Method for removing low molecular polymer in acetylene device circulating solvent NMP

Abstract

The application provides a method for removing low-molecular polymers in a circulating solvent of an acetylene device. The method adopts a liquid phase extraction separation process to remove low-molecular polymers of condensed ring aromatic hydrocarbons in the circulating solvent, uses a compounded extractant, the extractant is a mixture of long-chain alkanes and hydroxyl-containing compounds, and the separation is carried out by using an extraction tower. The method has excellent performances of high selectivity and high removal rate, and the removal rate of the low-molecular polymers in the circulating solvent of the acetylene device can reach more than 95%.

Description

Technical Field

[0001] This invention belongs to the field of liquid phase extraction, specifically relating to a method for removing low molecular weight polymers from NMP, the circulating solvent in an acetylene unit. Background Technology

[0002] Acetylene, an important chemical raw material, can be prepared through various methods including partial oxidation, calcium carbide method, electric arc method, and plasma method. Among these, the electric arc method and plasma method have high energy consumption, and the plasma method is not yet mature for industrial application. Currently, the calcium carbide method and the partial oxidation of natural gas are commonly used to produce acetylene. Compared to the calcium carbide method, the partial oxidation of natural gas to acetylene has advantages such as low energy consumption, simple process, and environmental friendliness. It is widely used both domestically and internationally. Acetylene is produced from natural gas through partial oxidation cracking, compression, and enrichment. In the acetylene enrichment system of the partial oxidation of natural gas to acetylene process, the byproduct higher alkynes are prone to polymerization. These polymers are mainly low-molecular-weight polycyclic aromatic hydrocarbons. The polymers deposit and form scale in equipment and pipelines, causing blockages in equipment, heat exchangers, and pipelines, affecting heat transfer efficiency, increasing pressure drop in heat exchangers, creating safety hazards, and reducing operating cycles and production efficiency.

[0003] Patent CN102701896 discloses a composite solvent for acetylene purification and a purification method thereof. The purification device consists of an absorption tower, three desorption towers, and auxiliary equipment. First, the feed gas is countercurrently contacted with the composite solvent in the absorption tower, where acetylene, higher alkynes, and CO2 are absorbed. Then, high-concentration acetylene is desorbed in the first desorption tower, residual acetylene is desorbed in the second desorption tower, and higher alkynes and CO2 are desorbed from the third desorption tower. This composite solvent exhibits high selectivity, good stability, and easy regeneration; however, it cannot prevent the higher alkynes from reacting in the concentration unit to produce polycyclic aromatic hydrocarbons, thus causing system blockage and other issues affecting the long-term stable operation of the device.

[0004] Patent CN109652077A provides a method for preventing the polymerization of higher alkynes in an acetylene enrichment system. This method prevents the polymerization of higher alkynes in an acetylene enrichment system in a natural gas partial oxidation process for producing acetylene. The method uses polymerization inhibitors and coatings to prevent the polymerization of higher alkynes. Although the polymerization inhibition effect is good, it only plays a mitigating role.

[0005] Patent CN109796295A provides a natural gas cracking acetylene enrichment system. By adding potassium carbonate, it effectively reduces the corrosion problem inside the enrichment device, alleviates system blockage, ensures stable device operation, reduces NMP solvent consumption, and extends the equipment cleaning and maintenance cycle. This method also alleviates polymer production by controlling the system pH. However, the polymer cannot be removed from the system, which can easily cause blockage in subsequent processes.

[0006] Currently, methods for purifying polymers from circulating solvents in acetylene plants include polymerization inhibition, stripping, and extraction. While polymerization inhibition can suppress polymer formation, it cannot completely prevent it, and accumulated polymers in the solvent can cause system blockage. Stripping has limited removal capacity and carries the risk of acetylene / higher ytylene enrichment and explosion. Extraction, on the other hand, can directly remove polymers from the solvent, preventing polymer accumulation and contributing to the long-term stable operation of the acetylene enrichment unit. However, the removal efficiency of a single extractant is limited; therefore, compounding is used to improve selectivity and removal rate. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention aims to provide a method and application for removing low molecular weight polymers from the circulating solvent NMP in acetylene equipment. The method employs an extraction separation process to remove low molecular weight polymers of polycyclic aromatic hydrocarbons from the circulating solvent, using a compound extractant, which exhibits excellent performance with high selectivity and high removal rate.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for removing low molecular weight polymers from nitrogen methylpyrrolidone (NMP), a circulating solvent in an acetylene unit. The method uses an extraction process to remove low molecular weight polymers from NMP. The low molecular weight polymers are mainly polycyclic aromatic hydrocarbons, including naphthalene, methylnaphthalene, acenaphthene, and other components. Naphthalene and methylnaphthalene account for 80-90%, acenaphthene accounts for about 10%, and other components account for 5-10%. The above components can be qualitatively and quantitatively analyzed using gas chromatography.

[0010] The extraction process uses a compound extractant, which exhibits excellent performance in terms of high selectivity and high removal rate. The compound extractant is a mixture of long-chain alkanes and hydroxyl-containing compounds. The long-chain alkanes are selected from C5-C16 alkanes, and the alkanes mainly include n-hexane, n-heptane, n-octane, and nonane. Considering the ease of extractant recovery, n-hexane or n-heptane with low boiling points is preferred. The molecular formula of the hydroxyl-containing compound is R-OH, where R can be one of hydrogen, methyl, ethyl, propyl, or butyl. The hydroxyl-containing compound is one or more of water, methanol, ethanol, propanol, isopropanol, and / or butanol, with water or methanol being preferred.

[0011] In this invention, the compounding ratio of the compounded extractant is 1:1 to 3:1, calculated by mass, based on the ratio of long-chain alkanes to hydroxyl-containing compounds. The extractant prepared according to the above compounding method can be used to remove low molecular weight polymers from the circulating solvent NMP.

[0012] In this invention, the extraction process can be either batch extraction or extraction tower extraction, preferably extraction tower extraction, with the number of trays in the extraction tower being 30-50; the extraction ratio of the extraction process is 0.5:1-3:1, preferably 1:1-2:1, wherein the extraction ratio is the ratio of the amount of compound extractant to the amount of circulating solvent NMP, calculated by mass; the extraction temperature of the extraction process is 30-60℃, preferably 40-50℃;

[0013] In addition, the low molecular weight polymers in the circulating solvent are required to have a concentration of no more than 5% (mass concentration). When the concentration exceeds 5%, low molecular weight polymers will precipitate from the circulating solvent, which will affect the long-term stable operation of the extraction process. By using the above methods, the removal rate of low molecular weight polymers in the circulating solvent NMP of the acetylene unit can reach more than 95%.

[0014] Compared with the prior art, the positive effects of the present invention are as follows:

[0015] Long-chain alkanes have high solubility for polycyclic aromatic hydrocarbons (PAHs) but low solubility in NMP, making them suitable as extractants. However, using a single extractant can result in a low removal rate. Meanwhile, hydroxyl-containing compounds have low solubility for PAHs but good miscibility with NMP. By combining them, the solubility of PAHs in the system can be further reduced, thereby increasing their concentration in the extractant and giving them excellent performance in terms of high selectivity and high removal rate. Attached Figure Description

[0016] Figure 1 Schematic diagram of the extraction process Detailed Implementation

[0017] The present invention is further illustrated by the following embodiments, but the scope of the present invention is not limited to the following embodiments.

[0018] The circulating solvent is from the acetylene unit concentration unit of Wanhua Chemical Sichuan Co., Ltd. The circulating solvent contains 12,300 ppm (w) of polycyclic aromatic hydrocarbons, including 5,535 ppm (w) of naphthalene, 4,674 ppm (w) of naphthalene, 561 ppm (w) of naphthalene, and 1,530 ppm (w) of other components.

[0019] Concentration was analyzed using an Agilent 7890B gas chromatograph, and the water purifier was an 1825DF molar element type intelligent machine.

[0020] Raw material information:

[0021]

[0022] Example 1

[0023] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-hexane and high-purity water, with a dosage of 100g, including 50g of n-hexane and 50g of high-purity water, in a 1:1 ratio. The extraction ratio was 1:2. An extraction tower with 30 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 30℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0024] Example 2

[0025] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-hexane and high-purity water, with a dosage of 100g, including 75g of n-hexane and 25g of high-purity water, in a mixing ratio of 3:1 and an extraction ratio of 1:2. A four-stage autoclave extraction was used with 40 theoretical plates and an extraction temperature of 30℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0026] Example 3

[0027] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-heptane and high-purity water, with a dosage of 200g, including 133g of n-heptane and 67g of high-purity water, in a mixing ratio of 2:1 and an extraction ratio of 1:1. An extraction tower with 40 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 40℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0028] Example 4

[0029] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-heptane and methanol, with a dosage of 200g, including 133g of n-heptane and 67g of methanol, in a mixing ratio of 2:1 and an extraction ratio of 1:1. An extraction tower with 50 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 60℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0030] Example 5

[0031] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-hexane and methanol, with a dosage of 400g, including 200g of n-hexane and 200g of methanol, in a 1:1 ratio. The extraction ratio was 2:1. An extraction tower with 40 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 40℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0032] Comparative Example 1

[0033] This comparative extractant is only applicable to long-chain alkanes.

[0034] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. Hexane was used as the extractant without mixing or compounding. The extractant amount was 200g, including 200g of hexane, with an extraction ratio of 1:1. An extraction tower with 40 plates was used. The circulating solvent was fed from the top and discharged from the bottom, while the extractant was fed from the bottom and discharged from the top in a countercurrent contact. The extraction temperature was 40℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0035] Comparative Example 2

[0036] This comparative extractant is only applicable to hydroxyl-containing compounds.

[0037] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. High-purity water was used as the extractant, without mixing or compounding. The amount of extractant was 400g, including 400g of high-purity water. The extraction ratio was 2:1. An extraction tower with 40 plates was used. The circulating solvent was fed from the top and discharged from the bottom, while the extractant was fed from the bottom and discharged from the top in a countercurrent contact. The extraction temperature was 30℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0038] Comparative Example 3

[0039] This comparative study adjusted the amount of extractant.

[0040] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-hexane and high-purity water, with a dosage of 66g, including 44g of n-hexane and 22g of high-purity water, in a mixing ratio of 2:1 and an extraction ratio of 1:3. An extraction tower with 40 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 40℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0041] Comparative Example 4

[0042] This comparative study adjusts the extraction process parameters, mainly involving the number of trays and the extraction temperature.

[0043] The concentration unit used 200g of circulating solvent, containing 5535ppm(w) naphthalene, 4674ppm(w) naphthalene, 561ppm(w) naphthalene, and 1530ppm(w) of other components. The extractant was a mixture of n-hexane and high-purity water, with a dosage of 400g, including 300g of n-hexane and 100g of high-purity water, in a mixing ratio of 3:1 and an extraction ratio of 2:1. An extraction tower with 20 plates was used, with the circulating solvent entering from the top and exiting from the bottom, and the extractant entering from the bottom and exiting from the top in a countercurrent contact. The extraction temperature was 20℃. After stable continuous operation for 1 hour, the inlet and outlet circulating solvents were taken for comparative analysis.

[0044] Table 1. Extraction treatment effect

[0045]

[0046]

[0047] Table 2. Changes in components before and after extraction.

[0048]

[0049] Table 1 shows that the extraction removal rates of the examples are all >95%. Comparing the examples with Comparative Examples 1 and 2, the test results show that although using a single extractant has a certain removal capacity, the removal efficiency is limited. Using a compound extractant can improve the removal rate. Comparing the examples with Comparative Examples 3 and 4, different amounts of extractant and different extraction process parameters will affect the extraction removal rate.

[0050] Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for removing low-molecular-weight polymers from the circulating solvent N-methylpyrrolidone (NMP) in an acetylene unit, characterized in that, The method uses an extraction process to remove low-molecular-weight polymers from NMP. The extraction process uses a compound extractant, which is a mixture of long-chain alkanes and hydroxyl-containing compounds. The long-chain alkanes are one or more of n-hexane and n-heptane. The hydroxyl-containing compounds have the molecular formula R-OH, where R is hydrogen or methyl. The extraction process can be either batch extraction or an extraction tower, with the extraction tower having 30-50 trays. The extraction ratio is 0.5:1-3:1, where the extraction ratio is the ratio of the compound extractant to the amount of circulating NMP solvent used, calculated by mass. The extraction temperature is 30-60℃.

2. The method as described in claim 1, characterized in that, The low-molecular-weight polymers are mainly polycyclic aromatic hydrocarbons, including naphthalene, methylnaphthalene, acenaphthene, and other components.

3. The method as described in claim 1, characterized in that, Based on the ratio of long-chain alkanes to hydroxyl-containing compounds, the compounding ratio of the compound extractant is 1:1 to 3:1, calculated by mass.

4. The method according to any one of claims 1-3, characterized in that, The extraction ratio of the extraction process is 1:1-2:

1.

5. The method according to any one of claims 1-3, characterized in that, The extraction temperature of the extraction process is 40-50℃.

6. The method according to any one of claims 1-3, characterized in that, The concentration of low molecular weight polymers in the circulating solvent does not exceed 5 wt%.

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