A high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes

Abstract

This invention discloses a high-vacuum molecular distillation method for the fine separation of Fischer-Tropsch wax, belonging to the field of Fischer-Tropsch wax separation technology. Using stable hydrofractionation column bottom No. 1 soft wax as raw material, a continuous high-vacuum molecular distillation process is employed for multi-stage separation, including the following steps: First-stage thin-film evaporation: The raw material is fed into a first-stage thin-film evaporator and evaporated at a temperature of 170-260℃ and a vacuum of 10-100Pa. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to a decolorization and filtration unit; First decolorization filtration. This invention, by setting up a continuous multi-stage separation process combining first-stage thin-film evaporation, second-stage thin-film evaporation, and third-stage short-path distillation, and using stable hydrofractionation column bottom No. 1 soft wax as a single raw material, can simultaneously separate seven Fischer-Tropsch wax products with different dropping melting points: refined liquid wax, 45# wax, 60# wax, 70# wax, 80# wax, 105# wax, and 115# wax. This significantly enriches the product range of Fischer-Tropsch wax and solves the problem of limited product range in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of Fischer-Tropsch wax separation technology, and more specifically, to a high-vacuum molecular distillation method for the fine separation of Fischer-Tropsch wax. Background Technology

[0002] Fischer-Tropsch synthetic waxes are high-purity, high-melting-point waxes produced by the Fischer-Tropsch synthesis process. Due to their excellent properties such as high n-alkane content, sulfur-free and nitrogen-free, and low oil content, they are widely used in plastics processing, coatings, inks, adhesives, cosmetics, and food packaging. Existing Fischer-Tropsch wax separation technologies typically employ distillation or molecular distillation methods. For example, Chinese Patent (Publication No.: CN114874811A) discloses a refining apparatus and method for Fischer-Tropsch wax production, which uses a combination of a thin-film evaporator and first-, second-, and third-stage molecular distillers to perform multi-stage distillation separation of Fischer-Tropsch wax raw materials. Chinese Patent (Publication No.: CN216890815U) discloses a Fischer-Tropsch wax separation system with waste heat recovery, which uses a thin-film evaporator, a first-stage molecular distiller, a second-stage molecular distiller, and a third-stage molecular distiller connected in sequence to perform four-stage distillation separation of Fischer-Tropsch wax raw materials. Chinese Patent (Publication No.: CN118562531A) discloses a high-enthalpy, low-melting-point Fischer-Tropsch wax and its preparation method, which obtains Fischer-Tropsch wax components with a carbon atom number distribution mainly between 18 and 22 by performing thin-film evaporation-molecular distillation treatment on the raw material Fischer-Tropsch wax. The above technical solutions all use stable hydrogenation fractionation bottom soft wax or Fischer-Tropsch wax as raw materials, and after thin-film evaporation and single-stage or multi-stage molecular distillation, wax products with different melting points and heavy fractionated waxes are obtained.

[0003] However, existing Fischer-Tropsch wax separation technologies still have the following shortcomings: First, the product range is limited. The aforementioned patented technologies typically yield only 2-4 wax products with different melting points, leaving a large amount of heavy components unutilized and resulting in low added value. Second, the separation precision is insufficient. The resulting wax products generally have low n-alkane content, high oil content, poor color, and poor penetration stability, making it difficult to meet the stringent requirements for purity, color, and hardness stability in high-end applications. Third, the process lacks continuity. There is a lack of systematic decolorization and filtration treatment and heat tracing and insulation design for the conveying pipelines. During transportation and temporary storage, the material is prone to solidification and blockage due to temperature drops, leading to large quality fluctuations between product batches.

[0004] Based on this, the present invention designs a high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes, in order to solve the problems mentioned in the background art.

[0006] A high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes, using No. 1 soft wax from the bottom of a stable hydrogenation fractionation column as raw material, employs a continuous high-vacuum molecular distillation process for multi-stage separation, including the following steps:

[0007] S1. First-stage thin-film evaporation: The raw material is fed into the first-stage thin-film evaporator and evaporated at a temperature of 170-260℃ and a vacuum of 10-100Pa. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to the decolorization and filtration unit.

[0008] S2, First decolorization filtration: The heavy components of step S1 are filtered at a temperature of 120-150℃ and a pressure of 0.3-0.5MPa. The filtrate is divided into two streams: the first stream is collected as 105# wax product, and the second stream is sent to a secondary thin-film evaporator.

[0009] S3, Secondary Thin-Film Evaporation: The second filtrate from step S2 is fed into a secondary thin-film evaporator and separated at a temperature of 180-250℃ and a vacuum of 20-90Pa. The light component is collected by condensation as 45# wax product, and the heavy component is fed into a primary short-path distiller.

[0010] S4. First-stage short-path distillation: The heavy components from step S3 are fed into a first-stage short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 60# wax product, and the heavy components are fed into a second-stage short-path distiller.

[0011] S5. Secondary short-path distillation: The heavy components from step S4 are fed into a secondary short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 70# wax product, and the heavy components are fed into a tertiary short-path distiller.

[0012] S6. Three-stage short-path distillation: The heavy components from step S5 are fed into a three-stage short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 80# wax product, and the heavy components are sent to the second decolorization and filtration unit.

[0013] S7. Second decolorization and filtration: The heavy components from step S6 are filtered at a temperature of 120-150℃ and a pressure of 0.3-0.5MPa, and the filtrate is collected as 115# wax product.

[0014] Preferably, the scraping speed of the primary and secondary thin-film evaporators is 100-180 rpm, the condenser temperature is 70-80℃, the cold trap temperature is 10-40℃, and the heating temperature gradient of the primary, secondary, and tertiary short-path distillers increases progressively, with a temperature difference of 10-20℃ between adjacent stages.

[0015] Preferably, both the first and second decolorization filters use a combination of activated carbon and diatomaceous earth as the filter medium, with a filtration temperature of 120-150℃ and a filtration pressure of 0.3-0.5MPa.

[0016] Preferably, the conveying pipelines and collection tanks in steps S1 to S7 are all equipped with heat tracing and insulation layers, and the heat tracing temperature is maintained at 5-10°C above the melting point of the conveyed material.

[0017] Preferably, the evaporation temperature in the primary thin-film evaporator in step S1 is 190-240℃ and the vacuum degree is 20-80Pa, and the evaporation temperature in the secondary thin-film evaporator in step S3 is 200-230℃ and the vacuum degree is 30-70Pa.

[0018] Preferably, the distillation temperature of the first-stage short-path distillation apparatus is 220-250℃ and the vacuum degree is 0.5-5Pa, the distillation temperature of the second-stage short-path distillation apparatus is 235-260℃ and the vacuum degree is 0.3-3Pa, and the distillation temperature of the third-stage short-path distillation apparatus is 250-275℃ and the vacuum degree is 0.1-2Pa.

[0019] Preferably, the first and second decolorizing filters each employ two-stage series filtration independently: the first stage is diatomaceous earth pre-coating filtration, and the second stage is granular activated carbon fixed bed adsorption. After filtration, the color of the wax product is ≤1 and the penetration fluctuation is ≤±1dmm.

[0020] Preferably, the material residence time in both the primary and secondary thin-film evaporators is 5-15s, and the film thickness formed by scraping is 0.5-2mm.

[0021] Preferably, the distance between the evaporation surface and the condensation surface of the first-stage short-path distiller, the second-stage short-path distiller, and the third-stage short-path distiller is 20-50 mm, the condensation surface temperature is 60-90℃, and the content of n-alkanes in the separated fraction is ≥99.5 wt%.

[0022] Preferably, after decolorization and filtration, the 105# wax product and the 115# wax product are granulated or molded under nitrogen protection. The granulation temperature is controlled at 8-12°C above the melting point of the corresponding wax product, and the cooling water temperature is 25-35°C.

[0023] Compared with the prior art, the advantages of this invention are:

[0024] 1. This invention employs a continuous multi-stage separation process combining primary thin-film evaporation, secondary thin-film evaporation, and tertiary short-path distillation. Using the bottom 1# soft wax from a stable hydrogenation fractionation tower as a single raw material, it can simultaneously separate seven Fischer-Tropsch wax products with different dropping melting points: refined liquid wax, 45# wax, 60# wax, 70# wax, 80# wax, 105# wax, and 115# wax. This significantly enriches the range of Fischer-Tropsch wax products and solves the problem of limited product range in existing technologies.

[0025] 2. This invention controls the vacuum degree of the first-stage, second-stage, and third-stage short-path distillation within a high vacuum range of 0.1-10 Pa, and sets an increasing heating temperature gradient between adjacent short-path distillation stages with a temperature difference of 10-20℃. Combined with a design of 20-50 mm between the evaporation surface and the condensation surface, the resulting fraction contains ≥99.5 wt% n-alkanes and ≤0.8 wt% oil. The heavy fraction after the third-stage short-path distillation, after decolorization and filtration, can achieve a n-alkanes content of up to 99.9 wt% and an oil content as low as 0.1 wt%, thus realizing high-precision separation of Fischer-Tropsch wax.

[0026] 3. This invention employs a two-stage cascade filtration process in the first and second decolorization filtration stages, namely, the first stage is diatomaceous earth pre-coating filtration and the second stage is granular activated carbon fixed bed adsorption, and operates at a temperature of 120-150℃ and a pressure of 0.3-0.5MPa, so that the color of the filtered wax product is ≤1 and the penetration fluctuation is ≤±1dmm, which significantly improves the appearance color and hardness consistency of the wax product.

[0027] 4. This invention achieves short-time and efficient thermal separation by controlling the material residence time to 5-15s and the film thickness to 0.5-2mm in the primary and secondary thin-film evaporators, combined with a scraping speed of 100-180rpm. This avoids the thermal decomposition and oxidative deterioration of Fischer-Tropsch wax at high temperatures, ensuring the thermal stability and purity of the product.

[0028] 5. The present invention provides heat tracing and insulation layers to the conveying pipes and collection tanks in steps S1 to S7, and maintains the heat tracing temperature 5-10°C above the melting point of the conveyed material. At the same time, after the 105# wax and 115# wax products are decolorized and filtered, they are granulated or molded under nitrogen protection. This effectively prevents solidification blockage and oxidation discoloration of the material during the conveying, storage and molding process, and ensures the stable operation of continuous production and product quality. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of a high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes proposed in this invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To facilitate understanding of the technical solution of this invention, the main materials and product codes involved are defined as follows:

[0032] 1# Soft Wax: Refers to a low-melting-point, high-oil-content soft wax fraction obtained from the bottom of a fractionation tower after the Fischer-Tropsch synthesis product has undergone stable hydrogenation and fractionation. It is the starting material for this invention. "1#" is an internal designation used by the company or industry, indicating the specific melting point and viscosity grade of the soft wax.

[0033] Refined liquid wax: refers to the light component obtained after primary thin-film evaporation and separation, which is collected by condensation. It has a high content of n-alkane, low color, and low oil content, and can be used as a liquid wax product.

[0034] 45# wax, 60# wax, 70# wax, and 80# wax: These represent Fischer-Tropsch wax products obtained through different separation stages. The numbers represent the nominal melting point (in °C) of the wax product. For example, the melting point of 45# wax is approximately 45 °C, and the melting point of 60# wax is approximately 60 °C, and so on. All of the above products are light component fractions obtained through short-path distillation.

[0035] 105# wax and 115# wax: These represent Fischer-Tropsch wax products obtained after decolorization and filtration, respectively. The numbers also represent the nominal value of the dropping melting point (unit: °C). Among them, 105# wax is a portion of the filtrate collected directly after the first decolorization filtration, and 115# wax is the product collected after the second decolorization filtration of the heavy components from the third-stage short-path distillation.

[0036] Example 1

[0037] Using No. 1 soft wax from the bottom of a stable hydrogenation fractionation tower as raw material, multi-stage separation was carried out using a continuous high-vacuum molecular distillation process. The specific steps are as follows:

[0038] S1. First-stage thin-film evaporation: The raw material is fed into the first-stage thin-film evaporator. The evaporation temperature is 170℃, the vacuum degree is 10Pa, the scraper speed is 100rpm, the condenser temperature is 70℃, the cold trap temperature is 10℃, the material residence time is 5s, and the film thickness is 0.5mm. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to the decolorization and filtration unit.

[0039] S2, First Decolorization Filtration: The heavy components from step S1 are filtered at 120℃ and 0.3MPa using a two-stage filtration process. The first stage is a diatomaceous earth pre-coated filter, and the second stage is a granular activated carbon fixed-bed adsorption. The filtrate is divided into two streams: the first stream is collected as 105# wax product, and the second stream is sent to a secondary thin-film evaporator.

[0040] S3, Secondary Thin-Film Evaporation: The second filtrate from step S2 is fed into a secondary thin-film evaporator. The evaporation temperature is 180℃, the vacuum degree is 20Pa, the scraper rotation speed is 100rpm, the condenser temperature is 70℃, the cold trap temperature is 10℃, the material residence time is 5s, and the film thickness is 0.5mm. The light component is collected by condensation as 45# wax product, and the heavy component is sent to a primary short-path distillation unit.

[0041] S4. First-stage short-path distillation: The heavy components from step S3 are fed into a first-stage short-path still. The distillation temperature is 200℃, the vacuum degree is 0.1Pa, the distance between the evaporation surface and the condensation surface is 20mm, and the condensation surface temperature is 60℃. The light components are collected by condensation as 60# wax product, and the heavy components are fed into a second-stage short-path still.

[0042] S5. Second-stage short-path distillation: The heavy components from step S4 are fed into a second-stage short-path still. The distillation temperature is 210℃, the vacuum degree is 0.2Pa, the distance between the evaporation surface and the condensation surface is 20mm, and the condensation surface temperature is 60℃. The light components are collected by condensation as 70# wax product, and the heavy components are fed into a third-stage short-path still.

[0043] S6. Three-stage short-path distillation: The heavy components from step S5 are fed into a three-stage short-path still. The distillation temperature is 220℃, the vacuum degree is 0.1Pa, the distance between the evaporation surface and the condensation surface is 20mm, and the condensation surface temperature is 60℃. The light components are collected by condensation as 80# wax product, and the heavy components are sent to the second decolorization and filtration unit.

[0044] S7. Second decolorization filtration: The heavy components from step S6 are filtered at a temperature of 120°C and a pressure of 0.3 MPa using the same two-stage series filtration as the first decolorization filtration. The filtrate is collected as 115# wax product.

[0045] All conveying pipelines and collection tanks are equipped with heat tracing and insulation layers, and the heat tracing temperature is maintained at 5°C above the melting point of the conveyed material. 105# wax products and 115# wax products are granulated under nitrogen protection at a granulation temperature of 8°C above the melting point and a cooling water temperature of 25°C.

[0046] The performance of each wax product obtained in this embodiment was tested, and the test methods and standards are as follows:

[0047] Dropping melting point: Determined according to GB / T 47357-2026 "Determination of melting point and dropping melting point of Fischer-Tropsch synthetic waxes by differential scanning calorimetry" using differential scanning calorimetry (DSC).

[0048] Oil content: determined according to the Soxhlet extraction method (gravimetric method) in GB / T 14488.1-2008 "Determination of oil content in vegetable oils", and the residue was weighed after extraction with organic solvent.

[0049] Colorimetric values ​​were measured using an integrating sphere spectrophotometer in accordance with GB / T 11186-2025 "Methods for measuring the color of coatings". The Lab value was calculated and the result was expressed as a colorimetric number.

[0050] Penetration: According to GB / T 4509-2010 "Test Method for Penetration of Asphalt", a standard needle is used to vertically penetrate the wax sample within 5 seconds at 25℃, the depth is measured (unit: dmm), and the fluctuation range is recorded.

[0051] n-Alkane content: Gas chromatography-mass spectrometry (GC-MS) was used to separate the components by gas chromatography, identify the structure by mass spectrometry, and calculate the content by area normalization method.

[0052] The test results are shown in the table below:

[0053] Note: The fluctuation in needle penetration is controlled within the range of ≤±1 dmm.

[0054] Example 2

[0055] Using No. 1 soft wax from the bottom of a stable hydrogenation fractionation tower as raw material, multi-stage separation was carried out using a continuous high-vacuum molecular distillation process. The specific steps are as follows:

[0056] S1. First-stage thin-film evaporation: The raw material is fed into the first-stage thin-film evaporator. The evaporation temperature is 260℃, the vacuum degree is 100Pa, the scraping speed is 180rpm, the condenser temperature is 80℃, the cold trap temperature is 40℃, the material residence time is 15s, and the film thickness is 2mm. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to the decolorization and filtration unit.

[0057] S2, First Decolorization Filtration: The heavy components from step S1 are filtered at 150℃ and 0.5MPa using a two-stage filtration process. The first stage is a diatomaceous earth pre-coated filter, and the second stage is a granular activated carbon fixed-bed adsorption. The filtrate is divided into two streams: the first stream is collected as 105# wax product, and the second stream is sent to a secondary thin-film evaporator.

[0058] S3, Secondary Thin-Film Evaporation: The second filtrate from step S2 is fed into a secondary thin-film evaporator. The evaporation temperature is 250℃, the vacuum degree is 90Pa, the scraper rotation speed is 180rpm, the condenser temperature is 80℃, the cold trap temperature is 40℃, the material residence time is 15s, and the film thickness is 2mm. The light component is collected by condensation as 45# wax product, and the heavy component is sent to a primary short-path distiller.

[0059] S4. First-stage short-path distillation: The heavy components from step S3 are fed into a first-stage short-path still. The distillation temperature is 280℃, the vacuum degree is 10Pa, the distance between the evaporation surface and the condensation surface is 50mm, and the condensation surface temperature is 90℃. The light components are collected by condensation as 60# wax product, and the heavy components are fed into a second-stage short-path still.

[0060] S5. Second-stage short-path distillation: The heavy components from step S4 are fed into a second-stage short-path still. The distillation temperature is 280℃, the vacuum degree is 10Pa, the distance between the evaporation surface and the condensation surface is 50mm, and the condensation surface temperature is 90℃. The light components are collected by condensation as 70# wax product, and the heavy components are fed into a third-stage short-path still.

[0061] S6. Three-stage short-path distillation: The heavy components from step S5 are fed into a three-stage short-path still. The distillation temperature is 280℃, the vacuum degree is 10Pa, the distance between the evaporation surface and the condensation surface is 50mm, and the condensation surface temperature is 90℃. The light components are collected by condensation as 80# wax product, and the heavy components are sent to the second decolorization and filtration unit.

[0062] S7. Second decolorization filtration: The heavy components from step S6 are filtered at a temperature of 150℃ and a pressure of 0.5MPa using the same two-stage series filtration as the first decolorization filtration. The filtrate is collected as 115# wax product.

[0063] All conveying pipelines and collection tanks are equipped with heat tracing and insulation layers, and the heat tracing temperature is maintained at 10°C above the melting point of the conveyed material. 105# wax products and 115# wax products are granulated under nitrogen protection at a granulation temperature of 12°C above the melting point and a cooling water temperature of 35°C.

[0064] The performance of each wax product obtained in this embodiment was tested, and the testing methods and standards were the same as in Example 1.

[0065] The test results are shown in the table below:

[0066] Note: The fluctuation in needle penetration is controlled within the range of ≤±1 dmm.

[0067] Example 3

[0068] Using No. 1 soft wax from the bottom of a stable hydrogenation fractionation tower as raw material, multi-stage separation was carried out using a continuous high-vacuum molecular distillation process. The specific steps are as follows:

[0069] S1. First-stage thin-film evaporation: The raw material is fed into the first-stage thin-film evaporator. The evaporation temperature is 215℃, the vacuum degree is 55Pa, the scraper speed is 140rpm, the condenser temperature is 75℃, the cold trap temperature is 25℃, the material residence time is 10s, and the film thickness is 1.2mm. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to the decolorization and filtration unit.

[0070] S2, First Decolorization Filtration: The heavy components from step S1 are filtered at 135℃ and 0.4MPa using a two-stage filtration process. The first stage is a diatomaceous earth pre-coated filter, and the second stage is a granular activated carbon fixed-bed adsorption. The filtrate is divided into two streams: the first stream is collected as 105# wax product, and the second stream is sent to a secondary thin-film evaporator.

[0071] S3, Secondary Thin-Film Evaporation: The second filtrate from step S2 is fed into a secondary thin-film evaporator. The evaporation temperature is 215℃, the vacuum degree is 55Pa, the scraper rotation speed is 140rpm, the condenser temperature is 75℃, the cold trap temperature is 25℃, the material residence time is 10s, and the film thickness is 1.2mm. The light component is collected by condensation as 45# wax product, and the heavy component is sent to a primary short-path distillation unit.

[0072] S4. First-stage short-path distillation: The heavy components from step S3 are fed into a first-stage short-path still. The distillation temperature is 235℃, the vacuum degree is 2.5Pa, the distance between the evaporation surface and the condensation surface is 35mm, and the condensation surface temperature is 75℃. The light components are collected by condensation as 60# wax product, and the heavy components are fed into a second-stage short-path still.

[0073] S5. Second-stage short-path distillation: The heavy components from step S4 are fed into a second-stage short-path still. The distillation temperature is 248℃, the vacuum degree is 1.5Pa, the distance between the evaporation surface and the condensation surface is 35mm, and the condensation surface temperature is 75℃. The light components are collected by condensation as 70# wax product, and the heavy components are fed into a third-stage short-path still.

[0074] S6. Three-stage short-path distillation: The heavy components from step S5 are fed into a three-stage short-path still. The distillation temperature is 262℃, the vacuum degree is 1Pa, the distance between the evaporation surface and the condensation surface is 35mm, and the condensation surface temperature is 75℃. The light components are collected by condensation as 80# wax product, and the heavy components are sent to the second decolorization and filtration unit.

[0075] S7. Second decolorization filtration: The heavy components from step S6 are filtered at a temperature of 135℃ and a pressure of 0.4MPa using the same two-stage series filtration as the first decolorization filtration. The filtrate is collected as 115# wax product.

[0076] All conveying pipelines and collection tanks are equipped with heat tracing and insulation layers, and the heat tracing temperature is maintained at 8°C above the melting point of the conveyed material. 105# wax products and 115# wax products are granulated under nitrogen protection at a granulation temperature of 10°C above the melting point and a cooling water temperature of 30°C.

[0077] The performance of each wax product obtained in this embodiment was tested, and the testing methods and standards were the same as in Example 1.

[0078] The test results are shown in the table below:

[0079] Note: The fluctuation in needle penetration is controlled within the range of ≤±1 dmm.

[0080] Based on the test results of Examples 1-3, the following conclusions can be drawn:

[0081] The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch wax provided by this invention uses No. 1 soft wax from the bottom of a stable hydrogenation fractionation tower as raw material. Through a seven-step continuous process of primary thin-film evaporation, primary decolorization filtration, secondary thin-film evaporation, primary short-path distillation, secondary short-path distillation, tertiary short-path distillation, and secondary decolorization filtration, seven different grades of Fischer-Tropsch wax products, namely refined liquid wax, 45# wax, 60# wax, 70# wax, 80# wax, 105# wax, and 115# wax, can be efficiently separated.

[0082] Examples 1-3 adopted the endpoint and intermediate values ​​of the process parameters (including temperature, vacuum degree, scraping speed, residence time, film thickness, distillation temperature difference, etc.) defined in the claims, and all successfully achieved fine separation of Fischer-Tropsch wax, proving that the technical solution of the present invention has a wide process operation window and good industrial adaptability.

[0083] Performance tests were conducted on each product according to national standard methods (GB / T 47357-2026, GB / T 14488.1, GB / T 11186, GB / T 4509) and gas chromatography-mass spectrometry. The results showed that the color of all wax products was ≤1, the penetration fluctuation was ≤±1dmm, the n-alkane content was ≥99.5wt%, and the oil content was ≤0.8wt%. Notably, with the increase of the separation stage, the n-alkane content of the heavy fraction wax products gradually increased to 99.9wt%, and the oil content gradually decreased to 0.1wt%, demonstrating the excellent separation effect of the multi-stage separation process of this invention.

[0084] In summary, the high-vacuum molecular distillation method for fine separation of Fischer-Tropsch wax provided by this invention can achieve efficient and fine separation of Fischer-Tropsch wax, and the resulting product has high purity, excellent color, and stable performance. It effectively solves the technical problems of single product grade and insufficient separation accuracy in existing Fischer-Tropsch wax separation technologies.

[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for fine separation of Fischer-Tropsch waxes using high-vacuum molecular distillation, characterized in that, Using No. 1 soft wax from the bottom of a stable hydrogenation fractionation tower as raw material, multi-stage separation is carried out using a continuous high-vacuum molecular distillation process, including the following steps: S1. First-stage thin-film evaporation: The raw material is fed into the first-stage thin-film evaporator and evaporated at a temperature of 170-260℃ and a vacuum of 10-100Pa. The light component is collected by condensation as refined liquid wax, and the heavy component is sent to the decolorization and filtration unit. S2, First decolorization filtration: The heavy components of step S1 are filtered at a temperature of 120-150℃ and a pressure of 0.3-0.5MPa. The filtrate is divided into two streams: the first stream is collected as 105# wax product, and the second stream is sent to a secondary thin-film evaporator. S3, Secondary Thin-Film Evaporation: The second filtrate from step S2 is fed into a secondary thin-film evaporator and separated at a temperature of 180-250℃ and a vacuum of 20-90Pa. The light component is collected by condensation as 45# wax product, and the heavy component is fed into a primary short-path distiller. S4. First-stage short-path distillation: The heavy components from step S3 are fed into a first-stage short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 60# wax product, and the heavy components are fed into a second-stage short-path distiller. S5. Secondary short-path distillation: The heavy components from step S4 are fed into a secondary short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 70# wax product, and the heavy components are fed into a tertiary short-path distiller. S6. Three-stage short-path distillation: The heavy components from step S5 are fed into a three-stage short-path distiller and separated at a temperature of 200-280℃ and a vacuum of 0.1-10Pa. The light components are collected by condensation as 80# wax product, and the heavy components are sent to the second decolorization and filtration unit. S7. Second decolorization and filtration: The heavy components from step S6 are filtered at a temperature of 120-150℃ and a pressure of 0.3-0.5MPa, and the filtrate is collected as 115# wax product.

2. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, The scraping speed of the primary and secondary thin-film evaporators is 100-180 rpm, the condenser temperature is 70-80℃, and the cold trap temperature is 10-40℃. The heating temperature gradient of the primary, secondary, and tertiary short-path distillers increases progressively, and the temperature difference between adjacent stages is 10-20℃.

3. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, Both the first and second decolorization filters use a combination of activated carbon and diatomaceous earth as the filter medium, with a filtration temperature of 120-150℃ and a filtration pressure of 0.3-0.5MPa.

4. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, The conveying pipelines and collection tanks in steps S1 to S7 are all equipped with heat tracing and insulation layers, and the heat tracing temperature is maintained 5-10°C above the melting point of the conveyed material.

5. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, In step S1, the evaporation temperature in the primary thin-film evaporator is 190-240℃ and the vacuum degree is 20-80Pa. In step S3, the evaporation temperature in the secondary thin-film evaporator is 200-230℃ and the vacuum degree is 30-70Pa.

6. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, The distillation temperature of the first-stage short-path still is 220-250℃ and the vacuum degree is 0.5-5Pa; the distillation temperature of the second-stage short-path still is 235-260℃ and the vacuum degree is 0.3-3Pa; and the distillation temperature of the third-stage short-path still is 250-275℃ and the vacuum degree is 0.1-2Pa.

7. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 3, characterized in that, The first and second decolorizing filters each independently employ two-stage series filtration: the first stage is diatomaceous earth pre-coating filtration, and the second stage is granular activated carbon fixed bed adsorption. After filtration, the color of the wax product is ≤1 and the penetration fluctuation is ≤±1dmm.

8. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 5, characterized in that, The material residence time in both the primary and secondary thin-film evaporators is 5-15 seconds, and the film thickness formed by scraping is 0.5-2 mm.

9. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 6, characterized in that, The distance between the evaporation surface and the condensation surface of the first-stage, second-stage, and third-stage short-path distillation apparatus is 20-50 mm, the condensation surface temperature is 60-90℃, and the content of n-alkanes in the separated fraction is ≥99.5 wt%.

10. The high-vacuum molecular distillation method for fine separation of Fischer-Tropsch waxes according to claim 1, characterized in that, After decolorization and filtration, the 105# wax product and the 115# wax product are granulated or molded under nitrogen protection. The granulation temperature is controlled at 8-12°C above the melting point of the corresponding wax product, and the cooling water temperature is 25-35°C.

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