MULTISTEP PROCESS FOR THE PREPARATION OF HEXAMETHYLENE DIISOCYANATE, PENTAMETHYLENE DIISOCYANATE OR TOLUENE DIISOCYANATE

Abstract

The present invention relates to a multistep process for the preparation of organic diisocyanates by converting the corresponding diamine precursors, urea and hydroxy compounds into monomeric diurethanes, converting these diurethanes into diurethanes of high boiling hydroxy compounds, and finally cleavage of the latter diurethanes to form the diisocyanates and recover the high boiling hydroxy compounds.

Claims

1. A process for preparing hexamethylenediisocyanate, pentamethylenediisocyanate or toluenediisocyanate comprising the following steps: (I) reacting a primary diamine of the general formula (1), urea and a hydroxy compound of the general formula (2) with removal of ammonia to a diurethane of the general formula (3), ##STR00005## wherein R represents a bivalent hydrocarbon radical derived from 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate or pentamethylene diisocyanate by removing the two isocyanate groups, R represents a hydrocarbon radical derived from an aliphatic or an aromatic hydroxy compound with a standard boiling point 230 C. by removing the OH group, (II) Converting converting the diurethane obtained in step (I) to a diurethane of the general formula (4) by a transesterification reaction with a hydroxy compound of the general formula (5), ##STR00006## wherein R is the same as above, R represents a hydrocarbon radical which can be derived from an aliphatic or an aromatic hydroxy compound with a standard boiling point >280 C. by removing the OH group, (III) Subjecting subjecting the diurethane of the general formula (4) to a thermal cleavage reaction to prepare the diisocyanate of the general formula (6)
OCNRNCO(6) wherein R is the same as above, and the hydroxy compound of the general formula (5) (IV) Separating separating the diisocyanate of the general formula (6) from the hydroxy compound of the general formula (5) by distillation.

2. The process according to claim 1, wherein the molecular mass of ROH is at least 40 g/mol lower than the molecular mass of ROH.

3. The process according to claim 1, wherein the primary diamine (1) for formation of the diurethanes of the general formula (3) is 1,5-pentanediamine (PDA) or 1,6-hexanediamine (HDA).

4. The process according to claim 1, wherein the hydroxy compound ROH used for the formation of the diurethanes of the general formula (3) that has a standard boiling point between 80 C. and 210 C.

5. The process according to claim 1, wherein the hydroxy compound ROH has a standard boiling point between 280 C. and 370 C.

6. The process according to claim 1, wherein a catalyst is present during the transesterification step.

7. The process according to claim 1, wherein the cleavage reaction is a thermolytic cleavage carried out in a thin film evaporator.

8. The process according to claim 1, wherein a catalyst is used in the cleavage reaction.

9. The process according to claim 1, wherein the molecular mass of ROH is at least 100 g/mol lower than the molecular mass of ROH.

10. The process according to claim 1, wherein the molecular mass of ROH is between 110 g/mol and <160 g/mol lower than the molecular mass of ROH

Description

EXAMPLE 1A (COMPARATIVE EXAMPLE)

[0068] The comparative example 1 is the formation of N,N-hexanediyl-di(carbamic acid(4-cumylphenyl)ester) according to the method described in example 14 (step 14-1) of EP 2 679 575 A1 on a technical scale.

[0069] A first raw material mixture A is prepared that contains 2.9 wt % of HDA, 4.6 wt % of urea and 92.5 wt % of p-cumylphenol. A second raw material mixture B is prepared that contains 7.5 wt % of urea and 92.5 wt % of p-cumylphenol. Mixture A is then introduced into a heated reaction column at a rate of 70 t/h and mixture B is introduced at a rate of 29.3 t/h. Accordingly, the total mass flows of the individual components into the reaction column are 2.0 t/h for HDA, 5.4 t/h for urea and 91.8 t/h for p-cumylphenol. The molar ratio of the compounds is about 25:5:1 (p-cumylphenol:urea:HDA).

[0070] The reaction is performed at 2 kPa and 215 C. with removal of ammonia from the reaction system. The desired N,N-hexanediyl-di(carbamic acid(4-cumylphenyl)ester) is formed in good yield.

EXAMPLE 1B (THERMAL CLEAVAGE)

[0071] The product of example la can be subjected to thermal cleavage which results in the formation of hexamethylenediisocyanate (HDI) and p-cumylphenol. A process for this thermal cleavage is described in example 14 (step 14-3) with reference to example 9 (step 9-3) of EP 2 679 575 A1. The gaseous cleavage products are introduced into a distillation column, where pure HDI is obtained as the distillate whereas p-cumylphenol is contained in the bottom product of the distillation.

EXAMPLE 2A (PROCESS ACCORDING TO THE INVENTION, STEP (I) ACCORDING TO THE PRESENT INVENTION)

[0072] In a first step, 1,6-hexamethylene-O,O-diphenylurethane is prepared. The method is again based on the method from example 14 (step 14-1) of EP 2 679 575 A1 to allow better comparison. Of course it is also possible to adapt the methods described in EP 0 320 235 A2. A first raw material mixture C is prepared that contains 6.8 wt % of HDA, 11.6 wt % of urea and 81.6 wt % of phenol. A second raw material mixture D is prepared that contains 11 wt % of urea and 89 wt % of phenol. Mixture C is then introduced into a heated reaction column at a rate of 30 t/h and mixture D is introduced at a rate of 18 t/h. Accordingly the total mass flows of the individual components into the reaction column are, 2.0 t/h for HDA, 5.4 t/h for urea and 40.5 t/h of phenol. The molar ratio of the compounds is about 25:5:1 (phenol:urea:HDA).

[0073] The reaction is performed at 2 kPa and 215 C. with removal of ammonia from the reaction system. The desired 1,6-hexamethylene-O,O-diphenylurethane is formed in good yield.

EXAMPLE 2B (TRANSESTERIFICATION, STEP (II) ACCORDING TO THE PRESENT INVENTION)

[0074] The product of example 2a can be subjected to a transesterification reaction, adapting methods known from the literature (see for example [0054-0061] of EP 2088 137 B1 or [0347-0370] of EP 2 679 575 A1). For that purpose, the content of 1,6-hexamethylene-O,O-diphenylurethane in the product mixture from example 2a is determined before it is transferred to a column type transesterification reactor where it is converted with excess amount of p-cumylphenol. Phenol contained in the reaction mixture is removed from the reaction system via the vapor phase in order to drive the equilibrium reaction towards the desired product N,N-hexanediyl-di(carbamic acid(4-cumylphenyl)ester).

EXAMPLE 2C (THERMAL CLEAVAGE & DISTILLATION, STEPS (III) AND (IV) ACCORDING TO THE PRESENT INVENTION)

[0075] The product of example 2b can be subjected to thermal cleavage which results in the formation of hexamethylenediisocyanate (HDI) and p-cumylphenol. A process for this thermal cleavage is described in example 14 (step 14-3) with reference to example 9 (step 9-3) of EP 2 679 575 A1. The gaseous cleavage products are introduced into a distillation column, where pure HDI is obtained as the distillate whereas p-cumylphenol is contained in the bottom product of the distillation.

EXAMPLE 3A (PROCESS ACCORDING TO THE INVENTION, STEP (I) ACCORDING TO THE PRESENT INVENTION)

[0076] In a first step, toluene-2,4-dibutylurethane is prepared. The method is based on the method described in example 18 (step 18-1) of EP 2 679 575 A1. A first raw material mixture E is prepared at 115 C. that contains 7.6 wt % of 2,4-toluene diamine (2,4-TDA), 13.0 wt % of urea and 79.4 wt % of n-butanol. A second raw material mixture F is prepared at 115 C. that contains 13 wt % of urea and 87 wt % of n-butanol. Mixture E is then introduced into a heated reaction column at a rate of 27 t/h and mixture F is introduced at a rate of 11.5 t/h. Accordingly the total mass flows of the individual components into the reaction column are, 2.0 t/h for 2,4-TDA, 5.0 t/h for urea and 31.4 t/h of n-butanol. The molar ratio of the compounds is about 25:5:1 (n-butanol:urea:2,4-TDA). The reaction is performed at 2 kPa and 215 C. with removal of ammonia from the reaction system. The desired toluene-2,4-dibutylurethane is formed in good yield.

EXAMPLE 3B (TRANSESTERIFICATION, STEP (II) ACCORDING TO THE PRESENT INVENTION)

[0077] The product of example 3a can be subjected to a transesterification reaction, adapting methods known from the literature (see for example [0054-0061] of EP 2088 137 B1 or [0347-0370] of EP 2 679 575 A1). For that purpose, the content of toluene-2,4-dibutylurethane in the product mixture from example 2a is determined before it is transferred to a column type transesterification reactor where it is converted with excess amount of p-cumylphenol. N-butanol is removed from the reaction system via the vapor phase in order to drive the equilibrium reaction towards the desired product toluene-2,4-bis((4-cumylphenyl)urethane).

EXAMPLE 3C (THERMAL CLEAVAGE & DISTILLATION, STEPS (III) AND (IV) ACCORDING TO THE PRESENT INVENTION)

[0078] The product of example 3b can be subjected to thermal cleavage which results in the formation of 2,4-toluene diisocyanate (TDI) and p-cumylphenol. A suitable process for this thermal cleavage that can be adapted for the different starting material is described in example 9 (step 9-3) of EP 2 679 575 A1. The gaseous cleavage products are introduced into a distillation column, where pure TDI is obtained as the distillate whereas p-cumylphenol is contained in the bottom product of the distillation.

Discussion of the Examples

[0079] High stoichiometric excess of urea and aromatic hydroxy compound is required in order to suppress the formation of higher oligomers and/or polymers that would cause fouling inside the reaction system. Therefore, for converting 2.0 t/h of the diamine, a total of 91.8 t/h of the p-cumylphenyl has to be fed to the reactor as shown in example 1 a. This is economically unfavorable since the high mass flow is associated with high costs for handling the high material flow. Using the inventive process, the stoichiometric ratios can be kept constant while the mass flows in the urethanization reaction are significantly reduced.