METHOD FOR EXTRACTING DIISOCYANATES FROM DISTILLATION RESIDUES

Abstract

The invention relates to a method for extracting diisocyanates that are solid at room temperature from a distillation residue, comprising the following steps: (i) providing at least one residue containing diisocyanates that are solid at room temperature, and (ii) treating the residue at a temperature of ≥120° C. to <200° C. so as to obtain diisocyanates that are solid at room temperature, the residue provided in step (i) containing ≥32 to ≤60 wt. % of bitumen and the treatment in step (ii) being carried out in at least one thin-film evaporator and/or falling-film evaporator.

Claims

1. A process for recovering room temperature solid diisocyanates from a distillation residue, comprising the following steps: (i) providing at least one residue containing room temperature solid diisocyanates and (ii) treating the residue at a temperature of ≥120° C. to <200° C. to obtain room temperature solid diisocyanates, wherein the residue provided in step (i) contains ≥32% to ≤60% by weight of bitumen and the treatment in step (ii) is effected in at least one thin-film evaporator and/or falling-film evaporator.

2. The process as claimed in claim 1, characterized in that the temperature in step (ii) is ≥130° C. to <190° C., preferably ≥140° C. to ≤180° C. and more preferably ≥150° C. to ≤165° C.

3. The process 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.

4. The process as claimed in claim 1, characterized in that the residue in the treatment in step (ii) contains ≥0% by weight to ≤4% by weight, based in each case on the total amount of the residue containing room temperature solid diisocyanates, of monomeric diisocyanates having a boiling temperature above the boiling temperature of the room temperature solid diisocyanate.

5. The process as claimed in claim 1, characterized in that the residue has an average residence time in the treatment in step (ii) of ≥1 to ≤15 minutes, in the at least one thin-film evaporator and/or falling-film evaporator.

6. The process as claimed in claim 1, characterized in that the treatment in step (ii) takes place at a pressure of ≥0.4 mbar to ≤4.0 mbar.

7. The process as claimed in claim 1, characterized in that the treatment in step (ii) takes place at a coolant temperature below the melting point of the room temperature solid diisocyanate.

8. The process as claimed in claim 1, characterized in that the treatment in step (ii) gives ≥60% by weight of the room temperature solid diisocyanates that are still present in the residue in step (i).

9. The process as claimed in claim 1, characterized in that the residue containing room temperature solid diisocyanates which is provided in step (i) comes from the phosgenation of the corresponding diamines.

10. A room temperature solid diisocyanate, obtained or obtainable by a process as claimed in claim 1.

11. The use of a thin-film evaporator for recovering aromatic diisocyanates that are solid at room temperature from a residue containing aromatic diisocyanates that are solid at room temperature.

12. A composition comprising at least one room temperature solid diisocyanate as claimed in claim 10 and at least one NCO-reactive compound, preferably at least one polyester polyol.

13. A process for producing an elastomer, in which at least one composition as claimed in claim 12 is cured, optionally while heating.

14. An elastomer produced or producible by a process as claimed in claim 13.

Description

EXAMPLES

[0068] All percentages are based on weight, unless stated otherwise.

[0069] 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.

[0070] 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.

[0071] The bitumen used was sourced from Shell and corresponded to Shell 70/100 bitumen quality.

Example 1 (Inventive)

[0072] A mixture containing 50% residue from the phosgenation of 1,5-NDA to 1,5-NDI and 50% bitumen was fed to a vacuum distillation in a thin-film evaporator at metering rate 240 g/h. The mixture that contained 38.25% 1,5-NDI monomer was distilled at 160° C. and 0.9 mbar. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of non-distillable components and bitumen. The bottoms discharge still contained 4.25% 1,5-NDI monomer, which corresponded to a yield of 88.9%.

Example 2 (Inventive)

[0073] A mixture containing 50% residue from the phosgenation of 1,5-NDA to 1,5-NDI and 50% bitumen was fed to a vacuum distillation in a thin-film evaporator at metering rate 257 g/h. The mixture that contained 38.25% 1,5-NDI monomer was distilled at 160° C. and 0.9 mbar. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of non-distillable components and bitumen. The bottoms discharge still contained 3.19% 1,5-NDI monomer, which corresponded to a yield of 91.7%.

Example 3 (Inventive)

[0074] A mixture containing 60% residue from the phosgenation of 1,5-NDA to 1,5-NDI and 40% bitumen was fed to a vacuum distillation in a thin-film evaporator at metering rate 260 g/h. The mixture that contained 45.90% 1,5-NDI monomer was distilled at 160° C. and 0.9 mbar. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of non-distillable components and bitumen. The bottoms discharge still contained 9.79% 1,5-NDI monomer, which corresponded to a yield of 78.7%.

Comparative Example 1

[0075] A mixture containing 70% residue from the phosgenation of 1,5-NDA to 1,5-NDI and 30% bitumen was fed to a vacuum distillation in a thin-film evaporator at metering rate 285 g/h. The mixture that contained 48.5% 1,5-NDI monomer was distilled at 170° C. and 1 mbar. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of 1,5-NDI monomer, non-distillable components and bitumen. The bottoms discharge still contained 31.6% 1,5-NDI monomer, which corresponded to a yield of 34.8%.

Comparative Example 2

[0076] A mixture containing 70% residue from the phosgenation of 1,5-NDA to 1,5-NDI and 30% bitumen was fed to a vacuum distillation in a thin-film evaporator at metering rate 330 g/h. The mixture that contained 53.55% 1,5-NDI monomer was distilled at 160° C. and 1 mbar. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of non-distillable components and bitumen. The bottoms discharge still contained 18.38% 1,5-NDI monomer, which corresponded to a yield of 65.7%.

Comparative Example 3

[0077] Residue from the phosgenation of 1,5-NDA to 1,5-NDI still containing 62.5% 1,5-NDI monomer was fed without further dilution at a metering rate of 150 g/h at 150° C. and 1 mbar to a vacuum distillation in a thin-film evaporator. The monomeric 1,5-NDI was condensed in solid form; the bottoms discharge that was still liquid at this temperature consisted of 1,5-NDI monomer and non-distillable components. The bottoms discharge still contained 50.5% 1,5-NDI monomer, which corresponded to a yield of 19%.

Comparative Example 4

[0078] 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 continuously 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 process was 50-60%.

Discussion of the Examples

[0079] It becomes clear from the comparison of the results of the inventive examples with the comparative examples that a distinctly improved yield can be achieved by the process of the invention. Moreover, the remaining residue to be discharged after the distillation is still free-flowing since further oligomerization reactions are very substantially suppressed by the gentle mode of operation, which constitutes an important advantage for the continuous mode of operation. The room temperature solid diisocyanates obtained from the process of the invention are notable for particularly high purity and can be used without restrictions for production of elastomers.