Liquid extraction process for increasing wax melting point by using supercritical CO2

Abstract

The invention discloses a liquid extraction process for increasing the melting point of wax by using supercritical CO2. The liquid extraction process comprises the following steps: filling low-melting-point solid wax into an extraction kettle and melting the low-melting-point solid wax into liquid wax; cO2 supercritical fluid is input from the bottom of the extraction kettle, the CO2 supercritical fluid which is fully fused with liquid wax carries extracted wax oil, part of wax, water and other impurities to overflow and enter a three-stage separation kettle, different substances are separated out step by step, and CO2 in closed circulation is subjected to mass transfer extraction separation in the phase change process of the liquid state, the supercritical fluid and the gas state; the melting point of the high-melting-point liquid wax is 115-125 DEG C. The invention provides a liquid extraction process capable of improving the purity and melting point of the low-melting-point wax, the raw material source is wide, the cost is low, large-scale production is easy to realize, the yield is high, the produced high-melting-point wax has high additional value, the industrial pain point is solved, the economic benefit is considerable, and the liquid extraction process has practical significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of extraction, and particularly relates to a purification extraction process, specifically a liquid extraction process for increasing the melting point of wax by using supercritical CO2. Background Art

[0002] Wax with a high melting point can improve the heat resistance and quick-drying property of adhesives, and is mainly applied in fields such as plastic processing, bright wax, textile auxiliaries, hot melt adhesives, inks, coatings, food, and cosmetics, with broad market prospects.

[0003] Fischer-Tropsch wax is an alkane polymer synthesized from hydrocarbon-based syngas or natural gas, mainly relying on high-quality and inexpensive raw materials in coal chemical industry for iron-based or cobalt-based synthesis, having a relatively obvious price advantage compared with crude oil wax. Taking the wax oil produced by a coal-to-oil plant as the raw material, it is easy to obtain Fischer-Tropsch wax products with different low melting points such as 52 °C, 60 °C, 70 °C, etc. by the Fischer-Tropsch process. To obtain Fischer-Tropsch wax with a high melting point, further processing is still required. However, high-melting-point Fischer-Tropsch wax needs to be imported in large quantities.

[0004] The existing technical solutions for increasing the melting point of Fischer-Tropsch wax are as follows: 1. Mixing high-melting-point organic compounds: Mixing beeswax with polyethylene materials, and melting and mixing them at high temperature can significantly increase the melting point of beeswax. After mixing, it affects the purity of the wax, resulting in limitations for high-end applications such as food, cosmetics, and aerospace.

[0005] 2. Adding rosin: Adding rosin to paraffin wax can effectively increase its melting point. Rosin is a common additive that can significantly increase the melting point of paraffin wax to about 90 °C. This method has limited effect on increasing the melting point of Fischer-Tropsch wax.

[0006] 3. Using a nucleating agent: For polyethylene wax, its melting point can be increased by adding a nucleating agent and performing recrystallization treatment. This method also affects the purity of Fischer-Tropsch wax and has a high cost.

[0007] 4. Adding high-melting-point additives: In various waxes such as adhesive wax, repair wax, and precision casting wax, high-melting-point additives such as carnauba wax and montan wax can be added to increase their melting point. In addition, adding a small amount of metal oxides, hydroxides, or carbonates can also increase the melting point of wax. This method makes the composition of Fischer-Tropsch wax complex and has an even higher cost.

[0008] 5. Using stearic acid: Stearic acid can increase the melting point and hardness of candles, usually with an addition amount between 5% and 20%. This method has limited effect on increasing the melting point of Fischer-Tropsch wax and changes the composition of Fischer-Tropsch wax, resulting in limited use.

[0009] The above technical solution for increasing the melting point of Fischer-Tropsch wax can be used in general application scenarios, but it is difficult to achieve an ideal effect of increasing the melting point, difficult to be applied in scenarios with higher melting points, and difficult to create higher economic value. Summary of the Invention

[0010] The object of the present invention is to provide a liquid extraction process using supercritical CO2 to increase the melting point of wax in view of the problems existing in the prior art; this liquid extraction process can not only increase the purity and melting point of low-melting-point Fischer-Tropsch wax, but also generally increase the purity and melting point of other low-melting-point waxes.

[0011] The object of the present invention is solved by the following technical solutions: A liquid extraction process using supercritical CO2 to increase the melting point of wax, characterized in that the steps of this liquid extraction process are as follows: A. Load low-melting-point solid wax into the extraction kettle, close the feed valve, start the stirrer and heat the extraction kettle at the same time to melt the solid wax into liquid wax; B. Open the superfluid input valve at the bottom of the extraction kettle and input CO2 supercritical fluid from the bottom of the extraction kettle; C. After the pressure in the extraction kettle reaches 33 MPa to 35 MPa, open the extraction throttle valve, and the CO2 supercritical fluid fully integrated with the liquid wax in the extraction kettle carries the extracted wax oil, as well as part of the wax, water and other impurities and overflows into the lower part of the first separation kettle at a temperature of 105 °C to 115 °C; D. After the pressure in the first separation kettle reaches 10 MPa to 11 MPa, open the first separation throttle valve, and the CO2 supercritical fluid carries wax oil, water and other impurities and overflows into the lower part of the second separation kettle at a temperature of 65 °C to 70 °C; E. After the pressure in the second separation kettle reaches 7.8 MPa to 8.5 MPa, open the second separation throttle valve, and the CO2 supercritical fluid carries water and other impurities and overflows into the lower part of the third separation kettle at a temperature of 22 °C to 25 °C; F. After the pressure in the third separation kettle reaches 5.5 MPa to 6 MPa, open the third separation throttle valve, and the gaseous CO2 overflows and enters the gaseous CO2 purifier for purification; G. The purified gaseous CO2 is condensed into liquid CO2 by a condenser and then returned to the liquid CO2 storage tank. The liquid CO2 is pressurized by a booster pump and heated by a heater to become CO2 supercritical fluid and is input from the bottom into the extraction kettle; H. The CO2 supercritical fluid fully integrated with the liquid wax in the extraction kettle carries the extracted wax oil, as well as part of the wax, water and other impurities and overflows into the lower part of the first separation kettle at a temperature of 105 °C to 115 °C and a pressure of 10 MPa to 11 MPa; I. The CO2 supercritical fluid in the first separation kettle overflows, carrying wax oil, water and other impurities, into the lower part of the second separation kettle with a temperature of 65°C to 70°C and a pressure of 7.8 MPa to 8.5 MPa; J. The CO2 supercritical fluid in the second separation kettle overflows, carrying water and other impurities, into the lower part of the third separation kettle with a temperature of 22°C to 25°C and a pressure of 5.5 MPa to 6 MPa; K. The gaseous CO2 in the third separation kettle overflows and enters the gaseous CO2 purifier for purification, then enters step G; L. Continuously execute steps G to K in a cycle for 1 h to 3 h for continuous cyclic liquid extraction, and then enter step M; M. Close the superfluid input valve at the bottom of the extraction kettle, the booster pump and the heater. When the pressures in the extraction kettle, the first separation kettle, the second separation kettle and the third separation kettle are close to that of the liquid CO2 storage tank, start the gas recovery compressor to reduce the pressures in the extraction kettle, the first separation kettle, the second separation kettle and the third separation kettle to atmospheric pressure, and then close the third separation throttle valve and the liquid CO2 storage tank return valve, and enter step N; N. Open the extraction discharge valve at the bottom of the extraction kettle to obtain high-melting-point liquid wax with a melting point of 115°C to 125°C, open the first separation discharge valve at the bottom of the first separation kettle to obtain low-melting-point liquid wax, open the second separation discharge valve at the bottom of the second separation kettle to obtain wax oil, and open the third separation discharge valve at the bottom of the third separation kettle to obtain water and other impurities.

[0012] The melting point of the low-melting-point solid wax in step A is <80°C; the oil content of the low-melting-point solid wax in step A is not less than 1%; the loading amount of the extraction kettle is 80% to 86% of its volume.

[0013] The oil content of the high-melting-point liquid wax in step N is not more than 0.1%, and the yield of the high-melting-point liquid wax in step N is 75% to 85%.

[0014] The low-melting-point liquid wax in step N can be used as a raw material again and added to the extraction kettle for the supercritical CO2 liquid extraction process.

[0015] In step N, the stirrer is closed before opening the extraction discharge valve or after the discharging is completed.

[0016] The set temperature of the extraction kettle is 125°C to 130°C.

[0017] The heating equipment on the extraction kettle includes an extraction internal heating coil and an extraction external heating jacket. The heating media of both the extraction internal heating coil and the extraction external heating jacket are thermal oil, and the thermal oil is respectively input from the bottom and output from the top of the extraction internal heating coil and the extraction external heating jacket.

[0018] The heating equipment on the first separation kettle includes a separation internal heating coil and a separation external heating jacket. The heating mediums of the separation internal heating coil and the separation external heating jacket are both heat-conducting oil, and the heat-conducting oil is respectively input from the bottom and output from the top of the separation internal heating coil and the separation external heating jacket.

[0019] The heating equipment on the second separation kettle is an external constant-temperature jacket. The heat-insulating medium used in the external constant-temperature jacket is constant-temperature water, and the constant-temperature water is input from the bottom and output from the top of the external constant-temperature jacket.

[0020] The heating equipment on the third separation kettle is an external cooling jacket. The cooling medium used in the external cooling jacket is cooling water, and the cooling water is input from the bottom and output from the top of the external cooling jacket.

[0021] Temperature sensors and pressure sensors are respectively arranged on the extraction kettle, the first separation kettle, the second separation kettle, and the third separation kettle.

[0022] To improve production efficiency, 2 or more extraction kettles can be set. The extraction kettles are arranged in parallel relative to the separation kettles, or multiple pairs of extraction kettles and separation kettles are arranged in parallel.

[0023] For example, if double extraction kettles or triple extraction kettles arranged in parallel are respectively connected to the three subsequent series-connected separation kettles, then during the cyclic extraction of one extraction kettle, the other extraction kettles can be loaded and unloaded, realizing continuous extraction and separation, which can greatly improve production efficiency and is suitable for industrialized and large-scale production.

[0024] The low-melting-point solid wax in step A includes animal wax, plant wax, mineral wax, synthetic wax, etc. Among them, animal wax includes beeswax, insect white wax, Sichuan wax, spermaceti wax, etc. These waxes usually come from animal secretions or tissues; plant waxes such as carnauba wax, coconut wax, soybean wax, etc. These waxes are mainly extracted from plants and have natural plant characteristics; mineral waxes such as paraffin wax, montan wax, etc. Mineral waxes are usually obtained through petroleum refining or mineral processing, such as Fischer-Tropsch wax; synthetic waxes include polyethylene wax (PE wax), polypropylene wax (PP wax), etc. These waxes are obtained through chemical synthesis and have specific physical and chemical properties.

[0025] Principle of supercritical CO2 extraction: Liquid CO2 is pressurized by a booster pump to exceed the critical pressure of 7.39 Mpa and then heated by a heater to exceed the critical temperature of 31.2 °C. The liquid CO2 will turn into a CO2 supercritical fluid. The CO2 supercritical fluid has great penetrability, solubility and mass transfer ability for oils and fats. The oils and fats in the extraction kettle will be carried by the CO2 supercritical fluid to the separation kettle for decompression separation. The CO2 supercritical fluid will turn into ordinary gaseous CO2 and overflow, while the carried oils and fats will be left in the separation kettle. The gaseous CO2 returns to the liquid CO2 storage tank through cooling and liquefaction, and then is pressurized by the booster pump and heated by the heater for recycling. Among them, CO2 is just a chemically stable medium that conducts mass transfer during the phase change process from liquid, superfluid to gas, so as to achieve the purpose of extraction and separation.

[0026] Characteristics of supercritical CO2 extraction: No residual solvent: Since CO2 is used as the extractant, no other organic solvents are required in the whole process. Therefore, there will be no harmful solvents remaining in the extract, ensuring the naturalness of the product. Environmentally friendly: CO2 is stable, non-toxic, non-flammable and does not pollute the environment during the extraction process, and can avoid the oxidation of the product. It is an environmentally friendly extraction method. High extraction efficiency: During the supercritical CO2 extraction process, extraction and separation are combined into one. When the saturated CO2 supercritical fluid of the dissolved substance enters the separator, due to the decrease in pressure or the change in temperature, CO2 and the extract quickly become two phases (gas-liquid separation). Not only is the extraction efficiency high, but also the energy consumption is less, improving the production efficiency. Simple process: Both pressure and temperature can be used as parameters to adjust the extraction process. By changing the temperature and pressure, the purpose of extraction can be achieved. The process is simple and easy to master, and the extraction speed is fast. Wide application range: Supercritical CO2 extraction is applicable to a variety of substances, including high-boiling point, low-volatility, easily pyrolyzed substances, and the separation of natural substances. It is especially suitable for the extraction and purification of biological, food, cosmetic and pharmaceutical products, etc. Recyclable: CO2 can be recycled repeatedly in production, effectively reducing costs.

[0027] The biggest feature of the liquid extraction process for increasing the melting point of wax provided by the present invention is liquid supercritical CO2 extraction. Why not use solid supercritical CO2 extraction? Because the most important part of supercritical CO2 extraction is the pretreatment of the extraction raw materials. Due to the limitations of the energy and penetration power of the CO2 supercritical fluid, the particle size of the raw materials is usually optimally 40-60 mesh (0.25-0.4 mm). The particle size of the finished product of Fischer-Tropsch wax is greater than 5 mm, which is not conducive to extraction. Attempting to crush the finished product into powder, it is found that the powder is prone to sticking and agglomerating, and the melting point of the wax is relatively low, and it is more likely to stick at a temperature exceeding 31.2 °C in the CO2 supercritical fluid. Considering that the melting point of the raw material wax is not high (generally not more than 80 °C), the liquid supercritical CO2 extraction method is therefore used to extract the residual oil in the wax. The present invention has the following advantages compared with the prior art: Based on the current situation in the industry that low-melting-point wax is easy to produce, high-melting-point wax is difficult to produce due to process problems, and the market demand for high-melting-point wax is strong (especially for high-end demands such as aerospace), the liquid extraction process for increasing the melting point of wax provided by the present invention provides a liquid extraction process that can improve the purity and melting point of low-melting-point wax. The liquid extraction process has a high yield and is easy to achieve large-scale production, not only solving the pain points of the industry, but also having considerable economic benefits, and has practical significance.

[0028] The raw material of the liquid extraction process for increasing the melting point of wax provided by the present invention uses low-melting-point wax. The raw material source is wide and the cost is low. Since the yield is high enough and the high-melting-point wax produced has high added value, it is suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Appendix Figure 1 is a schematic diagram of a liquid extraction process for increasing the melting point of wax using supercritical CO2 provided by the present invention.

[0030] Wherein: 1 - liquid CO2 storage tank; 2 - booster pump; 3 - heater; 4 - extraction kettle; 40 - top feed port; 41 - stirrer; 42 - internal heating coil for extraction; 43 - external heating jacket for extraction; 44 - superfluid input valve; 45 - extraction discharge valve; 46 - extraction throttle valve; 5 - first separation kettle; 50 - internal heating coil for separation; 51 - external heating jacket for separation; 52 - first separation throttle valve; 6 - second separation kettle; 60 - external constant temperature jacket; 61 - second separation throttle valve; 7 - third separation kettle; 70 - external cooling jacket; 71 - third separation throttle valve; 8 - gaseous CO2 purifier; 9 - condenser. DETAILED DESCRIPTION OF THE INVENTION

[0031] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. Like reference numerals in the figures denote like or similar structures, and thus their detailed description will be omitted.

[0032] The terms "a", "an", "the", and "said" are used to denote the presence of one or more elements / components / etc.; the terms "comprising" and "having" are used to mean an open inclusion and mean that there may be additional elements / components / etc. in addition to the listed elements / components / etc.

[0033] As Figure 1 shown in the schematic diagram of a liquid extraction process for increasing the melting point of wax using supercritical CO2, which includes a liquid CO2 storage tank 1, a booster pump 2, a heater 3, an extraction kettle 4, a first separation kettle 5, a second separation kettle 6, a third separation kettle 7, a gaseous CO2 purifier 8, a condenser 9, and a gas recovery compressor. The liquid CO2 storage tank 1 is connected to the heater 3 through a pipeline with a valve and a booster pump 2. The heater 3 is connected to the bottom of the extraction kettle 4 through a superfluid input pipe. The gas outlet at the shoulder of the extraction kettle 4 is connected to the first separation kettle 5 through a CO2 supercritical fluid overflow pipe equipped with an extraction throttle valve 46. The gas outlet at the shoulder of the first separation kettle 5 is connected to the second separation kettle 6 through a CO2 supercritical fluid overflow pipe equipped with a first separation throttle valve 52. The gas outlet at the shoulder of the second separation kettle 6 is connected to the third separation kettle 7 through a CO2 supercritical fluid overflow pipe equipped with a second separation throttle valve 61. The gas outlet at the shoulder of the third separation kettle 7 is connected to the gaseous CO2 purifier 8 through a pipeline equipped with a third separation throttle valve 71. The gaseous CO2 purifier 8 is connected to the liquid CO2 storage tank 1 through the condenser 9, and all the devices will form a CO2 operation loop. The gas recovery compressor is arranged on the pipeline between the third separation throttle valve 71 and the liquid CO2 storage tank return valve (located on the pipeline connecting the condenser 9 and the liquid CO2 storage tank 1).

[0034] Specifically, a stirrer 41, an internal extraction heating coil 42, an external extraction heating jacket 43, a temperature sensor and a pressure sensor are assembled on the extraction kettle 4. A feed valve is arranged on the feed pipe communicating with one side of the stirrer 41 and the top feed port 40, and an extraction throttle valve 46 is installed on the CO2 supercritical fluid overflow pipe on the other side. An extraction discharge valve 45 is arranged on the bottom discharge pipe of the extraction kettle 4, and a superfluid input valve 44 is arranged on the superfluid input pipe arranged at the bottom of the extraction kettle 4; the heating media of the internal extraction heating coil 42 and the external extraction heating jacket 43 are both heat-conducting oil, and the heat-conducting oil is respectively input from the bottom and output from the top of the internal extraction heating coil 42 and the external extraction heating jacket 43. The internal extraction heating coil 42 and the external extraction heating jacket 43 can cooperate to stably heat the substances in the extraction kettle 4 to 125°C to 130°C, and the pressure in the extraction kettle 4 can reach 33 MPa to 35 MPa under the loading of the CO2 supercritical fluid; the temperature sensor and the pressure sensor are used to monitor the temperature and pressure of the extraction kettle 4 in real time and give real-time feedback. A separation internal heating coil 50, a separation external heating jacket 51, a temperature sensor and a pressure sensor are assembled on the first separation kettle 5. The heating media of the separation internal heating coil 50 and the separation external heating jacket 51 are both heat-conducting oil, and the heat-conducting oil is respectively input from the bottom and output from the top of the separation internal heating coil 50 and the separation external heating jacket 51. The separation internal heating coil 50 and the separation external heating jacket 51 can cooperate to keep the temperature of the substances in the first separation kettle 5 at 105°C to 115°C, and the pressure in the first separation kettle 5 can be kept at 10 MPa to 11 MPa under the control of the extraction throttle valve 46; the CO2 supercritical fluid overflow pipe equipped with the extraction throttle valve 46 is inserted from the top of the first separation kettle 5 and extends downward into the lower part of the inner cavity of the first separation kettle 5, and a first separation throttle valve 52 is installed on the CO2 supercritical fluid overflow pipe arranged at the shoulder of the first separation kettle 5; a discharge pipe with a first separation discharge valve is arranged at the bottom of the first separation kettle 5; the temperature sensor and the pressure sensor are used to monitor the temperature and pressure of the first separation kettle 5 in real time and give real-time feedback. An external constant temperature jacket 60, a temperature sensor and a pressure sensor are assembled on the second separation kettle 6. The external constant temperature jacket 60 can keep the temperature of the substances in the second separation kettle 6 at 65°C to 70°C, and the pressure in the second separation kettle 6 can be kept at 7.8 MPa to 8.5 MPa under the control of the first separation throttle valve 52; the CO2 supercritical fluid overflow pipe equipped with the first separation throttle valve 52 is inserted from the top of the second separation kettle 6 and extends downward into the lower part of the inner cavity of the second separation kettle 6, and a second separation throttle valve 61 is installed on the CO2 supercritical fluid overflow pipe arranged at the shoulder of the second separation kettle 6; a discharge pipe with a second separation discharge valve is arranged at the bottom of the second separation kettle 6; the temperature sensor and the pressure sensor are used to monitor the temperature and pressure of the second separation kettle 6 in real time and give real-time feedback.The third separation kettle 7 is equipped with an external cooling jacket 70, a temperature sensor and a pressure sensor. The external cooling jacket 70 can cool the temperature of the substances in the third separation kettle 7 to 22°C - 25°C, and the pressure in the third separation kettle 7 can be maintained at 5.5 MPa - 6 MPa under the control of the second separation throttle valve 61; the CO2 supercritical fluid overflow pipe equipped with the second separation throttle valve 61 is inserted from the top of the third separation kettle 7 and extends downward into the lower part of the inner cavity of the third separation kettle 7, and a third separation throttle valve 71 is installed on the pipeline arranged at the shoulder of the third separation kettle 7; a discharge pipe with a third separation discharge valve is arranged at the bottom of the third separation kettle 7; the temperature sensor and the pressure sensor are used to monitor the temperature and pressure of the third separation kettle 7 in real time and give real-time feedback.

[0035] Since the electronic structure in the chemical formula of CO2 is symmetric, CO2 is a non-polar solvent as a solvent, and wax and oil are also non-polar. According to the principle that substances with the same polarity are soluble, when extracting oil with supercritical CO2, part of the wax will also be carried out at the same time. After the extraction process, most of the high-purity wax (i.e., high-melting-point wax, remaining in the extraction kettle 4) and wax with a large oil content (i.e., low-melting-point wax, remaining in the first separation kettle 5) will be obtained. The wax with a large oil content can be continuously added to the extraction kettle 4 for supercritical CO2 extraction; the low-melting-point wax separated in the first separation kettle 5 is discharged from its lower discharge port; since the volatilization temperature of wax oil is about 350°C, the wax oil left in the second separation kettle 6 can be discharged from its lower discharge port; CO2 is in a common gaseous state in the third separation kettle 7, and water and other impurities are left in the third separation kettle 7 and can be discharged from its lower discharge port at the lower outlet.

[0036] Since the solubility saturation of supercritical CO2 for wax is smaller than that for wax oil, for example, the wax oil content in Fischer-Tropsch wax is small (the oil content of Fischer-Tropsch wax with a melting point of 60°C is about 2.5%). After supercritical CO2 extraction, the oil content of the wax is reduced to 0.1%, the melting point can be increased to 115°C - 125°C, and the one-time charging yield can reach 75 - 85%. Embodiment

[0037] A liquid extraction process for increasing the melting point of wax by using supercritical CO2 is characterized in that the steps of the liquid extraction process are as follows: A. Open the feed valve at the top of the extraction kettle 4, load the solid Fischer-Tropsch wax with a melting point of 60°C into the extraction kettle 4 from the top feed port 40, measure the volume of the Fischer-Tropsch wax, load it to 85% of the volume of the extraction kettle 4, close the feed valve, set the working temperature of the extraction kettle 4 to 130°C, turn on the heat conduction oil oil pump of the extraction internal heating coil 42 and the extraction external heating jacket 43 for heating, and at the same time start the stirrer 41, and then wait for the solid Fischer-Tropsch wax in the extraction kettle 4 to melt into liquid Fischer-Tropsch wax; B. After the solid Fischer-Tropsch wax in the extraction kettle 4 melts into liquid Fischer-Tropsch wax, start the booster pump 2, the heater 3 and the corresponding multiple valves. The liquid CO2 is pressurized by the booster pump 2 and heated by the heater 3 from the liquid CO2 storage tank 1 into a CO2 supercritical fluid (which can also be abbreviated as: superfluid). The CO2 supercritical fluid enters from the bottom of the extraction kettle 4 through the superfluid input valve 44; C. After the pressure in the extraction kettle 4 reaches 35 MPa, open the extraction throttle valve 46. Due to the built-in stirrer 41, the CO2 supercritical fluid fully mixed with the liquid wax in the extraction kettle 4 carries the extracted wax oil, as well as part of the wax, water and other impurities and overflows from the top of the extraction kettle 4 into the lower part of the first separation kettle 5 at a temperature of 115°C; D. The pressure of the first separation kettle 5 is regulated by the extraction throttle valve 46. After the pressure in the first separation kettle 5 reaches 10.6 MPa, open the first separation throttle valve 52. The CO2 supercritical fluid in the first separation kettle 5 carrying wax oil, water and other impurities continues to overflow into the lower part of the second separation kettle 6 at a temperature of 70°C; E. The pressure of the second separation kettle 6 is regulated by the first separation throttle valve 52. After the pressure in the second separation kettle 6 reaches 8 MPa, open the second separation throttle valve 61. The CO2 supercritical fluid in the second separation kettle 6 carrying water and other impurities continues to overflow into the lower part of the third separation kettle 7 at a temperature of 22°C; F. The pressure of the third separation kettle 7 is regulated by the second separation throttle valve 61. After the pressure in the third separation kettle 7 reaches 5.6 MPa, open the third separation throttle valve 71. The gaseous CO2 in the third separation kettle 7 overflows and enters the gaseous CO2 purifier 8 for purification; G. The purified gaseous CO2 is condensed into liquid CO2 by the condenser 9 and then returns to the liquid CO2 storage tank 1. The liquid CO2 is pressurized by the booster pump 2 and heated by the heater 3 into a CO2 supercritical fluid and is input from the bottom into the extraction kettle 4 with a pressure of 35 MPa and a temperature of 130°C; H. The CO2 supercritical fluid fully mixed with the liquid wax in the extraction kettle 4 carries the extracted wax oil, as well as part of the wax, water and other impurities and overflows into the lower part of the first separation kettle 5 at a temperature of 115°C and a pressure of 10.6 MPa; I. The CO2 supercritical fluid in the first separation kettle 5 carrying wax oil, water and other impurities continues to overflow into the lower part of the second separation kettle 6 at a temperature of 70°C and a pressure of 8 MPa; J. The CO2 supercritical fluid in the second separation kettle 6 carrying water and other impurities continues to overflow into the lower part of the third separation kettle 7 at a temperature of 22°C and a pressure of 5.6 MPa; K. The gaseous CO2 in the third separation kettle 7 overflows and enters the gaseous CO2 purifier 8 for purification, entering step G; L. Execute steps G to K in a loop for continuous cyclic liquid extraction for 2.5 h, and then proceed to step M; M. Close the superfluid input valve 44 at the bottom of the extraction kettle 4, turn off the booster pump 5 and the heater 6. When the pressures in the extraction kettle 4, the first separation kettle 5, the second separation kettle 6, and the third separation kettle 7 are close to that of the liquid CO₂ storage tank 1, start the gas recovery compressor to reduce the pressures in the extraction kettle 4, the first separation kettle 5, the second separation kettle 6, and the third separation kettle 7 to atmospheric pressure. Then close the third separation throttle valve 71 and the liquid CO₂ storage tank liquid return valve, and proceed to step N; N. Open the extraction discharge valve 45 at the bottom of the extraction kettle 4 to obtain high-melting-point liquid Fischer-Tropsch wax with a melting point of 115°C (oil content reduced to 0.1%). Open the first separation discharge valve at the bottom of the first separation kettle 5 to obtain low-melting-point liquid Fischer-Tropsch wax. Open the second separation discharge valve at the bottom of the second separation kettle 6 to obtain wax oil. Open the third separation discharge valve at the bottom of the third separation kettle 7 to obtain water and other impurities.

[0038] During the whole process, CO₂ is in a closed cycle without emissions. According to the melting point and residual oil rate of the raw materials, the yield of high-melting-point Fischer-Tropsch wax after continuous cyclic extraction for 2.5 hours is about 80%. Currently, the wholesale price of Fischer-Tropsch wax with a melting point of 60°C in the market is 0.7 ten thousand yuan per ton, and the wholesale price of Fischer-Tropsch wax with a melting point of 115°C is 1.6 ten thousand yuan per ton. The cost of processing 60°C Fischer-Tropsch wax into 115°C Fischer-Tropsch wax by this process is about 0.1 ten thousand yuan per ton, and the yield is 80%. Then, the value added by processing 1 ton of 60°C Fischer-Tropsch wax = 1.6×80% - 0.7 - 0.1 = 0.48 ten thousand yuan, and the cost profit rate = 0.48 / (0.7 + 0.1) = 60%. The profit is very considerable.

[0039] Explanation of the melting point of Fischer-Tropsch wax: According to the detection and analysis, the melting point of Fischer-Tropsch wax or other waxes is inversely proportional to the wax oil content in it. Since there is residual wax oil in the process of producing Fischer-Tropsch wax, Fischer-Tropsch wax presents varieties with different melting point temperatures. The higher the oil content, the lower the melting point; the lower the oil content, the higher the melting point. Therefore, the present invention uses the supercritical CO₂ extraction process to reduce the residual wax oil in Fischer-Tropsch wax and increase its melting point.

[0040] In the embodiments of the present invention, the term "a plurality of" refers to two or more, unless otherwise clearly defined. Terms such as "installation", "connection", "fixation", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific situations.

[0041] In the description of the embodiments of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the embodiments of the present invention.

[0042] In the description of this specification, the description of terms such as "one embodiment" and "one preferred embodiment" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0043] The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention; technologies not involved in the present invention can be realized through the prior art.

Claims

1. A liquid extraction process for increasing the melting point of wax using supercritical CO2, characterized in that: The steps of this liquid extraction process are as follows: A. Load low-melting-point solid wax into the extraction kettle, close the feed valve, start the stirrer and heat the extraction kettle simultaneously to melt the solid wax into liquid wax. B. Open the supercritical fluid input valve at the bottom of the extraction kettle and input CO2 supercritical fluid from the bottom of the extraction kettle. C. After the pressure in the extraction kettle reaches 33 MPa to 35 MPa, open the extraction throttle valve. The CO2 supercritical fluid fully mixed with the liquid wax in the extraction kettle overflows, carrying the extracted wax oil, as well as part of the wax, water, and other impurities, into the lower part of the first separation kettle at a temperature of 105°C to 115°C. D. After the pressure in the first separation kettle reaches 10 MPa to 11 MPa, open the first separation throttle valve. The CO2 supercritical fluid carrying wax oil, water, and other impurities overflows into the lower part of the second separation kettle at a temperature of 65°C to 70°C. E. After the pressure in the second separation kettle reaches 7.8 MPa to 8.5 MPa, open the second separation throttle valve. The CO2 supercritical fluid carrying water and other impurities overflows into the lower part of the third separation kettle at a temperature of 22°C to 25°C. F. After the pressure in the third separation kettle reaches 5.5 MPa to 6 MPa, open the third separation throttle valve. The gaseous CO2 overflows and enters the gaseous CO2 purifier for purification. G. The purified gaseous CO2 is condensed into liquid CO2 by a condenser and then returned to the liquid CO2 storage tank. The liquid CO2 is pressurized by a booster pump and heated by a heater to become CO2 supercritical fluid and is input from the bottom into the extraction kettle. H. The CO2 supercritical fluid fully mixed with the liquid wax in the extraction kettle overflows, carrying the extracted wax oil, as well as part of the wax, water, and other impurities, into the lower part of the first separation kettle at a temperature of 105°C to 115°C and a pressure of 10 MPa to 11 MPa. I. The CO2 supercritical fluid in the first separation kettle carrying wax oil, water, and other impurities overflows into the lower part of the second separation kettle at a temperature of 65°C to 70°C and a pressure of 7.8 MPa to 8.5 MPa. J. The CO2 supercritical fluid in the second separation kettle carrying water and other impurities overflows into the lower part of the third separation kettle at a temperature of 22°C to 25°C and a pressure of 5.5 MPa to 6 MPa. K. The gaseous CO2 in the third separation kettle overflows and enters the gaseous CO2 purifier for purification, entering step G. L. Continuously execute steps G to K in a cycle for continuous cyclic liquid extraction for 1 h to 3 h, and then enter step M. M. Close the supercritical fluid input valve at the bottom of the extraction kettle, the booster pump, and the heater. When the pressures in the extraction kettle, the first separation kettle, the second separation kettle, and the third separation kettle are close to that of the liquid CO2 storage tank, start the gas recovery compressor to reduce the pressures in the extraction kettle, the first separation kettle, the second separation kettle, and the third separation kettle to atmospheric pressure. Then close the third separation throttle valve and the liquid CO2 storage tank return valve, and enter step N. N. Open the extraction discharge valve at the bottom of the extraction kettle to obtain high-melting-point liquid wax with a melting point of 115°C to 125°C. Open the first separation discharge valve at the bottom of the first separation kettle to obtain low-melting-point liquid wax. Open the second separation discharge valve at the bottom of the second separation kettle to obtain wax oil. Open the third separation discharge valve at the bottom of the third separation kettle to obtain water and other impurities.

2. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The melting point of the low-melting-point solid wax in step A is <80°C; the oil content of the low-melting-point solid wax in step A is not less than 1%; the loading amount of the extraction kettle in step A is 80% to 86% of its volume.

3. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1 or 2, characterized in that: The oil content of the high-melting-point liquid wax in step N is not more than 0.1%, and the yield of the high-melting-point liquid wax in step N is 75% to 85%.

4. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The low-melting-point liquid wax in step N can be added as a raw material into the extraction kettle again for the supercritical CO2 liquid extraction process.

5. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The set temperature of the extraction kettle is 125°C to 130°C.

6. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1 or 5, characterized in that: The heating equipment on the extraction kettle includes an extraction internal heating coil and an extraction external heating jacket. The heating medium of both the extraction internal heating coil and the extraction external heating jacket is thermal oil, and the thermal oil is respectively input from the bottom and output from the top of the extraction internal heating coil and the extraction external heating jacket.

7. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The heating equipment on the first separation kettle includes a separation internal heating coil and a separation external heating jacket. The heating medium of both the separation internal heating coil and the separation external heating jacket is thermal oil, and the thermal oil is respectively input from the bottom and output from the top of the separation internal heating coil and the separation external heating jacket.

8. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The heating equipment on the second separation kettle is an external constant-temperature jacket. The heat preservation medium used in the external constant-temperature jacket is constant-temperature water, and the constant-temperature water is input from the bottom and output from the top of the external constant-temperature jacket.

9. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: The heating equipment on the third separation kettle is an external cooling jacket. The cooling medium used in the external cooling jacket is cooling water, and the cooling water is input from the bottom and output from the top of the external cooling jacket.

10. The liquid extraction process for increasing the melting point of wax by using supercritical CO2 according to claim 1, characterized in that: Temperature sensors and pressure sensors are respectively arranged on the extraction kettle, the first separation kettle, the second separation kettle, and the third separation kettle.

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