Method for separating and recovering white oil and dichloromethane mixed solution

Abstract

The invention provides a white oil and dichloromethane mixed liquid separation and recovery method, which comprises the following steps: feeding a white oil and dichloromethane mixed liquid to a first-stage evaporator, heating by the first-stage evaporator, separating to obtain first-stage dichloromethane steam and first-stage concentrated liquid, pressurizing and heating the separated first-stage dichloromethane steam by a compressor, and concentrating the first-stage concentrated liquid to obtain second-stage concentrated liquid; pressurizing to serve as a heating medium of a first-stage evaporator, and carrying out heat exchange condensation to obtain first-stage dichloromethane liquid; the first-stage concentrated liquid is sent to a second-stage evaporator to be further separated to obtain second-stage dichloromethane steam and second-stage concentrated liquid, the second-stage dichloromethane steam is condensed to obtain second-stage dichloromethane liquid, the second-stage concentrated liquid is subjected to gas stripping to obtain refined white oil, and third-stage dichloromethane steam obtained in the gas stripping process is condensed to obtain third-stage dichloromethane liquid. The compressor is mainly driven by electric energy, the efficiency of converting the electric energy into heat energy is high, namely, the heat pump principle is adopted, and therefore energy consumption is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification of white oil and dichloromethane, and in particular to a method for separating and recovering a mixed liquid of white oil and dichloromethane. Background Art

[0002] The specialty fiber and lithium battery separator industry usually uses white oil as a swelling agent or pore-forming agent in the wet production process. Due to the safety of dichloromethane, dichloromethane solvent is often used to elute the white oil on the surface of the specialty fiber and inside the separator by multi-stage extraction, thereby forming a special fiber filament or microporous structure. The white oil content in the mixed liquid produced by the production line is usually 2-20wt%, and the dichloromethane content is 80-98wt%. In this process, white oil and dichloromethane are used in large quantities, so a reasonable separation and recovery process is designed to obtain high-purity white oil and dichloromethane, which are then used in the production of specialty fibers and lithium battery separators, which can reduce the consumption of raw materials, effectively reduce production costs, and is beneficial to the environment.

[0003] White oil, also known as paraffin oil, white oil, mineral oil. It is a colorless, transparent, oily liquid with no odor. It is a mineral oil that has been specially refined. The basic composition of white oil is a saturated hydrocarbon structure, while the content of aromatic hydrocarbons, nitrogen, oxygen, sulfur and other substances is close to zero. Moreover, white oil has good chemical stability and does not corrode fiber textiles. It is the most widely used oil-soluble raw material in cosmetics. It can also be used to prepare bath oils, various skin care creams, honey, hair care products, lipsticks and other similar cosmetics. It is mainly used to increase the brightness and smoothness of the product. It is also used more in some rubbers. The relative density is 0.86-0.905 (25℃), the boiling point is 250~400℃, insoluble in water, glycerin, cold ethanol; soluble in benzene, ether, chloroform, carbon disulfide, hot ethanol. It can be mixed with most fatty oils except castor oil, and camphor, menthol and most natural or artificial musks can be dissolved.

[0004] Dichloromethane is a colorless, transparent liquid with a pungent odor similar to ether. It is insoluble in water, but soluble in ethanol and ether. It is a non-flammable, low-boiling-point solvent, often used to replace flammable petroleum ether, ether, etc. The boiling point is 39.75°C, and the relative density is 1.325 (25°C).

[0005] At present, the separation and recovery of the mixed liquid of white oil and dichloromethane generally adopts the method of primary standard atmospheric pressure distillation + gas stripping for separation and purification. Due to the high content of dichloromethane in the mixed liquid, a large amount of steam is consumed. At the same time, the dichloromethane vapor evaporated requires a large amount of circulating water and low-temperature water for cooling. This distillation technology has the problem of high energy consumption.

[0006] In addition, the separation and recovery by two-stage evaporation + scraper evaporator consumes a large amount of steam, which will also cause the white oil to coke and darken in color. The amount of white clay or bleaching sand used during bleaching will increase, increasing production costs, and the product indicators are not good. The white oil content in the dichloromethane liquid after condensation is as high as 200ppm or more.

[0007] In addition, the double-effect evaporation + distillation + gas stripping method is used for separation and recovery. Although the amount of steam consumed is greatly reduced, it only saves 35%-45% of operating energy compared with the traditional method, and the indicators of the dichloromethane product are not good. The white oil content in the dichloromethane liquid after condensation is as high as over 200ppm. Summary of the invention

[0008] The purpose of the present invention is to provide a method for separating and recovering a mixed liquid of white oil and dichloromethane in view of the defects of the prior art, comprising the following steps: The mixed liquid of white oil and dichloromethane is sent to the primary evaporator, and after being heated by the primary evaporator, the primary dichloromethane vapor and the primary concentrated liquid of white oil and dichloromethane are separated, and the primary dichloromethane vapor is pressurized and heated by a compressor and used as the heating medium of the primary evaporator, and is condensed by heat exchange to obtain the primary dichloromethane liquid; The first concentrated liquid of white oil and dichloromethane is sent to the second evaporator for heating and then separated to obtain second dichloromethane vapor and second concentrated liquid of white oil and dichloromethane. The second dichloromethane vapor is condensed to obtain second dichloromethane liquid. The second concentrated liquid of white oil and dichloromethane is further subjected to gas stripping to obtain refined white oil. Meanwhile, the third dichloromethane vapor obtained in the gas stripping process is condensed to obtain third dichloromethane liquid.

[0009] Further, after preheating the white oil and dichloromethane mixture, the white oil and dichloromethane mixture is passed through a primary evaporator and a secondary evaporator in sequence to obtain dichloromethane liquid and a secondary concentrated liquid of the white oil and dichloromethane mixture, and then the secondary concentrated liquid of the white oil and dichloromethane mixture is passed through a gas stripping tower to obtain refined white oil through gas stripping; The primary evaporation device comprises a primary evaporator, a primary separator, a compressor, and a startup evaporator. When the white oil and dichloromethane mixture is first introduced into the tube side of the primary evaporator, the startup evaporator generates steam and introduces it into the shell side of the primary evaporator to heat the white oil and dichloromethane mixture to obtain primary dichloromethane steam and primary concentrated liquid of the white oil and dichloromethane mixture. The primary separator separates the primary dichloromethane steam from the primary concentrated liquid of the white oil and dichloromethane mixture, and the separated primary concentrated liquid of the white oil and dichloromethane mixture is transported to the secondary evaporation device. The separated primary dichloromethane steam is pressurized and heated by the compressor and then introduced into the shell side of the primary evaporator again to heat the white oil and dichloromethane mixture in the tube side of the primary evaporator subsequently, and the primary dichloromethane liquid obtained after the primary dichloromethane steam is cooled is collected. The secondary evaporation device comprises a secondary evaporator, a secondary separator and a condenser. The primary concentrated liquid of the white oil and dichloromethane mixture is passed into the tube side of the secondary evaporator, and the external fresh steam is passed into the shell side of the secondary evaporator to heat the primary concentrated liquid of the white oil and dichloromethane mixture to obtain secondary dichloromethane steam and secondary concentrated liquid of the white oil and dichloromethane mixture. After the secondary separator separates the secondary dichloromethane steam and the secondary concentrated liquid of the white oil and dichloromethane mixture, the separated secondary dichloromethane steam is passed into the condenser to obtain secondary dichloromethane liquid. The separated secondary concentrated liquid of the white oil and dichloromethane mixture is passed into a gas stripping tower to obtain refined white oil through gas stripping. The tertiary dichloromethane vapor obtained in the gas stripping process is condensed and combined with the primary dichloromethane liquid and the secondary dichloromethane liquid to obtain all the dichloromethane liquid separated from the white oil and dichloromethane mixture.

[0010] Furthermore, the pressure of the first-stage evaporator tube side is standard atmospheric pressure, and the temperature is 45~65°C; the pressure of the first-stage evaporator shell side is 153~350KPa, and the temperature is 52~81°C.

[0011] Furthermore, the pressure of the first-stage evaporator tube side is negative pressure, and the temperature is 24-32° C.; the pressure of the first-stage evaporator shell side is 72-99 kPa, and the temperature is 31-39° C. Further, the pressure of the first-stage evaporator tube side is 40-55 kPa.

[0012] Furthermore, in the mixed liquid of white oil and dichloromethane, the content of white oil is 2-20wt%, and the content of dichloromethane is 80-98wt%.

[0013] Furthermore, the compression ratio of the compressor is 1.5~3.5.

[0014] Furthermore, the content of dichloromethane in the primary concentrate of the mixture of white oil and dichloromethane is 25-65wt%.

[0015] Furthermore, the separation and recovery method of the white oil and dichloromethane mixed liquid is achieved by the following device, including: The preheater is connected to the tube side feed port of the primary evaporator, the tube side dichloromethane steam outlet of the primary evaporator is connected to the dichloromethane steam inlet of the primary separator, the tube side concentrate liquid outlet of the primary evaporator is connected to the tube side feed port of the secondary evaporator, the gas phase extraction outlet of the primary separator is connected to the gas phase inlet of the compressor, the gas phase outlet of the compressor is connected to the shell side inlet of the primary evaporator, the shell side outlet of the primary evaporator is connected to the dichloromethane condensate tank, and the concentrate liquid outlet of the primary separator is connected to the tube side feed port of the secondary evaporator.

[0016] The startup evaporator is provided with a tube-side inlet and a tube-side outlet. The tube-side inlet of the startup evaporator is respectively connected to the tube-side outlet of the first-stage evaporator and the concentrated liquid outlet of the first-stage separator, and the tube-side outlet of the startup evaporator is connected to the shell-side inlet of the first-stage evaporator. The startup evaporator is used to provide the first-stage evaporator with fresh steam for startup heating of the heat pump.

[0017] The tube-side dichloromethane vapor outlet of the secondary evaporator is connected to the dichloromethane vapor inlet of the secondary separator, the tube-side concentrated liquid outlet of the secondary evaporator is connected to the feed inlet of the gas stripping tower, the gas phase extraction outlet of the secondary separator is connected to the gas phase inlet of the condenser, the gas phase outlet of the condenser is connected to the first dichloromethane condensate outlet, the concentrated liquid outlet of the secondary separator is connected to the feed inlet of the gas stripping tower, the refined white oil outlet of the gas stripping tower is connected to the refined white oil storage tank, the two ends of the gas stripping tower evaporator are respectively connected to the shell-side feed inlet and shell-side discharge of the gas stripping tower, the nitrogen conveying device is connected to the nitrogen feed inlet of the gas stripping tower, and the dichloromethane discharge port of the gas stripping tower is connected to the second dichloromethane condensate outlet.

[0018] Furthermore, the pressure of the secondary evaporator tube side is standard atmospheric pressure.

[0019] The beneficial effects of the present invention are: 1. In the present invention, the dichloromethane vapor generated by the primary evaporator is directly returned to the primary evaporator as a heat source after being pressurized and heated by the compressor. This process realizes the recycling of the latent heat of steam, and only the electric energy of the compressor is needed to increase the steam temperature, without the need for additional steam input. This solution mainly relies on electric energy to drive the compressor, and the efficiency of converting electric energy into heat energy is high (heat pump principle). This solution usually has a high energy efficiency ratio, and is particularly suitable for volatile substances with low boiling points (such as dichloromethane).

[0020] 2. By setting the pressure of the first-stage evaporator, whether in the tube side or the shell side, to negative pressure, the boiling point of the liquid phase is lowered and only needs to be heated to a lower temperature, thereby further reducing energy consumption.

[0021] 3. The technical solution of the present invention saves about 70% of energy consumption compared with the first-stage standard atmospheric pressure distillation + gas stripping method in the background technology, and saves about 30% of energy consumption compared with the double-effect evaporation + distillation + gas stripping method in the background technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a heat pump distillation device for separating and recovering white oil and dichloromethane according to an embodiment of the present invention.

[0023] Figure numerals: 1-preheater; 2-primary evaporator; 3-primary separator; 4-compressor; 5-start-up evaporator; 6-dichloromethane condensate tank; 7-secondary evaporator; 8-gas stripping tower; 9-secondary separator; 10-condenser; 11-gas stripping tower evaporator; 12-refined white oil storage tank; 13-first dichloromethane condensate outlet; 14-second dichloromethane condensate outlet; 15-nitrogen delivery device. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] The term "negative pressure" refers to a pressure that is negative relative to standard atmospheric pressure.

[0026] like Figure 1 As shown, a heat pump distillation device for separating and recovering white oil and dichloromethane comprises the following structure; The preheater 1 is connected to the tube side feed port of the primary evaporator 2, the tube side dichloromethane vapor outlet of the primary evaporator 2 is connected to the dichloromethane vapor inlet of the primary separator 3, the tube side concentrate liquid outlet of the primary evaporator 2 is connected to the tube side feed port of the secondary evaporator 7, the gas phase extraction outlet of the primary separator 3 is connected to the gas phase inlet of the compressor 4, the gas phase outlet of the compressor 4 is connected to the shell side inlet of the primary evaporator 2, the shell side outlet of the primary evaporator 2 is connected to the dichloromethane condensate tank 6, and the concentrate liquid outlet of the primary separator 3 is connected to the tube side feed port of the secondary evaporator 7.

[0027] The startup evaporator 5 is provided with a tube side inlet and a tube side outlet. The tube side inlet of the startup evaporator 5 is respectively connected to the tube side outlet of the primary evaporator 2 and the concentrate outlet of the primary separator 3, and the tube side outlet of the startup evaporator 5 is connected to the shell side inlet of the primary evaporator 2. The startup evaporator 5 is used to provide the primary evaporator with fresh steam for startup heating of the heat pump.

[0028] The tube-side dichloromethane vapor outlet of the secondary evaporator 7 is connected to the dichloromethane vapor inlet of the secondary separator 9, the tube-side concentrated liquid outlet of the secondary evaporator 7 is connected to the feed port of the gas stripping tower 8, the gas phase extraction outlet of the secondary separator 9 is connected to the gas phase inlet of the condenser 10, the gas phase outlet of the condenser 10 is connected to the first dichloromethane condensate outlet 13, the concentrated liquid outlet of the secondary separator 9 is connected to the feed port of the gas stripping tower 8, the refined white oil outlet of the gas stripping tower 8 is connected to the refined white oil storage tank 12, the two ends of the gas stripping tower evaporator 11 are respectively connected to the shell-side feed port and the shell-side discharge port of the gas stripping tower 8, the nitrogen delivery device 15 is connected to the nitrogen feed port of the gas stripping tower 8, and the dichloromethane discharge port of the gas stripping tower 8 is connected to the second dichloromethane condensate outlet 14.

[0029] The primary concentrate of the white oil and dichloromethane mixture output by the primary evaporator 2 can also be returned to the primary evaporator 2 for re-purification through the startup evaporator 5. The first dichloromethane condensate outlet 13 and the second dichloromethane condensate outlet 14 can be directly connected to the dichloromethane condensate tank 6, or directly connected to the production line. The content of dichloromethane in the primary concentrate is 25-65wt%. Example 1

[0030] A method for separating and recovering a mixed liquid of white oil and dichloromethane comprises the following steps: After preheating the white oil and dichloromethane mixture, the white oil and dichloromethane mixture is passed through a primary evaporator and a secondary evaporator in sequence to obtain dichloromethane liquid and a secondary concentrated liquid of the white oil and dichloromethane mixture, and then the secondary concentrated liquid of the white oil and dichloromethane mixture is passed through a gas stripping tower to obtain refined white oil through gas stripping; The primary evaporation device comprises a primary evaporator, a primary separator, a compressor, and a startup evaporator. When the white oil and dichloromethane mixture is first introduced into the tube side of the primary evaporator, the startup evaporator generates steam and introduces it into the shell side of the primary evaporator to heat the white oil and dichloromethane mixture to obtain primary dichloromethane steam and primary concentrated liquid of the white oil and dichloromethane mixture. The primary separator separates the primary dichloromethane steam from the primary concentrated liquid of the white oil and dichloromethane mixture, and the separated primary concentrated liquid of the white oil and dichloromethane mixture is transported to the secondary evaporation device. The separated primary dichloromethane steam is pressurized and heated by the compressor and then introduced into the shell side of the primary evaporator again to heat the white oil and dichloromethane mixture in the tube side of the primary evaporator subsequently, and the primary dichloromethane liquid obtained after the primary dichloromethane steam is cooled is collected. The secondary evaporation device comprises a secondary evaporator, a secondary separator and a condenser. The primary concentrated liquid of the white oil and dichloromethane mixture is passed into the tube side of the secondary evaporator, and the external fresh steam is passed into the shell side of the secondary evaporator to heat the primary concentrated liquid of the white oil and dichloromethane mixture to obtain secondary dichloromethane steam and secondary concentrated liquid of the white oil and dichloromethane mixture. After the secondary separator separates the secondary dichloromethane steam and the secondary concentrated liquid of the white oil and dichloromethane mixture, the separated secondary dichloromethane steam is passed into the condenser to obtain secondary dichloromethane liquid. The separated secondary concentrated liquid of the white oil and dichloromethane mixture is passed into a gas stripping tower to obtain refined white oil through gas stripping. The tertiary dichloromethane vapor obtained in the gas stripping process is condensed and combined with the primary dichloromethane liquid and the secondary dichloromethane liquid to obtain all the dichloromethane liquid separated from the white oil and dichloromethane mixture.

[0031] The flow rate of the white oil and dichloromethane mixture before treatment is 20m³ / h, of which the white oil content is 5%wt and the dichloromethane content is 95%wt; The pressure of the tube side of the primary evaporator 2 is standard atmospheric pressure, and the temperature of the tube side of the primary evaporator 2 is 45°C; the pressure of the shell side of the primary evaporator 2 is 153kpa, and the temperature of the shell side of the primary evaporator 2 is 52°C. The flow rate of the primary concentrate separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 3.6m³ / h, and the dichloromethane content in the primary concentrate is about 59wt%.

[0032] The pressure of the secondary evaporator 7 tube side is standard atmospheric pressure, the temperature is 125°C, and the flow rate of the crude white oil separated by the secondary evaporator 7 is 1.9m³ / h.

[0033] The pressure of the stripping tower 8 is negative pressure, and refined white oil is produced from the stripping tower kettle.

[0034] The compression ratio of the compressor is 1.5~3.5. Example 2

[0035] A method for separating and recovering a mixture of white oil and dichloromethane, except for the following differences, the other steps are consistent with those of Example 1: The pressure of the tube side of the primary evaporator 2 is standard atmospheric pressure, and the temperature of the tube side of the primary evaporator 2 is 52°C; the pressure of the shell side of the primary evaporator 2 is 225kpa, and the temperature of the shell side of the primary evaporator 2 is 65°C. The flow rate of the primary concentrate separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 2.7m³ / h. Example 3

[0036] A method for separating and recovering a mixture of white oil and dichloromethane, except for the following differences, the other steps are consistent with those of Example 1: The pressure of the tube side of the primary evaporator 2 is standard atmospheric pressure, and the temperature of the tube side of the primary evaporator 2 is 65°C; the pressure of the shell side of the primary evaporator 2 is 350kpa, and the temperature of the shell side of the primary evaporator 2 is 81°C. The flow rate of the concentrated liquid separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 2.3m³ / h. Example 4

[0037] A method for separating and recovering a mixture of white oil and dichloromethane, except for the following differences, the other steps are consistent with those of Example 1: The pressure of the tube side of the primary evaporator 2 is negative pressure (40kpa), and the temperature of the tube side of the primary evaporator 2 is 24℃; the pressure of the shell side of the primary evaporator 2 is 72kpa, and the temperature of the shell side of the primary evaporator 2 is 31℃. The flow rate of the primary concentrate separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 2.8m³ / h. Example 5

[0038] A method for separating and recovering a mixture of white oil and dichloromethane, except for the following differences, the other steps are consistent with those of Example 1: The pressure of the tube side of the primary evaporator 2 is negative pressure (50kpa), and the temperature of the tube side of the primary evaporator 2 is 28℃; the pressure of the shell side of the primary evaporator is 90kpa, and the temperature of the shell side of the primary evaporator 2 is 37℃. The flow rate of the concentrated liquid separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 2.9m³ / h. Example 6

[0039] A method for separating and recovering a mixture of white oil and dichloromethane, except for the following differences, the other steps are consistent with those of Example 1: The pressure of the tube side of the primary evaporator 2 is negative pressure (55kpa), and the temperature of the tube side of the primary evaporator 2 is 32℃; the pressure of the shell side of the primary evaporator is 99kpa, and the temperature of the shell side of the primary evaporator 2 is 39℃. The flow rate of the concentrated liquid separated by the white oil and dichloromethane mixture through the primary evaporator 2 is 2.8m³ / h. Comparative Example 1

[0040] The flow rate of the mixed liquid of white oil and dichloromethane is 20m³ / h, wherein the content of white oil is 5%wt and the content of dichloromethane is 95%wt; the mixed liquid of white oil and dichloromethane is sent to a standard atmospheric pressure distillation tower, a part of the gas phase at the top of the distillation tower is refluxed to the top of the tower after being condensed by the top condenser, and the other part is sent to the dichloromethane storage tank, the concentrated liquid in the bottom of the distillation tower is sent to the second reboiler for further concentration, the temperature of the second reboiler bottom is heated to 115°C, the crude white oil in the bottom of the reboiler is sent to the gas stripping tower, the pressure is 10kpaG, the temperature of the gas stripping tower bottom is heated to 130°C, and the refined white oil is produced from the bottom of the gas stripping tower. Comparative Example 2

[0041] The flow rate of the mixed liquid of white oil and dichloromethane is 20m³ / h, of which the content of white oil is 5%wt and the content of dichloromethane is 95%wt; the mixed liquid of white oil and dichloromethane is sent to the double-effect evaporator, the first-effect evaporator is heated by steam, the temperature is 85℃, and the pressure is 0.19MPaG; the second-effect evaporator is at standard atmospheric pressure and the pressure is 45℃, the first-effect dichloromethane steam evaporated from the first-effect evaporator enters the second-effect evaporator to heat the mixed liquid, the first-effect dichloromethane steam is condensed into liquid after heat exchange and sent to the dichloromethane storage tank; the second-effect dichloromethane steam evaporated from the second-effect evaporator is condensed and cooled by the condenser and sent to the dichloromethane storage tank. The flow rate of the first-effect and second-effect concentrated liquid is 3m³ / h, which is sent to the standard atmospheric pressure distillation tower at a temperature of 100℃, and the crude white oil separated by the distillation tower is sent to the gas stripping tower, and the gas stripping tower produces refined white oil.

[0042] Examples 1-6 and Comparative Examples 1 and 2 were used to separate and purify white oil and dichloromethane. The results are shown in Tables 1 and 2 below: The energy saving effect in the table is calculated based on the traditional two-tower + three-reboiler distillation process. The energy consumption is mainly composed of the following four parts: fresh saturated steam consumption, circulating water consumption, low-temperature water consumption, and power consumption (including compressor power consumption and pump power consumption).

[0043] Table 1 Basic unit price for energy consumption calculation project Electricity (yuan / Kw•h) Steam (yuan / t) Circulating water (yuan / m³) Low temperature water (yuan / m³) unit price 0.75 300 0.3 1 Table 2 Comparison of energy consumption of each process project Steam t / h Circulating water m³ / h Low temperature water m³ / h Power consumption kw·h Total operating energy consumption Yuan / h Energy saving effect% Example 1 0.5 65 19 221 354.3 76.8 Example 2 0.3 44 40 375 424.5 72.2 Example 3 0.2 35 65 564 558.5 63.4 Example 4 0.31 44 27 301 358.95 76.5 Example 5 0.39 44 26 306 385.7 74.7 Example 6 0.31 44 26 308 363.2 76.2 Comparative Example 1 4.4 474 31 42 1524.7 / Comparative Example 2 2.4 258 33 68 881.4 42.2 Note: The white oil used is 50-68# white oil.

[0044] By comparing Examples 1-6 with Comparative Examples 1 and 2, it can be seen that the method for separating and recovering a mixed liquid of white oil and dichloromethane provided in the present application saves about 70% of the operating energy consumption compared with the recovery and purification process provided in Comparative Example 1, and saves about 30% of the operating energy consumption compared with the recovery and purification process provided in Comparative Example 2.

[0045] Comparative Example 1 uses a first-level standard atmospheric pressure distillation + gas stripping method for separation and purification. Since the content of dichloromethane in the mixed liquid is relatively large, a large amount of fresh steam is required. At the same time, the dichloromethane vapor evaporated requires a large amount of circulating water and low-temperature water for condensation and cooling. This distillation technology has the problem of high energy consumption.

[0046] In the technical solution of the present invention, the primary dichloromethane vapor generated by the primary evaporator 2 is directly returned to the primary evaporator 2 as a heat source after being pressurized and heated by the compressor 4. This process realizes the recycling of the latent heat of steam, and only the electric energy of the compressor 4 is needed to increase the steam temperature, without the need for additional fresh steam input. This solution mainly relies on electric energy to drive the compressor, and the efficiency of converting electric energy into thermal energy is relatively high (heat pump principle). This solution usually has a high energy efficiency ratio, and is particularly suitable for volatile substances with low boiling points (such as dichloromethane).

[0047] Compared with Comparative Example 2, the technical solution of the present invention (Examples 1-6) realizes the efficient recycling of the latent heat of dichloromethane vapor, reduces the dependence on external heat sources, and simplifies the subsequent separation steps (eliminating the high-energy consumption distillation tower), so the total energy consumption is significantly lower than that of Comparative Example 2. Although Comparative Example 2 uses the secondary steam of the first effect to heat the second effect through double-effect evaporation, it is limited by the decreasing law of temperature difference of multi-effect evaporation (the operating temperature of the second effect must be lower than that of the first effect), and the heat transfer efficiency gradually decreases. Therefore, it is limited by the decreasing efficiency of multi-effect evaporation and the high energy consumption of the distillation tower, and the overall energy efficiency is lower than that of direct electric energy drive. At the same time, in Examples 3-6, the first-stage evaporator 2 is negative pressure in both the tube side and the shell side, so that the boiling point of the liquid phase is reduced, and it only needs to be heated to a lower temperature, so the energy consumption is further reduced.

[0048] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for separating and recovering a mixed liquid of white oil and dichloromethane, characterized in that: The following steps are involved: The mixed liquid of white oil and dichloromethane is sent to the primary evaporator, and after being heated by the primary evaporator, the primary dichloromethane vapor and the primary concentrated liquid are separated. The primary dichloromethane vapor is pressurized and heated by a compressor and used as the heating medium of the primary evaporator, and is condensed by heat exchange to obtain the primary dichloromethane liquid. The primary concentrated liquid is sent to the secondary evaporator for heating and then separated to obtain secondary dichloromethane vapor and secondary concentrated liquid. The secondary dichloromethane vapor is condensed to obtain secondary dichloromethane liquid. The secondary concentrated liquid is then subjected to gas stripping to obtain refined white oil. Meanwhile, the tertiary dichloromethane vapor obtained in the gas stripping process is condensed to obtain tertiary dichloromethane liquid.

2. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: After preheating the white oil and dichloromethane mixture, the white oil and dichloromethane mixture is sequentially passed through a primary evaporator and a secondary evaporator to obtain dichloromethane liquid and a secondary concentrated liquid of the white oil and dichloromethane mixture, and then the secondary concentrated liquid of the white oil and dichloromethane mixture is sent to a gas stripping tower to obtain refined white oil through gas stripping; The primary evaporation device comprises a primary evaporator, a primary separator, a compressor, and a startup evaporator. When the white oil and dichloromethane mixture is first introduced into the tube side of the primary evaporator, the startup evaporator generates steam and introduces it into the shell side of the primary evaporator to heat the white oil and dichloromethane mixture to obtain primary dichloromethane steam and primary concentrated liquid of the white oil and dichloromethane mixture. The primary separator separates the primary dichloromethane steam from the primary concentrated liquid of the white oil and dichloromethane mixture, and the separated primary concentrated liquid of the white oil and dichloromethane mixture is transported to the secondary evaporation device. The separated primary dichloromethane steam is pressurized and heated by the compressor and then introduced into the shell side of the primary evaporator again to heat the white oil and dichloromethane mixture in the tube side of the primary evaporator subsequently, and the primary dichloromethane liquid obtained after the primary dichloromethane steam is cooled is collected. The secondary evaporation device comprises a secondary evaporator, a secondary separator and a condenser. The primary concentrated liquid of the white oil and dichloromethane mixture is passed into the tube side of the secondary evaporator, and the external fresh steam is passed into the shell side of the secondary evaporator to heat the primary concentrated liquid of the white oil and dichloromethane mixture to obtain secondary dichloromethane steam and secondary concentrated liquid of the white oil and dichloromethane mixture. After the secondary separator separates the secondary dichloromethane steam and the secondary concentrated liquid of the white oil and dichloromethane mixture, the separated secondary dichloromethane steam is passed into the condenser to obtain secondary dichloromethane liquid. The separated secondary concentrated liquid of the white oil and dichloromethane mixture is passed into a gas stripping tower to obtain refined white oil through gas stripping. The tertiary dichloromethane vapor obtained in the gas stripping process is condensed and combined with the primary dichloromethane liquid and the secondary dichloromethane liquid to obtain all the dichloromethane liquid separated from the white oil and dichloromethane mixture.

3. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: The pressure of the first-stage evaporator tube side is standard atmospheric pressure, and the temperature is 45-65°C; the pressure of the first-stage evaporator shell side is 153-350KPa, and the temperature is 52-81°C.

4. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: The pressure of the first-stage evaporator tube side is negative pressure, and the temperature is 24-32°C; the pressure of the first-stage evaporator shell side is 72-99 kPa, and the temperature is 31-39°C.

5. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 4, characterized in that: The pressure of the first-stage evaporator tube side is 40~55Kpa.

6. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: In the mixed liquid of white oil and dichloromethane, the content of white oil is 2-20wt%, and the content of dichloromethane is 80-98wt%.

7. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: The content of dichloromethane in the primary concentrate is 25-65wt%.

8. The method for separating and recovering a mixed liquid of white oil and dichloromethane according to claim 1, characterized in that: The method for separating and recovering the mixed liquid of white oil and dichloromethane is realized by the following device, including: The preheater (1) is connected to the tube side feed port of the primary evaporator (2), the tube side dichloromethane vapor outlet of the primary evaporator (2) is connected to the dichloromethane vapor inlet of the primary separator (3), the tube side concentrate liquid outlet of the primary evaporator (2) is connected to the tube side feed port of the secondary evaporator (7), the gas phase extraction outlet of the primary separator (3) is connected to the gas phase inlet of the compressor (4), the gas phase outlet of the compressor (4) is connected to the shell side inlet of the primary evaporator (2), the shell side outlet of the primary evaporator (2) is connected to the dichloromethane condensate tank (6), and the concentrate liquid outlet of the primary separator (3) is connected to the tube side feed port of the secondary evaporator (7); The startup evaporator (5) is provided with a tube side inlet and a tube side outlet. The tube side inlet of the startup evaporator (5) is respectively connected to the tube side outlet of the first-stage evaporator (2) and the concentrate outlet of the first-stage separator (3), and the tube side outlet of the startup evaporator (5) is connected to the shell side inlet of the first-stage evaporator (2). The startup evaporator (5) is used to provide the first-stage evaporator (2) with fresh steam for startup heating of the heat pump; The tube-side dichloromethane vapor outlet of the secondary evaporator (7) is connected to the dichloromethane vapor inlet of the secondary separator (9), the tube-side concentrated liquid outlet of the secondary evaporator (7) is connected to the feed inlet of the gas stripping tower (8), the gas phase extraction outlet of the secondary separator (9) is connected to the gas phase inlet of the condenser (10), the gas phase outlet of the condenser (10) is connected to the first dichloromethane condensate outlet (13), the concentrated liquid outlet of the secondary separator (9) is connected to the feed inlet of the gas stripping tower (8), the refined white oil outlet of the gas stripping tower (8) is connected to the refined white oil storage tank (12), the two ends of the gas stripping tower evaporator (11) are respectively connected to the shell-side feed inlet and shell-side discharge of the gas stripping tower (8), the nitrogen delivery device (15) is connected to the nitrogen feed inlet of the gas stripping tower (8), and the dichloromethane discharge port of the gas stripping tower (8) is connected to the second dichloromethane condensate outlet (14).

Images