EP2772528B1 - process for the removal of an isocyanate-based residue - Google Patents

Description

The present invention is a process for removing an isocyanate-based residue from a substrate.

In particular, in the production of isocyanates, isocyanate-containing prepolymers, polyurethanes or polyureas can lead to the formation of deposits in production plants. Thus, solid oligomeric and / or polymeric residues often form based on isocyanates, which adhere to walls of reaction vessels and pipelines. These residues must be removed on a regular basis to prevent deterioration of quality and safety during further production.

In principle, various measures can be taken to remove isocyanate-based residues from a substrate. On the one hand, mechanical removal is possible. In this case, for example, water or a water-powder mixture can be used to remove the residue abrasive from the substrate. However, it is disadvantageous that such methods are very complicated if a complete cleaning is to take place and additionally damage to the substrate can not be completely prevented. Alternatively, solvents can be used which dissolve the residues either physically or chemically. By physical dissolution is meant a process in which the residue is detached from the substrate and at least partially brought into solution, without causing any chemical reactions with the solvent in the residue itself. That in this case, no chemical bonds are made or broken. In chemical dissolution, however, reactive solvents are used which are capable of reacting with the residue. In the process, chemical bonds are broken in the residue, so that smaller molecules are formed from the oligomeric or polymeric structures, which then in turn go into solution physically.

When using physically or chemically acting solvents for the purification of production facilities, various aspects have to be taken into account: An essential point is the cleaning effect as such, ie the question in which time a residue can be completely removed from a substrate under defined conditions. However, it is also important whether the solvent used is questionable or harmless with regard to occupational safety and hygiene. So should be dispensed as far as possible harmful to health solvents. Nor is the use of substances that are highly flammable or within wide limits with air explosive mixtures form. It is also important that the solvents do not damage the production facilities, remaining residues do not disturb the further production and any residues that may get into the product do not disturb its quality. Finally, because of the large volumes required, it is also relevant whether the solvent can be produced industrially, is available at a low price and can be reused several times after purification.

Basically it has been shown that the exclusive use of physically acting solvents with regard to the cleaning effect leads to unsatisfactory results, since so the residues can not be removed sufficiently in an economically feasible time. Therefore, chemical solvents are used in most cases today.

Various solvent mixtures have been described in the prior art, with which polymeric residues of substrates can be removed. For example, in the JP 04-154900 discloses a process in which solid acrylonitrile-based copolymer residues are detached from a reactor wall with mixtures of an apolar solvent (N, N-dimethylformamide, dimethylsulfoxide), a hydroxyamine (monoethanolamine, monoisopropanolamine), or a diol (ethylene glycol) and sodium hydroxide. The removal of an isocyanate-based residue from a substrate is not described in this document. In addition, substances containing N, N-dimethylformamide and dimethylsulfoxide are used here, which are of health concern. Thus, contact with N, N-dimethylformamide can lead to liver damage. In addition, it is classified as a CMR substance. Concentrated dimethyl sulphoxide in turn has cytotoxic properties and, in addition, can hardly be worked up by distillation, since it begins to decompose thermally at its normal boiling point of 189 ° C., which can even take place explosively.

From the US 5,782,989 In turn, a process is known which allows residues of a vinyl polymer to be removed from a substrate. In this case, a mixture is used which consists essentially of acetone and additionally contains a further polar organic solvent having one or more hydroxyl or amino groups (propylene glycol) and a strong base (sodium hydroxide). Also, this prior art document is unrelated to the removal of an isocyanate-based residue from a substrate. In addition, the acetone contained in the mixture as a main component is highly flammable and forms an explosive mixture with air in wide limits.

The DD 280 661 A3 discloses, finally, a process for purifying reaction vessels in which a residue of an ester group-containing polymer is removed from a substrate. The method primarily uses monoethanolamine as a cleaning solution. It is also described that the mixtures of monoethanolamine with diethanolamine, ethanolamine with propylene glycol and sec-butanol solution with monoethanolamine can be used for purification.

• in kurzer Zeit eine hohe Reinigungswirkung erzielt wird,
• das Substrat möglichst wenig angegriffen wird,
• Stoffe eingesetzt werden, die mit Hinblick auf Produktqualität, Arbeitssicherheit und -hygiene unbedenklich sind,
• Stoffe eingesetzt werden, die weder leicht entzündlich sind noch in breiten Grenzen mit Luft explosive Gemische bilden,
• Stoffe eingesetzt werden, die großtechnisch herstellbar und zu einem niedrigen Preis verfügbar sind und nach einer Aufreinigung mehrfach verwendet werden können.

It is an object of the present invention to provide a process for removing an isocyanate-based residue from a substrate, in which

• a high cleaning effect is achieved in a short time,
• the substrate is attacked as little as possible,
• Substances are used that are harmless with regard to product quality, occupational safety and hygiene,
• Substances that are neither flammable nor form explosive mixtures with air within wide limits,
• Substances are used which are industrially produced and available at a low price and can be used several times after a purification.

This object is achieved according to the invention by a process in which the residue is dissolved with a mixture comprising a polyol according to claim 1, an inorganic base and an amine from the substrate.

It has surprisingly been found that isocyanate-based residues can be dissolved quickly, easily, economically, without affecting the product, occupational safety and hygiene and without damaging the substrate when using the special mixture comprising at least the three components according to the invention.

Isocyanate-based residues within the meaning of the invention are basically all residues which are formed by reaction of isocyanates with themselves or other compounds. Examples are oligomers of isocyanates, isocyanate-containing prepolymers, polyurethanes or polyureas. The isocyanate-based residues may in particular have a polymeric structure.

Substrates according to the invention are all surfaces of solid substances. Examples are in particular reaction vessels such as reactors or pipelines. The substrates may consist in particular of metals or metal alloys.

According to a first preferred embodiment of the invention it is provided that the mixture consists of 10 to 50, more preferably 15 to 35 and particularly preferably 20 to 30 weight percent of the amine.

Also preferred is when the amine is a primary amine or a secondary one. However, especially preferred is when the amine is a primary amine.

The amine may preferably also have at least one hydroxyl group. In this case, it is particularly preferred if the amine is monoethanolamine. When using the latter compound, a particularly high cleaning effect can be achieved.

A particularly good cleaning effect is given if the polyol according to claim 1 has two hydroxyl groups. This effect is exacerbated when the at least two hydroxyl groups are attached to adjacent carbon atoms. In the latter case, it is again very particularly preferred when the hydroxyl groups are terminally bonded.

It has been shown that with increasing chain length of the hydrocarbon radical particularly good cleaning effects can be achieved.

Very particularly good cleaning effects are also achieved when the polyol is selected from the group of propanediol, butanediol, pentanediol, hexanediol. In this case, it is further preferred if the polyol is a compound selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 2,3-butanediol, 1,2-hexanediol. Due to its good cleaning effect, the large-scale availability, the good Distillability and the low price of 1,2-propanediol is again the most preferred of this group.

According to a further preferred embodiment of the process according to the invention, it is provided that the mixture consists of 40.00 to 89.99, more preferably 60.00 to 84.90 and particularly preferably 68.00 to 79.50 percent by weight of the polyol.

In particular, the inorganic base may be an alkali hydroxide, an alkaline earth hydroxide or ammonium hydroxide. The inorganic base is preferably selected from the group LiOH, NaOH, KOH and particularly preferably comprises or consists of KOH.

The mixture may consist of 0.01 to 10, preferably 0.1 to 5 and more preferably 0.5 to 2.0 weight percent of the inorganic base.

A particularly good cleaning effect can also be achieved if a mixture is used which comprises or consists of a polyol as polyol, an alkali hydroxide as an inorganic base and a monohydroxyamine as the amine. It is particularly preferred here if the diol is 1,2-propanediol, the base is KOH and at the same time the monohydroxyamine is monoethanolamine. Most preferably, a mixture comprising 70 to 80% by weight of 1,2-propanediol, 0.5 to 3% by weight of KOH and 15 to 30% by weight of monoethanolamine is used, the amounts being selected to complement 100% by weight.

It is also particularly preferred if the mixture contains no toxic substances and no CMR substances.

A particularly good cleaning effect is achieved even when the mixture has a temperature of 100 to 250 ° C and preferably from 120 to 180 ° C.

It has also been found that the process according to the invention is particularly suitable for removing a residue which comprises or consists of a polyurethane polymer.

According to a further preferred embodiment of the invention, it is provided that a mixture is used which consists of the polyol, the inorganic base and the amine, ie a mixture which contains no further constituents except for customary impurities.

It is also advantageous if the mixture in which the residue has already been dissolved is applied by distillation in a further step. This allows a reuse of the mixture in a further dissolution step.

The invention will be explained in more detail below with reference to examples.

The following abbreviations were used: CMR: carcinogenic, mutagenic, reprotoxic η: cleaning effect DMF: N, N-dimethylformamide MEA: Monoethanolamine MEG: Monoethylene glycol MPA: 1-methoxy-2-propyl KOH: potassium hydroxide NaOH: sodium hydroxide t: Time, duration of experiment

Determination of the cleaning effect:

To determine the cleaning effect, first samples were prepared in which a solid, strongly adhering isocyanate-based product was applied to aluminum dishes. For this purpose, in each case one of the substances listed in Table 1, each of which was a product of Bayer MaterialScience AG, was applied to a previously balanced aluminum dish. Subsequently, the aluminum dish with the substance present on it was dried in a drying oven until a layer of a solid residue had formed, the weight of which no longer changed even on further drying. The process of coating and drying in layers was repeated several times if necessary. Since Desmocoll 540 is a solid granulate Here, the entire required amount of sample was applied, melted and baked at once. The weight of the residue was then determined last by weighing the aluminum dish and subtracting the weight of the aluminum dish. The residues each had a weight of about 1-10g. Table 1 product description Impranil DLU Aqueous aliphatic polycarbonate ester polyether polyurethane dispersion Desmocoll 540 Largely linear hydroxyl polyurethane (granules) Dispercoll U 54 Anionic, high molecular weight aqueous polyurethane dispersion

The cleaning action would then be with the help of the device FIG. 1 checked.

The apparatus comprises a reaction vessel 1, a sample 2, an oil bath 3, a stirring motor 4, a temperature sensor 5 and a condenser 6. The reaction vessel 1 contains the sample 2, which in turn is connected to the stirring motor 4. Furthermore, the temperature sensor 5 is arranged in the reaction vessel 1. The condenser 6 is in turn connected to an opening in the reaction vessel 1, not shown. The reaction vessel is finally partially immersed in the oil bath 3 and filled up to the line marked with a triangle with the respectively to be examined solvent mixture (about 2 liters, in the diol-monoethanol mixtures, the weight ratio of diol monoethanolamine was always 3: 1) , Not shown in the figure is a heating and control unit which is designed to keep the oil bath 3, taking into account the temperature data of the probe 5 at a defined temperature.

To determine the cleaning effect, the respective solvent mixture was first introduced into the reaction vessel 1 and then brought to a temperature of 140 ° C. with the aid of the heating and control unit, the oil bath 3 and the temperature sensor 5 and kept constant there. Any solvent mixture evaporating was liquefied by the condenser 6 and thus returned to the reaction vessel 1. The respective sample 2 was then connected to the stirring motor 4 and introduced into the reaction vessel 1, that the sample 2 was completely covered with the solvent mixture. The sample was rotated by means of the stirrer at a constant speed of about 12 / min in the solvent mixture. Sample 2 remained in reaction vessel 1 for a specified time (measurement points in Figures 1-6).

At the end of the set time, sample 2 was removed from reaction vessel 1 and briefly immersed in a methyl ether ketone (MEK) bath to remove residual solvent mixture. After a 30-minute drying in the heating cabinet (105 ° C), the weight of the sample was carried out.

The cleaning effect was then determined according to the following formula: $$\mathrm{\eta }=\left(\frac{{\mathrm{m}}_{\mathrm{weighing}}-{\mathrm{m}}_{\mathrm{Final\; weight}}}{{\mathrm{m}}_{\mathrm{weighing}}}\right)\cdot \mathrm{100}\%$$

In the formula, m _{sample weight} for the weight of the specimen is facing the solution trial and m _{Final weight} for the weight after the test solution.

To facilitate the evaluation, the measurement points were compensated by second- or third-degree regressions, the illustrations only showing experiments in which a cleaning effect was detectable within a time of 300 minutes.

The Figure 1 to 3 show the comparison of the cleaning action of solvents or solvent mixtures compared to dimethylformamide (DMF).

When using 1,2-propanediol without the addition of monoethanolamine (MEA) or potassium hydroxide (KOH), no complete cleaning action is observed after 300 minutes.

From Figures 1 to 3 it can be seen that the mixtures with 1-, 2-butanediol have a better cleaning effect than the mixtures with 1, 2-propanediol.

It can be seen that the addition of 1% KOH causes a significant improvement in the cleaning effect compared to the pure substances. It also shows that the mixture of 1,2-propanediol, MEA and KOH has the best cleaning effect on all samples.

KOH can not be worked up thermally and thus represents a consumable. Therefore, it was examined what influence a lower concentration of KOH in the solvent mixture has on the cleaning effect. For this purpose, the KOH concentration was reduced to 0.1%. Furthermore, it should be investigated whether Potassium hydroxide can also be replaced by sodium hydroxide (NaOH), without any loss of cleaning effect.

The results shown in Figures 4 to 6 clearly show that KOH shows a significantly better cleaning action compared to NaOH. Furthermore, it is apparent from the figures that even the addition of 0.1% KOH to 1-, 2-propanediol-MEA mixtures leads to a significantly better cleaning effect. In the case of Dispercoll U54 and Impranil DLU, the addition of 0.1% KOH leads to a comparable improvement in the cleaning effect as that of the addition of 1% NaOH.

Overall, it has been found that with a mixture of 1,2-propanediol and MEA containing 1 weight percent KOH, the best cleaning effect can be achieved.

With the help of the regression equations shown in Tables 2 and 3, the time was determined after each 95% of the sample were solved. The values shown in Table 4 are plotted in relation to the values of DMF both absolute and relative. In addition, the various cleaning agents are sorted by their cleaning effect from good to bad. The basis for this is the cleaning effect on samples of Dispercoll U54. Table 2: Regression equations for Desmocoll 540 and Dispercoll U 54 Dispercoll U 54 Desmocoll 540 DMF η = 0.0063 * t ^ 2 + 0.5268 * t + 0.5152 η = 0.0025 * t ^ 2 + 0.5358 * t - 3.1791 1-methoxy-2-propyl η = -0.0006 * t ^ 2 + 0.4787 * t - 3E-14 η = 9E-05 * t ^ 2 + 0.328 * t + 3E-14 MEG - - 1,2-propanediol - - MEA η = -0.0397 * t ^ ² + 4.0453 * t - 9E-14 η = -0.161 * t ^ ² + 2.6326 * t - 3E-14 1,2-propanediol + MEA η = -0.0184 * t ^ 2 + 2.7677 * t - 6E-14 η = -0.0024 * t ^ 2 + 1.2866 * t + 0.2125 1,2-propanediol + 1% KOH η = 0.0008 * t ^ 3 - 0.1101 * t ^ 2 + 5.5154 * t + 1E-11 η = 0.0002 * t ^ 3 - 0.0445 * t ^ 2 + 3.4884 * t + 0.2364 1,2-propanediol + MEA + 0.1% KOH η = -0.0483 * t ^ 2 + 4.5641 * t - 1E-13 η = -0.0145 * t ^ 2 + 2.3972 * t - 0.0328 1,2-propanediol + MEA + 1% KOH η = -0.1707 * t ^ 2 + 8.4543 * t + 3E-14 η = -0.062 * t ^ 2 + 5.1889 * t 1,2-propanediol + MEA + 1% NaOH η = -0.0465 * t ^ 2 + 4.4482 * t - 9E-14 η = -0.0349 * t ^ 2 + 3.7754 * t MEG + MEA η = -0.014 * t ^ 2 + 2.5026 * t - 6E-14 η = 0.0002 * t ^ 2 + 0.8355 * t - 3.9351 1,2-butanediol + MEA η = -0.0341 * t ^ 2 + 3.7114 * t - 6E-14 η = -0.0061 * t ^ 2 + 1.694 * t - 1.7749 1,2-butanediol + 1% KOH η = -0.105 * t ^ 2 + 6.3451 * t - 3E-14 η = 0.0004 * t ^ 3 - 0.0691 * t ^ 2 + 4.4135 * t + 0.7561 Impranil DLU DMF η = 0.0007 * t ^ 2 + 0.7322 * t - 1.6531 1 -methoxy-2-propyl acetate η = 0.0003 * t ^ 2 + 0.181 * t - 3E-14 MEG - 1,2-propanediol - MEA η = 0.023 * t ^ 2 + 1.4792 * t 1,2-propanediol + MEA η = -0.0078 * t ^ 2 + 1.7985 * t - 0.6988 1,2-propanediol + 1% KOH η = -0.0024 * t ^ 2 + 1.2866 * t + 0.2125 1,2-propanediol + MEA + 0.1% KOH η = -0.0109 * t ^ 2 + 2.0939 * t - 0.1147 1,2-propanediol + MEA + 1% KOH η = 7E-05 * t ^ 3 - 0.0249 * t ^ 2 + 2.7888 * t + 0.4546 1,2-propanediol + MEA + 1% NaOH η = -0.0134 * t ^ 2 + 2.3112 * t - 0.0375 MEG + MEA η = -0.001 * t ^ 2 + 0.931 * t - 1.3341 1,2-butanediol + MEA η = -0.0084 * t ^ 2 + 1.8686 * t + 0.0233 1,2-butanediol + 1% KOH η = -0.0049 * t ^ 2 + 1.5266 * t + 1.5153

In addition to those in the Fig. 1-6 listed solvents or solvent mixtures are shown in Table 4, the results of the cleaning effects of other solvents or solvent mixtures: MEA, monoethylene glycol (MEG), 1-methoxy-2-propyl acetate (MPA), 1-, 2-butanediol + MEA, MEG + MEA. The above-mentioned test conditions also apply to the test results listed in Table 4. Table 4: Cleaning time to achieve 95% cleaning efficiency in relation to DMF Dispercoll U 54 Δt (η = 95%) [Min] [%] 1,2-propanediol + MEA + 1% KOH 11 13 1,2-propanediol + MEA + 1% NaOH 32 36 1,2-propanediol + MEA + 0.1% KOH 32 36 1,2-butanediol + 1% KOH 27 31 MEA 37 42 1,2-butanediol + MEA 39 44 1,2-propanediol + 1% KOH 41 47 1,2-propanediol + MEA 53 60 MEG + MEA 55 63 DMF 88 100 1-methoxy-2-propyl > 300 > 305 1,2-propanediol > 300 > 305 MEG > 300 > 305

It can be seen that overall the best cleaning result was achieved with the mixture of 1-, 2-propanediol + MEA + 1% KOH. Pure solvents (DMF, MEG, MEA, MPA, diol) and mixtures of diol + MEA as comparative experiments have a poorer cleaning action. The mixtures of 1,2-butanediol with MEA or with KOH in turn have a better cleaning action than the mixtures with 1,2-propanediol. The mixture of 1,2-propanediol with MEA has a better cleaning effect than the mixture of MEG and MEA.

Claims (12)

1. Process for removing an isocyanate-based residue from a substrate, wherein the residue is dissolved from the substrate using a mixture comprising a polyol, an inorganic base and an amine, where the polyol is selected from the group consisting of propanediol, butanediol, pentanediol and hexanediol and the two hydroxyl groups of this polyol are bound to adjacent carbon atoms.
2. Process according to Claim 1, characterized in that the mixture comprises from 10 to 50% by weight, preferably from 15 to 35% by weight and particularly preferably from 20 to 30% by weight, of the amine.
3. Process according to Claim 1 or 2, characterized in that the amine is a primary amine or a secondary amine and preferably a primary amine.
4. Process according to any of Claims 1 to 3, characterized in that the amine has at least one hydroxyl group.
5. Process according to Claim 4, characterized in that the amine is monoethanolamine.
6. Process according to any of Claims 1 to 5, characterized in that the mixture comprises from 40.00 to 89.99% by weight, preferably from 60.00 to 84.90% by weight and particularly preferably from 68.00 to 79.50% by weight, of the polyol.
7. Process according to any of Claims 1 to 6, characterized in that the inorganic base is an alkali metal hydroxide, an alkaline earth metal hydroxide or ammonium hydroxide.
8. Process according to any of Claims 1 to 7, characterized in that the inorganic base is selected from the group consisting of LiOH, NaOH, KOH and is particularly preferably KOH.
9. Process according to any of Claims 1 to 8, characterized in that the mixture comprises from 0.01 to 10% by weight, preferably from 0.1 to 5% by weight and particularly preferably from 0.5 to 2.0% by weight, of the inorganic base.
10. Process according to any of Claims 1 to 9, characterized in that the mixture does not contain any toxic substances nor any substances which are carcinogenic, mutagenic or toxic for reproduction (CMR substances).
11. Process according to any of Claims 1 to 10, characterized in that the mixture has a temperature of from 100 to 250°C and preferably from 120 to 180°C.
12. Process according to any of Claims 1 to 11, characterized in that the residue comprises or consists of a polyurethane polymer.

Images