N-vinylacetamide manufacturing method and thermal decomposition apparatus

Abstract

Provided is a method for producing an N-vinylacetamide which can prevent raw material gas (vaporized raw material) from being liquefied by re-condensation, suppress the problem of pyrolysis reactor blockage by resin, and enable stable and continuous operation of the pyrolysis reactor for a long period of time. The method for producing an N-Vinylacetamide includes: a supply step for supplying a raw material comprising an N-(1-methoxyethyl)acetamide (MEA) to an evaporator; an evaporation step for evaporating the raw material in the evaporator and using the evaporated raw material as a vaporized raw material; a superheating step for supplying the vaporized raw material to a superheater, and superheating the vaporized raw material such that an superheating temperature of the vaporized raw material is 5 °C (boiling point of the N-(1-methoxyethyl)acetamide (MEA) under an internal pressure of the superheater is +5 °C) to 200 °C higher than the boiling point of the N-(1-methoxyethyl)acetoamide (MEA) under the internal pressure of the superheater; and a pyrolysis step for supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing the superheated vaporized raw material, wherein the content of the N-(1-methoxyethyl)acetamide in the raw material occupies 80-100 mass%.

Description

[Technical field]

[0001] The present invention relates to a method for producing N-vinylacetamide and an apparatus for thermal decomposition thereof. [Background technology]

[0002] Many methods have been proposed for the production of N-vinyl carboxylic acid amide (see, for example, Patent Document 1). Patent Document 1 discloses a method for producing N-vinyl carboxylic acid amide by evaporating and pyrolyzing an N-(2-alkoxyethyl) carboxylic acid amide raw material. In this way, in the method for producing N-vinyl carboxylic acid amide by pyrolysis, for example, heat radiation to the atmosphere, heat absorption in the pyrolysis reactor (pyrolysis step), pressure change due to mechanical trouble, stop of supply of heat source, etc., the raw material gas (vaporized raw material) may be liquefied by recondensation in the evaporator, in the pipe connecting the evaporator and the pyrolysis reactor, or in the pyrolysis reactor, and the liquefied raw material may flow into the high-temperature pyrolysis reactor. As a result, (i) the liquefied raw material flows on the inner wall of the tube of the pyrolysis reactor, or (ii) the liquefied raw material is polymerized before being reevaporated on the inner wall of the tube of the pyrolysis reactor, resulting in the generation of tar-like or solid aggregates (also called Hartz), which may cause a blockage problem of the tube of the pyrolysis reactor and make stable operation difficult. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 002494 Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide a method for producing N-vinylacetamide that can solve the above problems, prevent the raw material gas (vaporized raw material) from being liquefied by recondensation, suppress the Hartz clogging problem in the pyrolysis reactor, and enable stable continuous operation for a long period of time. [Means for solving the problem]

[0005] As a result of intensive research by the inventors to solve the above-mentioned problems, they have found that it is possible to prevent the raw material gas (vaporized raw material) from being liquefied by re-condensation by providing a superheater (superheating step) between an evaporator (evaporation step) and a thermal decomposition reactor (thermal decomposition step) and by satisfying at least one of the following: (i) superheating the raw material gas (vaporized raw material) in the superheater (superheating step) to a temperature (the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure + 5°C) that is a predetermined temperature higher than the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure and 200°C inclusive; and (ii) imparting a predetermined amount of heat to the raw material gas (vaporized raw material), thereby completing the present invention. That is, the present invention provides the following (1) to (15). (1) A method for producing N-vinyl acetamide, comprising: a supply step of supplying a raw material containing N-(1-methoxyethyl)acetamide (MEA) to an evaporator; an evaporation step of evaporating the raw material in the evaporator to obtain a vaporized raw material; a superheating step of supplying the vaporized raw material to a superheater and superheating the vaporized raw material to a temperature that is 5°C higher than the boiling point of the N-(1-methoxyethyl)acetamide at the internal pressure of the superheater (the boiling point of the N-(1-methoxyethyl)acetamide at the internal pressure of the superheater + 5°C) and 200°C or lower; and a pyrolysis step of supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing it, wherein the content of the N-(1-methoxyethyl)acetamide in the raw material is 80 to 100 mass%. (2) A method for producing N-vinyl acetamide, comprising: a supplying step of supplying a raw material containing N-(1-methoxyethyl)acetamide (MEA) to an evaporator; an evaporation step of evaporating the raw material in the evaporator to obtain a vaporized raw material; a superheating step of supplying the vaporized raw material to a superheater and superheating the vaporized raw material by applying a heat quantity of 1.0 kJ / mol or more to the vaporized raw material; and a pyrolysis step of supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing it, wherein the content of N-(1-methoxyethyl)acetamide in the raw material is 80 to 100 mass%. (3) The method for producing N-vinylacetamide according to (1) or (2) above, wherein the evaporation step is carried out under reduced pressure. (4) The method for producing N-vinylacetamide according to any one of the above (1) to (3), wherein the thermal decomposition step is carried out under reduced pressure. (5) The method for producing N-vinylacetamide according to any one of the above (1) to (4), wherein the evaporator is of a falling film type. (6) The method for producing N-vinylacetamide according to any one of the above (1) to (4), wherein the evaporator is of a forced film type. (7) The method for producing N-vinylacetamide according to any one of (1) to (6) above, wherein a downstream end of the evaporator and an upstream end of the superheater are connected via a first pipe, and the downstream end of the first pipe is at the highest position in the first pipe. (8) The method for producing N-vinylacetamide according to any one of (1) to (7) above, wherein a downstream end of the superheater and an upstream end of the thermal decomposition reactor are connected via a second pipe, and the upstream end of the second pipe is at the highest position in the second pipe. (9) The method for producing N-vinylacetamide according to any one of (1) to (8) above, further comprising a recovery step between the evaporation step and the pyrolysis step, of recovering a liquid raw material that is not vaporized among the raw material supplied to the evaporator and a liquid raw material obtained by liquefying a part of the vaporized raw material, wherein the recovery step is a step of recovering the liquid raw material by a raw material recovery device provided between the evaporator and the pyrolysis reactor. (10) The method for producing N-vinylacetamide according to (9) above, wherein a downstream end of the evaporator and an upstream end of the raw material recovery device are joined together. (11) The method for producing N-vinylacetamide according to (9) or (10) above, wherein a downstream end of the raw material recovery device and an upstream end of the superheater are joined together. (12) The method for producing N-vinylacetamide according to any one of (9) to (11) above, wherein the vaporized raw material is supplied to the pyrolysis reactor after passing through the raw material recovery device. (13) The method for producing N-vinylacetamide according to any one of (9) to (12) above, wherein the raw material recovery apparatus comprises a cylindrical section for circulating the vaporized raw material, a recovery section for colliding a part or all of the flow of the vaporized raw material flowing inside the cylindrical section to recover a liquid raw material that is not vaporized among the raw material supplied to the evaporator and a liquid raw material obtained by liquefying a part of the vaporized raw material, and a discharge pipe for discharging the liquid raw material recovered by the recovery section to the outside of the cylindrical section. (14) A thermal decomposition apparatus comprising: an evaporator capable of evaporating a raw material to generate a vaporized raw material; a superheater connected to the evaporator and capable of superheating the vaporized raw material to a temperature that is 5°C higher than the boiling point of the N-(1-methoxyethyl)acetamide at an internal pressure of the superheater (i.e., a temperature that is 5°C higher than the boiling point of the N-(1-methoxyethyl)acetamide at an internal pressure of the superheater) to 200°C or lower; and a thermal decomposition reactor connected to the superheater and capable of thermally decomposing the superheated vaporized raw material. Effect of the Invention

[0006] According to the present invention, a method for producing N-vinylacetamide can be provided that prevents the raw material gas (vaporized raw material) from being liquefied due to recondensation, suppresses the problem of Hartz clogging of the pyrolysis reactor, and can be operated stably and continuously for a long period of time. [Brief description of the drawings]

[0007] [Figure 1] 1 is a flowchart showing a method for producing N-vinylacetamide of the present invention. [Diagram 2]FIG. 1 is a schematic overall view of a process for producing N-vinylacetamide according to the present invention, in which an evaporator is a falling film evaporator. [Diagram 3] FIG. 1 is a schematic overall view of a process for producing N-vinylacetamide according to the present invention, in which an evaporator is a forced film evaporator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In this specification, preferred definitions may be selected arbitrarily, and combinations of preferred definitions may be considered more preferred. In this specification, the expression "XX to YY" means "at least XX and at most YY." In this specification, the lower limit and upper limit described in stages for the preferred numerical range (e.g., range of content, etc.) can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

[0009] [Method for producing N-vinylacetamide] The method for producing N-vinylacetamide according to the embodiment of the present invention includes a supply step S1, an evaporation step S2, an optional recovery step S3, a superheating step S4, and a pyrolysis step S5, as shown in Fig. 1. The method for producing N-vinylacetamide according to the embodiment of the present invention will be described in detail below.

[0010] (Supply process S1) The supply step S1 is a step of supplying a raw material containing N-(1-methoxyethyl)acetamide (MEA) to an evaporator.

[0011] The method for producing N-vinylacetamide according to the embodiment of the present invention uses N-(1-methoxyethyl)acetamide represented by the following structural formula (1) as a part or all of a raw material. [ka] The content of N-(1-methoxyethyl)acetamide in the raw material is not particularly limited as long as it is 80 to 100% by mass, but is preferably 90 to 100% by mass, and more preferably 95 to 100% by mass. The components other than N-(1-methoxyethyl)acetamide in the raw material are not particularly limited, and examples thereof include acetamide, methanol, and the like.

[0012] In the supply step S1, the supply rate of the raw material to the evaporator depends on the size and capacity of the evaporator, but from the viewpoint of stably evaporating the raw material, it is preferably 5 to 350 kg / h, more preferably 10 to 150 kg / h, and even more preferably 15 to 80 kg / h.

[0013] (Evaporation process S2) The evaporation step S2 is a step in which the raw material is evaporated in an evaporator to obtain a vaporized raw material. The evaporator used in the evaporation step S2 is not particularly limited, but from the viewpoint of efficiently evaporating the raw material, it is preferably either a falling film evaporator or a forced film evaporator.

[0014] The evaporation step S2 can be carried out under reduced pressure or normal pressure, but is preferably carried out under reduced pressure. Specifically, the reaction pressure in the evaporation step S2 is preferably 1 to 30 kPa, more preferably 3 to 25 kPa, and even more preferably 5 to 22 kPa. The evaporation step S2 must be carried out at a temperature at which the material can be heated and evaporated to form a vaporized raw material. Specifically, the evaporation step S2 is preferably carried out at 100 to 200°C, more preferably at 110 to 190°C, and even more preferably at 120 to 180°C.

[0015] In the evaporation step S2, from the viewpoint of reducing the heat transfer area of ​​the evaporator to make the evaporator more compact, it is preferable to apply the minimum amount of heat required to evaporate the raw material. If the amount of heat applied in the evaporation step S2 exceeds the minimum amount of heat required to evaporate the raw material, a more sufficient amount of heat will be applied in preparation for heat release to the atmosphere and heat absorption in the pyrolysis reaction step.

[0016] (Recovery process S3) The recovery step S3 is an optional step between the evaporation step S2 and the pyrolysis step S5, which recovers the liquid raw material that was not vaporized among the raw material supplied to the evaporator and the liquid raw material that is a part of the vaporized raw material that has been liquefied. The vaporized raw material in the vaporized state is supplied to the pyrolysis step. The recovery step S3 is preferably performed by a raw material recovery device provided between the evaporator and the pyrolysis reactor. In FIG. 1, the order is the evaporation step S2, the recovery step S3, and the superheating step S4, but this is not limiting, and for example, the order may be the evaporation step S2, the superheating step S4, and the recovery step S3.

[0017] When even a small amount of liquid raw material is introduced into the pyrolysis reactor, Hartz occurs, which blocks the pyrolysis reactor and makes it impossible to continue operation. Even if the Hartz does not block the entire volume of the pyrolysis reactor, it will block a small volume on the raw material introduction side of the pyrolysis reactor, making it impossible to continue operation. By recovering the liquid raw material in a recovery pot outside the system of the manufacturing equipment in the recovery step S3, it is possible to more reliably suppress the introduction of the liquid raw material into the pyrolysis reactor, and as a result, it is possible to continue operation for a longer period of time. Examples of factors that cause liquid raw materials to be generated during the operation of manufacturing equipment include heat release into the atmosphere, heat absorption in the pyrolysis reactor (pyrolysis process), fluctuations in operating pressure due to mechanical failures and operational errors, stoppage or insufficient heat source for the evaporator due to mechanical failures and operational errors, poor evaporation due to scale (black skin) formed in the evaporator reducing the heat transfer area, and the introduction of raw materials when the equipment is not sufficiently heated at the start of operation.

[0018] (Superheating step S4) The superheating step S4 is a step of supplying the vaporized raw material to a superheater and superheating it, and satisfies at least one of the following: (i) the superheating temperature of the vaporized raw material is at least 5°C higher than the boiling point of N-(1-methoxyethyl)acetamide at the superheater pressure (the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure + 5°C) and not more than 200°C; and (ii) a heat quantity of 1.0 kJ / moL or more is applied to the vaporized raw material. The superheating temperature of the vaporized raw material in the superheating step S4 is not particularly limited as long as it is a temperature 5°C higher than the boiling point of N-(1-methoxyethyl)acetamide at the pressure inside the superheater (the boiling point of N-(1-methoxyethyl)acetamide at the pressure inside the superheater +5°C) and not higher than 200°C, but is preferably 165 to 200°C, more preferably 170 to 195°C, and even more preferably 173 to 190°C. Note that the upper limit of the superheating temperature of the vaporized raw material does not mean the boiling point temperature plus that temperature, but simply means that upper limit temperature.

[0019] In this specification, "superheating temperature of the vaporized raw material" means "the maximum temperature of the vaporized raw material in the superheater", and is usually the temperature of the vaporized raw material at the downstream end of the superheater (outlet gas temperature).

[0020] Since the temperature of saturated steam of the heat transfer medium at 2.0 MPaG (gauge pressure) (upper limit industrial steam pressure) is 215°C, it is preferable that the upper limit of the superheating temperature is 200°C from the viewpoint of cost as well.

[0021] The amount of heat applied to the vaporized raw material in the superheating step S4 is not particularly limited as long as it is 1.0 kJ / mol or more, and is preferably 1.0 to 9.0 kJ / mol, more preferably 1.5 to 8.0 kJ / mol, and even more preferably 2.0 to 7.0 kJ / mol.

[0022] The above-mentioned superheat temperature of the vaporized raw material and the lower limit value of the amount of heat applied to the vaporized raw material are determined as follows. From the outlet of the superheater to the tubes in the pyrolysis device, there are places where heat cannot be input (for example, the seams of the jacket, the channels of the pyrolysis device), and even in these places where heat cannot be input, the temperature drops due to heat absorption in the pyrolysis process. This temperature drop due to heat absorption in the pyrolysis process can be calculated from the amount of heat released, the reaction rate, the heat of reaction, and the residence time. Taking into account the calculated temperature drop and the temperature error (margin), the superheating temperature of the vaporized raw material and the lower limit of the amount of heat to be applied to the vaporized raw material are determined.

[0023] On the other hand, the above-mentioned superheat temperature of the vaporized raw material and the upper limit value of the amount of heat applied to the vaporized raw material are determined as follows. In order to prevent the reaction outside the pyrolysis device from proceeding too quickly, it is necessary to control the pyrolysis reaction so that the reaction rate is sufficiently slow compared to the reaction rate in the pyrolysis device. Therefore, from the viewpoint of controlling the pyrolysis reaction, the upper limit of the superheat temperature of the vaporized raw material and the amount of heat applied to the vaporized raw material are usually set, but there are also cases where the upper limit of the superheat temperature of the vaporized raw material and the amount of heat applied to the vaporized raw material are set depending on the usable heat medium temperature.

[0024] The heating step S4 can be carried out under reduced pressure or normal pressure, but is preferably carried out under reduced pressure. Specifically, the pressure in the heating step S4 is preferably 1 to 30 kPa, more preferably 3 to 25 kPa, and even more preferably 5 to 22 kPa.

[0025] (Pyrolysis process S5) The pyrolysis step S5 is a step of supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing it. The flow of the vaporized raw material supplied to the pyrolysis reactor is not particularly limited as long as it is a flow that flows into the pyrolysis reactor, and may be an upward flow or a downward flow.

[0026] The thermal decomposition step S5 can be carried out under reduced pressure or normal pressure, but is preferably carried out under reduced pressure. Specifically, the reaction pressure in the thermal decomposition step S5 is preferably 1 to 30 kPa, more preferably 3 to 25 kPa, and even more preferably 5 to 22 kPa. The pyrolysis step S5 is preferably carried out at 250 to 500°C, more preferably at 300 to 480°C, and even more preferably at 350 to 450°C, from the viewpoint of efficient pyrolysis. From the viewpoint of ensuring reliable pyrolysis, the residence time in the pyrolysis step S5 is preferably 0.1 to 10 seconds, more preferably 0.2 to 9 seconds, and even more preferably 0.3 to 8 seconds. From the viewpoint of efficiently carrying out pyrolysis, the pyrolysis reactor preferably has a multi-tube structure.

[0027] The raw material to be supplied to the pyrolysis reactor is preferably the vaporized raw material after the recovery process. By supplying the vaporized raw material after the recovery process to the pyrolysis reactor, it is possible to more reliably prevent the liquid raw material from being introduced into the pyrolysis reactor, and more reliably prevent the occurrence of Hartz waves.

[0028] The N-vinylacetamide obtained by the above steps is represented by the following structural formula (2), and is obtained from N-(1-methoxyethyl)acetamide represented by structural formula (1) contained in the raw material. [ka]

[0029] (First manufacturing equipment) As shown in FIG. 2, a first production apparatus for carrying out the method for producing N-vinylacetamide according to the embodiment of the present invention includes a raw material supplying apparatus 10 for carrying out a supplying step S1, an evaporator (falling film evaporator) 20A for carrying out an evaporation step S2, a raw material recovering apparatus 30A for carrying out a recovering step S3, a superheater 40A for carrying out a superheating step S4, a pyrolysis reactor 50 for carrying out a pyrolysis step S5, a cooler 60 for cooling and liquefying the reactants pyrolyzed in the pyrolysis step S5, and a reaction liquid receiver 70 for storing the reactants liquefied in the cooling section 60. The downstream end of the raw material supplying device 10 is connected to the upstream end of the evaporator 20A via piping 12, the downstream end of the evaporator 20A is connected to the upstream end of the raw material recovery device 30A, the downstream end of the raw material recovery device 30A is connected to the upstream end of the superheater 40A, the downstream end of the superheater 40A is connected to the upstream end of the pyrolysis reactor 50, the downstream end of the pyrolysis reactor 50 is connected to the upstream end of the cooler 60, and the downstream end of the cooler 60 is connected to the upstream end of the reaction liquid receiver 70. The falling film evaporator is an evaporator that evaporates the liquid raw material by making it flow down the inner surface of the evaporation tube in the form of a film, for example, an evaporator having a structure in which many tubes are installed inside the shell and the liquid flows down the inner walls of these tubes. The superheater 40A has a structure similar to that of the distiller 20A. The raw material recovery device 30A is provided with a recovery pot 42 for recovering the recovered liquid raw material. The reaction liquid receiver 70 is provided with a pressure pump 71, and the pressure of the entire production apparatus can be adjusted by the pressure pump 71. The pressure of the entire production apparatus can be confirmed by a pressure gauge PI provided in the reaction liquid receiver 70.

[0030] The raw material recovery device 30A may have any structure as long as it does not allow the liquid raw material to be introduced into the superheater 40A and the pyrolysis reactor 50. 2, the raw material recovery apparatus 30A preferably has a configuration including a cylindrical section 32 through which the vaporized raw material flows, a recovery section 33 that causes a part or all of the flow of the vaporized raw material flowing inside the cylindrical section 32 to collide with each other, and recovers the liquid raw material that was not vaporized among the raw material supplied to the evaporator and the liquid raw material that is a part of the vaporized raw material that has been liquefied, and an exhaust pipe 34 that discharges the liquid raw material recovered by the recovery section 33 to the outside of the cylindrical section 32. The raw material recovery apparatus 30A preferably further has a flow suppression section 31 in order to cause all of the vaporized raw material flowing inside the cylindrical section 32 to collide with the recovery section 33. The flow restricting section 31 preferably has a tapered shape that restricts the flow of the vaporized raw material downstream. The recovery section 33 is preferably in the shape of a dish for receiving the flow of the vaporized raw material, and has a collecting section for collecting the liquid raw material. With the raw material recovery device 30A having the above-mentioned configuration, the liquid raw material that was not vaporized among the raw material supplied to the evaporator and the liquid raw material that is a part of the vaporized raw material that has been liquefied are recovered by colliding with the recovery section 33, and the liquid raw material is discharged to the outside of the tube section 32 by the discharge pipe 34. The vaporized raw material that has collided with the recovery section 33 passes through the gap between the recovery section 33 and the flow suppression section 31, and heads toward the superheater 40A and the pyrolysis reactor 50. In other words, with the raw material recovery device 30A having the above-mentioned configuration, the vaporized raw material from which the liquid raw material has been recovered by colliding with the recovery section 33 is introduced into the superheater 40A and the pyrolysis reactor 50.

[0031] The liquid raw material recovered by the raw material recovery device 30A is sent to a recovery pot 42. The recovery pot 42 can control the liquid raw material by gate valves 35a and 35b. The recovery pot 42 can adjust the pressure of the recovery pot 42 by a pressure pump 36 and gate valves 35a to 35d. The pressure of the recovery pot 42 can be confirmed by a pressure gauge PI. The liquid raw material recovered by the raw material recovery device 30A constantly flows into the recovery pot 42 through the gate valves 35a and 35b. The amount of the raw material recovered into the recovery pot 42 can be confirmed by a liquid level gauge LI such as a liquid level confirmation window installed in the recovery pot 42. When recovering the liquid raw material stored in the recovery pot 42, the gate valves 35b and 35c are closed, the nitrogen valve 37a is opened, nitrogen is introduced from the nitrogen supply device 37 into the recovery pot 42 to return it to normal pressure, and the extraction valve 41 is opened. After recovery, the extraction valve 41 and the nitrogen valve 37a are closed, the gate valve 36a is opened, and the pressure is adjusted to the same pressure as the entire manufacturing apparatus by the pressure pump 36, and then the gate valve 35c is opened, and then the gate valve 35b is opened, thereby making it possible to recover the liquid raw material. The temperature of the raw material recovery device 30A is appropriately selected from a temperature range in which the vaporized raw material generated in the evaporator 20A does not condense. The temperature of the recovery pot 42 may be any temperature at which the recovered liquid raw material does not solidify.

[0032] The liquid raw material recovered in the raw material recovery unit 30A is preferably supplied to the evaporator 20A. In the first manufacturing apparatus shown in Fig. 2, the liquid raw material recovered in the recovery pot 42 is supplied to the evaporator 20A. By supplying the recovered liquid raw material to the evaporator 20A again, efficient use of the raw material can be realized.

[0033] As shown in Fig. 2, it is preferable that the downstream end of the evaporator 20A is joined to the upstream end of the raw material recovery unit 30A. By joining the downstream end of the evaporator 20A to the upstream end of the raw material recovery unit 30A, the vaporized raw material heated and evaporated in the evaporator 20A can be sent directly to the raw material recovery unit 30A. In other words, it is possible to prevent a part of the vaporized raw material from liquefying between the evaporator 20A and the raw material recovery unit 30A.

[0034] As shown in Fig. 2, it is preferable that the downstream end of the raw material recovery apparatus 30A and the upstream end of the superheater 40A are joined together. By joining the downstream end of the raw material recovery apparatus 30A and the upstream end of the superheater 40A together, the vaporized raw material recovered in the raw material recovery apparatus 30A can be sent directly to the superheater 40A. In other words, it is possible to prevent a part of the vaporized raw material from liquefying between the raw material recovery apparatus 30A and the superheater 40A.

[0035] 2, it is preferable that the downstream end of the superheater 40A and the upstream end of the pyrolysis reactor 50 are joined together. By joining the downstream end of the superheater 40A and the upstream end of the pyrolysis reactor 50 together, the vaporized raw material superheated in the superheater 40A can be sent directly to the pyrolysis reactor 50. In other words, it is possible to prevent a part of the vaporized raw material from liquefying between the superheater 40A and the pyrolysis reactor 50.

[0036] 2, it is preferable that the downstream end of the pyrolysis reactor 50 and the upstream end of the cooler 60 are joined together. By joining the downstream end of the pyrolysis reactor 50 and the upstream end of the cooler 60 together, the target product obtained by pyrolysis in the pyrolysis reactor 50 can be sent directly to the cooler 60.

[0037] 2, it is preferable that the downstream end of the cooler 60 and the upstream end of the reaction liquid receiver 70 are joined together. By joining the downstream end of the cooler 60 and the upstream end of the reaction liquid receiver 70 together, the target substance cooled in the cooler 60 can be sent directly to the reaction liquid receiver 70.

[0038] (Second manufacturing equipment) As shown in FIG. 3, the second production apparatus for carrying out the method for producing N-vinylacetamide according to the embodiment of the present invention includes a raw material supplying device 10 for carrying out a supplying step S1, an evaporator (forced film evaporator) 20B for carrying out an evaporation step S2, a superheater 40B for carrying out a superheating step S4, a raw material recovery device 30B for carrying out a recovery step S3, a pyrolysis reactor 50 for carrying out a pyrolysis step S5, a cooler 60 for cooling and liquefying the reactant pyrolyzed in the pyrolysis step S5, and a reaction liquid receiver 70 for storing the reactant liquefied in the cooling section 60. The downstream end of the raw material supplying device 10 is connected to the upstream end of the evaporator 20B via piping 12, the downstream end of the evaporator 20B is connected to the upstream end of the superheater 40B via the first piping 90, the downstream end of the superheater 40B is connected to the upstream end of the raw material recovery device 30B via the second piping front stage section 100a, the downstream end of the raw material recovery device 30B is connected to the upstream end of the pyrolysis reactor 50 via the second piping rear stage section 100b, the downstream end of the pyrolysis reactor 50 is connected to the upstream end of the cooler 60 via piping 13, and the downstream end of the cooler 60 is connected to the upstream end of the reaction liquid receiver 70 via piping 14. A forced film evaporator is an evaporator in which liquid raw material is flowed in the form of a film running down the inner surface of an evaporation tube, and a propulsive force is generated by the air flow inside the evaporation tube by rotating a fan or the like with a motor (for example, motor M in Figure 3), and the film-like raw material inside the evaporation tube is forcibly advanced by the propulsive force, thereby evaporating the raw material. In the superheater 40B, the pipe 95 connecting the first pipe 90 and the second pipe 100 meanders, so that a predetermined amount of heat is imparted to the gas raw material in the pipe 95, and the gas raw material reaches a predetermined temperature. The raw material recovery device 30B is provided with a recovery pot 42 for recovering the recovered liquid raw material. The reaction liquid receiver 70 is provided with a pressure pump 71, and the pressure of the entire production apparatus can be adjusted by the pressure pump 71. The pressure of the entire production apparatus can be confirmed by a pressure gauge PI provided in the reaction liquid receiver 70.

[0039] The evaporator 20B is preferably provided with a recovery pot 21 for recovering the liquid raw material that was not vaporized among the raw material supplied to the evaporator 20B and the liquid raw material that was obtained by liquefying a part of the vaporized raw material. The recovery pot 21 is preferably provided at a lower position than the evaporator 20B in order to facilitate recovery of the liquid raw material. The recovery pot 21 includes a gate valve 22a that separates the evaporator 20B from the recovery pot 21, and an extraction valve 22b that extracts the liquid raw material recovered in the recovery pot 21 to the outside of the system. The recovery pot 21 can control the liquid raw material by the gate valve 22a and the extraction valve 22b. When recovering the liquid raw material that was not vaporized among the raw material supplied to the evaporator 20B, the extraction valve 22b is closed and the gate valve 22a is opened. When extracting the liquid raw material recovered in the recovery pot 21, the gate valve 22a is closed and the extraction valve 22b is opened.

[0040] 3, the downstream end of the evaporator 20B and the upstream end of the superheater 40B are connected via a first pipe 90, and it is preferable that the downstream end of the first pipe 90 is the highest in the first pipe 90. By configuring the downstream end of the first pipe 90 to be the highest in the first pipe 90, the liquid raw material that has not been vaporized among the raw material flowing through the first pipe 90 and the liquid raw material that is a part of the vaporized raw material that has been liquefied enter and remain in the superheater 40B, and thus the operation can be performed without generating agglomerates due to thermal history.

[0041] As shown in Fig. 3, the downstream end of the superheater 40B and the upstream end of the raw material recovery unit 30B are connected via a front stage 100a of the second pipe, and it is preferable that the upstream end of the front stage 100a of the second pipe is the highest in the front stage 100a of the second pipe. By configuring the upstream end of the front stage 100a of the second pipe to be the highest in the front stage 100a of the second pipe, the liquid raw material, which is a part of the vaporized raw material flowing through the front stage 100a of the second pipe, can be efficiently recovered by the raw material recovery unit 30B.

[0042] As shown in Fig. 3, the downstream end of the raw material recovery apparatus 30B and the upstream end of the pyrolysis reactor 50 are connected via the rear stage 100b of the second pipe, and it is preferable that the upstream end of the rear stage 100b of the second pipe is the lowest in the rear stage 100b of the second pipe. By configuring the upstream end of the rear stage 100b of the second pipe to be the lowest in the rear stage 100b of the second pipe, even if a part of the vaporized raw material flowing through the rear stage 100b of the second pipe is liquefied, the liquefied liquid raw material can be efficiently recovered by the raw material recovery apparatus 30B.

[0043] 3, the downstream end of the superheater 40B and the upstream end of the thermal decomposition reactor 50 are connected via a second pipe 100 (a front stage 100a and a rear stage 100b of the second pipe), and it is preferable that the upstream end of the second pipe 100 is configured to be the highest in the second pipe 100. By configuring the upstream end of the second pipe 100 to be the highest in the second pipe 100, even if a part of the vaporized raw material flowing through the second pipe 100 is liquefied, the liquefied liquid raw material can be efficiently recovered by the raw material recovery device 30B.

[0044] The liquid raw material recovered by the raw material recovery unit 30B is sent to the recovery pot 42. From the viewpoint of facilitating recovery of the liquid raw material, the recovery pot 42 is preferably disposed at a lower position than the raw material recovery unit 30B. The recovery pot 42 can control the liquid raw material by the gate valve 35e and the extraction valve 41. The recovery pot 42 can adjust the pressure of the recovery pot 42 by the pressure pump 36, the gate valve 35e, and the extraction valve 41. The pressure of the recovery pot 42 can be confirmed by the pressure gauge PI. The liquid raw material recovered by the raw material recovery device 30B constantly flows into the recovery pot 42 through the gate valve 35e. The amount of the liquid recovered into the recovery pot 42 can be confirmed by a liquid level gauge LI, such as a liquid level confirmation window, installed in the recovery pot 42. When recovering the liquid raw material stored in the recovery pot 42, the gate valve 35e is closed, the nitrogen valve 37a is opened, nitrogen is introduced from the nitrogen supply device 37 into the recovery pot 42 to return it to normal pressure, and the extraction valve 41 is opened. After recovery, the extraction valve 41 and the nitrogen valve 37a are closed, the gate valve 36a is opened, and the pressure is adjusted to the same pressure as the entire manufacturing apparatus by the pressure pump 36, and then the gate valve 35e is opened, thereby making it possible to recover the liquid raw material. The temperature of the raw material recovery device 30B is appropriately selected within a temperature range in which the vaporized raw material generated in the evaporator 20B and superheated in the superheater 40B does not condense. The temperature of the recovery pot 42 may be any temperature at which the recovered liquid raw material does not solidify.

[0045] The liquid raw material recovered in the raw material recovery unit 30B is preferably supplied to the evaporator 20B. In the second production apparatus shown in Fig. 3, the liquid raw material recovered in the recovery pot 42 is supplied to the evaporator 20B. In the second production apparatus shown in Fig. 3, the liquid raw material recovered in the recovery pot 21 is also preferably supplied to the evaporator 20B. By supplying the recovered liquid raw material to the evaporator again, efficient use of the raw material can be achieved.

[0046] 3, the rear section 100b of the second pipe is preferably connected to the side or top of the raw material recovery unit 30B. By connecting the rear section 100b of the second pipe to the side or top of the raw material recovery unit 30B, it is possible to prevent the liquid raw material recovered by the raw material recovery unit 30B from flowing into the rear section 100b of the second pipe.

[0047] 3, the downstream end of the raw material recovery apparatus 30B may be joined to the upstream end of the pyrolysis reactor 50. By joining the downstream end of the raw material recovery apparatus 30B to the upstream end of the pyrolysis reactor 50, the vaporized raw material from which the liquid raw material has been recovered in the raw material recovery apparatus 30B can be sent directly to the pyrolysis reactor 50. In other words, it is possible to prevent a part of the vaporized raw material from liquefying between the raw material recovery apparatus 30B and the pyrolysis reactor 50.

[0048] In addition, in the manufacturing apparatus shown in FIG. 3, instead of the raw material recovery apparatus 30B, the gate valve 35e, the pressure pump 36, the recovery pot 42, and the withdrawal valve 41, the raw material recovery apparatus 30A, the gate valves 35a to 35d, the pressure pump 36, the recovery pot 42, and the withdrawal valve 41 in FIG. 2 may be provided.

[0049] [Pyrolysis equipment] A thermal decomposition apparatus according to an embodiment of the present invention includes an evaporator capable of evaporating a raw material to generate a vaporized raw material, a superheater connected to the evaporator and capable of superheating the vaporized raw material to a temperature 5°C higher than the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure (boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure +5°C) and up to 200°C, and a thermal decomposition reactor connected to the superheater and capable of thermally decomposing the superheated vaporized raw material, and may further include the above-mentioned raw material recovery apparatus, cooler, reaction liquid receiver, recovery pot, nitrogen supply apparatus, pressure pump, gate valve, nitrogen valve, withdrawal valve, first piping, second piping, level gauge, motor, pressure gauge, etc. as necessary. The above-mentioned method for producing N-vinylacetamide according to the embodiment of the present invention is preferably carried out by using the pyrolysis apparatus according to the embodiment of the present invention. EXAMPLES

[0050] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0051] Example 1 The production apparatus shown in FIG. 2 was used. The evaporator used was a falling film type evaporator, a shell-and-tube type evaporator (tube diameter: 25.4 mm, tube length: 2500 mm, number of tubes: 22) with a structure in which multiple tubes are installed inside the shell and liquid flows down the inner walls of these tubes. Saturated steam of 0.7MPaG (gauge pressure) (temperature 170℃) was introduced into the shell side of the evaporator, and N-(1-methoxyethyl)acetamide, the liquid raw material, was supplied to the tube side at a rate of 20kg / h so that it flowed down the inner wall of the tube and evaporated under reduced pressure conditions of 20kPa (absolute pressure) using a pressure reducing device (pressure pump) installed in the reaction liquid receiver. The gas temperature at the outlet of the evaporator at this time was 160℃ (the boiling point of N-(1-methoxyethyl)acetamide at 20kPa (absolute pressure)). The raw material recovery device was equipped with flanges with an outer diameter of 267.4 mm on the top and bottom, which were connected to the evaporator and superheater, respectively. Saturated steam at 0.7 MPaG (gauge pressure) was introduced into the cylindrical part (jacket) of the raw material recovery device to heat the vaporized raw material so that it would not condense. The superheater used was a shell-and-tube type superheater (tube diameter: 25.4 mm, tube length: 390 mm, number of tubes: 22) with many tubes installed inside the shell, just like the evaporator. Saturated steam at 1.85 MPaG (gauge pressure) (temperature 211°C) was introduced into the shell side of the superheater, and superheating was performed by adding a heat quantity of 5.65 kJ / mol to the process gas (vaporized raw material) generated in the evaporator. The gas temperature at the superheater outlet was 185°C (160°C + 25°C). The tube of the pyrolysis reactor was heated to 440°C by electromagnetic induction heating, and the vaporized raw material introduced into the tube was pyrolyzed under reduced pressure conditions to obtain N-vinylacetamide. The system was operated continuously for 90 days under the above conditions, and no particular problems were observed.

[0052] Example 2 Using the same manufacturing apparatus as in Example 1, shown in FIG. 2, continuous operation was carried out for 90 days under the same operating conditions as in Example 1, except that the process gas (vaporized raw material) generated in the evaporator was superheated by adding a heat quantity of 3.39 kJ / mol so that the process gas temperature at the superheater outlet became 175°C (160°C + 15°C). No particular problems were encountered.

[0053] Example 3 Using the same manufacturing apparatus as in Example 1, as shown in FIG. 2, continuous operation was carried out for 90 days under the same operating conditions as in Example 1, except that the process gas (vaporized raw material) generated in the evaporator was superheated by adding a heat quantity of 7.91 kJ / mol so that the process gas temperature at the superheater outlet became 195°C (160°C + 35°C). No particular problems were encountered.

[0054] Comparative Example 1 Continuous operation was carried out using the same production equipment and operating conditions as in Example 1, except that the superheater was not provided in the production equipment shown in Figure 2 of Example 1. On the 45th day after the start of operation, disturbances in the temperature of the pyrolysis reactor were confirmed, and the operation was stopped because it became uncontrollable. When the production equipment was opened and inspected, tarry and solid hartz were generated and clogged the inlet of the pyrolysis reactor.

[0055] Comparative Example 2 Using the same manufacturing apparatus as in Example 1 shown in Figure 2, the process gas (vaporized raw material) generated in the evaporator was superheated by adding a heat quantity of 0.45 kJ / mol so that the process gas temperature at the superheater outlet was 162°C (160°C + 2°C). Continuous operation was performed under the same operating conditions as in Example 1, and on the 54th day after the start of operation, disturbances were confirmed in the temperature of the pyrolysis reactor, and operation was stopped because it became uncontrollable. When the manufacturing apparatus was opened and inspected, tarry and solid Hartz were generated and clogged the inlet of the pyrolysis reactor. [Industrial Applicability]

[0056] The N-vinylacetamide obtained by the production method of the present invention is useful not only for the production of N-vinylacetamide polymers used as flocculants, liquid absorbents, thickeners, etc., but also as a useful monomer in a wide range of industrial applications. [Explanation of symbols]

[0057] 10: Raw material supply device 11: Gate valve 12~14: Piping 20A, 20B: Evaporator 21: Collection Pot 22a, 22b: Extraction valve 30A, 30B: Raw material recovery device 31: Distribution control department 32: Cylinder part 33: Recovery Department 34: Discharge piping 35a~35e: Gate valve 36, 71: Pressure pump 36a: Gate valve 37: Nitrogen supply device 37a: Nitrogen valve 40A, 40B: Superheater 41: Extraction valve 42: Recovery Pot 50: Pyrolysis reactor 60:Cooler 70: Reaction liquid receiver 90: First pipe 95: Piping 100: Second piping 100a: Front section 100b: Rear section LI:Liquid level gauge M: Motor PI: Pressure gauge S1: Supply process S2: Evaporation process S3: Recovery process S4: Superheating process S5: Pyrolysis process

Claims

1. A supply step of supplying a raw material including N-(1-methoxyethyl)acetamide (MEA) to an evaporator; an evaporation step of evaporating the raw material in the evaporator to obtain a vaporized raw material; a superheating step of supplying the vaporized raw material to a superheater and superheating the vaporized raw material to a temperature 5° C. higher than the boiling point of the N-(1-methoxyethyl)acetamide at the internal pressure of the superheater (the boiling point of the N-(1-methoxyethyl)acetamide at the internal pressure of the superheater + 5° C.) to 200° C.; a pyrolysis step of supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing the raw material, The content of the N-(1-methoxyethyl)acetamide in the raw material is 80 to 100 mass %.

2. A supply step of supplying a raw material including N-(1-methoxyethyl)acetamide (MEA) to an evaporator; an evaporation step of evaporating the raw material in the evaporator to obtain a vaporized raw material; a superheating step of supplying the vaporized raw material to a superheater and superheating the vaporized raw material by applying a heat amount of 1.0 kJ / mol or more to the vaporized raw material; a pyrolysis step of supplying the superheated vaporized raw material to a pyrolysis reactor and pyrolyzing the raw material, The content of the N-(1-methoxyethyl)acetamide in the raw material is 80 to 100 mass %.

3. The method for producing N-vinylacetamide according to claim 1 or 2, wherein the evaporation step is carried out under reduced pressure.

4. The method for producing N-vinylacetamide according to any one of claims 1 to 3, wherein the thermal decomposition step is carried out under reduced pressure.

5. The method for producing N-vinylacetamide according to any one of claims 1 to 4, wherein the evaporator is a falling film evaporator.

6. The method for producing N-vinylacetamide according to any one of claims 1 to 4, wherein the evaporator is of a forced film type.

7. A downstream end of the evaporator and an upstream end of the superheater are connected via a first pipe, The method for producing N-vinylacetamide according to any one of claims 1 to 6, wherein the downstream end of the first pipe is at the highest position in the first pipe.

8. The downstream end of the superheater and the upstream end of the pyrolysis reactor are connected via a second pipe, The method for producing N-vinylacetamide according to any one of claims 1 to 7, wherein the upstream end of the second pipe is at the highest position in the second pipe.

9. The method further includes a recovery step between the evaporation step and the pyrolysis step, in which a liquid source that is not vaporized among the source supplied to the evaporator and a liquid source obtained by liquefying a part of the vaporized source are recovered, The method for producing N-vinylacetamide according to any one of claims 1 to 8, wherein the recovery step is a step of recovering the liquid raw material by a raw material recovery device provided between the evaporator and the pyrolysis reactor.

10. The method for producing N-vinylacetamide according to claim 9, wherein a downstream end of the evaporator and an upstream end of the raw material recovery device are joined together.

11. The method for producing N-vinylacetamide according to claim 9 or 10, wherein a downstream end of the raw material recovery device and an upstream end of the superheater are joined together.

12. The method for producing N-vinylacetamide according to any one of claims 9 to 11, wherein the vaporized raw material is supplied to the pyrolysis reactor after passing through the raw material recovery device.

13. The raw material recovery device includes: a cylindrical portion through which the vaporized raw material flows; a recovery section that causes a part or all of the flow of the vaporized raw material flowing inside the cylindrical section to collide with each other, and recovers a liquid raw material that is not vaporized from the raw material supplied to the evaporator and a liquid raw material that is a part of the vaporized raw material that has been liquefied; 13. The method for producing N-vinylacetamide according to claim 9, further comprising a discharge pipe for discharging the liquid raw material recovered by the recovery section to the outside of the cylindrical section.

14. an evaporator capable of evaporating a raw material to generate a vaporized raw material; a superheater connected to the evaporator and capable of superheating the vaporized raw material to a temperature 5° C. higher than the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure (the boiling point of N-(1-methoxyethyl)acetamide at the superheater internal pressure +5° C.) or higher and 200° C. or lower; a pyrolysis reactor connected to the superheater and capable of pyrolyzing the superheated vaporized raw material.

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