Preparation method of high-purity heptane

Abstract

The invention belongs to the technical field of preparation of high-purity heptane, and particularly relates to a preparation method of high-purity heptane. The preparation method comprises the following steps: (1) preparing an adsorbent; (2) feeding the raw material naphtha into a hydrofining reactor, and carrying out refining reactions such as desulfurization and olefin saturation to obtain refined naphtha; (3) the refined naphtha enters an adsorption tower containing the adsorbent prepared in the step (1) for adsorption separation and desorption, and desorbed oil is obtained; and (4) separating high-purity n-heptane and high-purity n-hexane by using the desorbed oil as a raw material through rectification equipment. The purity of the high-purity n-heptane prepared by the method is greater than or equal to 99.5%, and the yield is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-purity n-heptane preparation, and particularly relates to a method for preparing high-purity heptane. Background Art

[0002] n-Heptane is a straight-chain saturated alkane with the chemical formula and is one of the various isomers of heptane. As an important organic solvent and chemical raw material, n-heptane has a wide range of applications in the fields of pharmaceuticals, coatings, paints, and fine chemical production. Its purity directly affects the quality and performance of the final product. Currently, the purity of n-heptane available on the market is usually above 90%, but with the development of the industry and technological progress, for some high-end applications, such as electronic-grade chemicals and special analytical reagents, the purity requirement for n-heptane has been increased to above 99.5%, and the demand is becoming increasingly urgent.

[0003] Chinese Patent CN107586250B discloses a method for preparing high-purity n-hexane and high-purity n-heptane, which is prepared from the desorbed oil of naphtha adsorption separation. In the present invention, the desorbed oil of naphtha adsorption separation is subjected to rectification processing to obtain a high-purity n-hexane solvent product with a purity > 99% and a high-purity n-heptane solvent product with a purity of 99%; the recovery yields can reach > 80% and > 78% respectively. The desorbed oil used in this method is the desorbed oil rich in normal paraffins obtained by subjecting naphtha to hydrotreating pretreatment and then adsorptive separation through 5A molecular sieve. It has been found in practice that the mass content of normal paraffins in the desorbed oil obtained by adsorptive separation through 5A molecular sieve is not stable. Especially when the mass content of normal paraffins is low, the purity of n-heptane cannot reach 99.5%, and the yield of this method is also not ideal. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing high-purity heptane, which uses a specific adsorbent for adsorptive separation to obtain a desorbed oil with a high content of normal paraffins, and then prepares n-heptane with a purity ≥ 99.5% through a continuous rectification process, while the yield is also improved.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing high-purity heptane, comprising the following steps: (1) Preparing an adsorbent, comprising the following steps: S1: Mixing HY molecular sieve and MCM-41 molecular sieve to obtain a mixed molecular sieve; S2: Immersing the mixed molecular sieve in hydrochloric acid, stirring, filtering, and calcining the solid to obtain a calcined molecular sieve; S3: Immerse the calcined molecular sieve completely in a toluene solution of hexamethyldisilazane, reflux, filter, wash the solid, and dry it under vacuum to obtain a passivated molecular sieve; S4: Immerse the passivated molecular sieve completely in an ethanol solution of nitrobenzoic acid, stir, filter, and heat the solid in a nitrogen atmosphere to obtain a molecular sieve bonded with nitrobenzene groups; S5: Immerse the molecular sieve bonded with nitrobenzene groups completely in an aqueous solution of magnesium nitrate, shake, filter, and calcine the solid to obtain a molecular sieve loaded with metal oxides; S6: In a nitrogen atmosphere, subject the molecular sieve loaded with metal oxides to degassing treatment to obtain an adsorbent; (2) The feedstock naphtha enters a hydrofining reactor for a refining reaction to obtain refined naphtha; (3) The refined naphtha enters an adsorption tower containing the adsorbent prepared in step (1) for adsorption separation and desorption to obtain desorbed oil; (4) Using the desorbed oil as a raw material, high-purity n-heptane and high-purity n-hexane are separated by a distillation device; the distillation device includes two distillation towers connected in sequence, namely an n-hexane distillation tower and an n-heptane distillation tower. High-purity n-hexane is cut out from the top of the n-hexane distillation tower, and high-purity n-heptane is cut out from the top of the n-heptane distillation tower.

[0006] In the present invention, by mixing HY molecular sieve and MCM-41 molecular sieve in a specific ratio, a mesoporous-microporous composite molecular sieve is obtained, which has both macroporous diffusion channels and microporous selective adsorption sites; first, the pores are activated by calcination and the template agent is removed, and then the silane groups cover the acidic sites on the surface of the molecular sieve, reducing the adsorption of n-heptane by passivating the acidic sites: Then, the nitrobenzene groups are anchored on the surface of the molecular sieve through hydrogen bonds, introducing π-electron acceptor groups to enhance the adsorption of aromatics. Finally, It is loaded on the surface of the molecular sieve by ion exchange and calcined to generate magnesium oxide nanoparticles loaded on the molecular sieve. The basic surface of MgO has a strong interaction with the methyl groups of branched isomers through van der Waals forces, and can selectively adsorb branched isomers while repelling straight-chain n-heptane.

[0007] The weight ratio of the HY molecular sieve to the MCM-41 molecular sieve is (2 - 3):1.

[0008] The present invention can improve the purity and yield of n - heptane by using two types of molecular sieves in a specific ratio. This is mainly because the pore diameter of the mesopores of MCM - 41 allows branched - chain isomers and aromatics to quickly diffuse into the HY micropore region, avoiding the low adsorption efficiency caused by large diffusion resistance in traditional microporous molecular sieves. The straight - chain molecules of n - heptane need to adopt an extended conformation in the micropores, resulting in a decrease in entropy, while the branched - chain isomers are more likely to enter due to their compact structure. The micropores screen and retain some branched - chain isomers, and the MCM - 41 molecular sieve captures large - molecule aromatics: the pore channels repel n - heptane through steric hindrance and enhance the adsorption of branched - chain isomers. Through the optimized design of the mixing ratio (2 - 3):1, sufficient microporous adsorption sites are ensured to cover the main impurities.

[0009] Preferably, in S2, the stirring temperature and time are 80 - 85 °C and 4 - 6 h; in S3, the reflux temperature and time are 120 - 130 °C and 12 - 15 h; in S4, the stirring temperature and time are 60 - 65 °C and 8 - 10 h; in S4, the heating temperature and time are 300 - 320 °C and 2 - 4 h; in S5, the oscillation time is 4 - 6 h.

[0010] Preferably, in step (2), a hydrofining catalyst is used for the refining reaction, and the conditions of the refining reaction are: pressure 1.7 - 2.3 MPa, temperature 240 - 260 °C.

[0011] Preferably, in step (3), the adsorption pressure is 0.5 - 1.0 MPa, and the desorption pressure is 0.5 - 1.0 MPa; the adsorption temperature is 250 - 320 °C, and the desorption temperature is 250 - 320 °C; the adsorption time is 20 - 30 minutes, and the desorption time is 20 - 30 minutes.

[0012] Preferably, in step (4), the operating temperature of the hexane distillation column: the top - tower temperature is 67 °C, the bottom - tower temperature is 128 °C, and the operating pressure is 0.05 MPa; and the operating temperature of the heptane distillation column: the top - tower temperature is 97 °C, the bottom - tower temperature is 145 °C, and the operating pressure is 0.05 MPa.

[0013] Preferably, in step (4), the mass content of n - paraffin in the desorbed oil is ≥99.5%, the sulfur mass content is ≤0.5 ppm, the nitrogen mass content is ≤0.5 ppm, the bromine index is ≤5 mgBr / 100 g, and the aromatic mass content is ≤10 ppm.

[0014] Preferably, in step (4), each distillation column is fed in the middle, and the bottom material of the previous tower is the feed of the next tower.

[0015] Preferably, in step (4), the reflux ratio of the hexane distillation column is 3 - 4, the number of theoretical plates is 70, and the processing load is 4.6 L / h; the reflux ratio of the heptane distillation column is 3 - 5, the number of theoretical plates is 80, and the processing load is 4.0 L / h.

[0016] Preferably, the hydrofining catalyst used in the hydrofining reaction in step (2) is a three-leaf clover particle with a diameter of Ø2.0×2 - 8 mm, a specific surface area of ≥150 m 2 / g, and a bulk density of 0.72 - 0.82 g / cm 3 , and a radial compressive strength of ≥150 N / cm.

[0017] Preferably, the high-purity n-heptane obtained in step (4) has a purity of ≥99.5% and a yield of ≥20%.

[0018] The low reflux ratio used in the present invention can produce high-purity n-heptane. On the premise of ensuring product quality, energy consumption is reduced by lowering the reflux ratio, achieving the goal of energy conservation and emission reduction.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. By using a mixture of HY zeolite and MCM-41 zeolite with a specific ratio and modifying them, the adsorbent obtained can improve the purity and yield of n-heptane; the purity of high-purity n-heptane is ≥99.5%, and the yield of high-purity n-heptane is ≥20%. The high-quality products prepared can meet the needs of high-end applications. At the same time, the purity and yield of n-hexane prepared are also improved.

[0020] 2. Compared with the prior art, the low reflux ratio used in the present invention can produce high-purity n-heptane. On the premise of ensuring product quality, energy consumption is reduced by lowering the reflux ratio, achieving the goal of energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of a preparation method of high-purity heptane. DETAILED DESCRIPTION OF THE INVENTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0023] All raw materials used in the following embodiments of the present invention are commercially available products: HY zeolite, Ost Catalysis Materials (Dalian) Co., Ltd., pore size 0.74 nm, crystal grains 0.5 - 10 μm.

[0024] MCM-41 zeolite, Ost Catalysis Materials (Dalian) Co., Ltd., pore size 2 - 5 nm, crystal grain size 1 - 10 μm.

[0025] Clover particles: diameter 2.0 mm, length 2 - 8 mm, specific surface area 150 - 200 m 2 / g, bulk density 0.80 g / cm 3 , radial compressive strength 150 - 200 N / cm.

[0026] Example 1 This example provides a method for preparing high-purity heptane, including the following steps: (1) Prepare an adsorbent, including the following steps: S1: Mix HY zeolite and MCM-41 zeolite with a weight ratio of 2.5:1 to obtain a mixed zeolite; S2: Immerse the mixed zeolite completely in 1.1 mol / L hydrochloric acid, stir at 82 °C for 5 h, filter, and calcine the solid at 560 °C for 7 h to obtain a calcined zeolite; S3: Immerse the calcined zeolite completely in a toluene solution of 13 wt% hexamethyldisilazane, reflux at 125 °C for 14 h, filter, wash the solid successively with toluene and ethanol, and dry it under vacuum to obtain a passivated zeolite; S4: Immerse the passivated zeolite completely in an ethanol solution of 6 wt% nitrobenzoic acid, stir at 62 °C for 9 h, filter, and heat the solid at 310 °C for 3 h in a nitrogen atmosphere to obtain a nitrobenzene group-bonded zeolite; S5: Immerse the nitrobenzene group-bonded zeolite completely in 0.1 mol / L magnesium nitrate aqueous solution, oscillate at 25 °C and 160 rpm for 5 h, filter, and calcine the solid at 460 °C for 4 h to obtain a zeolite loaded with metal oxide; S6: In a nitrogen atmosphere, degas the zeolite loaded with metal oxide at 300 °C for 4 h to remove residual organic matter and obtain an adsorbent.

[0027] (2) Prepare desorbed oil: Carry out a secondary hydrorefining reaction on the refined naphtha. The reaction part uses a hydrorefining catalyst. At a pressure of 2.0 MPa and a temperature of 250 °C, convert trace sulfur and the like contained in the raw material into hydrogen sulfide that is easy to remove, and at the same time, convert a small amount of olefin saturation reaction into alkanes to obtain refined naphtha. Send the refined naphtha into an adsorption tower containing an adsorbent for adsorption; the height-to-diameter ratio of the adsorption tower is 4.0, the adsorption pressure is 0.7 MPa, and the adsorption temperature is 290 °C; the desorbent is n-tetradecane, with a flow rate of 2 m 3 / (m 3Desorbent · h) Inject n-tetradecane for desorption. The desorption pressure is 0.7 MPa, and the desorption temperature is 290 °C; the adsorption time is 25 minutes, and the desorption time is 25 minutes to obtain desorbed oil. The mass content of n-alkanes in the desorbed oil is ≥ 99.5%, the sulfur mass content is ≤ 0.5 ppm, the nitrogen mass content is ≤ 0.5 ppm, the bromine index is ≤ 5 mgBr / 100 g, and the aromatic hydrocarbon mass content is ≤ 10 ppm.

[0028] (3)Preparation of high-purity n-heptane and high-purity n-hexane: Using the desorbed oil as the raw material, high-purity n-heptane and high-purity n-hexane are prepared through a distillation device; the distillation device includes two distillation towers connected in sequence, namely the n-hexane distillation tower and the n-heptane distillation tower. Each distillation tower is fed in the middle, the bottom material of the previous tower is the feed of the next tower. The top of the n-hexane distillation tower is 67 °C, the bottom is 128 °C, the pressure is 0.05 MPa, the reflux ratio of the n-hexane distillation tower is 4, the theoretical number of plates is 70, and the processing load is 4.6 L / h; the top of the n-heptane distillation tower is 97 °C, the bottom is 145 °C, the pressure is 0.05 MPa, the reflux ratio of the n-heptane distillation tower is 4, the theoretical number of plates is 80, and the processing load is 4.0 L / h. High-purity n-hexane is cut out from the top of the n-hexane distillation tower, and high-purity n-heptane is cut out from the top of the n-heptane distillation tower.

[0029] Example 2 This example provides a method for preparing high-purity n-heptane, including the following steps: (1)Preparation of the adsorbent. The preparation method of the adsorbent includes the following steps: S1: Mix HY zeolite and MCM-41 zeolite with a weight ratio of 2:1 to obtain a mixed zeolite; S2: Immerse the mixed zeolite completely in 1.0 mol / L hydrochloric acid, stir at 80 °C for 6 h, filter, and calcine the solid at 550 °C for 8 h to obtain a calcined zeolite; S3: Immerse the calcined zeolite completely in a toluene solution of 12 wt% hexamethyldisilazane, reflux at 130 °C for 12 h, filter, wash the solid with toluene and ethanol in sequence, and dry it in vacuum to obtain a passivated zeolite; S4: Immerse the passivated zeolite completely in an ethanol solution of 7 wt% nitrobenzoic acid, stir at 65 °C for 8 h, filter, and heat the solid at 320 °C for 2 h in a nitrogen atmosphere to obtain a nitrobenzene group-bonded zeolite; S5: Immerse the nitrobenzene group-bonded zeolite completely in 0.1 mol / L magnesium nitrate aqueous solution, oscillate at 20 °C and 200 rpm for 4 h, filter, and calcine the solid at 480 °C for 3 h to obtain a zeolite loaded with metal oxide; S6: In a nitrogen atmosphere, degas the zeolite loaded with metal oxide at 300 °C for 4 h to remove residual organic matter and obtain the adsorbent.

[0030] (2) Preparation of desorbed oil: The refined naphtha is subjected to secondary hydrofining reaction. A hydrofining catalyst is used in the reaction part. At a pressure of 2.0 MPa and a temperature of 250 °C, trace sulfur and the like contained in the raw material are converted into hydrogen sulfide which is easy to remove. At the same time, a small amount of olefin saturation reaction is converted into alkanes to obtain refined naphtha. The refined naphtha is sent to an adsorption tower containing an adsorbent for adsorption. The height-diameter ratio of the adsorption tower is 4.0, the adsorption pressure is 0.7 MPa, and the adsorption temperature is 290 °C; the desorbent is n-tetradecane, and n-tetradecane is injected at a flow rate of 2 m 3 / (m 3 desorbent·h) for desorption. The desorption pressure is 0.7 MPa and the desorption temperature is 290 °C; the adsorption time is 25 minutes and the desorption time is 25 minutes to obtain desorbed oil. The mass content of n-alkanes in the desorbed oil is ≥99.5%, the sulfur mass content is ≤0.5 ppm, the nitrogen mass content is ≤0.5 ppm, the bromine index is ≤5 mgBr / 100 g, and the aromatic hydrocarbon mass content is ≤10 ppm.

[0031] (3) Preparation of high-purity n-heptane and high-purity n-hexane: Using the desorbed oil as the raw material, high-purity n-heptane and high-purity n-hexane are prepared through a distillation device; the distillation device includes two distillation towers connected in sequence, namely an n-hexane distillation tower and an n-heptane distillation tower. Each distillation tower is fed in the middle. The bottom material of the previous tower is the feed of the next tower. The top of the n-hexane distillation tower is 67 °C, the bottom is 128 °C, the pressure is 0.05 MPa, the reflux ratio of the n-hexane distillation tower is 4, the theoretical number of plates is 97, and the processing load is 4.6 L / h; the top of the n-heptane distillation tower is 97 °C, the bottom is 145 °C, the pressure is 0.05 MPa, the reflux ratio of the n-heptane distillation tower is 4, the theoretical number of plates is 80, and the processing load is 4.0 L / h. High-purity n-hexane is cut out from the top of the n-hexane distillation tower, and high-purity n-heptane is cut out from the top of the n-heptane distillation tower.

[0032] Example 3 The difference between this example and Example 1 is that in S4, the heating temperature and time are 300 °C and 2 h.

[0033] Example 4 The difference between this example and Example 1 is that in S4, the heating temperature and time are 320 °C and 4 h.

[0034] Example 5 The difference between this example and Example 1 is that in step (2), the conditions of the refining reaction are: pressure 1.7 MPa, temperature 240 °C.

[0035] Example 6 The difference between this example and Example 1 is that in step (2), the conditions of the refining reaction are: pressure 2.3 MPa, temperature 260 °C.

[0036] Example 7 The differences between this embodiment and Embodiment 1 are as follows: in step (3), the adsorption pressure is 0.5 MPa, the desorption pressure is 0.5 MPa; the adsorption temperature is 250 °C, the desorption temperature is 250 °C; the adsorption time is 20 minutes, and the desorption time is 20 minutes.

[0037] Example 8 The differences between this embodiment and Embodiment 1 are as follows: in step (3), the adsorption pressure is 1.0 MPa, the desorption pressure is 1.0 MPa; the adsorption temperature is 320 °C, the desorption temperature is 320 °C; the adsorption time is 30 minutes, and the desorption time is 30 minutes.

[0038] Comparative Example 1 The differences between this comparative example and Embodiment 1 are as follows: the adsorbent is replaced with a mixed molecular sieve, and the mixed molecular sieve includes HY molecular sieve and MCM-41 molecular sieve with a weight ratio of 2.5:1.

[0039] Comparative Example 2 The differences between this comparative example and Embodiment 1 are as follows: step S1 is different.

[0040] Specifically: S1: Mix HY molecular sieve and MCM-41 molecular sieve with a weight ratio of 1.5:1 to obtain a mixed molecular sieve.

[0041] Comparative Example 3 The differences between this comparative example and Embodiment 1 are as follows: step S1 is different.

[0042] Specifically: Replace the mixed molecular sieve with HY molecular sieve.

[0043] Comparative Example 4 The differences between this comparative example and Embodiment 1 are as follows: the preparation method of the adsorbent is different.

[0044] The preparation method of the adsorbent includes the following steps: S1: Mix HY molecular sieve and MCM-41 molecular sieve with a weight ratio of 2.5:1 to obtain a mixed molecular sieve; S2: Immerse the mixed molecular sieve completely in 1.1 mol / L hydrochloric acid, stir at 82 °C for 5 h, filter, and calcine the solid at 560 °C for 7 h to obtain a calcined molecular sieve; S3: Immerse the calcined molecular sieve completely in a toluene solution of 13 wt% hexamethyldisilazane, reflux at 125 °C for 14 h, filter, wash the solid with toluene and ethanol in sequence, and dry it under vacuum to obtain a passivated molecular sieve; S4: Immerse the passivated molecular sieve completely in 0.1 mol / L magnesium nitrate aqueous solution, oscillate at 25 °C and 160 rpm for 5 h, filter, and calcine the solid at 460 °C for 4 h to obtain a molecular sieve loaded with metal oxide; S5: In a nitrogen atmosphere, the molecular sieve loaded with metal oxide is degassed at 300 °C for 4 h to remove residual organic substances, obtaining an adsorbent.

[0045] Comparative Example 5 The difference between this comparative example and Example 1 is: different preparation methods of the adsorbent.

[0046] The preparation method of the adsorbent includes the following steps: S1: Mix HY molecular sieve and MCM-41 molecular sieve with a weight ratio of 2.5:1 to obtain a mixed molecular sieve; S2: Immerse the mixed molecular sieve completely in 1.1 mol / L hydrochloric acid, stir at 82 °C for 5 h, filter, and calcine the solid at 560 °C for 7 h to obtain a calcined molecular sieve; S3: Immerse the calcined molecular sieve completely in a toluene solution of 13 wt% hexamethyldisilazane, reflux at 125 °C for 14 h, filter, wash the solid successively with toluene and ethanol, and dry it under vacuum to obtain a passivated molecular sieve; S4: Immerse the passivated molecular sieve completely in an ethanol solution of 6 wt% nitrobenzoic acid, stir at 62 °C for 9 h, filter, and heat the solid at 310 °C for 3 h in a nitrogen atmosphere to obtain a nitrobenzene group-bonded molecular sieve; S5: In a nitrogen atmosphere, the molecular sieve of the nitrobenzene group-bonded molecular sieve is degassed at 300 °C for 4 h to remove residual organic substances, obtaining an adsorbent.

[0047] Performance test Use the preparation methods of high-purity heptane in Examples 1-8 and Comparative Examples 1-5 to prepare high-purity hexane and high-purity heptane. Each component is measured by gas chromatography, and the purity and yield are shown in Table 1.

[0048] Purity: mass of n-heptane (n-hexane) in the cut fraction at the top of the n-heptane (n-hexane) rectification column ÷ total mass of the cut fraction at the top of the n-heptane (n-hexane) rectification column × 100%; Yield: mass of the cut fraction at the top of the n-heptane (n-hexane) rectification column ÷ mass of the naphtha feedstock × 100%.

[0049] Table 1 Test results of product purity and yield High-purity n-heptane purity % High-purity n-heptane yield % High-purity n-hexane purity % High-purity n-hexane yield % Example 1 99.62 21.13 99.41 23.54 Example 2 99.57 20.64 99.35 22.67 Example 3 99.53 20.36 99.37 22.86 Example 4 99.58 20.58 99.42 23.11 Example 5 99.55 20.27 99.38 22.59 Example 6 99.61 20.41 99.45 22.77 Example 7 99.54 20.39 99.40 22.80 Example 8 99.59 20.50 99.49 23.27 Comparative Example 1 99.03 18.32 99.07 20.18 Comparative Example 2 99.45 20.01 99.23 22.13 Comparative Example 3 99.39 19.94 99.26 21.74 Comparative Example 4 99.26 19.02 99.19 21.10 Comparative Example 5 99.21 18.89 99.12 21.32 As can be seen from Table 1, the purity and yield of n-heptane and n-hexane in Examples 1-8 are significantly improved compared with the prior art.

[0050] In Comparative Example 1, unmodified molecular sieve is used as the adsorbent, and the purity and yield of n-heptane and n-hexane decrease significantly.

[0051] In Comparative Example 2 and Comparative Example 3, the raw material ratio of the molecular sieve was changed, and the purity and yield of n-heptane and n-hexane decreased, indicating that the HY molecular sieve and the MCM-41 molecular sieve under specific ratios produced a synergistic effect.

[0052] In Comparative Example 4 and Comparative Example 5, the modification methods of the adsorbent were different, and the purity and yield of n-heptane and n-hexane decreased, indicating that only by modifying the mixed molecular sieve according to Example 1 could the purity and yield of the product be better improved.

[0053] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing high-purity heptane, characterized in that, It includes the following steps: (1) Prepare an adsorbent, including the following steps: S1: Mix HY zeolite and MCM-41 zeolite to obtain a mixed zeolite; S2: Immerse the mixed zeolite in hydrochloric acid, stir, filter, and calcine the solid to obtain a calcined zeolite; S3: Completely immerse the calcined zeolite in a toluene solution of hexamethyldisilazane, reflux, filter, wash the solid, and vacuum dry to obtain a passivated zeolite; S4: Completely immerse the passivated zeolite in an ethanol solution of nitrobenzoic acid, stir, filter, and heat the solid under a nitrogen atmosphere to obtain a nitrobenzene group-bonded zeolite; S5: Completely immerse the nitrobenzene group-bonded zeolite in an aqueous solution of magnesium nitrate, oscillate, filter, and calcine the solid to obtain a zeolite loaded with metal oxide; S6: Under a nitrogen atmosphere, perform degassing treatment on the zeolite loaded with metal oxide to obtain an adsorbent; (2) Feed the raw naphtha into a hydrofining reactor for a refining reaction to obtain refined naphtha; (3) Feed the refined naphtha into an adsorption tower containing the adsorbent prepared in step (1) for adsorption separation and desorption to obtain a desorbed oil; (4) Using the desorbed oil as a raw material, separate high-purity n-heptane and high-purity n-hexane through a distillation device; the distillation device includes two distillation towers connected in sequence, namely an n-hexane distillation tower and an n-heptane distillation tower. High-purity n-hexane is cut out from the top of the n-hexane distillation tower, and high-purity n-heptane is cut out from the top of the n-heptane distillation tower.

2. The preparation method of high-purity heptane according to claim 1, characterized in that, In S4, the heating temperature and time are 300 - 320 °C and 2 - 4 h.

3. The method for preparing high-purity heptane according to claim 1, characterized in that, In step (2), a hydrofining catalyst is used for the refining reaction, and the conditions for the refining reaction are: pressure 1.7 - 2.3 MPa, temperature 240 - 260 °C.

4. The preparation method of high-purity heptane according to claim 1, characterized in that, In step (3), the adsorption pressure is 0.5 - 1.0 MPa, and the desorption pressure is 0.5 - 1.0 MPa; the adsorption temperature is 250 - 320 °C, and the desorption temperature is 250 - 320 °C; the adsorption time is 20 - 30 minutes, and the desorption time is 20 - 30 minutes.

5. The method for preparing high-purity heptane according to claim 1, characterized in that, In step (4), for the n-hexane distillation tower, the operating temperature: the top temperature is 67 °C, the bottom temperature is 128 °C, and the operating pressure is 0.05 MPa; for the n-heptane distillation tower, the operating temperature, the top temperature is 97 °C, the bottom temperature is 145 °C, and the operating pressure is 0.05 MPa.

6. The preparation method of high-purity heptane according to claim 1, characterized in that, In step (4), the mass content of n-alkanes in the desorbed oil is ≥ 99.5%, the sulfur mass content is ≤ 0.5 ppm, the nitrogen mass content is ≤ 0.5 ppm, the bromine index is ≤ 5 mgBr / 100 g, and the aromatic hydrocarbon mass content is ≤ 10 ppm.

7. The method for preparing high-purity heptane according to claim 1, wherein In step (4), each distillation tower is fed in the middle, and the bottom material of the previous tower is the feed for the next tower.

8. The method for preparing high-purity heptane according to claim 7, wherein, In step (4), the reflux ratio of the n-hexane distillation tower is 3 - 4, the number of theoretical plates is 70, and the processing load is 4.6 L / h; the reflux ratio of the n-heptane distillation tower is 3 - 5, the number of theoretical plates is 80, and the processing load is 4.0 L / h.

9. The preparation method of high-purity heptane according to claim 8, wherein The hydrofining catalyst used in the hydrofining reaction in step (2) is a clover-shaped particle, and the specific surface area of the clover-shaped particle is ≥ 150 m 2 / g, the bulk density is 0.72 - 0.82 g / cm 3 , and the radial compressive strength is ≥ 150 N / cm.

10. The preparation method of high-purity heptane according to claim 1, characterized in that, In step (4), the purity of the obtained high-purity n-heptane is ≥ 99.5%, and the yield of high-purity n-heptane is ≥ 20%.

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