Method for separating 1-fluoro-1, 1-dichloroethane and 1, 1, 1, 3, 3-pentafluorobutane azeotrope through extractive distillation

Abstract

The invention relates to a method for separating azeotrope of 1-fluoro-1, 1-dichloroethane and 1, 1, 1, 3, 3-pentafluorobutane through extractive distillation. According to the method for separating the 1-fluoro-1, 1-dichloroethane and the 1, 1, 1, 3, 3-pentafluorobutane azeotrope through extractive distillation, an extracting agent is added into the 1-fluoro-1, 1-dichloroethane and the 1, 1, 1, 3, 3-pentafluorobutane azeotrope, and the extracting agent is one or more of n-amyl alcohol and n-heptanol. The method adopts intermittent extractive distillation or continuous extractive distillation operation, and has the advantages of simple and efficient separation process, high product purity and the like. The loss rate of the extracting agent is low, the extracting agent can be recycled, and environmental pollution can be avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation and purification, and particularly relates to a method for separating azeotropes of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation. Background Art

[0002] 1-Fluoro-1,1-dichloroethane (HCFC-141b) is a versatile chemical used as a foaming agent for products such as construction, refrigerators, and water heaters, a cleaning agent and dry-cleaning agent for mechanical parts such as metals, electronics, and instruments, an extractant for natural organic compounds, a refrigerant for polyurethane plastic foaming agents, a cutting oil coolant, and mixed with other solvents for cleaning metals, plastics, fabrics, and leather. In addition, it is also used as a cleaning agent for disposable medical devices, a foaming agent for rigid and flexible polyurethane foams, and a raw material for the production of polytrifluorochloroethylene. However, due to its potential destructive effect on the ozone layer, the application of HCFC-141b is gradually being reduced and banned. 1,1,1,3,3-Pentafluorobutane (HFC-365mfc), as a more environmentally friendly alternative to HCFC-141b, has overlapping applications with HCFC-141b, especially in the refrigerant market. With restrictions on the use of HCFC-141b, hydrofluorocarbons (HFCs) such as HFC-365mfc have become more ideal choices because they can meet the needs of refrigeration and foaming while reducing the impact on the environment.

[0003] In the process of preparing vinylidene fluoride (VDF) by pyrolysis of HCFC-142b, industrial waste liquid containing HCFC-141b and HFC-365mfc will be produced. At present, it is generally treated by incineration, which not only wastes resources but is also not environmentally friendly. Since HCFC-141b and HFC-365mfc can form azeotropes under normal pressure, it is very difficult to separate the two, and ordinary distillation cannot separate the two. The patent application publication number US75102391A discloses a method for separating HCFC-141b and HFC-365mfc by liquid-liquid extraction using ethylene glycol as an extractant. The selectivity of the extractant for HCFC-141b (25°C) is 1.24-3.85. HCFC-141b is extracted from the mixture by multi-stage extraction to achieve the separation of the two. However, this method uses a large amount of extractant and has low efficiency, which not only increases costs, but also makes the subsequent processing process more complicated. The patent with application publication number US34760389A discloses a method for separating HCFC-141b and HFC-365mfc by azeotropic distillation, specifically, adding hydrogen fluoride to a mixture of HCFC-141b and HFC-365mfc, the amount of hydrogen fluoride added is at least 3 times the molar amount of HCFC-141b, obtaining HFC-365mfc product at the bottom of the distillation tower, and obtaining a mixture of hydrogen fluoride and HCFC-141b with a near azeotropic composition (molar ratio of about 3:1) at the top of the tower. The top product is phase-separated at a low temperature of about -25°C to -15°C to obtain an upper liquid phase enriched in hydrogen fluoride and a lower liquid phase enriched in HCFC-141b, and the lower liquid phase is distilled to obtain an HCFC-141b product at the bottom of the tower. This method has a high separation efficiency, but the process is complicated, the energy consumption is high, the fluorination reaction is prone to occur, and hydrogen fluoride is highly corrosive and toxic. Summary of the invention

[0004] The invention aims to provide a method for separating azeotropes of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation, so as to solve the technical problems of large amount of extractant and complicated process in the prior art when separating azeotropes of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for separating an azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation, wherein an extractant is added to the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane, and the extractant is one or more of n-pentanol and n-heptanol.

[0007] Furthermore, the mass fraction of 1-fluoro-1,1-dichloroethane in the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is 20 to 95%.

[0008] Furthermore, the mass flow rate ratio of the extractant to the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is 0.1:1 to 10:1, preferably 1:1 to 3:1.

[0009] The extraction method of the present invention can be an intermittent extraction and distillation operation or a continuous extraction and distillation operation.

[0010] Furthermore, the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane and the extractant are fed into an extractive distillation tower respectively, the extractant feeding position is located above the feeding position of the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane, 1-fluoro-1,1-dichloroethane is obtained at the top of the extractive distillation tower, and a mixture of 1,1,1,3,3-pentafluorobutane and the extractant is obtained at the bottom of the extractive distillation tower; the mixture of 1,1,1,3,3-pentafluorobutane and the extractant enters an extractant recovery tower, 1,1,1,3,3-pentafluorobutane is obtained at the top of the extractant recovery tower, and the extractant is recovered at the bottom of the extractant recovery tower for recycling; the distillation method in the extractive distillation tower is continuous extractive distillation.

[0011] Furthermore, the pressure in the extractive distillation tower is atmospheric pressure, the top temperature of the extractive distillation tower is 20-70°C, and the reflux ratio is 0.1:1-10:1. Preferably, the top temperature of the extractive distillation tower is 32°C, and the reflux ratio is 0.1:1-2:1.

[0012] Furthermore, the pressure in the extractant recovery tower is atmospheric pressure, the top temperature of the extractant recovery tower is 30-80°C, and the reflux ratio is 0.1:1-10:1. Preferably, the top temperature of the extractant recovery tower is 42°C, and the reflux ratio is 0.1:1-2:1.

[0013] Furthermore, the number of plates of the extractive distillation tower is 20 to 60, the extractant enters the extractive distillation tower from the 2nd to 30th plates, and the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is subjected to the extractive distillation tower from the 3rd to 40th plates. Preferably, the number of plates of the extractive distillation tower is 35 to 40, the extractant enters the extractive distillation tower from the 4th to 6th plates, and the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is subjected to the extractive distillation tower from the 10th to 15th plates.

[0014] Furthermore, the number of plates of the extractant recovery tower is 10 to 50, and the 1,1,1,3,3-pentafluorobutane and the extractant mixture enter the extractant recovery tower from the 2nd to 40th plates. Preferably, the number of plates of the extractant recovery tower is 18 to 25, and the 1,1,1,3,3-pentafluorobutane and the extractant mixture enter the extractant recovery tower from the 9th to 12th plates.

[0015] 1-Fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane azeotrope are added to the distillation tower kettle and heated, and an extractant is added after full reflux operation, and the full reflux operation is continued to obtain 1-Fluoro-1,1-dichloroethane at the top of the distillation tower; the distillation method in the distillation tower is intermittent extractive distillation.

[0016] Furthermore, the time of the first total reflux is 1 to 3 hours, and the time of the second total reflux is 1 to 2 hours.

[0017] Beneficial effects of the present invention:

[0018] The present invention adopts extraction and distillation operation, and has the advantages of simple and efficient separation process, high product purity, etc. The loss rate of the extractant is low, and the extractant can be recycled, which can avoid causing environmental pollution.

[0019] The invention has simple process, is easy to operate, can reduce cost investment, is green and environmentally friendly, and can be used industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a diagram of the apparatus used in the intermittent extractive distillation operation in Examples 1-4;

[0021] Figure 2 This is a diagram of the apparatus used for the continuous extractive distillation operation in Examples 5-14.

[0022] In the figure: 1, electric heating jacket; 2, distillation tower kettle; 3, thermometer 1; 4, distillation tower; 5, thermometer 2; 6, high-level tank; 7, condenser; 8, product collection tank; T1, extraction distillation tower; T2, extraction agent recovery tower; H1, condenser 1; H2, reboiler 1; H3, condenser 2; H4, reboiler 2; V1, reflux tank 1; V2, kettle liquid tank 1; V3, reflux tank 2; V4, kettle liquid tank 2; P1, kettle liquid pump 1; P2, kettle liquid pump 2; DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0024] The device used in the intermittent extraction distillation operation includes: a distillation tower 4, the distillation tower 4 is wrapped with insulation cotton, and the distillation tower kettle 2 is provided with an electric heating jacket 1; the top of the distillation tower 4 is connected to a high-level tank 6 and a condenser 7, and the condenser 7 is connected to a product collection tank 8.

[0025] The device used in the continuous extraction and distillation operation includes: an extraction and distillation tower T1, condensers H1, H3, reflux tanks V1, V3, kettle liquid tanks V2, V4, reboilers H2, H4, an extractant recovery tower T2, and kettle liquid pumps P1, P2. The condenser H1 is connected to the top of the extraction and distillation tower T1, the reflux tank V1 is connected to the condenser H1, the reboiler H2 is connected to the bottom of the extraction and distillation tower T1, and the kettle liquid tank V2 and the kettle liquid pump P1 are connected to the reboiler H2; the condenser H3 is connected to the top of the extraction agent recovery tower T2, the reflux tank V3 is connected to the condenser H3, the reboiler H4 is connected to the bottom of the extraction agent recovery tower T2, and the kettle liquid tank V4 and the kettle liquid pump P2 are connected to the reboiler H4.

[0026] Example 1

[0027] The extraction method of Example 1 is an intermittent extraction distillation operation, and the specific steps are as follows: the inner diameter of the distillation tower is 2 cm, the effective packing height of the distillation tower is 200 cm, and the number of theoretical plates is 35. 200 g of HCFC-141b and HFC-365mfc azeotropes with a mass fraction of 77% of HCFC-141b are added to the distillation tower kettle, n-pentanol is added to the high-level tank, and the condenser is connected to a low-temperature constant temperature stirring reaction bath set at -15°C. The electric heating jacket is turned on to heat the distillation tower kettle, and a full reflux operation is performed without adding an extractant until the whole tower is in a stable state, and the full reflux is continued for 2 hours. The high-level tank valve is opened, and n-pentanol is added to the tower at a mass ratio of 0.2 between the extractant and the raw material, and the full reflux operation is performed for 1 hour to reduce the content of HFC-365mfc in the distillation tower top fraction. When the temperature at the top of the distillation tower is stabilized, the high-level tank valve is adjusted to extract the fraction at a reflux ratio of 1. The mass fraction of HCFC-141b at the top of the distillation tower is 93.8%.

[0028] Examples 2-4 use the same intermittent extractive distillation operation as Example 1. Comparative Examples 1 and 2 provide a conventional intermittent distillation method for separating azeotropic mixtures of HCFC-141b and HFC-365mfc. The relevant process parameters and product purity of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0029] Table 1 Relevant process parameters and product purity of Examples 1-4 and Comparative Examples 1-2

[0030]

[0031] Example 5

[0032] Example 5 adopts a continuous extractive distillation operation mode: the extractive distillation tower has 40 theoretical plates, n-pentanol is added from the 5th plate at a flow rate of 10000 kg / h; HCFC-141b and HFC-365mfc azeotrope are added from the 10th plate of the extractive distillation tower at a flow rate of 1000 kg / h. The pressure in the extractive distillation tower is normal pressure, the reflux ratio is 5, and the top temperature of the extractive distillation tower is 32°C.

[0033] The top product of the extractive distillation tower is condensed in a condenser and stored in a reflux tank. A portion of the product (HCFC-141b) is extracted and a portion of the product is refluxed to the extractive distillation tower. A mixture of HFC-365mfc and n-pentanol is obtained at the bottom of the tower.

[0034] The extractant recovery tower has 22 theoretical plates, and the HFC-365mfc and n-pentanol mixture at the bottom of the extractant distillation tower is added to the extractant recovery tower from the 11th plate. The pressure in the extractant recovery tower is normal pressure, and the reflux ratio is 2. The top temperature of the extractant recovery tower is 42°C, and the n-pentanol obtained at the bottom of the tower is recycled back to the extractant distillation tower for repeated use.

[0035] The top product of the extractant recovery tower is condensed by condenser 2 and stored in reflux tank 2, a part of which is taken out as the product (HFC-365mfc), and a part of which is refluxed to the extractant recovery tower. The extractant obtained at the bottom of the extractant recovery tower has a purity of more than 99.9% and a loss rate of less than 0.1%.

[0036] Examples 6-14 adopt the same continuous extraction distillation operation mode as Example 5. The relevant process parameters and product purity of Examples 5-14 are shown in Tables 2 and 3.

[0037] Table 2 Relevant process parameters and product purity of Examples 5-9

[0038]

[0039] Table 3 Relevant process parameters and product purity of Examples 10-14

[0040]

Claims

1. A method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation, characterized in that: An extractant is added to the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane, wherein the extractant is one or more of n-pentanol and n-heptanol.

2. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 1, characterized in that: The mass fraction of 1-fluoro-1,1-dichloroethane in the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is 20-95%.

3. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 1, characterized in that: The mass flow ratio of the extractant to the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is 0.1:1 to 10:

1.

4. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to any one of claims 1 to 3, characterized in that: The following steps are involved: The azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane and the extractant are fed into an extractive distillation tower respectively, the extractant feeding position is located above the feeding position of the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane, 1-fluoro-1,1-dichloroethane is obtained at the top of the extractive distillation tower, and a mixture of 1,1,1,3,3-pentafluorobutane and the extractant is obtained at the bottom of the extractive distillation tower; the mixture of 1,1,1,3,3-pentafluorobutane and the extractant enters an extractant recovery tower, 1,1,1,3,3-pentafluorobutane is obtained at the top of the extractant recovery tower, and the extractant is recovered at the bottom of the extractant recovery tower for recycling; the distillation method in the extractive distillation tower is continuous extractive distillation.

5. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 4, characterized in that: The pressure inside the extractive distillation tower is normal pressure, the top temperature of the extractive distillation tower is 20-70° C., and the reflux ratio is 0.1:1-10:

1.

6. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 4, characterized in that: The pressure in the extractant recovery tower is normal pressure, the top temperature of the extractant recovery tower is 30-80° C., and the reflux ratio is 0.1:1-10:

1.

7. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 4, characterized in that: The number of plates of the extractive distillation tower is 20 to 60, the extractant enters the extractive distillation tower from the 2nd to 30th plates, and the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane is extracted and distilled from the 3rd to 40th plates.

8. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 4, characterized in that: The extractant recovery tower has 10 to 50 plates, and the 1,1,1,3,3-pentafluorobutane and the extractant mixture enter the extractant recovery tower from the 2nd to 40th plates.

9. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1-Fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane azeotrope are added to the distillation tower kettle and heated, and an extractant is added after full reflux operation, and the full reflux operation is continued to obtain 1-Fluoro-1,1-dichloroethane at the top of the distillation tower; the distillation method in the distillation tower is intermittent extractive distillation.

10. The method for separating the azeotrope of 1-fluoro-1,1-dichloroethane and 1,1,1,3,3-pentafluorobutane by extractive distillation according to claim 9, characterized in that: The time of the first total reflux is 1 to 3 hours, and the time of the second total reflux is 1 to 2 hours.

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