A flash evaporation system for separating DMAC and acetic acid

Abstract

This application provides a flash evaporation system for separating DMAC and acetic acid, connected between a feed tank and a distillation column. The system includes a high-pressure flash tank connected to the feed tank and a low-pressure flash tank connected in series with the high-pressure flash tank. Both the high-pressure and low-pressure flash tanks are provided with an inlet, a vapor phase outlet, and a liquid phase outlet. The liquid phase outlet of the high-pressure flash tank is connected to the inlet of the low-pressure flash tank via a pressure reducing valve, and the liquid phase outlet of the low-pressure flash tank is connected to the inlet of the distillation column. A preheater is connected between the outlet of the feed tank and the inlet of the high-pressure flash tank. The vapor phase outlets of both the high-pressure and low-pressure flash tanks are connected to a condenser. This flash evaporation system, by employing a series connection of a high-pressure and a low-pressure flash tank for two-stage pressure-reducing flash evaporation of the mixture, achieves efficient pre-separation, reduces the load on the distillation column, and improves overall separation efficiency.

Description

Technical Field

[0001] This application relates to the field of chemical separation technology, specifically to a flash evaporation system for separating DMAC and acetic acid. Background Technology

[0002] N,N-Dimethylacetamide (DMAC) is a common organic solvent. In actual industrial production processes, DMAC often forms mixtures with components such as acetic acid, requiring effective separation to achieve DMAC recycling or improve product quality.

[0003] Currently, the common industrial method for separating DMAC and acetic acid is distillation. However, because DMAC and acetic acid have similar boiling points, they easily form azeotropes, making direct feeding of feed containing both DMAC and acetic acid into a distillation column inefficient. Furthermore, in actual separation processes, the presence of high-molecular-weight organic compounds and other impurities in the feed can reduce relative volatility, increasing the difficulty of separation.

[0004] Besides the direct distillation method mentioned above, another common approach is to use neutralization to treat the DMAC refining bottom liquid generated in spandex production. This involves adding liquid alkali to the mixture to neutralize the acetic acid, producing sodium acetate, which is then separated by pan distillation. However, the sodium acetate produced in this neutralization process mixes with unreacted DMAC and high-molecular-weight heavy components to form waste salt. This waste salt typically contains a high concentration of DMAC (approximately 15%-30%), resulting in DMAC loss. Furthermore, this waste salt is classified as hazardous waste, and subsequent incineration or landfill disposal is not only costly but also poses an environmental risk of heavy metal pollution to the soil. In addition, this process also suffers from low azeotropic separation efficiency and the easy entrainment of heavy components.

[0005] Flash evaporation, as an important pretreatment method, utilizes the instantaneous vaporization of liquids when pressure suddenly decreases, which can effectively achieve the initial separation of light and heavy components.

[0006] However, existing flash evaporation devices have limited pressure drop, resulting in insufficient separation of light and heavy components during the flash evaporation process. The light components are not vaporized sufficiently, and some heavy components still escape with the light components. The separation accuracy is low, which cannot effectively reduce the load on the subsequent distillation column, nor can it fundamentally solve the waste salt pollution problem caused by the neutralization method. Utility Model Content

[0007] The purpose of this invention is to provide a flash evaporation system for separating DMAC and acetic acid, which can achieve efficient pre-separation, reduce the load on the distillation column, improve the overall separation efficiency, and prevent the generation of waste salt from the source.

[0008] This application is achieved through the following technical solution, specifically:

[0009] A flash evaporation system for separating DMAC and acetic acid, connected between a feed tank and a distillation column, includes: a high-pressure flash tank connected to the feed tank and a low-pressure flash tank connected in series with the high-pressure flash tank. Both the high-pressure and low-pressure flash tanks are respectively provided with a feed inlet, a vapor phase outlet, and a liquid phase outlet. The liquid phase outlet of the high-pressure flash tank is connected to the feed inlet of the low-pressure flash tank via a pressure reducing valve, and the liquid phase outlet of the low-pressure flash tank is connected to the feed inlet of the distillation column. A preheater is connected between the outlet of the feed tank and the feed inlet of the high-pressure flash tank, and the vapor phase outlets of both the high-pressure and low-pressure flash tanks are connected to a condenser.

[0010] In this scheme, a high-pressure flash tank and a low-pressure flash tank are connected in series. The raw material is preheated by a preheater before entering the high-pressure flash tank, where a sudden pressure drop achieves initial flash separation of light and heavy components. The liquid phase from the high-pressure flash tank is then depressurized by a pressure reducing valve and enters the low-pressure flash tank for secondary flash evaporation, allowing the remaining acetic acid to vaporize more fully, thus achieving a more thorough separation of light and heavy components. This two-stage pressure-reducing flash evaporation method significantly increases the overall pressure drop compared to existing flash evaporation devices, improves the vaporization rate and separation accuracy of DMAC, effectively reduces the load on the subsequent distillation column, and solves the problems of limited pressure drop and insufficient separation in existing single-stage flash evaporation technologies.

[0011] As an improvement to the high-pressure flash tank in this application, the high-pressure flash tank is provided with a swirl plate inside.

[0012] As an improvement to the low-pressure flash tank in this application, a wire mesh demister is provided at the steam outlet of the low-pressure flash tank.

[0013] As an improvement to this application, the flash evaporation system further includes a first filter connected between the raw material tank and the high-pressure flash tank, and / or a second filter connected between the low-pressure flash tank and the distillation column.

[0014] Furthermore, the first filter includes a high-temperature resistant bag filter.

[0015] Furthermore, the second filter includes a plate and frame filter.

[0016] The beneficial effects of this application are as follows:

[0017] This application employs a series connection of a high-pressure flash tank and a low-pressure flash tank. The raw material is preheated in a preheater before entering the high-pressure flash tank, where a sudden pressure drop achieves initial flash separation of light and heavy components. The liquid phase from the high-pressure flash tank is then depressurized by a pressure reducing valve and enters the low-pressure flash tank for secondary flash evaporation, allowing for more complete vaporization of the remaining acetic acid and thus achieving a more thorough separation of light and heavy components. This two-stage pressure-reducing flash evaporation system significantly increases the overall pressure drop compared to existing flash evaporation devices, improves the vaporization rate and separation accuracy of acetic acid, effectively reduces the load on the subsequent distillation column, and solves the problems of limited pressure drop and insufficient separation in existing single-stage flash evaporation technologies. Furthermore, since this system does not involve chemical reactions, it avoids environmental pollution caused by waste salt disposal.

[0018] In addition to the technical problems solved by this utility model, the technical features constituting the technical solution, and the advantages brought about by the technical features of these technical solutions as described above, other technical problems that this utility model can solve, other technical features contained in the technical solution, and the advantages brought about by these technical features will be further explained in detail with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a flash evaporation system for separating DMAC and acetic acid in an embodiment of this application;

[0020] Figure 2 This is a partial cross-sectional structural diagram of the high-pressure flash tank in the embodiments of this application;

[0021] Figure 3 This is a partial cross-sectional structural diagram of the low-pressure flash tank in the embodiments of this application.

[0022] Explanation of reference numerals in the attached figures:

[0023] 1. Raw material tank; 2. Distillation column; 3. High-pressure flash tank; 31. Cyclone swirl plate; 4. Low-pressure flash tank; 41. Wire mesh demister; 5. Preheater; 6. Condenser. Detailed Implementation

[0024] The following will be combined with the appendix Figures 1-3 The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to more clearly illustrate the technical solution of this application, and are therefore merely examples and should not be used to limit the scope of protection of this application. Furthermore, the technical features involved in the various embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0025] In view of the problems existing in the background technology or products, Figure 1 A schematic diagram of a flash evaporation system for separating DMAC and acetic acid, according to an embodiment of this application, is shown. Figure 1 As shown in the figure, this application provides a flash evaporation system for separating DMAC and acetic acid, connected between a feed tank 1 and a distillation column 2. The system includes: a high-pressure flash tank 3 connected to the feed tank 1 and a low-pressure flash tank 4 connected in series with the high-pressure flash tank 3. Both the high-pressure flash tank 3 and the low-pressure flash tank 4 are respectively provided with a feed inlet, a vapor phase outlet, and a liquid phase outlet. The liquid phase outlet of the high-pressure flash tank 3 is connected to the feed inlet of the low-pressure flash tank 4 via a pressure reducing valve. The liquid phase outlet of the low-pressure flash tank 4 is connected to the feed inlet of the distillation column 2. A preheater 5 is connected between the outlet of the feed tank 1 and the feed inlet of the high-pressure flash tank 3. The vapor phase outlets of both the high-pressure flash tank 3 and the low-pressure flash tank 4 are connected to a condenser 6.

[0026] Specifically, raw material tank 1 stores a mixture containing acetic acid, DMAC, and a small amount of high-molecular-weight organic matter. The outlet of raw material tank 1 is connected to the feed end of preheater 5 via a conveying pipe. Preheater 5 is used to heat the mixture from raw material tank 1 to a set preheating temperature, for example, 139-155°C. Preheater 5 can heat the mixture using heat transfer oil or high-temperature gas. High-pressure flash tank 3 is designed to maintain a relatively high pressure level under operating pressure, for example, the operating pressure can be set between 0.3-0.5 MPaG. When the preheated mixture enters high-pressure flash tank 3, the pressure inside the tank suddenly drops, and the light components in DMAC vaporize to form a gas phase, which is discharged from the gas phase outlet of high-pressure flash tank 3. The liquid phase outlet of high-pressure flash tank 3 is connected to the feed inlet of low-pressure flash tank 4 via a pressure reducing valve (not shown in the figure). This pressure reducing valve can be precisely positioned to control the pressure entering low-pressure flash tank 4, for example, reducing the pressure to between -0.06 and -0.1 MPaG. The low-pressure flash tank 4 is designed to operate at a lower pressure than the high-pressure flash tank 3. Inside the low-pressure flash tank 4, the remaining acetic acid further vaporizes to form a gas phase, which is discharged from the gas phase outlet of the low-pressure flash tank 4. The gas phase outlets of both the high-pressure flash tank 3 and the low-pressure flash tank 4 are connected to a condenser 6, which can be a shell-and-tube condenser or a plate condenser, etc., to condense the acetic acid in the gas phase into a liquid. The liquid phase outlet of the low-pressure flash tank 4 is connected to the feed inlet of a distillation column 2, which is used to further purify the liquid phase containing a higher concentration of DMAC through distillation.

[0027] Figure 2 A partial cross-sectional structural diagram of the high-pressure flash tank in an embodiment of this application is shown. Figure 2As shown, preferably, the high-pressure flash tank 3 is equipped with a swirl plate 31 inside. The swirl plate 31 causes the liquid entering the high-pressure flash tank 3 to form a swirling motion inside the tank, thereby enhancing the mass and heat transfer process between the droplets and the gas phase, forcing the droplets to be thrown against the tank wall under the action of centrifugal force, forming finer droplets, thereby significantly improving the vaporization rate of DMAC and increasing the degree of vaporization separation of light and heavy components.

[0028] Figure 3 A partial cross-sectional structural diagram of a low-pressure flash tank according to an embodiment of this application is shown. Figure 3 As shown, preferably, a wire mesh demister 41 is provided at the vapor outlet of the low-pressure flash tank 4. The wire mesh demister 4 can effectively capture tiny droplets entrained from the gas phase outlet of the low-pressure flash tank 4. When the gas phase passes through the wire mesh, the tiny droplets collide with and adhere to the wire mesh under inertia, eventually merging into larger droplets and flowing back into the tank by gravity, thereby reducing DMAC loss and further improving the overall separation accuracy and DMAC recovery rate.

[0029] In one implementation, the flash system further includes a first filter connected between the raw material tank 1 and the high-pressure flash tank 3, and / or a second filter connected between the low-pressure flash tank 4 and the distillation column 2.

[0030] Specifically, the function of the first filter is to remove any high-molecular-weight organic matter or other impurities that may be present in the raw material before it enters the high-pressure flash tank 3, preventing them from clogging pipes, affecting heat transfer efficiency, or even causing equipment damage after entering the flash tank or distillation column. Preferably, the first filter includes a high-temperature resistant bag filter. The high-temperature resistant bag filter can withstand the high-temperature environment after the raw material is preheated, and its structure can effectively intercept larger particulate matter and high-molecular-weight impurities, protecting downstream equipment.

[0031] The function of the second filter is to further remove any remaining fine solid particles or polymers from the liquid phase after the two flash separations, preventing these impurities from entering distillation column 2 and avoiding secondary reactions or accumulation within the column that could affect distillation efficiency and product purity. Preferably, the second filter includes a plate and frame filter. Plate and frame filters have a large filtration area and high filtration accuracy, effectively removing fine impurities from the liquid phase and providing a cleaner medium for the feedstock entering the distillation column.

[0032] This embodiment effectively ensures the cleanliness of raw materials and gas-liquid mixtures by setting up a two-stage filtration device, avoiding the accumulation and blockage of impurities, and improving the separation efficiency of the entire system and the continuity and stability of equipment operation.

[0033] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "set", "equipped with", "connected", and "installed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. A flash system for separating DMAC and acetic acid, which is connected between a raw material tank (1) and a rectifying column (2), characterized by, include: A high-pressure flash tank (3) is connected to the raw material tank (1), and a low-pressure flash tank (4) is connected in series with the high-pressure flash tank (3). The high-pressure flash tank (3) and the low-pressure flash tank (4) are respectively provided with a feed inlet, a gas phase outlet and a liquid phase outlet. The liquid phase outlet of the high-pressure flash tank (3) is connected to the feed inlet of the low-pressure flash tank (4) through a pressure reducing valve. The liquid phase outlet of the low-pressure flash tank (4) is connected to the feed inlet of the distillation column (2). A preheater (5) is connected between the outlet of the raw material tank (1) and the feed inlet of the high-pressure flash tank (3). The gas phase outlets of the high-pressure flash tank (3) and the low-pressure flash tank (4) are both connected to a condenser (6).

2. A flash system for separating DMAC and acetic acid as claimed in claim 1 wherein, The high-pressure flash tank (3) is equipped with a swirl plate (31).

3. The flash system for separating DMAC and acetic acid as claimed in claim 1 wherein, A wire mesh demister (41) is installed at the gas phase outlet of the low-pressure flash tank (4).

4. The flash system for separating DMAC and acetic acid of claim 1, wherein, It also includes a first filter connected between the raw material tank (1) and the high-pressure flash tank (3), and / or a second filter connected between the low-pressure flash tank (4) and the distillation column (2).

5. A flash system for separating DMAC and acetic acid as claimed in claim 4 wherein, The first filter includes a high-temperature resistant bag filter.

6. A flash system for separating DMAC and acetic acid as claimed in claim 4 wherein, The second filter includes a plate and frame filter.

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