JP2017190287A - Method for producing N-vinylformamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing N-vinylformamide that can achieve high yields in a pressure condition of normal pressure or higher without decompression operation.SOLUTION: A method for producing N-vinylformamide includes the pyrolysis of an organic compound to be conducted at 80.0-300 kPa.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing N-vinylformamide. Specifically, N- (α-substituted-ethyl) formamide or ethylidene bisformamide is subjected to gas phase pyrolysis under normal pressure or higher conditions without performing a decompression operation. The present invention relates to a method for producing N-vinylformamide.

  N-vinylformamide is an important compound as a polymerizable monomer that gives a water-soluble polymer used in applications such as a flocculant. As its production method, for example, a method of thermally decomposing N- (α-substituted-ethyl) formamide or ethylidenebisformamide in a gas phase is known. As a general thermal decomposition method, N- (α-substituted-ethyl) formamide or ethylidene bisformamide is heated as a reaction raw material in an evaporator and is made into a gaseous state, which is empty at a temperature of 300 to 600 ° C., or Thermal decomposition is carried out in a tubular reactor filled with a packing, and then the cracked gas is cooled to obtain N-vinylformamide (Patent Documents 1 and 2) or the former stage is an empty tubular reactor, and the latter stage is A method of stably obtaining N-vinylformamide using a composite reactor that is a packed tubular reactor (Patent Document 3) is known. However, when N-vinylformamide is obtained by pyrolysis by these methods, the formation of harz, which is a tar-like and solid soil component, is prevented, and in order to obtain a high product yield, the pyrolysis reaction Therefore, it is necessary to carry out the process under reduced pressure, which is not advantageous in terms of energy cost and apparatus. For this reason, further improvement is requested | required about the manufacturing method of N-vinylformamide which does not use an industrially evacuated decompression device.

Japanese Patent Laid-Open No. 50-076015 JP 61-134359 A JP-A-5-301851

  This invention makes it a subject to provide the manufacturing method of N-vinylformamide which can achieve a high yield on the pressure conditions more than a normal pressure, without performing pressure reduction operation.

  In view of the above problems, as a result of intensive studies on a thermal decomposition method that does not require a reduced pressure condition while achieving a high reaction yield, by applying specific reaction conditions, a high pressure can be obtained even under normal pressure without performing a reduced pressure operation. The inventors have found that N-vinylformamide can be produced in a reaction yield, and have reached the present invention.

  That is, the present invention relates to a method for producing N-vinylformamide in which an organic compound is thermally decomposed at 80.0 to 300 kPa.

  The present invention also relates to the above production method, wherein the organic compound is at least one of N- (α-substituted-ethyl) formamide or ethylidenebisformamide.

  The present invention also relates to the above production method wherein the residence time of the reaction gas in the reaction tube is 0.1 to 2.0 seconds.

  The present invention also relates to the above-described production method in which the thermal decomposition is performed without depressurization.

Furthermore, this invention relates to the said manufacturing method whose internal diameter of the said reaction tube is 0.25-1.00 mm.

  According to the method of the present invention, it is possible to provide a method for producing N-vinylformamide capable of achieving a high yield under pressure conditions of normal pressure or higher without performing a depressurization operation.

  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, for example, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, s Examples thereof include alkoxy groups such as -butoxy group and t-butoxy group, and cyano groups. N- (α-substituted-ethyl) formamide having a higher alkoxy group can also be used. Among the above compounds, N- (α-methoxyethyl) formamide, in which the α-substituent is a methoxy group, is particularly preferable because of its low boiling point and easy evaporation.

  When these raw materials are pyrolyzed, N-vinylformamide and by-products are produced. When an alkoxy group is employed as the α-substituent of the raw material, the corresponding alcohol is generated as a byproduct. When a cyano group is employed, highly toxic hydrogen cyanide is produced as a byproduct. When pyrolysis is performed using ethylidenebisformamide as a raw material, formamide is produced as a by-product.

  At the time of the pyrolysis, first, the raw material N- (α-substituted-ethyl) formamide is vaporized under reduced pressure, and the pressure at that time is usually a pressure around normal pressure, and the heating temperature is Usually, it is about 80-210 degreeC.

  The lower limit of the reaction pressure for the thermal decomposition is preferably 80 kPa or more, more preferably 90 kPa or more. Moreover, as an upper limit of the reaction pressure of the said thermal decomposition, 300 kPa or less is preferable and 150 kPa or less is more preferable. If it is in the said range, since it is near atmospheric pressure, it can react efficiently also in terms of energy cost and apparatus.

  The lower limit of the thermal decomposition reaction temperature is preferably 300 ° C. or higher, and more preferably 380 ° C. or higher. Moreover, as an upper limit of the reaction temperature of the said thermal decomposition, 500 degrees C or less is preferable and 450 degrees C or less is more preferable. If it is in the said range, it can react efficiently also in terms of energy cost and apparatus. Setting the reaction temperature for the thermal decomposition to 500 ° C. or higher is not preferable in terms of energy cost. Further, if it is less than 300 ° C., Harz is generated and the yield is reduced, which is not preferable. It is relatively difficult to make the reaction temperature higher than 500 ° C. in a large reaction apparatus, and it is not preferable in terms of energy cost. On the other hand, when the reaction temperature is less than 200 ° C., a small amount of Harz adheres to the tube wall, causing clogging and reducing the yield of N-vinylformamide.

  Since the reaction temperature of the thermal decomposition in the present invention is approximately 300 to 500 ° C., it is necessary to heat the reactor from the outside and maintain the temperature of the reaction section. Although there is no restriction | limiting in a heating method, Usually, the heat generating body with which the electric heater was incorporated, oil, or heating steam can be used. Since the thermal decomposition reaction is an endothermic reaction, the reaction section needs to rapidly supply heat from the outside. Therefore, it is preferable that the representative diameter of the reaction part is small, and it is preferable that the tube diameter is approximately approximately 0.25 to 1.0 mm.

  In order to evaporate the raw material N- (α-methoxyethyl) formamide at normal pressure, a temperature of 200 ° C. or higher is necessary. However, in the present invention, a minute reaction is performed in order to quickly raise the temperature from vaporization of the raw material to a predetermined thermal decomposition temperature. Rapid heating can also be carried out using a so-called microreactor. In the present invention, as a condition for performing good thermal decomposition at normal pressure or higher, the gas linear velocity in the reaction tube is preferably 0.1 to 10 m / sec in calculation. Here, the calculated gas linear velocity means a value obtained by dividing a gas flow rate (capacity) when an ideal gas is used by a reaction tube cross-sectional area.

  The residence time of the gas in the reactor is usually preferably 0.1 to 2.0 seconds. Since the inside of the reactor is accompanied by a pressure loss due to the gas linear velocity, the pressurized state starts from around normal pressure, but the pressure range at that time is preferably 80 to 300 kPa. If it is in the said range, it can react more efficiently in terms of energy cost and apparatus, so that it is near normal pressure.

  The tubular reactor of the present invention may be a single tube type, a multiple tube type, or a combination thereof, and the tube diameter is not particularly limited. However, since the pyrolysis reaction is an endothermic reaction, in particular, the gas mixture is heated to a desired temperature. It is necessary to select a size that can be heated and held sufficiently. Moreover, as a reactor, a pipe reactor using ordinary piping as it is can be used without using a special apparatus.

  Such a pyrolysis reactor can also be designed so that the front stage is a vertical single tube empty type and the rear stage is a multi-tube packed type, and the outer diameter of the rear stage is different from that of the previous stage. Moreover, it is also possible to design a vertical type empty reactor and a packed reactor independently and connect them to each other. In this case, it is preferable to keep the temperature of the two reactors so as not to drop below the temperature of the empty reactor so that Harz is not generated at the connecting portion of the two reactors.

  Since the reaction temperature of thermal decomposition in the present invention is about 300 to 500 ° C., it is necessary to heat the reactor from the outside and maintain the inside at the reaction temperature of thermal decomposition. The heating method of the tubular reactor of the present invention is usually a heating element incorporating a linear or planar electric heater, or a method of heating from the outside of the reactor with, for example, steam, oil, molten inorganic salt, or the like. It can also be used. The reaction pressure may be the same as the evaporation pressure when evaporating the raw material N- (α-methoxyethyl) formamide, and is preferably 80 to 300 kPa. The residence time of the gas in the reaction tube is usually about 0.1 to 2 seconds.

  The temperature of the tubular reactor means the temperature of the inner wall of the reaction tube. In order to carry out the thermal decomposition reaction of the present invention, the raw material N- (α-substituted-ethyl) formamide or ethylidenebisformamide is evaporated by heating in the evaporator from near atmospheric pressure to slightly positive pressure, and the gas is immediately removed. The mixture containing N-vinylformamide, the by-product and some starting materials can be condensed and recovered by introducing into the reactor, performing a thermal decomposition reaction, and then cooling the decomposed gas.

In addition, N-vinylformamide can be isolated by distilling and purifying the condensed and recovered mixture as necessary.
The reason why Harz adhesion to the inner wall of the reactor can be prevented by the present invention is not clear in detail, but is considered as follows. From a part of N-vinylformamide produced by thermal decomposition, if it is less than 200 ° C., a by-product having a high boiling point is generated due to a dimerization reaction or the like. Thus, it can be considered that N-vinylformamide is formed.

  Since the thermal decomposition reaction is an endothermic reaction, if the heating is not sufficient, the wall temperature of the reactor due to the endotherm is lowered and hartzing is likely to occur. Therefore, if the reactor is kept empty, 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. In the empty column reactor, it is thought that a small amount of by-product with a high boiling point is deposited on the wall and becomes harz. In the empty column reactor, when a high-boiling by-product is generated, it hardly adheres to the vertical wall surface, and most of it falls to the lower distiller and is removed from the system. When high boiling matter adheres to the vertical wall surface, it becomes a microdroplet, and it is considered that re-evaporation and re-decomposition occur and it does not become Harz.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

<Evaluation method of thermal decomposition reaction>
The condensate of the reaction gas after pyrolysis was diluted 10,000 times with pure water and analyzed by HPLC (SHIMADZU SPD-20A). Analysis conditions are wavelength 220 nm, oven temperature 40 ° C., separation column is ODP2HP-4E (SHODEX, φ4.6 mm × 250 mm), flow rate 1.0 mL / min, eluent (sodium phosphate dihydrogen dihydrate 0.78 wt% buffer) Liquid). Reaction conversion and selectivity were determined by measuring the concentration of N-vinylformamide and N- (α-alkoxyl-ethyl) formamide from the analytical value of HPLC by an absolute calibration curve method.

<Reaction raw materials>
94.0 to 96.0 wt% N- (α-methoxyethyl) formamide (manufactured by Mitsubishi Rayon Co., Ltd.) was used as a reaction raw material described in Examples and Comparative Examples. The reaction raw material contained 0.1 to 2.0 wt% of methanol, formamide, acetaldehyde and the like as impurities.

<Thermal decomposition equipment and thermal decomposition method>
In Examples and Comparative Examples, thermal decomposition reaction was performed using the apparatus shown in FIG. As the thermal decomposition apparatus, an apparatus including a liquid feeding syringe pump 1 (Harvard PHD4400), a SUS tube 5, an electrically heated SUS plate heater 3, and cooling tubes 2 and 4 was used. The electrically heated SUS plate heater is composed of two SUS plates and has a concave digging on one surface. In this recess, a SUS tube having a maximum outer diameter of 1/16 inch and a length of 1 m was used. What used the cooling pipe in the both ends of the plate heater was used. The SUS tube was connected to the liquid feeding syringe pump, and then the SUS tube was fitted into the SUS plate heater recess. The SUS tubes at both ends of the plate heater pass through the inside of the cooling pipe. In the cooling pipe, a 10 ° C. refrigerant circulated in the cooling pipe (2a, 2b, 4a, 4b), and the temperature of the plate heater inlet and outlet of the SUS tube was kept constant at the refrigerant temperature. An outline of this apparatus is shown in FIG.

  The thermal decomposition reaction was performed inside a SUS tube heated by controlling the surface temperature of the plate heater in the temperature range of 300 ° C. to 500 ° C. with an accuracy of ± 1.0 ° C. For the reaction time of the gas, the reaction was performed while controlling the flow rate in the tube by operating the extrusion flow rate of the liquid delivery syringe pump. The flow rate in the tube can also be controlled by changing the length and inner diameter of the SUS tube inside the plate. The reaction gas is rapidly cooled at the outlet cooling section, and the thermal decomposition reaction stops. Since the reaction gas is accompanied by the pressure loss of the SUS tube, the reaction pressure is in a pressurized state corresponding to the pressure loss depending on the linear velocity of the gas and the tube inner diameter.

<Example 1>
Set the surface temperature (reaction temperature) of the plate heater to 475 ° C, use an SUS tube with an inner diameter of 0.5 mm, set the extrusion flow rate of the syringe pump so that the reaction time is 1.0 second, and heat A decomposition reaction was performed. As a result, a good N-vinylformamide product liquid was obtained with a reaction conversion rate of 96.5% and a reaction selectivity of 98.2%. The reaction conditions and reaction results are shown in Table 1.

<Examples 2 to 10>
A thermal decomposition reaction was carried out in the same manner as in Example 1 in place of the reaction conditions shown in Table 1. The reaction conditions and reaction results are shown in Table 1. In any of Examples 2 to 10, the thermal decomposition reaction can be carried out under normal pressure conditions of about normal pressure or about the pressure loss in the pipe without performing a pressure reduction operation, and as a result, an N-vinylformamide product liquid can be obtained. did it.

<Example 11>
Set the surface temperature (reaction temperature) of the plate heater to 450 ° C, set the extrusion flow rate of the syringe pump to a reaction time of 0.25 seconds using a SUS tube with an inner diameter of 0.25 mm, and heat A decomposition reaction was performed. Under the condition of an inner diameter of the reaction tube of 0.25 mm, the pressure loss in the tube was 200 kPa, and the reaction proceeded under a pressurized condition of 200 kPa. As a result of the reaction, a good N-vinylformamide production solution was obtained with a reaction conversion rate of 97.2% and a reaction selectivity of 98.0%. The reaction conditions and reaction results are shown in Table 1.

<Comparative Example 1>
Evaporated 95.0% N- (α-methoxyethyl) formamide was subjected to a thermal decomposition reaction under a reduced pressure of 13.3 kPa and a maximum reaction temperature of 420 ° C. A reaction tube having an inner diameter of 40 mm was used, and the reaction time was 1.0 second. As a result of the reaction, a good N-vinylformamide product liquid was obtained with a reaction conversion rate of 98.0% and a reaction selectivity of 98.0%. However, a heavy pressure reducing device and a pressure reducing operation using the same were required. It was. The reaction conditions and reaction results are shown in Table 1.

  In the case of Example 3, although there was no pressure reduction operation, both the reaction selectivity and the reaction conversion rate were higher than those of Comparative Example 1 having the same reaction time.

  INDUSTRIAL APPLICABILITY According to the present invention, it can be widely applied as a method for producing N-vinylformamide capable of achieving a high yield under pressure conditions of normal pressure or higher without performing a pressure reduction operation.

Schematic configuration diagram of thermal decomposition equipment

DESCRIPTION OF SYMBOLS 1 Liquid feeding syringe pump 2 Inlet cooling pipe 2a Pre-reaction refrigerant inlet 2b Pre-reaction refrigerant outlet 3 SUS plate heater 4 Outlet cooling pipe 4a Post-reaction refrigerant inlet 4b Post-reaction refrigerant outlet 5 SUS tube

Claims (5)

  A method for producing N-vinylformamide, wherein the organic compound is thermally decomposed at 80.0 to 300 kPa.   The process according to claim 1, wherein the organic compound is at least one of N- (α-substituted-ethyl) formamide or ethylidenebisformamide.   The production method according to claim 1 or 2, wherein the residence time of the reaction gas in the reaction tube is 0.1 to 2.0 seconds.   The manufacturing method as described in any one of Claims 1-3 performed without performing the said pressure decomposition by pressure reduction operation. The manufacturing method according to any one of claims 1 to 4, wherein an inner diameter of the reaction tube is 0.25 to 1.00 mm.