METHOD FOR RECOVERING DIISOCYANATES FROM DISTILLATION RESIDUES

Abstract

The invention relates to a method for recovering a diisocyanate that is solid at room temperature from a distillation residue originating from a production process of the diisocyanate, comprising the following steps: (i) mixing the distillation residue with at least one polyisocyanate on the basis of one or more diisocyanates different from the diisocyanate that is solid at room temperature, in such a way that a mixture is obtained that contains 70 to 90 wt. % of the distillation residue and 10 to 30 wt. % of the at least one polyisocyanate, each relative to the mixture, (ii) subjecting the mixture to distillation in a thin-film evaporator and/or a downflow evaporator, thereby obtaining a sump discharge and a gaseous product stream, and (iii) condensing the gaseous product stream and obtaining a solid containing the diisocyanate that is solid at room temperature, the at least one polyisocyanate in step (i) having a residual monomer content of ≤3.0 wt. % as determined by gas chromatography with an internal standard according to EN ISO 10283:2007-11.

Claims

1. A method of separating a diisocyanate which is solid at 23° C. and 1000 mbar from a distillation residue from a method for preparing the diisocyanate, comprising the following steps: mixing the distillation residue with at least one polyisocyanate based on one or more diisocyanates other than the diisocyanate which is solid at 23° C. and 1000 mbar, in such a way as to obtain a mixture containing 70% to 90% by weight of the distillation residue and 10% to 30% by weight of the at least one polyisocyanate, based in each case on the mixture, (ii) distilling the mixture in a thin-film evaporator and/or a falling-film evaporator to obtain a bottoms output and a gaseous product stream, and (iii) condensing the gaseous product stream to obtain a solid material comprising the diisocyanate which is solid at 23° C. and 1000 mbar, wherein the at least one polyisocyanate in step (i) has a residual monomer content of ≤3.0% by weight, determined by gas chromatography with an internal standard to DIN EN ISO 10283:2007-11.

2. The method as claimed in claim 1, characterized in that the at least one polyisocyanate in step (i) has a residual monomer content of ≤1.5% by weight, determined by gas chromatography with an internal standard to DIN EN ISO 10283:2007-11.

3. The method as claimed in claim 1, characterized in that the distillation residue in step (i) contains from 30% to 70% by weight of the diisocyanate which is solid at 23° C. and 1000 mbar, based on the distillation residue.

4. The method as claimed in claim 1, characterized in that, in step (i), 85% to 75% by weight of the distillation residue is mixed with 15% to 25% by weight of the at least one polyisocyanate, based on the sum total of the masses of the distillation residue and the at least one polyisocyanate.

5. The method as claimed in claim 1, characterized in that step (ii) is performed at a temperature of 130° C. to 180° C. and a pressure of 0.4 to 4 mbar.

6. The method as claimed in claim 1, characterized in that the bottoms output from step (ii) is not in solid form at the prevailing temperature at the outlet from the thin-film evaporator or falling-film evaporator.

7. The method as claimed in claim 1, characterized in that the solid matter from step (iii) contains at least 95% by weight of the diisocyanate which is solid at 23° C. and 1000 mbar, based on the solid material.

8. The method as claimed in claim 1, characterized in that the at least one polyisocyanate in step (i) is a polyisocyanate obtainable by modification of simple aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates.

9. The method as claimed in claim 1, characterized in that, in step (i), less than 5% by weight of bitumen, based on the mass of the distillation residue, is present.

10. The method as claimed in claim 1, characterized in that the method for preparing the diisocyanate is a phosgenation of a diamine.

11. The method as claimed in claim 1, characterized in that the diisocyanate which is solid at 23° C. and 1000 mbar is selected from the group consisting of naphthalene 1,5-diisocyanate, naphthalene 1,8-diisocyanate, phenylene 1,4-diisocyanate, tetralin diisocyanate, o-toluidine diisocyanate, durene diisocyanate, benzidine diisocyanate and/or anthrylene 1,4-diisocyanate.

12. In a method of separating off the diisocyanate which is solid at 23° C. and 1000 mbar by distillation by means of a thin-film evaporator and/or falling-film evaporator, the improvement comprising including a mixture containing 70% to 90% by weight of a distillation residue from a process for preparing a diisocyanate which is solid at 23° C. and 1000 mbar and 10% to 30% by weight of at least one polyisocyanate based on one or more diisocyanates other than the diisocyanate which is solid at 23° C. and 1000 mbar, based in each case on the mixture.

13. A composition comprising a solid material comprising a diisocyanate which is solid at 23° C. and 1000 mbar from step (iii) of a method as claimed in claim 1 and at least one NCO-reactive compound.

14. A method of producing an elastomer, in which at least one composition as claimed in claim 13 is chemically reacted, optionally while heating.

15. An elastomer produced by the method as claimed in claim 14.

16. The method as claimed in claim 8, characterized in that the at least one polyisocyanate in step (i) is selected from the group consisting of 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4,4′-dii socyanatodicyclohexylmethane, bis(isocyanatomethyl)norbornane (NBDI), 2,4- and 2,6-dii socyanatotoluene (TDI) and/or 2,4′- and 4,4′-diisocyanatodiphenylmethane (MDI).

Description

EXAMPLES

[0076] Monomeric naphthalene diisocyanate (NDI) was separated from distillation residues by various methods. For this purpose, the distillation residue was mixed with various polyisocyanates and subjected to a distillation.

[0077] The following polyisocyanates were used:

[0078] Polyisocyanate 1: an aliphatic polyisocyanate based on pentamethylene diisocyanate (PDI) and having an NCO content of 21.9% by weight and a viscosity of 9500 mPas at 23° C.

[0079] Polyisocyanate 2: an aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI) and having an NCO content of 11.0% by weight and a viscosity of 6000 mPas at 23° C.

[0080] Polyisocyanate 3: an aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI) and having an NCO content of 21.8% by weight and a viscosity of 3000 mPas at 23° C.

[0081] Polyisocyanate 4: an aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI) and having an NCO content of 23.0% by weight and a viscosity of 1200 mPas at 23° C.

[0082] Polyisocyanate 5: an aromatic polyisocyanate based on diphenylmethane diisocyanate (MDI) and having an NCO content of 31.3% by weight and a viscosity of 680 mPas at 25° C.

[0083] All viscosity measurements were recorded with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219:1994-10 at a shear rate of 250 s-1.

[0084] The residual monomer contents were adjusted by addition of the appropriate monomeric diisocyanate (PDI, HDI or MDI) for the examples in table 1 and measured according to DIN EN ISO 10283:2007-11 by gas chromatography with an internal standard.

[0085] The purity of the NDI was determined by gas chromatography. The measurements were effected using a Hewlett Packard HP 6890 with an FID detector and HP-Chemstation software using an Optima 5 column and the following parameters: split rate: 8.31:1 mL/min; flow rate: 96.4 mL/min; pressure: 0.7 bar, carrier gas: helium, injection volume: 1 μL, inliner straight split liner filled with Carbofritt.

[0086] The NDI residues before and after distillation were analyzed by means of GPC to DIN 55672-1:2007-08. The yield was then determined by subtracting the area percentage of the monomer still remaining from the area percentage of the original amount of monomer, which were determined in each case by GPC to DIN 55672-1:2007-08.

TABLE-US-00001 TABLE 1 Overview of examples 1 to 8 conducted: Example Inventive Comparative Mixture 1 2 3 4 5 6 7 8 9 10 11 Distillation residue from the 85 80 75 75 80 80 75 80 100 75 75 phosgenation of 1,5-NDA to 1,5-NDI [% by wt.] Polyisocyanate 1 — — — — 20 — — — — — — Polyisocyanate 2 — — — — — — — — — — — Polyisocyanate 3 15 20 25 25 — — 25 — — 25 25 Polyisocyanate 4 — — — — — 20 — — — — — Polyisocyanate 5 — — — — — — — 20 — — — Residual monomer content [% by wt.] 0.10 0.10 0.10 0.54 0.10 0.06 2.0 33 — 5.0 10.0 Proportion of monomeric 1,5-NDI in 58.4 58.4 58.4 58.4 58.4 58.4 58.4 58.4 62.5 58.4 58.4 the distillation residue [% by wt. based on the distillation residue] Distillation conditions Temperature [° C.] 155 155 155 155 155 155 155 155 150 155 155 Pressure [mbar] 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.9 1.0 0.85 0.85 Dosage rate [g/h] 270 270 270 270 270 270 270 260 150 270 270 Proportion of monomeric 1,5-NDI 73.7 60.7 27.5 43.0 88.2 80.9 82.0 n.d. 19.0 n.d. n.d. monomer recovered (yield) [%] Proportion of 1,5-NDI monomer in 15.4 22.9 42.3 33.3 6.9 11.2 10.5 n.d. 50.5 n.d. n.d. bottoms output [%] Purity of 1,5-NDI monomer [%] 99.9 99.9 99.9 99.7 99.8 99.9 99.8 n.d. 99.8 n.d. n.d. n.d. = not determinable
The figures in % by weight for the mixture are based on the mass the overall mixture. The residual monomer content is based on the mass of the respective polyisocyanate used. The respective mixture was sent to a vacuum distillation in a thin-film evaporator under the conditions specified, with condensation of the monomeric 1,5-NDI in solid form. The bottoms output that was still liquid at this temperature consisted in each case of 1,5-NDI monomer, non-distillable components and poly isocyanate. All examples and comparative examples were conducted inacomentional glass thin-film evaporator with an exaporator area of 0.1 m2 (diameter 100 mm, length 300 mm).

Discussion of Results

[0087] Comparison of inventive examples 1 to 7 with comparative examples 9 to 11 shows that the method of the invention can recover high proportions of the room temperature solid diisocyanate from the distillation residue, and demonstrates the significance of the residual monomer content in the additive polyisocyanate since, in the case of relatively high residual monomer contents in the comparative examples, there was conglutination in the thin-film evaporator and it was not possible to condense the monomeric 1,5-NDI in solid form. The proportion of recovered monomeric 1,5-NDI monomer is not determinable analytically here. Comparative example 9 shows that, without addition of the polyisocyanate of the invention, distillation was possible only at a distinctly reduced dosage rate and led to a distinctly lower yield.

[0088] A further advantage of the method of the invention is that the bottoms output is free-flowing since further oligomerization reactions have been very substantially suppressed by the low temperatures and shorter thermal stress in the performance of the method of the invention compared to conventional methods, which constitutes a significant advantage for the continuous mode of operation. The room temperature solid diisocyanates obtained from the method of the invention are notable for high purity and can be used without restrictions for production of elastomers.