JP5696481B2 - Method for producing N-vinylformamide - Google Patents

Description

  The present invention relates to a method for producing N-vinylformamide, and more specifically, in a method for producing N-vinylformamide in which N- (α-substituted-ethyl) formamide raw material is evaporated and thermally decomposed under reduced pressure. The present invention relates to a method for producing N-vinylformamide that solves the problems caused by the problem.

  In the method for producing N-vinylformamide, in which the N- (α-substituted-ethyl) formamide raw material is evaporated and thermally decomposed under reduced pressure, tar-like and solid harz are generated. And in the long-term continuous operation, the blockage problem by Harz of the connection pipe of an evaporator and a pyrolyzer is caused, and stable operation becomes difficult. It is also known that the quality of N-vinylformamide gradually deteriorates when Harz is gradually accumulated in the pipe. Deterioration of quality here means deterioration of storage stability of monomer and decrease of polymerization activity, that is, delay of polymerization start, decrease of molecular weight of polymerization pair obtained by polymerization, increase of residual monomer, increase of insoluble matter, etc. Point to.

  As a proposal to solve the clogging problem caused by Harz, a method of using a pyrolysis reactor in which the front stage of the reactor is an empty tubular reactor and the latter stage is composed of a packed tubular reactor has been proposed (patent) Reference 1). However, such a method is not necessarily sufficient although it has a certain effect.

JP-A-3-181451

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an improved method for producing N-vinylformamide so as to more effectively solve the problem of blocking due to Harz.

That is, the gist of the present invention is that, in a method for producing N-vinylformamide in which N- (α-substituted-ethyl) formamide raw material is evaporated and thermally decomposed under reduced pressure, a falling film evaporator and pyrolysis are used as production devices. Both are arranged with a height difference between the flow-through thin film evaporator and the pyrolyzer so that the lower outlet at the side of the flow-through thin film evaporator is lower than the inlet of the pyrolyzer. In the manufacturing method of N-vinylformamide, the apparatus to which the Harz storage container opened to the connection piping is connected to the inclined portion is used.

  According to the present invention, the problem of blockage caused by Harz is not caused even during long-term continuous operation.

Explanatory drawing of an example of the manufacturing apparatus used by this invention

  Hereinafter, the present invention will be described in detail. In the present invention, N- (α-substituted-ethyl) formamide is used as a starting material. Here, examples of the α-substituent include a lower alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an s-butoxy group, and a t-butoxy group, or a cyano group. Note that N- (α-substituted-ethyl) formamide having a higher alkoxy group can also be used as a raw material, but the above compounds are particularly preferable because evaporation is difficult.

  When the raw materials as described above are pyrolyzed, by-products are produced together with N-vinylformamide. A by-product is hydrogen cyanide when an alkoxy group is employed as the α-substituent of the raw material, and a corresponding alcohol or cyano group is employed. When ethylidene bisformamide is used as a raw material, formamide is produced as a by-product.

  In the present invention, as an apparatus for producing N-vinylformamide, an evaporator and a pyrolyzer are provided, both of which are connected by a connecting pipe having an upwardly inclined part at least partially, and a connecting pipe is connected to the inclined part of the connecting pipe Use a device to which a Harz container opened to is connected.

  Although it does not restrict | limit especially as an evaporator, From a viewpoint which can shorten the residence time of a raw material, a falling type thin film evaporator and a rotary thin film evaporator are preferable. The evaporator (1) in the illustrated example is a falling film evaporator. In addition, it is better to attach a mist catcher and a collision plate to the evaporator because the mist scattering also causes Harz. On the other hand, the pyrolyzer generally has a tubular structure and may be an empty tower or a packed tower. In order to increase the heat transfer efficiency, a multi-tube structure having a heat medium multi-tube attached to the outer peripheral portion is preferable.

  The evaporator (1) and the pyrolyzer (2) are connected by a connecting pipe (3) having an upward inclined portion at least in part. As shown in the figure, by arranging the evaporator (1) and the pyrolyzer (2) with a height difference so that the outlet of the evaporator (1) is lower than the inlet of the pyrolyzer (2), An inclined part will be formed in the connection piping which connects both. In such an arrangement state, it is possible to easily introduce the raw material gas from the evaporator (1) to the thermal cracker (2) without using special equipment. Further, in the illustrated example, the evaporator (1) and the pyrolyzer (2) are arranged separately with a certain interval, but they may be arranged in contact with each other without any interval.

  The connecting pipe (3) shown in the figure has an inclined portion connected to the outlet of the evaporator (1), but may include a short straight pipe connected to the bottom of the evaporator (1). The illustrated connection pipe (3) includes a short straight pipe connected to the inlet cone of the pyrolyzer (2). However, the straight pipe may be eliminated to form an inclined portion. In this case, the entire connection pipe (3) is an inclined pipe. Further, when the evaporator (1) and the thermal decomposer (2) are arranged in contact with each other, a straight pipe portion connected to each bottom of the evaporator (1) and the thermal decomposer (2) is provided. May be. In addition, when using the rotary thin film evaporator arranged horizontally, if a connection with a short straight pipe connected to the outlet is used, the rotary thin film evaporator and the pyrolyzer are used. It is easy to provide a height difference between them. In any case, it is preferable to use a connection pipe (3) in which a horizontal portion does not substantially exist.

  The inclination angle (α) of the inclined portion in the connection pipe (3) is usually 10 to 60 °, preferably 20 to 40 °. Moreover, it is a ratio of the inclination part in the whole length of connection piping (3), and is normally 10 to 100%.

  The Harz storage container (4) opens to the connecting pipe (3) and is connected to the inclined portion of the connecting pipe. Although the illustrated Harz storage container (4) has a bottom-open cylindrical structure, it may have a spherical structure. Further, depending on the size, it is not always necessary to have an open bottom. In this case, the Harz storage container (4) is removed from the connecting pipe (3), for example, at regular inspections, and the stored Harz is collected.

  Although illustration was abbreviate | omitted for the above-mentioned manufacturing apparatus, the evaporator (1), the pyrolyzer (2), the connection piping (3), and the Harz storage container (4) are provided with the heating means. Usually, the heating means is achieved by adopting a jacket structure and circulating a heat medium.

  The raw material introduced into the evaporator (1) is heated and evaporated, and is introduced into the thermal cracker (2) as a raw material gas through the connection pipe (3). The operating temperature of the evaporator (1) is usually 80-210 ° C. The operating temperature of the pyrolyzer (2) is usually 300 ° C. to 600 ° C., and the residence time is usually 0.01 to 10 seconds. The operating pressures of the evaporator (1) to the pyrolyzer (2) (pressure for evaporating the raw material and pressure for pyrolyzing) are usually 3 to 600 Torr. Such a decompressed state is achieved by a decompression facility (not shown) connected to the top of the pyrolyzer (2). The temperatures of the connecting pipe (3) and the Harz storage container (4) are appropriately selected from a temperature range in which the raw material gas generated in the evaporator (1) is not condensed.

  In the present invention, the upward inclined portion of the connecting pipe (3) flows down and is collected in the Harz storage container (4). Therefore, the problem of blockage due to Harz is not caused even during long-term continuous operation.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the meaning is exceeded.

<Polymerization test of N-vinylformamide>
The N-vinylformamide polymerization activity test was performed using N-vinylformamide obtained by distillation purification of the obtained thermal decomposition product. The polymerization was reverse phase suspension polymerization using cyclohexane as a continuous phase and N-vinylformamide as a dispersion phase, and was performed using polyoxyethylene alkyl ether as a dispersion stabilizer. As the initiator, water-soluble azobisamidinopropane dihydrochloride was used (amount used: 4000 ppm with respect to monomer), and the conditions were an aqueous monomer concentration of 60% and an initiation temperature of 55 ° C. The monomer aqueous solution was dropped over 2 hours, and then the temperature was raised to 60 ° C. and aged for 1 hour.

Example 1:
The manufacturing apparatus shown in FIG. 1 was used.

  The evaporator (1) has a structure in which a large number of tubes communicating with a decompression system are erected inside the shell, and a liquid is allowed to flow down on the inner walls of these tubes. The raw material liquid flowing down the inner wall is evaporated by heating under reduced pressure.

  The pyrolyzer (2) has a structure in which a number of tubes communicating with the decompression system are erected inside the shell, and a raw material gas is introduced inside these tubes, and superheated nitrogen at 350 ° C. is introduced into the lower shell side. Then, superheated nitrogen at 430 ° C. is introduced into the upper shell side, and the raw material gas introduced into the tube is pyrolyzed under reduced pressure.

  The connecting pipe (3) has an inner diameter of 200 mm, an inclined part (length: 1800 mm, inclined angle α: 30 °) connected to the outlet of the evaporator (1), and a cone at the inlet of the pyrolyzer (2). The Harz storage container (4) has an open bottom cylindrical structure with an inner diameter of 200 mm and a length of 673 mm, and is connected to the front of the flange on the evaporator side. Connected to the low end of the. And heating nitrogen is introduce | transduced into each jacket part of a connection piping (3) and a Harz storage container (4), and the tube wall temperature at the time of operation is maintained at 230 degreeC.

  The pressure reduction equipment connected to the top of the pyrolyzer (2) keeps the whole at a reduced pressure so as to reach 80 Torr at the outlet of the pyrolyzer (2), and the raw material continuously supplied from the top of the evaporator (1) N- (α-substituted-ethyl) formamide is evaporated at a rate of 295 kg / hr, introduced into the lower end of the thermal cracker (2) through the connecting pipe (3), and the outlet gas temperature is increased in the thermal cracker (2). It was thermally decomposed by heating to 420 ° C.

  Although continuous operation was performed for 24 days, no problems occurred. The operation was stopped, and the amount of Harz collected in the Harz container (4) was measured. As a result, it was 4.8 kg (2 kg in the amount per 10 days). Moreover, as a result of conducting a polymerization test on the obtained N-vinylformamide, the polymerization performance was stable.

Comparative Example 1:
In Example 1, N-vinylformamide was produced by performing continuous operation in the same manner as in Example 1 except that the production apparatus in which the Harz storage container (4) was removed was used. On the 10th day after the start of operation, there was a blockage in the connecting pipe, and the operation was stopped. An increase in color was observed in the raw material recovered from the evaporator (1) and the obtained N-vinylformamide. Further, as a result of conducting a polymerization test on the obtained N-vinylformamide, a delay in the polymerization rate was observed.

1: Evaporator 2: Pyrolyzer 3: Connection piping 4: Harz storage container

Claims (3)

In a method for producing N-vinylformamide in which a raw material of N- (α-substituted-ethyl) formamide is evaporated and thermally decomposed under reduced pressure, the production apparatus includes a falling film evaporator and a pyrolyzer, both of which flow down The flow-down thin film evaporator and the pyrolyzer are arranged with a height difference so that the lower outlet of the side of the thin film evaporator is lower than the inlet of the pyrolyzer, and the connection pipe is opened at the inclined part of the connection pipe A method for producing N-vinylformamide, characterized in that a device to which the Harz storage container is connected is used. The method for producing N-vinylformamide according to claim 1, wherein the inclination angle α of the inclined portion in the connecting pipe is 10 to 60 °. The method for producing N-vinylformamide according to claim 1 or 2, wherein the proportion of the inclined portion in the entire length of the connecting pipe is 10 to 100%.

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