JP3254724B2 - Method for producing N-vinylformamide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing N-vinylformamide, and more particularly, to N-(. Alpha.-substituted-).
The present invention relates to a method for producing N-vinylformamide by supplying a gas obtained by evaporating ethyl) formamide or ethylidenebisformamide under reduced pressure to a pyrolysis reactor in a gas phase and pyrolyzing at a temperature of 150 to 600 ° C. is there.

[0002]

2. Description of the Related Art N-vinylformamide is important as a polymerizable monomer which gives a water-soluble polymer used for applications such as flocculants. Examples of the production method include N- (α-alkoxyethyl) formamide and N- (α-alkoxyethyl) formamide.
A method of pyrolyzing-(α-cyanoethyl) formamide or ethylidenebisformamide in a gas phase is known.

[0003] As a specific thermal decomposition method, conventionally, the above-mentioned reaction raw material is heated to a gaseous state by an evaporator, and this is converted into a gaseous state by 30 minutes.
A method is known in which pyrolysis is carried out at a temperature of 0 to 600 ° C. in an empty tower or a tubular reactor filled with packing, and then the cracked gas is cooled to obtain N-vinylformamide (Japanese Patent Application Laid-Open No. Sho 50). -76015, JP-A-61-13435
9).

However, when the thermal decomposition reaction is carried out by this method, there is a tendency that tar-like and solid-state Hartz adhere to the wall or the packing of the tubular reactor, and the tubular reactor is clogged and the stable operation is carried out. It can be difficult. The present inventors have proposed to use a pyrolysis reactor having an empty tower type tubular reactor in the first stage of the reactor and a packed tubular reactor in the second stage in order to prevent the adhesion of Harz (Japanese Patent Laid-Open Publication No. HEI 9 (1996) -197686). 3-181451).

[0005]

However, in the reactor, although a sufficient effect can be obtained in a small-sized test apparatus in which the temperature of the reaction raw material can be rapidly raised in a short time, sufficient effects can be obtained. In a large-sized apparatus, even if the above-described conditions of the small-sized test apparatus are applied as they are, it is difficult to rapidly raise the temperature of the reaction raw material, and thus the effect of preventing Harz is not sufficient. Therefore, a method of increasing the residence time of the reaction raw material gas in the reactor, a method of increasing the heating of the reactor, and the like can be considered.
The improvement by these methods has limitations and is not advantageous in terms of productivity and energy cost.

[0006]

Means for Solving the Problems In view of the above-mentioned circumstances, the present inventors have conducted intensive studies on a method for suppressing Harz adhering in a tubular reactor. The present inventors have found that the use of the film under temperature conditions can completely prevent the adhesion of Harz, and have reached the present invention.

That is, the gist of the present invention is to provide an N- (α-substituted-
Ethyl) formamide or ethylidenebisformamide is evaporated under reduced pressure and pyrolyzed in the gas phase at a temperature of 150 to 600 ° C. to produce N-vinylformamide. In the latter stage, a pyrolysis reactor composed of a packed tubular reactor was used, and the gas phase temperature at the outlet of the empty tower tubular reactor was set to 200 to 400 ° C., and the inside of the packed tubular reactor was cooled. N maintained at 200 to 600 ° C.
The method for the production of vinylformamide.

Hereinafter, the present invention will be described in detail. As the α-substituent of the ethyl group of N- (α-substituted-ethyl) formamide of the starting material of the present invention, for example, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-
Examples thereof include a lower alkoxy group such as a butoxy group, an s-butoxy group, and a t-butoxy group, and a cyano group. In addition,
N- (α-substituted-ethyl) having a higher alkoxy group
Formamide can also be used, but the above compounds are particularly preferred because they are difficult to evaporate.

When these raw materials are thermally decomposed, as an N-vinylformamide and a by-product, when an alkoxy group is used as the α-substituent of the raw material, a corresponding alcohol or hydrogen cyanide is formed when a cyano group is used. I do. In addition, when pyrolysis is performed using ethylidenebisformamide as a raw material, formamide is generated as a by-product.

The above-mentioned raw material is vaporized under reduced pressure to obtain a gaseous state. The pressure at that time is usually 3 to 600 Torr, and the heating temperature is usually 80 to 210 ° C.
Then, the evaporated gas is immediately supplied to the tubular reactor of the present invention as an ascending flow to perform thermal decomposition. In the present invention, as the tubular reactor for the thermal decomposition reaction, it is an essential requirement that the first stage is a vertical hollow column tubular reactor and the second stage is a packed tubular reactor. Here, the former vertical type means a tubular shape that is substantially perpendicular (90 degrees) to the horizontal plane,
Practically includes tubes that are slightly inclined. The allowable angle varies depending on the pipe diameter and the pipe length, but is usually at least 45 degrees or more, preferably 60 degrees or more with respect to the horizontal plane.

On the other hand, the latter stage is not particularly limited in the installation direction, and may be a vertical type or a horizontal type. The ratio of the former stage and the latter stage is
Usually it is 1: 9-9: 1 by volume. The filler used for the filling portion is usually glass or stainless steel beads having a particle size of 3 to 12 mm or a diameter of 5 to 15 mm.
Or a Raschig ring of stainless steel or the like. In addition, the filling part holds the partition filler by a wire mesh or the like at an end in accordance with a conventional method.

The tubular reactor of the present invention may be a single tube type, a multi-tube type or a combination thereof, and the diameter of the tube is not particularly limited. However, since the thermal decomposition reaction is an endothermic reaction, particularly in the former stage, It is necessary to select a size that can sufficiently heat and maintain the gas mixture at a desired temperature. In addition, a so-called pipe reactor using ordinary pipes without any special equipment may be used as the reactor. Further, for example, a pipe reactor can be used as the empty tower reactor at the first stage, and a multi-tube reactor can be used as the subsequent packed tubular reactor at the second stage.

[0013] In many cases, such a pyrolysis reactor is composed, as a single reactor, by combining and integrating the former and latter stages (composite tubular reactor), but is not necessarily limited to this. . As described above, it is also possible to design the former stage to be a vertical single tube hollow tower type and the latter stage to be a multi-tube filling type so that the outer diameter of the latter stage is different from that of the former stage. In addition, it is also possible to independently design two vertical empty tower reactors and a packed reactor and use them by connecting them. In this case, it is preferable to maintain the temperature of the connecting portion of the two reactors so as not to be lower than the temperature of the superficial reactor so that Hartz is not generated at the connecting portion.

The pyrolysis temperature in the present invention is 150 to 60.
Since it is 0 ° C., it is necessary to heat the reactor from the outside and keep the inside at the pyrolysis temperature. As a heating method of the tubular reactor of the present invention, a method of heating from the outside of the reactor by a heating element having a linear or planar electric heater therein, or, for example, steam, oil, and a molten inorganic salt is usually used. Conceivable. The reaction pressure may be the same as the above-mentioned evaporation pressure. The residence time of the gas in the reaction tube is usually 0.1 to 5 seconds.

In the present invention, in the thermal decomposition, a part of the reaction usually proceeds in the empty column in the former stage, and the rest is completed in the packed portion in the latter stage. As the temperature conditions for the thermal decomposition, the empty column in the former stage is usually heated to 200 to 450 ° C, and the gas phase temperature at the outlet of the empty column is 200 to 400 ° C, preferably 240 to 360 ° C.
Set to ° C.

It is relatively difficult to increase the temperature of the gas phase above 400 ° C. in a large-sized reactor, and it is not preferable in view of energy costs. Further, when the gas phase temperature is 20
Below 0 ° C, a small amount of Harz adheres to the tube wall,
It is not preferable because the yield of N-vinylformamide also decreases. Further, the temperature of the filling section in the latter stage is 200 to 600 ° C., preferably, higher than the gas phase temperature at the outlet of the empty column in the former stage, and in the range of 350 to 500 ° C.
This is because it is advantageous to increase the temperature in order to complete the thermal decomposition of unreacted substances in the former stage. Further, if the temperature is increased to more than 600 ° C., a side reaction or N-vinylformamide generated To cause a decrease in the yield due to decomposition of the compound.

The above-mentioned temperature of the tubular reactor refers to the temperature of the inner wall of the reaction tube, and the temperature of the gas phase at the outlet of the empty column in the preceding stage refers to the gas measured at the center of the outlet of the tube. Refers to the temperature of the phase. In order to carry out the thermal decomposition reaction of the present invention, the raw material N- (α-substituted-ethyl) formamide or ethylidenebisformamide is heated and evaporated under reduced pressure in an evaporator, and the gas is immediately transferred to the reactor. The mixture containing N-vinylformamide, the above-mentioned by-products and some starting materials can be condensed and recovered by introducing, performing a thermal decomposition reaction, and then cooling the decomposed gas.
The source gas evaporated by the evaporator continues to be 150
It is desirable to immediately introduce as a rising flow into a vertical empty column constituting the former step of the thermal decomposition reactor maintained at a temperature of up to 600 ° C. In addition, if necessary, N-vinylformamide can be isolated from the condensed and recovered mixture by distillation.

The reason why the present invention can prevent the adhesion of Harz to the inner wall of the reactor is unknown, but it is considered as follows. From a part of N-vinylformamide generated by thermal decomposition, if the temperature is lower than 200 ° C., a high-boiling by-product due to a dimerization reaction or the like is generated. It is known that N-vinylformamide is produced.

On the other hand, since the thermal decomposition reaction is an endothermic reaction,
If the heating is not sufficient, the endothermic wall temperature of the reactor is lowered, and it is easy to cause Harz formation. Therefore, if the reactor at the former stage is left empty, a rapid thermal decomposition reaction is suppressed and the wall temperature is easily maintained to some extent, but a small amount of Harz is still generated. Then, in the horizontal horizontal empty tower, it is considered that high boiling substances generated to a small extent are deposited on the wall surface and turned into Hartz. On the other hand, in a vertical vertical empty tower, even if high boilers are generated, they are difficult to adhere to the vertical wall surface, and most of them will fall to the lower distillation part and be removed outside the system. Presumed. Also, even if a high-boiling substance adheres to the wall surface, it is considered that since it is a fine droplet, it can be easily re-evaporated and re-decomposed, and does not form a Hartz. In addition, after the reaction has progressed to some extent, it enters the subsequent packed-type reactor, so that the thermal decomposition reaction can be completed here, and the temperature of the inner wall and the packed material of the packed-type reactor does not drop so much due to endotherm. It is estimated to be.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

[0021]

【Example】

Example 1 An experiment was performed with the apparatus shown in FIG. N- in wet-wall evaporator 1
(Α-methoxyethyl) formamide 2 kg / hr
This gas was evaporated under a reduced pressure of 20 Torr at a temperature of 178 ° C., and this gas was immediately subjected to an empty column reactor (2a) having a diameter of 40 mm and a length of 1 m, followed by a stainless steel Raschig ring having a diameter of 6 mm and a length of 40 mm. A 1 m-filled reactor section (2b) was introduced into the reactors 2a and 2b, which were heated to the temperatures shown in Table 1 in the gaseous phase on the outside, and introduced into the reactors 2a and 2b in order. Was cooled to 15 ° C. in a condenser, and the reaction gas was condensed to obtain a mixture containing N-vinylformamide. Such a thermal decomposition reaction was continuously performed for 100 hours. After the reaction, the device was disassembled and the amount of Harz adhered to the inside of the tubular reactor was measured. Table 1 shows the results of the thermal decomposition temperature conditions, the yield of N-vinylformamide, and the amount of Harz in the above reaction.

Examples 2 and 3 and Comparative Example 1 Table 1 shows the results of continuous operation in the same apparatus as in Example 1 except that the heating temperature of the air column was changed and the apparatus was operated in the same manner as in Example 1. . Examples 4 to 6 and Comparative Example 2 The test was performed with the apparatus shown in FIG. The apparatus in FIG. 2 has the same size as the apparatus in FIG. 1 in the empty tower and the reactor in the filling section, but the reactor in the filling section is arranged in a horizontal horizontal direction. The reaction raw materials were evaporated in the same manner as in Example 1, and the results of continuous reaction under various conditions are shown in Table 1.

Comparative Examples 3 to 6 The tests were carried out with the apparatus shown in FIG. The apparatus in FIG. 3 has the same size as the apparatus in FIG. 1 in the empty tower and the reactor in the filling section, but both reactors are arranged in a horizontal horizontal direction. The reaction raw materials were evaporated in the same manner as in Example 1, and the results of continuous reaction under various conditions are shown in Table 1.

[0024]

[Table 1]

[0025]

Industrial Applicability According to the present invention, N-vinylformamide can be stably obtained in high yield without adhesion of Harz in the thermal decomposition reactor, and is suitable for industrial mass production. is there.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an experimental apparatus used in Examples 1 to 3 and Comparative Example 1.

FIG. 2 is an explanatory view showing an experimental device used in Examples 4 to 6 and Comparative Example 2.

FIG. 3 is an explanatory view showing an experimental device used in Comparative Examples 3 to 6.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Evaporator 2 Combined tubular reactor 2a Empty tower reactor part 2b Packing reactor part 3 Cooler 4 Vacuum pump

Continuation of the front page (56) References JP-A-3-181451 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 231/12 C07C 233/03

Claims (1)

(57) [Claims] 1. A process for producing N-vinylformamide by evaporating N- (α-substituted-ethyl) formamide or ethylidenebisformamide under reduced pressure and pyrolyzing in the gas phase at a temperature of 150 to 600 ° C. The first stage is a vertical hollow tower type tubular reactor, the second stage is a pyrolysis reactor composed of a packed tubular reactor, and the gas phase temperature at the outlet of the hollow tower type tubular reactor is 20.
0 to 400 ° C., and the inside of the packed tubular reactor is 200 to 6
A method for producing N-vinylformamide, which is maintained at 00 ° C.