0022] The test feed solution was prepared by mixing ethylene glycol and water at a mass ratio of 28:72, and adding sodium chloride to form a high-conductivity ethylene glycol feed solution with a conductivity of 451 μS / cm at room temperature. This ethylene glycol feed solution was pumped into the membrane module, and an ethylene glycol dehydration test was conducted at an operating temperature of 90°C and a pressure of 100 Pa. The flux and selectivity were recorded 2 hours after the start of the test, and the selectivity retention rate was recorded after 6 days of operation.

[0023] Example 2 The only difference between this embodiment and Embodiment 1 is that this embodiment uses an SSZ-13 molecular sieve membrane with a silicon-to-aluminum ratio of 10.1, and undergoes modification treatment through the following steps: (1) will 1,4-Phenylacetic acid (BDC) and deionized water were dissolved in DMF in a molar ratio of Zr:BDC:H2O:DMF=1:1:1:500 to prepare a modification solution. (2) The above-mentioned SSZ-13 molecular sieve membrane was immersed in the above-mentioned modification solution and synthesized at 120°C for 6 hours. After the synthesis was completed, it was rinsed with DMF and dried to form the modified SSZ-13 molecular sieve membrane (EM image of membrane surface as shown). Figure 2 (As shown). The testing process is the same as in Example 1.

[0024] Example 3 The only difference between this example and Example 1 is that the conductivity of the ethylene glycol solution is 1822 μS / cm. The testing procedure is the same as in Example 1.

[0025] Comparative Example 1 The only difference between this comparative example and Example 2 is that the SSZ-13 molecular sieve membrane was not modified. The testing procedure was the same as in Example 1.

[0026] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that the conductivity of the ethylene glycol solution is 4501 μS / cm. The testing procedure is the same as in Example 1.

[0027] The test results of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1: Table 1 As shown in the table above, SSZ-13 molecular sieve membranes with a high silica-to-alumina ratio exhibit good flux, selectivity, and stability in ethylene glycol solutions with specific high conductivity. Modification of SSZ-13 molecular sieve membranes with a low silica-to-alumina ratio using MOF significantly improves their stability in high conductivity solutions. However, excessively high conductivity can still compromise membrane stability, necessitating pretreatment with ion exchange resins to reduce the conductivity of the ethylene glycol solution to a suitable range.

[0028] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for dehydrating a high-conductivity ethylene glycol solution, characterized in that, A high-conductivity ethylene glycol solution is directly passed through an SSZ-13 molecular sieve membrane for pervaporation and dehydration without any pretreatment to reduce conductivity. The conductivity of the ethylene glycol solution is ≥50μS / cm and ≤2000μS / cm.

2. The method according to claim 1, characterized in that, The silicon-to-aluminum ratio of the SSZ-13 molecular sieve membrane is ≥5.

3. The method according to claim 1, characterized in that, The pH of the ethylene glycol solution is 3-7.

5.

4. The method according to claim 1, characterized in that, The measures for reducing conductivity pretreatment include one or more combinations of ion exchange, chemical neutralization, and adsorption.

5. The method according to claim 1, characterized in that, The SSZ-13 molecular sieve membrane is an unmodified molecular sieve membrane or a modified molecular sieve membrane, wherein the unmodified molecular sieve membrane has a silicon-to-aluminum ratio greater than 15.

6. The method according to claim 1, characterized in that, The SSZ-13 molecular sieve membrane is prepared by in-situ growth, secondary growth, or dry gel conversion.

7. The method according to claim 5, characterized in that, The modified molecular sieve membrane is an SSZ-13 molecular sieve membrane with an in-situ loaded MOF layer, wherein the MOF is UiO-66 and the MOF layer is not selective for ethylene glycol dehydration.

8. The method according to claim 7, characterized in that, The in-situ supported MOF layer is prepared by immersing an SSZ-13 molecular sieve membrane in a synthesis solution containing zirconium salt, ligand, and solvent for 3-12 hours.

9. The method according to claim 1, characterized in that, When the conductivity of the ethylene glycol solution is greater than 2000 μS / cm, the conductivity of the ethylene glycol solution is first reduced to ≤2000 μS / cm before the ethylene glycol solution is passed into the SSZ-13 molecular sieve membrane for pervaporation and dehydration.

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