Method for improving purity of n-octane

Abstract

The invention belongs to the technical field of n-octane purification, and provides a method for improving the purity of n-octane, which comprises the following steps: carrying out two-stage molecular sieve dehydration on an n-octane crude product, and carrying out hydrogenation reaction on the dehydrated product under the action of a Ni-Mo / Al2O3 catalyst to obtain a mixed fraction containing n-octane and trace impurities; introducing the mixed fraction into a two-stage molecular distillation system for fractionation, collecting a target fraction at 120-130 DEG C, adsorbing the target fraction through a modified Y-type molecular sieve adsorption column, and removing residual olefin and sulfide to obtain an intermediate product; and cooling the intermediate product to below 50 DEG C, carrying out membrane separation through a zeolite filled ceramic membrane assembly, and carrying out backwashing at intervals in the membrane separation process to obtain a normal octane product. According to the method disclosed by the invention, by matching process chains of dehydration, hydrogenation, distillation, adsorption and membrane separation, the purity of n-octane breaks through 99.5%, and an efficient, low-consumption and stable technical solution is provided for production of high-purity chemicals.

Description

Technical Field

[0001] This invention belongs to the field of n-octane purification technology and relates to a method for improving the purity of n-octane. Background Technology

[0002] As a key raw material in the petrochemical industry, improving the purity of n-octane faces multiple technical barriers. With the upgrading of global oil product quality and increasingly stringent environmental regulations, the purity standard for industrial-grade n-octane has been raised to over 99.5%, with particularly stringent requirements for the removal of trace impurities such as sulfides and olefins. Existing processes generally have the following limitations: Insufficient deep impurity removal capability: Although traditional hydrogenation-adsorption coupling technology can partially remove olefins, its removal efficiency for polar molecules such as thiols is limited, making it difficult to stably control the sulfur content below 10 ppm. Poor system stability: short adsorbent regeneration cycle (<8 hours), frequent high-temperature steam regeneration causes carrier structure collapse, and single-cycle life is less than 300 hours; Imbalance between energy consumption and economic efficiency: The energy consumption of multi-stage distillation and regeneration processes is as high as 2.3 tons of standard coal per ton of product, and the entrainment of heavy components leads to a decrease in the yield of the target product. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for improving the purity of n-octane. Through the synergistic process chain of dehydration-hydrogenation-distillation-adsorption-membrane separation, the purity of n-octane can be increased to over 99.5%, providing an efficient, low-consumption, and stable technical solution for the production of high-purity chemicals.

[0004] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for improving the purity of n-octane, the method comprising: (I) Crude n-octane is dehydrated, and the dehydrated product is hydrogenated in the presence of Ni-Mo / Al2O3 catalyst to obtain a mixed fraction containing n-octane and trace impurities; (II) The mixed fraction is fractionated to collect the target fraction at 120~130℃. The target fraction is adsorbed by a modified Y-type molecular sieve adsorption column to obtain the intermediate product. The modified Y-type molecular sieve adsorption column is prepared by sequentially acidifying, calcining, particle exchange, gradient calcining activation, coupling agent passivation and pressing of Y-type molecular sieve. (III) After cooling the intermediate product, membrane separation is performed through a zeolite-filled ceramic membrane module; the zeolite-filled ceramic membrane module is obtained by impregnating an alumina porous ceramic membrane with a zeolite solution and then drying it with gradient hot air; backwashing is performed at intervals during the membrane separation process to obtain n-octane product.

[0005] Furthermore, the method includes: (I) The crude n-octane is dehydrated by two-stage molecular sieves, and the dehydrated product is hydrogenated in the presence of Ni-Mo / Al2O3 catalyst to obtain a mixed fraction containing n-octane and trace impurities. (II) The mixed fraction obtained in step (I) is passed into a two-stage molecular distillation system for fractionation to collect the target fraction at 120-130℃, for example, 120℃, 121℃, 122℃, 123℃, 124℃, 125℃, 126℃, 127℃, 128℃, 129℃ or 130℃. The target fraction is then adsorbed through a modified Y-type molecular sieve adsorption column to remove residual olefins and sulfides, thereby obtaining an intermediate product. The modified Y-type molecular sieve adsorption column is prepared by sequentially acidifying, calcining, particle exchange, gradient calcining activation, coupling agent passivation and pressing of industrial-grade Y-type molecular sieve. (III) After cooling the intermediate product obtained in step (II) to below 50°C, membrane separation is performed using a zeolite-filled ceramic membrane module. The zeolite-filled ceramic membrane module is obtained by impregnating an alumina porous ceramic membrane with a zeolite solution and then drying it with gradient hot air. Backwashing is performed at intervals during the membrane separation process to obtain n-octane product.

[0006] The n-octane purification method provided by this invention achieves efficient separation and deep removal of impurities through multi-stage synergistic processing, significantly improving product purity and process economy. First, two-stage molecular sieve dehydration effectively removes free and bound water from crude n-octane, avoiding the risk of water poisoning of the subsequent hydrogenation catalyst, while simultaneously controlling the molecular sieve regeneration cycle to reduce energy consumption. In the hydrogenation reaction stage, the Ni-Mo / Al2O3 catalyst precisely promotes saturated hydrogenation of olefins through a bimetallic synergistic effect, increasing the olefin conversion rate to over 98%, while suppressing the side reaction of deep hydrogenation to form alkanes, ensuring the selectivity of the target product, n-octane. Subsequently, a two-stage molecular distillation system achieves stepwise separation of light and heavy components through precise temperature control, combined with the highly effective adsorption of residual olefins and sulfides by a modified Y-type molecular sieve adsorption column, significantly reducing impurity content to the ppm level. Finally, a zeolite-filled ceramic membrane module achieves ultimate separation of n-octane from trace impurities through size sieving and surface hydrophobic properties, while a backwashing design extends the membrane module's lifespan and maintains high throughput. The n-octane purification method provided by this invention achieves a purity of over 99.5% through a synergistic process chain of dehydration-hydrogenation-distillation-adsorption-membrane separation, providing an efficient, low-consumption, and stable technical solution for the production of high-purity chemicals.

[0007] This invention achieves highly efficient purification of n-octane through a multi-dimensional synergistic mechanism, with its core technology lying in the deep adaptation of raw material characteristics to the separation process. Addressing the complexity of impurities such as water, olefins, and sulfides in crude n-octane, the process design employs a staged treatment scheme: the initial two-stage molecular sieve dehydration removes water step-by-step through gradient temperature control. The first-stage high-temperature dehydration utilizes the strong hydrophilicity of the molecular sieve to rapidly remove free water, while the liquid water micro-regions formed within the pores achieve efficient desorption through hydrogen bond breaking. The second-stage low-temperature dehydration selectively captures bound water by controlling the hydrophilicity and hydrophobicity of hydroxyl groups on the pore surface, avoiding pore structure collapse caused by siloxane bond hydrolysis at high temperatures. This gradient dehydration mechanism ensures dehydration efficiency and creates a low-water-activity environment for subsequent hydrogenation reactions, effectively suppressing the risk of catalyst poisoning.

[0008] During the hydrogenation reaction, the synergistic effect of the Ni-Mo / Al2O3 catalyst ensures selective conversion of impurities. The bimetallic component forms active sites through interfacial charge regulation: Ni atoms promote hydrogen molecule dissociation through d-orbital electron transfer, while Mo... 6+ Alkene molecules are adsorbed via Lewis acid sites. Under hydrogen pressures of 3–5 MPa, alkenes preferentially undergo hydrogenation saturation reactions, with reaction kinetics following the Langmuir-Hinshelwood mechanism. Precise control of the hydrogen partial pressure ensures both the supply of active hydrogen and avoids increased mass transfer resistance due to excessive dilution. Simultaneously, sulfides in crude n-octane undergo hydrogenolysis to generate H₂S in this system, with the reaction pathway influenced by Mo. 4+ / Mo 6+ The regulation of redox pairs allows the sulfur content to be reduced to the ppm level. This selective conversion mechanism not only improves the purity of the raw materials but also reduces the load on subsequent distillation and separation.

[0009] The coupling of molecular distillation and adsorption technology further enhances separation efficiency. Two-stage molecular distillation achieves precise separation of n-octane from light and heavy components through a vacuum gradient: the first-stage light component removal column preferentially evaporates volatile impurities such as acetone and methanol under low pressure, while the second-stage n-octane purification column utilizes an ultra-low pressure environment to separate the azeotrope of n-octane and isooctane. Compared to traditional distillation, this process eliminates the need for multi-stage trays, reducing energy consumption by over 40%. Subsequently, the modified Y-type molecular sieve adsorption column, through acidification treatment, creates a mesoporous structure that confines olefin molecules, while Bronsted acidic sites selectively capture sulfides. A silane-coupled passivation layer prevents excessive adsorption of n-octane. This stratified adsorption mechanism extends the single-cycle operation of the adsorption column to 12-16 hours, reducing regeneration energy consumption by 60% compared to traditional processes.

[0010] The introduction of membrane separation technology enables the complete interception of trace impurities. Zeolite-filled ceramic membranes form a size sieving barrier through the shape-selective effect of NaA-type zeolite, allowing n-octane molecules to preferentially permeate due to their kinetic diameter matching, while sulfides are retained due to steric hindrance. The membrane fouling control mechanism maintains flux stability through periodic backwashing and gradient hot air drying, extending the membrane module's lifespan to 2-3 years. This synergistic physical-chemical separation mechanism results in a final product purity exceeding 99.5%, while avoiding energy-intensive secondary purification steps.

[0011] As a preferred technical solution of the present invention, in step (I), the dehydration includes two-stage molecular sieve dehydration, specifically including a first-stage dehydration and a second-stage dehydration performed sequentially.

[0012] In some optional instances, the temperature of the first-stage dehydration is 85~95°C, for example, it can be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0013] In some optional instances, the dehydration time for the first stage is 3 to 4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] In some optional instances, the temperature of the two-stage dehydration is 45~55℃, for example, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] In some optional instances, the two-stage dehydration time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] In some optional instances, the operating pressure for the first-stage dehydration and the second-stage dehydration is 0.4 to 0.6 MPa, for example, 0.4 MPa, 0.42 MPa, 0.44 MPa, 0.46 MPa, 0.48 MPa, 0.5 MPa, 0.52 MPa, 0.54 MPa, 0.56 MPa, 0.58 MPa or 0.6 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0017] In some alternative examples, the reaction pressure of the hydrogenation reaction is 3 to 5 MPa, for example, 3.0 MPa, 3.2 MPa, 3.4 MPa, 3.6 MPa, 3.8 MPa, 4.0 MPa, 4.2 MPa, 4.4 MPa, 4.6 MPa, 4.8 MPa or 5.0 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0018] In some alternative examples, the reaction temperature of the hydrogenation reaction is 180~220°C, for example, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C or 220°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0019] In some optional instances, the hydrogen-to-oil ratio of the hydrogenation reaction is (80~120):1, for example, it can be 80:1, 85:1, 90:1, 95:1, 100:1, 105:1, 110:1, 115:1 or 120:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] In some optional examples, the space velocity of the hydrogenation reaction is 5–10 h⁻¹. -1 For example, it could be 5.0h -1 5.5h -1 6.0h -1 6.5h -1 7.0h -1 7.5h -1 8.0h -1 8.5h -1 9.0h -1 9.5h -1 or 10.0h -1 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0021] As a preferred technical solution of the present invention, in step (I), the Ni-Mo / Al2O3 catalyst is prepared by the following method: (a) Nickel nitrate and ammonium molybdate are dissolved in water and mixed to obtain a nickel-molybdenum solution; aluminum nitrate solution is mixed with the nickel-molybdenum solution to obtain a precursor solution; (b) Under stirring and heating conditions, sodium carbonate solution was added to the precursor solution, the reaction was carried out, and the mixture was filtered to obtain a precipitate; (c) The precipitate is allowed to stand for aging, washed and dried to obtain a precursor. The precursor is then calcined and cooled to obtain a Ni-Mo / Al2O3 catalyst.

[0022] Furthermore, the Ni-Mo / Al2O3 catalyst was prepared using the following method: (a) Dissolve nickel nitrate and ammonium molybdate in deionized water and mix thoroughly to obtain a nickel-molybdenum solution; mix aluminum nitrate solution with the nickel-molybdenum solution to obtain a precursor solution; (b) Under stirring and heating conditions, sodium carbonate solution is added dropwise to the precursor solution obtained in step (a) to induce a precipitation reaction. Nitrogen gas is continuously introduced for protection during the reaction. After the reaction is completed, the solution is filtered to obtain the precipitate. (c) The precipitate obtained in step (b) is subjected to static aging, washing and drying to obtain a precursor. The precursor is calcined in air atmosphere and naturally cooled to room temperature to obtain the Ni-Mo / Al2O3 catalyst.

[0023] In the catalytic hydrogenation process, firstly, the Ni-Mo bimetallic synergistic effect significantly improves the selective hydrogenation efficiency of olefins. 6+ By adsorbing olefin molecules at Lewis acid sites, their activation energy is lowered, while hydrogen species provided by Ni active sites preferentially undergo addition reactions with olefin double bonds rather than direct cleavage to form alkanes. This synergistic effect results in a C=C bond hydrogenation selectivity of up to 98%, avoiding the side reaction of excessive hydrogenation to form saturated alkanes. Secondly, the confinement effect formed by the strong interaction between the mesoporous structure and the support effectively suppresses carbon deposition. Intermediate products generated in the reaction (such as olefin oligomers) can be rapidly desorbed through the mesoporous channels, preventing the formation of a carbon deposit coating on the catalyst surface.

[0024] As a preferred technical solution of the present invention, in step (a), the molar ratio of Ni and Mo in nickel nitrate and ammonium molybdate is 1:(1.5~1.7), for example, it can be 1:1.5, 1:1.52, 1:1.54, 1:1.56, 1:1.58, 1:1.6, 1:1.62, 1:1.64, 1:1.66, 1:1.68 or 1:1.7, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] This invention specifically defines the molar ratio of Ni to Mo in nickel nitrate and ammonium molybdate as 1:(1.5~1.7). The molar ratio of Ni to Mo directly affects the spatial distribution of active sites and the efficiency of electron interaction.

[0026] When the Mo content is too low, Mo 6+ Insufficient Lewis acid site density on the support surface leads to decreased olefin adsorption capacity, resulting in a reduced hydrogenation reaction rate. Simultaneously, while Ni exhibits sufficient hydrogen dissociation activity, the lack of matching acid sites hinders the effective migration of hydrogen species to olefin adsorption sites, causing a disconnect between hydrogen dissociation and the hydrogenation reaction. In this situation, although the catalyst can maintain a certain level of activity, selectivity is difficult to optimize, and the probability of side reactions (such as over-hydrogenation to alkanes) increases significantly.

[0027] When the Mo content is too high, Mo 6+ Excessive introduction of Mo can trigger two negative effects; on the one hand, excessive Mo... 6+ This will occupy the active sites on the support surface, squeezing the distribution space of Ni, causing the hydrogen dissociation ability of Ni to be inhibited due to the weakened metal-support interaction. At this time, although the Lewis acid site density of Mo increases, the insufficient supply of hydrogen species makes it difficult for olefin hydrogenation reactions to proceed efficiently. On the other hand, Mo 6+ Mo's strong affinity for sulfur could be used as a sacrificial protection against sulfur poisoning, but excessive Mo will form dense Mo-S bonding sites, which will instead accelerate the accumulation of sulfur on the catalyst surface and reduce its resistance to sulfur poisoning.

[0028] When the molar ratio of Ni to Mo is in the range of 1:(1.5~1.7), the d orbital electrons of Ni and Mo are complementary: the 3d orbital electrons of Ni transfer to the H2 molecule, promoting its dissociation into active hydrogen species; Mo 6+ The 4d orbitals are obtained through a partially reduced state (Mo). 4 + The formation of these sites creates Lewis acid sites with strong adsorption capacity for olefin molecules. The redistribution of interfacial charges between the two creates a synergistic effect, resulting in a high spatial match between the migration pathways of active hydrogen species and the adsorption sites of olefins, thereby enhancing the intrinsic activity of the hydrogenation reaction. Furthermore, at this ratio, the total amount of Mo ensures sufficient acid site density without the risk of sulfur poisoning due to excess, thus improving the catalyst's stability in sulfur-containing feedstocks by more than 30%.

[0029] In some alternative examples, the concentrations of nickel nitrate and ammonium molybdate in the nickel-molybdenum solution are 1 to 1.5 mol / L, for example, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.25 mol / L, 1.3 mol / L, 1.35 mol / L, 1.4 mol / L, 1.45 mol / L, or 1.5 mol / L, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0030] In some alternative examples, the concentration of the aluminum nitrate solution is 0.8 to 1.2 mol / L, for example, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L or 1.2 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] In some optional examples, the volume ratio of the aluminum nitrate solution to the nickel-molybdenum solution is (1.2~1.8):1, for example, it can be 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, 1.5:1, 1.55:1, 1.6:1, 1.65:1, 1.7:1, 1.75:1 or 1.8:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] The present invention specifically defines the volume ratio of aluminum nitrate solution to nickel-molybdenum solution as (1.2~1.8):1. As a precursor for the support, the volume of aluminum nitrate solution directly affects the pore structure and specific surface area of ​​the Al2O3 support.

[0033] When the amount of aluminum nitrate solution added is too small, the concentration of Al2O3 precursor is relatively insufficient, leading to a reduction in the amount of Al2O3 support generated after calcination. However, the loading of the Ni-Mo active component does not decrease synchronously. Insufficient Al2O3 support results in a sparse pore structure, failing to provide sufficient anchoring sites for the Ni-Mo active phase. The active component is prone to agglomeration or peeling due to a lack of mechanical support. Secondly, the reduced metal-support interface contact area weakens the synergistic effect of Ni's hydrogen dissociation ability and Mo's acidic sites, leading to a decrease in the hydrogenation reaction rate. Thirdly, excess Ni-Mo solute may exist in a loosely packed form, creating an "active site shielding" effect, hindering the diffusion of reactant molecules (such as alkenes and H2) to the active sites, while increasing the probability of side reactions (such as deep hydrogenation to form alkanes).

[0034] Conversely, if too much aluminum nitrate solution is added, resulting in an excess of Al2O3 support and insufficient loading density of the Ni-Mo active component, this will cause two problems: firstly, the dilution effect of the active component will reduce the number of active sites per unit volume, leading to a decrease in olefin conversion; secondly, the formation of excess Al2O3 may clog the pores, hindering the mass transfer between reactants and products, requiring increased operating pressure to maintain the permeation flux, significantly increasing energy consumption. Furthermore, excess Al2O3 may introduce incompletely calcined mesophases (such as δ-Al2O3), reducing the thermal stability and sulfur poisoning resistance of the support.

[0035] When the volume ratio of aluminum nitrate solution to nickel-molybdenum solution is in the range of (1.2~1.8):1, an appropriate amount of Al2O3 support can form a stable porous structure, which not only ensures the rapid diffusion of reactant molecules, but also provides dense anchoring sites for the Ni-Mo active phase. The ratio precisely satisfies the optimal balance between metal dispersion and interfacial electronic effects: Ni 2+ Mo 7+ Uniform dispersion on the Al2O3 surface forms active particles with a particle size of 3-5 nm, avoiding deactivation of active sites due to agglomeration; Ni's d orbital electrons are transferred to Mo through interfacial interactions. 6+ This forms a highly active Ni-Mo-O solid solution, improving the efficiency of hydrogen dissociation and olefin adsorption; the Al2O3 support and the Ni-Mo active phase form a mechanically interlocked structure, inhibiting physical stripping during recycling and extending the catalyst life to more than 8000 hours.

[0036] In some optional instances, in step (b), the concentration of the sodium carbonate solution is 0.5 to 1 mol / L, for example, it can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L or 1 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some alternative examples, the dropping rate of the sodium carbonate solution is 1.5 to 2 mL / min, for example, 1.5 mL / min, 1.55 mL / min, 1.6 mL / min, 1.65 mL / min, 1.7 mL / min, 1.75 mL / min, 1.8 mL / min, 1.85 mL / min, 1.9 mL / min, 1.95 mL / min or 2 mL / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] In some optional instances, the heating temperature of the sodium carbonate solution during the dropwise addition process is 70~80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] In some optional instances, the stirring speed of the sodium carbonate solution during the dropwise addition process is 600 to 800 rpm, for example, 600 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, 720 rpm, 740 rpm, 760 rpm, 780 rpm or 800 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] In some alternative instances, the addition of the sodium carbonate solution is stopped when the pH of the reaction solution reaches 8 to 8.5, thus terminating the reaction. For example, this could be 8, 8.1, 8.2, 8.3, 8.4, or 8.5, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0041] In some optional instances, in step (c), the temperature for static aging is 80~90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] In some optional instances, the settling time is 4 to 6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] In some alternative instances, the drying temperature is 110~120°C, for example, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] In some optional instances, the drying time is 10 to 12 hours, for example, 10 hours, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11 hours, 11.2 hours, 11.4 hours, 11.6 hours, 11.8 hours, or 12 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0045] In some optional instances, the heating rate of the precursor during calcination is 2 to 5 °C / min, for example, it can be 2.0 °C / min, 2.5 °C / min, 3.0 °C / min, 3.5 °C / min, 4.0 °C / min, 4.5 °C / min or 5.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] In some optional instances, the calcination temperature of the precursor is 600~700℃, for example, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃ or 700℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] In some optional instances, the calcination time of the precursor is 3 to 5 hours, for example, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, or 5.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0048] As a preferred technical solution of the present invention, in step (II), the two-stage molecular distillation system includes a primary light component removal tower and a secondary n-octane purification tower connected in series.

[0049] In some optional instances, the distillation temperature of the primary light component removal column is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] In some alternative examples, the distillation pressure of the primary light component removal column is 0.1 to 0.3 Pa, for example, 0.1 Pa, 0.12 Pa, 0.14 Pa, 0.16 Pa, 0.18 Pa, 0.2 Pa, 0.22 Pa, 0.24 Pa, 0.26 Pa, 0.28 Pa, or 0.3 Pa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] In some alternative examples, the distillation temperature of the secondary n-octane refining column is 120~130°C, for example, 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C or 130°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In some alternative instances, the distillation pressure of the secondary n-octane refining column is 0.01 to 0.1 Pa, for example, 0.01 Pa, 0.02 Pa, 0.03 Pa, 0.04 Pa, 0.05 Pa, 0.06 Pa, 0.07 Pa, 0.08 Pa, 0.09 Pa, or 0.1 Pa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0053] In some optional examples, the adsorption temperature of the modified Y-type molecular sieve adsorption column is 30~50℃, for example, it can be 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0054] In some optional examples, the adsorption space velocity of the modified Y-type molecular sieve adsorption column is 3-5 h⁻¹. -1 For example, it could be 3.0h -1 3.2h -1 3.4h -1 3.6h -1 3.8h -1 4.0h -1 4.2h -1 4.4h -1 4.6h -1 4.8h -1 Or 5.0h -1 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0055] As a preferred technical solution of the present invention, in step (II), the modified Y-type molecular sieve adsorption column is prepared by the following method: (1) Add Y-type molecular sieve to hydrochloric acid solution, mix and heat to acidify, filter, wash and dry to obtain acidified molecular sieve; then calcine and cool to obtain pretreated molecular sieve; (2) Dissolve ammonium nitrate in water and mix to obtain ammonium nitrate solution; pack the pretreated molecular sieve into the exchange column, pass the ammonium nitrate solution into the exchange column for ion exchange, collect the effluent during the ion exchange process, and dry the pretreated molecular sieve after ion exchange to obtain the exchange molecular sieve; (3) The exchange molecular sieve is activated by calcination to obtain calcined molecular sieve; the calcined molecular sieve is dispersed in a silane coupling agent solution, mixed, filtered, washed and dried to obtain passivated molecular sieve; the passivated molecular sieve is mixed with graphite binder, filled into a mold and pressed to obtain modified Y-type molecular sieve adsorption column.

[0056] Furthermore, the modified Y-type molecular sieve adsorption column is prepared by the following method: (1) Add industrial-grade Y-type molecular sieve to hydrochloric acid solution, mix and heat to acidify, filter, wash and dry after acidification to obtain acidified molecular sieve; calcine the acidified molecular sieve and cool it naturally to room temperature to obtain pretreated molecular sieve. (2) Dissolve ammonium nitrate in deionized water and mix well to obtain an ammonium nitrate solution; pack the pretreated molecular sieve obtained in step (1) into an exchange column, and pass the ammonium nitrate solution into the exchange column for ion exchange. Collect the effluent during the ion exchange process. Stop the ion exchange when the concentration of ammonium ions in the effluent is <0.5 g / L. Dry the pretreated molecular sieve after ion exchange to obtain an exchange molecular sieve. (3) In a nitrogen atmosphere, the exchange molecular sieve obtained in step (2) is subjected to two-stage gradient calcination activation to obtain a calcined molecular sieve; the calcined molecular sieve is dispersed in a silane coupling agent solution, mixed and stirred at room temperature, and then filtered, washed and dried to obtain a passivated molecular sieve; the passivated molecular sieve is mixed evenly with a graphite binder, filled into a columnar mold and pressed to form a columnar modified Y-type molecular sieve adsorption column.

[0057] The preparation process of modified Y-type molecular sieve adsorption columns involves multi-level structural regulation and surface chemical modification, thereby constructing a separation material that combines high specific surface area, selective adsorption capacity, and stability.

[0058] During the acidification process of molecular sieves, industrial-grade Y-type molecular sieves undergo acidification with hydrochloric acid solution, resulting in the selective dissolution of non-framework aluminum species in the framework and the formation of a mesoporous structure. This process not only expands the pore volume but, more importantly, restructures the acidity distribution on the pore surface: by controlling the acidification conditions (such as hydrochloric acid concentration and temperature), the degree of Al-O bond breaking is regulated, allowing the inner wall of the pores to retain an appropriate number of Lewis acid sites, providing a reserve of active sites for subsequent ion exchange. The subsequent calcination treatment further removes residual structural water, causing partial dealuminization of the molecular sieve framework and forming a regular mesoporous-macroporous composite pore system. This optimized pore structure significantly improves mass transfer efficiency, enabling reactant molecules to rapidly diffuse to the active sites while avoiding the excessive mass transfer resistance caused by the narrow pores in traditional molecular sieves.

[0059] During ion exchange, ammonium nitrate solution selectively occupies the cation sites of the pretreated molecular sieve under isothermal conditions. + With molecular sieve framework Na + Ion exchange occurs, and its efficiency is controlled by the solid-liquid ratio, flow rate, and solution pH. After the exchange is completed, uniformly distributed acidic sites are formed on the surface of the molecular sieve. These acidic sites have a strong adsorption affinity for olefin molecules and inhibit the adsorption of larger molecules such as aromatics through electrostatic repulsion.

[0060] During the gradient calcination process, the molecular sieve undergoes phased lattice reconstruction and surface reconstruction: the low-temperature stage promotes the decomposition of ammonium salts to generate a porous structure, while the high-temperature stage removes adsorbed water and structural hydroxyl groups, exposing more Lewis acid sites. This gradient activation process further increases the specific surface area of ​​the molecular sieve to 400~500m² / g, while maintaining the orderliness of the pore structure. In addition, the nitrogen gas introduced during the calcination process effectively inhibits the formation of metal oxides and avoids non-selective coverage of active sites. The resulting composite pore system and acidic site distribution enable the adsorption column to exhibit high selectivity for olefin impurities, with an adsorption capacity 3~5 times higher than that of unmodified molecular sieves.

[0061] In the silane coupling agent passivation process, the molecular sieve surface is selectively passivated through chemical modification with the silane coupling agent. Under room temperature stirring conditions, silane molecules are anchored to the outer surface of the molecular sieve via Si-O-Al bonds, forming a hydrophobic protective layer. This passivation layer, on the one hand, blocks the physical adsorption of small molecule impurities (such as CO2 and N2), and on the other hand, regulates the adsorption selectivity through steric hindrance effects, maintaining high affinity for highly polar olefin molecules while exhibiting low adsorption energy for non-polar components (such as alkanes). By controlling the amount of silane coupling agent and the reaction time, the integrity of the hydrophobic layer is ensured while avoiding excessive coverage that could lead to the loss of active sites.

[0062] The modified Y-type molecular sieve adsorption column exhibits multiple advantages in its performance: Firstly, its unique pore structure endows the material with excellent dynamic adsorption capacity, achieving an adsorption capacity of 12-15 mg / g for residual olefins in n-octane, with an adsorption rate more than twice that of the unmodified material; secondly, the selective regulation of surface acidic sites enables the adsorption selectivity coefficient of sulfides (such as thiols) to reach 150-200 mL / g, far exceeding that of traditional adsorbents; fourthly, the stable crystalline phase structure formed by gradient calcination can maintain more than 85% of the initial adsorption performance after repeated regeneration (steam purging at 120-150℃), significantly extending its service life; fifthly, the introduction of a hydrophobic passivation layer effectively suppresses the competitive adsorption of water vapor, maintaining stable separation efficiency even under fluctuating humidity conditions.

[0063] As a preferred technical solution of the present invention, in step (1), the particle size of the industrial-grade Y-type molecular sieve is 0.5~1mm, for example, it can be 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.85mm, 0.9mm, 0.95mm or 1mm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] In some alternative examples, the ratio of the industrial-grade Y-type molecular sieve to the hydrochloric acid solution is 1g:(1.5~2)mL, for example, it can be 1g:1.5mL, 1g:1.55mL, 1g:1.6mL, 1g:1.65mL, 1g:1.7mL, 1g:1.75mL, 1g:1.8mL, 1g:1.85mL, 1g:1.9mL, 1g:1.95mL or 1g:2mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0065] In some alternative instances, the concentration of the hydrochloric acid solution is 0.1 to 0.5 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0066] In some alternative instances, the acidification heating temperature is 80~90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0067] In some alternative instances, the acidification time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0068] In some alternative examples, the calcination rate of the acidified molecular sieve is 8-10 °C / min, for example, it can be 8.0 °C / min, 8.2 °C / min, 8.4 °C / min, 8.6 °C / min, 8.8 °C / min, 9.0 °C / min, 9.2 °C / min, 9.4 °C / min, 9.6 °C / min, 9.8 °C / min or 10.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0069] In some optional examples, the calcination temperature of the acidified molecular sieve is 500~550℃, for example, 500℃, 505℃, 510℃, 515℃, 520℃, 525℃, 530℃, 535℃, 540℃, 545℃ or 550℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0070] In some optional instances, the calcination time of the acidified molecular sieve is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0071] In some alternative instances, in step (2), the concentration of the ammonium nitrate solution is 1 to 1.5 mol / L, for example, it can be 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.25 mol / L, 1.3 mol / L, 1.35 mol / L, 1.4 mol / L, 1.45 mol / L or 1.5 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0072] This invention specifically limits the concentration of ammonium nitrate solution to 1~1.5 mol / L. By controlling the concentration and amount of ammonium nitrate solution, the concentration of NH4+ is controlled. + With Na in the molecular sieve framework + The degree of cation exchange is adjusted, thereby regulating the synergy between Brønsted acid site density and pore structure.

[0073] When the concentration of ammonium nitrate solution is below 1 mol / L, NH4 + Insufficient Na concentration leads to a significant decrease in ion exchange efficiency. + The replacement rate is slow, making it difficult to complete the full exchange within a limited time, resulting in residual Na within the molecular sieve channels. + High concentrations weaken the formation of bronsted acidic sites. In this case, the adsorption capacity of the molecular sieve for olefins will decrease significantly, and the uneven distribution of acidic sites may lead to non-selective adsorption of impurities such as sulfides, reducing separation purity. In addition, low-concentration ammonium nitrate solution may introduce excessive sodium ion residues, exacerbating the risk of dealumination of the molecular sieve framework, damaging the stability of the mesoporous structure, and ultimately shortening the lifespan of the adsorption column.

[0074] If the concentration of ammonium nitrate solution exceeds 1.5 mol / L, high concentrations of NH4+ will result in... + This can lead to uncontrolled ion exchange processes within the molecular sieve channels. Excessive NH4... + Localized enrichment within the pores not only hinders NH4 + Diffusion into deeper pores can also lead to the excessive formation of acidic sites. This non-uniform distribution significantly reduces the selective adsorption capacity of the molecular sieve—high-density Brønsted acidic sites may simultaneously adsorb olefins and sulfides, resulting in a decrease in the purity of the target product. Simultaneously, H⁺ generated from the decomposition of high-concentration ammonium nitrate may erode the molecular sieve framework, accelerating the breaking of Al-O bonds, causing widening or collapse of the pore size distribution, further weakening mass transfer efficiency. For example, during the high-temperature calcination stage, excess NH₄⁺... + Decomposing residual impurities may trigger side reactions, generating amorphous phase substances and disrupting the regular pore structure of the molecular sieve.

[0075] When the concentration of ammonium nitrate solution is in the range of 1~1.5 mol / L, appropriate NH4+ is needed. + The concentration is such that it ensures both the kinetic efficiency of ion exchange and avoids excessive aggregation of acidic sites. NH4 + It can penetrate into the molecular sieve pores at a controllable rate, completing uniform cation exchange and forming a gradient distribution of Brønsted acidic sites—the near-surface region provides sufficient acidic sites for efficient olefin adsorption, while the internal pores retain moderate acidity to regulate mass transfer resistance. Furthermore, appropriate NH4+... + The concentration avoids excessive dealumination of the molecular sieve framework, enabling the material to maintain a stable mesoporous structure after multiple regeneration cycles, extending its service life to over 8000 hours.

[0076] In some optional instances, the packing density of the pretreated molecular sieve in the exchange column is 0.5 to 0.8 g / mL, for example, 0.5 g / mL, 0.55 g / mL, 0.6 g / mL, 0.65 g / mL, 0.7 g / mL, 0.75 g / mL or 0.8 g / mL, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0077] In some alternative examples, the solid-liquid ratio of the ammonium nitrate solution to the pretreated molecular sieve is (3~8) mL:1g, for example, it can be 3.0 mL:1g, 3.5 mL:1g, 4.0 mL:1g, 4.5 mL:1g, 5.0 mL:1g, 5.5 mL:1g, 6.0 mL:1g, 6.5 mL:1g, 7.0 mL:1g, 7.5 mL:1g or 8.0 mL:1g, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0078] In some optional instances, the flow rate of the ammonium nitrate solution is such that the volume of the ammonium nitrate solution passing through the bed of the pretreated molecular sieve per hour is 1 to 2 times the bed volume, for example, it can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 times, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0079] In some alternative instances, the temperature of the ammonium nitrate solution is 80-90°C, for example, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, or 90°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0080] In some optional instances, the drying temperature of the pretreated molecular sieve after ion exchange is 80~100°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0081] In some optional instances, the drying time of the pretreated molecular sieve after ion exchange is 6 to 8 hours, for example, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0082] In some optional instances, step (3) includes the two-stage gradient calcination activation comprising a first calcination and a second calcination performed sequentially.

[0083] In some alternative instances, the heating rate of the first calcination is 0.5 to 1.5 °C / min, for example, it can be 0.5 °C / min, 0.55 °C / min, 0.6 °C / min, 0.65 °C / min, 0.7 °C / min, 0.75 °C / min, 0.8 °C / min, 0.85 °C / min, 0.9 °C / min, 0.95 °C / min or 1 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0084] In some optional instances, the calcination temperature of the first calcination is 200~300℃, for example, it can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, the holding time for the first calcination is 1 to 2 hours, for example, it can be 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0086] In some alternative examples, the heating rate of the second calcination is 1 to 2 °C / min, for example, it can be 1.0 °C / min, 1.1 °C / min, 1.2 °C / min, 1.3 °C / min, 1.4 °C / min, 1.5 °C / min, 1.6 °C / min, 1.7 °C / min, 1.8 °C / min, 1.9 °C / min or 2.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0087] In some optional instances, the second calcination temperature is 400~500℃, for example, it can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0088] In some optional instances, the second calcination holding time is 1 to 2 hours, for example, it can be 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0089] In some optional examples, the mass fraction of the silane coupling agent in the silane coupling agent solution is 1 to 2 wt%, for example, it may be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0090] In some alternative examples, the ratio of the silane coupling agent solution to the calcined molecular sieve is (1~5) mL:1g, for example, it can be 1.0 mL:1g, 1.5 mL:1g, 2.0 mL:1g, 2.5 mL:1g, 3.0 mL:1g, 3.5 mL:1g, 4.0 mL:1g, 4.5 mL:1g or 5.0 mL:1g, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0091] The present invention specifically defines the ratio of silane coupling agent solution to calcined molecular sieve as (1~5) mL:1g. The silane coupling agent is anchored on the outer surface of the molecular sieve through chemical bonding to form a hydrophobic protective layer. Its core lies in the formation of Si-O-Al covalent bonds to firmly bind silane molecules to the Al-O framework of the molecular sieve.

[0092] When the amount of silane coupling agent solution is too low, a continuous hydrophobic layer cannot form on the surface of the molecular sieve, and only some active sites are passivated. This leads to enhanced competitive adsorption of polar substances such as water vapor. At this time, the electrostatic repulsion of the hydrophobic layer on sulfides (such as thiols) is weakened, and the adsorption selectivity decreases significantly. In addition, a low proportion of silane may result in uncovered active sites on the outer surface of the molecular sieve. These sites are easily occupied by impurities during adsorption, reducing the adsorption capacity for olefins.

[0093] Conversely, if the amount of silane coupling agent solution is too high, the excess silane molecules will undergo self-polymerization on the surface of the molecular sieve, forming a dense hydrophobic film. This dense layer will not only completely seal the mesoporous structure of the molecular sieve and hinder the diffusion of reactant molecules, but will also cover some of the Bronsted acidic sites, resulting in a sharp decrease in adsorption capacity. Furthermore, the integrity of the hydrophobic layer is easily damaged during the regeneration process, shortening the service life of the adsorption column.

[0094] When the ratio of silane coupling agent solution to calcined molecular sieve is in the range of (1~5) mL:1g, both surface modification coverage and pore permeability can be balanced. Silane molecules can uniformly cover the outer surface of the molecular sieve, forming a hydrophobic layer of appropriate thickness. This layer effectively blocks the adsorption of water vapor and polar impurities while retaining sufficient mesoporous channels for rapid diffusion of olefin molecules, thus achieving efficient capture of trace olefins in n-octane during dynamic adsorption. At the same time, the appropriately thick hydrophobic layer avoids physical blockage of the molecular sieve pores, allowing the adsorption column to maintain stable separation efficiency even under fluctuating humidity conditions.

[0095] In some optional instances, the mixing and stirring time of the calcined molecular sieve and the silane coupling agent solution is 1 to 3 hours, for example, 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0096] In some optional instances, the drying temperature is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0097] In some optional instances, the drying time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0098] In some optional instances, the amount of graphite binder is 1 to 5 wt% of the mass of the passivated molecular sieve, for example, it may be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0099] In some alternative instances, the compression molding pressure is 3 to 8 MPa, for example, 3.0 MPa, 3.5 MPa, 4.0 MPa, 4.5 MPa, 5.0 MPa, 5.5 MPa, 6.0 MPa, 6.5 MPa, 7.0 MPa, 7.5 MPa or 8.0 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0100] In some optional instances, the holding time for the compression molding is 5 to 15 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, 11 seconds, 12 seconds, 13 seconds, 14 seconds or 15 seconds, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0101] In some optional examples, the diameter of the modified Y-type molecular sieve adsorption column is 3 to 5 mm, for example, it can be 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4.0 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm or 5.0 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0102] As a preferred technical solution of the present invention, in step (III), the pressure of membrane separation is 0.8~1.2MPa, for example, it can be 0.8MPa, 0.85MPa, 0.9MPa, 0.95MPa, 1MPa, 1.05MPa, 1.1MPa, 1.15MPa or 1.2MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0103] In some optional instances, the membrane separation temperature is 40 to 50°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0104] In some optional instances, backwashing is performed every 8 to 12 hours during membrane separation, for example, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0105] In some optional instances, the purity of the n-octane product is ≥99.5%, such as 99.5%, 99.6%, 99.7%, 99.8%, or 99.9%, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0106] As a preferred technical solution of the present invention, in step (III), the zeolite-filled ceramic membrane assembly is prepared by the following method: (i) The porous alumina ceramic membrane is calcined to obtain a calcined ceramic membrane, which is then immersed in nitric acid solution for ultrasonic cleaning, removed, washed, and dried to obtain a pretreated ceramic membrane; (ii) Disperse NaA type zeolite in water to obtain a zeolite dispersion, then add sodium hexametaphosphate, mix to obtain a zeolite solution, and add hydrochloric acid solution to adjust the pH; (iii) Place the pretreated ceramic membrane into the reactor, evacuate and maintain the vacuum for a period of time, then release the vacuum, and then add the zeolite solution adjusted to pH in step (ii) to completely submerge the pretreated ceramic membrane for impregnation, and then take it out for drying; (iv) The dried pretreated ceramic membrane is then subjected to step (iii), and the impregnation and drying are repeated multiple times to obtain the zeolite-filled ceramic membrane assembly.

[0107] Furthermore, the zeolite-filled ceramic membrane assembly is prepared using the following method: (i) The porous alumina ceramic membrane is calcined to obtain a calcined ceramic membrane. The calcined ceramic membrane is then immersed in a nitric acid solution for ultrasonic cleaning, and then taken out for washing and drying to obtain a pretreated ceramic membrane. (ii) Disperse NaA type zeolite in deionized water to obtain a zeolite dispersion, add sodium hexametaphosphate to the zeolite dispersion, mix well to obtain a zeolite solution, and add hydrochloric acid solution to the zeolite solution to adjust its pH value. (iii) Place the pretreated ceramic membrane obtained in step (i) into a reaction vessel, evacuate the reaction vessel and maintain it for a period of time, then release the vacuum, add the zeolite solution after adjusting the pH value in step (ii) into the reaction vessel to completely submerge the pretreated ceramic membrane, impregnate it under normal pressure for a period of time, and then take out the impregnated pretreated ceramic membrane for gradient hot air drying. (iv) The pretreated ceramic membrane after gradient hot air drying is further subjected to step (iii), and the impregnation and gradient hot air drying are repeated multiple times to obtain the zeolite-filled ceramic membrane assembly.

[0108] This invention provides a process for preparing a zeolite-filled ceramic membrane module. Through multi-level structural regulation and surface chemical modification, a separation material with high permeation flux, high selectivity and long lifespan is constructed.

[0109] In the pretreatment stage of the alumina porous ceramic membrane, high-temperature calcination causes the substrate to form a γ-Al₂O₃ crystalline phase. Its three-dimensional interconnected pore structure (pore size approximately 0.1–0.5 μm) provides a stable attachment framework for zeolite crystals. The mesoporous network formed during calcination not only enhances the membrane's mechanical strength but also balances permeability and mechanical stability through porosity regulation. Subsequently, ultrasonic cleaning with nitric acid solution further removes surface impurities, exposing more hydroxyl active sites and laying the foundation for subsequent zeolite chemical bonding. This pretreatment scheme endows the membrane substrate with excellent chemical and thermal stability, enabling long-term operation under high temperature and high pressure conditions, and providing reliable physical support for n-octane purification.

[0110] The zeolite loading process employs a gradient impregnation technique. Vacuum suction allows the NaA-type zeolite solution to fully penetrate the ceramic membrane pores. The directional arrangement of zeolite particles within the pores forms selective permeation channels, and the uniform pore size in its crystal structure creates a size sieving effect on n-octane molecules. The addition of sodium hexametaphosphate as a dispersant effectively suppresses zeolite agglomeration, keeping the loaded layer thickness within the range of 5–10 μm. Gradient hot air drying slowly removes adsorbed water, preventing zeolite lattice collapse and preserving its shape-selective catalytic properties. Repeated impregnation-drying cycles significantly increase the zeolite loading, forming a multi-layered zeolite crystal array within the pores, enhancing the redundancy of the separation performance. This structural design allows n-octane molecules to preferentially permeate due to the high degree of fit between their kinetic diameter and the zeolite pore size, while impurities such as sulfides and olefins are effectively retained.

[0111] In the membrane separation process, the zeolite-filled ceramic membrane module prepared by this invention has the following advantages: On the one hand, efficient separation is achieved through the physical shape-selective effect of zeolite-filled ceramic membrane modules. Octane molecules preferentially permeate due to the high degree of fit between their kinetic diameter and the zeolite pore size, while impurities such as sulfides and olefins are effectively retained. Simultaneously, as the final purification unit in the entire process, the zeolite-filled ceramic membrane module inherits the processing effects of preceding steps such as dehydration, hydrogenation, distillation, and adsorption. Its high selective separation capability can intercept trace amounts of incompletely converted olefins from the hydrogenation reaction, polar impurities remaining from desulfurization adsorption, and even heavy component entrainment that may be generated during molecular distillation. This end-of-line control ensures that the final product purity exceeds 99.5%, meeting the stringent requirements for the synthesis of high-value-added chemicals. Furthermore, the physical process of membrane separation avoids the energy burden of traditional adsorption regeneration, reducing overall process energy consumption by more than 50% compared to traditional methods.

[0112] On the other hand, long-term operational stability is another significant advantage of this component. The γ-Al2O3 crystal phase formed by gradient calcination is highly matched with the lattice parameters of zeolite, reducing interfacial stress. The repeated impregnation process forms a mechanically interlocked structure between the zeolite particles and the substrate, avoiding peeling during repeated use. This long-term stability ensures the continuity and reliability of the n-octane purification process and reduces maintenance costs.

[0113] As a preferred technical solution of the present invention, in step (i), the pore size of the porous alumina ceramic membrane is 0.1~0.5μm, for example, it can be 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm or 0.5μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0114] In some optional examples, the porosity of the alumina porous ceramic membrane is 35-40%, for example, it can be 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5% or 40%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0115] In some optional examples, the calcination temperature of the alumina porous ceramic membrane is 400~500℃, for example, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0116] In some optional examples, the calcination holding time of the alumina porous ceramic membrane is 1 to 3 hours, for example, it can be 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h or 3.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0117] In some alternative instances, the concentration of the nitric acid solution is 0.1 to 0.3 mol / L, for example, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, or 0.3 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0118] In some optional instances, the ultrasonic cleaning time is 30 to 40 minutes, for example, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0119] In some optional instances, in step (ii), the particle size of the NaA-type zeolite is 0.3~0.5μm, for example, it can be 0.3μm, 0.32μm, 0.34μm, 0.36μm, 0.38μm, 0.4μm, 0.42μm, 0.44μm, 0.46μm, 0.48μm or 0.5μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0120] In some optional instances, the mass fraction of NaA-type zeolite in the zeolite dispersion is 5 to 8 wt%, for example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, or 8.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0121] This invention specifically limits the mass fraction of NaA-type zeolite in the zeolite dispersion to 5-8 wt%. The mass fraction of NaA-type zeolite directly affects its distribution and function within the ceramic membrane pores.

[0122] When the mass fraction of NaA-type zeolite is below 5 wt%, the zeolite particles do not fill the pores sufficiently, resulting in an excessively low density of effective adsorption sites. At this point, although the shape-selective sieving effect of the zeolite can still partially function, the limited number of active sites per unit volume significantly reduces the adsorption capacity for olefins and sulfides, making it difficult to meet the separation requirements of high-purity products. Furthermore, at low loading levels, the interaction between zeolite particles is weak, making them prone to localized detachment during fluid scouring or pressure fluctuations, thus shortening the lifespan of the adsorption column.

[0123] If the mass fraction of NaA-type zeolite exceeds 8 wt%, the excessive zeolite packing will lead to a sharp increase in diffusion resistance within the pores. In this case, n-octane molecules must overcome higher mass transfer resistance to reach the zeolite surface, resulting in a significant decrease in permeation flux and a substantial increase in energy consumption costs. More importantly, excessively high zeolite concentrations can cause tight packing between particles, forming a dense, heterogeneous structure that hinders the deep adsorption of sulfides (such as thiols). Furthermore, the introduction of excessive zeolite may damage the mechanical strength of the ceramic membrane substrate, making it prone to cracking or localized spalling during long-term operation, further reducing separation stability.

[0124] When the mass fraction of NaA-type zeolite in the zeolite dispersion is in the range of 5~8wt%, the loading density and pore structure of zeolite can be taken into account at the same time. Zeolite particles can be embedded in the ceramic membrane pores in the form of single-layer dispersion or multi-layer orderly arrangement, which not only ensures the high density of active sites per unit volume, but also maintains the openness of the mesoporous structure.

[0125] In some optional instances, the amount of sodium hexametaphosphate added is 0.05 to 0.15 wt% of the mass of the zeolite dispersion, for example, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, or 0.15 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0126] In some alternative instances, 0.1 mol / L hydrochloric acid solution is added to the zeolite solution to adjust its pH to 4.5-5.5, for example, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4 or 5.5, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0127] In some optional instances, in step (iii), the reactor is evacuated to -0.08 to -0.1 MPa, for example, -0.08 MPa, -0.082 MPa, -0.084 MPa, -0.086 MPa, -0.088 MPa, -0.09 MPa, -0.092 MPa, -0.094 MPa, -0.096 MPa, -0.098 MPa, or -0.1 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0128] In some optional instances, the reactor is maintained under vacuum for 10 to 20 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0129] In some optional instances, the immersion time of the pretreated ceramic membrane in the zeolite solution is 10 to 15 minutes, for example, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes, or 15 minutes, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0130] In some optional instances, the gradient hot air drying process includes a first hot air drying and a second hot air drying performed sequentially.

[0131] In some optional instances, the hot air temperature of the first hot air dryer is 60~70°C, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0132] In some optional instances, the first hot air drying time is 1 to 1.5 hours, for example, it can be 1.0 hours, 1.05 hours, 1.1 hours, 1.15 hours, 1.2 hours, 1.25 hours, 1.3 hours, 1.35 hours, 1.4 hours, 1.45 hours or 1.5 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0133] In some optional instances, the hot air temperature of the second hot air dryer is 80~90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0134] In some optional instances, the second hot air drying time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0135] In some optional instances, step (iv) involves repeating the impregnation and hot air drying process 2 to 3 times.

[0136] Compared with the prior art, the beneficial effects of the present invention are as follows: The n-octane purification method provided by this invention achieves efficient separation and deep removal of impurities through multi-stage synergistic processing, significantly improving product purity and process economy. First, two-stage molecular sieve dehydration effectively removes free and bound water from crude n-octane, avoiding the risk of water poisoning of the subsequent hydrogenation catalyst, while simultaneously controlling the molecular sieve regeneration cycle to reduce energy consumption. In the hydrogenation reaction stage, the Ni-Mo / Al2O3 catalyst precisely promotes saturated hydrogenation of olefins through a bimetallic synergistic effect, increasing the olefin conversion rate to over 98%, while suppressing the side reaction of deep hydrogenation to form alkanes, ensuring the selectivity of the target product, n-octane. Subsequently, a two-stage molecular distillation system achieves stepwise separation of light and heavy components through precise temperature control, combined with the highly effective adsorption of residual olefins and sulfides by a modified Y-type molecular sieve adsorption column, significantly reducing impurity content to the ppm level. Finally, a zeolite-filled ceramic membrane module achieves ultimate separation of n-octane from trace impurities through size sieving and surface hydrophobic properties, while a backwashing design extends the membrane module's lifespan and maintains high throughput. The n-octane purification method provided by this invention achieves a purity of over 99.5% through a synergistic process chain of dehydration-hydrogenation-distillation-adsorption-membrane separation, providing an efficient, low-consumption, and stable technical solution for the production of high-purity chemicals. Attached Figure Description

[0137] Figure 1The process flow diagrams for the purification of n-octane provided in Examples 1-13 of this invention are shown. Detailed Implementation

[0138] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of the present invention. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0139] Example 1 This embodiment provides a method for improving the purity of n-octane, such as... Figure 1 As shown, the method for improving the purity of n-octane includes: (1) The crude n-octane was subjected to two-stage molecular sieve dehydration. The first-stage dehydration temperature was 85℃ and the time was 4h, and the second-stage dehydration temperature was 45℃ and the time was 3h. The operating pressure for both the first-stage and second-stage dehydration was 0.4MPa. The dehydrated product obtained after two-stage molecular sieve dehydration was subjected to hydrogenation reaction under the action of Ni-Mo / Al2O3 catalyst. The reaction pressure for hydrogenation reaction was 4MPa, the reaction temperature was 180℃, the hydrogen-to-oil ratio was 120:1, and the space velocity was 5h. -1 After the hydrogenation reaction is completed, a mixed fraction containing n-octane and trace impurities is obtained; The Ni-Mo / Al2O3 catalyst was prepared using the following method: (1.1) Dissolve nickel nitrate and ammonium molybdate in deionized water. The molar ratio of Ni to Mo in nickel nitrate and ammonium molybdate is 1:1.5. After mixing evenly, a nickel-molybdenum solution is obtained. The concentration of nickel nitrate and ammonium molybdate in the nickel-molybdenum solution is 1 mol / L. Mix aluminum nitrate solution with nickel-molybdenum solution at a volume ratio of 1.2:1 to obtain a precursor solution. (1.2) Under the conditions of stirring speed of 600 rpm and heating at 70 °C, 0.5 mol / L sodium carbonate solution was added dropwise to the precursor solution obtained in step (1.1) at a dropping rate of 1.5 mL / min to induce precipitation reaction. Nitrogen gas was continuously introduced for protection during the reaction. When the pH value of the reaction solution reached 8, the addition of sodium carbonate solution was stopped to terminate the reaction. After the reaction was completed, the solution was filtered to obtain the precipitate. (1.3) The precipitate obtained in step (1.2) was aged at 80℃ for 6h, then washed with deionized water, and dried at 110℃ for 12h to obtain the precursor; the precursor was heated to 600℃ and held at 2℃ / min in air atmosphere for 5h, and then naturally cooled to room temperature to obtain the Ni-Mo / Al2O3 catalyst. (2) The mixed fraction obtained in step (1) is fed into a two-stage molecular distillation system for fractionation. The distillation temperature of the first-stage light component removal tower is 100℃ and the distillation pressure is 0.3Pa. The distillation temperature of the second-stage n-octane purification tower is 120℃ and the distillation pressure is 0.1Pa. The target fraction at 120℃ is collected. The target fraction is then adsorbed through a modified Y-type molecular sieve adsorption column at an adsorption temperature of 30℃ and an adsorption space velocity of 3h. -1 Remove residual olefins and sulfides to obtain intermediate products; The modified Y-type molecular sieve adsorption column was prepared using the following method: (2.1) Industrial-grade Y-type molecular sieve (NaY type molecular sieve, silicon-to-aluminum ratio of 5, the same below) with a particle size of 0.5 mm was added to a 0.1 mol / L hydrochloric acid solution. The ratio of industrial-grade Y-type molecular sieve to hydrochloric acid solution was 1 g: 1.5 mL. The mixture was stirred at 80 °C for 3 h to acidify. After acidification, the mixture was filtered, washed with deionized water and dried to obtain acidified molecular sieve. The acidified molecular sieve was heated to 500 °C at a heating rate of 8 °C / min and kept at that temperature for 3 h. After naturally cooling to room temperature, the pretreated molecular sieve was obtained. (2.2) Dissolve ammonium nitrate in deionized water and mix well to obtain an ammonium nitrate solution with a concentration of 1 mol / L; pack the pretreated molecular sieve obtained in step (2.1) into an exchange column with a packing density of 0.5 g / mL, and pass an ammonium nitrate solution at 80℃ into the exchange column for ion exchange. The solid-liquid ratio of the ammonium nitrate solution to the pretreated molecular sieve is 3 mL: 1 g. The volume of ammonium nitrate solution passing through the bed of the pretreated molecular sieve per hour is 1 times the bed volume. Collect the effluent during the ion exchange process. Stop the ion exchange when the concentration of ammonium ions in the effluent is <0.5 g / L. Dry the pretreated molecular sieve after ion exchange at 80℃ for 8 hours to obtain the exchange molecular sieve. (2.3) In a nitrogen atmosphere, the exchange molecular sieve obtained in step (2.2) was activated by two-stage gradient calcination. The heating rate of the first calcination was 0.5℃ / min, the calcination temperature was 200℃, and the holding time was 2h. The heating rate of the second calcination was 1℃ / min, the calcination temperature was 400℃, and the holding time was 2h. After calcination, calcined molecular sieves were obtained. The calcined molecular sieves were dispersed in a silane coupling agent solution (the silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution, with a volume ratio of anhydrous ethanol to deionized water of 9:1). Silane coupling was performed. The silane coupling agent KH550 in the solution had a mass fraction of 1 wt%, and the ratio of the silane coupling agent solution to the calcined molecular sieve was 1 mL: 1 g. The mixture was stirred at room temperature for 1 h, followed by filtration, washing with deionized water, and drying at 100 °C for 3 h. After drying, a passivated molecular sieve was obtained. The passivated molecular sieve was then mixed evenly with a graphite binder (graphite powder), with the amount of graphite binder being 1 wt% of the mass of the passivated molecular sieve. The mixture was filled into a columnar mold and pressed at 3 MPa for 15 s to obtain a columnar modified Y-type molecular sieve adsorption column with a diameter of 3 mm. (3) After cooling the intermediate product obtained in step (2) to 50°C, membrane separation is performed through a zeolite-filled ceramic membrane module. The membrane separation pressure is 0.8 MPa and the membrane separation temperature is 50°C. Backwashing is performed every 8 hours during the membrane separation process to obtain n-octane product. The zeolite-filled ceramic membrane module was prepared using the following method: (3.1) A porous alumina ceramic membrane with a pore size of 0.1 μm and a porosity of 35% (diameter 25 mm, 7 round holes, pore size 6 mm, length 1000 mm, purchased from Wufeng Ceramics Co., Ltd., the same below) was calcined at a temperature of 400℃ and a holding time of 3 h to obtain a calcined ceramic membrane; the calcined ceramic membrane was immersed in a 0.1 mol / L nitric acid solution for ultrasonic cleaning for 30 min, and then taken out for washing with deionized water and drying to obtain a pretreated ceramic membrane; (3.2) Disperse NaA type zeolite (purity 99%, purchased from Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., the same below) with a particle size of 0.3 μm in deionized water to obtain a zeolite dispersion. The mass fraction of NaA type zeolite in the zeolite dispersion is 5 wt%. Add sodium hexametaphosphate to the zeolite dispersion. The amount of sodium hexametaphosphate added is 0.05 wt% of the mass of the zeolite dispersion. After mixing evenly, a zeolite solution is obtained. Add 0.1 mol / L hydrochloric acid solution to the zeolite solution to adjust its pH value to 4.5. (3.3) The pretreated ceramic membrane obtained in step (3.1) is placed in the reactor, the reactor is evacuated to -0.08MPa and maintained for 20min, then the vacuum is released, and the zeolite solution after pH adjustment in step (3.2) is added to the reactor to completely submerge the pretreated ceramic membrane. It is immersed for 10min under normal pressure, and then the pretreated ceramic membrane is taken out and subjected to the first hot air drying and the second hot air drying in sequence. The hot air temperature of the first hot air drying is 60℃ and the drying time is 1.5h, and the hot air temperature of the second hot air drying is 80℃ and the drying time is 3h. (3.4) Continue to step (3.3) after the pretreated ceramic membrane is dried by gradient hot air, repeat the impregnation and gradient hot air drying twice to obtain the zeolite-filled ceramic membrane assembly.

[0140] Example 2 This embodiment provides a method for improving the purity of n-octane, such as... Figure 1 As shown, the method for improving the purity of n-octane includes: (1) Crude n-octane was dehydrated by two-stage molecular sieve treatment. The first-stage dehydration temperature was 90℃ and the time was 3.5h, while the second-stage dehydration temperature was 50℃ and the time was 2.5h. The operating pressure for both stages was 0.5MPa. The dehydrated product obtained after the two-stage molecular sieve dehydration was then hydrogenated under the action of a Ni-Mo / Al2O3 catalyst. The reaction pressure for the hydrogenation reaction was 4.5MPa, the reaction temperature was 200℃, the hydrogen-to-oil ratio was 100:1, and the space velocity was 7.5h. -1 After the hydrogenation reaction is completed, a mixed fraction containing n-octane and trace impurities is obtained; The Ni-Mo / Al2O3 catalyst was prepared using the following method: (1.1) Nickel nitrate and ammonium molybdate are dissolved in deionized water. The molar ratio of Ni to Mo in nickel nitrate and ammonium molybdate is 1:1.6. After mixing evenly, a nickel-molybdenum solution is obtained. The concentration of nickel nitrate and ammonium molybdate in the nickel-molybdenum solution is 1.2 mol / L. A 1.0 mol / L aluminum nitrate solution is mixed evenly with the nickel-molybdenum solution at a volume ratio of 1.5:1 to obtain a precursor solution. (1.2) Under the conditions of stirring speed of 700 rpm and heating at 75 °C, 0.75 mol / L sodium carbonate solution was added dropwise to the precursor solution obtained in step (1.1) at a dropping rate of 1.8 mL / min to induce precipitation reaction. Nitrogen gas was continuously introduced for protection during the reaction. When the pH value of the reaction solution reached 8.2, the addition of sodium carbonate solution was stopped to terminate the reaction. After the reaction was completed, the solution was filtered to obtain the precipitate. (1.3) The precipitate obtained in step (1.2) was allowed to stand and age for 5 h at 85 °C, then washed with deionized water, and dried at 115 °C for 11 h to obtain the precursor; the precursor was heated to 650 °C at a heating rate of 3.5 °C / min and held for 4 h in air atmosphere, and then naturally cooled to room temperature to obtain the Ni-Mo / Al2O3 catalyst. (2) The mixed fraction obtained in step (1) is fed into a two-stage molecular distillation system for fractionation. The distillation temperature of the first-stage light component removal tower is 105℃ and the distillation pressure is 0.2 Pa. The distillation temperature of the second-stage n-octane purification tower is 125℃ and the distillation pressure is 0.05 Pa. The target fraction at 125℃ is collected. The target fraction is then adsorbed through a modified Y-type molecular sieve adsorption column at an adsorption temperature of 40℃ and an adsorption space velocity of 4 h⁻¹. -1 Remove residual olefins and sulfides to obtain intermediate products; The modified Y-type molecular sieve adsorption column was prepared using the following method: (2.1) Industrial-grade Y-type molecular sieve with a particle size of 0.8 mm was added to a 0.3 mol / L hydrochloric acid solution. The ratio of industrial-grade Y-type molecular sieve to hydrochloric acid solution was 1 g: 1.8 mL. The mixture was stirred at 85 °C for 2.5 h to acidify. After acidification, the mixture was filtered, washed with deionized water and dried to obtain acidified molecular sieve. The acidified molecular sieve was heated to 520 °C at a heating rate of 9 °C / min and kept at that temperature for 2.5 h. After naturally cooling to room temperature, the pretreated molecular sieve was obtained. (2.2) Dissolve ammonium nitrate in deionized water and mix well to obtain an ammonium nitrate solution with a concentration of 1.2 mol / L; pack the pretreated molecular sieve obtained in step (2.1) into an exchange column with a packing density of 0.65 g / mL, and pass an ammonium nitrate solution at 85℃ into the exchange column for ion exchange. The solid-liquid ratio of the ammonium nitrate solution to the pretreated molecular sieve is 5 mL: 1 g. The volume of ammonium nitrate solution passing through the bed of the pretreated molecular sieve per hour is 1.5 times the bed volume. Collect the effluent during the ion exchange process. Stop the ion exchange when the concentration of ammonium ions in the effluent is <0.5 g / L. Dry the pretreated molecular sieve after ion exchange at a drying temperature of 90℃ for 7 h. The dried molecular sieve is then obtained. (2.3) In a nitrogen atmosphere, the exchange molecular sieve obtained in step (2.2) was activated by two-stage gradient calcination. The heating rate of the first calcination was 1.0℃ / min, the calcination temperature was 250℃, and the holding time was 1.5h. The heating rate of the second calcination was 1.5℃ / min, the calcination temperature was 450℃, and the holding time was 1.5h. After calcination, calcined molecular sieves were obtained. The calcined molecular sieves were dispersed in a silane coupling agent solution (the silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution, in which the volume ratio of anhydrous ethanol to deionized water was 9:1). The silane coupling agent KH550 in the silane coupling agent solution had a mass fraction of 1.5 wt%, and the ratio of the silane coupling agent solution to the calcined molecular sieve was 3 mL: 1 g. The mixture was stirred at room temperature for 2 h, followed by filtration, washing with deionized water, and drying at 105 °C for 2.5 h. After drying, a passivated molecular sieve was obtained. The passivated molecular sieve was then mixed evenly with a graphite binder at a mass of 3 wt% of the passivated molecular sieve. The mixture was filled into a columnar mold and pressed at 5 MPa for 10 s to obtain a columnar modified Y-type molecular sieve adsorption column with a diameter of 4 mm. (3) After cooling the intermediate product obtained in step (2) to 45°C, membrane separation is performed through a zeolite-filled ceramic membrane module. The membrane separation pressure is 1.0 MPa and the membrane separation temperature is 45°C. Backwashing is performed every 10 hours during the membrane separation process to obtain n-octane product. The zeolite-filled ceramic membrane module was prepared using the following method: (3.1) A porous alumina ceramic membrane with a pore size of 0.3 μm and a porosity of 38% was calcined at a temperature of 450℃ and a holding time of 2h to obtain a calcined ceramic membrane. The calcined ceramic membrane was then immersed in a 0.2 mol / L nitric acid solution for ultrasonic cleaning for 35 min, and then removed for washing with deionized water and drying to obtain a pretreated ceramic membrane. (3.2) Disperse NaA type zeolite with a particle size of 0.4 μm in deionized water to obtain a zeolite dispersion with a mass fraction of 6.5 wt% of NaA type zeolite in the zeolite dispersion. Add sodium hexametaphosphate to the zeolite dispersion with an amount of 0.1 wt% of the mass of the zeolite dispersion. After mixing evenly, obtain a zeolite solution. Add 0.1 mol / L hydrochloric acid solution to the zeolite solution to adjust its pH value to 5.0. (3.3) The pretreated ceramic membrane obtained in step (3.1) is placed in the reactor, the reactor is evacuated to -0.09MPa and maintained for 15min, then the vacuum is released, and the zeolite solution after pH adjustment in step (3.2) is added to the reactor to completely submerge the pretreated ceramic membrane. It is immersed for 12min under normal pressure, and then the pretreated ceramic membrane is taken out and subjected to the first hot air drying and the second hot air drying in sequence. The hot air temperature of the first hot air drying is 65℃ and the drying time is 1.2h, and the hot air temperature of the second hot air drying is 85℃ and the drying time is 2.5h. (3.4) Continue to step (3.3) after the pretreated ceramic membrane is dried by gradient hot air, repeat the impregnation and gradient hot air drying twice to obtain the zeolite-filled ceramic membrane assembly.

[0141] Example 3 This embodiment provides a method for improving the purity of n-octane, such as... Figure 1 As shown, the method for improving the purity of n-octane includes: (1) The crude n-octane was subjected to two-stage molecular sieve dehydration. The first-stage dehydration temperature was 95℃ and the time was 3h, and the second-stage dehydration temperature was 55℃ and the time was 2h. The operating pressure for both the first-stage and second-stage dehydration was 0.6MPa. The dehydrated product obtained after two-stage molecular sieve dehydration was subjected to hydrogenation reaction under the action of Ni-Mo / Al2O3 catalyst. The reaction pressure for hydrogenation reaction was 3MPa, the reaction temperature was 220℃, the hydrogen-to-oil ratio was 80:1, and the space velocity was 10h. -1 After the hydrogenation reaction is completed, a mixed fraction containing n-octane and trace impurities is obtained; The Ni-Mo / Al2O3 catalyst was prepared using the following method: (1.1) Nickel nitrate and ammonium molybdate are dissolved in deionized water. The molar ratio of Ni to Mo in nickel nitrate and ammonium molybdate is 1:1.7. After mixing evenly, a nickel-molybdenum solution is obtained. The concentration of nickel nitrate and ammonium molybdate in the nickel-molybdenum solution is 1.5 mol / L. Aluminum nitrate solution with a concentration of 1.2 mol / L is mixed evenly with the nickel-molybdenum solution at a volume ratio of 1.8:1 to obtain a precursor solution. (1.2) Under the conditions of stirring speed of 800 rpm and heating at 80℃, 1 mol / L sodium carbonate solution was added dropwise to the precursor solution obtained in step (1.1) at a dropping rate of 2 mL / min to induce precipitation reaction. Nitrogen gas was continuously introduced for protection during the reaction. When the pH value of the reaction solution reached 8.5, the addition of sodium carbonate solution was stopped to terminate the reaction. After the reaction was completed, the solution was filtered to obtain the precipitate. (1.3) The precipitate obtained in step (1.2) was allowed to stand and age for 4 hours at 90℃, then washed with deionized water, and dried at 120℃ for 10 hours to obtain the precursor; the precursor was heated to 700℃ and held at 5℃ / min in air atmosphere for 3 hours, and then naturally cooled to room temperature to obtain the Ni-Mo / Al2O3 catalyst. (2) The mixed fraction obtained in step (1) is fed into a two-stage molecular distillation system for fractionation. The distillation temperature of the first-stage light component removal tower is 110℃ and the distillation pressure is 0.1 Pa. The distillation temperature of the second-stage n-octane purification tower is 130℃ and the distillation pressure is 0.01 Pa. The target fraction at 130℃ is collected. The target fraction is then adsorbed through a modified Y-type molecular sieve adsorption column at an adsorption temperature of 50℃ and an adsorption space velocity of 5 h⁻¹. -1 Remove residual olefins and sulfides to obtain intermediate products; The modified Y-type molecular sieve adsorption column was prepared using the following method: (2.1) Add industrial-grade Y-type molecular sieve with a particle size of 1 mm to 0.5 mol / L hydrochloric acid solution. The ratio of industrial-grade Y-type molecular sieve to hydrochloric acid solution is 1 g: 2 mL. Mix and stir at 90 °C for 2 h to acidify. After acidification, filter, wash with deionized water and dry to obtain acidified molecular sieve. Heat the acidified molecular sieve to 550 °C at a heating rate of 10 °C / min and keep it at that temperature for 2 h. After naturally cooling to room temperature, obtain pretreated molecular sieve. (2.2) Dissolve ammonium nitrate in deionized water and mix well to obtain an ammonium nitrate solution with a concentration of 1.5 mol / L; pack the pretreated molecular sieve obtained in step (2.1) into an exchange column with a packing density of 0.8 g / mL, and pass an ammonium nitrate solution at 90℃ into the exchange column for ion exchange. The solid-liquid ratio of the ammonium nitrate solution to the pretreated molecular sieve is 8 mL: 1 g. The volume of ammonium nitrate solution passing through the bed of the pretreated molecular sieve per hour is twice the bed volume. Collect the effluent during the ion exchange process. Stop the ion exchange when the concentration of ammonium ions in the effluent is <0.5 g / L. Dry the pretreated molecular sieve after ion exchange at a drying temperature of 100℃ for 6 h. The exchanged molecular sieve is obtained after drying. (2.3) In a nitrogen atmosphere, the exchange molecular sieve obtained in step (2.2) was activated by two-stage gradient calcination. The heating rate of the first calcination was 1.5℃ / min, the calcination temperature was 300℃, and the holding time was 1h. The heating rate of the second calcination was 2℃ / min, the calcination temperature was 500℃, and the holding time was 1h. After calcination, calcined molecular sieves were obtained. The calcined molecular sieves were dispersed in a silane coupling agent solution (the silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution, in which the volume ratio of anhydrous ethanol to deionized water was 9:1). The silane coupling agent KH550 in the silane coupling agent solution had a mass fraction of 2wt%, and the ratio of the silane coupling agent solution to the calcined molecular sieve was 5mL:1g. The mixture was stirred at room temperature for 3h, followed by filtration, washing with deionized water, and drying at 110℃ for 2h to obtain a passivated molecular sieve. The passivated molecular sieve was then mixed evenly with a graphite binder at a mass of 5wt% of the passivated molecular sieve and filled into a columnar mold. The mold was pressed at 8MPa for 5s to obtain a columnar modified Y-type molecular sieve adsorption column with a diameter of 5mm. (3) After cooling the intermediate product obtained in step (2) to 40°C, membrane separation is performed through a zeolite-filled ceramic membrane module. The membrane separation pressure is 1.2 MPa and the membrane separation temperature is 40°C. Backwashing is performed every 12 hours during the membrane separation process to obtain n-octane product. The zeolite-filled ceramic membrane module was prepared using the following method: (3.1) A porous alumina ceramic membrane with a pore size of 0.5 μm and a porosity of 40% was calcined at a temperature of 500℃ and a holding time of 1 h to obtain a calcined ceramic membrane; the calcined ceramic membrane was immersed in a 0.3 mol / L nitric acid solution for ultrasonic cleaning for 40 min, and then removed for washing with deionized water and drying to obtain a pretreated ceramic membrane; (3.2) Disperse NaA type zeolite with a particle size of 0.5 μm in deionized water to obtain a zeolite dispersion with a mass fraction of 8 wt% for NaA type zeolite. Add sodium hexametaphosphate to the zeolite dispersion at a mass of 0.15 wt% of the zeolite dispersion. After mixing evenly, obtain a zeolite solution. Add 0.1 mol / L hydrochloric acid solution to the zeolite solution to adjust its pH value to 5.5. (3.3) Place the pretreated ceramic membrane obtained in step (3.1) into the reactor, evacuate the reactor to -0.1MPa and maintain it for 10min, then release the vacuum, add the zeolite solution after adjusting the pH value in step (3.2) into the reactor to completely submerge the pretreated ceramic membrane, immerse it under normal pressure for 15min, then take out the pretreated ceramic membrane after immersion, and perform the first hot air drying and the second hot air drying in sequence. The hot air temperature of the first hot air drying is 70℃ and the drying time is 1h, and the hot air temperature of the second hot air drying is 90℃ and the drying time is 2h. (3.4) Continue to step (3.3) after the pretreated ceramic membrane is dried by gradient hot air, repeat the impregnation and gradient hot air drying three times to obtain the zeolite-filled ceramic membrane assembly.

[0142] Example 4 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (1.1), the molar ratio of Ni and Mo in nickel nitrate and ammonium molybdate is adjusted to 1:1.3. Other operating steps and process parameters are exactly the same as in Example 1.

[0143] Example 5 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (1.1), the molar ratio of Ni and Mo in nickel nitrate and ammonium molybdate is adjusted to 1:2. Other operating steps and process parameters are exactly the same as in Example 1.

[0144] Example 6 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (1.1), the volume ratio of aluminum nitrate solution and nickel-molybdenum solution is adjusted to 1:1. Other operating steps and process parameters are exactly the same as in Example 1.

[0145] Example 7 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (1.1), the volume ratio of aluminum nitrate solution and nickel-molybdenum solution is adjusted to 2:1. Other operating steps and process parameters are exactly the same as in Example 1.

[0146] Example 8 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (2.2), the concentration of ammonium nitrate solution is adjusted to 0.5 mol / L. Other operating steps and process parameters are exactly the same as in Example 1.

[0147] Example 9 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (2.2), the concentration of ammonium nitrate solution is adjusted to 2 mol / L. Other operating steps and process parameters are exactly the same as in Example 1.

[0148] Example 10 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (2.3), the ratio of silane coupling agent solution to calcined molecular sieve is adjusted to 0.5 mL: 1 g. Other operating steps and process parameters are exactly the same as in Example 1.

[0149] Example 11 This embodiment provides a method for improving the purity of n-octane. The difference from Example 1 is that in step (2.3), the ratio of silane coupling agent solution to calcined molecular sieve is adjusted to 7 mL: 1 g. Other operating steps and process parameters are exactly the same as in Example 1.

[0150] Example 12 This embodiment provides a method for improving the purity of n-octane. The difference from Embodiment 1 is that in step (3.2), the mass fraction of NaA-type zeolite in the zeolite dispersion is adjusted to 3wt%. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0151] Example 13 This embodiment provides a method for improving the purity of n-octane. The difference from Embodiment 1 is that in step (3.2), the mass fraction of NaA-type zeolite in the zeolite dispersion is adjusted to 10wt%. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0152] The purity of the crude n-octane used in Examples 1-13 and the purity of the obtained n-octane products were tested, and the test results are shown in Table 1. Examples 1 and 4-13 used the same batch of crude n-octane as the starting material.

[0153] Table 1: Test Results

[0154] The test data from Examples 1, 4, and 5 show that the purity of the n-octane product in Example 4 (98.5%) is lower than that in Example 1 (99.8%). This is because the molar ratio of Ni to Mo in the Ni-Mo / Al2O3 catalyst (1:1.3) is lower than the optimal ratio (1:(1.5~1.7)), resulting in a lower Mo content. 6+The insufficient Lewis acid site density reduces olefin adsorption capacity, decreases hydrogenation selectivity, and leads to incomplete removal of residual olefins and sulfides. Similarly, the purity of the n-octane product (98.0%) in Example 5 is further reduced because the molar ratio of Ni to Mo in the Ni-Mo / Al2O3 catalyst (1:2) is higher than the optimal ratio, resulting in insufficient removal of residual olefins and sulfides. 6+ Excessive hydrogenation can trigger side reactions that generate impurity phases such as MoS2, which cover active sites and block pores, leading to a decrease in hydrogenation efficiency and a reduction in thiol rejection rate.

[0155] The test data from Examples 1, 6, and 7 show that the purity of the n-octane product in Example 6 (98.3%) is lower than that in Example 1 (99.8%). This is because the volume ratio of aluminum nitrate solution to nickel-molybdenum solution (1:1) is lower than the optimal range (1.2~1.8:1), resulting in lower Al content. 3+ An imbalance in the ratio of the active component to the Ni-Mo component caused the Al2O3 support pores to collapse, reducing the specific surface area, limiting reactant diffusion, and decreasing the utilization rate of the hydrogenation active sites. Similarly, the purity of the n-octane product (98.2%) in Example 7 further decreased because the volume ratio of aluminum nitrate solution to nickel-molybdenum solution (2:1) exceeded the optimal range, resulting in excess Al. 3+ This causes aluminum-oxygen tetrahedral distortion, disordered pore structure, increased mass transfer resistance, and a decrease in olefin hydrogenation conversion rate.

[0156] The test data from Examples 1, 8, and 9 show that the purity of the n-octane product in Example 8 (98.0%) is lower than that in Example 1 (99.8%). This is because the concentration of the ammonium nitrate solution (0.5 mol / L) is lower than the optimal range (1~1.5 mol / L), resulting in higher NH4+ concentration. + Insufficient exchange resulted in high sodium ion residue, decreased stability of acidic sites, and reduced olefin adsorption capacity. Similarly, the purity of the n-octane product in Example 9 (97.8%) was further reduced because the concentration of ammonium nitrate solution (2 mol / L) exceeded the optimal range. Excessive ion exchange disrupted the charge balance of the skeleton, induced surface hydroxylation, weakened hydrophobicity, and reduced sulfide adsorption selectivity.

[0157] The test data from Examples 1, 10, and 11 show that the purity of the n-octane product in Example 10 (98.7%) is lower than that in Example 1 (99.8%). This is because the ratio of silane coupling agent solution to calcined molecular sieve (0.5 mL: 1 g) is lower than the optimal range (1~5) mL: 1 g), resulting in incomplete hydrophobic layer coverage, enhanced competitive adsorption of water vapor, decreased n-octane permeation flux, and residual trace amounts of olefins. Similarly, the purity of the n-octane product in Example 11 (97.5%) is further reduced because the ratio of silane coupling agent solution to calcined molecular sieve (7 mL: 1 g) exceeds the optimal range. This causes excessive coating of the molecular sieve surface with silane, blocking mesoporous channels, hindering the diffusion of guest molecules, and significantly reducing the thiol rejection rate.

[0158] The test data from Examples 1, 12, and 13 show that the purity of the n-octane product in Example 12 (98.2%) is lower than that in Example 1 (99.8%). This is because the mass fraction of NaA-type zeolite in the zeolite-filled ceramic membrane (3wt%) is lower than the optimal range (5~8wt%), resulting in sparse zeolite particle distribution, insufficient pore synergistic effect, weakened size sieving effect, and decreased impurity retention rate. Similarly, the purity of the n-octane product in Example 13 (97.0%) is further reduced because the mass fraction of NaA-type zeolite in the zeolite-filled ceramic membrane (10wt%) exceeds the optimal range. Excessive zeolite causes particle agglomeration, pore blockage, a sharp increase in diffusion resistance, and insufficient permeation flux, leading to deterioration of separation efficiency.

[0159] The inventors declare that the above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for improving the purity of n-octane, characterized in that, include: (I) Crude n-octane is dehydrated, and the dehydrated product is hydrogenated in the presence of Ni-Mo / Al2O3 catalyst to obtain a mixed fraction containing n-octane and trace impurities; (II) The mixed fraction is fractionated to collect the target fraction at 120~130℃. The target fraction is adsorbed by a modified Y-type molecular sieve adsorption column to obtain the intermediate product. The modified Y-type molecular sieve adsorption column was prepared by sequentially acidifying, calcining, particle exchange, gradient calcining activation, coupling agent passivation, and pressing Y-type molecular sieve. (III) After cooling the intermediate product, membrane separation is performed through a zeolite-filled ceramic membrane module; the zeolite-filled ceramic membrane module is obtained by impregnating an alumina porous ceramic membrane with a zeolite solution and then drying it with gradient hot air; backwashing is performed at intervals during the membrane separation process to obtain n-octane product.

2. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (I), the dehydration includes two-stage molecular sieve dehydration, specifically including a first-stage dehydration and a second-stage dehydration performed sequentially; The temperature for the first stage of dehydration is 85~95℃; The first stage of dehydration takes 3-4 hours; The temperature for the second-stage dehydration is 45~55℃; The second-stage dehydration time is 2-3 hours; The operating pressure for the first-stage dehydration and the second-stage dehydration is 0.4~0.6MPa; The reaction pressure for the hydrogenation reaction is 3-5 MPa; The reaction temperature for the hydrogenation reaction is 180~220℃; The hydrogen-to-oil ratio in the hydrogenation reaction is (80~120):1; The space velocity of the hydrogenation reaction is 5-10 h⁻¹. -1 .

3. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (I), the Ni-Mo / Al2O3 catalyst is prepared by the following method: (a) Nickel nitrate and ammonium molybdate are dissolved in water and mixed to obtain a nickel-molybdenum solution; aluminum nitrate solution is mixed with the nickel-molybdenum solution to obtain a precursor solution; (b) Under stirring and heating conditions, sodium carbonate solution was added to the precursor solution, the reaction was carried out, and the mixture was filtered to obtain a precipitate; (c) The precipitate is allowed to stand for aging, washed and dried to obtain a precursor. The precursor is then calcined and cooled to obtain a Ni-Mo / Al2O3 catalyst.

4. The method for improving the purity of n-octane according to claim 3, characterized in that, In step (a), the molar ratio of Ni to Mo in the nickel nitrate and ammonium molybdate is 1:(1.5~1.7); The concentrations of nickel nitrate and ammonium molybdate in the nickel-molybdenum solution are 1~1.5 mol / L; The concentration of the aluminum nitrate solution is 0.8~1.2 mol / L; The volume ratio of the aluminum nitrate solution to the nickel-molybdenum solution is (1.2~1.8):1; In step (b), the concentration of the sodium carbonate solution is 0.5~1 mol / L; The sodium carbonate solution was added at a rate of 1.5~2 mL / min; The heating temperature of the sodium carbonate solution during the dropwise addition process is 70~80℃; The stirring speed of the sodium carbonate solution during the dropwise addition process is 600~800 rpm; Stop adding the sodium carbonate solution when the pH of the reaction solution reaches 8-8.5, and terminate the reaction. In step (c), the temperature for static aging is 80~90℃; The settling and aging time is 4-6 hours; The drying temperature is 110~120℃; The drying time is 10-12 hours; The heating rate for calcining the precursor is 2~5℃ / min; The calcination temperature of the precursor is 600~700℃; The calcination time of the precursor is 3-5 hours.

5. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (II), the two-stage molecular distillation system includes a primary light component removal tower and a secondary n-octane purification tower connected in series. The distillation temperature of the primary light component removal tower is 100~110℃; The distillation pressure of the primary light component removal tower is 0.1~0.3 Pa; The distillation temperature of the secondary n-octane refining column is 120~130℃; The distillation pressure of the secondary n-octane refining column is 0.01~0.1 Pa; The adsorption temperature of the modified Y-type molecular sieve adsorption column is 30~50℃; The adsorption space velocity of the modified Y-type molecular sieve adsorption column is 3-5 h⁻¹. -1 .

6. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (II), the modified Y-type molecular sieve adsorption column is prepared by the following method: (1) Add Y-type molecular sieve to hydrochloric acid solution, mix and heat to acidify, filter, wash and dry to obtain acidified molecular sieve; then calcine and cool to obtain pretreated molecular sieve; (2) Dissolve ammonium nitrate in water and mix to obtain an ammonium nitrate solution; The pretreated molecular sieve is packed into an exchange column, and an ammonium nitrate solution is introduced into the exchange column for ion exchange. The effluent is collected during the ion exchange process, and the pretreated molecular sieve after ion exchange is dried to obtain the exchange molecular sieve. (3) Exchange molecular sieves are activated by calcination to obtain calcined molecular sieves; Calcined molecular sieves are dispersed in a silane coupling agent solution, mixed, filtered, washed and dried to obtain passivated molecular sieves; the passivated molecular sieves are mixed with graphite binder, filled into a mold and pressed to form a modified Y-type molecular sieve adsorption column.

7. The method for improving the purity of n-octane according to claim 6, characterized in that, In step (1), the particle size of the Y-type molecular sieve is 0.5~1mm; The ratio of the Y-type molecular sieve to the hydrochloric acid solution is 1g:(1.5~2)mL; The concentration of the hydrochloric acid solution is 0.1~0.5 mol / L; The acidification heating temperature is 80~90℃; The acidification time is 2-3 hours; The calcination rate of the acidified molecular sieve is 8~10℃ / min; The calcination temperature of the acidified molecular sieve is 500~550℃; The calcination time of the acidified molecular sieve is 2-3 hours; In step (2), the concentration of the ammonium nitrate solution is 1~1.5 mol / L; The pretreated molecular sieve is packed at a density of 0.5~0.8 g / mL in the exchange column; The solid-liquid ratio of the ammonium nitrate solution to the pretreated molecular sieve is (3~8) mL:1g; The flow rate of the ammonium nitrate solution is such that the volume of the ammonium nitrate solution passing through the bed of the pretreated molecular sieve per hour is 1 to 2 times the bed volume; The temperature of the ammonium nitrate solution is 80~90℃; The drying temperature of the pretreated molecular sieve after ion exchange is 80~100℃; The drying time for the pretreated molecular sieve after ion exchange is 6-8 hours; In step (3), the calcination activation includes a two-stage gradient calcination activation, specifically including a first calcination and a second calcination performed sequentially. The heating rate of the first calcination is 0.5~1.5℃ / min; The roasting temperature of the first roasting is 200~300℃; The holding time for the first roasting is 1-2 hours; The heating rate for the second calcination is 1~2℃ / min; The second roasting temperature is 400~500℃; The second roasting time is 1-2 hours; The mass fraction of the silane coupling agent in the silane coupling agent solution is 1~2 wt%; The ratio of the silane coupling agent solution to the calcined molecular sieve is (1~5) mL: 1 g; The mixing and stirring time of the calcined molecular sieve and silane coupling agent solution is 1-3 hours; The drying temperature is 100~110℃; The drying time is 2-3 hours; The amount of the graphite binder is 1-5 wt% of the mass of the passivated molecular sieve; The pressure for compression molding is 3~8MPa; The holding time for the pressing process is 5-15 seconds. The diameter of the modified Y-type molecular sieve adsorption column is 3~5 mm.

8. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (III), the pressure of the membrane separation is 0.8~1.2 MPa; The membrane separation temperature is 40~50℃; Backwashing is performed every 8-12 hours during membrane separation. The purity of the n-octane product is ≥99.5%.

9. The method for improving the purity of n-octane according to claim 1, characterized in that, In step (III), the zeolite-filled ceramic membrane assembly is prepared using the following method: (i) The porous alumina ceramic membrane is calcined to obtain a calcined ceramic membrane, which is then immersed in nitric acid solution for ultrasonic cleaning, removed, washed, and dried to obtain a pretreated ceramic membrane; (ii) Disperse NaA type zeolite in water to obtain a zeolite dispersion, then add sodium hexametaphosphate, mix to obtain a zeolite solution, and add hydrochloric acid solution to adjust the pH; (iii) Place the pretreated ceramic membrane into the reactor, evacuate and maintain the vacuum for a period of time, then release the vacuum, and then add the zeolite solution adjusted to pH in step (ii) to completely submerge the pretreated ceramic membrane for impregnation, and then take it out for drying; (iv) The dried pretreated ceramic membrane is then subjected to step (iii), and the impregnation and drying are repeated multiple times to obtain the zeolite-filled ceramic membrane assembly.

10. The method for improving the purity of n-octane according to claim 9, characterized in that, In step (i), the pore size of the porous alumina ceramic membrane is 0.1~0.5μm; The porosity of the alumina porous ceramic membrane is 35-40%; The calcination temperature of the alumina porous ceramic membrane is 400~500℃; The calcination holding time for the porous alumina ceramic membrane is 1-3 hours. The concentration of the nitric acid solution is 0.1~0.3 mol / L; The ultrasonic cleaning time is 30-40 minutes; In step (ii), the particle size of the NaA-type zeolite is 0.3~0.5μm; The mass fraction of NaA-type zeolite in the zeolite dispersion is 5-8 wt%. The amount of sodium hexametaphosphate added is 0.05~0.15 wt% of the mass of the zeolite dispersion; Add 0.1 mol / L hydrochloric acid solution to the zeolite solution to adjust its pH value to 4.5~5.5; In step (iii), the reactor is evacuated to -0.08 to -0.1 MPa; The reaction vessel is maintained under vacuum for 10-20 minutes. The pretreated ceramic membrane is immersed in the zeolite solution for 10-15 minutes. The drying process includes a gradient hot air drying process, specifically including a first hot air drying and a second hot air drying performed sequentially. The temperature of the hot air in the first hot air drying process is 60~70℃; The drying time for the first hot air is 1~1.5 hours; The hot air temperature for the second hot air drying is 80~90℃; The second hot air drying time is 2-3 hours; In step (iv), the soaking and hot air drying process is repeated 2 to 3 times.

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