Method and system for Fischer-Tropsch wax deoiling using supercritical fluids

Abstract

This invention provides a method and system for deoiling Fischer-Tropsch wax using supercritical fluid. The method includes contacting Fischer-Tropsch wax with an extractant in a supercritical fluid state for extraction, so that the oil components in the Fischer-Tropsch wax dissolve in the extractant and are separated from the Fischer-Tropsch wax, thus completing the deoiling process. The Fischer-Tropsch wax deoiling method of this invention has advantages such as strong dissolving power, high selectivity, and fast mass transfer rate, which can efficiently remove oil components from Fischer-Tropsch wax at a low cost. Furthermore, the Fischer-Tropsch wax deoiling method of this invention is relatively clean and environmentally friendly, as it does not use potentially carcinogenic substances such as toluene and methyl ethyl ketone (MEK). The supercritical fluid extractant can be easily converted to a gaseous state after subsequent treatment, making it easy to separate from the liquid oil components and preventing the residue of harmful substances during the extraction and separation process.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and more specifically, to a method and system for deoiling Fischer-Tropsch wax using supercritical fluids. Background Technology

[0002] Fischer-Tropsch wax is an important type of wax product. It is composed of a small amount of methyl-branched straight-chain saturated high-carbon alkanes with a relative molecular weight of 500-1000 and a carbon number distribution of C20-C80. It is chemically stable at room temperature and contains almost no impurities such as sulfur, nitrogen, or aromatics. Domestically produced Fischer-Tropsch wax products are generally classified according to their melting point grades, with main product models including 50#, 60#, 70#, 85#, 95#, 100#, 105#, and 110#. Due to the lack of relevant standards for Fischer-Tropsch wax products in China, downstream users have used petroleum wax product indicators to measure Fischer-Tropsch wax after it entered the market in recent years. According to GB / T 3554-2008, the method for determining the oil content of petroleum wax, the oil content refers to the proportion of components that cannot crystallize at low temperature (-32℃) and can be dissolved in methyl ethyl ketone (MEK) solvent in the sample. Although Fischer-Tropsch wax has a high degree of orthomorphism, it still contains a small amount of oil components, especially in low- and medium-melting-point grades after cutting, where the oil content is relatively high, ranging from approximately 1% to 9% by mass. From the overall structural composition of Fischer-Tropsch wax, the oil components are relatively simple, and the components meeting the definition of oil content should mainly be low-carbon chain alkanes. Domestic Fischer-Tropsch wax products lag significantly behind imported products (oil content less than 0.5%), failing to meet the needs of high-end customers. Therefore, to obtain high-end Fischer-Tropsch wax products with specifications comparable to imported products, deoiling treatment is necessary.

[0003] Common existing technologies for degreasing Fischer-Tropsch wax include two processes: sweating degreasing and solvent degreasing. The sweating degreasing process involves melting the wax and allowing it to flow onto the wall of a sweating tank. After the wax solidifies on the cold tank wall, the tank wall is slowly heated, causing the lower-melting-point components (i.e., the oil components) to melt and flow out of the wax. This process is similar to sweating, hence the name "sweating" for this process. For example, patent CN106883890A discloses a method for sweating and producing paraffin wax. This method utilizes airflow through the wax layer during sweating to carry away liquid oil, forcibly separating the wax and oil. Pressure is applied to the wax layer during sweating to accelerate the separation and ensure airflow through the wax layer, thereby producing a high-melting-point paraffin wax product. For example, patent CN105779002A discloses a method for sweating and preparing microcrystalline wax. The method uses a sweating device to uniformly spread metal particles on the surface of the wax layer after the cooling and crystallization process is completed, and forces airflow through the wax layer during the heating and sweating process to carry out the oil in liquid state.

[0004] The aforementioned sweating and deoiling process utilizes the different melting points of various hydrocarbon components in wax for separation and purification. The different molecular weights and structures of the components in Fischer-Tropsch wax result in different melting points. For example, among n-alkanes, those with higher molecular weights have higher melting points; while isoalkanes with the same molecular weight have lower melting points than n-alkanes. To ensure the final product meets the required oil content, the sweating time is usually extended, but this prolongs the production cycle. Increasing the sweating termination temperature is also used, but this can cause the wax cake to sometimes detach from the internal support surface of the deoiling device and flow directly into the wax oil collector at the bottom, leading to a decrease in product yield. Therefore, existing sweating and deoiling processes are prone to problems such as slow and incomplete solid-liquid phase separation, and high average oil content in the deoiled wax, which further leads to low production efficiency, low product yield, and a large footprint for industrial equipment.

[0005] Solvent deoiling technology separates oil and wax from the product by utilizing the different solubilities of the solvent on the oil and wax. First, the wax is melted and diluted with a solvent, then slowly cooled. Wax has lower solubility in cold solvents, while oil has higher solubility. This difference in solubility allows for separation. The insoluble wax is then separated by filtration. The solvent in the separated oil and wax is recovered, ultimately yielding wax oil and deoiled wax. The methyl ethyl ketone (MEK)-toluene solvent (dewaxing) deoiling process is currently the most widely used paraffin wax deoiling process, and its process conditions are relatively mature. Patent CN104560196A discloses a method for preparing deoiled wax using a ketone / benzene mixed solvent. It modifies the existing three-stage solvent deoiling process, changing the two-stage deoiling process into a three-stage process, thus improving the yield of deoiled wax while meeting the required oil content.

[0006] In addition, methyl isobutyl ketone (MBE) solvent degreasing is also a relatively effective degreasing method. MBE can be used as a single solvent in the degreasing process, or it can be combined with solvents such as butanone (MEK) to form a mixed solvent system for degreasing. Because MBE has a higher boiling point than MEK, it has a greater advantage in degreasing high-melting-point waxes. Patent CN106554822A discloses a method for degreasing Fischer-Tropsch waxes, using a single MBE solvent to degrease the Fischer-Tropsch wax. After several dilutions and cooling crystallizations, a solvent-containing crystalline liquid is obtained. The crystalline liquid is filtered to obtain a degreased wax paste, which is then evaporated to recover the solvent, yielding the wax product.

[0007] In solvent degreasing processes, toluene and methyl ethyl ketone (MEK) mixtures are currently the most widely used degreasing solvents. However, with the gradual implementation of environmental standards requiring products to be free of benzene, toluene, xylene, and other benzene-based contaminants, and the carcinogenicity of residual trace amounts of solvent, their application in high-end fields is limited. Furthermore, methyl isobutyl ketone (MEK) solvent has disadvantages such as a high boiling point, high solvent recovery temperature, and high viscosity at low temperatures, reducing filtration speed. More importantly, in solvent degreasing processes, the energy consumption during wax cooling and crystallization, as well as solvent regeneration, is significant, increasing production costs and impacting the product's economic viability.

[0008] Currently, low- and medium-melting-point Fischer-Tropsch waxes have high oil content, which cannot meet the needs of high-end users. Existing sweating deoiling processes are prone to slow and incomplete solid-liquid phase separation, resulting in high average oil content in the deoiled wax. This leads to low production efficiency, low product yield, and large industrial plant footprint. Existing solvent deoiling processes suffer from solvent residue, high production costs, and high energy consumption. Therefore, it is necessary to develop a new, green, efficient, environmentally friendly, and low-cost deoiling method based on the composition and structural characteristics of Fischer-Tropsch wax products. Summary of the Invention

[0009] The main objective of this invention is to provide a method and system for Fischer-Tropsch wax deoiling using supercritical fluids, in order to solve the problems of low deoiling efficiency, environmental unfriendliness, or high cost in existing sweating deoiling and solvent deoiling processes.

[0010] To achieve the above objectives, according to one aspect of the present invention, a method for deoiling Fischer-Tropsch wax is provided, wherein the Fischer-Tropsch wax has a melting point of 50–80°C and an oil content of 1–9 wt%. The method comprises: contacting the Fischer-Tropsch wax with an extractant having a supercritical fluid state for extraction, so that the oil component in the Fischer-Tropsch wax dissolves in the extractant and is separated from the Fischer-Tropsch wax, thereby completing the deoiling process; wherein the extractant is selected from one or more of supercritical fluids C1–C4 alkanes, supercritical fluids C2–C4 olefins, supercritical fluids C1–C3 alcohols, or supercritical fluids carbon dioxide.

[0011] Furthermore, the extractant is selected from one or more of the supercritical fluids ethane, propane, carbon dioxide, or propylene.

[0012] Furthermore, the ratio of the total weight of the extractant to the total weight of Fischer-Tropsch wax is 5 to 50:1, preferably 10 to 30:1.

[0013] Furthermore, when the extractant is selected from supercritical fluid ethane, the extraction temperature is 40–90°C and the extraction pressure is 5–20 MPa; when the extractant is selected from supercritical fluid propane, the extraction temperature is 50–80°C and the extraction pressure is 10–20 MPa; when the extractant is selected from supercritical fluid carbon dioxide, the extraction temperature is 50–90°C and the extraction pressure is 10–30 MPa; and when the extractant is selected from supercritical fluid propylene, the extraction temperature is 30–60°C and the extraction pressure is 10–25 MPa.

[0014] Furthermore, after extraction, the Fischer-Tropsch wax deoiling method also includes: gas-liquid separation of the extractant containing dissolved oil components to obtain liquid oil components and gaseous extractant respectively; 33-89 wt% of the liquid oil components are refluxed as raw materials to participate in extraction again; wherein the temperature of gas-liquid separation is 50-90°C and the pressure of gas-liquid separation is 3-20 MPa.

[0015] Furthermore, after gas-liquid separation, the Fischer-Tropsch wax deoiling method also includes cooling the gaseous extractant to convert it into a liquid extractant for reuse as a regenerated extractant in the extraction process.

[0016] To achieve the above objectives, according to one aspect of the present invention, a Fischer-Tropsch wax deoiling system is provided, comprising a Fischer-Tropsch wax supply unit, an extractant supply unit, and an extraction unit; the extraction unit includes an extraction tower; the extraction tower has a Fischer-Tropsch wax inlet connected to the Fischer-Tropsch wax supply unit for adding Fischer-Tropsch wax into the extraction unit; the extraction tower also has an extractant inlet connected to the extractant supply unit for introducing extractant into the extraction unit; and the Fischer-Tropsch wax inlet is higher than the extractant inlet; the top of the extraction tower has a light component outlet for discharging the extractant containing dissolved oil components after extraction; the bottom of the extraction tower has a heavy component outlet for discharging the deoiled wax product after extraction.

[0017] Furthermore, the extraction unit also includes: a gas-liquid separator, the inlet of which is connected to the light component outlet of the extraction tower, for gas-liquid separation of the extractant containing dissolved oil components after extraction, so as to obtain liquid oil components and gaseous extractant respectively; and the upper part of the gas-liquid separator has a gaseous extractant outlet for discharging the gaseous extractant after gas-liquid separation; the lower part of the gas-liquid separator has an oil component outlet for discharging the oil component after gas-liquid separation; an oil component collection tank, the inlet of which is connected to the oil component outlet of the gas-liquid separator; and a deoiled wax product collection tank, the inlet of which is connected to the heavy component outlet of the extraction tower.

[0018] Furthermore, the upper part of the extraction tower also has a reflux inlet, which is connected to the oil component outlet of the gas-liquid separator, so that some oil components can be refluxed back into the extraction tower as raw materials to participate in the extraction again; and a reflux cooler and a reflux transfer pump are sequentially installed on the connecting channel between the reflux inlet and the oil component outlet.

[0019] Furthermore, the gaseous extractant outlet of the gas-liquid separator is connected to the extractant supply unit via a connecting pipe, and a cooler is also installed on the connecting pipe.

[0020] Furthermore, an extractant delivery pump and a first heater are sequentially installed on the communication channel between the extractant supply unit and the extractant inlet.

[0021] Furthermore, a Fischer-Tropsch wax delivery pump is installed on the communication channel between the Fischer-Tropsch wax supply unit and the Fischer-Tropsch wax inlet; a second heater is independently installed inside the Fischer-Tropsch wax supply unit, inside the oil component collection tank, and inside the product wax collection tank.

[0022] Furthermore, the outer wall of the extraction tower, the outer wall of the pipe connecting the Fischer-Tropsch wax inlet to the Fischer-Tropsch wax supply unit, the outer wall of the pipe connecting the inlet of the deoiled wax product collection tank to the heavy component outlet of the extraction tower, and the outer wall of the pipe connecting the extractant inlet to the heater are each independently provided with a first jacket, and the first jacket is heated by circulating hot oil for heat preservation.

[0023] Furthermore, the outer walls of the gas-liquid separator, the outer walls of the extractant supply unit, the outer walls of the pipe connecting the light component outlet of the extraction tower and the inlet of the gas-liquid separator, the outer walls of the pipe connecting the oil component outlet of the gas-liquid separator and the reflux material inlet of the extraction tower, the outer walls of the pipe connecting the gaseous extractant outlet of the gas-liquid separator and the inlet of the extractant supply unit, and the outer walls of the pipe connecting the outlet of the extractant supply unit and the inlet of the heater are each independently equipped with a second jacket, and the second jacket is kept cold by circulating refrigerant.

[0024] Furthermore, the Fischer-Tropsch wax inlet is 4.5–25 m higher than the extractant inlet.

[0025] Compared to existing sweating and solvent-based deoiling processes, the Fischer-Tropsch wax deoiling method of this invention has advantages such as strong dissolving power, high selectivity, and fast mass transfer rate. It can efficiently remove oil components from Fischer-Tropsch wax at a lower cost. Furthermore, this method is cleaner and more environmentally friendly, as it does not use potentially carcinogenic substances such as toluene and methyl ethyl ketone (MEK). The supercritical fluid extractant can be easily converted to a gaseous state after simple processing, facilitating separation from the liquid oil components and preventing the residue of harmful substances during the extraction and separation process. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 A schematic diagram of a Fischer-Tropsch wax degreasing system according to one embodiment of the present invention is shown; and

[0028] Figure 2 A schematic diagram of a Fischer-Tropsch wax deoiling system according to another embodiment of the present invention is shown.

[0029] The above figures include the following reference numerals:

[0030] 10. Fischer-Tropsch wax supply unit; 11. Fischer-Tropsch wax transfer pump; 20. Extractant supply unit; 21. Extractant transfer pump; 22. First heater; 30. Extraction unit; 31. Extraction tower; 32. Gas-liquid separator; 33. Oil component collection tank; 34. Deoiled wax product collection tank; 35. Reflux cooler; 36. Reflux transfer pump; 37. Cooler. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] As described in the background section of this application, existing sweating and solvent degreasing processes suffer from problems such as low degreasing efficiency, environmental unfriendliness, or high cost. To address this issue, this application provides a Fischer-Tropsch wax degreasing method. The Fischer-Tropsch wax has a melting point of 50–80°C and an oil content of 1–9 wt%. The method includes: contacting the Fischer-Tropsch wax with an extractant in a supercritical fluid state for extraction, so that the oil components in the Fischer-Tropsch wax dissolve in the extractant and are separated from the Fischer-Tropsch wax, thus completing the degreasing process; wherein the extractant is selected from one or more of supercritical fluid C1–C4 alkanes, supercritical fluid C2–C4 olefins, supercritical fluid C1–C3 alcohols, or supercritical fluid carbon dioxide.

[0033] The inventors have discovered that when using extractants in a supercritical fluid state for Fischer-Tropsch wax deoiling, such extractants possess unique physicochemical properties. Their density is close to that of a liquid, exhibiting strong dissolving power for oily substances in Fischer-Tropsch wax. Furthermore, their viscosity and diffusion coefficient are much higher than those of liquids, making them more like gases, thus providing excellent mass transfer performance. This allows for the efficient extraction of low-boiling-point, low-molecular-weight oil components from Fischer-Tropsch wax to achieve deoiling. Commonly used supercritical fluid substances can be used as extractants for Fischer-Tropsch wax deoiling. These extractants can be selected from one or more of the following: supercritical fluid C1-C4 alkanes (e.g., methane, ethane, propane, butane), supercritical fluid C2-C4 olefins (e.g., ethylene, propylene, butene), supercritical fluid C1-C3 alcohols (e.g., methanol, ethanol, propanol), or supercritical fluid carbon dioxide.

[0034] In particular, this method of deoiling Fischer-Tropsch wax is very suitable for Fischer-Tropsch waxes with medium to low melting points (50–80°C) and high oil content (1–9 wt%). Conventional sweating and solvent extraction processes often fail to remove the oily components. This application utilizes a supercritical fluid extractant to extract Fischer-Tropsch waxes with such high oil content. Because the extractant is in a supercritical state, it exhibits excellent fluidity and permeability, a fast mass transfer rate, and a density close to that of a liquid. It also possesses strong solubility for the oil components of Fischer-Tropsch waxes, enabling highly selective extraction of low-boiling-point, low-molecular-weight oil components, thus completing the deoiling process.

[0035] The Fischer-Tropsch wax deoiling method of this invention has advantages such as strong dissolving ability, high selectivity, and fast mass transfer rate. It can efficiently remove oil components from Fischer-Tropsch wax at a low cost. Furthermore, the Fischer-Tropsch wax deoiling method of this invention is relatively clean and environmentally friendly. The entire process does not use potentially carcinogenic substances such as toluene and methyl ethyl ketone (MEK). Moreover, the supercritical fluid extractant can be easily converted to a gaseous state after simple subsequent treatment, making it easy to separate from the liquid oil components. The product contains virtually no supercritical extraction solvent, preventing the residue of substances harmful to human health during the extraction and separation process.

[0036] It should be noted that the oil component in the Fischer-Tropsch wax mentioned above refers to ortho-long-chain hydrocarbons with carbon numbers ranging from C12 to C20, and the oil content refers to the weight content of the oil component in the Fischer-Tropsch wax.

[0037] In a preferred embodiment, the extractant is selected from one or more of supercritical fluids, including ethane, propane, carbon dioxide, or propylene. The extractants of this invention exhibit excellent solubility and selectivity for the oil components in Fischer-Tropsch waxes, possess suitable critical temperatures and pressures, and offer a simpler process, making them highly suitable as supercritical fluid extractants for Fischer-Tropsch wax deoiling. Ethane is the preferred and optimal extractant. Under the same pressure, propane, propylene, and carbon dioxide have lower solubility for the oil components in Fischer-Tropsch waxes than ethane, and require higher pressures when using propane, propylene, and carbon dioxide for extraction. More preferably, the extractant is supercritical fluid ethane.

[0038] To further improve the deoiling efficiency of the product, in a preferred embodiment, the Fischer-Tropsch wax is selected from one or more of 50#, 60#, or 70# Fischer-Tropsch wax. Specifically, 50# Fischer-Tropsch wax has a carbon number distribution of C12–C37, a melting point of 50–59°C, and an oil content of 7–9 wt%; 60# Fischer-Tropsch wax has a carbon number distribution of C17–C46, a melting point of 60–69°C, and an oil content of 3–7 wt%; and 70# Fischer-Tropsch wax has a carbon number distribution of C22–C50, a melting point of 70–79°C, and an oil content of 1–3 wt%.

[0039] In a preferred embodiment, the Fischer-Tropsch wax is contacted with the extractant in a supercritical fluid state via countercurrent contact. During this countercurrent contact process, the Fischer-Tropsch wax can further increase the contact opportunities between the extractant and the supercritical fluid extractant, thereby improving the oil removal efficiency.

[0040] In a preferred embodiment, the ratio of the total weight of the extractant to the total weight of Fischer-Tropsch wax is 5–50:1, for example, 5:1, 10:1, 15:1, 20:1, 30:1, 40:1, or 50:1. The applicant has found that the weight ratio of the extractant to Fischer-Tropsch wax does not have a linear relationship with the extraction and deoiling results. Although at lower extractant-to-wax ratios (the ratio of the total weight of the extractant to the total weight of Fischer-Tropsch wax), the supercritical fluid extractant and Fischer-Tropsch wax can achieve sufficient contact, the extraction rate per unit time is low. At the same time, the extractant-to-wax ratio should not be too high. If an excessively high ratio is used, the residence time of the supercritical fluid extractant during extraction is shortened, and the oil components in the Fischer-Tropsch wax do not completely dissolve in the supercritical fluid before flowing out of the extraction tower, which is detrimental to extraction and also consumes more supercritical fluid extractant, resulting in resource waste and unnecessary cost increases. Therefore, the applicant further controls the extractant-to-wax ratio within the above-mentioned range to further balance extraction efficiency and low production costs. A more preferred ratio is 10–30:1.

[0041] To further improve the oil removal efficiency and yield of the product and control production costs, in some preferred embodiments, when the extractant is selected from supercritical fluid ethane, the extraction temperature is 40–90°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or 90°C, and the extraction pressure is 5–20 MPa, for example, 5 MPa, 8 MPa, 10 MPa, 12 MPa, 15 MPa, 18 MPa, or 20 MPa; when the extractant is selected from supercritical fluid propane, the extraction temperature is 50–80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C, and the extraction pressure is 10–20 MPa, for example, 10 MPa, 12 MPa, or 15 MPa. When the extractant is selected from supercritical fluid carbon dioxide, the extraction temperature is 50–90℃, for example, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, and the extraction pressure is 10–30MPa, for example, 10MPa, 12MPa, 15MPa, 18MPa, 20MPa, 25MPa, 30MPa; when the extractant is selected from supercritical fluid propylene, the extraction temperature is 30–60℃, for example, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, and the extraction pressure is 10–25MPa, for example, 10MPa, 12MPa, 15MPa, 18MPa, 20MPa, 25MPa.

[0042] The solubility of the oil component in Fischer-Tropsch wax in a supercritical fluid extractant increases with increasing fluid density. Therefore, based on this property, the density of the supercritical fluid can be controlled by adjusting the parameters of temperature and pressure, thereby altering the solubility of the oil component in the supercritical fluid and achieving the goal of extracting the oil component from Fischer-Tropsch wax. Under the aforementioned extraction temperature and pressure conditions, the supercritical fluid extractant exhibits high solubility for the oil component in Fischer-Tropsch wax, thus improving the deoiling efficiency of Fischer-Tropsch wax.

[0043] Specifically, under a constant extraction temperature, the density of the supercritical fluid increases with increasing extraction pressure, leading to a greater solubility of the supercritical fluid extractant in the oil components of Fischer-Tropsch wax and a significant improvement in deoiling efficiency. However, excessively high extraction pressure places higher demands on the entire equipment and increases operating costs accordingly. Therefore, considering the overall impact of extraction pressure, higher extraction pressure is not always better. Similarly, under a constant extraction pressure, the effect of extraction temperature on the supercritical fluid extractant extraction process is complex. On the one hand, increased temperature leads to a decrease in the density of the supercritical fluid extractant, thereby reducing its solubility and hindering extraction. On the other hand, increased temperature also increases the saturated vapor pressure of the oil components in Fischer-Tropsch wax, increasing the mass transfer rate and the intermolecular forces between the oil components and the supercritical fluid extractant, which is beneficial for deoiling. The effects of both temperature and pressure on extraction deoiling are intertwined, with some offsetting effects. Therefore, the selection of extraction temperature and pressure must be considered comprehensively.

[0044] To further improve the deoiling efficiency and product yield, in a preferred embodiment, the Fischer-Tropsch wax deoiling method further includes: after extraction, performing gas-liquid separation on the extractant containing dissolved oil components to obtain liquid oil components and gaseous extractant respectively; and refluxing 33-89 wt% of the liquid oil components as raw material for further extraction. This refluxing operation allows for more thorough removal of oil components from the Fischer-Tropsch wax. As the supercritical fluid extractant continuously contacts the Fischer-Tropsch wax, the oil components originally dissolved in the supercritical fluid extractant will redefine. The precipitated components continue to contact and dissolve with the rising supercritical fluid, similar to distillation. The refluxing oil components increase the contact opportunities between the oil components and the supercritical fluid, reducing the dissolution of non-oil components, thereby improving deoiling efficiency. Simultaneously, the refluxing oil components contain trace amounts of wax components. Through refluxing extraction, during contact with the supercritical fluid, the wax components precipitate from the oil components, thereby increasing the yield of the deoiled wax product.

[0045] In the above gas-liquid separation process, the temperature for gas-liquid separation is 50–90℃ or the pressure for gas-liquid separation is 3–20 MPa. In the separation process between the supercritical fluid extractant and the oil component, simply changing the temperature or pressure parameters below the critical value of the supercritical fluid extractant will decrease the supercritical fluid density, causing the extractant to transform from the supercritical phase to the gas phase, thus allowing the oil component to be separated from the extractant. If the temperature is fixed, the oil component can be separated from the extractant by reducing the pressure; conversely, if the pressure is fixed, the oil component can also be separated from the extractant by changing the temperature.

[0046] To further improve the utilization rate of the extractant and control production costs, in a preferred embodiment, after gas-liquid separation, the Fischer-Tropsch wax deoiling method further includes: cooling the extractant after gas-liquid separation to convert it into a liquid extractant for reuse as a regenerated extractant in extraction.

[0047] The present invention also provides a Fischer-Tropsch wax deoiling system, such as Figure 1 As shown, it includes a Fischer-Tropsch wax supply unit 10, an extractant supply unit 20, and an extraction unit 30. The extraction unit 30 includes an extraction tower 31. The extraction tower 31 has a Fischer-Tropsch wax inlet, which is connected to the Fischer-Tropsch wax supply unit 10 for introducing Fischer-Tropsch wax into the extraction unit 30. The extraction tower 31 also has an extractant inlet, which is connected to the extractant supply unit 20 for introducing extractant into the extraction unit 30. The Fischer-Tropsch wax inlet is higher than the extractant inlet. The top of the extraction tower 31 has a light component outlet for discharging the extractant containing dissolved oil components after extraction. The bottom of the extraction tower 31 has a heavy component outlet for discharging the deoiled wax product after extraction.

[0048] The Fischer-Tropsch wax deoiling system of the present invention includes a Fischer-Tropsch wax supply unit, an extractant supply unit, and an extraction unit. The Fischer-Tropsch wax supply unit and the extractant supply unit are respectively connected to the Fischer-Tropsch wax inlet and the extractant inlet of the extraction unit. The Fischer-Tropsch wax supply unit supplies Fischer-Tropsch wax to the extraction tower, and the extractant supply unit supplies extractant to the extraction tower. In this application, the Fischer-Tropsch wax inlet of the extraction tower is set higher than the extractant inlet of the extraction tower, which can increase the contact time between Fischer-Tropsch wax and extractant and improve the deoiling efficiency of the product. The extractant is in a supercritical state in the extraction tower, and the Fischer-Tropsch wax is in a liquid state in the extraction tower. The supercritical extractant and the liquid Fischer-Tropsch wax come into contact in the extraction tower to extract the oil components from the Fischer-Tropsch wax. After extraction, the supercritical extractant carrying the oil components is discharged from the light component outlet of the extraction tower 31, and the extracted deoiled wax product is discharged from the heavy component outlet of the extraction tower.

[0049] In a preferred embodiment, the extraction unit 30 further includes: a gas-liquid separator 32, the inlet of which is connected to the light component outlet of the extraction tower 31, for gas-liquid separation of the extractant containing dissolved oil components after extraction, so as to obtain liquid oil components and gaseous extractant respectively; and the upper part of the gas-liquid separator 32 has a gaseous extractant outlet for discharging the gaseous extractant after gas-liquid separation; the lower part of the gas-liquid separator 32 has an oil component outlet for discharging the oil component after gas-liquid separation; an oil component collection tank 33, the inlet of which is connected to the oil component outlet; and a deoiled wax product collection tank 34, the inlet of which is connected to the heavy component outlet.

[0050] The extraction unit of this invention is further equipped with a gas-liquid separator, an oil component collection tank, and a deoiled wax product collection tank. This application incorporates a gas-liquid separator in the extraction unit. The inlet of the gas-liquid separator is connected to the light component outlet of the extraction tower, enabling effective separation of the supercritical extractant containing dissolved oil components flowing out from the top of the extraction tower, thus obtaining liquid oil components and gaseous extractant. The upper and lower parts of the gas-liquid separator are respectively provided with a gaseous extractant outlet and an oil component outlet. The gaseous extractant, after gas-liquid separation, flows out from the gaseous extractant outlet back into the extractant supply unit, while the liquid oil component flows out from the oil component outlet and enters the oil component collection tank.

[0051] To further improve the deoiling efficiency of Fischer-Tropsch wax, in a preferred embodiment, the upper part of the extraction tower 31 is also provided with a reflux inlet, which is connected to the oil component outlet of the gas-liquid separator 32, so that part of the oil component is refluxed back to the extraction tower 31 as raw material to participate in extraction again; and a reflux cooler 35 and a reflux transfer pump 36 are sequentially arranged on the connecting channel between the reflux inlet and the oil component outlet.

[0052] The extraction tower of this invention is specifically provided with a reflux inlet at the top, which allows a portion of the oil component flowing out of the gas-liquid separator's oil component outlet to flow back into the extraction tower and participate in the extraction process again as raw material. This arrangement further improves the oil removal efficiency of Fischer-Tropsch wax. The reflux transfer pump of this application is used to transport a portion of the oil component flowing out of the gas-liquid separator's oil component outlet to a reflux cooler. The transported oil component is then cooled to the same extraction temperature as inside the extraction tower by the reflux cooler before being transported into the extraction tower.

[0053] To facilitate rapid separation of the extractant containing dissolved oil components, in a preferred embodiment, a pressure regulating valve is installed on the communication channel between the light component outlet of the extraction tower 31 and the inlet of the gas-liquid separator 32. This pressure regulating valve can be used to adjust the feed liquid pressure. By adjusting the operating pressure through the pressure regulating valve, the pressure is reduced, significantly decreasing the solubility of the extractant. This allows the dissolved oil component product to precipitate from the extractant, resulting in rapid separation of the extractant and the oil component.

[0054] To enable the recovery of the gaseous extractant after gas-liquid separation as a regenerating extractant, in a preferred embodiment, a cooler 37 is provided on the connection channel between the gaseous extractant outlet of the gas-liquid separator 32 and the inlet of the extractant supply unit 20. This cooler condenses the gaseous extractant into a liquid extractant for recovery as a regenerating extractant. In this invention, a cooler is provided at the connection point between the gaseous extractant outlet of the gas-liquid separator and the inlet of the extractant supply unit. The cooling temperature of the cooler is the same as the internal temperature of the extractant supply unit, ranging from 10 to 30°C.

[0055] In a preferred embodiment, an extractant delivery pump 21 and a first heater 22 are sequentially arranged on the communication channel between the extractant supply unit 20 and the extractant inlet on the extraction tower 31. The extractant delivery pump 21 of the present invention is used to deliver the extractant from the extractant supply unit 20 into the first heater 22. The first heater is used to heat the extractant to the same extraction temperature as inside the extraction tower, and the heated extractant then flows into the interior of the extraction tower.

[0056] In a preferred embodiment, a Fischer-Tropsch wax delivery pump 11 is installed on the communication channel between the Fischer-Tropsch wax supply unit 10 and the Fischer-Tropsch wax inlet on the extraction tower 31. A second heater is independently installed inside the Fischer-Tropsch wax supply unit 10, the oil component collection tank 33, and the product wax collection tank 34. The Fischer-Tropsch wax delivery pump of the present invention is used to deliver the Fischer-Tropsch wax in the Fischer-Tropsch wax supply unit 10 to the interior of the extraction tower. The second heaters installed in the Fischer-Tropsch wax supply unit, the oil component collection tank, and the product wax collection tank of the present invention are used for temperature control, maintaining the temperature of the Fischer-Tropsch wax supply unit at 50–90°C, the temperature of the oil component collection tank at 100–150°C, and the temperature of the deoiled wax product collection tank at 100–150°C.

[0057] In a preferred embodiment, jackets are provided on the outer wall of the extraction tower 31, the outer wall of the connecting pipe between the Fischer-Tropsch wax outlet of the Fischer-Tropsch wax supply unit 10 and the Fischer-Tropsch wax inlet of the extraction tower 31, the outer wall of the connecting pipe between the inlet of the deoiled wax product collection tank 34 and the heavy component outlet of the extraction tower 31, and the outer wall of the connecting pipe between the extractant inlet of the extraction tower 31 and the heater 22; the jackets are insulated by circulating hot oil heating. This arrangement prevents the Fischer-Tropsch wax from solidifying in the Fischer-Tropsch wax deoiling system.

[0058] In a preferred embodiment, jackets are provided on the outer walls of the gas-liquid separator 32, the extractant supply unit 20, the connecting pipe between the light component outlet of the extraction tower 31 and the inlet of the gas-liquid separator 32, the connecting pipe between the oil component outlet of the gas-liquid separator 32 and the reflux material inlet of the extraction tower 31, the connecting pipe between the gaseous extractant outlet of the gas-liquid separator 32 and the inlet of the extractant supply unit 20, and the connecting pipe between the outlet of the extractant supply unit 20 and the inlet of the heater 22. Circulating refrigerant is used to keep the jackets cold.

[0059] To further improve the deoiling efficiency of Fischer-Tropsch wax, in one optional embodiment, the Fischer-Tropsch wax inlet is 4.5–25 m higher than the extractant inlet.

[0060] To prevent trace amounts of extractant from remaining in the oil component, in a preferred embodiment, the oil component collection tank 33 has an outlet at the bottom for collecting the degassed oil component, and an exhaust gas outlet at the top for removing residual extractant from the oil component. The exhaust gas outlet is connected to a conventional exhaust gas treatment system in the art to treat this portion of the exhaust gas. This is a method that those skilled in the art can implement according to their own process requirements, and will not be elaborated further here.

[0061] To prevent trace amounts of extractant from remaining in the deoiled wax product, in a preferred embodiment, the bottom of the deoiled wax product collection tank 34 has an outlet for collecting the degassed deoiled wax product, and the top of the deoiled wax product collection tank 34 has a tail gas outlet for removing residual extractant from the deoiled wax product. The tail gas outlet is connected to a conventional tail gas treatment system in the art for treating this part of the tail gas. This is a method that those skilled in the art can implement according to their own process requirements, and will not be described in detail here.

[0062] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0063] Test method:

[0064] Melting point: ASTM D3461.

[0065] Oil content: GBT 3554-200.

[0066] Penetration: ASTM D1321.

[0067] Yield: De-oiled Fischer-Tropsch wax product / Fischer-Tropsch wax raw material.

[0068] Example 1

[0069] Adopting such Figure 1 The Fischer-Tropsch wax deoiling system shown is used for deoiling. The specific process is as follows: Fischer-Tropsch wax of grade 50 (7.94 wt% oil content) is extracted by countercurrent contact with supercritical fluid ethane to dissolve the oil component in the wax and separate it from the wax. The extracted ethane containing the dissolved oil component undergoes gas-liquid separation to obtain liquid oil and gaseous ethane. 83.3 wt% of the liquid oil component is refluxed as feedstock for further extraction. The gaseous ethane after gas-liquid separation is cooled to liquefy ethane for reuse in extraction. Deoiling is completed when the deoiled wax product reaches the required oil content. The ratio of the total weight of supercritical fluid ethane to the total weight of Fischer-Tropsch wax is 20:1, the extraction temperature is 60℃, the extraction pressure is 10 MPa, and the gas-liquid separation temperature and pressure are 60℃ and 5 MPa.

[0070] The specific operation process of its Fischer-Tropsch wax degreasing system is as follows:

[0071] (1) Before the extraction process begins, gaseous ethane is used to pressurize the entire Fischer-Tropsch wax deoiling system to maintain the Fischer-Tropsch wax deoiling system at a pressure of 1 MPa. Gaseous ethane is introduced multiple times to replace the air, ensuring that there is no air in the entire Fischer-Tropsch wax deoiling system.

[0072] (2) Add molten 50# Fischer-Tropsch wax to the Fischer-Tropsch wax supply unit 10 for later use. The temperature of the Fischer-Tropsch wax control unit is controlled at 60°C. Add liquid ethane to the extractant supply unit 20 for later use. The temperature of the extractant supply unit is controlled at 30°C.

[0073] (3) After the system starts feeding, the Fischer-Tropsch wax transfer pump 11 is started to transport the molten 50# Fischer-Tropsch wax through the Fischer-Tropsch wax inlet of the extraction tower 31 to the top of the extraction tower 31. The extraction tower 31 is equipped with two sections of structured packing. The liquid ethane in the extractant supply unit 20 is transported to the first heater 22 through the extractant transfer pump 21. The first heater 22 heats the extractant to the same extraction temperature of 60°C as the extraction tower 31, and then it enters the bottom of the extraction tower 31 from the extractant inlet. The Fischer-Tropsch wax inlet is 9m higher than the extractant inlet.

[0074] (4) The ratio of the total weight of ethane to the total weight of 50# Fischer-Tropsch wax in the extraction tower 31 is controlled to be 10:1. The extraction temperature in the extraction tower 31 is controlled to be 60℃ and the extraction tower pressure is 10MPa, so that the liquid ethane is converted to a supercritical state. The supercritical fluid ethane and 50# Fischer-Tropsch wax are in countercurrent contact inside the extraction tower, and the oil components of small molecules of long-chain hydrocarbons in Fischer-Tropsch wax are separated from 50# Fischer-Tropsch wax, dissolved in supercritical fluid ethane, and flow out from the light component outlet of the extraction tower 31.

[0075] (5) The ethane containing dissolved oil components flowing out of the light component outlet of the extraction tower 31 passes through the pressure regulating valve, which adjusts the pressure to reduce it to 5 MPa. As a result, the solubility of ethane decreases, and the oil components precipitate out of the ethane. The precipitated oil components and ethane enter the gas-liquid separator 32 for separation. The gaseous ethane flows out of the gaseous extractant outlet of the gas-liquid separator 32, is condensed into liquid by the cooler 37, and then enters the extractant supply unit 20.

[0076] (6) 83.3 wt% of the oil component flowing out from the oil component outlet of the gas-liquid separator 32 is returned to the reflux cooler 35 for cooling. After its temperature is reduced to the same extraction temperature of 60°C as the extraction tower, it enters the extraction tower 31 again through the reflux feed inlet of the extraction tower 31 via the reflux transfer pump 36 to participate in extraction again. The feed temperature of the reflux transfer pump 36 is lower than the bubble point of the oil component to prevent cavitation of the reflux transfer pump 36. The remaining oil component that is not returned flows into the oil component collection tank 33. The second heater in the oil component collection tank 33 heats the oil component, causing the residual ethane in the oil component to be released through the tail gas outlet of the oil component collection tank 33 and enter the tail gas treatment system. The degassed oil component flows out from the bottom outlet of the oil component collection tank 33 for collection.

[0077] (7) The deoiled wax product enters the deoiled wax product collection tank 34 from the heavy component outlet of the extraction tower 31. The second heater in the deoiled wax product collection tank 34 heats the product, causing the residual ethane in the deoiled wax product to be released through the tail gas outlet of the deoiled wax product collection tank 34 and enter the tail gas treatment system. The degassed deoiled wax product flows out from the bottom outlet of the deoiled wax product collection tank 34 for collection.

[0078] Example 2

[0079] The only difference from Example 1 is that the Fischer-Tropsch wax used is grade 60# Fischer-Tropsch wax (oil content of 3.71 wt%), the extraction temperature is 65°C, and the extraction pressure is 15 MPa.

[0080] Example 3

[0081] The only difference from Example 1 is that the Fischer-Tropsch wax used is grade 70# Fischer-Tropsch wax (oil content of 2.24 wt%), the extraction temperature is 70°C, and the extraction pressure is 20 MPa.

[0082] Melting point, oil content, and penetration were tested for Examples 1 to 3. The test results are shown in Table 1.

[0083] Table 1

[0084]

[0085] Example 4

[0086] The only difference from Example 1 is that the extraction temperature is 40°C.

[0087] Example 5

[0088] The only difference from Example 1 is that the extraction temperature is 50°C.

[0089] Example 6

[0090] The only difference from Example 1 is that the extraction temperature is 70°C.

[0091] Example 7

[0092] The only difference from Example 1 is that the extraction temperature is 80°C.

[0093] Melting point, oil content, and penetration were tested for Examples 4 to 7. The test results are shown in Table 2.

[0094] Table 2

[0095]

[0096] Example 8

[0097] The only difference from Example 1 is that the extraction pressure is 5 MPa.

[0098] Example 9

[0099] The only difference from Example 1 is that the extraction pressure is 15 MPa.

[0100] Example 10

[0101] The only difference from Example 1 is that the extraction pressure is 20 MPa.

[0102] Melting point, oil content, and penetration were tested for Examples 8 to 10. The test results are shown in Table 3.

[0103] Table 3

[0104]

[0105] Example 11

[0106] Adopting such Figure 2 The Fischer-Tropsch wax deoiling system shown differs from Example 1 only in that the ethane extractant containing the oil component after extraction is subjected to gas-liquid separation to obtain liquid oil component and gaseous ethane respectively; the liquid oil component will not be refluxed but directly collected to complete the deoiling process.

[0107] Example 12

[0108] The only difference from Example 1 is that 75 wt% of the liquid oil component obtained after gas separation is refluxed as raw material and used again for extraction.

[0109] Example 13

[0110] The only difference from Example 1 is that 80 wt% of the liquid oil component obtained after gas separation is refluxed as raw material and used again for extraction.

[0111] Example 14

[0112] The only difference from Example 1 is that 85.7 wt% of the liquid oil component obtained after gas separation is refluxed as raw material and used again for extraction.

[0113] Melting point, oil content, and penetration were tested for Examples 11 to 14. The test results are shown in Table 4.

[0114] Table 4

[0115]

[0116] Example 15

[0117] The only difference from Example 1 is that, during the extraction process, the total weight ratio of the supercritical fluid ethane to the total weight of Fischer-Tropsch wax is 2:1.

[0118] Example 16

[0119] The only difference from Example 1 is that, during the extraction process, the total weight ratio of supercritical fluid ethane to the total weight of Fischer-Tropsch wax is 5:1.

[0120] Example 17

[0121] The only difference from Example 1 is that, during the extraction process, the total weight ratio of the supercritical fluid ethane to the total weight of Fischer-Tropsch wax is 50:1.

[0122] Example 18

[0123] The only difference from Example 1 is that, during the extraction process, the total weight ratio of the supercritical fluid ethane to the total weight of Fischer-Tropsch wax is 80:1.

[0124] Melting point, oil content, and penetration were tested for Examples 15 to 18. The test results are shown in Table 5.

[0125] Table 5

[0126]

[0127] Example 19

[0128] The only difference from Example 1 is that the extractant is supercritical fluid propane, and the extraction temperature is 60°C and the extraction pressure is 15 MPa.

[0129] Example 20

[0130] The only difference from Example 1 is that the extractant is supercritical fluid carbon dioxide, and the extraction temperature is 60°C and the extraction pressure is 20 MPa.

[0131] Example 21

[0132] The only difference from Example 1 is that the extractant is supercritical fluid propylene, the extraction temperature is 60°C, and the extraction pressure is 20 MPa.

[0133] Melting point, oil content, and penetration were tested for Examples 19 to 21. The test results are shown in Table 6.

[0134] Table 6

[0135]

[0136]

[0137] Comparative Example 1

[0138] The solvent deoiling process was used to deoil 50# Fischer-Tropsch wax. The specific process steps were as follows: the deoiling solvent methyl isobutyl ketone and 50# Fischer-Tropsch wax (oil content of 7.94 wt%) were mixed at a solvent-wax weight ratio of 1:1 for liquid-liquid extraction (extraction temperature of 50℃ and extraction pressure of atmospheric pressure). The mixture of 50# Fischer-Tropsch wax and deoiling solvent after full contact with the extraction was cooled and crystallized (crystallization temperature of -20℃). Then, the wax paste and filtrate were separated by vacuum filtration to finally obtain the deoiled wax product.

[0139] Comparative Example 2

[0140] The only difference from Example 1 is that the extractant in the extraction tower is gaseous ethane, and the extraction temperature is 100°C and the pressure is 1 MPa.

[0141] Comparative Example 3

[0142] The only difference from Example 1 is that 50# Fischer-Tropsch wax is replaced with 52# petroleum wax (with an oil content of 9.74 wt% and a main component of more than 90% isoparaffins).

[0143] Melting point, oil content, and penetration were tested for comparative examples 1 to 3. The test results are shown in Table 7.

[0144] Table 7

[0145]

[0146] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: 1. The Fischer-Tropsch wax deoiling method of the present invention has advantages such as strong dissolving ability, high selectivity, and fast mass transfer rate, which can efficiently remove oil components from Fischer-Tropsch wax, and is simple to operate and has low production cost; 2. The Fischer-Tropsch wax deoiling method of the present invention is relatively clean and environmentally friendly. Since the entire process does not use easily carcinogenic substances such as toluene and methyl ethyl ketone, and the supercritical fluid extractant is easily converted into a gaseous state, it is easy to separate from the liquid oil components. The product basically does not contain supercritical extraction solvent, preventing the residue of substances harmful to the human body during the extraction and separation process; 3. The present invention The present invention selects ethane, propane, propylene, and carbon dioxide as raw materials for supercritical fluid extractants. These materials are inexpensive, have high purity, are easy to produce, and can be repeatedly recycled in production, thereby effectively reducing production costs. 4. The Fischer-Tropsch wax deoiling method of the present invention combines the extraction and separation processes into one, which is simple, easy to operate, and has a fast extraction speed and high deoiling efficiency. When the saturated extractant containing the oil components in the Fischer-Tropsch wax undergoes gas-liquid separation, the pressure drops, and the extractant and oil components quickly separate into two phases of gas-liquid separation. This not only results in high extraction efficiency but also low energy consumption, improving production efficiency and reducing production costs.

[0147] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for deoiling Fischer-Tropsch wax having a melting point of 50 to 80°C and an oil content of 1 to 9 wt%, characterized by, The Fischer-Tropsch wax deoiling method comprises: extracting the Fischer-Tropsch wax by contacting the Fischer-Tropsch wax with an extractant having a supercritical fluid state, so that the oil component in the Fischer-Tropsch wax is dissolved in the extractant and separated from the Fischer-Tropsch wax, and deoiling is completed; wherein the extractant is selected from one or more of supercritical fluid ethane, supercritical fluid propane, supercritical fluid carbon dioxide or supercritical fluid propylene; when the extractant is selected from supercritical fluid ethane, the extraction temperature is 40-90℃, and the extraction pressure is 5-20MPa; when the extractant is selected from supercritical fluid propane, the extraction temperature is 50-80℃, and the extraction pressure is 10-20MPa; when the extractant is selected from supercritical fluid carbon dioxide, the extraction temperature is 50-90℃, and the extraction pressure is 10-30MPa; when the extractant is selected from supercritical fluid propylene, the extraction temperature is 30-60℃, and the extraction pressure is 10-25MPa; after the extraction, the Fischer-Tropsch wax deoiling method further comprises: gas-liquid separation of the extractant in which the oil component is dissolved, to obtain liquid oil component and gaseous extractant respectively; and refluxing 33-89wt% of the liquid oil component as raw material to participate in the extraction again.

2. The method of dewaxing Fischer-Tropsch wax according to claim 1, characterized in that, The Fischer-Tropsch wax is selected from one or more of 50#, 60# or 70# Fischer-Tropsch wax.

3. The method according to claim 1 or 2, c h a r a c t e r i z e d in that The ratio of the total weight of the extractant to the total weight of the Fischer-Tropsch wax is 5-50:

1.

4. The method of dewaxing a Fischer-Tropsch wax according to claim 3, wherein, The ratio of the total weight of the extractant to the total weight of the Fischer-Tropsch wax is 10-30:

1.

5. The Fischer-Tropsch wax deoiling method according to claim 1, wherein the temperature of the gas-liquid separation is 50-90℃, and the pressure of the gas-liquid separation is 3-20MPa.

6. The method of dewaxing a Fischer-Tropsch wax according to claim 5, wherein, after the gas-liquid separation, the Fischer-Tropsch wax deoiling method further comprises: cooling the gaseous extractant to change it into liquid extractant to be recycled as regenerated extractant to participate in the extraction again.

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