Distillation purification system and purification method of hexafluoropropylene oligomer

Abstract

The invention discloses a distillation and purification system for a hexafluoropropylene oligomer. The distillation and purification system comprises a distillation kettle, a cooling device and a storage tank, the distillation kettle is communicated with the cooling device, the cooling device comprises a first-stage heat exchange pipe, a first-stage buffer tank, a second-stage heat exchange pipe and a second-stage buffer tank which are communicated in sequence, and the top of the second-stage buffer tank is communicated with a tail gas pipe provided with a gas stop valve and a negative pressure pipe; liquid outlet pipes are respectively arranged at the bottoms of the first-stage buffer tank and the second-stage buffer tank; a view cup and a three-way valve are arranged on each liquid outlet pipe; the storage tank comprises a first storage tank and a second storage tank, and the cooling device is communicated with the first storage tank and the second storage tank through a three-way valve. Through the arrangement of the negative pressure pipe and the switchable storage tank, normal pressure distillation and negative pressure distillation can be carried out in the same system in a segmented manner, and the device has the characteristics of high condensation recovery rate, good separation effect and small occupied area. The invention further discloses a purification method, the distillation and purification system is arranged before rectification, the content of impurities entering a rectification tower is effectively reduced, and therefore products with higher purity are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of pretreatment of organic fluoride polymers before distillation, and particularly relates to a distillation purification system and a purification method suitable for hexafluoropropylene oligomers, especially hexafluoropropylene trimers before distillation. Background Art

[0002] Hexafluoropropylene oligomers have good thermal stability and chemical stability and are very important chemical raw materials. In the prior art, the preparation methods of hexafluoropropylene oligomers include gas phase method and liquid phase method. Among them, the liquid phase method is an addition reaction under the action of a polar solvent and a catalyst. The solvents include DMF, DMSO, acetonitrile, etc., and the catalysts include KF, KSCN, KOCN, KCN, crown ethers, ammonium fluoride, etc. The yield and productivity are high and the use is more common. The crude hexafluoropropylene oligomer prepared by the liquid phase method contains impurity components such as solvents, catalysts and reaction by-products.

[0003] In the existing production method, the crude product obtained by the addition reaction is usually left to stand for a period of time to separate the gas and liquid, and then distilled to obtain the target product. The problems with this method are: 1. A long standing time is required after the addition reaction so that the gas and liquid can be fully separated, which restricts production efficiency; 2. Even after a long period of gas-liquid separation, the catalyst, reaction intermediates, and by-products in the crude product introduced into the distillation tower will still occupy a certain proportion. Under the high temperature environment of the distillation tower, on the one hand, the impurities brought in will undergo secondary reactions to produce new impurities of unknown composition; on the other hand, some of the existing impurities are prone to decomposition at high temperatures and produce decomposition products with volatility similar to that of the target product. The decomposition products are very easy to mix into the target product, and because the content of this type of decomposition product is low, it is difficult to separate it from the target product, which directly affects the purity of the target product. Summary of the invention

[0004] The object of the present invention is to provide a distillation purification system for hexafluoropropylene oligomers and a purification method comprising the distillation purification system, so as to solve the problem that in the existing preparation process of hexafluoropropylene oligomers, only a standing process is used to pretreat the crude product, resulting in that impurities in the target product after distillation are difficult to remove and the product purity cannot meet the quality requirements.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a distillation and purification system for hexafluoropropylene oligomers, comprising a distillation kettle, a two-stage cooling device and a storage tank;

[0007] The distillation kettle is provided with a stirring device and a heating device, the top of the distillation kettle is provided with a feed inlet and a gas outlet, and the bottom of the distillation kettle is provided with a kettle residue outlet, the feed inlet is used to introduce the crude product to be purified, and the gas outlet is connected to the cooling device;

[0008] The cooling device comprises a primary heat exchange pipe, a primary cache tank, a secondary heat exchange pipe and a secondary cache tank which are connected in sequence, and refrigerant circulates in the primary heat exchange pipe and the secondary heat exchange pipe, the gas outlet is connected to the top of the primary heat exchange pipe through a first gas path, the top of the primary cache tank is connected to the top of the secondary heat exchange pipe through a second gas path, the top of the secondary cache tank is connected to a tail gas pipe and a negative pressure pipe, the ends of the tail gas pipe and the negative pressure pipe are both connected to an external tail gas collection system, the tail gas pipe is provided with a first gas shut-off valve, the negative pressure pipe is provided with a second gas shut-off valve and is connected to a negative pressure source, the first gas shut-off valve and the second gas shut-off valve are opened and closed alternately, and when the second gas shut-off valve is opened and the first gas shut-off valve is closed, the distillation kettle, the cooling device and the storage tank are all in a negative pressure state; liquid outlet pipes are respectively provided at the bottom of the primary cache tank and the secondary cache tank, and a three-way valve is provided on the liquid outlet pipe;

[0009] The storage tank comprises a first storage tank and a second storage tank, the first storage tank is used to store light component impurities obtained by distillation, the second storage tank is used to store the target product after distillation and purification, the first-level cache tank and the second-level cache tank are connected to the first storage tank or the second storage tank through the three-way valve, the first storage tank is connected to the front-end polymerization kettle, and the second storage tank is connected to the rear-end distillation tower;

[0010] The liquid outlet pipes are each provided with a sight glass, which is used to observe the liquid state in the primary cache tank and the secondary cache tank, and to open and close the first gas stop valve and the second gas stop valve according to the observation results, and to adjust the connectivity state of the three-way valve.

[0011] Based on the above technical scheme, the distillation and purification system of the present invention has two modes: atmospheric distillation and negative pressure distillation, and the distillations in different modes share a set of cooling devices. Combined with the switching of storage tanks, effective separation of light component impurities, heavy component impurities and target products can be achieved, and the light component impurities in the first storage tank can be re-introduced into the polymerization kettle to participate in the reaction, and the hexafluoropropylene polymers in the second storage tank are introduced into the rear-end distillation process, which has the characteristics of good separation effect, small site occupation, low equipment investment cost and high raw material utilization rate.

[0012] Preferably, the refrigerant of the first-stage heat exchange tube is circulating cooling water, and the refrigerant of the second-stage heat exchange tube is ethylene glycol. The purpose of this design is to achieve graded heat exchange through refrigerants with different cooling temperatures, to achieve sufficient condensation of the distilled gas, to help improve the recovery rate of the distilled components, and to reduce the organic content in the exhaust gas.

[0013] Preferably, the liquid outlet pipe is provided with a flow monitoring device at the front end of the three-way valve at the rear end of the sight glass, and the flow monitoring device includes a liquid collecting annular groove, a detection branch, a flow meter and a control device. The liquid collecting annular groove is an annular groove surrounded by L-shaped protrusions on the inner wall of the liquid outlet pipe. The upper end of the detection branch is connected with the liquid collecting annular groove, and the lower end is connected with the inside of the liquid outlet pipe. When liquid flows in the liquid outlet pipe, the liquid flowing against the wall is blocked by the liquid collecting annular groove and flows through the detection branch and then returns to the liquid outlet pipe. The flow meter is arranged on the detection branch and detects the flow in the detection branch. The flow meter is connected to the control device. The control device is connected by signal; the first gas stop valve and the second gas stop valve are pneumatic ball valves, and the three-way valve is a three-way pneumatic ball valve; the control device is connected by signal with the first gas stop valve, the second gas stop valve and the three-way valve and controls their opening and closing. The purpose of this design is to automatically monitor the liquid situation in the liquid outlet pipe through the flow monitoring device, and to realize the automatic opening and closing of the first gas stop valve and the second gas stop valve to switch between normal pressure and negative pressure states through the control device, and to automatically adjust the connection state of the three-way valve to switch the first storage tank and the second storage tank, which has the characteristics of higher intelligence and more precise control.

[0014] Preferably, the heating device of the distillation kettle includes a half-tube arranged on the outer wall of the distillation kettle and a coil arranged inside the distillation kettle. The coil is arranged around the stirring device. Heat medium circulates in both the half-tube and the coil. The heat medium is water vapor or heat transfer oil. This design is conducive to making the temperature rise of the distillation kettle stable, the temperature control more precise, and the distribution more uniform.

[0015] Preferably, the front end of the distillation kettle is also connected to an extraction tank for extracting some light component impurities, the upper end of the extraction tank is provided with an extractant outlet, the middle part is provided with a liquid inlet for introducing the crude product to be purified, the lower end is provided with an extractant inlet, and the bottom is provided with a liquid outlet for discharging the extracted product, and the liquid outlet is connected to the feed inlet of the distillation kettle. This design can remove some light component substances in advance before distillation, so that the distillation purification effect is better.

[0016] The present invention also provides a method for purifying hexafluoropropylene oligomers, comprising the aforementioned distillation purification system for hexafluoropropylene oligomers, and comprising the following steps:

[0017] S1, pre-treatment: the crude hexafluoropropylene oligomer to be purified obtained by the addition reaction is introduced from the top feed port of the distillation kettle according to the single processing amount, and the tail gas pipe at the top of the second buffer tank is opened, and the negative pressure pipe is closed; the refrigerant circulation of the primary heat exchange pipe and the secondary heat exchange pipe is started; the three-way valve is adjusted to make the liquid outlet pipe connected to the first storage tank;

[0018] S2, one-stage distillation, removal of light component impurities: set the threshold of the heating device to 60-90°C, start the stirring device and the heating device, start the first stage of atmospheric distillation, and when the temperature of the distillation kettle reaches the threshold, continue to maintain a constant temperature state. The light component impurities with a lower distillation point are first vaporized and enter the cooling device through the first gas path, and flow through in sequence: the first-stage heat exchange tube is condensed, the condensate and the uncondensed gas enter the first-stage buffer tank, the uncondensed gas enters the second-stage heat exchange tube through the second gas path for secondary condensation, and the condensate and the non-condensable gas enter the second-stage buffer tank, wherein the condensate in the first-stage buffer tank and the second-stage buffer tank enters the first storage tank through the liquid outlet pipe, and the non-condensable gas enters the tail gas collection system through the tail gas pipe at the top of the second-stage buffer tank, and the first storage tank is connected to the front end polymerization kettle;

[0019] S3, two-stage distillation, rinse cooling device: observe the sight glass on the liquid outlet pipe. When there are no more droplets in the sight glass connected to the primary cache tank and the secondary cache tank, close the tail gas pipe, open the negative pressure pipe, start the negative pressure source, and make the cooling device, storage tank and distillation kettle reach the negative pressure state in turn. Do not adjust the distillation temperature. The distillation kettle enters the second stage of negative pressure distillation. Keep the liquid outlet pipe connected to the first storage tank. At this time, the hexafluoropropylene polymer vaporizes and enters the cooling device to be condensed, and replaces the light component impurities remaining in the primary heat exchange pipe, the primary cache tank, the secondary heat exchange pipe, the secondary cache tank and the liquid outlet pipe in turn, and flows into the first storage tank;

[0020] S4, two-stage distillation, obtain the target product: observe the sight glass, when droplets appear in both sight glasses again, the cooling device is rinsed, switch the three-way valve on the liquid outlet pipe to connect it with the second storage tank, continue the negative pressure distillation, and the hexafluoropropylene polymer obtained by condensation of the cooling device is stored in the second storage tank, and the second storage tank is connected to the rear distillation tower;

[0021] S5, still residue treatment: observe the sight glass, when the two sight glasses are converted to dropless again, adjust the three-way valve to connect the liquid outlet pipe to the first storage tank again; at the same time, close the negative pressure source, cut off the heat medium circulation of the still, open the still residue discharge port at the bottom of the still to discharge the heavy component impurities that have not been distilled, complete the distillation purification, and the still enters the standby state;

[0022] Based on the above technical scheme, the conventional static gas-liquid separation process is replaced by a pre-purification process of a distillation kettle + two-stage cooling before distillation, and the distillation is divided into two stages. In the first stage, atmospheric distillation is used to separate light component impurities such as solvents and catalysts. In the second stage, the same distillation temperature as the first stage is maintained and negative pressure distillation is performed. The distillation point of hexafluoropropylene oligomers is lowered by negative pressure, so that they are separated at a lower temperature. At the same time, it is avoided that part of the heavy component impurities are decomposed to generate new impurities with the same volatilization temperature as the hexafluoropropylene oligomers at the atmospheric distillation point temperature of the hexafluoropropylene oligomers, and finally the mixed light components and heavy component impurities in the target product are further separated, especially the impurity components that are easily decomposed at the boiling point temperature and the volatilization temperature of the target product to produce impurity components with a volatility similar to that of the target product are separated in advance, so that the impurity content of the crude product entering the distillation tower is lower, and the secondary reaction amount in the distillation tower and the impurity content in the finished product are effectively reduced, thereby obtaining higher purity hexafluoropropylene oligomers.

[0023] Furthermore, in steps S1 to S4, the condensation temperature of the primary heat exchanger is 5 to 30°C, and the condensation temperature of the secondary heat exchanger is -50 to -10°C. The design aims to achieve graded condensation in different temperature ranges, which is beneficial to energy saving on the one hand, and to sufficient condensation and recovery of the distillation components on the other hand, thereby improving the recovery rate, reducing the organic content of the tail gas, and being more environmentally friendly.

[0024] Preferably, the refrigerant of the primary heat exchanger is circulating cooling water, and the refrigerant of the secondary heat exchanger is ethylene glycol. The design purpose is to preferentially use water with a large specific heat capacity for heat exchange and cooling, and then use ethylene glycol with a lower temperature for heat exchange, which has a higher heat exchange efficiency and is conducive to energy saving.

[0025] Furthermore, the negative pressure value of the second stage negative pressure distillation in steps S3 and S4 is -60 to -40 kPa. This setting can vaporize the hexafluoropropylene polymer at a preset distillation temperature, which is 110 to 130° C. under normal pressure, thereby effectively avoiding the decomposition reaction of the heavy component substances.

[0026] Preferably, the method further comprises a crude product pretreatment in step S0: the crude hexafluoropropylene oligomer to be distilled and the extractant are introduced into an extraction tank for stirring and mixing, the crude hexafluoropropylene oligomer to be distilled enters from the top and exits from the bottom, the extractant enters from the bottom and exits from the top, and the extracted crude hexafluoropropylene oligomer is introduced into the distillation kettle in step S1; the purpose of this design is to separate part of the light component impurities in the crude product in advance through the compatibility of the extractant with light component impurities such as solvents and catalysts, and the insolubility of the target product, thereby reducing the time consumption of one stage of the distillation kettle, thereby improving the purity of the final product and improving the production efficiency.

[0027] Beneficial Effects

[0028] One of the above technical solutions has the following advantages or beneficial effects:

[0029] (1) In order to solve the problem in the prior art that the solvent and catalyst are separated by a standing process before distillation, the impurity content is high and the product purity is difficult to improve, the present invention adopts a pre-purification process of a distillation kettle + two-stage cooling to replace the standing process, and switches between the two modes of atmospheric distillation and negative pressure distillation through the setting of a negative pressure pipe and a switchable storage tank, and at the same time shares a set of cooling devices with two-stage heat exchange. By switching the storage tanks, light component impurities, heavy component impurities and target products can be effectively separated and recovered, and the present invention has the characteristics of high condensation recovery rate, good separation effect, small site occupation, low equipment investment cost and high raw material utilization rate.

[0030] (2) By replacing the conventional static gas-liquid separation process with a pre-purification process of a still + two-stage cooling before distillation, the light components and heavy components impurities mixed in the target product are further separated, especially the impurity components that are easily decomposed at the boiling point temperature and volatilization temperature of the target product to produce a volatility similar to that of the target product are separated in advance, thereby making the impurity content of the crude product entering the distillation tower lower, effectively reducing the amount of secondary reactions in the distillation tower and the impurity content in the finished product, and thus obtaining a higher purity hexafluoropropylene polymer.

[0031] (3) The distillation is divided into two stages. In the first stage, atmospheric distillation is performed to separate light impurities such as solvents and catalysts. In the second stage, the same distillation temperature as the first stage is maintained and negative pressure distillation is performed. The distillation point of hexafluoropropylene polymers is lowered by negative pressure, so that hexafluoropropylene polymers can be separated. This avoids the process complexity of multiple temperature adjustments and prevents some heavy impurities from being decomposed to generate new impurities with the same volatilization temperature as the hexafluoropropylene polymers at the atmospheric distillation point temperature of the hexafluoropropylene polymers. This is more conducive to improving the purity of the back-end distillation product. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0034] Figure 2 It is a schematic diagram of the internal structure of the distillation kettle of the present invention;

[0035] Figure 3 For the present invention Figure 1 A schematic diagram of the structure enlargement of part A;

[0036] Figure 4 This is a schematic diagram of a flow monitoring device according to a second embodiment of the present invention;

[0037] Figure 5 For the present invention Figure 4 Schematic diagram of the cross-section structure of part B;

[0038] Figure 6 This is a schematic diagram of the structure of an extraction tank according to Embodiment 3 of the present invention;

[0039] In the figure: distillation kettle 1; stirring device 11; stirring shaft 111; heating device 12; half pipe 121; coil 122; feed inlet 13; gas outlet 14; kettle residual outlet 15; first gas path 16; cooling device 2; primary heat exchange pipe 21; primary buffer tank 22; second gas path 23; secondary heat exchange pipe 24; secondary buffer tank 25; tail gas pipe 26; first gas stop valve 261; negative pressure pipe 27; second gas stop valve 271; liquid outlet pipe 28; sight glass 281; three-way valve 282; refrigerant inlet 201; refrigerant outlet 202; storage tank 3; first storage tank 31; second storage tank 32; flow monitoring device 4; liquid collecting ring groove 41; L-shaped protrusion 411; detection branch 42; flow meter 43; extraction tank 5; liquid inlet 51; liquid outlet 52; extractant inlet 53; extractant outlet 54. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0041] Embodiment 1

[0042] This embodiment is a preferred embodiment of the present invention. Figure 1 As shown, this embodiment provides a distillation and purification system for hexafluoropropylene oligomers, comprising a distillation kettle 1, a two-stage cooling device 2 and a storage tank 3;

[0043] The still 1 is provided with a stirring device 11 and a heating device 12. The stirring device 11 includes a stirring shaft 111 inserted into the inner cavity of the still 1. The heating device 12 can be a direct heating device 12 such as a heating rod, or a heat transfer device with a circulating heat medium, such as Figure 2 As shown, the heating device 12 in this embodiment is a heat transfer device, including a half pipe 121 arranged on the outer wall of the still 1 and a coil 122 arranged in the still 1, the coil 122 is arranged around the stirring shaft 111 of the stirring device 11, and heat medium circulates in the half pipe 121 and the coil 122, and the heat medium is water vapor or heat transfer oil. This design is conducive to making the still 1 temperature rise stable and the temperature control more accurate and the distribution more uniform. Preferably, the inlet ends of the half pipe 121 and the coil 122 are provided with a flow regulating valve of the heat medium to achieve the effect of temperature control by controlling the circulating flow.

[0044] The distillation kettle 1 is provided with a feed inlet 13 and a gas outlet 14 at the top and a kettle residual discharge outlet 15 at the bottom. The feed inlet 13 is used to introduce the crude product to be purified, and the gas outlet 14 is connected to the cooling device 2.

[0045] The cooling device 2 includes a primary heat exchange tube 21, a primary buffer tank 22, a secondary heat exchange tube 24 and a secondary buffer tank 25 which are connected in sequence. Refrigerant circulates in the primary heat exchange tube 21 and the secondary heat exchange tube 24. The refrigerant enters from a refrigerant inlet 201 at the upper end of the heat exchange tube and is discharged from a refrigerant outlet 202 at the lower end of the heat exchange tube. Preferably, the refrigerant in the primary heat exchange tube 21 is circulating cooling water, and the refrigerant in the secondary heat exchange tube 24 is ethylene glycol, so as to realize graded heat exchange condensation and improve the recovery rate of the distillation components. The top of the distillation kettle 1 The gas outlet 14 at the end is connected to the top of the first-level heat exchange pipe 21 through the first gas path 16, the top of the first-level cache tank 22 is connected to the top of the second-level heat exchange pipe 24 through the second gas path 23, and the top of the second-level cache tank 25 is connected to a tail gas pipe 26 and a negative pressure pipe 27, and the ends of the tail gas pipe 26 and the negative pressure pipe 27 are both connected to an external tail gas collection system (not shown in the drawings), the tail gas pipe 26 is provided with a first gas shut-off valve 261, and the negative pressure pipe 27 is provided with a second gas shut-off valve 271 and is connected to a negative pressure source, and the first gas The gas stop valve 261 and the second gas stop valve 271 are opened and closed alternately to switch the entire system between normal pressure and negative pressure, that is, when the first gas stop valve 261 is opened, the second gas stop valve 271 is closed, and vice versa, when the first gas stop valve 261 is closed, the second gas stop valve 271 is opened; when the second gas stop valve 271 is opened and the first gas stop valve 261 is closed, the distillation kettle 1, the cooling device 2 and the storage tank 3 are all in a negative pressure state; the first-level cache tank 22 and the second-level cache tank 25 are respectively provided with liquid outlet pipes at the bottom 28, the liquid outlet pipe 28 is provided with a three-way valve 282; the storage tank 3 includes a first storage tank 31 and a second storage tank 32, the first storage tank 31 is used to store light component impurities obtained by distillation, and the second storage tank 32 is used to store the target product after distillation and purification, the first-level cache tank 22 and the second-level cache tank 25 are connected to the first storage tank 31 or the second storage tank 32 through the three-way valve 282, the first storage tank 31 is connected to the front-end polymerization kettle (not shown in the drawings), and the second storage tank 32 is connected to the rear-end distillation tower (not shown in the drawings);

[0046] like Figure 3As shown, the liquid outlet pipe 28 is provided with a sight glass 281, which is used to observe the liquid state in the primary cache tank 22 and the secondary cache tank 25, and open and close the first gas stop valve 261 and the second gas stop valve 271 according to the observation results, and adjust the connection state of the three-way valve 282, that is, when the state in the sight glass 281 switches from liquid droplets to liquid-free state, the first gas stop valve 261 is closed, and the second gas stop valve 271 is opened, so that the entire system is in a negative pressure environment; when the state in the sight glass 281 switches from liquid-free state to liquid state, the connection direction of the three-way valve 282 is adjusted to connect the liquid outlet pipe 28 with the second storage tank 32; when the state in the sight glass 281 switches from liquid droplets to liquid-free state again, the second gas stop valve 271 is closed, and the first gas stop valve 261 is opened, so that the entire system is restored to a normal pressure environment, and the connection direction of the three-way valve 282 is adjusted again to connect the liquid outlet pipe 28 with the first storage tank 31 again.

[0047] In this embodiment, the distillation and purification system is set to two modes: atmospheric distillation and negative pressure distillation. The distillations in different modes share a set of two-stage cooling devices 2 with different temperatures. Combined with the application of the sight glass 281, the tail gas pipe 26 and the negative pressure pipe 27 are switched. The first storage tank 31 and the second storage tank 32 can realize the effective separation of light component impurities, heavy component impurities and target products. The light component impurities in the first storage tank 31 can be re-introduced into the polymerization kettle to participate in the reaction, and the hexafluoropropylene polymers in the second storage tank 32 are introduced into the rear-end distillation process, which has the advantages of high condensation recovery rate, good separation effect, small site occupation, low equipment investment cost and high raw material utilization rate.

[0048] Embodiment 2

[0049] This embodiment provides a distillation and purification system for hexafluoropropylene oligomers, which is different from the first embodiment in that:

[0050] Based on the structure of the first embodiment, Figure 4 As shown, the liquid outlet pipe 28 is provided with a flow monitoring device 4 at the front end of the three-way valve 282 at the rear end of the sight glass 281. Figure 5 As shown, the flow monitoring device 4 includes a liquid collecting annular groove 41, a detection branch 42, a flow meter 43 and a control device (not shown in the drawings). The liquid collecting annular groove 41 is an annular groove surrounded by an L-shaped protrusion 411 on the inner wall of the liquid outlet pipe 28. The upper end of the detection branch 42 is connected to the liquid collecting annular groove 41, and the lower end is connected to the inside of the liquid outlet pipe 28. When liquid flows in the liquid outlet pipe 28, the liquid flowing against the wall is blocked by the liquid collecting annular groove 41 and flows through the detection branch 42 and then returns to the liquid outlet pipe 28. The flow meter 43 is arranged on the detection branch 42 and detects the flow in the detection branch 42. The flow meter 43 is connected to the control device signal.

[0051] To facilitate automatic switching, the first gas stop valve 261 and the second gas stop valve 271 are pneumatic ball valves, and the three-way valve 282 is a three-way pneumatic ball valve; the control device is connected to the first gas stop valve 261, the second gas stop valve 271 and the three-way valve 282 by signal and controls their opening and closing.

[0052] The advantages of this embodiment are: through the setting of the flow monitoring device 4, the liquid situation in the liquid outlet pipe 28 can be automatically monitored, and the first gas stop valve 261 and the second gas stop valve 271 can be automatically opened and closed to switch between normal pressure and negative pressure states through the control device, and the connection state of the three-way valve 282 can be automatically adjusted to switch between the first storage tank 31 and the second storage tank 32, which has the characteristics of higher intelligence and more precise control.

[0053] Embodiment 3

[0054] This embodiment provides a distillation and purification system for hexafluoropropylene oligomers, which is different from the first or second embodiment in that:

[0055] Based on the structure of the first or second embodiment, Figure 6 As shown, the front end of the distillation kettle 1 is also connected to an extraction tank 5 for extracting some light component impurities, the upper end of the extraction tank 5 is provided with an extractant outlet 54, the middle part is provided with a liquid inlet 51 for introducing a crude product to be purified, the lower end is provided with an extractant inlet 53, and the bottom is provided with a liquid outlet 52 for discharging the extracted product, and the liquid outlet 52 is connected to the feed inlet 13 of the distillation kettle 1.

[0056] The advantage of this embodiment is that, by setting the extraction tank 5, some light components can be removed in advance before distillation, so that the distillation purification effect is better.

[0057] Embodiment 4

[0058] This embodiment provides a method for purifying hexafluoropropylene oligomers, including the distillation purification system of hexafluoropropylene oligomers as in Embodiments 1 to 3. The specific structure is as shown in the attached Figure 1 As shown, the following steps are involved:

[0059] S1, pre-treatment: the crude hexafluoropropylene oligomer to be purified obtained by the addition reaction is introduced from the top feed port 13 of the distillation kettle 1 according to the single processing amount, and the tail gas pipe 26 at the top of the second buffer tank is opened, and the negative pressure pipe 27 is closed; the refrigerant circulation of the primary heat exchange tube 21 and the secondary heat exchange tube 24 is started, preferably, the refrigerant of the primary heat exchanger is circulating cooling water, and the condensation temperature is 5 to 30°C, and the refrigerant of the secondary heat exchanger is ethylene glycol, and the condensation temperature is -50 to -10°C; the three-way valve 282 is adjusted to make the liquid outlet pipe 28 connected to the first storage tank 31;

[0060] S2, one-stage distillation, removal of light component impurities: set the threshold of the heating device 12 to 60-90°C, start the stirring device 11 and the heating device 12, and start the first stage of atmospheric distillation. When the temperature of the distillation kettle 1 reaches the threshold, maintain a constant temperature state, and the light component impurities with a lower distillation point are first vaporized and enter the cooling device 2 through the first gas path 16, and flow through in sequence: the first-level heat exchange tube 21 is condensed, and the condensate and uncondensed gas enter the first-level cache tank 22, and the uncondensed gas enters the second-level heat exchange tube 24 through the second gas path 23 for secondary condensation, and the condensate and non-condensable gas enter the second-level cache tank 25, wherein the condensate in the first-level cache tank 22 and the second-level cache tank 25 enters the first storage tank 31 through the liquid outlet pipe 28, and the non-condensable gas enters the tail gas collection system through the tail gas pipe 26 at the top of the second-level cache tank 25, and the first storage tank 31 is connected to the front end of the polymerization kettle to reintroduce the condensate into the polymerization kettle to participate in the reaction;

[0061] S3, two-stage distillation, rinse cooling device 2: observe the sight glass 281 on the liquid outlet pipe 28. When there are no more droplets in the sight glass 281 connected to the primary cache tank 22 and the secondary cache tank 25, close the tail gas pipe 26, open the negative pressure pipe 27, start the negative pressure source, and make the cooling device 2, the storage tank 3 and the distillation kettle 1 reach the negative pressure state in turn. Preferably, the negative pressure value is set to -60 to -40 kPa; without adjusting the distillation temperature, the distillation kettle 1 enters the second stage of negative pressure distillation, and keeps the liquid outlet pipe 28 connected to the first storage tank 31. At this time, the hexafluoropropylene polymer vaporizes and enters the cooling device 2 to be condensed, and replaces the light component impurities remaining in the primary heat exchange pipe 21, the primary cache tank 22, the secondary heat exchange pipe 24, the secondary cache tank 25 and the liquid outlet pipe 28 in turn, and flows into the first storage tank 31;

[0062] S4, two-stage distillation, obtain the target product: observe the situation of the sight glass 281, when the two sight glass 281 both have droplets again, the cooling device 2 is rinsed, the three-way valve 282 on the liquid outlet pipe 28 is switched to connect it with the second storage tank 32, and the negative pressure distillation is continued. The hexafluoropropylene polymer condensed by the cooling device 2 is stored in the second storage tank 32, and the second storage tank 32 is connected to the distillation tower at the rear end to introduce the condensed hexafluoropropylene polymer into the distillation tower for distillation;

[0063] S5, still residue treatment: observe the condition of the sight glass 281. When the two sight glass 281 are converted to drop-free again, adjust the three-way valve 282 to connect the liquid outlet pipe 28 with the first storage tank 31 again; at the same time, close the negative pressure source, cut off the heat medium circulation of the still 1, open the still residue discharge port 15 at the bottom of the still 1 to discharge the heavy component impurities that have not been distilled, complete the distillation purification, and the still 1 enters the standby state;

[0064] The advantage of this embodiment is that the conventional static gas-liquid separation process is replaced by the pre-purification process of the distillation kettle 1 + two-stage cooling before distillation, and the distillation is divided into two stages. In the first stage, atmospheric distillation is performed to separate light impurities such as solvents and catalysts. In the second stage, the same distillation temperature as the first stage is maintained and negative pressure distillation is performed. The distillation point of the hexafluoropropylene oligomer is lowered by negative pressure, so that it is separated at a lower temperature, and at the same time, it is avoided that part of the heavy component impurities are decomposed to generate new impurities with the same volatilization temperature as the hexafluoropropylene oligomer at the atmospheric distillation point temperature of the hexafluoropropylene oligomer, and finally the mixed light components and heavy component impurities in the target product are further separated, especially the impurity components that are easily decomposed at the boiling point temperature and the volatilization temperature of the target product to produce impurity components with a volatility similar to that of the target product are separated in advance, so that the impurity content of the crude product entering the distillation tower is lower, and the secondary reaction amount in the distillation tower and the impurity content in the finished product are effectively reduced, thereby obtaining a higher purity hexafluoropropylene oligomer.

[0065] Embodiment 5

[0066] The present embodiment provides a method for purifying hexafluoropropylene oligomers. On the basis of the fourth embodiment, a crude product pretreatment step S0 is added at the front end of step S1 and the rear end of the polymerization kettle. The specific steps are: the crude hexafluoropropylene oligomer to be distilled and the extractant are introduced into the extraction tank 5 for stirring and mixing, the crude hexafluoropropylene oligomer to be distilled enters from the top and exits from the bottom, the extractant enters from the bottom and exits from the top, and the extracted crude hexafluoropropylene oligomer is introduced into the distillation kettle 1 of step S1; the extraction tank 5 can adopt the structure described in the third embodiment (see the attached drawing). Figure 6 ).

[0067] The advantages of this embodiment are: by utilizing the compatibility of the extractant with light impurities such as solvents and catalysts, as well as the insolubility of the target product, some light impurities in the crude product can be separated in advance, reducing the time consumption of one stage of the distillation kettle 1, thereby improving the purity of the final product and improving production efficiency.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the present invention.

Claims

1. A distillation and purification system for hexafluoropropylene oligomers, Features: It includes a still, a two-stage cooling device and a storage tank; The distillation kettle is provided with a stirring device and a heating device, the top of the distillation kettle is provided with a feed inlet and a gas outlet, and the bottom of the distillation kettle is provided with a kettle residue outlet, the feed inlet is used to introduce the crude product to be purified, and the gas outlet is connected to the cooling device; The cooling device comprises a primary heat exchange pipe, a primary cache tank, a secondary heat exchange pipe and a secondary cache tank which are connected in sequence, and refrigerant circulates in the primary heat exchange pipe and the secondary heat exchange pipe, the gas outlet is connected to the top of the primary heat exchange pipe through a first gas path, the top of the primary cache tank is connected to the top of the secondary heat exchange pipe through a second gas path, the top of the secondary cache tank is connected to a tail gas pipe and a negative pressure pipe, the ends of the tail gas pipe and the negative pressure pipe are both connected to an external tail gas collection system, the tail gas pipe is provided with a first gas shut-off valve, the negative pressure pipe is provided with a second gas shut-off valve and is connected to a negative pressure source, the first gas shut-off valve and the second gas shut-off valve are opened and closed alternately, and when the second gas shut-off valve is opened and the first gas shut-off valve is closed, the distillation kettle, the cooling device and the storage tank are all in a negative pressure state; liquid outlet pipes are respectively provided at the bottom of the primary cache tank and the secondary cache tank, and a three-way valve is provided on the liquid outlet pipe; The storage tank comprises a first storage tank and a second storage tank, the first storage tank is used to store light component impurities obtained by distillation, the second storage tank is used to store the target product after distillation and purification, the first-level cache tank and the second-level cache tank are connected to the first storage tank or the second storage tank through the three-way valve, the first storage tank is connected to the front-end polymerization kettle, and the second storage tank is connected to the rear-end distillation tower; The liquid outlet pipes are each provided with a sight glass, which is used to observe the liquid state in the primary cache tank and the secondary cache tank, and to open and close the first gas stop valve and the second gas stop valve according to the observation results, and to adjust the connectivity state of the three-way valve.

2. A distillation and purification system for hexafluoropropylene oligomers according to claim 1, Features: The refrigerant of the first-stage heat exchange tube is circulating cooling water, and the refrigerant of the second-stage heat exchange tube is ethylene glycol.

3. A distillation and purification system for hexafluoropropylene oligomers according to claim 1, Features: The liquid outlet pipe is provided with a flow monitoring device at the front end of the three-way valve at the rear end of the sight glass, and the flow monitoring device includes a liquid collecting annular groove, a detection branch, a flow meter and a control device. The liquid collecting annular groove is an annular groove surrounded by L-shaped protrusions on the inner wall of the liquid outlet pipe. The upper end of the detection branch is connected with the liquid collecting annular groove, and the lower end is connected with the inside of the liquid outlet pipe. When liquid flows in the liquid outlet pipe, the liquid flowing against the wall is blocked by the liquid collecting annular groove and flows through the detection branch and then returns to the liquid outlet pipe. The flow meter is arranged on the detection branch and detects the flow in the detection branch. The flow meter is connected to the control device by signal. The first gas stop valve and the second gas stop valve are pneumatic ball valves, and the three-way valve is a three-way pneumatic ball valve; the control device is connected to the first gas stop valve, the second gas stop valve and the three-way valve by signal and controls their opening and closing.

4. A distillation and purification system for hexafluoropropylene oligomers according to claim 1, Features: The heating device of the distillation kettle comprises a half pipe arranged on the outer wall of the distillation kettle and a coil arranged in the distillation kettle, the coil is arranged around the stirring device, and heat medium circulates in both the half pipe and the coil, and the heat medium is water vapor or heat transfer oil.

5. A distillation and purification system for hexafluoropropylene oligomers according to claim 1, Features: The front end of the distillation kettle is also connected to an extraction tank for extracting some light component impurities. The upper end of the extraction tank is provided with an extraction agent outlet, the middle part is provided with a liquid inlet for introducing the crude product to be purified, the lower end is provided with an extraction agent inlet, and the bottom is provided with a liquid outlet for discharging the extracted product. The liquid outlet is connected to the feed inlet of the distillation kettle.

6. A method for purifying hexafluoropropylene oligomers, Features: A distillation and purification system for hexafluoropropylene oligomers comprising the system as claimed in any one of claims 1 to 5, and comprising the following steps: S1, pre-treatment: the crude hexafluoropropylene oligomer to be purified obtained by the addition reaction is introduced from the top feed port of the distillation kettle according to the single processing amount, and the tail gas pipe at the top of the second buffer tank is opened, and the negative pressure pipe is closed; the refrigerant circulation of the primary heat exchange pipe and the secondary heat exchange pipe is started; the three-way valve is adjusted to make the liquid outlet pipe connected to the first storage tank; S2, one-stage distillation, removal of light component impurities: set the threshold of the heating device to 60-90°C, start the stirring device and the heating device, start the first stage of atmospheric distillation, and when the temperature of the distillation kettle reaches the threshold, continue to maintain a constant temperature state. The light component impurities with a lower distillation point are first vaporized and enter the cooling device through the first gas path, and flow through in sequence: the first-stage heat exchange tube is condensed, the condensate and the uncondensed gas enter the first-stage buffer tank, the uncondensed gas enters the second-stage heat exchange tube through the second gas path for secondary condensation, and the condensate and the non-condensable gas enter the second-stage buffer tank, wherein the condensate in the first-stage buffer tank and the second-stage buffer tank enters the first storage tank through the liquid outlet pipe, and the non-condensable gas enters the tail gas collection system through the tail gas pipe at the top of the second-stage buffer tank, and the first storage tank is connected to the front end polymerization kettle; S3, two-stage distillation, rinse cooling device: observe the sight glass on the liquid outlet pipe. When there are no more droplets in the sight glass connected to the primary cache tank and the secondary cache tank, close the tail gas pipe, open the negative pressure pipe, start the negative pressure source, and make the cooling device, storage tank and distillation kettle reach the negative pressure state in turn. Do not adjust the distillation temperature. The distillation kettle enters the second stage of negative pressure distillation. Keep the liquid outlet pipe connected to the first storage tank. At this time, the hexafluoropropylene polymer vaporizes and enters the cooling device to be condensed, and replaces the light component impurities remaining in the primary heat exchange pipe, the primary cache tank, the secondary heat exchange pipe, the secondary cache tank and the liquid outlet pipe in turn, and flows into the first storage tank; S4, two-stage distillation, obtain the target product: observe the sight glass, when droplets appear in both sight glasses again, the cooling device is rinsed, switch the three-way valve on the liquid outlet pipe to connect it with the second storage tank, continue the negative pressure distillation, and the hexafluoropropylene polymer obtained by condensation of the cooling device is stored in the second storage tank, and the second storage tank is connected to the rear distillation tower; S5, still residue treatment: observe the sight glass. When the two sight glass are converted to drop-free again, adjust the three-way valve to reconnect the liquid outlet pipe with the first storage tank; at the same time, close the negative pressure source, cut off the heat medium circulation of the still, open the still residue outlet at the bottom of the still to discharge the heavy component impurities that have not been distilled, complete the distillation and purification, and the still enters the standby state.

7. A method for purifying hexafluoropropylene oligomers according to claim 6, Features: In steps S1 to S4, the condensation temperature of the primary heat exchanger is 5 to 30°C, and the condensation temperature of the secondary heat exchanger is -50 to -10°C.

8. A method for purifying hexafluoropropylene oligomers according to claim 7, Features: The refrigerant of the primary heat exchanger is circulating cooling water, and the refrigerant of the secondary heat exchanger is ethylene glycol.

9. The method for purifying hexafluoropropylene oligomer according to claim 6, Features: The negative pressure value of the second stage negative pressure distillation in steps S3 and S4 is -60 to -40 kPa.

10. The method for purifying hexafluoropropylene oligomer according to claim 6, Features: The process also includes crude product pretreatment in step S0: introducing crude hexafluoropropylene polymer to be distilled and an extractant into an extraction tank for stirring and mixing, the crude hexafluoropropylene polymer to be distilled enters from the top and exits from the bottom, the extractant enters from the bottom and exits from the top, and the extracted crude hexafluoropropylene polymer is introduced into the distillation kettle in step S1.

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