CN115386397B - Refining method and system for refined wax and Fischer-Tropsch crude wax - Google Patents

Abstract

The invention relates to the technical field of Fischer-Tropsch wax refining, in particular to a refining method and a refining system for refined wax and Fischer-Tropsch crude wax, wherein the method comprises the following steps: (1) Mixing Fischer-Tropsch wax, an extracting agent and an optional cosolvent to obtain a mixed wax liquid; wherein the extractant comprises at least one of an ester solvent, an alcohol solvent and Fischer-Tropsch synthetic naphtha; (2) Sequentially extracting, aging, crystallizing, crystal growing and separating the mixed wax liquid serving as a liquid to be extracted to obtain a wax extract and a wax liquid; (3) And carrying out flash evaporation treatment on the cerate to obtain refined wax with the melting point of 50-130 ℃. The method has the advantages of mild operation condition, low energy consumption, easy engineering amplification, and the obtained refined wax has high melting point and low oil content.

Description

Refining method and system for refined wax and Fischer-Tropsch crude wax

Technical Field

The invention belongs to the technical field of Fischer-Tropsch wax refining, and in particular relates to a refining method and system for refined wax and Fischer-Tropsch crude wax.

Background Art

Fischer-Tropsch synthesis (FT synthesis for short) technology is a process for synthesizing hydrocarbons using a mixture of CO and _H2 as raw materials under the action of a catalyst and appropriate reaction conditions. The synthetic product is called Fischer-Tropsch synthetic oil. After regular distillation, liquefied gas fraction, naphtha fraction, gasoline fraction, diesel fraction, heavy oil fraction and Fischer-Tropsch crude wax can be separated. The relative molecular weight of Fischer-Tropsch crude wax is between 500-2000, and it is mainly composed of straight-chain saturated alkanes, and the carbon number distribution is usually between 15-120. The wax separated from Fischer-Tropsch crude wax generally has the characteristics of high crystallinity, high melting point, narrow melting point range, low needle penetration, low melt viscosity, high stability, low aromatic content, almost no impurities such as sulfur and nitrogen, as well as hardness and wear resistance. It can be widely used in candles, food packaging coatings, daily chemical products, PVC product processing lubricants, hot melt adhesives, plastic processing, inks and coatings, gloss wax, warm mix asphalt additives and other fields.

CN110066680A and CN104673383A relate to methods for producing high melting point refined wax using Fischer-Tropsch wax. The common feature of these methods is that the Fischer-Tropsch wax is subjected to multi-stage distillation separation under an ultimate vacuum of less than 10 Pa and at 220-320°C using the boiling point difference of the hydrocarbon components to obtain high melting point wax products of different grades. The advantage of this method is that the process route is simple, but the main problems are as follows: 1) The difficulty of device construction is great, and the equipment performance requirements are high, making it difficult to carry out large-scale industrial application of 10,000 tons; 2) Due to the limitations of distillation temperature and vacuum conditions, wax with a melting point greater than 80°C cannot be directly distilled out, and the fraction with a melting point greater than 80°C can only flow out in the form of heavy residue at the bottom of the kettle, so it is difficult to control its quality; 3) In terms of product quality, the oil content of the Fischer-Tropsch wax product obtained by distillation technology is relatively high, usually 1-4wt%, which is difficult to meet the industry requirement of <0.8wt%; 4) Fischer-Tropsch wax is a long-chain alkane molecule with the characteristic of easy cracking, and the small amount of olefins, oxygen-containing compounds, and other impurities present in the raw materials are easily cracked, carbonized, and coked due to heat during the high-temperature distillation process. Chemical changes such as cracking, carbon deposition, and coking not only affect the separation operation, but also affect the technical indicators of the wax product, especially causing the color of the wax product to deteriorate.

"Study on Dewaxing Crystallization Process Factors of Ketone-Benzene Unit" discloses a solvent dewaxing method, which uses petroleum vacuum distillate oil as raw material, adds a large amount of ketones (such as butanone) and toluene mixed solvent to form a mixed solution, and then freezes and cools to crystallize wax, and separates wax crystals from oil with the help of a vacuum filter to ensure the yield and quality of the main product dewaxed oil, while producing paraffin products as by-products. This technology uses petroleum vacuum distillate oil as raw material, the raw material fraction is relatively narrow, the wax content is only 20-30wt%, and the carbon number is usually not more than 35, and the melting point of the obtained paraffin is generally lower than 70°C. The content of normal alkanes in Fischer-Tropsch crude wax is usually greater than 50wt%, and the carbon number distribution is wide. The crystallization properties of high-carbon wax molecules determine that it is difficult for Fischer-Tropsch crude wax to form a large lamellar crystal structure in the ketone-benzene system, resulting in a large filtration resistance of the crystal slurry during filtration, and a poor separation effect. Therefore, it is not suitable to use the ketone-benzene dewaxing method to process Fischer-Tropsch crude wax to produce high-melting point wax with a melting point higher than 70°C. In addition, ketones are easily polymerized and remain in paraffin. Long-term storage will cause the color of the wax to deteriorate. Moreover, toluene is highly toxic and carcinogenic, and its use is currently restricted.

Summary of the invention

The purpose of the present invention is to solve the deficiencies in the prior art and provide a method and system for refining refined wax and Fischer-Tropsch crude wax. The method has the advantages of mild operating conditions, low energy consumption, and easy engineering scale-up, and the refined wax obtained has a high melting point and low oil content.

In order to achieve the above object, the first aspect of the present invention provides a method for refining Fischer-Tropsch crude wax, the method comprising:

(1) mixing Fischer-Tropsch crude wax, an extractant and an optional co-solvent to obtain a mixed wax liquid; wherein the extractant comprises at least one of an ester solvent, an alcohol solvent and Fischer-Tropsch synthetic naphtha;

(2) using the mixed wax liquid as the liquid to be extracted and sequentially subjecting it to extraction, aging, crystallization, crystal growth and separation operations to obtain wax paste and wax liquid;

(3) flash evaporating the wax paste to obtain a refined wax with a melting point of 50-130°C.

A second aspect of the present invention provides a Fischer-Tropsch crude wax refining system, the system comprising at least one group of refined wax production units; wherein the refined wax production units comprise an extraction device, a crystallization device, a separation device and a recovery device.

The third aspect of the present invention provides a refined wax produced by the method described in the first aspect of the present invention, wherein the refined wax is Fischer-Tropsch wax with a melting point of 50-130° C. and an oil content of ≤0.8wt%, preferably ≤0.5wt%.

Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

1) The Fischer-Tropsch crude wax refining method provided by the present invention avoids the technical requirements of high vacuum degree, has low requirements on equipment, and has low requirements on the sealing performance of pipelines; the operating conditions are mild, and no cracking reaction of long-chain alkane molecules is caused, and the chromaticity of the refined wax obtained is good; the process energy consumption is low, the engineering scale-up is relatively easy, and it is suitable for large-scale industrial application;

2) The Fischer-Tropsch crude wax refining method provided by the present invention can finely separate the whole fraction of the Fischer-Tropsch crude wax by flexibly adjusting the operating conditions to obtain refined wax with any melting point between 50-130° C., with a rich variety of product brands;

3) The method for refining Fischer-Tropsch crude wax provided by the present invention uses an extractant with high selectivity for light and heavy components in the Fischer-Tropsch crude wax, so that the oil content of the obtained refined wax is less than 0.8wt%, and the product purity is high;

4) The refining method of Fischer-Tropsch crude wax provided by the present invention has good raw material adaptability, is less affected by the distillation range and carbon number distribution of Fischer-Tropsch crude wax, can process all fractions in the raw material, and has high raw material utilization rate;

5) The method for refining Fischer-Tropsch crude wax provided by the present invention adopts a specific extractant and/or cosolvent, and a two-stage step crystallization method of first cooling to an aging temperature for aging, and then performing crystallization and crystal growth, which can effectively control the morphology and particle size of the crystals, obtain crystals with larger grains, and thus improve the speed of solid-liquid separation;

6) The method for refining Fischer-Tropsch crude wax provided by the present invention can realize continuous production of refined waxes with different melting points under mild conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of a method for refining Fischer-Tropsch crude wax provided by the present invention;

FIG2 is a process flow chart of another method for refining Fischer-Tropsch crude wax provided by the present invention;

FIG3 is a structural diagram of a Fischer-Tropsch crude wax refining system provided by the present invention.

Reference numerals

1. Raw wax tank 2. Extractant storage tank 3. Preheater

4. Mixer 5. Heat exchanger 6. Extractor

7. Cooling device 8. Aging kettle 9. Crystallizer

10. Crystal growing kettle 11. Filter 12. Conveyor

13. Wax paste flash tower 14. Wax paste flash tower condenser 15 Wax liquid flash tower

16. Wax liquid flash tower condenser

DETAILED DESCRIPTION

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

A first aspect of the present invention provides a method for refining Fischer-Tropsch crude wax, the method comprising:

(1) mixing Fischer-Tropsch crude wax, an extractant and an optional co-solvent to obtain a mixed wax liquid; wherein the extractant comprises at least one of an ester solvent, an alcohol solvent and Fischer-Tropsch synthetic naphtha;

(2) using the mixed wax liquid as the liquid to be extracted and sequentially subjecting it to extraction, aging, crystallization, crystal growth and separation operations to obtain wax paste and wax liquid;

(3) flash evaporating the wax paste to obtain a refined wax with a melting point of 50-130°C.

Among them, the content of normal alkanes in Fischer-Tropsch crude wax is generally above 50wt%. When using traditional crystallization technology, such as ketone-benzene dewaxing technology, it is impossible to obtain wax crystals with larger grains due to the high wax content, resulting in huge resistance to solid-liquid separation, and thus it is difficult to separate wax with a melting point greater than 70°C. The inventors of the present invention have found through research that after mixing the Fischer-Tropsch crude wax with a specific extractant and an optional co-solvent, and then extracting, aging, crystallizing and growing the wax in sequence, wax crystals with larger grain sizes can be obtained, thereby reducing the resistance to solid-liquid separation, and achieving separation of refined wax with a melting point of 50-130°C from the Fischer-Tropsch crude wax under mild operating conditions, especially refined wax with a melting point of 70-130°C.

In step (1):

In a preferred embodiment, the Fischer-Tropsch crude wax refers to the heavy fraction remaining after the product generated by CO and _H2 under the action of a Fischer-Tropsch synthesis catalyst is subjected to regular vacuum distillation to cut out the light fraction with a boiling point less than 350°C. The Fischer-Tropsch crude wax is solid at room temperature.

In a preferred embodiment, the carbon number distribution of the Fischer-Tropsch crude wax is between _C15 - _C120 , the melting point is ≥70°C, preferably 80-135°C; the 10% distillation temperature is ≥350°C, the 50% distillation temperature is ≥500°C; the normal alkane content is ≥50wt%, preferably 50-95wt%. The 10% distillation temperature refers to the temperature when the distillation volume reaches 10%, and the 90% distillation temperature refers to the temperature when the distillation volume reaches 90%.

In a preferred embodiment, the method further comprises: pretreating the Fischer-Tropsch crude wax before mixing it with the extractant and the optional co-solvent. Wherein, after the pretreatment, some light components in the Fischer-Tropsch crude wax can be removed to increase the melting point of the pretreated Fischer-Tropsch crude wax. Preferably, the melting point of the pretreated Fischer-Tropsch crude wax is ≥75°C, preferably 85-135°C. Further preferably, the pretreatment operation comprises: preheating the Fischer-Tropsch crude wax to 200-310°C, and then performing reduced pressure distillation at an absolute pressure of 100-5000Pa to obtain a pretreated crude wax with a 10% distillation temperature ≥500°C.

In a preferred embodiment, the ester solvent is selected from at least one of ethyl acetate, ethyl propionate, butyl acetate, ethyl butyrate, n-propyl acetate, isopropyl acetate, isobutyl acetate, and isooctyl acetate; the alcohol solvent is selected from at least one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, ethylene glycol, pentanol, hexanol, and 1-octanol; the distillation range of the Fischer-Tropsch synthesis naphtha is 90-220°C and the oxygen content of the Fischer-Tropsch synthesis naphtha is between 0.5-5wt%. Among them, the Fischer-Tropsch synthesis naphtha refers to the product generated by CO and _H2 under the action of the Fischer-Tropsch synthesis catalyst, which is cut by regular vacuum distillation and has a distillation range of 90-220°C and an oxygen content of 0.5-5wt%.

In a preferred embodiment, the extraction solvent is Fischer-Tropsch naphtha and an alcohol solvent, wherein the volume ratio of Fischer-Tropsch naphtha to the alcohol solvent is 0.2-5:1, preferably 0.5-3:1.

In a preferred embodiment, the extraction solvent is Fischer-Tropsch naphtha and an ester solvent, wherein the volume ratio of Fischer-Tropsch naphtha to the ester solvent is 0.2-3:1, preferably 0.4-2:1.

In a preferred embodiment, the extraction solvent is an ester solvent and an alcohol solvent, wherein the volume ratio of the ester solvent to the alcohol solvent is 1-8:1, preferably 2-4:1.

In a preferred embodiment, the extraction solvent is two of ethyl acetate, ethyl propionate, butyl acetate, ethyl butyrate, n-propyl acetate, isopropyl acetate, isobutyl acetate, and isooctyl acetate; wherein the volume ratio of the ester with a large relative molecular weight to the ester with a small relative molecular weight is 0.3-3:1, preferably 0.5-2:1.

In a preferred embodiment, the Fischer-Tropsch crude wax and the extractant are mixed to obtain a mixed wax liquid; wherein the volume ratio of the Fischer-Tropsch crude wax to the extractant is 1:1-10, preferably 1:1.5-8.

In a preferred embodiment, the Fischer-Tropsch crude wax, the extractant and the cosolvent are mixed, and the cosolvent is selected from naphtha with a distillation range of 70-180° C. and/or petroleum ether with a distillation range of 90-120° C. The volume ratio of the Fischer-Tropsch crude wax to the extractant is 1:1-10, preferably 1:1.5-8; the volume ratio of the cosolvent to the extractant is 0.02-0.15:1, preferably 0.05-0.1:1.

In a preferred embodiment, before mixing the Fischer-Tropsch crude wax with the extractant, the Fischer-Tropsch crude wax is preheated to obtain liquid Fischer-Tropsch crude wax.

Among them, after preheating, the solid Fischer-Tropsch crude wax can be converted into liquid, which can improve the mixing uniformity of the Fischer-Tropsch crude wax and the extractant and/or co-solvent, so as to avoid the formation of tiny suspended particles of the Fischer-Tropsch crude wax in the mixed wax liquid due to insufficient dissolution.

In step (2):

In a preferred embodiment, the operating pressures of the extraction, aging, crystallization, crystal growing and separation are all 0.1-1.5 MPa, preferably 0.3-0.8 MPa.

In a further preferred embodiment, the extraction, aging, crystallization, crystal growing and separation are performed at the same operating pressure.

In a more preferred embodiment, the operating pressures of the extraction, aging, crystallization, crystal growing and solid-liquid separation are sequentially reduced, and the pressure difference between adjacent operations is 0.02-0.05 MPa.

In a preferred embodiment, in step (2), the melting point of the wax contained in the extract is used as the reference temperature, and the operating temperatures of extraction, aging, crystallization, crystal growth and separation are determined in sequence according to the reference temperature.

In a preferred embodiment, the extraction conditions include: the extraction temperature is 0-30°C higher than the base temperature, preferably 5-20°C higher.

In a preferred embodiment, the extraction conditions also include: the extraction time is 10-120 min, preferably 20-100 min.

In a preferred embodiment, the mixed solution after extraction is cooled to the aging temperature while being stirred.

In a preferred embodiment, the aging conditions include: the aging temperature is 3-40°C lower than the reference temperature, preferably 5-30°C lower; the aging time is 5-60 min, preferably 5-40 min.

The aging in the present invention refers to placing the mixed solution after the extraction operation at a constant temperature for a period of time.

In a preferred embodiment, the crystallization conditions include: cooling from the aging temperature to the crystal growing temperature at a cooling rate of 0.1-10°C/min, preferably 0.2-5°C/min, wherein the crystal growing temperature is 5-45°C lower than the aging temperature, preferably 10-40°C lower.

In the present invention, the cooling rate can be 0.1℃/min, 0.2℃/min, 0.3℃/min, 0.5℃/min, 1℃/min, 1.5℃/min, 2℃/min, 2.5℃/min, 3℃/min, 3.5℃/min, 4℃/min, 4.5℃/min, 5℃/min, 5.5℃/min, 6℃/min, 6.5℃/min, 7℃/min, 7.5℃/min, 8℃/min, 8.5℃/min, 9℃/min, 9.5℃/min, 10℃/min, or any value in the range formed by any two of these point values.

In a preferred embodiment, the crystal growing conditions include: the crystal growing time is 5-120 min, preferably 20-120 min.

Among them, the crystal growing in the present invention refers to placing the slurry at a constant temperature for a period of time at a crystal growing temperature, and the average grain size of the crystals in the slurry after crystal growing is ≥50μm, preferably 60-200μm. Among them, the average grain size of the crystals can be 60μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, or any value in the range formed by any two of these point values.

In a preferred embodiment, the solid-liquid separation conditions include: the solid-liquid separation temperature is 5-45°C lower than the aging temperature, preferably 10-40°C lower; and further preferably the same as the crystal growing temperature. Among them, the inventors have found through research that solid-liquid separation at the crystal growing temperature can effectively prevent the destruction of crystal morphology due to factors such as the separation of light components and the melting of heavy components in the Fischer-Tropsch crude wax, and can ensure that the solid-liquid separation has a high efficiency, which is conducive to improving product purity and reducing oil content.

Since the average grain size of the crystals in the slurry after crystal growth in the present invention is ≥50um, the resistance of solid-liquid separation can be effectively reduced, so the present invention does not specifically limit the solid-liquid separation method, and the solid-liquid separation method can be centrifugal separation or filtration separation, preferably filtration separation. The filtration separation includes filtration, filter cake washing and filter cake drying.

In step (3):

In a preferred embodiment, the present invention does not impose any special restrictions on the flash evaporation operation, as long as the extractant and the optional co-solvent can be separated. In the present invention, the separated extractant and the optional co-solvent can be recycled.

In a preferred embodiment, the oil content of the refined wax is ≤0.8wt%, preferably ≤0.5wt%; the melting range of the refined wax is ≤40°C, preferably 10-35°C.

In order to further reduce the oil content of the refined wax, in a preferred embodiment, step (3) also includes a deoiling treatment: first, the wax paste is deoiled to obtain a deoiled wax paste and a deoiled wax liquid, and then the deoiled wax paste is flash evaporated to obtain a refined wax with a melting point of 50-130°C; the deoiled wax liquid is flash evaporated to recover the extractant and/or co-solvent to obtain light oil.

The deoiling treatment comprises mixing the wax paste and the extractant in a volume ratio of 1:0.5-10, preferably 1:1-5, and then placing at a crystal growing temperature for 10-120 minutes, preferably 15-80 minutes; and then separating at the crystal growing temperature to obtain deoiled wax paste and deoiled wax liquid. In the present invention, the crystal growing temperature corresponds to the crystal growing temperature for obtaining the corresponding wax paste.

In a preferred embodiment, the oil content of the refined wax is ≤0.5wt%, preferably ≤0.4%; the melting range of the refined wax is ≤35°C, preferably 10-30°C.

In a preferred embodiment, the refined wax is granulated or powdered.

In a preferred embodiment, the method further comprises: (4) sampling and analyzing the wax liquid, testing the wax content and the melting point of the wax in the wax liquid; when the wax content in the wax liquid is ≥0.1wt% and the melting point of the wax in the wax liquid is ≥50°C, repeating step (2) with the wax liquid as the liquid to be extracted; preferably, when the wax content in the wax liquid is <0.1wt% or the melting point is <50°C, flashing the wax liquid, recovering the extractant and the optional co-solvent, and obtaining a low-melting-point wax with a melting point less than 50°C.

In step (4):

In a preferred embodiment, the wax content in the wax liquid is tested by the weighing reduction method: a portion of the wax liquid is taken as a test sample, the mass of the test sample is first weighed, recorded as m1, and then the test sample is dried in a vacuum oven to remove the extractant and/or cosolvent until the weight of the test sample no longer changes, and the mass of the test sample after drying is taken out and weighed, recorded as m2, and the wax content is equal to {(m1-m2)/m1}*100. The melting point of the sample after removing the extractant and/or cosolvent is tested using the ASTM D3954 method, and the obtained melting point is the melting point of the wax in the wax liquid.

In the present invention, the wax liquid obtained after separation contains, in addition to the extractant and the optional co-solvent, a large amount of residual Fischer-Tropsch crude wax. The wax liquid is used as the liquid to be extracted and step (2) is repeated to separate other refined waxes with a melting point between 50-130°C.

In a preferred embodiment, the mixed wax liquid obtained by mixing the Fischer-Tropsch crude wax, the extractant and the optional co-solvent is first used as the liquid to be extracted, and extraction, aging, crystallization, crystal growth and separation operations are performed in sequence to obtain wax paste I and wax liquid I; the wax paste I is flashed to obtain 1# refined wax, and the wax liquid I is sampled and analyzed. If the wax content in the wax liquid I is ≥0.1wt% and the melting point of the wax in the wax liquid I is ≥50°C, the wax liquid I is used alone as the liquid to be extracted and the extraction, aging, crystallization, crystal growth and separation operations are repeated in sequence to obtain wax paste II and wax liquid II. Liquid II; flash the wax paste II to obtain 2# refined wax, sample and analyze the wax liquid II, if the wax content in the wax liquid II is ≥0.1wt% and the melting point of the wax in the wax liquid II is ≥50°C, then use the wax liquid II as the liquid to be extracted to repeat the extraction, aging, crystallization, crystal growth and separation operations again, until the wax content in the wax liquid N obtained after separation is <0.1wt% or the melting point is <50°C, stop the repeated operations, flash the wax liquid N, recover the extractant and the optional auxiliary agent, and obtain a low melting point wax or light oil with a melting point of less than 50°C. Wherein, the wax liquid N represents the wax liquid obtained after the Nth separation.

A second aspect of the present invention provides a Fischer-Tropsch crude wax refining system, the system comprising at least one group of refined wax production units; wherein the refined wax production units comprise an extraction device, a crystallization device, a separation device and a recovery device.

In the present invention, the extraction device is used to perform a mixing operation of Fischer-Tropsch crude wax, an extractant and an optional co-solvent, and a solvent extraction operation; the crystallization device is used to perform aging, crystallization and crystal growing operations; the separation device is used to perform a separation operation of wax paste and wax liquid, and the recovery device is used to perform a flash evaporation operation of wax paste and/or wax liquid to recover the extractant and the optional co-solvent.

In the present invention, the system further comprises a cooling device before aging, which is used to cool the mixed liquid after extraction to the aging temperature.

Among them, the present invention does not specifically limit the extraction device, cooling device, crystallization device, separation device and recovery device, and the commonly used extraction devices, cooling devices, crystallization devices, separation devices and recovery devices in the art can all be used in the present invention.

In the present invention, the extraction device comprises a raw wax tank 1, an extractant storage tank 2, a preheater 3, a mixer 4, a heat exchanger 5 and an extractor 6. Preferably, it also comprises a co-solvent storage tank.

In the present invention, the cooling device 7 is selected from a crystallizer and/or a cooling kettle with a stirring function, such as a crystallizer.

In the present invention, the crystallization device includes an aging kettle 8, a crystallizer 9 and a crystal growing kettle 10; the separation device includes a filter 11 and a conveyor 12, wherein the aging kettle 8 and the crystallizer have a stirring device, and the conveyor 12 is used to transport the separated wax paste.

In the present invention, the recovery device includes a wax paste flash tower 13 , a wax paste flash tower condenser 14 connected to the wax paste flash tower 13 , a wax liquid flash tower 15 , and a wax liquid flash tower condenser 16 connected to the wax liquid flash tower 15 .

In the present invention, the liquid Fischer-Tropsch crude wax in the raw wax tank 1 is transported to the mixer 4 via a metering pump, and the extraction solvent in the extractant storage tank 2 is transported to the preheating device 3 via a metering pump for preheating, and then enters the mixer 4, where it is fully mixed in liquid-liquid with the Fischer-Tropsch crude wax to obtain a mixed wax liquid; the outlet of the mixer 4 is connected to the heat exchanger 5, and the mixed wax liquid is heated to the extraction temperature and then enters the extractor 6, and the outlet of the extractor 6 is connected to the cooling device 7, in which the extracted mixed liquid is cooled to the aging temperature while stirring, and then the extracted mixed liquid is transported to the aging kettle 8 for aging, and the outlet of the aging kettle 8 is connected to the inlet of the crystallizer 9, and the aging liquid is cooled to the crystal growing temperature in the crystallizer 9, and then enters the crystal growing kettle 10, and the outlet of the crystal growing kettle 10 is connected to the inlet of the filter 11, and solid-liquid separation is performed in the filter 11. The wax paste separated in the filter 11 is conveyed to the wax paste flash tower 13 by the conveyor 12 for flash evaporation. The gas phase separated from the top of the wax paste flash tower 13 is condensed by the wax paste flash tower condenser 14 to recover the extractant and/or cosolvent, and the refined wax is obtained from the bottom of the wax paste flash tower 13. The wax liquid separated in the filter 11 enters the wax liquid flash tower 15 for flash evaporation. The gas phase separated from the top of the wax liquid flash tower 15 is condensed by the wax liquid flash tower condenser 15 to recover the extractant and/or cosolvent, and the low melting point wax is obtained from the bottom of the wax liquid flash tower 15.

In the present invention, preferably, the system also includes a granulation and molding system for refined wax, such as a granulator, a spray powder (granule) making machine, and the like.

In a preferred embodiment, the system comprises two groups of refined wax production units, one of which is used to process the mixed wax liquid obtained by mixing the Fischer-Tropsch crude wax, the extractant and the optional co-solvent, and the other is used to process the wax liquid.

In a preferred embodiment, the system further comprises a raw material pretreatment device, wherein the raw material pretreatment device is used to perform vacuum distillation on the Fischer-Tropsch crude wax. Preferably, the raw material pretreatment device comprises a vacuum distillation tower, a vacuum system, a gas phase condenser, a gas phase condensate storage tank, and a tower bottom distillate storage tank.

In a preferred embodiment, the system further comprises a de-oiling device, wherein the de-oiling device is used to de-oil the wax paste. Preferably, the de-oiling device comprises a liquid-solid mixer, an extraction tank, a solid-liquid separation device and auxiliary conveying and control equipment.

The third aspect of the present invention provides a refined wax produced by the method described in the first aspect of the present invention, wherein the refined wax is Fischer-Tropsch wax with a melting point of 50-130° C. and an oil content of ≤0.8wt%, preferably ≤0.5wt%.

In a preferred embodiment, the melting point of the refined wax can be 50°C, 60°C, 66°C, 70°C, 75°C, 78°C, 80°C, 90°C, 92°C, 95°C, 100°C, 105°C, 110°C, 113°C, 120°C, 130°C, or any value in the range formed by any two of these point values.

In a preferred embodiment, the oil content of the refined wax can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt%, 0.8wt%, or any value in the range formed by any two of these point values.

In a preferred embodiment, the melting range of the refined wax is ≤40° C., preferably ≤35° C. The melting range may be 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., or any value in the range formed by any two of these point values.

The present invention will be described in detail below through examples. In the present invention, the test standards and methods of various performance indicators are as follows:

1) Melting point: tested according to ASTM D3954 method;

2) Chroma (Saibote number): tested according to GB/T 3555 method;

3) Oil content: According to the GB/T 3554 method, butanone is used as the solvent for samples with a melting point below 78°C, and methyl isobutyl ketone (MIBK) is used as the solvent for samples with a melting point greater than or equal to 78°C.

4) Crystal size: Take the crystals in the crystallization slurry, randomly measure the sizes of no less than 50 wax crystals using a polarizing microscope, and calculate the average value.

5) Melting range: measured by differential scanning calorimeter (DSC). In a _N2 atmosphere, the sample is cooled from the melting point temperature T+50°C to the melting point temperature T-100°C at a rate of 10°C/min. The cooling curve is measured, with the starting temperature point of the exothermic peak as the first temperature point, and the low temperature point at 95% of the exothermic peak area as the second temperature point. The temperature difference between the two is the melting range temperature.

6) Distillation: According to the method of ASTM D2887 extension.

The Fischer-Tropsch crude wax used in the examples and comparative examples is from the Ningxia Coal Industry Company of the State Energy Group, wherein the melting point of the Fischer-Tropsch crude wax I is 95°C, the melting range is 65°C, the 10% distillation temperature is 405°C, the 50% distillation temperature is 530°C, 80% of the carbon number is distributed in C ₁₈ -C ₈₆ , it is solid at room temperature, and the normal alkane content is 85wt%;

The melting point of Fischer-Tropsch wax II is 105°C, the melting range is 71°C, the 10% distillation temperature is 412°C, and the 50% distillation temperature is 550°C; 80% of the carbon number distribution is C18-C86, it is solid at room temperature, and the normal alkane content is 80wt%.

The Fischer-Tropsch naphtha comes from the Ningxia Coal Company of the State Energy Group, with a distillation range of 90-220°C and an oxygen content of 1.5wt%.

Example 1

(1) preheating Fischer-Tropsch crude wax I to obtain liquid Fischer-Tropsch crude wax I, and then mixing the liquid Fischer-Tropsch crude wax I with an extractant, Fischer-Tropsch synthetic naphtha, in a volume ratio of 1:8 to obtain a mixed wax liquid;

(2) The mixed wax liquid is used as the liquid to be extracted and extracted at 115°C and 0.5MPa for 60min. The mixed liquid after extraction is cooled to 85°C while stirring for aging. The aging time is 30min. Then, the aged liquid is crystallized and cooled to 75°C at a cooling rate of 1°C/min. Crystallization is carried out at 75°C for 20min. The average grain size of the crystals in the slurry after crystallization is 95um. The slurry after crystallization is separated at 75°C and filtered to obtain wax paste I and wax liquid I. The pressure decreases in the extraction, aging, crystallization, crystallization and separation processes, and the pressure difference between adjacent operations is 0.02MPa.

(3) flash evaporating the wax paste I to separate the extractant and obtain a refined wax No. 1 having a melting point of 113° C.;

(4) Sampling and analyzing the wax liquid I, the wax content in the wax liquid I was measured to be 9.5 wt %; the melting point of the wax was 80° C., and step 2 was repeated using the wax liquid I as the liquid to be extracted;

The method of repeating step 2 using the wax liquid I as the liquid to be extracted is as follows:

(2-1), extracting the wax liquid I at 85°C and 0.1MPa for 60min; cooling the extracted mixed solution to 55°C while stirring for aging, the aging time is 20min; then crystallizing the aged solution after aging, cooling it to 43°C at a cooling rate of 0.3°C/min, growing crystals at 43°C for 55min, and the average grain size of the crystals in the slurry after growing crystals is 105um; separating the slurry after growing crystals at 43°C, filtering to obtain wax paste II and wax liquid II; wherein the pressure during the aging, crystallization, growing crystals, and separation processes is the same as the extraction pressure;

(3-1), flash evaporating the wax paste II to separate the extractant to obtain refined wax No. 2 with a melting point of 92°C;

(4-1), sampling and analyzing the wax liquid II, and measuring the wax content in the wax liquid II to be 5.7wt%; the melting point of the wax is 70°C, and the wax liquid II is used as the liquid to be extracted and step 2 is repeated;

The method of repeating step 2 using the wax liquid II as the liquid to be extracted is as follows:

(2-2), extracting the wax liquid II at 75°C and 0.1MPa for 15min, cooling the extracted mixed solution to 35°C while stirring for aging, and the aging time is 45min; then crystallizing the aged solution, cooling it to 15°C at a cooling rate of 2°C/min, and growing crystals at 15°C for 15min, and the average grain size of the crystals in the slurry after growing crystals is 110um; separating the slurry after growing crystals at 15°C, filtering to obtain wax paste III and wax liquid III; wherein the pressure during the aging, crystallization, growing crystals, and separation processes is the same as the extraction pressure;

(3-2), flash evaporating the wax paste III to separate the extractant to obtain refined wax #3 with a melting point of 78°C;

(4-2), sampling and analyzing the wax liquid III, and measuring the wax content in the wax liquid III to be 3.1wt%; the melting point of the wax is 55°C, and the wax liquid III is used as the liquid to be extracted and step 2 is repeated;

The method of repeating step 2 using the wax liquid III as the liquid to be extracted is as follows:

(2-3), extracting the wax liquid III at 60°C and 0.1MPa for 15min, cooling the extracted mixed solution to 25°C while stirring for aging, the aging time is 10min; then crystallizing the aged solution, cooling it to -15°C at a cooling rate of 5°C/min, growing crystals at -15°C for 15min, and the average grain size of the crystals in the slurry after growing crystals is 138um; separating the slurry after growing crystals at -15°C, filtering to obtain wax paste IV and wax liquid IV; wherein the pressure in the above aging, crystallization, growing crystals, and separation processes is the same as the extraction pressure;

(3-3), flash evaporating the wax paste IV, separating the extractant, and obtaining 4# refined wax with a melting point of 66°C;

(4-3) The wax liquid IV is sampled and analyzed, and the wax content in the wax liquid IV is measured to be 0.6wt% and the melting point of the wax is 48°C; the wax liquid IV is flash evaporated to separate the extractant to obtain 5# low melting point wax with a melting point of 48°C.

The specific operating conditions in Example 1 are shown in Table 1, and the properties of the wax liquids, refined waxes and low-melting-point waxes obtained in Example 1 are shown in Table 3.

Example 2

Same as Example 1, except that:

In step (1), the extractant in Example 1 is replaced with Fischer-Tropsch naphtha and ethanol, wherein the volume ratio of Fischer-Tropsch naphtha to ethanol is 1:1; the volume ratio of Fischer-Tropsch crude wax I to the extractant is 1:5;

In step (4), the wax liquid I is subjected to step (2) repeatedly until the wax content in the obtained wax liquid N is less than 0.1 wt% or the melting point is less than 50°C.

The specific operating conditions in Example 2 are shown in Table 1, and the properties of the wax liquids, refined waxes and low-melting-point waxes obtained in Example 2 are shown in Table 3.

Example 3

Same as Example 1, except that:

In step (1), the Fischer-Tropsch crude wax I in Example 1 is replaced with Fischer-Tropsch crude wax II, and the extractant is replaced with n-propyl acetate and ethylene glycol, wherein the volume ratio of n-propyl acetate to ethylene glycol is 3:1; the liquid Fischer-Tropsch crude wax II is mixed with the extractant and the cosolvent to obtain a mixed wax liquid; wherein the cosolvent is naphtha, and the distillation range of the naphtha is 70-180°C; the mixing ratio of the Fischer-Tropsch crude wax II to the extractant is 1:9, and the volume ratio of the cosolvent to the extractant is 0.06:1;

In step (4), the wax liquid I is subjected to step (2) repeatedly until the wax content in the obtained wax liquid N is less than 0.1 wt% or the melting point is less than 50°C.

The specific operating conditions in Example 3 are shown in Table 1, and the properties of the wax liquids, refined waxes and low-melting-point waxes obtained in Example 3 are shown in Table 3.

Example 4

Same as Example 1, except that:

In step (1), the Fischer-Tropsch crude wax I in Example 1 is replaced with Fischer-Tropsch crude wax II, the extractant is replaced with n-butanol, and the liquid Fischer-Tropsch crude wax II is mixed with the extractant and the co-solvent to obtain a mixed wax liquid; wherein the co-solvent is petroleum ether, the distillation range of petroleum ether is 90-120° C., the mixing ratio of Fischer-Tropsch crude wax II to the extractant is 1:9, and the volume ratio of the co-solvent to the extractant is 0.05:1;

In step (4), the wax liquid I is subjected to step (2) repeatedly until the wax content in the obtained wax liquid N is less than 0.1 wt% or the melting point is less than 50°C.

The specific operating conditions in Example 4 are shown in Table 1, and the properties of the wax liquids, refined waxes and low-melting-point waxes obtained in Example 4 are shown in Table 3.

Example 5

Same as Example 1, except that:

In step (1), the extractant is replaced with isooctyl acetate, and the liquid Fischer-Tropsch crude wax I is mixed with the extractant and the co-solvent to obtain a mixed wax liquid; wherein the co-solvent is naphtha, the distillation range of naphtha is 70-180° C., the mixing ratio of the Fischer-Tropsch crude wax I to the extractant is 1:5, and the volume ratio of the co-solvent to the extractant is 0.1:1;

In step (4), the wax liquid I is subjected to step (2) repeatedly until the wax content in the obtained wax liquid N is less than 0.1 wt% or the melting point is less than 50°C.

The specific operating conditions in Example 5 are shown in Table 1, and the properties of the wax liquids, refined waxes and low-melting-point waxes obtained in Example 5 are shown in Table 3.

Example 6

The same as Example 4, except that: wax paste I, wax paste II, wax paste III, wax paste IV, wax paste V and wax paste VI are respectively deoiled to obtain 1-6# refined waxes.

The operation method of deoiling wax paste I is as follows: wax paste I and extractant (n-butanol) are mixed in a volume ratio of 1:1, placed at 75°C for 20 minutes, and then filtered to obtain deoiled wax paste I and deoiled wax liquid I; deoiled wax paste I is flash evaporated to obtain 1# refined wax, and deoiled wax liquid I is flash evaporated to obtain 1# light oil;

Among them, the deoiling treatment of wax paste II, wax paste III, wax paste IV, wax paste V and wax paste VI is the same as the deoiling treatment operation of wax paste I, and the corresponding operating conditions of the deoiling treatment are shown in Table 2.

The specific operating conditions in Example 6 are shown in Table 1, and the properties of the refined waxes and low melting point waxes obtained in Example 6 are shown in Table 3.

Example 7

Same as Example 1, except that:

Pre-treating the Fischer-Tropsch crude wax I: heating the Fischer-Tropsch crude wax I to 300° C., performing vacuum distillation at an absolute pressure of 100 Pa, cutting off the light fraction, and obtaining a 10% pre-treated crude wax with a distillation temperature of 520° C., a melting point of 100° C., and a melting range of 55° C. from the bottom of the vacuum device;

The pretreated crude wax is mixed with an extractant (isooctyl acetate and ethyl acetate, volume ratio 2:1) and a co-solvent (naphtha with a distillation range of 70-180°C) to obtain a mixed wax liquid; wherein the pretreated crude wax and

Table 1

Table 2

Deoiling conditions Wax paste I Wax paste II Wax paste III Wax paste IV Wax paste V Wax paste VI Temperature/℃ 75 65 55 40 29 -5 Solvent ratio (vol) 1:1 1:3 1:3 1:2 1:3 1:5 Time/min 20 25 40 50 60 80

Table 3

The crystal size in Table 3 is the size of the crystal in the slurry, and the low melting point wax is the product obtained by flashing the wax liquid N in the embodiment. The yield takes 1# refined wax as an example, which refers to the mass ratio of 1# refined wax to Fischer-Tropsch crude wax.

Comparative Example 1

Liquid Fischer-Tropsch crude wax I and a mixture of extractants butanone and toluene (volume ratio 7:3) were mixed in a volume ratio of 8:1, and then extracted at 120°C and 0.5 MPa for 60 minutes to obtain a mixed solution; the mixed solution was cooled to a crystallization temperature of 75°C and kept at a constant temperature for 10 minutes to obtain a crystal slurry;

The obtained crystal slurry was transferred to a vacuum drum filter for solid-liquid separation at 75° C. to obtain wax paste and mixed wax liquid;

The wax paste was flash evaporated to separate the extractant to obtain 1# refined wax with a melting point of 101° C. The product properties are shown in Table 4.

Table 4

1# Refined wax Crystal size, μm 15.5 Chroma 20 Oil content/% 2.4 Melting point/℃ 101 Melting range/℃ 54 Yield/% 64

It can be seen from Comparative Example 1 that in the comparative example system, since the components in the Fischer-Tropsch wax cannot form large crystal particles, on the one hand, the filtration separation resistance is too large and the filtration speed is reduced, and on the other hand, the product is not well separated, which is manifested in a wide melting range and a high oil content.

Comparative Example 2

Liquid Fischer-Tropsch crude wax I was subjected to multi-stage short-path distillation treatment at an absolute pressure of 10 Pa according to the method described in patent CN110066680A, and 5 components were cut out, namely <220°C, 220-240°C, 240-270°C, 270-290°C, and >290°C. The product properties are shown in Table 5.

Table 5

Fraction >290℃ 270-290℃ 240-270℃ 220-240℃ <220℃ Chroma 12 26 26 28 twenty four Oil content/% 1.08 1.48 2.21 3.01 3.89 Melting point/℃ 95 72 66 53 40 Melting range/℃ 52 25 twenty three 25 20 Yield, % 48 19 18 10 5

It can be seen from Comparative Example 2 that in the short-path distillation method, the distillation temperature of 290°C has reached the decomposition temperature of the Fischer-Tropsch wax, and further increasing the temperature will cause the decomposition of the Fischer-Tropsch wax; therefore, the short-path distillation method is not suitable for continuing to finely separate heavy components >290°C, and the resulting product has problems such as a wide melting range, a low melting point, a high oil content, and a low chroma.

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims (20)

1. A process for refining fischer-tropsch wax, the process comprising:

(1) Mixing Fischer-Tropsch wax, an extracting agent and an optional cosolvent to obtain a mixed wax liquid; wherein the extractant consists of at least one of an ester solvent, an alcohol solvent and Fischer-Tropsch synthetic naphtha;

(2) Sequentially extracting, aging, crystallizing, crystal growing and separating the mixed wax liquid serving as a liquid to be extracted to obtain a wax extract and a wax liquid;

(3) Flash-evaporating the cerate to obtain refined wax with the melting point of 50-130 ℃;

Wherein the ester solvent is at least one selected from ethyl acetate, ethyl propionate, butyl acetate, ethyl butyrate, n-propyl acetate, isopropyl acetate, isobutyl acetate and isooctyl acetate;

The alcohol solvent is at least one selected from ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, ethylene glycol, amyl alcohol, hexanol and 1-octanol; the Fischer-Tropsch synthetic naphtha has a distillation range of 90-220 ℃ and an oxygen content of 0.5-5 wt%;

the cosolvent is selected from naphtha with the distillation range of 70-180 ℃ and/or petroleum ether with the distillation range of 90-120 ℃.

2. The method of claim 1, further comprising (4) sampling the wax liquid, testing the wax content in the wax liquid and the melting point of the wax in the wax liquid, and repeating step (2) with the wax liquid as the liquid to be extracted when the wax content in the wax liquid is not less than 0.1wt% and the melting point of the wax in the wax liquid is not less than 50 ℃.

3. The process according to claim 2, wherein when the wax content in the wax liquid is < 0.1wt% or the melting point is < 50 ℃, the wax liquid is subjected to flash evaporation, and the extractant and optional co-solvent are recovered to obtain a low melting point wax or light oil having a melting point of less than 50 ℃.

4. The method of claim 1, wherein the fischer-tropsch wax and the extractant are mixed in a volume ratio of 1:1-10.

5. The method of claim 4, wherein the fischer-tropsch wax and the extractant are mixed in a volume ratio of 1:1.5-8.

6. The method of claim 1, wherein the fischer-tropsch wax, the extractant and the co-solvent are mixed, wherein the fischer-tropsch wax to extractant volume ratio is 1:1-10, wherein the volume ratio of the cosolvent to the extractant is 0.02-0.15:1.

7. The method of claim 6, wherein the fischer-tropsch wax, the extractant and the co-solvent are mixed, wherein the fischer-tropsch wax to extractant volume ratio is 1:1.5-8, wherein the volume ratio of the cosolvent to the extractant is 0.05-0.1:1.

8. The method according to claim 1, wherein in the step (2), the operating temperatures of extraction, aging, crystallization and separation are sequentially determined based on the reference temperature with respect to the melting point of wax contained in the liquid to be extracted as the reference temperature.

9. The method of claim 1, wherein the conditions of extraction comprise: the solvent extraction temperature is 0-30 ℃ higher than the reference temperature.

10. The method of claim 9, wherein the conditions of extraction include: the solvent extraction temperature is 5-20 ℃ higher than the reference temperature.

11. The method of claim 1, wherein the aging conditions comprise: the aging temperature is 3-40deg.C lower than the reference temperature, and the aging time is 5-60min.

12. The method of claim 11, wherein the aging conditions comprise: the aging temperature is 5-30deg.C lower than the reference temperature, and the aging time is 5-40min.

13. The method of claim 1, wherein the crystallization conditions comprise: cooling from the aging temperature to the crystal growing temperature at a cooling speed of 0.1-10 ℃/min, wherein the crystal growing temperature is 5-45 ℃ lower than the aging temperature.

14. The method of claim 13, wherein the crystallization conditions include: cooling from the cooling speed of 0.2-5 ℃/min to the crystal growing temperature, wherein the crystal growing temperature is 10-40 ℃ lower than the aging temperature.

15. The method of claim 1, wherein the crystallization conditions comprise: the crystal growing time is 5-120min; the average grain size of the crystals in the slurry after crystal growth is more than or equal to 50 mu m.

16. The method of claim 15, wherein the crystallization conditions comprise: the crystal growing time is 20-120min; the average grain size of the crystals in the slurry after crystal growth is 60-200 mu m.

17. The method of claim 1, wherein step (3) further comprises a deoiling treatment: deoiling the wax extract to obtain deoiled wax extract and deoiled wax liquid, and performing flash evaporation treatment on the deoiled wax extract to obtain refined wax with a melting point of 50-130 ℃.

18. The method of claim 17, wherein the deoiling comprises mixing the stencil and the extractant in a volume ratio of 1: mixing at a ratio of 0.5-10, and standing at crystal growth temperature for 10-120min; and then separating at the crystal growing temperature to obtain deoiling wax paste and deoiling wax liquid.

19. The method of claim 18, wherein the deoiling comprises mixing the stencil and the extractant in a volume ratio of 1: mixing at a ratio of 1-5, and standing at the crystal growing temperature for 115-80min; and then separating at the crystal growing temperature to obtain deoiling wax paste and deoiling wax liquid.

20. A system for refining fischer-tropsch wax, the system comprising at least one set of refined wax production units; wherein the refined wax production unit comprises an extraction device, a crystallization device, a separation device and a recovery device;

The extraction device comprises a raw material wax tank (1), an extractant storage tank (2), a preheater (3), a mixer (4), a heat exchanger (5) and an extractor (6); the crystallization device comprises an aging kettle (8), a crystallizer (9) and a crystal growing kettle (10); the separation device comprises a filter (11) and a conveyor (12); the recovery device comprises a wax paste flash tower (13), a wax paste flash tower condenser (14) connected with the wax paste flash tower (13), a wax liquid flash tower (15) and a wax liquid flash tower condenser (16) connected with the wax liquid flash tower (15).