JP3314417B2 - Method for producing N-vinylformamide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing N-vinylformamide (hereinafter abbreviated as "NVF"). Specifically, the present invention relates to a method for producing NVF having excellent storage stability during storage and transportation.

[0002]

2. Description of the Related Art NVF can be used as a polymerizable monomer material. In particular, a modified product of the polymer is expected to be applied as a cationic polymer having a vinylamine unit to a flocculant for dehydrating organic sludge and a chemical for papermaking in recent years. However, it is known that NVF is partially deteriorated during storage, distillation and purification, or during reaction, and is likely to cause quality deterioration. And the altered NVF
When using a polymer, there arises a problem that a high-viscosity polymer cannot be obtained stably.

Conventionally, the following methods have been proposed as means for suppressing the decomposition and polymerization of N-vinylformamide during distillation. Japanese Patent Application Laid-Open No. Sho 62-195352 proposes adjusting the pH of NVF to around neutral when NVF is purified by distillation. It is said that when the pH of NVF is high, an inorganic acid such as sulfuric acid or hydrochloric acid, or an organic acid such as acetic acid or formic acid may be added.

[0004] JP-A-63-190862 discloses that crude NVF is contact-treated with a weakly acidic cation exchange resin,
A method is described in which a trace amount of a basic impurity considered to promote the decomposition of NVF is removed and distillation is performed. JP-A-61-289068 discloses that as stabilizers during purification of NVF by distillation or storage stability, hydroquinone, phenothiazine, phenylenediamine and the like which have been conventionally used as stabilizers for vinyl compounds are effective. Although insufficient, it is described that thioureas are effective only.

Japanese Patent Application Laid-Open No. Sho 62-190153 proposes a method in which a certain amount of formamide is present in NVF when NVF is purified by distillation. Also,
The following methods are known as means for stably storing NVF. JP-A-63-264559 proposes storing NVF in a sealed container under an inert gas atmosphere. In addition, the publication discloses that storage stability is improved by adjusting the pH of the NVF with an aqueous alkali solution or the like so that the pH becomes 6 to 8 when the NVF is diluted with 5 times by weight of water.

[0006]

The above-mentioned known techniques (1) to (4) have a certain effect, but they are still not sufficient, and further improvement in quality is required for industrial use of NVF. Alternatively, there is a need for an improved method for stabilizing NVF. For example, the method is NVF
Although effective for removing trace basic components therein, there is a problem that the storage stability of purified NVF obtained by distillation is not constant. Is excellent in stabilizing NVF at the time of distillation at a high temperature, but it cannot be said that the storage stability effect at around normal temperature is sufficient. With respect to the above method, it is rather common that crude NVF originally contains a considerable amount of formamide, and the stabilizing effect is not sufficient. If formamide is added to crude NVF and distilled,
The labor required for separating NVF and formamide increases accordingly. Further, the NVF stabilization method has great restrictions on industrial handling, and cannot always achieve satisfactory NVF stabilization.

[0007]

Means for Solving the Problems The present inventors have been using N.
For the purpose of industrialization of VF, the inventors studied the production method, purification method and storage stabilization of NVF including means for solving the above problems, and found that NVF
It has been found that a very small amount of an acid component in NVF, which is considered to be generated by the oxidative decomposition of, is an important factor, particularly formic acid.

Further, the present inventors have conducted intensive studies on the basis of such knowledge, and as a result, have found a method for producing a stable NVF by distillation and purification with a focus on the removal of acid components from crude NVF. Reached. That is, the gist of the present invention is that after adding an oxide, hydroxide or carbonate of an alkaline earth metal to crude N-vinylformamide, distillation is performed, and then the distillate is separated into a distillate containing NVF by 5%. An inorganic acid is added so that the pH at the time of dilution with water in a weight-fold amount becomes 4.5 to 8.5, and the mixture is distilled again.
VF manufacturing method.

The method for synthesizing the NVF of interest in the present invention is not particularly limited. The synthesis method includes N- (α
-Alkoxyethyl) formamide to remove alcohol (US Pat. No. 3,914,304)
), A method for eliminating hydrogen cyanide from formylalanine nitrile (Japanese Patent Application Laid-Open No. 61-134359), and a method for thermally decomposing ethylenebisformamide (U.S. Pat. Nos. 4,490,557 and 4,578,515). and so on. In each of these methods, 100 °
The thermal decomposition is performed at the above high temperature to obtain NVF. Among these methods, in terms of high yield of NVF and no by-products of harmful substances such as hydrogen cyanide, the thermal decomposition method is to remove alcohol from N- (α-alkoxyethyl) -formamide. Is preferred. Therefore, the method will be mainly described below.

[0010] N- (α-alkoxyethyl) formamide is usually obtained by an etherification reaction of N- (α-hydroxyethyl) formamide with an alcohol.
In this case, a monovalent aliphatic lower alcohol such as methanol, ethanol, or propanol is generally used as the alcohol in this case. In the obtained N-α-alkoxyethylformamide, there is no problem even if the raw material components remain, and it is usually subjected to the next thermal decomposition step as it is without purification.

Various conditions are selected for the method of thermal decomposition depending on the type of alcohol used in the above-mentioned etherification reaction.
A method of thermally decomposing in the gas phase at 0 to 500 ° C. and condensing and recovering the product vapor, under a reduced pressure of 1 to 20 mmHg, 90 to 200
C. and pyrolysis in the liquid phase while distilling off the product. The mixed solution containing NVF obtained by the pyrolysis method contains N-vinylformamide and alcohol as a by-product as main components.

The crude NVF in the present invention includes the above-mentioned pyrolysis mixture, a solution from which light boiling components such as alcohol in the pyrolysis mixture are removed, and N.P. once purified by distillation or the like.
Even VF includes a wide range of liquids containing NVF, such as those whose purity has decreased during storage. Crude NVF
Typical examples include those obtained by adjusting the purity of NVF to usually 80% by weight or more by simple distillation or vacuum concentration of the above-mentioned pyrolysis mixture. Such a crude NVF
Usually contains, in addition to the NVF component, as a by-product component derived from the NVF production process, a raw material compound, formamide, alcohol, and the like which remain without being thermally decomposed. Further, usually, several tens ppm to several% of various types of ammonia, picoline, ethylpicoline, and other basic impurities having an unknown structure are present. Although it is difficult to quantitatively grasp the total amount of the basic impurities, it can be estimated to some extent from the pH value of the NVF solution, and it is generally considered to be about several tens ppm to several%. Conventionally, it has been considered that the basic impurities promote the decomposition of NVF during distillation. The reason that the stability of NVF is improved by adjusting the pH of NVF with sulfuric acid, formic acid, or the like when the above-mentioned NVF is purified by distillation is that the basic impurities are neutralized with an acid to form a salt. Was thought to be inactivated. In addition, salt is better for NVF
The efficiency of separation and removal of basic impurities therein is improved.

However, according to the study by the present inventors, there is a correlation between a decrease in purity of NVF during storage and an increase in the amount of formic acid, which is a trace impurity in NVF.
It became apparent that the purity of NVF during storage was reduced, which could not be sufficiently explained by the amount of basic impurities in NVF. NV
The increase of formic acid in F is promoted by oxygen mixed in NVF, and further, when the formic acid concentration exceeds a predetermined amount, specifically, about 250 ppm by weight with respect to NVF, cationic polymerization of NVF is likely to occur. , Low molecular weight poly NV
It was found that F was produced and as a result, the purity of NVF was reduced. When the formic acid concentration in the NVF is larger than a predetermined amount, the storage stability of the NVF is particularly deteriorated, and the effect of the conventional known method for stabilizing the storage of the NVF is almost negligible.

The above-mentioned crude NVF having a purity of 80% by weight or more contains acidic impurities such as formic acid and acetic acid together with the above basic impurities. Most of the acidic impurities, usually 90% by weight or more, are formic acid. It is considered that this formic acid is generated as a by-product in the reaction step and also generated by oxidative decomposition of NVF. Formic acid can hardly be removed by a known method for purifying NVF.
Formic acid in various grades of NVF, by weight or more, is usually estimated at hundreds to 10,000 ppm by weight. NVF
It is considered that the formic acid therein is present mostly as free formic acid and partially as a salt with basic impurities. Although these formic acid components can be easily quantitatively analyzed by ion chromatography, conventionally, formic acid as an impurity in NVF has never been specifically confirmed. Even more, it was completely unexpected that formic acid is an important factor that greatly affects the storage stability of NVF. As to how unexpected this is, in the aforementioned Japanese Patent Application Laid-Open No. 62-195352, formic acid, which is considered to adversely affect the storage stability of NVF in this study, may be added to NVF. It is clear from the description.

In the method for producing NVF of the present invention, impurities in crude NVF, in particular, acidic impurities such as formic acid and basic impurities are removed by distillation by a specific method to obtain NVF having extremely high stability. Hereinafter, the distillation operation of the present invention will be described. Crude NVF, for example, the pyrolysis solution containing NVF, has a pH in a wide range of usually 4 to 9 when the solution is diluted with 5 times by weight of water depending on the method and conditions of the pyrolysis. . In the present invention, for the purpose of removing acidic impurities, particularly formic acid, a specific basic compound is added to crude NVF, and the pH of the solution diluted with 5 times by weight of water is usually 6%.
-12, preferably 8-11. As the basic compound, oxides, hydroxides or carbonates of alkaline earth metals, for example, calcium oxide, magnesium oxide, barium oxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, calcium carbonate, magnesium carbonate, Barium carbonate and the like are exemplified, and among them, calcium oxide is preferable. In general, it is not always preferable to increase the pH by adding a basic compound in view of the stability of NVF, but it is surprising that the oxide, hydroxide or carbonate of an alkaline earth metal is unexpectedly added. The salt has a high removal efficiency of formic acid and a small problem of NVF decomposition.

The amount of the basic compound to be added depends on the amount of the acidic substance in the crude NVF, but is usually 0.01 to 3.0% by weight based on the crude NVF. If the added amount is too small compared to the acidic substance in the crude NVF, the removal efficiency of the acidic substance will be low.
This is not preferred from the viewpoint of the stability of F. However, even if it is added in excess, there is no particular problem as long as it cannot be completely dissolved in the liquid and exists in an insoluble state. After the addition of the basic compound, the crude NVF may be mixed at a temperature of usually −10 to 30 ° C. for usually 0.1 to 2 hours.

It is preferable that the formate formed after the addition and mixing or the excess insoluble basic compound is filtered. The method of adding the basic compound is not particularly limited, but a method of adding the powder as it is or as a methanol solution is preferable. Also, if the crude NVF is N
In the case of a thermal decomposition liquid containing VF, it is not always necessary to remove light boiling components in the thermal decomposition liquid. For example, in the thermal decomposition solution of N- (α-alkoxyethyl) -formamide,
Although a large amount of alcohol is contained in addition to VF, the alcohol tends to promote the reaction between the acidic substance in the crude NVF and the basic compound in the treatment with the basic compound.

Therefore, for example, when NVF once distilled is converted to crude NVF and further purification is desired, or when a pyrolyzed liquid containing NVF obtained by a method that does not produce alcohols is purified as crude NVF, Is the NVF
It is preferable to add an alcohol such as methanol therein and then add the basic compound. After adding a specific basic compound to the crude NVF as described above, distillation is performed. The distillate containing NVF separated by the distillation is one from which acidic substances have been substantially removed, and the pH when the distillate is diluted with 5 times by weight of water is usually 8 to 11. It is thought that the pH is affected by the amount of the basic substance in the distillate.

In the present invention, a small amount of an inorganic acid is added to the distillate, and the pH of the distillate when diluted with 5 times by weight of water is adjusted.
Is adjusted to 4.5 to 8.5, preferably 6.0 to 8.0. Examples of the inorganic acid include sulfuric acid, phosphoric acid, and nitric acid, with sulfuric acid being preferred. By distilling the distillate fraction thus adjusted in pH again, the basic impurities in the crude NVF can be removed.

The mode of the two distillations is not particularly limited, and may be precision distillation using a multi-stage column or thin-film distillation. The thin-film evaporator has a separation efficiency similar to that of flash evaporation and cannot separate impurities such as formamide in crude NVF, but removes high boiling impurities including trace amounts of acidic and basic impurities in crude NVF. Is enough, and
It is suitable for evaporating an object having low thermal stability such as NVF. The structure of the thin-film still is the same as that of a commercially available device, and does not need to have a special structure. Examples thereof include a rising thin-film type, a plate-type falling thin-film type, and a tube-type falling thin-film type. The operating conditions for thin film distillation are usually 1 to 20 Torr, preferably 2 to 10 Torr.
Under a reduced pressure of r, the vapor temperature is usually 60 to 150 ° C, preferably 70 to 120 ° C, and the average residence time of the liquid is usually 30.
Seconds to 10 minutes, preferably 1 to 5 minutes are indicated. By performing thin-film distillation under such conditions, most of the liquid is recovered as an evaporating component.

If acidic and basic impurities have been removed from the crude NVF by the above thin film distillation, even if formamide of about 1 to 20% is mixed in the recovered NVF, for example, the polymerization activity of the NVF may be reduced. Has little effect on the storage stability of NVF. However, if necessary, the above-mentioned NVF fraction can be introduced into a column and subjected to precision distillation to obtain a higher purity NVF fraction.
However, specifically, NVF having a purity of usually 95% or more can be obtained. The operating conditions of the distillation column are appropriately selected according to the requirement for the purity of the NVF to be recovered, but the column pressure is usually 1 to 20 Torr, preferably 2 to 10 Torr, and the top temperature is usually 60 to 90 ° C., preferably Is usually from 5 to 50, preferably from 10 to 3 as a theoretical plate number of the column.
0 is the condition. The structure inside the column is the same as that of a general distillation column, and examples thereof include a packed type, a tray type, and the like.

In the present invention, formic acid present in NVF is usually reduced to 250 ppm by weight or less, preferably to 200 ppm by weight with respect to NVF by carrying out the above method.
pm or less, more preferably 150 ppm by weight or less.
F can be obtained. Such NVFs have significantly improved storage stability as compared with conventionally known NVF products. If the NVFs are kept in a nitrogen atmosphere, the purity of the NVFs and the polymerization activity of the NVFs may decrease even after storage at room temperature for several months. Little decrease is observed. Furthermore, if an antioxidant such as hydroquinone or phenylenediamine, which is known as a stabilizer for a polymerizable vinyl compound, is added to the NVF usually in an amount of 10 to 10,000 ppm by weight, the stability of the NVF is further improved. It can also be done.

[0023]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. Note that “%” represents “% by weight” unless otherwise specified.

Example 1 (Structure of N- (α-methoxyethyl) formamide (hereinafter referred to as “ether compound”)) Formamide and acetaldehyde were placed in a 5-liter glass reactor equipped with a stirrer and a temperature controller. N- (α-hydroxyethyl) formamide (hereinafter referred to as “hydroxy form”) crystals obtained by reacting in the presence of a potassium carbonate catalyst (purity 73%,
(Formamide content 0.5%, K ₂ CO ₃ content 0.5%)
3 kg were charged, and 3.15 kg of methanol (4 mole times based on the hydroxy form) and 25 g of sulfuric acid (K ₂ CO 3
_{And the} etherification reaction was carried out under stirring at a temperature of 25 to 40 ° C. until the remaining amount of the hydroxy compound in the reaction system became 1%. (Reaction time: 3 hours) Then, the pH was adjusted to 7 by adding 20% caustic soda to neutralize the catalyst. Further, after removing the light-boiling component under reduced pressure of 50 mmHg,
The ether compound was recovered by distillation under reduced pressure of mHg.

(Production of N-vinylformamide) The ether obtained above was placed in a stainless steel tube equipped with a heater and having a diameter of 10 mm and a length of 500 mm under a reduced pressure of 100 mmHg at 2 g / min while maintaining the internal temperature at 400 ° C. , On the other hand, pyrolysis is carried out by immediately condensing the discharged gas, and 2.3 kg of distillate (NVF 64
%, Methanol 31%). The pH of a liquid obtained by diluting the distillate with 5 times by weight of water was 4.5.

(Distillation of Pyrolysis Mixture Containing NVF) 2.9 gr of calcium oxide was added to the above distillate, and the mixture was heated at 10 ° C. for 1 hour.
The mixture was kept under stirring for a period of time, and then insolubles were removed by filtration. The pH when the filtrate was diluted with 5 times by weight of water was 9.9. Next, light boiling components such as methanol were removed from the filtrate under the conditions of a pressure of 50 Torr and 50 ° C.

Using a thin film still under glass rectification (heat transfer surface diameter: 50 mm, height: 200 mm), the solution was subjected to a pressure of 3 To.
rr, steam temperature 125 ° C., mixed liquid feed amount 500 g /
Evaporation was performed under the conditions of hr and an average residence time of the mixed solution of 5 minutes. As a result, 97% of the mixture was evaporated. The composition of the evaporating fraction was 69% N-vinylformamide, 3% formamide, 1% ether, and the recovery of N-vinylformamide was 97%. The pH at the time when the evaporated matter was diluted with 5 times by weight of water was 9.7. On the other hand, the non-evaporated components were removed from the system without being circulated to the thin film still.

Next, 7 ml of a 1N sulfuric acid methanol solution was added to 1.49 kg of the recovered evaporator. The formula was diluted with 5 times by weight of water and the pH was 6.5. This liquid was subjected to an evaporation treatment under the same thin-film distillation apparatus and under the same conditions as described above. 95% of the feed liquid evaporates, and the composition of the evaporate is NV
F95%, formamide 4.5%, ether form 0.5%
And the recovery of NVF was 96%. The amount of formic acid contained was analyzed by ion chromatography and found to be 40 pp.
m and the pH was 6.8 when the liquid was diluted with 5 times by weight of water.

(Stability Evaluation Test) The obtained NVF was polymerized to produce a water-soluble polymer, and the reduced viscosity of the obtained polymer was measured. Meanwhile, at the same time, 50 ml of the obtained NVF was charged into a 200 ml glass sealed container,
2 liters of nitrogen gas is supplied to the solution for 10 minutes,
After completely replacing the inside of the system with nitrogen gas, the system was sealed as it was, and an accelerated model test of storage was performed for 70 minutes in a constant temperature bath at a temperature of 80 ° C. Thereafter, the purity of this NVF was measured, followed by polymerization to produce a water-soluble polymer. The reduced viscosity of the obtained polymer was measured, and the values before and after the accelerated model test were compared. The results are shown in Table 1. The polymerization of NVF and the measurement of the reduced viscosity of the polymer obtained by the polymerization were performed by the following methods.

(Polymerization method) To a 60% aqueous solution of NVF monomer was added 3000 ppm of 2,2'-azopisamidinopropane hydrochloride to the monomer as a polymerization initiator and 0.5% ethyl cellulose as a dispersion stabilizer. Was subjected to suspension polymerization at a temperature of 70 ° C. in a cyclohexane medium in which was dissolved. The obtained polymer was dehydrated by azeotropic distillation, filtered and then dried under reduced pressure.

(Method of Measuring Reduced Viscosity) The polymer obtained by the above method was prepared into a 0.1% concentration solution using 1N saline, and the reduced viscosity of the solution was measured by an Ostwald viscometer.

Example 2 The procedure of Example 1 was repeated, except that the thermal decomposition reaction temperature was changed to 550 ° C., and a stability evaluation test was conducted in the same manner. The results are shown in Table 1. The amount of formic acid contained in NVF before the stability evaluation test was 150 ppm, and the pH when diluted with 5 times by weight of water was 6.4.

Comparative Example 1 Light boiling components such as methanol were directly removed from the distillate obtained by the thermal decomposition reaction obtained in Example 1, and then evaporated using a thin film still to obtain an NVF fraction. The formic acid content of the NVF fraction was 2000 ppm, and the pH when diluted with 5 times by weight of water was 4.5. Next, a 1/10 N caustic soda methanol solution was added to adjust the pH to 7.0 when diluted with 5 volumes of water, and a stability evaluation test was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 NVF was obtained under exactly the same conditions as in Comparative Example 1 except that the thermal decomposition reaction temperature was changed to 550 ° C., and a stability evaluation test was similarly performed. The results are shown in Table 1. The amount of formic acid contained in NVF before the stability evaluation test was 2500 pp.
m, and the pH when diluted with 5 times by weight of water was 8.8.

[0035]

[Table 1]

[0036]

According to the method of the present invention, it is possible to efficiently produce an extremely stable NVF with a small decrease in purity and a small decrease in polymerization activity even during long-term storage for several months.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-151113 (JP, A) JP-A-4-69371 (JP, A) JP-A-54-157520 (JP, A) JP-A-57-151 130960 (JP, A) JP-A-62-195352 (JP, A) JP-A-63-264559 (JP, A) JP-A-52-128318 (JP, A) JP-B-42-12403 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 233/03 C07C 231/18

Claims (2)

(57) [Claims] 1. An alkaline earth metal oxide, hydroxide or carbonate is added to crude N-vinylformamide, followed by distillation, and then the distillate containing N-vinylformamide is added to a fraction of 5%. PH when diluted with a weight-fold amount of water is 4.5 to 4.5
A method for producing N-vinylformamide having good stability, which comprises adding an inorganic acid to 8.5 and distilling again. 2. After adding an oxide, hydroxide or carbonate of an alkaline earth metal to the crude N-vinylformamide, distillate containing N-vinylformamide is collected by a thin-film evaporator, and the distillate is recovered. , An inorganic acid was added so that the pH when the distillate was diluted with 5 times by weight of water was 4.5 to 8.5, and the mixture was again passed through a thin film evaporator to obtain a fraction containing N-vinylformamide. A process for producing N-vinylformamide having good stability, comprising recovering a distillate and precision-distilling the distillate using a column.