METHOD FOR THE PURIFICATION OF ISOCYANATES

Abstract

The invention relates to a process for purifying at least one isocyanate selected from the group consisting of aliphatic, cycloaliphatic, araliphatic isocyanates and mixtures thereof, to a process for producing at least one isocyanate selected from the group consisting of aliphatic, cycloaliphatic, araliphatic isocyanates and mixtures thereof, to the isocyanate obtainable by this process, to a polyurethane constructed from at least one such isocyanate, to the use of this isocyanate and to an optical component containing at least one polyurethane according to the invention.

Claims

1. A process for purifying at least one isocyanate selected from the group consisting of aliphatic, cycloaliphatic, araliphatic isocyanates, and mixtures thereof, the process comprising the steps of: (A) providing the at least one isocyanate, (B1) filtering the at least one isocyanate from step (A) through a filter having a permeability of 5 to 1001/(m.sup.2.Math.min) under standard conditions of Δp=1 bar, H.sub.2O, 20° C., to obtain at least one purified isocyanate, or comprising the steps of: (A) providing the at least one isocyanate, (B2) filtering the at least one isocyanate from step (A) through a filter having a permeability of 5 to 1000 l/(m.sup.2.Math.min) under standard conditions of Δp=1 bar, H.sub.2O, 20° C., and (C) filtering the at least one isocyanate through a filter having a maximum pore size of 0.02 to 10 μm, wherein the sequence of steps is (A), (B2), (C) or (A), (C), (B2), to obtain at least one purified isocyanate.

2. The process as claimed in claim 1, wherein the at least one purified isocyanate, optionally after one or more intermediate steps, is employed in a further process step for synthesis of one selected from the group consisting of polyurethanes and polythiourethanes for optical applications.

3. The process as claimed in claim 1, wherein the at least one isocyanate is selected from the group consisting of bis(isocyanatomethyl)bicyclo[2.2.1]heptane (NBDI), 2,5 bis(isocyanatomethyl)bicyclo[2.2.1]heptane (2,5-NBDI), 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane (2,6-NBDI), pentamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane (H.sub.6XDI), xylylene diisocyanate, meta-xylylene diisocyanate, para-xylylene diisocyanate, and mixtures thereof.

4. The process as claimed in claim 1, wherein step (A) comprises distilling the at least one isocyanate, before steps (B1) or (B2).

5. The process as claimed in claim 1, wherein the filter employed in step (B1) or (B2) contains at least one material selected from the group consisting of natural fibers, synthetic polymers, perlite, kieselguhr, and mixtures thereof.

6. The process as claimed in claim 1, wherein step (B1) is operated at a specific filtrate flow of 50 to 1500 kg/(m.sup.2.Math.h).

7. A process for producing at least one isocyanate selected from the group consisting of aliphatic, cycloaliphatic, araliphatic isocyanates, and mixtures thereof, the process comprising the steps of: (A1) providing at least one amine corresponding to the isocyanate to be produced, (A2) reacting the at least one amine from step (A1) with phosgene or a derivative thereof to obtain the at least one isocyanate and (A3) purifying the at least one isocyanate from step (A2), wherein step (A3) comprises the step of: (B1) filtering the at least one isocyanate from step (A2) through a filter having a permeability of 5 to 1001/(m.sup.2.Math.min) under standard conditions of Δp=1 bar, H.sub.2O, 20° C., to obtain the at least one isocyanate, or step (A3) comprises the steps of: (B2) filtering the at least one isocyanate from step (A2) through a filter having a permeability of 5 to 1000 l/(m.sup.2.Math.min) under standard conditions of Δp=1 bar, H.sub.2O, 20° C., and (C) filtering the at least one isocyanate through a filter having a maximum pore size of 0.02 to 10 μm, wherein the sequence of steps is one selected from the group consisting of (A1), (A2) and (B1); (A1), (A2), (B2) and (C); (A1), (A2), (C) and (B2), to obtain the at least one isocyanate.

8. The process as claimed in claim 7, wherein step (A2) (A2) is carried out at a temperature of 5° C. to 500° C. and a pressure of 0.5 to 10 bar(a).

9. The process as claimed in claim 7, wherein in step (A3) the at least one isocyanate is distilled before filtering.

10. An isocyanate obtained by the process as claimed in claim 1.

11. An isocyanate obtained by the process as claimed in claim 1, wherein the isocyanate has a turbidity of less than 0.35 NTU determined according to DIN EN ISO 7027-1: 2016.

12. A polyurethane comprising at least one isocyanate as claimed in claim 10 and at least one polyol.

13. A polythiourethane comprising at least one isocyanate as claimed in claim 10 and at least one polythiol.

14. In a process for producing one of polyurethanes and polythiourethanes for optical applications, the improvement comprising including the isocyanate as claimed in claim 10.

15. An optical component containing at least one polyurethane as claimed in claim 12.

16. An optical component containing at least one polyurethane as claimed in claim 13.

17. The process as claimed in claim 1, wherein step (B1) is operated at a specific filtrate flow of 100 to 1000 kg/(m.sup.2.Math.h).

18. The process as claimed in claim 1, wherein step (B1) is operated at a specific filtrate flow of 200 to 500 kg/(m.sup.2.Math.h).

Description

EXAMPLES

[0118] According to the invention the permeability of the employed filters is to be understood as meaning the amount of pure water passing through the filter layer per unit time and area under standard conditions, i.e. 20° C. and 1 bar pressure difference. Permeability is determined using ultrapure water. The filter or a representative sample of the filter material is subjected to ultrapure water at 20° C. and the desired pressure difference of 1 bar between the inflow side and the filtrate side is established. The time and the amount of filtrate generated in this time are measured, and taking into account the known area of the filter the permeability may be calculated according to the formula:

Permeability=amount of filtrate in liters/(filter area in m.sup.2×time in min)

[0119] A suitable apparatus for the measurement is described for example in VDI Guideline 2762, sheet 2, pages 6-8. What is relevant for the process according to the invention is the initial permeability of the employed filter before use.

[0120] The maximum pore size of the employed filters is determined according to ASTM F316-03 2011 for flexible filters, for example membrane filters, and according to ASTM E218-99 2011 for rigid filters, for example glass or ceramic filters.

[0121] The turbidity of the isocyanates is determined according to DIN EN ISO 7027-1: 2016-11, wherein the isocyanate is treated as an aqueous medium according to this DIN standard.

[0122] Reaction of meta-xylylenediamine (meta-XDA) with phosgene in the gas phase affords meta-xylylene diisocyanate (meta-XDI). The crude product is purified by distillation at 170° C. and a pressure of 15 mbar(a). The thus obtained meta-XDI (“starting solution”, experiment 9 in table 1) has a turbidity of 25.4 NTU determined according to DIN EN ISO 7027-1:2016-11. This starting solution is filtered according to experiments 1, 2, 3, 4, 5, V6, 7 and V8 recited in table 1.

[0123] The results are shown in table 1. The inventive experiments 1, 2, 3, 4, 5 and 7 achieve turbidity values desired according to the invention of ≤0.35 NTU and so polyurethanes and/or polythiourethanes produced with this meta-XDI meet the stringent requirements for use in optical lenses whereas the comparative experiments V6 and V8 result in disadvantageously high turbidity values and so polyurethanes and/or polythiourethanes produced therefrom are not suitable for use in optical lenses.

TABLE-US-00001 TABLE 1 9 Starting Number 1 2 3 4 5 V6 7 V8 solution Permeability [l/m.sup.2 .Math. min] 29 29 100 100 146 146 925 925 — in the 1st filtration stage Maximum pore size [μm] — 0.2 0.2 0.2 0.2 — 0.2 — — in the 2nd filtration stage Turbidity [NTU].sup.1 0.27 0.23 0.32 0.29 0.26 14.7 0.32 20.8 25.4 V comparative experiment — not performed .sup.1determined according to DIN EN ISO 7027-1: 2016