JP5380931B2 - Method for producing methylene cross-linked polyphenyl polyisocyanate - Google Patents

Description

  The present invention relates to a method for producing a methylene-bridged 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. Thus, the reason why the hue of poly-MDI deteriorates due to 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 react with the urea phosgenated product (color-inducing substance). It is thought to change (or generate) .

  By the way, conventionally, it is known that 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 hue deterioration of poly MDI 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.

  On the other hand, there is also known a method for improving the hue of poly-MDI by not introducing hydrogen chloride into the reaction solution, but instead suppressing the solution temperature in the phosgenation reaction or removal of residual phosgene to a relatively low temperature. It has been. For example, Patent Document 2 discloses a method in which a phosgenation reaction is performed at 120 ° C. or less, and then residual phosgene is removed from the reaction solution at 100 to 120 ° C.

JP 7-233136 A JP-A-7-316122

  Although it is certainly possible to improve the hue of poly-MDI by introducing hydrogen chloride into the reaction solution after the phosgenation reaction as in the method described in Patent Document 1, a process for introducing hydrogen chloride is possible. Is necessary separately, leading to increased costs. In addition, a dedicated device for introducing hydrogen chloride such as a pump for handling hydrogen chloride is required, and the use of hydrogen chloride tends to cause corrosion of plant equipment. From the above viewpoint, it is desirable to improve the hue of poly MDI without introducing hydrogen chloride.

  On the other hand, in the method described in Patent Document 2, although the temperature is kept low in the phosgenation reaction step and the residual phosgene removal step, the by-produced urea compound and the residual phosgene coexist at 100 ° C. or higher. become. However, as a result of the study by the present inventors, under such temperature conditions, the reaction between the by-produced urea compound and the residual phosgene actually proceeds to produce a color-inducing substance, and hue improvement is not achieved. It turned out to be enough.

  An object of the present invention is to provide a method for producing a methylene-bridged polyphenyl polyisocyanate which can obtain a high hue improving effect without introducing hydrogen chloride from the outside.

The method for producing a methylene-bridged polyphenylene polyisocyanate according to the present invention is a method for producing a methylene-bridged polyphenylene polyisocyanate by reacting polymethylene polyphenylpolyamine with phosgene in the presence of an inert solvent at a temperature of 50 ° C. to 93 ° C. A phosgenation reaction step for reacting polyphenylpolyamine and phosgene, and a removal step for removing residual phosgene from 50 ° C. to 93 ° C. from the reaction solution obtained in the phosgenation reaction step. It is.

  In the method for producing a methylene-crosslinked polyphenylene polyisocyanate of the present invention, in the phosgenation reaction step, polymethylene polyphenylpolyamine and phosgene are reacted at 60 ° C. to 80 ° C., and in the removal step, 60 ° C. to 80 ° C. It is preferred to remove residual phosgene at 0 ° C.

  In the method for producing a methylene-bridged polyphenylene polyisocyanate according to the present invention, it is preferable to remove residual phosgene in the removal step under a pressure condition lower than that in the phosgenation reaction step.

  In the method for producing methylene-bridged polyphenylene polyisocyanate of the present invention, in the phosgenation reaction step, polymethylene polyphenyl polyamine and phosgene are reacted under a pressure condition of 50 kPa · G to 250 kPa · G, and in the removal step, The residual phosgene is preferably removed by reducing the pressure to normal pressure or lower. In the present application, “normal pressure” means a normal pressure on the earth, that is, 1 atmosphere (0 kPa · G).

  In the method for producing a methylene-bridged polyphenylene polyisocyanate of the present invention, it is preferable that residual phosgene is removed from the reaction solution by introducing an inert gas into the reaction solution in the removing step.

  In the method for producing a methylene-bridged polyphenylene polyisocyanate according to the present invention, it is preferable to remove residual phosgene from the reaction solution by reducing the pressure to normal pressure or lower in the removing step, and from −95 kPa · G to −50 kPa · G. It is more preferable to remove the residual phosgene from the reaction solution by reducing the pressure to a minimum.

According to the present invention, 50 ° C. After reacting polymethylene polyphenyl polyamines with phosgene at ~ 93 ° C., to remove residual phosgene at 50 ° C. ~ 93 ° C. from the resulting reaction solution. That is, in the phosgenation reaction step and the residual phosgene removal step, it is considered that the side reaction between the urea compound produced as a by-product in the phosgenation reaction and the residual phosgene proceeds greatly by setting the temperature of the reaction solution to 93 ° C. or lower. Both will not coexist at a temperature of 100 ° C. or higher. Thereby, the hue of poly MDI can be sufficiently improved without introducing hydrogen chloride into the reaction solution.

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

  In the method for producing a methylene-crosslinked polyphenylene polyisocyanate according to the present embodiment, after reacting polymethylene polyphenylpolyamine and phosgene (phosgenation reaction step), residual phosgene is removed from the reaction solution after the phosgenation reaction (removal 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 (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 carried out 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 (Chemical 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

  A 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.

  Here, the temperature (reaction liquid temperature) when causing the phosgenation reaction is preferably 50 ° C to 100 ° C, more preferably 60 ° C to 80 ° C.

  If the temperature exceeds 100 ° C., it is not possible to sufficiently suppress the generation of a color inducing substance that causes hue deterioration. The reason is presumed as follows.

In the phosgenation reaction step, it is considered that the side reaction represented by the following formula (5) proceeds in addition to the main reactions of the above formulas (1) to (4).
(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, when the temperature of the reaction liquid exceeds 100 ° C. with phosgene (COCl ₂ ) remaining in the reaction liquid, the side reaction further proceeds. That is, the urea compound (R-NHCONH-R) reacts with the remaining phosgene to produce a urea phosgenated product that is a coloring inducer.

  That is, a coloring inducer is generated when the following two conditions are satisfied: 1) phosgene remains in the reaction solution, and 2) the reaction solution temperature exceeds 100 ° C. Here, in the phosgenation reaction step, since phosgene is necessary to advance the main reaction (particularly, the above formulas (1) and (3)), it is necessary to make phosgene present in the reaction solution. Yes, the above condition 1) is necessarily satisfied. Therefore, the reaction solution temperature is preferably 100 ° C. or lower so as not to satisfy the condition 2).

  In addition, as mentioned above, as described above, as a conventional technique (for example, Patent Document 1), a technique for suppressing coloring by introducing hydrogen chloride into a reaction solution during a phosgenation reaction is known. Yes. By adding hydrogen chloride to a urea phosgenated product (color-inducing substance) obtained by the reaction of a urea compound and phosgene, the urea phosgenated product can be changed to another material that is harmless with respect to coloring. Because. Thus, when hydrogen chloride is added, there is no problem even if a urea phosgenation product is formed. Therefore, it is not necessary to suppress the reaction between the urea compound and phosgene by lowering the temperature to 100 ° C. or lower. On the other hand, in this embodiment, instead of not introducing hydrogen chloride from the outside, the reaction between the urea compound and phosgene is suppressed by keeping the temperature low.

  On the other hand, if the temperature of the reaction solution is low, it is advantageous in terms of suppressing the formation of coloring inducers, but if the temperature is too low, the rate of progress of the phosgenation reaction becomes very slow, which is not industrially suitable. is there. Therefore, the temperature of the phosgenation reaction step is preferably 50 ° C. or higher in consideration of a realistic reaction rate that can be applied to an actual production step.

  In addition, the urea compound by-produced in the above formula (5) is a substance that does not affect the hue itself, and as long as it remains as a urea compound (unless it reacts with phosgene to form a urea phosgenated product), Harmless with respect to hue. However, in producing polyMDI, it remains an impurity, and it is preferable to suppress the reaction of the formula (5) as much as possible in order to reduce the generation of urea compounds as impurities. Here, it is known that the reaction of the formula (5) hardly proceeds under a pressurized condition. Therefore, in this phosgenation reaction step, it is preferable to advance the reaction between polyamine and phosgene under a pressure of 50 kPa · G to 250 kPa · G.

(Removal process)
In the reaction solution obtained in the phosgenation reaction step, unreacted phosgene usually remains. Therefore, even if the generation of the color-inducing substance can be suppressed in the above-described phosgenation reaction step, the reaction proceeds when the heat treatment is performed by moving to a subsequent step (vacuum distillation or the like) with the unreacted phosgene remaining. The urea compound in the liquid reacts with the remaining phosgene (formula (5)), and a color-inducing substance is generated. Therefore, in this removal step, unreacted residual phosgene is removed from the reaction solution.

  Residual phosgene can be removed from the reaction solution by introducing an inert gas that does not react with the reaction solution, such as nitrogen, helium, or argon, or by reducing the atmospheric pressure to below the normal pressure. A method of vaporizing phosgene can be employed. Furthermore, you may combine both introduction of an inert gas, and pressure reduction.

  Further, the temperature of the reaction solution during this removal step is preferably 50 ° C. to 100 ° C., more preferably 60 ° C. to 80 ° C., similarly to the phosgenation reaction step.

  The reason for setting the temperature to 100 ° C. or lower is to suppress the formation of a color-inducing substance as in the phosgenation reaction step. That is, in order to suppress as much as possible that the urea compound produced | generated by reaction of the said Formula (5) reacts with residual phosgene, it is preferable to make reaction liquid temperature into 100 degrees C or less.

  On the other hand, if the temperature of the reaction solution is too low, phosgene in the reaction solution becomes difficult to vaporize and phosgene cannot be effectively removed. From this viewpoint, the reaction solution temperature in the removal step is preferably 50 ° C. or higher.

Further, as described above, when a side reaction phosgenation reaction in terms of (Equation (5)) inhibition was performed under pressurized conditions, and Oite reduced to the removal step, from the phosgenation step It is preferable to remove residual phosgene under low pressure conditions. Specifically, it is preferable to reduce the pressure to a pressure equal to or lower than normal pressure.

Of the main reactions (1) to (4) described in the phosgenation reaction step, the only reactions that actually require phosgene (COCl ₂ ) are the formulas (1) and (3). Therefore, first, the phosgenation reaction is carried out under pressure to cause the reactions of formulas (1) to (3) while suppressing the formation of urea compounds (the reaction of formula (4) also proceeds to some extent). Thereafter, the pressure is reduced when the reaction of the formula (3) requiring phosgene is almost completed, and the reaction of the formula (4) is advanced at the same time while removing the remaining phosgene under the low pressure condition.

  Thus, when residual phosgene is removed under low pressure conditions, vaporization of phosgene in the reaction solution is promoted, so that residual phosgene can be removed more efficiently.

  Further, the formula (4) (R—NHCOCl → R—NCO + HCl), which is a reaction that generates isocyanate, is also a reaction that generates hydrogen chloride (HCl). On the other hand, as the atmospheric pressure is lower, hydrogen chloride contained in the reaction solution is more easily vaporized, and the hydrogen chloride in the reaction solution tends to decrease. Therefore, by reducing the pressure in the removing step, the hydrogen chloride in the reaction solution is reduced, and the reaction of the formula (4) that generates hydrogen chloride proceeds. As a result, the generation of isocyanate (NHCOCl → NCO) is promoted. The Also from this viewpoint, it is preferable to reduce the pressure in the removing step and remove the residual phosgene under low pressure conditions.

  A poly MDI is obtained as described above. It is also possible to remove unreacted residual phosgene from the reaction solution and then concentrate the reaction solution to separate diphenylmethane diisocyanate (MDI) to obtain poly MDI. In this stage, since the residual phosgene has already been removed, even if the reaction solution is heated (for example, 200 ° C. or higher), a color inducing substance is not generated.

As described above, according to the present embodiment , after reacting polymethylene polyphenyl polyamine and phosgene at 50 ° C. to 100 ° C., residual phosgene is removed from the reaction solution at 50 ° C. to 100 ° C. That is, in the phosgenation reaction step and the residual phosgene removal step, it is considered that the side reaction between the urea compound produced as a by-product in the phosgenation reaction and the residual phosgene proceeds greatly by setting the temperature of the reaction solution to 100 ° C. or less. Both will not coexist at temperatures above ℃. This makes it possible to improve the hue sufficiently without introducing hydrogen chloride into the reaction solution.

  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 description, “%” means “mass%” unless otherwise specified.

  In the following Examples and Comparative Examples, as poly MDA, amine group concentration: 9.5 mol / kg, 2,2 ′ isomer and 2,4 ′ isomer: 14.3 mass%, 4,4 ′ isomer: 53.4 A mass%, trinuclear body: 32 mass% was used.

<Examples 1-3>
In Examples 1 to 3, poly MDI was produced through the following steps 1) to 5), and the respective hues were measured.
1) 700 g of chlorobenzene was charged into a 3 L pressurized reaction vessel equipped with a heat exchanger, and 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 monochlorobenzene solution of poly MDA adjusted to 30 ° C. (poly MDA concentration 10%) was charged all at once in the container, The mixture was stirred.

3) Immediately after the mixing, the mixture was raised to a predetermined reaction temperature, and this reaction temperature was maintained for 90 minutes to carry out a phosgenation reaction. The reaction temperature was 65 ° C. in Example 1, 78 ° C. in Example 2, and 93 ° C. in Example 3.

4) Next, the pressure in the container was lowered to normal pressure (0 kPa · G), and while maintaining the reaction temperature, nitrogen was passed at 3 L / min to remove residual phosgene over 70 minutes. The nitrogen aeration time is set so that the amount of phosgene in the reaction solution has a predetermined concentration (800 ppm or less, more preferably 300 ppm or less).

5) After removal of phosgene, monochlorobenzene was distilled off at 130 ° C./20 torr. Further, the obtained concentrated liquid was kept at 220 ° C. for 10 minutes under nitrogen flow and immediately cooled to 60 ° C. The solution color of MDI was measured visually.

<Examples 4 and 5>
In Examples 4 and 5, after the phosgenation reaction, the reaction temperature (65 ° C. in Example 4, 78 ° C. in Example 5) and the reaction pressure (120 kPa · G) are maintained (that is, the inside of the container is reduced to normal pressure). The remaining phosgene was removed by aeration of nitrogen at 3 L / min. However, in these Examples 4 and 5, it was necessary to ventilate nitrogen for 190 minutes in order to remove the phosgene remaining in the solution to a concentration equal to or less than that in Examples 1 to 3 described above. About other conditions, it is the same as the said Examples 1-3.

<Comparative Examples 1-4>
In Comparative Examples 1 to 4, the temperature during the phosgenation reaction and the temperature during the subsequent removal of residual phosgene were different from those of Examples 1 to 3, respectively. Specifically, the phosgenation reaction temperature was 78 ° C. in Comparative Example 1, 105 ° C. in Comparative Example 2, 115 ° C. in Comparative Example 3, and 115 ° C. in Comparative Example 4. The temperature at the time of phosgene removal was 115 ° C. in Comparative Example 1, 105 ° C. in Comparative Example 2, 115 ° C. in Comparative Example 3, and 78 ° C. in Comparative Example 4. About other conditions, it is the same as the said Examples 1-3.

<Solution color measurement method>
In a 450 ml colorless transparent bottle, 2 g of the sample obtained in each of Examples 1 to 5 and Comparative Examples 1 to 4 and 400 ml of acetone were added and dissolved, and the solution color was visually measured at 23 ° C. The value is indicated by APHA (Hazen unit color number).

<Verification>
Table 1 shows a summary of the phosgenation reaction conditions and phosgene removal conditions and the hues of the obtained poly-MDI solutions for each of Examples 1 to 5 and Comparative Examples 1 to 4.

  As shown in Table 1, in Examples 1 to 5 in which both the phosgenation reaction and phosgene removal are performed at a temperature of 100 ° C. or lower, the solution temperature is 100 ° C. to 120 ° C. in one or both of the phosgenation reaction and residual phosgene removal. It can be seen that the hue is greatly improved as compared with Comparative Examples 1 to 4.

  Further, in Examples 1, 2, 4, and 5 in which the phosgenation reaction temperature and the treatment temperature at the time of phosgene removal were in the range of 60 ° C. to 80 ° C., the hue was higher than in Example 3 where the temperature was higher than these. It turns out that it is improving further. The lower the hue, the better the color of a molded article such as polyurethane foam using the MDI, and therefore the phosgenation reaction temperature and the phosgene removal temperature are more preferably 60 ° C to 80 ° C.

  Examples 4 and 5 differ from Examples 1 and 2 in that the pressure is not reduced to normal pressure during phosgene removal, but the phosgenation reaction temperature and the treatment temperature during phosgene removal are 60 ° C to 80 ° C. The hue of the obtained poly MDI is about the same as in Examples 1 and 2. That is, from the viewpoint of obtaining a poly MDI having a good hue, pressure reduction during phosgene removal is not essential. However, as described above, in Examples 4 and 5 in which the pressure is not reduced during phosgene removal, phosgene cannot be efficiently removed, and the time required for removing the residual phosgene becomes long. Therefore, from the viewpoint of shortening the processing time, it is preferable to reduce the pressure when removing phosgene as in Examples 1 and 2.

  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 (6)

In a process for producing a methylene crosslinked polyphenylene polyisocyanate by reacting polymethylene polyphenyl polyamine with phosgene in the presence of an inert solvent,
A phosgenation reaction step of reacting polymethylene polyphenyl polyamine and phosgene at 50 ° C. to 93 ° C .;
A removal step of removing residual phosgene from 50 ° C. to 93 ° C. from the reaction solution obtained in the phosgenation reaction step;
A method for producing a methylene-bridged polyphenylene polyisocyanate, comprising: In the phosgenation reaction step, polymethylene polyphenyl polyamine and phosgene are reacted at 60 ° C. to 80 ° C.,
And in the said removal process, residual phosgene is removed at 60 to 80 degreeC, The manufacturing method of the methylene bridge | crosslinking polyphenylene polyisocyanate of Claim 1 characterized by the above-mentioned.   The method for producing a methylene-bridged polyphenylene polyisocyanate according to claim 1 or 2, wherein in the removing step, residual phosgene is removed under a pressure condition lower than that in the phosgenation reaction step. In the phosgenation reaction step, polymethylene polyphenyl polyamine and phosgene are reacted under a pressure condition of 50 kPa · G to 250 kPa · G,
4. The method for producing a methylene-bridged polyphenylene polyisocyanate according to claim 3, wherein in the removing step, the residual phosgene is removed by reducing the pressure to normal pressure or lower.   The methylene-bridged polyphenylene polyisocyanate according to any one of claims 1 to 4, wherein, in the removing step, residual phosgene is removed from the reaction solution by introducing an inert gas into the reaction solution. Method.   The method for producing a methylene-bridged polyphenylene polyisocyanate according to any one of claims 1 to 5, wherein in the removing step, residual phosgene is removed from the reaction solution by reducing the pressure to normal pressure or lower.