METHOD FOR RECOVERING DIISOCYANATES FROM DISTILLATION RESIDUES

Abstract

The invention relates to a method for recovering a diisocyanate which is solid at room temperature from a distillation residue from a process for producing the diisocyanate, comprising the following steps: (i) mixing the distillation residue with a bitumen such that a mixture is obtained which contains 70 to 90 wt % of the distillation residue and 10 to 30 wt % of the bitumen, each in relation to the mixture, (ii) distilling the mixture in a thin-film evaporator or a falling film evaporator to obtain a sump discharge and a gaseous product stream, (iii) condensing the gaseous product stream and obtaining a solid containing the diisocyanate which is solid at room temperature. The invention further relates to the use of a thin-film evaporator or falling film evaporator, to a composition containing the diisocyanate which is solid at room temperature, and to a method for producing an elastomer from this composition and to the elastomer itself.

Claims

1. A method of separating a room temperature solid diisocyanate from a distillation residue from a method for preparing the diisocyanate, comprising the following steps: mixing the distillation residue with a bitumen 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 bitumen, based in each case on the mixture, (ii) distilling the mixture in a thin-film evaporator or a falling-film evaporator to obtain a bottoms output and a gaseous product stream, (iii) condensing the gaseous product stream to obtain a solid material comprising the room temperature solid diisocyanate.

2. The method as claimed in claim 1, characterized in that the bitumen in the mixture from step (i) has a sulfur content of 2.5% to 3.1% by weight, based in each case on the bitumen.

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 room temperature solid diisocyanate, based in each case on the distillation residue.

4. The method as claimed in claim 1, characterized in that, in step (i), 85% to 70% by weight of the distillation residue is mixed with from 15% to 30% by weight of the bitumen, based in each case on the sum total of the masses of the distillation residue and the bitumen.

5. The method as claimed in claim 1, characterized in that step (ii) is performed at a temperature of 130° C. to 160° 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 material from step (iii) contains at least 95% by weight of the room temperature solid diisocyanate, based on the solid material.

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

9. The method as claimed in claim 1, characterized in that the room temperature solid diisocyanate is 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.

10. The use of a mixture containing 70% to 90% by weight of a distillation residue from a method for preparing a room temperature solid diisocyanate and 10% to 30% by weight of a bitumen, based in each case on the mixture, in a method of separating the diisocyanate by distillation by means of a thin-film evaporator or falling-film evaporator.

11. A composition comprising a solid material comprising a room temperature solid diisocyanate from step (iii) of a method as claimed in claim 1 and at least one NCO-reactive compound, preferably at least one polyester polyol.

12. A method of producing an elastomer, in which at least one composition as claimed in claim 11 is chemically reacted, optionally while heating.

13. An elastomer produced or producible by a method as claimed in claim 12.

Description

EXAMPLES

[0089] Monomeric naphthalene diisocyanate (NDI) was separated from distillation residues by various methods. For this purpose, the distillation residue was mixed with various types of bitumen and subjected to a distillation. The following bitumen was used:

[0090] Bitumen 70/100 from Shell: 3.5% by weight of sulfur

[0091] Bitumen 160/220 from Shell: 2.9% by weight of sulfur

[0092] Bitumen with 3.08% by weight of sulfur, mixture of bitumen 70/100 and 160/220

[0093] Bitumen with 3.23% by weight of sulfur, mixture of bitumen 70/100 and 160/220

[0094] The sulfur content was determined by sulfur elemental analysis after automatic pipe incineration at 1150° C. with addition of oxygen. This is followed by detection with an IR detector as SO.sub.2.

[0095] 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 5 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.

[0096] 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 Example Inventive Comparative Mixture 1 2 3 4 5 6 7 8 Distillation residue from the 70 70 85 70 70 70 90 60 phosgenation of 1,5-NDA to 1,5-NDI [% by wt.] Bitumen 160/220 (2.9% by weight of 30 30 15 — — — 10 sulfur) [% by wt.] Bitumen with 3.08% by weight of — — — 30 — — — sulfur [% by wt.] Bitumen with 3.32% by weight of — — — — — 30 — sulfur [% by wt.] Bitumen 70/100 (3.5% by weight of — — — — 30 — — 40 sulfur) [% by wt.] Proportion of monomeric 1,5-NDI 46.9 46.9 46.9 46.9 46.9 46.9 46.9 45.9 in the distillation residue [% by wt. based on the distillation residue] Distillation conditions Temperature [° C.] 155 155 155 155 155 155 155 160 Pressure [mbar] 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Dosage rate [g/h] 230 265 265 265 265 265 265 260 Proportion of monomeric 84.5 86.4 87.1 87.3 62.8 65.8 79.3 78.7 1,5-NDI monomer recovered (yield) [%] Proportion of 1,5-NDI monomer 7.3 8.3 6.1 6.0 17.4 17.4 9.7 9.8 in bottoms output [%] Purity of 1,5-NDI monomer [%] 99.5 99.9 — — — — — 99.7

[0097] The figures in % by weight for the mixture are based on the mass the overall mixture. 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 bitumen. All examples and comparative examples (except comparative example 9) were conducted in a conventional glass falling-film evaporator with an evaporator area of 0.1 m.sup.2 (diameter 100 mm, length 300 mm).

Comparative Example 9 (Without Thin-Film Evaporator)

[0098] Residue from the phosgenation of 1,5-NDA to 1,5-NDI still containing 70-85% 1,5-NDI monomer was fed at 150° C. to an amount of bitumen preheated to 160° C. (30% by weight of the residue) in a tank. 1,5-NDI monomer was distilled out of the mixture obtained while stirring continuously at 2-4 mbar and 160° C. The yield of the 1,5-NDI monomer recovered in this method was 50-60%.

DISCUSSION OF RESULTS

[0099] Comparison of the inventive examples with the comparative examples shows that it is possible by the method of the invention to recover a comparable or even a higher proportion of more than 80% of the monomeric diisocyanate from the distillation residue. Comparative example 8 did achieve a yield of almost 80%, but only by mixing the distillation residue with 40% by weight of bitumen, i.e. consuming more additives.

[0100] 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 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.