Preparation method of high-purity n-hexane based on non-aromatic selective extraction

Abstract

This invention relates to the technical field, specifically to a method for preparing high-purity n-hexane based on selective extraction of non-aromatic hydrocarbons. The method includes first suspending and polymerizing a first oil phase in a continuous aqueous phase to form cross-linked polymethacrylate core microspheres, then adding a second oil phase containing glycidyl methacrylate for further polymerization to obtain a cross-linked polymethacrylate microsphere matrix; swelling the microsphere matrix with n-heptane / ethyl acetate, then sequentially amination, followed by sequential reaction with n-butyl isocyanate and 2-(trifluoromethyl)phenyl isocyanate to obtain a selective extraction resin; activating and packing the resin into a column for the separation of non-aromatic C6 mixed hydrocarbons, collecting the fraction with a n-hexane mass fraction greater than 99.2 wt% to obtain high-purity n-hexane. This method has the advantages of high separation selectivity and good cycle stability.

Description

Technical Field

[0001] This invention relates to the technical field, specifically to a method for preparing high-purity n-hexane based on selective extraction of non-aromatic hydrocarbons. Background Technology

[0002] Hexane, as an important organic solvent, has wide applications in edible oil extraction, pharmaceutical intermediate refining, polymerization reaction solvents, and electronic chemical cleaning. With downstream industries demanding increasingly stringent requirements for product purity, stability, and safety, the market demand for high-purity hexane (typically requiring a mass fraction of 99% or higher) continues to grow. Industrially, hexane mainly originates from C6 mixed hydrocarbons in petroleum fractions. This mixture, in addition to hexane, also contains branched isomers such as 2-methylpentane and 3-methylpentane, as well as cycloalkanes such as cyclohexane and methylcyclopentane. Because these C6 non-aromatic components have similar boiling points to hexane, and some components even form azeotropes, traditional distillation separation methods are energy-intensive, lengthy, and have limited yields, making it difficult to obtain high-purity hexane economically and efficiently.

[0003] To address the aforementioned issues, adsorption-based or extraction-based separation techniques have gained attention in recent years. The basic principle is to utilize the differences in diffusion rates or adsorption affinities of hexane with branched alkanes and cycloalkanes within the pores of porous materials to achieve selective separation. Among these, extraction resins, as functionalized polymer materials, have become a research hotspot in this field due to their advantages such as strong structural designability, mild operating conditions, and ease of regeneration.

[0004] However, existing extraction resins or conventional adsorption separation materials generally suffer from the following technical bottlenecks when processing C6 mixed hydrocarbons: First, the pore structure of the resin matrix is ​​mostly through-pores that penetrate the entire particle, with excessively wide pore sizes and a lack of spatial partitioning, resulting in indistinct differences in the diffusion behavior of n-hexane with branched alkanes and cycloalkanes within the pores; second, the introduction of surface functional groups is often disordered, making it difficult to form an interface with a clear sieving function on the surface of the resin particles, resulting in a narrow selective separation window and difficulty in consistently achieving a n-hexane product purity of over 99%; furthermore, during long-term cyclic use, the resin repeatedly swells and shrinks in organic solvents, easily leading to pore structure deformation, surface functional group detachment or rearrangement, manifested as rapid selective decay, incomplete desorption, and large fluctuations in product purity over multiple cycles. These problems directly restrict the reliability of extraction separation technology in the continuous industrial production of high-purity n-hexane, making existing solutions unable to meet the long-term stable supply requirements of high-purity n-hexane in the fields of edible oil leaching solvent recovery and pharmaceutical intermediate refining. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for preparing high-purity n-hexane based on selective extraction of non-aromatic hydrocarbons, so as to solve the problems of high energy consumption, insufficient selectivity or poor cycle stability of existing distillation or adsorption separation methods when processing C6 mixed hydrocarbons with existing extraction resins.

[0006] To achieve the above objectives, the present invention provides a method for preparing high-purity n-hexane based on non-aromatic selective extraction, comprising the following steps:

[0007] (1) The first oil phase is subjected to suspension polymerization in a continuous aqueous phase to form cross-linked polymethyl methacrylate core microspheres; then the second oil phase is added to the reaction system and polymerization continues, so that the second oil phase preferentially swells and enters the outer layer of the core microspheres to obtain the cross-linked polymethyl methacrylate microsphere matrix;

[0008] (2) The cross-linked polymethacrylate microsphere matrix was placed in a swelling solution for swelling, and then first amination was performed with a first amination solution, and then second amination was performed with a second amination solution to obtain the modified resin.

[0009] (3) Using anhydrous toluene as a solvent, the modified resin was first reacted with n-butyl isocyanate under a nitrogen atmosphere, and then reacted with 2-(trifluoromethyl)phenyl isocyanate to obtain a selective extraction resin.

[0010] (4) After the selective extraction resin is activated, it is packed into a resin column, and the simulated C6 mixed hydrocarbon feed liquid is passed through the resin column. The fraction is collected to obtain high-purity n-hexane.

[0011] Preferably, the continuous aqueous phase in step (1) is composed of deionized water, polyvinyl alcohol, hydroxyethyl cellulose and sodium chloride, and the mass ratio of the deionized water, polyvinyl alcohol, hydroxyethyl cellulose and sodium chloride is 500g:4g:1g:2g.

[0012] Preferably, in step (1), the first oil phase is composed of methyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol, n-dodecane and 2,2'-azobisisobutyronitrile, and the mass ratio of methyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol, n-dodecane and 2,2'-azobisisobutyronitrile is 96g:30g:70g:40g:2g.

[0013] Preferably, the particle size of the cross-linked polymethacrylate microsphere matrix in step (1) is 300-600 μm.

[0014] Preferably, in step (1), the first oil phase is added to the continuous aqueous phase at 25°C, dispersed at 300 r / min for 20 min, and then heated to 72°C and kept at that temperature for 2 h.

[0015] Preferably, in step (1), the second oil phase is composed of methyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol and 2,2'-azobisisobutyronitrile, and the mass ratio of methyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol and 2,2'-azobisisobutyronitrile is 22-26g:16-20g:6g:15g:1g.

[0016] Preferably, in step (1), the second oil phase is slowly added dropwise along the reactor wall to the reaction system at 55°C for 60 minutes. After the addition is complete, the temperature is maintained at 55°C for 30 minutes, then raised to 72°C and maintained for 3 hours, and then raised to 80°C and maintained for 2 hours.

[0017] Preferably, the swelling solution in step (2) is composed of n-heptane and ethyl acetate.

[0018] Preferably, in step (2), the first amination is carried out using a first amination solution composed of 80g of anhydrous isopropanol and 7-9g of ethylenediamine, and the reaction is carried out at 18°C ​​for 20-25 minutes; after the first amination is completed, the first amination resin is obtained.

[0019] Preferably, in step (2), the second amination is carried out using a second amination solution composed of 160g of anhydrous isopropanol and 10-14g of 1,6-hexanediamine, and the reaction is carried out at 45°C for 2-2.5h. After the second amination is completed, the modified resin is obtained.

[0020] Preferably, in step (3), the modified resin, n-butyl isocyanate and 2-(trifluoromethyl)phenyl isocyanate are used in a ratio of 100g:5-7g:1-2g.

[0021] Preferably, the reaction temperature with n-butyl isocyanate in step (3) is 30°C and the reaction time is 3-4 h.

[0022] Preferably, the reaction temperature with 2-(trifluoromethyl)phenyl isocyanate in step (3) is 10°C and the reaction time is 45-60 min.

[0023] Preferably, the selective extraction resin described in step (4) is soaked in hexane, then packed into a glass column using a wet packing method, and further rinsed with hexane until the effluent is clear and stable, forming an activated resin bed.

[0024] Preferably, the simulated C6 mixed hydrocarbon feedstock liquid in step (4) is obtained by mixing 620g of n-hexane, 150g of 2-methylpentane, 100g of 3-methylpentane, 80g of cyclohexane and 50g of methylcyclopentane.

[0025] Preferably, the space velocity of the simulated C6 mixed hydrocarbon feedstock liquid through the resin column in step (4) is 1.0-1.4 h⁻¹.-1 .

[0026] Preferably, after collecting the fraction in step (4), the feed is stopped, and the resin column is desorbed with n-pentane. Then, the n-pentane in the column is replaced with n-hexane to complete one separation-regeneration cycle.

[0027] The beneficial effects of this invention are:

[0028] Compared with existing technologies, this invention uses cross-linked polymethacrylate microspheres as a matrix and constructs an interface structure with short-range polar sieving function in its shell region, achieving highly selective separation of n-hexane and significantly improving the stability of cyclic operation.

[0029] First, this invention employs stepwise amination treatment on a cross-linked polymethacrylate microsphere matrix to form a gradient functional group distribution from the outside to the inside in the shell region of the resin particles. This gradient structure, with short and long chains working together from the outside to the inside, enables efficient sieving of hexane and interfering components, avoiding the extension of internal mass transfer paths and the aggravation of desorption tailing caused by overall disordered modification, thus ensuring the high purity and high yield of the hexane product.

[0030] Secondly, by sequentially capping n-butyl isocyanate and 2-(trifluoromethyl)phenyl isocyanate, this invention further constructs an outer layer structure with a division of labor and synergistic effect on the basis of the polar sieving interface formed by amination modification. This effectively inhibits the continuous swelling and surface functional group rearrangement of the resin during the cyclic contact with organic solvents, thereby controlling the swelling rate of the resin at a low level and significantly enhancing the dimensional stability and structural integrity of the resin in long-term continuous operation.

[0031] In summary, this invention achieves a balance between separation selectivity, resolution efficiency, and cycle stability through a three-layer structure design: shell gradient amination, main urea crosslinking anchoring, and surface fluorinated swelling-limiting end capping. The three-layer structure is spatially layered and functionally synergistic, enabling the resin to maintain stable product purity and recovery rate after continuous multi-cycle operation. It also possesses excellent resolution efficiency and anti-swelling properties, providing a reliable technical solution for the industrial continuous production of high-purity n-hexane. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1: A method for preparing high-purity n-hexane based on selective extraction of non-aromatic hydrocarbons, the specific steps of which are as follows:

[0034] Preparation of selective extraction resins:

[0035] S1: Add 500g of deionized water to the reactor, heat to 90℃ while stirring at 300r / min, add 4g of polyvinyl alcohol in batches and keep warm for 40min until the system is clear and transparent, then cool down to 40℃, add 1g of hydroxyethyl cellulose and 2g of sodium chloride, continue stirring for 30min, and after the system is completely homogeneous, cool down to 25℃ and purge with nitrogen for 20min to obtain a continuous aqueous phase;

[0036] S2: In a separate dry flask, add 96g of methyl methacrylate, 30g of ethylene glycol dimethacrylate, 70g of cyclohexanol, 40g of n-dodecane and 2g of 2,2'-azobisisobutyronitrile, stir at 25°C until clear and homogeneous, then purge with nitrogen for 10 min to obtain the first oil phase;

[0037] S3: Add the first oil phase obtained in S2 to the continuous aqueous phase obtained in S1 at 25°C, control the stirring speed to 300r / min and disperse for 20min, then raise the temperature to 72°C and keep it for 2h, so that cross-linked polymethacrylate core microspheres are first formed inside the droplets. After the heat preservation is completed, keep stirring and continuously introduce nitrogen gas slowly.

[0038] S4: After the S3 reaction system is cooled to 55℃, take another flask and add 24g of methyl methacrylate, 18g of glycidyl methacrylate, 6g of ethylene glycol dimethacrylate, 15g of cyclohexanol and 1g of 2,2'-azobisisobutyronitrile. After stirring until clear, slowly add it dropwise along the wall of the flask to the S3 reaction system at 55℃ for 60min. After the addition is complete, continue to keep it at 55℃ for 30min to allow the second oil phase to preferentially swell and enter the outer layer of the existing seed microspheres. Then raise the temperature to 72℃ and keep it at 3h, and then raise the temperature to 80℃ and keep it at 2h.

[0039] S5: After the reaction of the S4 system is completed, cool to 25℃, filter and separate the microspheres, first wash with 60℃ deionized water until the filtrate has no obvious foam, then wash twice with anhydrous ethanol for 10 min each time to remove cyclohexanol, then wash twice with n-heptane for 10 min each time to remove n-dodecane, and finally wash once with anhydrous ethanol. Dry under vacuum at 50℃ for 12 h to constant weight. After drying, sieve according to standard, retain the resin particle size of 300-600 μm to obtain the cross-linked polymethyl methacrylate microsphere matrix;

[0040] S6: Take 100g of cross-linked polymethacrylate microsphere matrix and add it to a swelling solution composed of 160g of n-heptane and 20g of ethyl acetate. Gently roll the solution at 60r / min for 20min at 25℃. Then filter until there is no continuous free liquid on the resin surface and gently blow it with nitrogen for 1min to form a wet resin for later use.

[0041] S7: Immediately transfer the wet resin obtained in S6 into the first amination solution composed of 80g anhydrous isopropanol and 8g ethylenediamine, stir and react at 18°C ​​for 20min, filter quickly after the reaction is completed, and wash once with anhydrous isopropanol to obtain the first amination resin.

[0042] S8: Add 12g of 1,6-hexanediamine to 160g of anhydrous isopropanol, heat to 45℃ and stir until the solution is clear to obtain the second amination solution. Then, transfer the first amination resin obtained in S7 directly into the second amination solution without drying. Stir and react at 45℃ for 2h. After the reaction is completed, wash twice with anhydrous isopropanol and once with n-heptane, and then vacuum dry at 45℃ for 6h to obtain the modified resin.

[0043] S9: Add 100g of modified resin to 300g of anhydrous toluene and stir at 30°C for 30min under nitrogen protection to fully replace the residual polar solvent in the resin. Then dissolve 6g of n-butyl isocyanate in 30g of anhydrous toluene and add it dropwise to the above system within 30min. After the addition is complete, continue to react at 30°C for 3h.

[0044] S10: After the reaction of the S9 system is completed, the system temperature is lowered to 10°C. Then, 1 g of 2-(trifluoromethyl)phenyl isocyanate is dissolved in 20 g of anhydrous toluene and added dropwise to the above system over 20 min. After the addition is complete, the reaction continues at 10°C for 45 min. After the reaction is completed, the resin is filtered and separated. It is washed twice with anhydrous toluene, twice with anhydrous ethanol, and twice with n-hexane to remove unreacted isocyanate, adsorbed solvent, and low molecular weight byproducts. Then, it is vacuum dried at 45°C for 8 h to constant weight to obtain the selective extraction resin.

[0045] Selective extraction separation of n-hexane:

[0046] S11: Take 80g of selective extraction resin, add 160g of n-hexane and soak for 4h. After pouring out the soaking liquid, add another 80g of n-hexane and soak for 2h. Then, use the wet packing method to pack the resin into a conventional glass column with an inner diameter of 25mm and a filling height of 300mm. Continue to wash with n-hexane until the effluent is clear and stable to form an activated resin bed.

[0047] S12: Mix 620g of n-hexane, 150g of 2-methylpentane, 100g of 3-methylpentane, 80g of cyclohexane and 50g of methylcyclopentane evenly to obtain a simulated C6 mixed hydrocarbon feed liquid;

[0048] S13: The simulated C6 mixed hydrocarbon feedstock liquid obtained in S12 is passed into the activated resin bed obtained in S11 at 35°C, and the liquid hourly space velocity is controlled at 1.2 h⁻¹. -1For every 10g of effluent collected, a sample was taken and the content of each component was analyzed by gas chromatography. When the mass fraction of n-hexane in the effluent was higher than 99.2%, this portion of the effluent was combined as the n-hexane product fraction. When the mass fraction of n-hexane in the effluent dropped to below 99.2%, the collection of the product fraction was stopped.

[0049] S14: After the product fraction of S13 is collected, stop the feed and use 240g of n-pentane at 35℃ to analyze the resin bed until the total amount of branched alkanes and cycloalkanes in the effluent drops to near the detection limit. Then replace the n-pentane in the column with 80g of n-hexane to complete one separation-regeneration cycle.

[0050] S15: After 20 consecutive separation-regeneration cycles, the resin and product are tested.

[0051] Example 2: The difference from Example 1 is that in S4, 26g of methyl methacrylate, 16g of glycidyl methacrylate, 6g of ethylene glycol dimethacrylate, 15g of cyclohexanol, and 1g of 2,2'-azobisisobutyronitrile were added to a separate flask, stirred until clear, and then slowly added dropwise along the wall of the vessel to the S3 reaction system over 60 minutes at 55°C; in S6, 100g of cross-linked polymethacrylate microsphere matrix was added to a swelling solution composed of 170g of n-heptane and 15g of ethyl acetate, and gently rolled at 60r / min for 20 minutes at 25°C; in S7, the wet resin was immediately transferred to the first amination solution composed of 80g of anhydrous isopropanol and 7g of ethylenediamine, and stirred at 18°C ​​for 20 minutes; in S8, 10g of... 1,6-Hexanediamine was added to 160g of anhydrous isopropanol, heated to 45°C and stirred until the solution became clear to obtain a second amination solution. The first amination resin was then directly transferred into the second amination solution without drying, and the mixture was stirred at 45°C for 2 hours. In S9, 5g of n-butyl isocyanate was dissolved in 30g of anhydrous toluene and added dropwise to the above system over 30 minutes. After the addition was complete, the reaction was continued at 30°C for 3 hours. The remaining conditions were the same as in Example 1.

[0052] Example 3: The difference from Example 1 is that in S4, 22g of methyl methacrylate, 20g of glycidyl methacrylate, 6g of ethylene glycol dimethacrylate, 15g of cyclohexanol, and 1g of 2,2'-azobisisobutyronitrile were added to a separate flask and stirred until clear. Then, the mixture was slowly added dropwise along the wall of the flask to the S3 reaction system over 60 minutes at 55°C. In S6, 100g of cross-linked polymethacrylate microsphere matrix was added to a swelling solution composed of 150g of n-heptane and 25g of ethyl acetate and gently rolled at 60 rpm for 20 minutes at 25°C. In S7, the wet resin was immediately transferred to the first amination solution composed of 80g of anhydrous isopropanol and 9g of ethylenediamine and stirred at 18°C ​​for 20 minutes. In S8, 14g of... 1,6-Hexanediamine was added to 160g of anhydrous isopropanol, heated to 45°C and stirred until the solution became clear to obtain a second amination solution. The first amination resin was then directly transferred into the second amination solution without drying, and the reaction was carried out at 45°C for 2 hours. In S9, 7g of n-butyl isocyanate was dissolved in 30g of anhydrous toluene and added dropwise to the above system over 30 minutes. After the addition was complete, the reaction was continued at 30°C for 3 hours. In S10, 2g of 2-(trifluoromethyl)phenyl isocyanate was dissolved in 20g of anhydrous toluene and added dropwise to the above system over 20 minutes. After the addition was complete, the reaction was continued at 10°C for 45 minutes. The remaining conditions were the same as in Example 1.

[0053] Example 4: The difference from Example 1 is that in S6, 100g of cross-linked polymethacrylate microsphere matrix was added to a swelling solution composed of 160g of n-heptane and 20g of ethyl acetate, and gently rolled at 60r / min for 25min at 25℃; in S7, the wet resin was immediately transferred to a first amination solution composed of 80g of anhydrous isopropanol and 8g of ethylenediamine, and stirred at 18℃ for 25min; in S8, 12g of 1,6-hexanediamine was added to 160g of anhydrous isopropanol, heated to 45℃ and stirred until the solution was clear to obtain a second amination solution, and the first amination resin was directly transferred to the second amination solution without drying, and stirred at 45℃ for 2.5h; in S9, 6g of n-butyl isocyanate was dissolved in 30g of anhydrous toluene and added dropwise to the above system over 30min, and the reaction continued at 30℃ for 4h after the addition was completed; in S10, 1g of 2-(trifluoromethyl)phenyl isocyanate was dissolved in 20g of anhydrous toluene and added dropwise to the above system over 20min. After the addition was complete, the reaction was continued at 10°C for 60min. The remaining conditions were the same as in Example 1.

[0054] Comparative Example 1: The difference from Example 1 is that S2 and S4 are not carried out in steps. Instead, 120g of methyl methacrylate, 18g of glycidyl methacrylate, 36g of ethylene glycol dimethacrylate, 85g of cyclohexanol, 40g of n-dodecane and 3g of 2,2'-azobisisobutyronitrile are prepared into an oil phase at one time and added to the continuous aqueous phase obtained in S1 at 25°C. After dispersing for 20 minutes with a stirring speed of 300r / min, the suspension polymerization is completed directly according to the S3 heating program of Example 1, without performing step S4 of Example 1. The other conditions are the same as in Example 1.

[0055] Comparative Example 2: The difference from Example 1 is that in S7 of Example 1, ethylenediamine was replaced with an equal amount of 1,6-hexanediamine, and the other conditions were the same as in Example 1.

[0056] Comparative Example 3: The difference from Example 1 is that the order of adding S7 and S8 in Example 1 is reversed. Specifically, 12g of 1,6-hexanediamine is first added to 160g of anhydrous isopropanol, heated to 45°C and stirred until the solution is clear to obtain the first amination solution. Then, the wet resin obtained in S6 is transferred into the first amination solution and stirred at 45°C for 2 hours. After filtration, it is directly transferred into the second amination solution composed of 80g of anhydrous isopropanol and 8g of ethylenediamine without drying, and stirred at 18°C ​​for 20 minutes. The remaining conditions are the same as in Example 1.

[0057] Comparative Example 4: The difference from Example 1 is that 2-(trifluoromethyl)phenyl isocyanate is not added in S10 of Example 1, but 1g of n-butyl isocyanate is used instead of 1g of 2-(trifluoromethyl)phenyl isocyanate, only to keep the total added mass of the system consistent. Then, the selective extraction resin is obtained directly according to the washing and drying conditions of Example 1; the other conditions are the same as those of Example 1.

[0058] Comparative Example 5: The difference from Example 1 is that the order of adding S9 and S10 in Example 1 is reversed. Specifically, 1g of 2-(trifluoromethyl)phenyl isocyanate is first dissolved in 20g of anhydrous toluene and added dropwise to a system containing 100g of modified resin and 300g of anhydrous toluene over 20 minutes at 10°C. After the addition is complete, the reaction continues at 10°C for 45 minutes. Then, the temperature is raised to 30°C, and 6g of n-butyl isocyanate is dissolved in 30g of anhydrous toluene and added dropwise to the above system over 30 minutes. After the addition is complete, the reaction continues at 30°C for 3 hours. The remaining conditions are the same as in Example 1.

[0059] Comparative Example 6: The difference from Example 1 is that the second amination liquid treatment in S8 is omitted, and the 2-(trifluoromethyl)phenyl isocyanate treatment in S10 is omitted. The other conditions are the same as in Example 1.

[0060] Performance testing

[0061] The selective extraction resins obtained in the examples and comparative examples were used as test samples. They were first vacuum dried at 45°C for 12 hours, and then cooled to room temperature in a desiccator. Sampling was carried out according to GB / T 6678-2003, and resin particle sizes of 300-600 μm were selected according to GB / T 6003.1-2022. For the samples used for application performance testing, 80 g of resin was taken for activation, column packing, feeding, separation, desorption, and cycling tests. All samples were prepared in triplicate and tested in triplicate. The test results were taken as the arithmetic mean.

[0062] Specific surface area test: According to GB / T 19587-2017, take 0.50g of resin for each sample and place it in the sample tube of the specific surface area analyzer. Degas under vacuum at 80℃ for 8h. After degassing, cool to room temperature and determine the adsorption-desorption isotherm of the sample by nitrogen adsorption at liquid nitrogen temperature. Calculate the specific surface area using the BET method within the relative pressure range of 0.05-0.30.

[0063] Tests on the purity, effective yield of high-purity n-hexane, and recovery rate of n-hexane: Gas chromatography determination was performed according to GB / T 9722-2023, and the component quantification conditions were set according to SH / T 1674-2023. The results were expressed in accordance with GB / T17602-2018 and HG / T The impurity control strategy for hexane and isohexane products outlined in 5612-2019 is as follows: Each sample undergoes dynamic fixed-bed separation. A sample is taken every 10g of eluent. The contents of n-hexane, 2-methylpentane, 3-methylpentane, cyclohexane, and methylcyclopentane are determined using the external standard method. A 30m × 0.32mm × 0.25μm 5% phenylmethyl polysiloxane capillary column is used for gas chromatography. The injection temperature is 200℃, the detector temperature is 250℃, the split ratio is 50:1, and the column temperature program is 40℃ for 5 min, then increased to 90℃ at a rate of 5℃ / min and held for 5 min. All fractions of n-hexane with a mass fraction greater than 99.2wt% in the eluent are combined, and their cumulative mass is recorded as the effective yield of high-purity n-hexane. The n-hexane recovery rate is calculated as the ratio of the mass of n-hexane in the combined eluent to the total mass of n-hexane in the feed solution.

[0064] Test of the amount of n-pentane required for the endpoint of analysis: Gas chromatography quantification is still performed as described above. After the product fraction is collected, the resin bed is analyzed with n-pentane. A sample is taken once for every 10g of eluent collected, and the total content of 2-methylpentane, 3-methylpentane, cyclohexane and methylcyclopentane is determined. When the total mass fraction of the above four components in the eluent drops to below 0.10wt%, the cumulative mass of n-pentane added at this time is recorded as the amount of n-pentane required for the endpoint of analysis.

[0065] 20-cycle stability test: Each sample was subjected to 20 consecutive separation-regeneration cycles. The purity of the n-hexane product, the effective yield of high-purity n-hexane, and the n-hexane recovery rate were recorded for each cycle. The purity fluctuation was represented by the difference between the highest and lowest product purity in the 20 cycles, and the recovery rate retention rate was represented by the ratio of the n-hexane recovery rate in the 20th cycle to the n-hexane recovery rate in the 1st cycle.

[0066] Swelling rate test of resin in simulated C6 mixed hydrocarbons: The soaking principle was carried out in accordance with GB / T 11547-2008, as follows: Take 10g of each sample resin, first vacuum dry at 45℃ for 12h and record the initial apparent volume V0, then add 100g of simulated C6 mixed hydrocarbon raw material liquid, let it stand and soak at 35℃ for 24h, take it out and let it drain naturally in the same funnel for 5min, then put it into a 25mL graduated cylinder, read the apparent volume V1 under the same light shaking condition 10 times, and calculate the swelling rate according to (V1-V0) / V0×100%. Repeat the same test on the resin after 20 cycles to obtain the swelling rate of the resin after the 20th cycle. The above test results are shown in Table 1.

[0067] Table 1 Performance Test Results

[0068]

[0069] Data Analysis: As can be seen from the data of the examples in Table 1, the selective extraction resin prepared by the present invention exhibits a good balance between specific surface area, effective yield of high-purity n-hexane, n-hexane product purity, n-hexane recovery rate, amount of n-pentane required for the analytical endpoint, purity fluctuation after 20 cycles, recovery rate retention rate after 20 cycles, and resin swelling rate after the 20th cycle.

[0070] As can be seen from the data in Table 1 for Example 1 and Comparative Example 1, when glycidyl methacrylate is distributed into the entire cross-linked polymethacrylate microspheres in a single step without using two-stage suspension polymerization, the effective yield of high-purity n-hexane, the purity of the n-hexane product, and the n-hexane recovery rate all decrease significantly, while the amount of n-pentane required for the analytical endpoint, the purity fluctuation after 20 cycles, and the resin swelling rate after the 20th cycle all increase significantly. The main reason for this is that two-stage suspension polymerization is not simply an adjustment to the pelletizing step, but rather a prerequisite for subsequent shell confinement modification, playing a fundamental role in the final separation window and cycle stability.

[0071] As can be seen from the comparison of the data of Example 1 with Comparative Examples 2 and 3 in Table 1, the composition or order of addition of ethylenediamine and 1,6-hexanediamine has a significant impact on separation performance. When ethylenediamine was replaced with an equal amount of 1,6-hexanediamine in Comparative Example 2, it was difficult to form a high-density short-chain amine site in the outermost layer, the functional group distribution of the shell layer from the outside to the inside was weakened, and the diffusion-partition difference between n-hexane and branched alkanes and cycloalkanes was reduced. Reversing the order of addition of the two substances, although some short-chain sites can still be formed later, the sequential occupancy relationship of the inner and outer sites in the shell layer is changed, and the ideal spatial configuration of the outer layer being dense first and the inner layer being supplemented later cannot be achieved, resulting in a decrease in overall separation performance.

[0072] As can be seen from the data in Table 1 for Examples 1, 4, and 5, the timing of the addition of 2-(trifluoromethyl)phenyl isocyanate is crucial. The main reason is that the sequential treatment of n-butyl isocyanate first and then 2-(trifluoromethyl)phenyl isocyanate allows the main separation layer and the surface expansion-limiting layer to achieve spatial division of labor and synergy, demonstrating a significant effect where one plus one is greater than two.

[0073] As can be seen from the data in Table 1 for Example 1 and Comparative Example 6, when only the first amination treatment of ethylenediamine is retained and the second amination liquid treatment of 1,6-hexanediamine is eliminated, and the 2-(trifluoromethyl)phenyl isocyanate treatment is also eliminated, the specific surface area does not deteriorate significantly. However, the effective yield of high-purity n-hexane, the n-hexane recovery rate, the recovery rate retention rate after 20 cycles, and the resin swelling rate after the 20th cycle are significantly worse. The main reason for this is that the technical effect of the present invention does not come from a single functional group or a single step, but from the layered synergistic effect formed by ethylenediamine, 1,6-hexanediamine, n-butyl isocyanate, and 2-(trifluoromethyl)phenyl isocyanate in the same shell region.

[0074] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing high-purity n-hexane based on selective extraction of non-aromatic hydrocarbons, characterized in that, Includes the following steps: (1) The first oil phase is subjected to suspension polymerization in a continuous aqueous phase to form cross-linked polymethyl methacrylate core microspheres; then the second oil phase is added to the reaction system and polymerization continues, so that the second oil phase preferentially swells and enters the outer layer of the core microspheres to obtain the cross-linked polymethyl methacrylate microsphere matrix; (2) The cross-linked polymethacrylate microsphere matrix was placed in a swelling solution for swelling, and then first amination was performed with a first amination solution, and then second amination was performed with a second amination solution to obtain the modified resin. (3) Using anhydrous toluene as a solvent, the modified resin was first reacted with n-butyl isocyanate under a nitrogen atmosphere, and then reacted with 2-(trifluoromethyl)phenyl isocyanate to obtain a selective extraction resin. (4) After the selective extraction resin is activated, it is packed into a resin column, and the simulated C6 mixed hydrocarbon feed liquid is passed through the resin column. The fraction is collected to obtain high-purity n-hexane. Step (2) The first amination solution consists of 80g of anhydrous isopropanol and 7-9g of ethylenediamine; Step (2) The second amination solution consists of 160g of anhydrous isopropanol and 10-14g of 1,6-hexanediamine.

2. The preparation method according to claim 1, characterized in that, The continuous aqueous phase in step (1) consists of deionized water, polyvinyl alcohol, hydroxyethyl cellulose and sodium chloride. The mass ratio of the deionized water, polyvinyl alcohol, hydroxyethyl cellulose and sodium chloride is 500g:4g:1g:2g.

3. The preparation method according to claim 1, characterized in that, Step (1) The first oil phase is composed of methyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol, n-dodecane and 2,2'-azobisisobutyronitrile. By mass, the ratio of methyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol, n-dodecane and 2,2'-azobisisobutyronitrile is 96g:30g:70g:40g:2g.

4. The preparation method according to claim 1, characterized in that, Step (1) The second oil phase is composed of methyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol and 2,2'-azobisisobutyronitrile. By mass, the ratio of methyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, cyclohexanol and 2,2'-azobisisobutyronitrile is 22-26g:16-20g:6g:15g:1g.

5. The preparation method according to claim 1, characterized in that, In step (3), the modified resin, n-butyl isocyanate and 2-(trifluoromethyl)phenyl isocyanate are used in a ratio of 100g:5-7g:1-2g.

6. The preparation method according to claim 1, characterized in that, The reaction temperature with n-butyl isocyanate in step (3) is 30°C and the reaction time is 3-4 h.

7. The preparation method according to claim 1, characterized in that, The reaction temperature with 2-(trifluoromethyl)phenyl isocyanate in step (3) is 10°C and the reaction time is 45-60 min.

8. The preparation method according to claim 1, characterized in that, The simulated C6 mixed hydrocarbon feedstock liquid in step (4) is obtained by mixing 620g of n-hexane, 150g of 2-methylpentane, 100g of 3-methylpentane, 80g of cyclohexane and 50g of methylcyclopentane.

9. The preparation method according to claim 1, characterized in that, In step (4), the space velocity of the simulated C6 mixed hydrocarbon feed liquid through the resin column is 1.0-1.4 h⁻¹. -1 .

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