Method and device for separating chloropropene tail gas

Abstract

The application provides a chloropropylene tail gas separation method and a separation device. The separation method comprises the following steps: performing compression treatment on a to-be-separated gas comprising propylene and hydrogen chloride to obtain a compressed gas; performing first-stage heat exchange treatment, second-stage heat exchange treatment and third-stage heat exchange treatment on the compressed gas in sequence to obtain a cooled gas; performing rectification treatment on the cooled gas to obtain hydrogen chloride gas and propylene liquid; performing decompression and cooling treatment on the propylene liquid to obtain a cooled propylene stream; performing condensation treatment on the hydrogen chloride gas by using the cooled propylene stream to obtain cooled hydrogen chloride and an intermediate propylene stream; and collecting and processing the cooled hydrogen chloride as a first-stage heat exchange medium participating in the first-stage heat exchange treatment and the intermediate propylene stream as a second-stage heat exchange medium participating in the second-stage heat exchange treatment. The separation method has the characteristics of low energy consumption and no equipment corrosion risk.

Description

Technical Field

[0001] This invention relates to a method and apparatus for separating allyl chloride tail gas, belonging to the field of applied chemical engineering. Background Technology

[0002] In traditional allyl chloride production processes, a four-stage absorption process is typically used to separate hydrogen chloride gas from the tail gas. For example, Chinese patent CN103724155B describes a process for producing allyl chloride. In this process, the method for separating allyl chloride tail gas is as follows: the tail gas containing propylene and hydrogen chloride is first subjected to two separate water washing absorptions to obtain dilute hydrochloric acid; the gas after the two water washings is then washed again with a sodium hydroxide aqueous solution to completely remove hydrogen chloride; finally, the remaining propylene gas is washed with water, degreased, dried, and recycled.

[0003] Although the above process has the advantage of low energy consumption, it involves multiple steps of water washing or aqueous solution absorption during the separation process, which poses a risk that hydrogen chloride will dissolve in water and corrode the separation equipment and propylene chloride production equipment.

[0004] Therefore, developing a method for separating allyl chloride tail gas that combines the advantages of low energy consumption and no equipment corrosion risk has become a research direction. Summary of the Invention

[0005] This invention provides a method for separating allyl chloride tail gas. This separation method not only has low energy consumption but also eliminates the need for water treatment, thus offering advantages such as energy saving, environmental protection, and controllable cost.

[0006] The present invention also provides a separation device for allyl chloride tail gas, which is used to perform the above-described separation method. This device features low construction and operating costs and a long service life.

[0007] This invention provides a method for separating allyl chloride tail gas, comprising the following steps:

[0008] The gas to be separated, including propylene and hydrogen chloride, is compressed to obtain compressed gas.

[0009] The compressed gas is subjected to a first-stage heat exchange treatment, a second-stage heat exchange treatment, and a third-stage heat exchange treatment in sequence to obtain a cooled gas.

[0010] The cooled gas is subjected to distillation to obtain hydrogen chloride gas and propylene liquid; the propylene liquid is subjected to depressurization and cooling to obtain cooled propylene stream.

[0011] The cooled hydrogen chloride is used as the primary heat exchange medium in the primary heat exchange process, and the intermediate propylene stream is used as the secondary heat exchange medium in the secondary heat exchange process. After these processes, they are collected and treated separately.

[0012] In the separation method described above, the gas to be separated comprises 80-85 wt% propylene, 0-1 wt% propane, and 15-20 wt% hydrogen chloride.

[0013] In the separation method described above, the temperature of the cooling gas is not higher than 30°C.

[0014] In the separation method described above, the pressure of the compressed gas is 1.5 to 2.0 MPaG.

[0015] In the separation method described above, during the decompression and cooling process, the pressure of the cooled propylene stream is 0.1–0.2 MPaG, and the temperature is -30–-20°C.

[0016] In the separation method described above, the high-temperature distillation temperature is 30–50°C and the high-temperature distillation pressure is 1.5–2.0 MPaG; the low-temperature distillation temperature is 10–20°C and the low-temperature distillation pressure is 1.4–1.9 MPaG.

[0017] In the separation method described above, the tertiary heat exchange medium in the tertiary heat exchange treatment is chilled water.

[0018] In the separation method described above, the temperature of the compressed gas after the first-stage heat exchange treatment is 35-40°C; and the temperature of the compressed gas after the second-stage heat exchange treatment is 30-35°C.

[0019] The present invention also provides a separation device for propylene chloride tail gas, for performing the separation method described above, comprising: a compression unit, a primary heat exchange unit, a secondary heat exchange unit, a tertiary heat exchange unit, a distillation unit, a pressure reduction and cooling unit, a condensation unit, a hydrogen chloride collection unit, and a propylene collection unit;

[0020] The compression outlet of the compression unit is connected to the material inlet of the first-stage heat exchange unit; the material outlet of the first-stage heat exchange unit is connected to the material inlet of the second-stage heat exchange unit; the material outlet of the second-stage heat exchange unit is connected to the material inlet of the third-stage heat exchange unit; the material outlet of the third-stage heat exchange unit is connected to the inlet of the distillation unit; the high-boiling-point outlet of the distillation unit is also connected to the inlet of the decompression and cooling unit; the outlet of the decompression and cooling unit is connected to the medium inlet of the condensation unit; the medium outlet of the condensation unit is connected to the medium inlet of the second-stage heat exchange unit; the medium outlet of the second-stage heat exchange unit is connected to the propylene collection unit; the low-boiling-point outlet of the distillation unit is connected to the material inlet of the condensation unit; the material outlet of the condensation unit is connected to the medium inlet of the first-stage heat exchange unit; and the medium outlet of the first-stage heat exchange unit is connected to the hydrogen chloride collection unit.

[0021] In the separation device described above, the distillation unit is a distillation column, wherein the theoretical number of trays in the distillation column is 50 to 60, and / or the actual number of trays is 40 to 80.

[0022] The method for separating allyl chloride tail gas provided by this invention does not use water absorption to separate hydrogen chloride, so no water is introduced into the reaction system and there is no risk of equipment corrosion. At the same time, the separation method adopts a multi-stage heat exchange method and uses the separation product as a cooling medium, making full use of its own cooling capacity to directly cool the compressed gas, which makes the advantages of energy saving, environmental protection and cost control more prominent. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of the chloropropylene tail gas separation device of the present invention.

[0025] Figure 2 This is a schematic diagram of the chloropropylene tail gas separation device in Embodiments 1 and 2 of the present invention.

[0026] Explanation of reference numerals in the attached figures:

[0027] 101 - Compression unit; 201 - Primary heat exchange unit; 202 - Secondary heat exchange unit; 203 - Tertiary heat exchange unit; 301 - Distillation unit; 302 - Condensation unit; 303 - Pressure reduction and cooling unit; 401 - Hydrogen chloride collection unit; 402 - Propylene collection unit;

[0028] 501 - Compressor; 601 - Primary heat exchanger; 602 - Secondary heat exchanger; 603 - Tertiary heat exchanger; 701 - Distillation column; 702 - Condenser; 703 - Pressure reducing valve; 704 - Reboiler; 801 - Hydrogen chloride collector; 802 - Propylene collector. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The first aspect of this invention provides a method for separating allyl chloride tail gas, comprising the following steps:

[0031] 1) The gas to be separated, including propylene and hydrogen chloride, is compressed to obtain compressed gas;

[0032] 2) The compressed gas is subjected to first-stage heat exchange treatment, second-stage heat exchange treatment and third-stage heat exchange treatment in sequence to obtain cooled gas;

[0033] 3) The cooled gas is distilled to obtain hydrogen chloride gas and propylene liquid; the propylene liquid is subjected to reduced pressure and cooling to obtain cooled propylene stream.

[0034] 4) The hydrogen chloride gas was condensed using a cooled propylene stream to obtain cooled hydrogen chloride and intermediate propylene streams;

[0035] 5) After cooling hydrogen chloride is used as the primary heat exchange medium in the primary heat exchange treatment and intermediate propylene stream is used as the secondary heat exchange medium in the secondary heat exchange treatment, they are collected and treated separately.

[0036] The separation method of this invention is used to recover tail gas containing propylene and hydrogen chloride generated during the production of propylene chloride. This invention does not limit the temperature and pressure of the tail gas; exemplarily, the tail gas temperature is 30–40°C and the pressure is 0.01–0.1 MPaG.

[0037] The tail gas containing propylene is pressurized to obtain compressed gas. When this compressed gas is cooled (the cooling energy comes from the separation products after depressurization and cooling treatment), the propylene in the tail gas liquefies, thus separating from the hydrogen chloride. The cooled propylene obtained by depressurizing the propylene liquid contains cooling energy, which can be directly used to cool the compressed gas. This separation method effectively utilizes the energy absorbed by the allyl chloride tail gas during compression for the separation of propylene and hydrogen chloride, resulting in lower energy consumption and greater energy efficiency and environmental friendliness. Therefore, it is necessary to compress the allyl chloride tail gas before heat exchange treatment.

[0038] This invention does not limit the specific operating parameters of the compression process. For example, the operating pressure of the compression process (which can be understood as the outlet pressure of the device used to perform the compression process) can be 1.5–2.0 MPaG, and the operating temperature (which can be understood as the gas temperature at the outlet of the device used to perform the compression process) can be 40–45°C. The allyl chloride tail gas undergoes the above compression process to obtain compressed gas.

[0039] The compressed gas is cooled after undergoing three stages of heat exchange. Along the flow direction of the compressed gas, the temperature of the compressed gas (which can be understood as the gas temperature at the outlet of the device used to perform the heat exchange process) decreases sequentially after each heat exchange process.

[0040] When the components in a mixture have different volatility, they can be separated using distillation. The hydrogen chloride in the cooling gas has a different volatility than propylene. During distillation, the more volatile hydrogen chloride remains gaseous, yielding hydrogen chloride gas; the less volatile propylene leaves the gas phase as a liquid, yielding liquid propylene. When the liquid propylene is subjected to depressurization and cooling, its temperature decreases along with the pressure. During this process, a portion of the liquid propylene absorbs heat and vaporizes, while the remaining portion remains liquid. The resulting gas-liquid mixture is the cooled propylene stream. This invention does not limit the temperature or pressure of the cooled propylene stream; for example, the temperature can be -30 to -20°C, and the pressure can be 0.1 to 0.2 MPaG.

[0041] The cooled propylene stream first undergoes condensation treatment of the hydrogen chloride gas obtained from distillation. The hydrogen chloride gas remains gaseous after being cooled by the cooled propylene, resulting in cooled hydrogen chloride. In one specific embodiment, the temperature for cooling the hydrogen chloride is -20 to -10°C.

[0042] The cooled propylene stream is heated during the condensation process, becoming an intermediate propylene stream. This invention does not limit the physical state, temperature, or pressure of the intermediate propylene stream. For example, the intermediate propylene stream can be liquid, gaseous, or a gas-liquid mixture, with a temperature of -30 to -20°C and a pressure of 0.1 to 0.2 MPaG.

[0043] In addition, as is known in the art, in the distillation process, a portion of the propylene liquid obtained from the distillation process needs to be heated to a gaseous state through reboiling treatment and then returned to the equipment that performed the distillation process. At the same time, a portion of the cooled hydrogen chloride obtained from the condensation treatment also needs to be refluxed to the equipment that performed the distillation process to contact the returned gaseous propylene in a countercurrent manner in order to maintain the continuous operation of the distillation process.

[0044] Cooled hydrogen chloride and intermediate propylene streams are used as primary and secondary heat exchange media, respectively, to treat the compressed gas. This invention does not restrict the flow direction relationship between the heat exchange media and the compressed gas; they can flow in the same direction or in opposite directions, preferably in opposite directions during the heat exchange process. During the heat exchange process, the cooled hydrogen chloride absorbs heat carried by the compressed gas, causing its temperature to rise; exemplarily, the temperature of the hydrogen chloride after the temperature rise is 25–40°C. The intermediate propylene stream absorbs heat carried by the compressed gas and completely vaporizes into gaseous propylene; exemplarily, the temperature of the propylene after the temperature rise is 20–30°C. The gaseous propylene and the heated hydrogen chloride are collected by their respective collection units for recycling.

[0045] The present invention does not impose too many limitations on the heat exchange medium in the three-stage heat exchange process. For example, chilled water, Freon refrigerant or ethylene glycol refrigerant can be used.

[0046] The method for separating propylene chloride tail gas of the present invention involves compressing the propylene chloride tail gas to be separated, then cooling it through three heat exchange processes to obtain cooled gas, which is then separated into propylene and hydrogen chloride through distillation. The obtained propylene is used for cooling hydrogen chloride and compressed gas after being subjected to reduced pressure and cooling treatment, and the cooled hydrogen chloride is also used for cooling compressed gas. The propylene and hydrogen chloride used for cooling the gas to be separated can finally be collected separately.

[0047] Compared to the traditional four-stage absorption process, the separation method of this invention does not involve water washing or alkali washing, thus preventing the introduction of water into the reaction system and avoiding the risk of hydrogen chloride dissolving in water to form an acidic liquid that could corrode the equipment. At the same time, this invention uses a multi-stage heat exchange method to fully utilize the cooling capacity carried by the separation products to directly cool the compressed gas, achieving the separation of propylene and hydrogen chloride with low energy consumption. The purity of the separated propylene reaches 98-99%, and the purity of the hydrogen chloride reaches 99-99.999%.

[0048] In one specific embodiment of the present invention, the gas to be separated comprises 80-85 wt% propylene, 0-1 wt% propane, and 15-20 wt% hydrogen chloride. Propane and propylene are generated together during the separation process and do not affect the separation process.

[0049] In another specific embodiment of the present invention, the temperature of the cooling gas is not higher than 30°C. The temperature of the cooling gas affects the energy consumption of the propylene and hydrogen chloride separation method. When the temperature of the cooling gas is low, the temperature of the cooled propylene stream obtained by depressurization and cooling is also lower. On the one hand, the cooled propylene stream can provide sufficient cooling capacity for the condensation of hydrogen chloride gas during the condensation process, which not only helps to achieve the condensation of hydrogen chloride gas, but also allows the condensed cooled hydrogen chloride to participate in the primary heat exchange process of the compressed gas as an effective primary heat exchange medium. On the other hand, although the cooled propylene stream absorbs heat from the hydrogen chloride gas and becomes an intermediate propylene stream during the condensation process, the cooling capacity carried by the intermediate propylene stream can still participate in the secondary heat exchange process as a secondary heat exchange medium, achieving efficient and low-energy-consumption cooling of the compressed gas. When the temperature of the compressed gas is not higher than 30°C, preferably 25-30°C, the efficient and low-energy-consumption characteristics of the compressed gas cooling process are even more prominent.

[0050] Furthermore, since the temperature of the high-pressure stream decreases as the pressure decreases, cooling is generated in the lower-pressure stream obtained after depressurization. In one specific embodiment of the invention, the compressed gas pressure is further defined as 1.5–2.0 MPaG. In this case, the propylene liquid obtained through its diversion process generates sufficient cooling during depressurization to match the cooling required for heat exchange with the compressed gas, thus facilitating a more efficient and energy-saving cooling process for the compressed gas.

[0051] In one specific embodiment, the cooled propylene stream obtained after depressurization and cooling is in a gas-liquid mixture state, with a pressure of 0.1–0.2 MPaG and a temperature of -30–-20°C. When using this cooled propylene stream to cool the hydrogen chloride gas obtained from distillation through condensation, the liquid phase in the cooled propylene evaporates, causing the hydrogen chloride to cool. After condensation, the resulting intermediate propylene stream still maintains a gas-liquid mixture state, thus its temperature can still be maintained at -30–-20°C. When this intermediate propylene stream participates in heat exchange as a secondary heat exchange medium, the cooling capacity it provides is sufficient to match the cooling capacity required for cooling the compressed gas, enabling the compressed gas to complete the cooling process efficiently and with low energy consumption without additional cooling input.

[0052] Furthermore, to further optimize the cooling capacity carried by the separated products and better match the cooling capacity required for the hydrogen chloride gas and compressed gas after the propylene liquid is depressurized and cooled, in one specific embodiment of the distillation process, the high-temperature distillation temperature is 30–50°C, the high-temperature distillation pressure is 1.5–2.0 MPaG, the low-temperature distillation temperature is 10–20°C, and the low-temperature distillation pressure is 1.4–1.9 MPaG. In this case, the hydrogen chloride and compressed gas can be sufficiently cooled by the cooling capacity carried by the separated products, and the high efficiency and low energy consumption of the compressed gas cooling process are more prominent.

[0053] In another specific embodiment, industrial chilled water with a temperature of 7–12°C is preferably used as the heat exchange medium for the tertiary heat exchange treatment. Industrial chilled water has a large production scale and low cost. Using industrial chilled water reduces the input of cooling energy from other sources, making the energy-saving, environmentally friendly, and cost-controllable advantages of the separation method of this invention even more prominent.

[0054] Furthermore, when the temperature of the compressed gas after the first-stage heat exchange treatment is controlled at 35-40℃ and the temperature of the compressed gas after the second-stage heat exchange treatment is 30-35℃, the cooling capacity required for the compressed gas to cool down can be better matched with the cooling capacity carried by the cooled hydrogen chloride and intermediate propylene streams in the two-stage heat exchange treatment. The compressed gas can make full use of the cooling capacity of the separated products, resulting in a lower temperature of the cooled gas after the heat exchange treatment. At this time, the high efficiency and low energy consumption of the separation process are more prominent.

[0055] The present invention also provides a separation device for allyl chloride tail gas to perform the above separation method. Figure 1 This is a schematic diagram of the structure of the chloropropylene tail gas separation device of the present invention. Figure 1 As shown, the separation device includes: a compression unit 101, a primary heat exchange unit 201, a secondary heat exchange unit 202, a tertiary heat exchange unit 203, a distillation unit 301, a vacuum condensation unit 302, a vacuum cooling unit 303, a hydrogen chloride collection unit 401, and a propylene collection unit 402.

[0056] The compression outlet of compression unit 101 is connected to the material inlet of primary heat exchange unit 201; the material outlet of primary heat exchange unit 201 is connected to the material inlet of secondary heat exchange unit 202; the material outlet of secondary heat exchange unit 202 is connected to the material inlet of tertiary heat exchange unit 203; the material outlet of tertiary heat exchange unit 203 is connected to the inlet of distillation unit 301; the high-boiling-point outlet of distillation unit 301 is also connected to the inlet of pressure reducing and cooling unit 303; the outlet of pressure reducing and cooling unit 303 is connected to the medium inlet of condensation unit 302; the medium outlet of condensation unit 302 is connected to the medium inlet of secondary heat exchange unit 202; the medium outlet of secondary heat exchange unit 202 is connected to propylene collection unit 402; the low-boiling-point outlet of distillation unit 301 is connected to the material inlet of condensation unit 302; the material outlet of condensation unit 302 is connected to the medium inlet of primary heat exchange unit 201; and the medium outlet of primary heat exchange unit 201 is connected to hydrogen chloride collection unit 401.

[0057] The present invention does not limit the connection method between the units; for example, pipes can be used for connection.

[0058] The present invention does not limit the form of the compression unit 101, as long as the compression device used can increase the gas pressure. For example, the compression unit 101 is a reciprocating compressor.

[0059] The function of the primary heat exchange unit 201, secondary heat exchange unit 202, and tertiary heat exchange unit 203 of this invention is to change the temperature of the material by exchanging heat with the material through the heat exchange medium within the heat exchange unit. Here, "primary," "secondary," and "tertiary" only indicate the order in which the heat exchange units pass along the flow direction of the material, and do not represent any difference in their function / structure.

[0060] Heat exchange unit 201, secondary heat exchange unit 202, and tertiary heat exchange unit 203 each have at least a material inlet, a material outlet, a medium inlet, and a medium outlet. Specifically: the material inlet and the material outlet are connected; the medium inlet and the medium outlet are connected; the channel formed by the material inlet and the material outlet is not connected to the channel formed by the medium inlet and the medium outlet; and at least a portion of the materials in heat exchange unit 201, secondary heat exchange unit 202, and tertiary heat exchange unit 203, separated by two channels, possess good thermal conductivity. When the logistics enters the heat exchange unit 201, the secondary heat exchange unit 202, and the tertiary heat exchange unit 203 through the logistics inlet and leaves the heat exchange unit 201, the secondary heat exchange unit 202, and the tertiary heat exchange unit 203 through the logistics outlet, and the heat exchange medium enters the heat exchange unit 201, the secondary heat exchange unit 202, and the tertiary heat exchange unit 203 through the medium inlet and leaves the heat exchange unit 201, the secondary heat exchange unit 202, and the tertiary heat exchange unit 203 through the medium outlet, the heat exchange medium exchanges heat with the logistics through the materials of the heat exchange unit 201, the secondary heat exchange unit 202, and the tertiary heat exchange unit 203 separated by two channels, thereby changing the temperature of the logistics.

[0061] The distillation unit 301 includes a reboiling device that utilizes the difference in volatility between propylene and hydrogen chloride in the allyl chloride tail gas. Driven by thermal energy and constrained by phase equilibrium, the relatively volatile hydrogen chloride continuously transfers from the liquid phase to the gas phase, while the relatively less volatile propylene continuously migrates from the gas phase to the liquid phase, ultimately achieving the separation of propylene and hydrogen chloride. This invention does not limit the form of the distillation unit 301. In one embodiment, the distillation unit includes a distillation column and a reboiler. The reboiler heats a portion of the propylene liquid obtained from the column bottom into a gaseous state and returns the resulting gaseous propylene to the distillation column to maintain the operation of the distillation process.

[0062] In addition to a material inlet, a material outlet, a medium inlet, and a medium outlet, the condensing unit 302 also has a reflux outlet. The material inlet is connected to both the material outlet and the reflux outlet, forming a "T"-shaped channel. The medium inlet is connected to the medium outlet, forming another channel. Furthermore, the channel formed by the material inlet and the material outlet / reflux outlet is not interconnected with the channel formed by the medium inlet and the medium outlet, and at least a portion of the material constituting the condensing unit 302, which separates the two channels, has good thermal conductivity. When the material enters the condensing unit 302 through the material inlet and exchanges heat with the heat exchange medium, a portion leaves the condensing unit 302 through the material outlet, and the other portion leaves the condensing unit 302 through the reflux outlet, returning to the distillation unit 301.

[0063] The material refluxed to the distillation unit 301 is liquid propylene containing a portion of dissolved hydrogen chloride gas. Since the hydrogen chloride gas obtained from distillation still contains a small amount of propylene gas, this portion of the propylene gas is condensed into liquid propylene during the condensation process. Simultaneously, some hydrogen chloride gas dissolves in the liquid propylene, and both flow together from the reflux outlet of the condensation unit 302 back to the distillation unit 301. In one specific embodiment, the condensation unit 302 is a condenser.

[0064] The pressure-reducing and cooling unit 303 reduces the pressure of the liquid propylene flowing through it, thereby causing some of the liquid propylene to vaporize and absorb heat, thus obtaining cooled propylene with a lower temperature. This invention does not limit the form of the distillation unit 301; in one embodiment, the pressure-reducing and cooling unit 303 is a pressure-reducing valve.

[0065] The separation device of this invention achieves the separation of propylene and hydrogen chloride in allyl chloride tail gas using a relatively small number of processing units. Because the separation method employed by this device has low energy consumption and does not require water treatment, the separation device features low operating costs and a long service life. Furthermore, since no water is introduced, the selection of materials for the separation equipment does not need to consider factors preventing chloride ion corrosion, thus the separation device also features low construction costs.

[0066] In one specific embodiment, the distillation unit 301 is a distillation column. In this case, the high-temperature distillation temperature is the bottom temperature, the high-temperature distillation pressure is the bottom operating pressure, the low-temperature distillation temperature is the top temperature, and the low-temperature distillation pressure is the top operating pressure.

[0067] Furthermore, in a specific embodiment, when the distillation unit 301 is a distillation column, and the theoretical number of trays of the distillation column is 50-60, and / or the actual number of trays is 40-80, and the reflux ratio is 2-3, the propylene and hydrogen chloride separated by the distillation column have higher purity, with the propylene purity reaching 98-99% and the hydrogen chloride purity reaching 99-99.999%.

[0068] The following will combine Figure 1 The method for separating allyl chloride tail gas according to the present invention will be described as follows:

[0069] First, the gas to be separated, containing propylene and hydrogen chloride, is pressurized by compression unit 101 to obtain compressed gas. The compressed gas enters the inlet of the primary heat exchange unit 201 through the compression outlet of compression unit 101, where it undergoes primary heat exchange treatment, resulting in a temperature reduction. The compressed gas flowing out of the outlet of primary heat exchange unit 201 enters the secondary heat exchange unit 202, where it undergoes secondary heat exchange treatment, further reducing its temperature. The compressed gas flowing out of the outlet of secondary heat exchange unit 202 enters the tertiary heat exchange unit 203, where it undergoes tertiary heat exchange treatment, further reducing its temperature to obtain cooled gas.

[0070] The cooled gas flows out of the outlet of the three-stage heat exchange unit 203 and enters the distillation unit 301 for distillation, yielding a high-boiling-point separation product, propylene liquid, and a low-boiling-point separation product, hydrogen chloride gas. A portion of the propylene liquid is heated and vaporized by a device with reboiling function and returned to the distillation unit 301. The remaining propylene liquid enters the inlet of the depressurization and cooling unit 303 from the high-boiling-point outlet of the distillation unit 301, while the hydrogen chloride gas enters the inlet of the condensation unit 302 from the low-boiling-point outlet of the distillation unit 301.

[0071] Liquid propylene undergoes pressure reduction and cooling treatment in the pressure reduction and cooling unit 303 to obtain a cooled propylene stream. This cooled propylene stream enters the medium inlet of the condensation unit 302 from the outlet of the pressure reduction and cooling unit 303, where it is used to condense the low-boiling-point separation product, hydrogen chloride gas. A portion of the hydrogen chloride gas is cooled, resulting in a cooled hydrogen chloride and intermediate propylene stream; the remaining hydrogen chloride dissolves in a small amount of propylene contained in the low-boiling-point separation product and is refluxed to the distillation unit 301 from the reflux outlet of the condensation unit 302.

[0072] The intermediate propylene stream enters the secondary heat exchange unit 202 from the medium outlet of the condensation unit 302 for secondary heat exchange treatment of the gas to be separated. After heat exchange, the intermediate propylene stream enters the propylene collection unit 402 from the medium outlet of the secondary heat exchange unit 202 for recycling.

[0073] Cooled hydrogen chloride enters the medium inlet of the primary heat exchange unit 201 from the condensation unit 302 outlet for primary heat exchange treatment of the gas to be separated. After heat exchange, the hydrogen chloride enters the hydrogen chloride collection unit 401 from the medium outlet of the primary heat exchange unit 201 for recycling.

[0074] Figure 2 This is a schematic diagram of the allyl chloride tail gas separation device according to Embodiments 1 and 2 of the present invention. The following will be combined with... Figure 2 The method for separating allyl chloride tail gas provided by the present invention will be described in detail with specific embodiments.

[0075] Example 1

[0076] This embodiment provides a method for separating allyl chloride, including the following steps:

[0077] 1) In this embodiment, the temperature of the allyl chloride tail gas to be separated is 36°C, and the pressure is 0.05 MPaG. The propylene content is 83.7 wt%, the propane content is 0.1 wt%, and the hydrogen chloride content is 16.2 wt%. The gas to be separated is pressurized to 1.6 MPaG using compressor 501 to obtain compressed gas. Since compressor 501 performs work on the gas, the temperature of the compressed gas leaving compressor 501 is 41°C.

[0078] 2) The compressed gas is sequentially passed through a primary heat exchanger 601, a secondary heat exchanger 602, and a tertiary heat exchanger 603 for heat exchange treatment. Specifically, the primary heat exchanger 601 uses low-temperature hydrogen chloride from the material outlet of the condenser 702 as the heat exchange medium to cool the compressed gas to 36°C; the secondary heat exchanger 602 uses intermediate propylene from the medium outlet of the condenser 702 as the heat exchange medium to cool the compressed gas to 32°C; and the tertiary heat exchanger 603 uses industrial chilled water at a temperature of 7–12°C as the heat exchange medium to further cool the compressed gas to 26°C, ultimately yielding cooled gas.

[0079] 3) The cooled gas enters distillation column 701 for distillation. The theoretical number of plates in the distillation column is 55, the actual number of plates is 57, the reflux ratio is 2.7, the top temperature is -18℃, the bottom temperature is 37℃, the top operating pressure is 1.6 MPaG, and the bottom operating pressure is 1.8 MPaG. Hydrogen chloride gas is obtained at the top, and propylene liquid containing a small amount of propane is obtained at the bottom. A portion of the propylene liquid from the bottom is returned to distillation column 701 through reboiler 704, and the remaining propylene liquid is depressurized to 0.13 MPaG through pressure reducing valve 703. Part of the propylene liquid vaporizes and absorbs heat, and the temperature of the gas-liquid mixture of propylene decreases to -29℃, resulting in a cooled propylene stream.

[0080] 4) The cooled propylene stream enters the medium inlet of condenser 702, where the hydrogen chloride gas entering from the stream inlet of condenser 702 is condensed to obtain cooled hydrogen chloride at a temperature of -18℃. At the same time, the propylene contained in the hydrogen chloride is liquefied during the condensation process, and some of the dissolved hydrogen chloride gas is carried back to the distillation column 701. During the condensation process, most of the cooled propylene stream is converted into gaseous propylene, while a portion remains liquid at a temperature of -29℃, becoming the intermediate propylene stream.

[0081] 5) Cooling hydrogen chloride enters the primary heat exchanger 601 through the medium inlet, where it exchanges heat with the compressed gas, raising its own temperature to 28°C. It then enters the hydrogen chloride recovery unit 801 through the medium outlet of the primary heat exchanger 601 for recycling. The intermediate propylene stream enters the secondary heat exchanger 602 through the medium inlet, where it exchanges heat with the compressed gas, completely vaporizing and raising its temperature to 25°C. It then enters the propylene collector 802 through the medium outlet of the secondary heat exchanger 602 for recycling.

[0082] In this embodiment, the recovered hydrogen chloride has a purity of 99.86 wt% and the propylene has a purity of 99.88 wt%.

[0083] Example 2

[0084] This embodiment provides a method for separating allyl chloride, including the following steps:

[0085] 1) In this embodiment, the temperature of the allyl chloride tail gas to be separated is 38°C, and the pressure is 0.03 MPaG. The propylene content is 81.6 wt%, the propane content is 0.08 wt%, and the hydrogen chloride content is 18.32 wt%. The gas to be separated is pressurized to 1.8 MPaG using compressor 501 to obtain compressed gas. Since compressor 501 performs work on the gas, the temperature of the compressed gas leaving compressor 501 is 44°C.

[0086] 2) The compressed gas is sequentially passed through a primary heat exchanger 601, a secondary heat exchanger 602, and a tertiary heat exchanger 603 for heat exchange treatment. Specifically, the primary heat exchanger 601 uses low-temperature hydrogen chloride from the material outlet of the condenser 702 as the heat exchange medium to cool the compressed gas to 37°C; the secondary heat exchanger 602 uses intermediate propylene from the medium outlet of the condenser 702 as the heat exchange medium to cool the compressed gas to 34°C; and the tertiary heat exchanger 603 uses industrial chilled water at a temperature of 7–12°C as the heat exchange medium to further cool the compressed gas to 29°C, ultimately yielding cooled gas.

[0087] 3) The cooled gas enters distillation column 701 for distillation. The theoretical number of plates in the distillation column is 60, the actual number of plates is 63, the reflux ratio is 2.4, the top temperature is -16℃, the bottom temperature is 42℃, the top operating pressure is 1.8 MPaG, and the bottom operating pressure is 1.9 MPaG. Hydrogen chloride gas is obtained at the top, and propylene liquid containing a small amount of propane is obtained at the bottom. A portion of the propylene liquid from the bottom is returned to distillation column 701 through reboiler 704, and the remaining propylene liquid is depressurized to 0.16 MPaG through pressure reducing valve 703. Part of the propylene liquid vaporizes and absorbs heat, and the temperature of the gas-liquid mixture of propylene decreases to -24℃, resulting in a cooled propylene stream.

[0088] 4) The cooled propylene stream enters the medium inlet of condenser 702, where the hydrogen chloride gas entering from the stream inlet of condenser 702 is condensed to obtain cooled hydrogen chloride at a temperature of -14℃. At the same time, the propylene contained in the hydrogen chloride is liquefied during the condensation process, and some of the dissolved hydrogen chloride gas is carried back to the distillation column 701. During the condensation process, most of the cooled propylene stream is converted into gaseous propylene, while a portion remains liquid at a temperature of -24℃, becoming the intermediate propylene stream.

[0089] 5) Cooling hydrogen chloride enters the primary heat exchanger 601 through the medium inlet, where it exchanges heat with the compressed gas, raising its own temperature to 33°C. It then enters the hydrogen chloride recovery unit 801 through the medium outlet of the primary heat exchanger 601 for recycling. The intermediate propylene stream enters the secondary heat exchanger 602 through the medium inlet, where it exchanges heat with the compressed gas, completely vaporizing and raising its temperature to 31°C. It then enters the propylene collector 802 through the medium outlet of the secondary heat exchanger 602 for recycling.

[0090] In this embodiment, the recovered hydrogen chloride has a purity of 99.99 wt%, and the propylene has a purity of 99.9 wt%.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating allyl chloride tail gas, characterized in that, Includes the following steps: 1) The gas to be separated, including propylene and hydrogen chloride, is compressed to obtain compressed gas; 2) The compressed gas is subjected to a first-stage heat exchange treatment, a second-stage heat exchange treatment, and a third-stage heat exchange treatment in sequence to obtain a cooled gas; wherein, the first-stage heat exchange treatment uses cooling hydrogen chloride as the heat exchange medium to reduce the temperature of the compressed gas to 35~40℃; the second-stage heat exchange treatment uses intermediate propylene stream as the heat exchange medium to reduce the temperature of the compressed gas to 30~35℃; and the third-stage heat exchange treatment uses chilled water as the heat exchange medium to obtain a cooled gas with a temperature not higher than 30℃. 3) The cooled gas is subjected to distillation to obtain hydrogen chloride gas and propylene liquid; the propylene liquid is subjected to depressurization and cooling treatment to obtain a cooled propylene stream with a pressure of 0.1~0.2 MPaG and a temperature of -30~-20℃; the distillation treatment includes high-temperature distillation and low-temperature distillation, the high-temperature distillation temperature is 30~50℃, and the high-temperature distillation pressure is 1.5~2.0 MPaG; The cryogenic distillation temperature is 10~20℃, and the cryogenic distillation pressure is 1.4~1.9 MPaG; 4) The hydrogen chloride gas is condensed using the cooled propylene stream to obtain cooled hydrogen chloride at a temperature of -20 to -10°C and intermediate propylene stream at a temperature of -30 to -20°C. 5) The cooled hydrogen chloride is used as the primary heat exchange medium in the primary heat exchange treatment, and the intermediate propylene stream is used as the secondary heat exchange medium in the secondary heat exchange treatment, and then they are collected and treated separately.

2. The separation method according to claim 1, characterized in that, The gases to be separated include 80-85 wt% propylene, 0-1 wt% propane, and 15-20 wt% hydrogen chloride.

3. The separation method according to any one of claims 1 to 2, characterized in that, The pressure of the compressed gas is 1.5~2.0 MPaG.

4. A separation device for allyl chloride tail gas, characterized in that, The method for performing the separation method according to any one of claims 1-3 includes: a compression unit, a primary heat exchange unit, a secondary heat exchange unit, a tertiary heat exchange unit, a distillation unit, a decompression and cooling unit, a condensation unit, a hydrogen chloride collection unit, and a propylene collection unit; The compression outlet of the compression unit is connected to the material inlet of the first-stage heat exchange unit; the material outlet of the first-stage heat exchange unit is connected to the material inlet of the second-stage heat exchange unit; the material outlet of the second-stage heat exchange unit is connected to the material inlet of the third-stage heat exchange unit; the material outlet of the third-stage heat exchange unit is connected to the inlet of the distillation unit; the high-boiling-point outlet of the distillation unit is also connected to the inlet of the decompression and cooling unit; the outlet of the decompression and cooling unit is connected to the medium inlet of the condensation unit; the medium outlet of the condensation unit is connected to the medium inlet of the second-stage heat exchange unit; the medium outlet of the second-stage heat exchange unit is connected to the propylene collection unit; the low-boiling-point outlet of the distillation unit is connected to the material inlet of the condensation unit; the material outlet of the condensation unit is connected to the medium inlet of the first-stage heat exchange unit; and the medium outlet of the first-stage heat exchange unit is connected to the hydrogen chloride collection unit.

5. The separation device according to claim 4, characterized in that, The distillation unit is a distillation column, and the theoretical number of trays in the distillation column is 50 to 60, and / or the actual number of trays is 40 to 80.

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