JPH0651668B2 - Method for producing N-vinylformamide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing N-vinylformamide, more specifically, N- (α-substituted-ethyl) formamide at a temperature of 200 to 600 ° C. The present invention relates to a method for producing N-vinylformamide by thermally decomposing in a phase.

[Conventional technology]

N-vinylformamide is important as a polymerizable monomer that gives a water-soluble polymer that is an excellent flocculant, and its production method is, for example, a method of thermally decomposing N- (α-alkoxyethyl) formamide in a gas phase. , N- (α
A method of thermally decomposing -cyanoethyl) formamide in a gas phase is known.

As the thermal decomposition method, N- (α-alkoxyethyl) formamide or N- (α-cyanoethyl) formamide is heated in an evaporator to be gasified, and the gas is converted into a gas in a void column or a tubular reactor filled with a packing material, ~ 600
A method is known in which thermal decomposition is carried out at a temperature of ° C and then the decomposition gas is cooled to obtain N-vinylformamide.
(JP-A-50-76015 and JP-A-61-143535)
9) [Problems to be solved by the invention] However, when the thermal decomposition reaction is carried out by this method, there is a tendency that a part of the components is converted to Harz from the time when the decomposed gas leaves the reactor until it is cooled and liquefied. is there.

In the cooling process, it is necessary to quench the gas from the reactor in order to prevent Harz formation. However, it is very difficult in industrial operation to quench the hot gas uniformly and continuously. For example, when the decomposed gas is introduced into the externally cooled cooling zone, a temperature difference occurs between the wall surface and the inside, uniform quenching is difficult, and the gradually cooled component is easily converted into Harz.

Further, a method is known in which an inert liquid such as hydrocarbon is used as a refrigerant and a decomposition gas is introduced into the refrigerant, but an extremely large amount of inert liquid is required for quenching, and the condensate is not Since it is obtained as a mixture with an active liquid, N-
A step of separating and collecting vinylformamide and an inert liquid is required.

[Means for Solving the Problems]

In view of the above situation, the inventors of the present invention have conducted extensive studies on the Harz prevention cooling step, and as a result, cool the condensed liquid of the decomposition gas and spray it in the cooling zone to achieve uniform quenching. In addition, the inventors have found that, by not introducing a gas into a special refrigerant, a separation and recovery step is unnecessary, and a cleaning effect by a spray can be added to prevent the generation of Harz, thereby completing the present invention. That is, the gist of the present invention is to evaporate N- (α-substituted-ethyl) formamide under reduced pressure and continuously supply it to a pyrolyzer controlled at a temperature of 200 to 600 ° C. for thermal decomposition in a gas phase. In the method for obtaining N-vinylformamide by carrying out, a gas containing N-vinylformamide obtained by a thermal decomposition reaction is supplied to a cooling zone where a condensate obtained by condensing the gas is sprayed and cooled. It exists in the manufacturing method of N-vinyl fouamide which is characterized by condensing.

Hereinafter, the present invention will be described in detail.

Examples of the α-substituent of the ethyl group of the starting material N- (α-substituted-ethyl) formamide of the present invention include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, and s- Examples thereof include lower alkoxy groups such as butoxy group and t-butoxy group, and cyano group. Note that N- (α-substituted-ethyl) formamide having a higher alkoxy group can be used, but the above compound is particularly preferable because evaporation is difficult.

When these raw materials are pyrolyzed, N-vinylformamide and a by-product produce an alcohol corresponding to the α-substituent of the raw material, or hydrogen cyanide when a cyano group is employed.

The above raw material is vaporized under reduced pressure to form a gas, and the pressure at that time is usually 3 to 600 Torr, and the heating temperature is usually 80 to 210 ° C. Then, the vaporized gas is supplied to the tubular reactor for thermal decomposition.

As a reactor for the thermal decomposition reaction, an empty column or a packed column reactor filled with packing is used. As the packing material for the packed column, beads such as glass or stainless steel having a particle diameter of 3 to 12 mm, or Raschig rings such as glass or stainless steel having a diameter of 5 to 15 mm are usually used. The residence time of the gas in the reaction tube is usually 0.1 to 4 seconds.

As a heating method of the tubular reactor, a heating element having a linear or planar electric heater built-in, or a method of heating from the outside of the reactor with, for example, steam, oil, and molten inorganic salt can be considered. .

The inner wall temperature of the tubular reactor is 200 to 600 ° C, preferably 300 to 500 ° C. The reaction pressure may be the same as the above-mentioned evaporation pressure. In order to carry out the thermal decomposition reaction of the present invention, the raw material N- (α-substituted-ethyl) is used in an evaporator under reduced pressure.
The formamide is heated to evaporate and the gas is introduced into the reactor to react and decompose.

The present invention is characterized in that the decomposed gas from the reactor is introduced into a cooling zone where the condensed liquid of the gas is sprayed and rapidly cooled, but at this time, cooling is performed so that substantially all of the reaction gas is condensed. Adjust the temperature in the zone. Here, the temperature of the entire cooling zone (the temperature of the aggregating liquid extracted from the lower part and collected) is set to 70 ° C. or lower, preferably 60 ° C. or lower. In order to perform the uniform quenching as described above in the cooling zone, it is necessary to spray the cooled condensate. The temperature of the condensate to be sprayed depends on the amount of condensate to be sprayed,
Although it cannot be said unequivocally depending on the amount of decomposed gas to be introduced, the composition (especially the type of alcohol), etc., it is usually 50 ° C.
The following is preferably 45 ° C. or less. This temperature may be low enough to quench the decomposed gas, and it is not preferable that the temperature is so low that industrial operation becomes difficult. Therefore,
Usually, a method is employed in which a part of the condensate extracted from the lower part of the cooling zone is cooled to 0 to 50 ° C, preferably 5 to 45 ° C and sprayed. For example, as shown in FIG. 1, the cracked gas discharged from a downward-flowing tubular reactor is immediately supplied to a cooling zone below it, where it is rapidly cooled to condense the cracked gas and the entire condensate is withdrawn from the lower part. A method of collecting is practically desirable.

The flow rate of the spray varies depending on the temperature of the spray liquid, but is usually 1 to 300 times the reaction gas, preferably 10 times.
Double to 150 times.

The spray may cover the entire area with one nozzle, or a plurality of nozzles may be used. At this time, if a part of the spray is directed toward the inner wall and the inner wall is washed, the adherence of Harz to the wall can be completely prevented.

A part of the condensed liquid is extracted and the rest is cooled to 50 ° C. or lower, preferably 5 to 45 ° C. and recycled into a spray. The amount taken out is usually the same as the amount thermally decomposed in the reactor.

N-vinylformamide is usually recovered from the reaction liquid withdrawn by distillation.

Examples will be shown below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

〔Example〕

 Example 1 An experiment was conducted using the apparatus shown in FIG.

In the wet-wall type evaporator 1, 4 kg / hr of N- (α-methoxyethyl) formamide (purity 90%) was evaporated at 178 ° C. under a reduced pressure of 120 Torr (boiling point 151 ° C.) to obtain a diameter of 50
7 mm diameter glass beads having a length of 1.5 mm were charged, and the reactor 2 whose outside was heated to 450 ° C. by an electric heater was introduced and pyrolyzed. In the reactor 2, linear heaters were spread on the outside at intervals of 2 cm, and the inner wall temperature was adjusted to 400 to 450 ° C.

The cooler was arranged so that the pyrolysis gas was introduced from the upper part of a tube having an inner diameter of 8 cm and a length of 50 cm, and a spray nozzle for spraying the liquid at an apex angle of 45 degrees was attached at a position 5 cm below the upper part. Pyrolysis condensate (N-vinylformamide 6
0%, methanol 27%, N- (α-methoxyethyl)
It was 3% formamide. ) As described below
It was cooled and supplied. The condensed liquid was collected in a receiver and pumped to a spray nozzle at a rate of 5.4 liters / minute. The condensate was extracted from the receiver to the outside of the system at 3.3 kg / hour. Liquid to be sprayed is 25 ° C, liquid after condensation is 31 ° C
Kept in.

In this way, continuous operation was performed for 72 hours, and when the inside of the cooler was observed, Hartz was not formed on the inner wall of the cooler. The yield of N-vinylformamide was 97%.

Comparative Example 1 The same evaporator and reactor as in Example 1 were used, and the following cooler was connected to the reactor, but the pipe from the reactor to the cooler was not externally heated. The cooler is a stainless steel cylinder with an internal length of 10 cm and a length of 50 cm that allows cold water of 5 ° C to flow outside, and a coil of 8 mm diameter tube wound 8 times with a diameter of 5 cm is placed inside the cooler. Was continuously run for 72 hours, the yield of N-vinylformamide was 97%, but 10 g of solid Harz was provided in the pipe from the reactor to the cooler, and solid Harz was formed on the upper part of the cooler coil. 10
g accumulated.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the reactor used in the examples of the present invention. In the figure, 1 to 7 are as follows. 1 ... Evaporator 2 ... Pyrolysis reactor 3 ... Gas cooler 4 ... Condensate receiver 5 ... Condensate cooler 6 ... Spray nozzle 7 ... Vacuum pump

Claims (2)

[Claims] 1. N- (α-Substituted-ethyl) formamide is evaporated under reduced pressure and continuously fed to a pyrolyzer controlled at a temperature of 200 to 600 ° C. for pyrolysis in a gas phase. In the method of obtaining N-vinylformamide by
A gas containing N-vinylformamide obtained by a thermal decomposition reaction is condensed by being supplied to a cooling zone where a condensate obtained by condensing the gas is sprayed and rapidly cooled. Manufacturing method. 2. The method according to claim 1, wherein the substituent of N- (α-substituted-ethyl) formamide is a lower alkoxy group or a cyano group.