METHOD FOR PRODUCING ISOCYANATE MIXTURES CONTAINING ISOCYANURATE GROUPS

Abstract

The invention relates to a continuous method for producing an isocyanurate-containing isocyanate mixture, in which in a step a) a mixture of a first and a second isocyanate component and an isocyanate group trimerization catalyst is provided; in a step b) the mixture obtained in step a) is reacted in a first residence time zone at an elevated temperature; in a step c), the reaction mixture obtained in step b) is further heated in a second residence time zone, optionally after adding a stopper; and in a step d), the reaction mixture obtained in step c) is cooled down in a third residence time zone by way of lowering the temperature, thus obtaining the desired isocyanurate-containing isocyanate mixture.

Claims

1. A process for preparing an isocyanurate-containing isocyanate mixture, comprising: a) continuously providing an isocyanate mixture comprising isocyanate group trimerization catalyst by mixing a first isocyanate component, a second isocyanate component different from the first isocyanate component, and an isocyanate group trimerization catalyst; b) continuously guiding the mixture provided in step a) through a first dwell zone at a temperature in the range from 50° C. to 120° C. to obtain a uretdione- and isocyanurate-containing isocyanate mixture comprising the isocyanate group trimerization catalyst; c) continuously guiding the mixture obtained in step b) through a second dwell zone at a temperature in the range from 160° C. to 220° C. to obtain an isocyanurate-containing isocyanate mixture comprising inactive isocyanate group trimerization catalyst, wherein the guiding through the second dwell zone is optionally preceded by the addition of a stopper at a temperature in the temperature range from 50° C. to 120° C.; d) continuously guiding the mixture obtained in step c) through a third dwell zone at a temperature in the range from 10° C. to 100° C. to obtain the desired isocyanurate-containing isocyanate mixture.

2. The process as claimed in claim 1, in which step a) comprises: continuously introducing the first isocyanate component, the second isocyanate component, and the isocyanate group trimerization catalyst into a mixing device and mixing the first isocyanate component the second isocyanate component introduced, and the trimerization catalyst introduced to obtain the isocyanate mixture comprising isocyanate group trimerization catalyst.

3. The process as claimed in claim 1, in which step a) comprises: a.1) continuously introducing the isocyanate group trimerization catalyst and one of the first isocyanate component and the second isocyanate component into a first mixing device and mixing the isocyanate component introduced and the isocyanate group trimerization catalyst introduced to obtain a mixture comprising the isocyanate group trimerization catalyst and one of the first isocyanate component and the second isocyanate component; and a.2) continuously introducing the mixture which is obtained in step a.1) and the isocyanate component not introduced in step a.1) into a second mixing device and mixing the resulting mixture to obtain the isocyanate mixture comprising isocyanate group trimerization catalyst.

4. The process as claimed in claim 1, in which step a) comprises: a.1) continuously introducing the first isocyanate component and the second isocyanate component into a first mixing device and mixing the isocyanate components introduced in the first mixing device to obtain an isocyanate mixture; and a.2) continuously introducing the isocyanate group trimerization catalyst and the isocyanate mixture obtained in step a.1) into a second mixing device and mixing the isocyanate mixture introduced and the isocyanate group trimerization catalyst introduced to obtain the isocyanate mixture comprising isocyanate group trimerization catalyst.

5. The process as claimed in claim 4, in which, in step a), the isocyanate mixture leaving the mixing device continuously, before being introduced into the second mixing device, is guided through a dwell zone upstream of the second mixing device.

6. The process as claimed in claim 1, in which step a) is conducted at a temperature in the range from 10° C. to <50° C.

7. The process as claimed in claim 1, in which the nature and composition of the first isocyanate component and the second isocyanate component are matched to one another in such a way that the isocyanurate-containing isocyanate mixture obtained in step d) has an NCO content in the range from 24% by mass to 32% by mass and a viscosity in the range from 50 mPa.Math.s to 40,000 mPa.Math.s.

8. The process as claimed in claim 1, in which the first isocyanate component and second isocyanate component each comprise (i) methylene diphenylene diisocyanate, (ii) a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate, (iii) tolylene diisocyanate or a (iv) mixture of (i) or (ii) with (iii).

9. The process as claimed in claim 1, in which the isocyanate group trimerization catalyst used in step a) comprises one or more of a quaternary ammonium hydroxide, an alkali metal hydroxide, an alkali metal alkoxide, a trialkylphosphine, a para-substituted pyridine, an organometallic salt, a Lewis acid and an alkali metal salt of an organic acid.

10. The process as claimed in claim 9, in which a stopper comprising an organic acid chloride is added in step c), where the organic acid chloride is used in a molar ratio of acid chloride:isocyanate group trimerization catalyst in the range from 1:3 to 1:1.

11. The process as claimed in any of claim 1, in which the isocyanate group trimerization catalyst used in step a) comprises an alkylaminoalkylphenol.

12. The process as claimed in claim 11, in which no stopper is used to inactivate the isocyanate group trimerization catalyst.

13. The process as claimed in claim 5, in which the dwell zone upstream of the second mixing device (M2) is a tubular reactor optionally containing mixing elements.

14. The process as claimed in claim 1, in which the first, second and third dwell zone each comprise a stirred tank, optionally with upstream heat exchanger, or a temperature-controllable tubular reactor optionally containing mixing elements.

15. The process as claimed in claim 1, in which the first isocyanate component and second isocyanate component are produced in a corresponding isocyanate production plant, wherein the first isocyanate component and the second isocyanate component are each taken from a product stream from the corresponding isocyanate production plant, or the first isocyanate component and the second isocyanate component are each taken from a storage or transport vessel unconnected to the corresponding isocyanate production plant.

16. The process as claimed in claim 1, in which the temperature of the isocyanurate-containing isocyanate mixture comprising inactive isocyanate group trimerization catalyst which is obtained in step c) is adjusted to the temperature in step d) at a rate of temperature change in the range from 15° C./min to 200° C./min.

Description

EXAMPLES

[0089] Materials Used [0090] “Desmodur 44M”, “44M” for short (MMDI with a composition of 98.5% 4,4′-MMDI and 1.5% 2,4′-MMDI and a viscosity at 40° C. of 4.00 mPa.Math.s; Covestro Deutschland AG, Leverkusen). [0091] “Desmodur V20”, “44 V20” for short (mixture of MMDI and PMDI with a proportion by mass of MMDI in the range from 40% to 44% and a viscosity at 40° C. of 80.0 mPa.Math.s; Covestro Deutschland AG, Leverkusen). [0092] Benzoyl chloride (99%, Aldrich, Steinheim). [0093] Tris(dimethylaminomethyl)phenol (Araldite Hardener HY 960, Huntsman Advanced Materials, Basle). [0094] Triethyl phosphate (Levagard TEP, Lanxess, Cologne).

[0095] Test Conditions [0096] Viscosity by rotary viscometer (DIN 53019-1: 2008-09). [0097] Isocyanate content (DIN EN ISO 11909: 2007-05). [0098] The uretdione content was determined by IR spectroscopy. [0099] The PIR content is calculated by the following formula:

% PIR=[(starting NCO−final NCO)/(0.5−starting NCO)].Math.100 [0100] The commencement of crystallization of the product present in a closable sample tube is determined visually in a thermostat with a temperature ramp beginning at 25° C. with a delta of −2.5 K/day.

Example 1 (Comparative Example): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Discontinuous Process with Exclusively Chemical Deactivation of the Catalyst

[0101] In a stirred and heated 10 L glass three-neck flask equipped with a reflux condenser and overhead stirrer under N2 blanketing, 3.00 kg of 44M and 2.00 kg of 44 V20 were mixed with 90.2 g of catalyst solution (8.0% by mass of tris(dimethylaminomethyl)phenol in TEP) and stirred at 80° C. and ambient pressure for 1 h. The end of the reaction was determined by determining the NCO content of the reaction mixture at intervals of 15 min. On attainment of a content of 27.5% by mass of NCO, 3.6 g of benzoyl chloride as stopper was added, and the mixture was stirred at 80° C. for a further 10 min. After cooling to room temperature, cloudiness occurred after 5 hours.

[0102] Analysis: see table 1.

Example 2 (Comparative Example): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Discontinuous Process with Thermal Catalyst Deactivation at 140° C.

[0103] The procedure was as in example 1, except that, after the trimerization at 80° C., the reaction mixture was heated up to 140° C. within 25 min and was then allowed to cool down room temperature. After it had been cooled down to room temperature, cloudiness was observed, and had increased the next day.

Example 3 (Comparative Example): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Discontinuous Process with Thermal Catalyst Deactivation at 200° C.

[0104] The procedure was as in example 1, except that, after the trimerization at 80° C., the reaction mixture was heated up to 200° C. within 34 min and was then allowed to cool down to room temperature. After it had been cooled down to room temperature, cloudiness was observed, and had increased the next day.

Example 4 (Comparative Example): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Semicontinuous Process (without Thermal Aftertreatment; without Chemical Catalyst Inactivation)

[0105] 371.3 g/h of 44M and 247.5 g/h of 44 V20 were mixed continuously in a static mixer at a temperature of 40° C. The volume flow of the departing isocyanate mixture of 44 V20 and 44M was divided. A thinner capillary was introduced into a part of the volume flow, through which the catalyst solution (8.0% by mass of tris(dimethylaminomethyl)phenol in TEP) was guided at 12.3 g/h. The exit of the capillary and of the feed tube for the isocyanate mixture that surrounded it opened into a static mixer that also functioned as heat exchanger. The three streams (two streams of isocyanate mixture and one stream of catalyst solution) met in this static mixer and were mixed at 22° C., trimerized at 80° C. with a dwell time of 45 minutes, and then collected in a collecting vessel in which the product cooled down. Product samples were taken upstream of the collecting vessel for analysis. The product had a distinct drop in NCO after a storage time of 24 h (RT) (cf. table 1) and had solidified in the collecting vessel after 7 days.

[0106] Analysis: see table 1.

Example 5 (Comparative Example): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Semicontinuous Process (without Thermal Aftertreatment; with Chemical, Irreversible Catalyst Inactivation)

[0107] The procedure was as in example 4, except that for the product samples taken upstream of the collecting vessel for analysis were admixed with 0.08% by mass (based on the mass of sample) of benzoyl chloride to deactivate the catalyst. The chemically stopped product was stable and showed slight cloudiness after cooling.

[0108] Analysis: see table 1.

Example 6 (Inventive): Preparation of an Isocyanurate-Containing MMDI/PMDI Mixture by a Continuous Process with Irreversible, Thermal Catalyst Inactivation and “Quenching”

[0109] The procedure was as in example 4, except that the trimerization at 80° C. with a dwell time of 45 min (corresponding to step b) of the process of the invention) was followed by a further continuous-flow dwell zone in which the reaction mixture from step b) was heated to 200° C. within 4 min (corresponding to step c) of the process of the invention), which was followed by a last continuous-flow dwell zone in which the reaction mixture from step c) was cooled down to ambient temperature within 4 min (corresponding to step d) of the process of the invention). The product leaving this last dwell zone was collected in a collecting vessel. Product samples were taken upstream of the collecting vessel for analysis. The product had no cloudiness, and the NCO content was still at the same value as at the start after 24 h (see table 1).

TABLE-US-00001 TABLE 1 Analysis data of the starting MMDI/PMDI mixture and the products prepared in examples 1 to 6. NCO det. NCO det. UD.sup.[a] based PIR content Viscosity Start of after 0 h after 24 h on MW 500 calculated at 25° C. crystallization [% by mass] [% by mass] [% by mass] Appearance [% by mass] [mPa .Math. s] [° C.] MMDI/PMDI mixture 32.5 n. d. 0.18 clear 0 24 n. d. (44M + 44 V20) Example 1 (comp.) n. d. 27.1 1.11 slightly 33.2 854 10 cloudy Example 2 (comp.) 27.5 26.9 1.59 very 34.5 1470 n. d..sup.[c]  (27.0).sup.[b] cloudy Example 3 (comp.) 27.6 26.1 2.04 very 39.4 3470 n. d..sup.[c]  (26.9).sup.[b] cloudy Example 4 (comp.)   25.7.sup.[d] 22.9 n. d. solidified at RT — Example 5 (comp.) 27.3 27.5 1.11 clear 30.8 525   2.5 Example 6 (inv.) 27.5 27.5 0.82 clear 30.8 550  0 .sup.[a]UD = uretdione. .sup.[b]The value reported in brackets indicates the NCO content after the end of the heating to 140° C. or 200° C. .sup.[c]The start of crystallization could not be reliably determined owing to the high cloudiness and high viscosity (n. d. = not determined). .sup.[d]As a result of the time delay between sampling and NCO titration of about 15 min, the solution continues to react without chemical stopper, and the NCO content varies from that in examples 2 and 3, and 5 and 6.

[0110] Example 1 shows that the batchwise performance of the process with pure chemical catalyst deactivation leads to an elevated uretdione content, elevated viscosity, cloudiness and elevated crystallization temperature. If the chemical catalyst deactivation is replaced by a thermal catalyst deactivation at 140° C. (example 2), there is a further rise in uretdione content and viscosity and a further increase in cloudiness. If the deactivation temperature is increased further to 200° C., these unwanted effects increase further, whereas, when the process of the invention is employed with the same deactivation temperature (example 6, deactivation likewise at 200° C.), it is possible to obtain a clear product having a low uretdione content and constant NCO value that begins to crystallize only at 0° C. This process is also superior to the semicontinuous processes without (example 4) or with exclusively chemical (example 5) catalyst deactivation.