WO2010058647A1 - Method for producing methylene-crosslinked polyphenyl polyisocyanate - Google Patents

Abstract

A method for producing a methylene-crosslinked polyphenyl polyisocyanate, wherein sufficient hue improvement can be achieved while suppressing the amount of hydrogen chloride used therein. The method for producing a methylene-crosslinked polyphenyl polyisocyanate is characterized by comprising: a phosgenation step wherein a polymethylene polyphenyl polyamine and phosgene are reacted in the presence of an inert solvent; a solvent removal step wherein the inert solvent is removed from the reaction liquid obtained in the phosgenation step until the concentration of the solvent becomes 5-35% by mass; and a hydrogen chloride introduction step wherein hydrogen chloride is introduced into the reaction liquid after the solvent removal step.  The method is also characterized in that the temperature of the reaction liquid is kept within the range of 60-130˚C in the phosgenation step, the solvent removal step and the hydrogen chloride introduction step.  As a result, sufficient hue improvement can be achieved, while suppressing the amount of hydrogen chloride used therein.

Description

Method for producing methylene cross-linked polyphenyl polyisocyanate

The present invention relates to a method for producing a methylene-crosslinked polyphenyl polyisocyanate.

Industrially, methylene-crosslinked polyphenyl polyisocyanate (hereinafter referred to as poly MDI), which is a raw material for polyurethane foam, is made to react polymethylene polyphenyl polyamine with phosgene in the presence of an inert solvent. (Phosgenation reaction). Thereafter, diphenylmethane diisocyanate (hereinafter simply referred to as MDI, if necessary) can be separated by distillation under reduced pressure and adjusted to poly MDI containing a predetermined amount of MDI. However, the poly MDI obtained by such a method contains an acid content and a hydrolyzable chlorine-containing compound as impurities, and it is known that if these impurities are large, the reactivity during the production of urethane deteriorates. ing. Thus, in order to reduce such impurities, conventionally, heat treatment under reduced pressure has been performed.

However, when the heat treatment as described above is performed, the hue of the poly MDI deteriorates, which causes coloring of the urethane product. As described above, the reason why the hue of poly-MDI deteriorates due to the heat treatment is that the urea compound produced as a by-product in the phosgenation reaction reacts with phosgene remaining in the reaction solution by heating to become a urea phosgenated product. This is thought to be because urea phosgenated substances are changed into color-causing substances.

By the way, conventionally, when hydrogen chloride is introduced into a reaction solution of polyamine and phosgene, and heat treatment is performed in the presence of hydrogen chloride, the change from urea phosgenation to a color-causing substance can be prevented, and the hue of poly MDI It is known that deterioration can be suppressed. For example, Patent Document 1 discloses a method of removing residual phosgene from a reaction solution after a phosgenation reaction under a temperature condition of 140 ° C. or lower and then heating to 140 ° C. or higher in the presence of hydrogen chloride gas. Yes.

JP 7-233136 A

As described above, by introducing hydrogen chloride into the reaction solution after the phosgenation reaction step, deterioration of the hue of poly MDI due to heating can be suppressed, but the amount of the inert solvent contained in the reaction solution is large ( When the concentration of poly-MDI is low), the reaction between urea phosgenide and hydrogen chloride hardly occurs, so that the amount of hydrogen chloride necessary to suppress the generation of the color factor substance increases. In other words, the amount of hydrogen chloride that is unnecessarily discharged without reacting with the urea phosgenide increases. Thus, when the amount of hydrogen chloride used increases, the apparatus for handling hydrogen chloride increases in size, and corrosion of plant equipment due to hydrogen chloride tends to occur. However, Patent Document 1 does not describe anything about removing the inert solvent in order to reduce the amount of hydrogen chloride used after the phosgenation reaction step and before introducing hydrogen chloride. There is no mention of the concentration of the inert solvent immediately before the introduction of hydrogen chloride.

Further, in the method described in Patent Document 1, the residual phosgene is removed by heating the reaction solution to a temperature of 140 ° C. or lower before introducing hydrogen chloride gas. However, as a result of the study by the present inventors, under the conditions where the reaction solution temperature can reach 140 ° C., a part of the urea phosgenation product changes to a color factor substance before reacting with hydrogen chloride. Therefore, it was found that even if hydrogen chloride was introduced thereafter, the hue improvement was insufficient.

An object of the present invention is to provide a method for producing a methylene-bridged polyphenyl polyisocyanate capable of realizing sufficient hue improvement while suppressing the amount of hydrogen chloride used.

The method for producing a methylene-bridged polyphenyl polyisocyanate according to the present invention comprises a phosgenation reaction step in which polymethylene polyphenyl polyamine and phosgene are reacted in the presence of an inert solvent, and a reaction solution obtained in the phosgenation reaction step. A solvent removing step for removing the inert solvent until the concentration thereof becomes 5 to 35% by mass, and a hydrogen chloride introducing step for introducing hydrogen chloride into the reaction solution after the solvent removing step,
In the phosgenation reaction step, the solvent removal step, and the hydrogen chloride introduction step, the reaction solution temperature is maintained in the range of 60 ° C. to 130 ° C.

In the method for producing a methylene-bridged polyphenyl polyisocyanate according to the present invention, the concentration of the inert solvent from the reaction solution obtained in the phosgenation reaction step is adjusted to 5 to 20% by mass in the solvent removal step. It is preferable to remove until.

In the method for producing a methylene-bridged polyphenyl polyisocyanate according to the present invention, the inert solvent is removed from the reaction solution obtained in the phosgenation reaction step by reducing the pressure to normal pressure or lower in the solvent removal step. It is preferable to do.

According to the present invention, after reacting polymethylene polyphenylpolyamine and phosgene in the presence of an inert solvent, the inert solvent is removed from the reaction solution until the concentration becomes 5 to 35% by mass. Introduce hydrogen chloride. Thus, since hydrogen chloride is introduced after sufficiently removing the inert solvent from the reaction solution, the amount of wasted hydrogen chloride is reduced, and the amount of hydrogen chloride used can be reduced. Furthermore, since the phosgenation reaction step, the solvent removal step, and the hydrogen chloride introduction step are performed while maintaining the reaction solution temperature in the range of 60 ° C. to 130 ° C., the generation of coloring factor substances can be reliably suppressed, and poly MDI Sufficient hue improvement becomes possible.

Next, preferred embodiments of the present invention will be described in detail.

In the method for producing a methylene-crosslinked polyphenyl polyisocyanate according to this embodiment, after reacting polymethylene polyphenyl polyamine and phosgene (phosgenation reaction step), an inert solvent is removed from the reaction solution after the phosgenation reaction ( Solvent removal step), hydrogen chloride is introduced into the reaction liquid after the inert solvent is removed (hydrogen chloride introduction step). It can then be concentrated to separate diphenylmethane diisocyanate (MDI).

(Phosgenation reaction process)
The polymethylene polyphenyl polyamine (hereinafter also referred to as poly MDA) used in the phosgenation reaction step is represented by the following general formula (Formula 1). The method for producing this poly MDA is not particularly limited, but it is generally obtained by addition condensation of aniline and formaldehyde in the presence of an acid catalyst. In addition, n in the following formula (Formula 1) represents 0 or an integer of 1 or more.

In the above, when n = 0, the polyamine represented by the general formula (Chemical Formula 1) is methylenedianiline (MDA) and corresponds to a binuclear body. Further, when n = 1, it is a trinuclear body, when n = 2, it is a tetranuclear body, and when n = m, it is a (m + 2) nucleus. The polyamine represented by the general formula (Chemical Formula 1) may be a mixture of anilines derived from different skeletons (skeletons composed of one amino group and one benzene ring). That is, it may be a mixture of binuclear, trinuclear, tetranuclear, pentanuclear, and higher polynuclear bodies.

The phosgenation reaction can be performed by dissolving the poly MDA in an inert solvent and introducing phosgene into this. Here, usable inert solvents include aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as chlorotoluene, chlorobenzene and dichlorobenzene, esters such as butyl acetate and amyl acetate, and methyl isobutyl ketone. And ketones. The phosgenation method is not particularly limited, and can be performed using a known method such as a hydrochloride method, a two-stage cooling method, or a phosgene pressurization method. In addition, although it is possible to cause the reaction in batches, a method in which the reaction is continuously caused is preferable from an industrial viewpoint.

The polyamine phosgenation reaction can be represented by the following main reaction formulas (1) to (4). In the following formulas (1) to (4), R represents a residue in the general formula (Formula 1) excluding the amino group.
(1) R-NH ₂ + COCl ₂ → R-NHCOCl + HCl
(2) R-NH ₂ + HCl → R-NH ₂ .HCl
(3) R-NH ₂ .HCl + COCl ₂ → R-NHCOCl + 2HCl
(4) R-NHCOCl → R-NCO + HCl

The substance produced by the progress of the reactions represented by the above (1) to (4) is methylene-bridged polyphenyl polyisocyanate represented by the following general formula (Formula 2). In the following general formula (Formula 2), n represents 0 or an integer of 1 or more. When n = 0, it is a monomeric MDI (binuclear), and when n ≧ 1, a polymeric MDI. (3 nuclei or more). When the polyamine represented by the general formula (Chemical Formula 1) is a mixture of polynuclear bodies, the substance represented by the General Formula (Chemical Formula 2) is also a mixture of polynuclear bodies.

By the way, in the phosgenation reaction step described above, in addition to the main reactions of the above formulas (1) to (4), a side reaction represented by the following formula (5) may also proceed.
(5) 2R-NH ₂ + COCl ₂ → R-NHCONH-R + 2HCl

Here, R-NHCONH-R on the right side of the formula (5) is a urea compound by-produced during the phosgenation reaction and exists as an impurity in the reaction solution, but the urea compound itself affects the hue of poly-MDI. It is a substance that does not affect.

However, in the state where phosgene (COCl ₂ ) remains in the reaction solution, the side reaction further proceeds. That is, the urea compound (R-NHCONH-R) reacts with the remaining phosgene to produce a urea phosgenated product. In this state, when the reaction solution is heated to a certain temperature or higher in order to promote the phosgenation reaction (the main reaction of the above formulas (1) to (4)) or remove the residual phosgene, the above-described urea phosgenated product is obtained. It is considered that the substance decomposes into a color-causing substance by thermal decomposition, which leads to deterioration of the hue of poly MDI.

Therefore, in this embodiment, the generation of the color factor substance is suppressed by introducing hydrogen chloride into the reaction solution after the phosgenation reaction step. More specifically, by adding hydrogen chloride to the urea phosgenated product generated by the side reaction in the phosgenation reaction step, the urea phosgenated product is changed to another substance that is harmless with respect to coloring. Thus, if hydrogen chloride is added to detoxify the urea phosgenide, the generation of the color factor substance is suppressed even if the reaction solution temperature is increased.

However, if the temperature of the reaction solution is too high, a part of the urea phosgenation product is thermally decomposed before reacting with hydrogen chloride and changed into a color-causing substance. In the study by the present inventor, thermal decomposition behavior was observed around 140 ° C. Therefore, the reaction solution temperature in the phosgenation reaction step is preferably 130 ° C. or lower. On the other hand, if the reaction solution temperature is too low, the phosgenation reaction proceeds slowly. Furthermore, in order to make it difficult to cause a side reaction that leads to the generation of a color-causing substance, it is better that the amount of residual phosgene in the reaction solution is small, and the reaction solution temperature may be raised to some extent in order to vaporize and remove phosgene. preferable. From the above viewpoint, the reaction solution temperature is preferably maintained in the range of 60 to 130 ° C.

By the way, if the amount of the inert solvent present in the reaction solution is large (that is, the concentration of poly-MDI is low), when hydrogen chloride is subsequently introduced, urea phosgenide and hydrogen chloride present in the reaction solution Is difficult to react, and the amount of hydrogen chloride required to suppress the production of the color-causing substance increases. In other words, the amount of hydrogen chloride that is unnecessarily discharged without reacting with the urea phosgenide increases. Therefore, in the present embodiment, before introducing hydrogen chloride into the reaction solution (hydrogen chloride introduction step), the inert solvent in the reaction solution is removed (solvent removal step).

(Solvent removal step)
In the solvent removal step, the inert solvent is removed from the reaction solution obtained in the phosgenation reaction step until the concentration is 5 to 35% by mass. By concentrating the reaction solution until the solvent concentration becomes 35% by mass or less, the amount of hydrogen chloride used in the hydrogen chloride introduction step described later is reduced as compared to before concentration (solvent concentration exceeding 35% by mass). The lower the solvent concentration, the smaller the amount of hydrogen chloride used. However, under a temperature condition of 130 ° C. or lower, setting the solvent concentration to less than 5% by mass means that the scale of the concentration equipment (the column diameter or From the viewpoint of the performance of the pressure reducing pump, it is disadvantageous in terms of equipment cost. As described above, in this solvent removal step, it is preferable to remove the inert solvent until the concentration becomes 5 to 35% by mass. Furthermore, in order to further reduce the amount of hydrogen chloride used, it is more preferable to remove the inert solvent until the concentration reaches 5 to 20% by mass.

Similarly to the above-described phosgenation reaction step, the reaction solution temperature is also in the range of 60 to 130 ° C. in this solvent removal step from the viewpoint of suppressing the generation of coloring factor substances due to thermal decomposition of the urea phosgenation product. It is preferable to hold at. In addition, as a method for removing the inert solvent, as described above, under a relatively low temperature condition of 130 ° C. or lower, from the viewpoint of increasing the efficiency of removal (reducing the processing time), a method of reducing the pressure to normal pressure or lower is used. It is preferable to adopt. Further, the pressure (degree of vacuum) when the reduced pressure method is employed is preferably 30 to 700 torr, more preferably 30 to 450 torr.

(Hydrogen chloride introduction process)
As a method for introducing hydrogen chloride into the reaction solution after the solvent removal step, a method of passing hydrogen chloride gas through the reaction solution can be employed. Further, hydrogen chloride may be added continuously or batchwise, but a continuous method is preferred from an industrial standpoint.

Here, as described above, since the inert solvent in the reaction solution is removed to a low concentration (35% by mass or less) before introducing hydrogen chloride, the introduced hydrogen chloride and the urea phosgenide in the reaction solution are removed. It becomes easy to react. As a result, less hydrogen chloride is wasted without reacting with the urea phosgenide, and the amount of hydrogen chloride used can be reduced.

Similarly to the above-described phosgenation reaction step, the reaction liquid temperature is set to 60 to 130 ° C. in this hydrogen chloride introduction step from the viewpoint of suppressing the generation of coloring factor substances due to thermal decomposition of the urea phosgenation product. It is preferable to keep in a range.

As described above, according to the present invention, after the polymethylene polyphenyl polyamine and phosgene are reacted, the inert solvent is removed from the reaction solution until the concentration becomes 5 to 35% by mass, Introduce hydrogen chloride. Thus, since hydrogen chloride is introduced after sufficiently removing the inert solvent from the reaction solution, the amount of wasted hydrogen chloride is reduced, and the amount of hydrogen chloride used can be reduced. Furthermore, since the phosgenation reaction step, the solvent removal step, and the hydrogen chloride introduction step are performed while maintaining the reaction solution temperature in the range of 60 ° C. to 130 ° C., the generation of coloring factor substances can be reliably suppressed, and poly MDI Sufficient hue improvement becomes possible.

In order to further improve the coloration, it has been conventionally known to add a reducing agent such as a phenolic or phosphorous acid-based antioxidant or a metal hydride (borane) to the reaction solution, or to add alcohol or water. A coloring improvement method may be used in combination.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not construed as being limited in any way by the following examples.

In the following Examples 1 to 3 and Comparative Examples 1 to 8, as poly MDA, amine group concentration: 9.5 mol / kg, 2,2 ′ form and 2,4 ′ form: 14.3 mass%, 4,4 'Body: 53.4% by mass, trinuclear body: 32% by mass.

<Examples 1 to 3>
In Examples 1 to 3, poly MDI was produced through the following steps 1) to 6), and the hues of each were measured.
1) A pressurized reaction vessel equipped with a heat exchanger was charged with 700 g of chlorobenzene, the inside of the vessel was cooled to 10 ° C., and then 132 g of phosgene was blown into the vessel while stirring.

2) Next, after the pressure in the container containing the phosgene / chlorobenzene solution was set to 120 kPa · G, 700 g of a poly MDA chlorobenzene solution (poly MDA concentration of 10% by mass) adjusted to 30 ° C. was charged into the container at once. The mixture was stirred.

3) After the above mixing, the mixture was heated to 115 ° C. over about 30 minutes, and further maintained at 115 ° C. for 90 minutes for phosgenation reaction.

4) Next, chlorobenzene as an inert solvent was distilled off under the condition of a predetermined solvent removal temperature (120 ° C.) / 40 torr to obtain an MDI concentrated solution having a reduced solvent concentration. The solvent concentration of the concentrate after this solvent removal step was 14% by mass in Example 1, and 33% by mass in Examples 2 and 3. The solvent concentration is determined from the total amount of chlorobenzene introduced into the container before the phosgenation reaction and the outflow amount (removed amount) of chlorobenzene from the container in the solvent removal step. Was calculated.

5) Then, hydrogen chloride was bubbled through the obtained MDI concentrate at a predetermined treatment temperature (120 ° C.). The aeration amount of hydrogen chloride was 6 g in Example 1, 10 g in Example 2, and 6 g in Example 3.

6) After aeration of hydrogen chloride, the remaining chlorobenzene was removed (1% by mass or less) under the conditions of 150 ° C./40 torr to obtain crude MDI. Further, the obtained crude MDI was held at 220 ° C. for 10 minutes under nitrogen flow, and then immediately cooled to 60 ° C., and the solution color of the obtained poly MDI was visually measured.

<Comparative Examples 1 to 4>
In Comparative Examples 1 and 2, the solvent concentration after removing the solvent was set to 40% by mass, higher than those in Examples 1 to 3. On that basis, the hydrogen chloride aeration amount was 6 g in Comparative Example 1, while it was 17 g which was quite large in Comparative Example 2. In Comparative Example 3, the solvent was not removed at all (unrecovered), and as a result, the next hydrogen chloride was vented while the solvent concentration was as high as 93% by mass. In Comparative Example 4, although the solvent concentration was as low as 14% by mass, the temperature during the subsequent hydrogen chloride aeration was 140 ° C. The conditions other than these are the same as those in Examples 1 to 3.

<Comparative Examples 5 and 6>
In Comparative Examples 5 and 6, o-dichlorobenzene having a boiling point higher than that of chlorobenzene was used as the inert solvent. In addition, the temperature at the time of solvent removal was set to 140 ° C., a temperature higher than those in Examples 1 to 3. The temperature at the time of aeration of hydrogen chloride was 140 ° C. in Comparative Example 5 and 120 ° C. in Comparative Example 6. The conditions other than these are the same as those in Examples 1 to 3.

<Comparative Examples 7 and 8>
In Comparative Examples 7 and 8, after the phosgenation reaction step, nitrogen was bubbled at 120 ° C. instead of removing the solvent under reduced pressure. It is possible to remove the phosgene remaining in the reaction solution after the phosgenation reaction step by this aeration of nitrogen, but the inert solvent (chlorobenzene) in the reaction solution can hardly be removed. Therefore, the solvent concentration after nitrogen aeration was a very high value of 93% by mass. The hydrogen chloride aeration amount was 6 g in Comparative Example 7, while it was 32 g which was very large in Comparative Example 8. The conditions other than these are the same as in the first to third embodiments.

<Solution color measurement method>
In a 450 ml colorless transparent bottle, 2 g of the sample obtained in each of Examples 1 to 3 and Comparative Examples 1 to 8 and 400 ml of acetone were added and dissolved, and the solution color was measured visually at 23 ° C. The value is indicated by APHA (Hazen unit color number).

<Verification>
Table 1 summarizes the phosgenation reaction conditions, the solvent removal conditions, the hydrogen chloride aeration conditions, and the hues of the resulting poly-MDI solutions for each of Examples 1 to 3 and Comparative Examples 1 to 8. Show.

As shown in Table 1, before passing hydrogen chloride, chlorobenzene as an inert solvent is removed until the concentration becomes 35% by mass or less, and each step of phosgenation reaction, solvent removal, and hydrogen chloride aeration It can be seen that Examples 1 to 3 in which all of the above were carried out at 120 ° C. or lower showed good hue.

On the other hand, in Comparative Examples 1 and 2 in which the concentration of chlorobenzene is 40% by mass, since the chlorobenzene is not sufficiently removed, the hue deteriorates when the hydrogen chloride aeration amount is reduced (Comparative Example 1), and the hue is improved. Attempting to do so greatly increases the amount of ventilation (Comparative Example 2). Furthermore, it can be seen from Comparative Example 3 that chlorobenzene was not removed that the amount of hydrogen chloride aeration necessary to improve the hue was further increased.

Further, in Comparative Example 4 in which the temperature during ventilation of hydrogen chloride was set as high as 140 ° C., the hue was deteriorated as compared with the Example. Further, in Comparative Examples 5 and 6 in which o-dichlorobenzene having a high boiling point was used as an inert solvent and the temperature at the time of solvent removal was 140 ° C., the hue was deteriorated. That is, it can be seen that when the treatment temperature during solvent removal or hydrogen chloride ventilation is increased to 140 ° C. or higher, the hue deteriorates even when hydrogen chloride is added.

Furthermore, in Comparative Examples 7 and 8 in which nitrogen was ventilated before hydrogen chloride was aerated, the hue deteriorated (Comparative Example 7) or the aeration amount significantly increased (Comparative Example 8). In Comparative Examples 7 and 8, it seems that residual phosgene has been removed to some extent by aeration of nitrogen, but chlorobenzene as an inert solvent is hardly removed (substantially unrecovered). Thus, it can be seen that, even if phosgene is removed, if the solvent is not removed, the amount of hydrogen chloride necessary for improving the hue is still increased.

The poly MDI with very little coloration that can be obtained by the present invention is a field using the poly MDI as a raw material (such as a binder), or any field where a polyurethane resin obtained using the poly MDI as a raw material is used ( This is useful when low coloration is required in foams, paints, adhesives, sealants, elastomers, and the like.

Claims (3)

A phosgenation reaction step of reacting polymethylene polyphenyl polyamine with phosgene in the presence of an inert solvent;
A solvent removal step of removing the inert solvent from the reaction solution obtained in the phosgenation reaction step until the concentration thereof is 5 to 35% by mass;
A hydrogen chloride introduction step of introducing hydrogen chloride into the reaction solution after the solvent removal step,
A method for producing a methylene-bridged polyphenyl polyisocyanate, characterized in that a reaction liquid temperature is maintained in a range of 60 ° C. to 130 ° C. in the phosgenation reaction step, the solvent removal step, and the hydrogen chloride introduction step. 2. The methylene bridge according to claim 1, wherein, in the solvent removal step, the inert solvent is removed from the reaction solution obtained in the phosgenation reaction step until the concentration thereof becomes 5 to 20% by mass. A method for producing polyphenyl polyisocyanate. 3. The methylene-crosslinked poly according to claim 1, wherein in the solvent removal step, the inert solvent is removed from the reaction solution obtained in the phosgenation reaction step by reducing the pressure to normal pressure or lower. A method for producing phenyl polyisocyanate.