METHOD FOR RECOVERING DIISOCYANATES FROM DISTILLATION RESIDUES

Abstract

The invention relates to a method for recovering monomer diisocyanates, which are solid at room temperature, from a distillation residue, said method comprising the following steps: (i) preparing at least one residue which contains diisocyanates, which are solid at room temperature, and (ii) separating the residue in at least one kneader-dryer, paddle-dryer and/or roller-dryer in the presence of less than 2 wt % bitumen, based on the mass of the residue prepared in step (i), into a gaseous portion, containing monomer diisocyanate that is solid at room temperature, and a brittle residue depleted of diisocyanate, which is solid at room temperature.

Claims

1. A process for recovering monomeric, room temperature solid diisocyanates from a distillation residue, comprising the following steps: (i) providing at least one residue containing a room temperature solid diisocyanate, and (ii) separating the residue in at least one selected from the group consisting of a kneader-drier, a paddle drier and a drum drier in the presence of less than 2% by weight of bitumen, based on the mass of the residue provided in step (i), into a gaseous portion containing monomeric, room temperature solid diisocyanate, and a brittle residue depleted of room temperature solid diisocyanate.

2. The process as claimed in claim 1, wherein the kneader-drier, paddle drier or drum drier is designed without a cooling zone.

3. The process as claimed in claim 1, wherein the residue is separated in step (ii) in a drum drier.

4. The process as claimed in claim 1, wherein the separation in step (ii) is effected in the presence of 1% by weight of bitumen.

5. The process as claimed in claim 1, wherein the temperature in step (ii) is 130 C. to 270 C.

6. The process as claimed in claim 1, wherein the pressure in step (ii) is 1 mbar to 1020 mbar.

7. The process as claimed in claim 1, wherein the room temperature solid diisocyanate is selected from the group consisting of naphthalene 1,5-diisocyanate, naphthalene 1,8-diisocyanate, and phenylene 1,4-diisocyanate.

8. The process as claimed in claim 1, wherein the residue in the separation in step (ii) has an average dwell time in the at least one kneader-drier, paddle drier or drum drier of 0.5 minute to 4 hours minutes.

9. The process as claimed in claim 1, wherein the brittle residue obtained in step (ii) is discharged semicontinuously.

10. The process as claimed in claim 1, wherein the brittle residue obtained in step (ii) contains 5% by weight, of monomeric, room temperature solid diisocyanate based on the total mass of the residue.

11. The process as claimed in claim 1, wherein the residue containing room temperature solid diisocyanates that is provided in step (i) comes from the distillation of a diisocyanate prepared by phosgenating the corresponding diamines.

12. The monomeric, room temperature solid diisocyanate obtained by the process as claimed in claim 1.

13. In a process for minimizing the use of auxiliaries in the embrittlement of a residue containing room temperature solid diisocyanates, the improvement comprising including one of a kneader-drier, a paddle drier and a drum drier.

14. A composition comprising the at least one monomeric, room temperature solid diisocyanate as claimed in claim 12 and at least one NCO-reactive compound.

15. An elastomer obtained by curing, optionally while heating, the composition as claimed in claim 14.

16. The process as claimed in claim 1, wherein the separation in step (ii) is effected in the absence of bitumen.

17. The composition as claimed in claim 14, wherein the at least one NCO-reactive compound is a polyester polyol.

Description

EXAMPLE 1

[0058] A residue from a distillation of naphthalene 1,5-diisocyanate that has been prepared by phosgenation of naphthalene-1,5-diamine was applied to a Kofler heating bench. The residue still contained about 75% by weight of monomeric naphthalene 1,5-diisocyanate (determined as area % by GPC according to DIN 55672-1:2007-08). The Kofler heating bench was operated at 100 to 250 C. At 250 C. there was rapid embrittlement within 2 minutes, and the residue could be scratched off as a fine powder. The embrittlement also continued subsequently in regions at lower temperatures and, after about 3 hours, regions had also become embrittled at 160 C. and could be scratched off in the form of flakes. Below 130 C., there was no further embrittlement.

EXAMPLE 2

[0059] A residue from a distillation of naphthalene 1,5-diisocyanate that has been prepared by phosgenation of naphthalene-1,5-diamine was distilled under vacuum conditions in a laboratory distillation apparatus. The distillation apparatus was equipped with a torque-measuring stirrer, and the torque was observed in the course of the experiment. The pressure within the distillation apparatus was 2 mbar, and the temperature in the liquid phase at the end of the distillation was about 260 C. After a distillation time of about 7 minutes, there was a brief slight rise in torque up to 10 Ncm. Subsequently, the torque measured dropped again to values of <1 Ncm to form a brittle solid. After 60 minutes, the experiment was ended.

EXAMPLE 3

[0060] A residue from a distillation of tolylene diisocyanate that has been prepared by phosgenation of tolylenediamine in the gas phase was distilled under vacuum conditions in a laboratory distillation apparatus. The distillation apparatus was equipped with a torque-measuring stirrer, and the torque was observed in the course of the experiment. The pressure within the distillation apparatus was 100 mbar, and the temperature in the liquid phase at the end of the distillation was about 260 C. After a distillation time of about 15 minutes, there was a constant rise in torque. After 90 minutes, the experiment was ended. The torque had risen to 55 Ncm, and a highly viscous, thick mass remained in the liquid phase. No embrittlement was observed.