Process for recovering octafluorocyclobutane in tetrafluoroethylene residual liquid through pressure swing distillation

Abstract

The invention discloses a process for recovering octafluorocyclobutane in tetrafluoroethylene residual liquid through pressure swing distillation, belonging to the technical field of fluorine chemical industry, after octafluorocyclobutane and azeotrope thereof are recovered from residual liquid, the octafluorocyclobutane and R124 azeotrope are separated by combining a pressure swing distillation technology and a side-draw technology; wherein the pressure swing distillation technology comprises a normal pressure distillation tower and a high pressure distillation tower, octafluorocyclobutane is obtained from a tower kettle of the normal pressure distillation tower, all R124 and part of octafluorocyclobutane are extracted from a side line at the upper part of the tower, R124 is removed from the extracted mixture at the tower kettle of the high pressure distillation tower, and octafluorocyclobutane and a small amount of R124 are recovered at the tower top. According to the method, the octafluorocyclobutane can be effectively recovered and purified, and third-party substances such as an extracting agent and an entrainer are prevented from being introduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorine chemical industry, and in particular relates to a process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid. Background Art

[0002] Octafluorocyclobutane, also known as perfluorocyclobutane, referred to as C318, has stable chemical properties, is non-toxic, has zero ozone depletion potential (ODP), and has a low greenhouse effect. It is a green and environmentally friendly special gas, mainly used in high-voltage insulation, ultra-large-scale integrated circuit etchants, mixed refrigerants that replace chlorofluorocarbons, aerosols, cleaning agents (for the electronics industry), sprays, heat pump working fluids, etc. Octafluorocyclobutane can also be used as the main raw material for other chemical products. Tetrafluoroethylene and hexafluoropropylene are basic raw materials for the organic fluorine industry, comonomers of many fluorine-containing copolymers, and intermediates of many fluorine-containing compounds. Octafluorocyclobutane is also widely used as the main raw material in its production. In terms of refrigerants, domestic and foreign manufacturers have been seeking environmentally friendly and efficient refrigerants. Among these new refrigerants that have been developed and are under research, octafluorocyclobutane has also been widely used. In the process of manufacturing semiconductor equipment in the electronics industry, gaseous fluorine-containing compounds are needed. The most commonly used gas in the plasma dry etching process is fluorocarbon compounds, and the carbon contained in them can help remove oxygen from the oxide layer, including carbon tetrafluoride, octafluoropropane, octafluorocyclobutane, etc. Therefore, octafluorocyclobutane is also widely used in semiconductor etching. With the implementation of the Montreal Protocol and the rapid growth of the electronics industry, the role of octafluorocyclobutane is becoming increasingly important, and its usage is also increasing year by year. It is an important special fluorine-containing gas.

[0003] There are many methods for preparing octafluorocyclobutane, such as tetrafluoroethylene dimerization, tetrafluorocyclobutane electrochemical fluorination, dichlorodifluoromethane high temperature catalytic reaction, dichlorotetrafluoroethane pyrolysis, polytetrafluoroethylene depolymerization pyrolysis, hexafluoropropylene production and recovery of byproducts in the cracking process of chlorodifluoromethane. Therefore, it will contain a large amount of other fluorocarbon compounds, whose boiling points are similar to those of octafluorocyclobutane, and it is extremely difficult to obtain high-purity products. In addition, considering the influence of gas impurities on semiconductor technology, O2, N2, CO, CO2, H2O, C3F6, etc. are also important impurity indicators. In this patent, the octafluorocyclobutane byproduct produced in the production process of tetrafluoroethylene is mainly used for recovery, and this process causes more impurities to accompany the recovery of octafluorocyclobutane, resulting in higher requirements for obtaining high-purity octafluorocyclobutane.

[0004] Patent CN101134710A discloses a method for recovering octafluorocyclobutane from the residual liquid of tetrafluoroethylene production process, which relates to a method for recovering octafluorocyclobutane from the residual liquid of tetrafluoroethylene production process, including the steps of pre-distilling the residual liquid to obtain octafluorocyclobutane and components with similar boiling points, entering an extractive tower for distillation, wherein the extractant is one or more of carbon tetrachloride, ethylene glycol dimethyl ether, acetone, toluene or methanol, and the top component is octafluorocyclobutane. However, in the extractive distillation separation method, new substances need to be introduced, resulting in higher separation requirements, and components that are azeotropic with octafluorocyclobutane are not considered.

[0005] Patent CN206736135U discloses a device for recovering octafluorocyclobutane in tetrafluoroethylene residual liquid generated by cracking. The utility model discloses a device for recovering octafluorocyclobutane in tetrafluoroethylene residual liquid generated by cracking, comprising a TFE residual liquid storage tank, an HFP residual liquid intermediate tank, a feed pump, a light removal tower, a residual liquid separation tower, an octafluoro recovery tower and a finished product recovery storage tank connected in sequence, wherein the light removal tower is provided with a Y-shaped structured packing, wherein the Y-shaped structured packing is made of 316L stainless steel material, the light removal tower is connected to a residual liquid incineration device, the industrial incineration device is connected to a hydrofluoric acid recovery production tower, the residual liquid separation tower is connected to a primary compression system for collecting light components in the side line extraction, the octafluoro recovery tower is connected to the primary compression system, and the impurities obtained by the recovery device can be further recycled on the basis of improving the purity of the product. The utility model is suitable for recovering octafluorocyclobutane in tetrafluoroethylene residual liquid generated by cracking. In this patent, the separation of octafluorocyclobutane with a boiling point close to that of octafluorocyclobutane or with an azeotropic composition is not considered.

[0006] Patent CN104557447A discloses a method for the combined recovery and utilization of residual liquids from tetrafluoroethylene and hexafluoropropylene production. The invention relates to a method for the combined recovery and utilization of residual liquids from tetrafluoroethylene and hexafluoropropylene production. By introducing the residual liquid produced in the production of tetrafluoroethylene into the production process of hexafluoropropylene, octafluorocyclobutane is distilled and recovered together with the residual liquid produced in the production of hexafluoropropylene. No independent equipment and process operation are required, and octafluorocyclobutane in the tetrafluoro residual liquid can be recovered at a low cost. The very small amount of similar components contained in the recovered octafluorocyclobutane does not affect the quality of hexafluoropropylene after being specifically proportioned with the tetrafluoroethylene monomer, and can be directly used to produce hexafluoropropylene, realizing the perfect integration of the hexafluoropropylene production process and the residual liquid recovery process. However, the patent directly sends components with a boiling point close to octafluorocyclobutane to the production process of hexafluoropropylene, without considering obtaining high-purity octafluorocyclobutane.

[0007] Patent CN104529697A discloses a method for recovering high-purity octafluorocyclobutane from difluorochloromethane cracking residue. The invention relates to a method for recovering high-purity octafluorocyclobutane from difluorochloromethane cracking residue, comprising the following steps: (1) distilling difluorochloromethane cracking residue to obtain octafluorocyclobutane and its azeotrope; (2) entering the octafluorocyclobutane and its azeotrope obtained in step (1) into an extractive distillation tower for extractive distillation, obtaining octafluorocyclobutane at the top of the extractive distillation tower, obtaining a mixed component of an extractant and impurities in the bottom of the extractive distillation tower, and desorbing the mixed component through an extractive desorption tower to obtain an extractant that enters the extractive distillation tower for recycling. The invention uses a composite agent composed of an ionic liquid and an organic solution as an extractant, which can significantly increase the relative volatility of octafluorocyclobutane and its azeotrope, achieve efficient separation of the system, and the purity of octafluorocyclobutane is as high as 99.999%. However, although the introduction of a composite agent composed of an ionic liquid and an organic solution as an extractant can separate components that are close to boiling or azeotropic with octafluorocyclobutane, it introduces a variety of new substances, resulting in the appearance of new impurities in the separation of high-purity octafluorocyclobutane.

[0008] Patent CN113717027A discloses a method for purifying octafluorocyclobutane, including adsorption, oxidation and distillation of octafluorocyclobutane raw gas, wherein the oxidation is to oxidize the raw gas after adsorption through an oxidation column, wherein the oxidation column includes a carrier loaded with an oxidant, the carrier has a porous structure, and the carrier has a passage for the raw gas to flow in the direction of the raw gas flow. However, the patent does not consider the problem of near-boiling and azeotropic separation, and the processing capacity of adsorption and oxidation is low, and the adsorption medium and oxidant are required, which increases the industrialization cost.

[0009] Patent CN111004088A discloses a method and device for purifying octafluorocyclobutane gas. The invention relates to a method and device for purifying octafluorocyclobutane gas, and belongs to the field of fine chemical technology. The method described in the invention can obtain a high-purity octafluorocyclobutane product with a purity of more than 99.999% through reactive distillation, adsorption, filtration, continuous two distillations and filtration. The method adopts continuous operation to reduce the cold and heat consumed in the purification process, and the product yield is high and economical. Although reactive distillation can achieve energy saving and consumption reduction, the reactive distillation has a low degree of freedom, which makes the operation process difficult.

[0010] Patent CN110845299A discloses a method for removing perfluoroolefins from octafluorocyclobutane. The invention discloses a method for removing perfluoroolefins from octafluorocyclobutane. A mixed solution of octafluorocyclobutane containing perfluorocarbons is stored in a sampling bottle, the outlet valve of the sampling bottle is opened, and a heated acidic aqueous solution of a strong oxidant is introduced into the mixed solution of octafluorocyclobutane containing perfluoroolefins to react in an oxidation reactor. The heated acidic aqueous solution of the strong oxidant oxidizes the perfluoroolefins into corresponding perfluorocarboxylic acids or processes them into corresponding halogenated alkanes, while octafluorocyclobutane, as an alkane, does not react with the heated acidic aqueous solution of the strong oxidant. The gas after the reaction passes through an adsorption column and is deacidified and dehydrated under the action of an adsorbent to obtain octafluorocyclobutane containing perfluoroolefins as impurities, and the concentration of perfluoroolefins in parts per million is less than 10 ppm. The invention uses a strong oxidant to oxidize the perfluoroolefin impurities into perfluorocarboxylic acids or add them into halogenated alkanes, thereby achieving the effect of purifying octafluorocyclobutane. This patent removes perfluoroolefins under oxidation reaction conditions, but this method increases the complexity of the operation and has a relatively low processing capacity in the industrial process.

[0011] Patent CN105777483A discloses a method and system for purifying high-purity octafluorocyclobutane. The invention relates to a method for purifying high-purity octafluorocyclobutane, comprising the following steps: step A, system cleaning, using ammonia to purge the purification system, and evacuating the purification system after purging; step B, light removal distillation; step C, heavy removal distillation; step D, finished product bottling, the gas phase of the heavy removal distillation tower is loaded into a storage container to obtain the finished product. The invention relates to a purification system for high-purity octafluorocyclobutane, including a primary adsorber, a light removal distillation tower, a heavy removal distillation tower, a membrane press, a first deep adsorber and a second deep adsorber. The invention uses adsorbers multiple times to ensure that impurities can be completely removed, but if the ventilation volume is too large, the adsorption capacity will decrease, so the production capacity of the scheme is limited, and the separation of azeotropy and near boiling is not considered.

[0012] Patent CN113754513A discloses a method for removing a small amount of fluorinated olefins from octafluorocyclobutane and a device for removing the same. The invention discloses a method for removing a small amount of fluorinated olefins from octafluorocyclobutane. First, high-purity oxygen is introduced into a photo-oxidation reactor of octafluorocyclobutane containing a small amount of fluorinated olefins. After irradiation with ultraviolet light at a certain temperature and pressure stirring speed, the impurities of the fluorinated olefins are converted into polyacyl fluoride. Octafluorocyclobutane does not participate in the reaction due to its stable properties. The octafluorocyclobutane solution containing polyacyl fluoride is vaporized and then purified by alkali washing, water washing, adsorption dehydration, and then distillation to obtain an octafluorocyclobutane solution with a purified fluorinated olefin impurity of less than 10 ppm. The invention also discloses a device for removing a small amount of fluorinated olefins from octafluorocyclobutane, which mainly comprises a reaction kettle (1), a vaporizer (2), an alkali washing tower (3), a water washing tower (4), an adsorption device and a distillation tower (5). The invention oxidizes the fluorinated olefin impurities into polyether acyl fluoride, and then removes the impurities by alkali washing, water washing, dehydration and distillation, thereby achieving the effect of purifying octafluorocyclobutane. The invention adopts the method of reaction impurity removal, and does not consider the use of enhanced distillation technology to treat impurities.

[0013] Patent CN1292773A discloses a method for purifying perfluorocyclobutane. Octafluorocyclobutane containing less than 10 parts per million (mole) of halogenated impurities and a method for producing such substantially pure octafluorocyclobutane are disclosed. When implementing these methods, various azeotropic or azeotropic compositions containing octafluorocyclobutane are found to have use value. These compositions include: perfluorocyclobutane and 2-chloro-1,1,1,2-tetrafluoroethane; perfluorocyclobutane and 1,1,2,2-tetrafluoroethane; perfluorocyclobutane and 1,1,1,2-tetrafluoroethane; perfluorocyclobutane and 1,1-difluoroethane. Used to produce substantially high-purity octafluorocyclobutane, the inventive method includes: a) an azeotropic distillation method for separating octafluorocyclobutane from halogenated impurities, and b) an extractive distillation method for separating octafluorocyclobutane from halogenated impurities by using an entrainer selected from ethers, ketones, alcohols, hydrocarbons and hydrochloric acid. The invention introduces a third substance for extractive distillation. In the subsequent distillation treatment, the extractant needs to be completely removed. Summary of the invention

[0014] In view of the defects of the prior art, the present invention provides a process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation, which can achieve effective separation of octafluorocyclobutane azeotropes and avoid the introduction of third-party substances such as extractants and entrainers.

[0015] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0016] A process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation, after recovering octafluorocyclobutane and its azeotrope from the residual liquid, the octafluorocyclobutane and R124 azeotrope are separated by combining pressure swing distillation technology with side line extraction technology; wherein the pressure swing distillation technology comprises an atmospheric distillation tower and a high-pressure distillation tower, octafluorocyclobutane is obtained from the bottom of the atmospheric distillation tower, all R124 and part of the octafluorocyclobutane are extracted from the side line at the upper part of the tower, R124 is removed from the extracted mixture in the bottom of the high-pressure distillation tower, and octafluorocyclobutane and a small amount of R124 are recovered at the top of the tower.

[0017] Preferably, in order to obtain octafluorocyclobutane and its azeotrope from the residual liquid, first, a light component impurity with a boiling point lower than octafluorocyclobutane in the residual liquid is removed by using a light removal distillation tower, and a side line extraction technology is used in the stripping section of the light removal distillation tower to remove part of the heavy component impurities; then, a heavy component removal distillation tower is used to completely remove the heavy component in the material extracted from the side line of the light removal distillation tower, and the trace light component is removed again by using the side line extraction technology.

[0018] Preferably, the light-removal distillation tower removes the main light component impurities at the top of the tower, removes part of the heavy component impurities in the bottom of the tower, and performs side line extraction in the distillation section; the pressure of the light-removal distillation tower is selected to be 0.5-0.8MPa; the number of plates is selected to be 20-50; the reflux ratio is selected to be 8-13; the top temperature is selected to be 15-30°C; and the bottom temperature is selected to be 40-70°C.

[0019] Preferably, the side line extraction position of the light removal distillation tower is at 1 / 5-1 / 3 of the height of the effective filling section, and the extraction amount is 85-95% of the feed flow rate.

[0020] Preferably, the heavy-removal distillation tower removes all remaining heavy component impurities at the bottom of the tower, removes remaining trace light component impurities at the top of the tower, and performs side line extraction in the distillation section. The pressure of the heavy-removal distillation tower is selected to be 0.4-0.6MPa; the number of plates is selected to be 20-50; the reflux ratio is selected to be 15-30; the top temperature is selected to be 25-45°C; and the bottom temperature is selected to be 50-80°C.

[0021] Preferably, the side line extraction position of the de-heavy distillation tower is at a height of 4 / 5-2 / 3 of the effective filling section, and the extraction amount is 90-97% of the feed flow rate.

[0022] Preferably, the atmospheric distillation tower obtains high-purity octafluorocyclobutane in the bottom of the tower, and a part of the azeotrope of octafluorocyclobutane and R124 is produced from the side line of the top distillation section, and trace light components are discharged at the top of the tower. The pressure of the atmospheric distillation tower is selected from 0-0.05MPa; the number of plates is selected from 20-50; the reflux ratio is selected from 2-5.5; the top temperature is selected from -20-0°C; and the bottom temperature is selected from -7-10°C.

[0023] Preferably, the side line extraction position of the atmospheric distillation tower is at a height of 4 / 5-2 / 3 of the effective filling section, and the extraction amount is 90-97% of the feed flow rate.

[0024] Preferably, the high-pressure distillation tower removes most of the R124 at the bottom of the tower, obtains the azeotrope of octafluorocyclobutane and part of R124 at the top of the tower, and sends the azeotrope to the atmospheric pressure tower. The pressure of the high-pressure distillation tower is selected from 0.9-1.3 MPa; the number of plates is selected from 20-50; the reflux ratio is selected from 0.2-1.1; the top temperature is selected from 50-65°C; and the bottom temperature is selected from 55-70°C.

[0025] Preferably, the residual liquid comprises 50-70% octafluorocyclobutane, 15-30% R124, 3-8% light component impurities and 2-9% heavy component impurities; wherein the light component impurities include tetrafluoroethylene, difluoromonochloromethane and hexafluoropropylene; and the heavy component impurities include pentafluoromonochloropropylene and dichloromonofluoromethane.

[0026] In the recovered residual liquid, the main factor affecting the distillation of octafluorocyclobutane is 2-chloro-1,1,1,2-tetrafluoroethane (R124), and R124 and octafluorocyclobutane will also form an azeotrope. In addition to this component, there are also some light components and heavy impurities. For the removal of light and heavy impurities, ordinary distillation and side-line extraction are used to control their content, while for the removal of azeotropes, pressure swing distillation is used to achieve separation.

[0027] The technical solution of the present invention adopts a combination of ordinary distillation and side-line purification technology to effectively remove light components and heavy impurities in tetrafluoroethylene residual liquid, and uses pressure swing distillation technology and side-line extraction technology to separate R124 that produces azeotropy with octafluorocyclobutane, thereby obtaining octafluorocyclobutane without azeotropes, thereby achieving effective recovery and purification of octafluorocyclobutane.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] Firstly, the recovery of octafluorocyclobutane in tetrafluoroethylene residual liquid can realize comprehensive resource utilization, reduce the energy consumption of incineration, and achieve the goal of energy conservation and environmental protection.

[0030] Secondly, the combination of ordinary distillation and side-line purification technology can effectively remove impurities and reduce the energy consumption of the distillation tower.

[0031] Finally, the combination of pressure swing distillation technology and side-line withdrawal technology can achieve the effective separation of octafluorocyclobutane azeotropes, avoiding the introduction of third-party substances such as extractants and azeotropes.

[0032] The specific technical solutions and beneficial effects of the present invention will be described in detail in the following specific embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0034] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] According to the existing situation of tetrafluoroethylene (TFE) production equipment using difluorochloromethane dilution cracking, a certain amount of octafluorocyclobutane will be produced as a by-product. The current treatment plan for this part is to send it to incineration as residual liquid. On the one hand, this causes a waste of octafluorocyclobutane resources, and also increases the energy consumption of incineration, which will also have an impact on the environment; on the other hand, if the octafluorocyclobutane in the system is not transported out of the system, the octafluorocyclobutane will affect the tetrafluoroethylene distillation system. Therefore, it is necessary to recycle the valuable octafluorocyclobutane in the residual liquid.

[0037] In the recovered residual liquid, the main factor affecting the distillation of octafluorocyclobutane is 2-chloro-1,1,1,2-tetrafluoroethane (R124), and R124 and octafluorocyclobutane will also form an azeotrope. In addition to this component, there are also some light components and heavy impurities. For the removal of light and heavy impurities, ordinary distillation and side-line extraction are used to control their content, while for the removal of azeotropes, pressure swing distillation is used to achieve separation.

[0038] Since one of the factors that affect phase equilibrium is pressure, the composition of the azeotrope will change when the pressure changes. If the binary azeotrope is highly sensitive to pressure, the azeotropic point will change significantly with the pressure change. At this time, the azeotrope can be separated by using a distillation tower with different operating pressures. This method is called pressure swing distillation.

[0039] The azeotropic conditions of R124 and octafluorocyclobutane under different pressures are shown in Table 1. It can be seen from Table 1 that the azeotropic points of R124 and octafluorocyclobutane have different compositions under different pressures, so they can be separated by pressure swing distillation.

[0040] Table 1 Azeotropic composition data of R124 and octafluorocyclobutane under different pressures

[0041]

[0042] Therefore, in view of the existing problems of recovering and purifying octafluorocyclobutane from tetrafluoroethylene residual liquid, this embodiment provides a process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation, such as Figure 1 As shown, the following steps are included:

[0043] (1) The tetrafluoroethylene residue sent from the cracking in the TFE device and which has been preliminarily treated, including octafluorocyclobutane, R124, light component impurities, heavy component impurities, etc., is sent to a light component removal distillation tower, where the main light component impurities are removed at the top of the tower, and part of the heavy component impurities are removed at the bottom of the tower, and side-line production is carried out in the stripping section.

[0044] The pressure of the light removal distillation tower is 0.5-0.8MPa, the number of plates is 20-50, the reflux ratio is 8-13, the top temperature is 15-30°C, and the bottom temperature is 40-70°C. The side line extraction position is 1 / 5-1 / 3 of the height of the effective packing section, and the extraction volume is 85-95% of the feed flow rate.

[0045] (2) The material taken out from the side line in step 1 is sent to a de-heavy distillation tower, all heavy impurities are removed at the bottom of the tower, trace light impurities are removed at the top of the tower, and side line is taken out in the distillation section.

[0046] The pressure of the de-heavy distillation tower is 0.4-0.6MPa, the number of plates is 20-50, the reflux ratio is 15-30, the tower top temperature is 25-45°C, and the tower bottom temperature is 50-80°C. The side line extraction position is at the height of 4 / 5-2 / 3 of the effective packing section, and the extraction volume is 90-97% of the feed flow rate.

[0047] (3) The material taken out from the side line in step 2 is sent to an atmospheric distillation tower (hereinafter referred to as the atmospheric tower), and the light component impurities are further removed at the top of the tower, and high-purity octafluorocyclobutane (stored in a C318 storage tank) is obtained at the bottom of the tower, and the azeotrope is taken out from the side line in the distillation section.

[0048] The atmospheric pressure tower has a pressure of 0-0.05 MPa, a plate number of 20-50, a reflux ratio of 2-5.5, a tower top temperature of -20-0°C, and a tower bottom temperature of -7-10°C. The side line extraction position is at a height of 4 / 5-2 / 3 of the effective packing section, and the extraction volume is 90-97% of the feed flow rate.

[0049] (4) The material taken out from the side line in step 3 is sent to a high-pressure distillation tower (hereinafter referred to as the high-pressure tower) through a booster pump. At the bottom of the tower, the R124 with a high content is removed (the R124 residual liquid is stored in the R124 residual liquid storage tank), and the azeotrope is obtained at the top of the tower, and the azeotrope is sent to the atmospheric pressure tower, thereby increasing the yield of octafluorocyclobutane.

[0050] The high-pressure tower has a pressure of 0.9-1.3 MPa, a plate number of 20-50, a reflux ratio of 0.2-1.1, a tower top temperature of 50-65°C, and a tower bottom temperature of 55-70°C.

[0051] The impurities separated in the above steps are sent to the incineration system for incineration. Since the octafluorocyclobutane is recovered, the energy consumption of incineration can be reduced.

[0052] Example 1

[0053] The content of octafluorocyclobutane in the tetrafluoroethylene residual liquid raw material is 63.85%, the content of R124 is 27.59%, the light component impurities are 5.58%, and the heavy component impurities are 2.99%. The pressure of the light fractionation tower is 0.6MPa, the number of plates is 40, the reflux ratio is 10, the top temperature is 19.21℃, the bottom temperature is 48.85℃, the side sampling position is 1 / 5 of the height of the packing, and the side sampling amount is 90% of the feed; the pressure of the heavy fractionation tower is 0.4MPa, the number of plates is 40, the reflux ratio is 20, the top temperature is 34.94℃, the bottom temperature is 50.15℃, and the side sampling position is 4 / 5 of the height of the packing. The side sampling volume is 94% of the feed; the atmospheric tower pressure is 0.012MPa, the number of plates is 40, the reflux ratio is 3.5, the top temperature is -14.51℃, the bottom temperature is -5.95℃, the side sampling position is 4 / 5 of the height of the packing, and the side sampling volume is 97% of the feed; the high-pressure tower pressure is 1.0MPa, the number of plates is 40, the reflux ratio is 0.5, the top temperature is 58.49℃, and the bottom temperature is 59.45℃.

[0054] According to the above conditions, the content of octafluorocyclobutane in the C318 storage tank was 99.98%, and the content of R124 was 0.0073%; the content of R124 in the R124 residual liquid storage tank was 96.56%, and the content of octafluorocyclobutane was 3.44%; and the final octafluorocyclobutane recovery rate was 96.08%.

[0055] Example 2

[0056] The content of octafluorocyclobutane in the tetrafluoroethylene residual liquid raw material is 68.58%, the content of R124 is 19.26%, the light component impurities are 3.44%, and the heavy component impurities are 8.72%. The pressure of the light fractionation tower is 0.8MPa, the number of plates is 40, the reflux ratio is 12.3, the top temperature is 27.80℃, the bottom temperature is 66.34℃, the side sampling position is 1 / 5 of the height of the packing, and the side sampling amount is 93% of the feed; the pressure of the heavy fractionation tower is 0.5MPa, the number of plates is 40, the reflux ratio is 18, the top temperature is 41.29℃, the bottom temperature is 58.59℃, and the side sampling position is 4 / 5 of the height of the packing. The side sampling rate is 96% of the feed at the height of 4 / 5 of the packing, and the side sampling rate is 96% of the feed; the pressure of the atmospheric tower is 0.008MPa, the number of plates is 40, the reflux ratio is 4.5, the top temperature is -15.63℃, the bottom temperature is -5.24℃, the side sampling position is 1.1MPa, the number of plates is 40, the reflux ratio is 0.7, the top temperature is 61.88℃, and the bottom temperature is 67.92℃.

[0057] According to the above conditions, the content of octafluorocyclobutane in the C318 storage tank was 99.99%, and the content of R124 was 0.0023%; the content of R124 in the R124 residual liquid storage tank was 98.30%, and the content of octafluorocyclobutane was 1.70%; and the final octafluorocyclobutane recovery rate was 98.72%.

[0058] Example 3

[0059] The content of octafluorocyclobutane in the tetrafluoroethylene residual liquid raw material is 58.61%, the content of R124 is 28.33%, the light component impurities are 7.19%, and the heavy component impurities are 5.87%. The pressure of the light fractionation tower is 0.5MPa, the number of plates is 40, the reflux ratio is 11.3, the top temperature is 14.18℃, the bottom temperature is 49.93℃, the side sampling position is 1 / 5 of the height of the packing, and the side sampling amount is 88% of the feed; the pressure of the heavy fractionation tower is 0.3MPa, the number of plates is 40, the reflux ratio is 18.4, the top temperature is 27.54℃, the bottom temperature is 46.73℃, and the side sampling position is 4 / 5 of the packing. At the height, the side sampling volume is 96% of the feed; the pressure of the atmospheric tower is 0.031MPa, the number of plates is 40, the reflux ratio is 2.3, the top temperature is -8.38℃, the bottom temperature is -5.80℃, the side sampling position is 4 / 5 of the height of the packing, and the side sampling volume is 95% of the feed; the pressure of the high-pressure tower is 0.9MPa, the number of plates is 40, the reflux ratio is 0.25, the top temperature is 54.74℃, and the bottom temperature is 60.19℃.

[0060] According to the above conditions, the content of octafluorocyclobutane in the C318 storage tank was 99.96%, and the content of R124 was 0.0173%; the content of R124 in the R124 residual liquid storage tank was 95.41%, and the content of octafluorocyclobutane was 4.59%; the final octafluorocyclobutane recovery rate was 98.81%.

[0061] Example 4

[0062] The content of octafluorocyclobutane in the tetrafluoroethylene residual liquid raw material is 65.28%, the content of R124 is 22.37%, the light component impurities are 3.50%, and the heavy component impurities are 8.85%. The pressure of the light fractionation tower is 0.7MPa, the number of plates is 40, the reflux ratio is 12.2, the top temperature is 23.71℃, the bottom temperature is 55.70℃, the side sampling position is 1 / 5 of the height of the packing, and the side sampling amount is 94% of the feed; the pressure of the heavy fractionation tower is 0.55MPa, the number of plates is 40, the reflux ratio is 5.5, the top temperature is 43.18℃, the bottom temperature is 59.85℃, and the side sampling position is 4 / 5 of the packing At the height, the side sampling volume is 97% of the feed; the pressure of the atmospheric tower is 0.042MPa, the number of plates is 40, the reflux ratio is 4.7, the top temperature is -6.38℃, the bottom temperature is -3.75℃, the side sampling position is 4 / 5 of the height of the packing, and the side sampling volume is 96% of the feed; the pressure of the high-pressure tower is 1.3MPa, the number of plates is 40, the reflux ratio is 1.05, the top temperature is 68.10℃, and the bottom temperature is 75.16℃.

[0063] According to the above conditions, the content of octafluorocyclobutane in the C318 storage tank is 99.99%, and the content of R124 is 0.0020%; the content of R124 in the R124 residual liquid storage tank is 98.38%, and the content of octafluorocyclobutane is 1.62%; the final octafluorocyclobutane recovery rate is 99.03%.

[0064] In combination with the above embodiments, the present invention effectively recovers octafluorocyclobutane from tetrafluoroethylene residual liquid through various technical means, and obtains high-purity octafluorocyclobutane products, and avoids the introduction of third-party substances such as extractants and entrainers.

[0065] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes but is not limited to the contents described in the above specific embodiments. Any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. A process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation, characterized in that: After octafluorocyclobutane and its azeotrope are recovered from the residual liquid, the octafluorocyclobutane and R124 azeotrope are separated by combining pressure swing distillation technology with side line extraction technology; the pressure swing distillation technology includes an atmospheric distillation tower and a high-pressure distillation tower, octafluorocyclobutane is obtained from the bottom of the atmospheric distillation tower, and all R124 and part of the octafluorocyclobutane are extracted from the side line at the upper part of the tower, R124 is removed from the extracted mixture in the bottom of the high-pressure distillation tower, and octafluorocyclobutane and a small amount of R124 are recovered at the top of the tower.

2. A process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation according to claim 1, characterized in that: In order to obtain octafluorocyclobutane and its azeotrope from the residual liquid, firstly, a light component impurity with a boiling point lower than octafluorocyclobutane in the residual liquid is removed by using a light removal distillation tower, and a side line extraction technology is used in the distillation section of the light removal distillation tower to remove part of the heavy component impurities; then, a heavy component removal distillation tower is used to completely remove the heavy component in the material extracted from the side line of the light removal distillation tower, and the trace light component is removed again by using the side line extraction technology.

3. A process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation according to claim 2, characterized in that: The light removal distillation tower removes the main light component impurities at the top of the tower, removes part of the heavy component impurities at the bottom of the tower, and performs side line extraction in the distillation section; the pressure of the light removal distillation tower is selected to be 0.5-0.8MPa; the number of plates is selected to be 20-50; the reflux ratio is selected to be 8-13; the top temperature is selected to be 15-30°C; and the bottom temperature is selected to be 40-70°C.

4. A process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation according to claim 3, characterized in that: The side line extraction position of the light removal distillation tower is at 1 / 5-1 / 3 of the height of the effective filling section, and the extraction volume is 85-95% of the feed flow rate.

5. The process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation according to claim 2, characterized in that: The de-heavy distillation tower removes all remaining heavy component impurities at the bottom of the tower, removes remaining trace light component impurities at the top of the tower, and performs side line extraction in the distillation section; the pressure of the de-heavy distillation tower is selected to be 0.4-0.6MPa; the number of tower plates is selected to be 20-50; the reflux ratio is selected to be 15-30; the tower top temperature is selected to be 25-45°C; and the tower bottom temperature is selected to be 50-80°C.

6. A process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation according to claim 5, characterized in that: The side line extraction position of the de-heavy distillation tower is at a height of 4 / 5-2 / 3 of the effective filling section, and the extraction volume is 90-97% of the feed flow rate.

7. The process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation according to claim 1, characterized in that: The atmospheric distillation tower obtains high-purity octafluorocyclobutane in the tower bottom, extracts part of the azeotrope of octafluorocyclobutane and R124 in the side line of the tower top distillation section, and discharges trace light components at the tower top; the pressure of the atmospheric distillation tower is selected from 0-0.05MPa; the number of tower plates is selected from 20-50; the reflux ratio is selected from 2-5.5; the tower top temperature is selected from -20-0°C; and the tower bottom temperature is selected from -7-10°C.

8. A process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation according to claim 7, characterized in that: The side line extraction position of the atmospheric distillation tower is at a height of 4 / 5-2 / 3 of the effective filling section, and the extraction amount is 90-97% of the feed flow rate.

9. The process for recovering octafluorocyclobutane from tetrafluoroethylene residue by pressure swing distillation according to claim 1, characterized in that: The high-pressure distillation tower removes most of the R124 at the bottom of the tower, obtains the azeotrope of octafluorocyclobutane and part of R124 at the top of the tower, and sends the azeotrope to the atmospheric pressure tower; the pressure of the high-pressure distillation tower is selected to be 0.9-1.3MPa; the number of plates is selected to be 20-50; the reflux ratio is selected to be 0.2-1.1; the top temperature is selected to be 50-65°C; and the bottom temperature is selected to be 55-70°C.

10. The process for recovering octafluorocyclobutane from tetrafluoroethylene residual liquid by pressure swing distillation according to claim 1, characterized in that: The residual liquid comprises 50-70% octafluorocyclobutane, 15-30% R124, 3-8% light component impurities and 2-9% heavy component impurities; wherein the light component impurities include tetrafluoroethylene, difluoromonochloromethane and hexafluoropropylene; and the heavy component impurities include pentafluoromonochloropropylene and dichloromonofluoromethane.

Images