A recovery system and method for mercaptans and sulfides in a tail gas produced from methyl mercaptan

Abstract

This invention discloses a system and method for recovering thiols and sulfides from the tail gas of methanethiol preparation. The system utilizes a throttling and cooling condenser to condense the high-pressure synthesis tail gas. The condensed high-pressure synthesis tail gas is then throttled and depressurized through a regulating valve to convert it into a lower-temperature low-pressure synthesis gas. This low-temperature low-pressure synthesis gas is then used as a refrigerant in the tube side of the throttling and cooling condenser to condense the high-pressure synthesis tail gas in the shell side. No additional cooling equipment is required; the physicochemical properties of the tail gas are used to convert it into a refrigerant for condensation, thus saving costs, achieving good condensation efficiency, and resulting in excellent recovery of thiols and sulfides from the tail gas.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically to a system and method for recovering thiols and thioethers from the tail gas of methanethiol preparation. Background Technology

[0002] Condensation is the process of a phase change that occurs when the temperature of a hot object decreases, typically referring to the change of a substance from a gaseous state to a liquid state. In chemical production, the equipment used for cooling and condensation is usually a heat exchanger. Commonly used cooling and condensing media are ambient temperature circulating water, low-temperature water at 5-10°C, or chilled brine at -20-0°C. Because the temperature of the cooling and condensing media rises after cooling and condensing the high-temperature medium, it needs to be cooled down by a cooling tower or circulating cooling unit before being recycled, which consumes a significant amount of energy.

[0003] When methanol and hydrogen sulfide are synthesized into methanethiol (CH3SH), the high-temperature synthesis product gas at the reactor outlet needs to be cooled and condensed in three stages: raw material, circulating water, and low-temperature water. Analysis of the condensed tail gas still reveals the presence of methanethiol, dimethyl sulfide, and other products. Further condensation and recovery of the thiols and dimethyl sulfide from the tail gas requires the use of an even lower-temperature refrigerant, necessitating the installation of a circulating chilled brine unit. This results in high energy consumption and investment costs, making the recovery of these products counterproductive. Furthermore, in most cases, the actual conditions of the production facility do not provide suitable locations for installing chilled brine units, circulating chilled brine pumps, or chilled brine tanks. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a system and method for recovering thiols and sulfides from the tail gas of methanethiol preparation. By adjusting the throttling and pressure reduction of the regulating valve, the high-pressure synthesis gas is converted into a lower-temperature low-pressure synthesis gas, and the low-pressure synthesis gas is used to provide a coolant for the condensation of the high-pressure synthesis gas. The cooling device only requires the regulating valve, which saves costs and ensures the recovery effect. It solves the problems of expensive equipment, high cost and lack of space for installation when further recovering and cooling products such as thiols and sulfides from the tail gas.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a system for recovering thiols and sulfides from the tail gas of methanethiol preparation, comprising a low-temperature water condenser, wherein the shell-side outlet of the low-temperature water condenser is connected to the shell-side inlet of a throttling cooling condenser, the shell-side outlet of the throttling cooling condenser is connected to the feed inlet of a first cyclone separator, the outlet of the first cyclone separator is connected to the tube-side inlet of the throttling cooling condenser via an outlet pipe, and the outlet pipe is equipped with a regulating valve for throttling and pressure reduction, the tube-side outlet of the throttling cooling condenser is connected to the inlet of a tail gas buffer tank, the outlet of the tail gas buffer tank is connected to a second cyclone separator, and the liquid outlets of the low-temperature water condenser, the throttling cooling condenser, and the first cyclone separator are all connected to a crude thiols and sulfides tank via pipes.

[0006] Preferably, a secondary line and a valve are installed at the regulating valve.

[0007] More preferably, corresponding temperature sensors are provided on the outlet pipes located on both sides of the regulating valve, and a pressure sensor is provided at the outlet end of the regulating valve. Both the temperature sensor and the pressure sensor are connected to an external controller.

[0008] Preferably, the outlet pipe of the second cyclone separator is connected to a low-pressure exhaust gas treatment system.

[0009] A method for recovering thiols and thioethers from the tail gas of methanethiol production using the above-mentioned recovery system includes the following steps:

[0010] S1: The high-pressure synthesis gas at the shell-side outlet of the low-temperature water condenser is transported to the shell-side inlet of the throttling cooling condenser for condensation, and the mercaptan-containing sulfide liquid in the low-temperature water condenser is fed into the mercaptan crude product tank for collection.

[0011] S2: The condensed high-pressure synthesis gas enters the first cyclone separator from the shell-side outlet of the throttling and cooling condenser for liquid separation. The liquid containing mercaptan sulfide after separation is fed into the mercaptan sulfide crude product tank for collection.

[0012] S3: The high-pressure synthesis gas after separation enters the outlet pipe of the first cyclone separator. After being throttled and depressurized by the regulating valve, it is converted into low-pressure synthesis gas. The temperature of the low-pressure synthesis gas is lower than that of the high-pressure synthesis gas.

[0013] S4: The low-pressure synthesis gas converted after throttling and pressure reduction is introduced into the tube inlet of the throttling and cooling condenser through the outlet pipe. The throttling and cooling condenser uses the low-pressure synthesis gas to realize the condensation of the high-pressure synthesis gas in the high-temperature shell side of S1.

[0014] S5: The low-pressure synthesis gas after condensation enters the tail gas buffer tank from the tube side outlet of the throttling and cooling condenser for further processing.

[0015] S6: The low-pressure synthesis gas in the exhaust gas buffer tank undergoes secondary liquid separation treatment through the second cyclone separator.

[0016] Preferably, the components of the low-pressure synthesis gas and the high-pressure synthesis gas in S1 to S6 are both a mixture of methanethiol, thioether, carbon dioxide and nitrogen, and the content of methanethiol and thioether in the high-pressure synthesis gas is greater than that in the low-pressure synthesis gas.

[0017] More preferably, the high-pressure synthesis gas in S1~S3 has a temperature of 15℃~17℃ and a pressure of 1.0MPa~1.2MPa.

[0018] More preferably, the temperature of the low-pressure synthesis gas in S3~S4 is 5℃~7℃, and the pressure is 0.1MPa~0.2MPa.

[0019] Preferably, S6 further includes the liquid from the exhaust gas buffer tank and the second cyclone separator entering the liquid recovery system.

[0020] More preferably, S6 further includes the low-pressure synthesis gas after secondary liquid separation entering the low-pressure tail gas treatment system for further processing.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention uses a throttling and cooling condenser and a first cyclone separator to recover mercaptans and sulfides from the high-pressure synthesis tail gas in a low-temperature water condenser, thereby improving the recovery efficiency of residual mercaptans and sulfides in the tail gas.

[0023] 2. This invention converts high-pressure syngas into low-pressure syngas at a lower temperature through a regulating valve, and uses the low-pressure syngas to provide refrigerant for the condensation of high-pressure syngas in the throttling and cooling condenser. It also provides refrigerant for the recovery of tail gas through the physicochemical properties of the tail gas itself. No additional cooling equipment is required, which saves costs while ensuring the recovery effect and reducing the footprint of the device.

[0024] 3. This invention enables automated and continuous processing, ensuring efficient recycling. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0026] Figure 2 This is a schematic diagram of the method flow of the present invention;

[0027] In the diagram: 1. Low-temperature water condenser; 2. Throttling and cooling condenser; 3. First cyclone separator; 4. Outlet pipe; 5. Regulating valve; 6. Thiol and sulfide crude product tank; 7. Tail gas buffer tank; 8. Second cyclone separator. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown in the preferred embodiment 1, a system for recovering thiols and sulfides from the tail gas of methanethiol preparation includes a low-temperature water condenser 1. The shell-side outlet of the low-temperature water condenser 1 is connected to the shell-side inlet of a throttling cooling condenser 2. The shell-side outlet of the throttling cooling condenser 2 is connected to the feed inlet of a first cyclone separator 3. The outlet of the first cyclone separator 3 is connected to the tube-side inlet of the throttling cooling condenser 2 via an outlet pipe 4, and the outlet pipe 4 is equipped with a regulating valve 5 for throttling and pressure reduction. The tube-side outlet of the throttling cooling condenser 2 is connected to the inlet of a tail gas buffer tank 7. The outlet of the tail gas buffer tank 7 is connected to a second cyclone separator 8. The liquid outlets of the low-temperature water condenser 1, the throttling cooling condenser 2, and the first cyclone separator 3 are all connected to a crude thiols and sulfides tank 6 via pipes.

[0030] Example 1 provides a system for recovering thiols and sulfides from the tail gas of methanethiol production. By connecting the shell-side outlet of a low-temperature water condenser 1 to the shell-side inlet of a throttling cooling condenser 2, the high-pressure tail gas, still containing methanethiol and dimethyl sulfide after three stages of progressive cooling and condensation, enters the shell side of the throttling cooling condenser 2 for further condensation. The condensed high-pressure synthesis gas then enters the first cyclone separator 3 for liquid-liquid separation, separating the residual thiols and sulfides. The liquid thiols and sulfides in the low-temperature water condenser 1, the throttling cooling condenser 2, and the first cyclone separator 3 are collected through pipelines into a crude thiols and sulfides tank 6. The high-pressure synthesis gas after liquid-liquid separation is not immediately processed; it flows through the outlet pipe 4 and through the regulating valve 5 into the tube side of the throttling cooling condenser 2. When the gas passes through regulating valve 5, it is transformed into low-pressure synthesis gas with a lower temperature due to the throttling and pressure reduction effect of regulating valve 5. The low-pressure synthesis gas provides refrigerant for the condensation in the shell side of the throttling and cooling condenser 2 in the tube side. It provides refrigerant for the condensation and recovery of mercaptans and sulfides in the tail gas through the physicochemical properties of the tail gas itself, saving resources, eliminating the need for additional circulating refrigerated brine units, saving costs, and achieving good recovery effect. After providing refrigerant for condensation, the low-pressure synthesis gas in the tube side enters the tail gas buffer tank 7. On the one hand, it waits for processing in the tail gas buffer tank 7, and on the other hand, it collects any liquid accumulation that may exist after providing refrigerant. The residual low-pressure synthesis gas in the tail gas buffer tank 7 then enters the second cyclone separator 8 for secondary liquid separation. This liquid separation completely separates the residual liquid from the low-pressure synthesis gas, completing the complete recovery of liquid mercaptans and sulfides in the production tail gas.

[0031] As a preferred embodiment 2, a secondary line and valve are installed at the regulating valve 5. The valve on the secondary line is also a regulating valve 5 with throttling and pressure reducing function. According to the actual operation, the staff can switch between the regulating valve 5 on the main line and the secondary line to prevent the regulating valve body from freezing and blocking after throttling and cooling, which would affect the continuous treatment of exhaust gas.

[0032] In a preferred embodiment 3, corresponding temperature sensors are respectively installed on the outlet pipes 4 located on both sides of the regulating valve 5, and a pressure sensor is installed at the outlet end of the regulating valve 5. Both the temperature sensors and the pressure sensors are connected to an external controller. Embodiment 3 connects the external controller to the user terminal to facilitate monitoring and automatic control. The pressure sensor is used to detect whether the pressure parameters of the low-pressure syngas after depressurization meet the standards, and at the same time, to detect whether the valve body is blocked, thereby determining whether it is necessary to switch using the bypass line and valve of Embodiment 2. The temperature sensors on both sides are used to detect the temperatures at two temperature points, TI01 and TI02, at the inlet and outlet ends of the regulating valve 5, thereby ensuring that the temperature of the low-pressure syngas after throttling and depressurization meets the requirements and condensation can be achieved.

[0033] Based on Example 3, the pressure parameters after pressure reduction are set according to the production process requirements. If the production is stable, the pressure regulating valve 5 can be put into automatic control; if the production is unstable, it can be manually adjusted.

[0034] In a preferred embodiment 4, the inlet pipe diameter of the regulating valve 5 is DN50, and the outlet pipe diameter of the regulating valve 5 is DN100. This ensures that the usage requirements are met.

[0035] In a preferred embodiment 5, the outlet pipe of the second cyclone separator 8 is connected to the low-pressure tail gas treatment system. After secondary separation, the low-pressure syngas and the accumulated liquid are completely separated. At this point, the low-pressure syngas contains virtually no mercaptans or thioethers, and its main components are carbon dioxide and nitrogen. It then enters the low-pressure tail gas treatment system for final treatment.

[0036] As a preferred embodiment 6, a method for recovering thiols and thioethers from the tail gas of methanethiol preparation using the above-described recovery system includes the following steps:

[0037] S1: The high-pressure synthesis gas at the shell-side outlet of the low-temperature water condenser 1 is transported to the shell-side inlet of the throttling cooling condenser 2 for condensation, and the mercaptan sulfide-containing liquid in the low-temperature water condenser 1 is fed into the mercaptan sulfide crude product tank 6 for collection.

[0038] S2: The high-pressure synthesis gas after condensation enters the first cyclone separator 3 from the shell-side outlet of the throttling and cooling condenser 2 for liquid separation. The liquid containing mercaptan sulfide after separation is fed into the mercaptan sulfide crude product tank 6 for collection.

[0039] S3: The high-pressure synthesis gas after separation enters the outlet pipe 4 of the first cyclone separator 3. After being throttled and depressurized by the regulating valve 5, it is converted into low-pressure synthesis gas. The temperature of the low-pressure synthesis gas is lower than that of the high-pressure synthesis gas.

[0040] S4: The low-pressure synthesis gas converted after throttling and pressure reduction is introduced into the tube inlet of the throttling and cooling condenser 2 through the outlet pipe 4. The throttling and cooling condenser 2 uses the low-pressure synthesis gas to realize the condensation of the high-pressure synthesis gas in the high-temperature shell side of S1.

[0041] S5: The low-pressure synthesis gas after condensation enters the tail gas buffer tank 7 from the tube side outlet of the throttling and cooling condenser 2 for further processing.

[0042] S6: The low-pressure synthesis gas in the tail gas buffer tank 7 undergoes secondary liquid separation treatment through the second cyclone separator 8.

[0043] Example 6 provides a specific recovery method for the system provided in Example 1, with each step corresponding to its structure. S1 uses a throttling cooling condenser 2 to re-condense the high-pressure synthesis tail gas in the low-temperature water condenser 1. S2 uses a first cyclone separator 3 to perform a first liquid-liquid separation process on the condensed high-pressure synthesis gas. S3 passes the separated high-pressure synthesis gas through an outlet pipe 4 and a regulating valve 5 to convert it into a lower-temperature low-pressure synthesis gas. S4 introduces the low-pressure synthesis gas through the outlet pipe 4 into the tube side of the throttling cooling condenser 2 to provide refrigerant for the condensation in S1. S5 collects the low-pressure synthesis gas, which has completed its refrigerant function, into a tail gas buffer tank 7. S6 introduces the low-pressure synthesis gas from the tail gas buffer tank 7 into a second cyclone separator 8 for a second liquid-liquid separation process, achieving complete separation of the accumulated liquid and gas. This method utilizes the physicochemical properties of the tail gas itself to transform it into a refrigerant, providing a cold source for the condensation of the tail gas. It requires no additional equipment, is low-cost, makes full use of resources, and has a good cooling effect.

[0044] In a preferred embodiment 7, the low-pressure synthesis gas and high-pressure synthesis gas in S1-S6 are both mixtures of methanethiol, sulfides, carbon dioxide, and nitrogen, with the high-pressure synthesis gas containing more methanethiol and sulfides than the low-pressure synthesis gas. This is because the low-pressure and high-pressure synthesis gases are themselves the synthesis tail gases produced by the reaction, and the method and system exist to recover residual methanethiol and sulfides. Therefore, their gas composition is also a mixture of methanethiol, sulfides, carbon dioxide, and nitrogen. Before becoming low-pressure synthesis gas, the high-pressure synthesis gas has already undergone condensation in the low-temperature water condenser 1 and the throttling cooling condenser 2, as well as separation in the first cyclone separator 3. Therefore, the methanethiol and sulfide content in the high-pressure synthesis gas is higher than in the low-pressure synthesis gas. The gas composition also determines that throttling and pressure reduction can be used to achieve gas cooling.

[0045] As a preferred embodiment 8, the high-pressure synthesis gas in S1~S3 has a temperature of 15℃~17℃ and a pressure of 1.0MPa~1.2MPa.

[0046] As a preferred embodiment 9, the temperature of the low-pressure synthesis gas in S3~S4 is 5℃~7℃, and the pressure is 0.1MPa~0.2MPa.

[0047] Examples 8 and 9 provide reference values ​​for the temperature and pressure of high-pressure and low-pressure synthesis gas during the recovery of thiols and thioethers in the case of the synthesis of methanethiol from methanol and hydrogen sulfide.

[0048] As a preferred embodiment 10, S6 further includes the liquid in the exhaust gas buffer tank 7 and the second cyclone separator 8 entering the liquid recovery system. The liquid may not meet the requirements of the crude product due to its low content. Therefore, the liquid separated in the exhaust gas buffer tank 7 and the second cyclone separator 8 is recovered separately through the liquid recovery system.

[0049] As a preferred embodiment 11, S6 further includes the low-pressure syngas after secondary liquid separation entering the low-pressure tail gas treatment system for treatment. After secondary liquid separation, the accumulated liquid is completely separated from the low-pressure syngas. At this time, there are basically no mercaptans and thioethers in the low-pressure syngas, and the mercaptans and thioethers are recovered. The low-pressure syngas is almost entirely composed of carbon dioxide and nitrogen, which is then introduced into the low-pressure tail gas treatment system for treatment in order to be washed and recovered or discharged.

Claims

1. A recovery system for mercaptans and sulfides in tail gas produced against methyl mercaptan, comprising a low-temperature water condenser (1), characterized in that, The shell-side outlet of the low-temperature water condenser (1) is connected to the shell-side inlet of the throttling cooling condenser (2). The shell-side outlet of the throttling cooling condenser (2) is connected to the feed inlet of the first cyclone separator (3). The outlet of the first cyclone separator (3) is connected to the tube-side inlet of the throttling cooling condenser (2) through the outlet pipe (4). The outlet pipe (4) is equipped with a regulating valve (5) for throttling and pressure reduction. The tube-side outlet of the throttling cooling condenser (2) is connected to the inlet of the tail gas buffer tank (7). The outlet of the tail gas buffer tank (7) is connected to the second cyclone separator (8). The liquid outlets of the low-temperature water condenser (1), the throttling cooling condenser (2), and the first cyclone separator (3) are all connected to the mercaptan sulfide crude product tank (6) through pipes.

2. The system for recovering thiols and thioethers from the tail gas of methanethiol production according to claim 1, characterized in that, A secondary line and valve are installed at the regulating valve (5).

3. A recovery system for mercaptans and sulfides in a tail gas produced from methanethiol according to claim 2, characterized in that, A corresponding temperature sensor is provided on the outlet pipe (4) located on both sides of the regulating valve (5), and a pressure sensor is provided at the outlet end of the regulating valve (5). Both the temperature sensor and the pressure sensor are connected to an external controller.

4. The recovery system for mercaptans and sulfides in the tail gas produced from methanethiol according to claim 1, characterized by, The outlet pipe of the second cyclone separator (8) is connected to the low-pressure exhaust gas treatment system.

5. A method for recovering thiols and thioethers from the tail gas of methanethiol preparation using a recovery system according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: The high-pressure synthesis gas at the shell-side outlet of the low-temperature water condenser (1) is transported to the shell-side inlet of the throttling cooling condenser (2) for condensation. The mercaptan-containing sulfide liquid in the low-temperature water condenser (1) is fed into the mercaptan-sulfide crude product tank (6) for collection. S2: The high-pressure synthesis gas after condensation enters the first cyclone separator (3) from the shell-side outlet of the throttling and cooling condenser (2) for liquid separation. The liquid containing mercaptan sulfides after separation is fed into the mercaptan sulfide crude product tank (6) for collection. S3: The high-pressure synthesis gas after separation enters the outlet pipe (4) of the first cyclone separator (3), and after being throttled and depressurized by the regulating valve (5), it is converted into low-pressure synthesis gas. The temperature of the low-pressure synthesis gas is lower than that of the high-pressure synthesis gas. S4: The low-pressure synthesis gas converted after throttling and depressurization is introduced into the tube inlet of the throttling and cooling condenser (2) through the outlet pipe (4). The throttling and cooling condenser (2) uses the low-pressure synthesis gas to realize the condensation of the high-pressure synthesis gas in the high-temperature shell side of S1. S5: The low-pressure synthesis gas after condensation enters the tail gas buffer tank (7) from the tube side outlet of the throttling and cooling condenser (2) for further processing; S6: The low-pressure synthesis gas in the tail gas buffer tank (7) undergoes secondary liquid separation treatment through the second cyclone separator (8).

6. The recycling method according to claim 5, characterized in that, The components of the low-pressure synthesis gas and high-pressure synthesis gas in S1~S6 are both a mixture of methanethiol, thioether, carbon dioxide and nitrogen, and the content of methanethiol and thioether in the high-pressure synthesis gas is greater than that in the low-pressure synthesis gas.

7. The recycling method according to claim 6, characterized in that, The high-pressure synthesis gas in S1~S3 has a temperature of 15℃~17℃ and a pressure of 1.0MPa~1.2MPa.

8. The recycling method of claim 6, wherein, The low-pressure synthesis gas in S3~S4 has a temperature of 5℃~7℃ and a pressure of 0.1MPa~0.2MPa.

9. The recycling method of claim 5, wherein, The S6 also includes the liquid from the exhaust gas buffer tank (7) and the second cyclone separator (8) entering the liquid recovery system.

10. The recycling method according to claim 9, characterized in that, The S6 also includes the low-pressure synthesis gas after secondary liquid separation entering the low-pressure tail gas treatment system for further processing.

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