A Process for Manufacturing Isocyanates and/or Polycarbonates

Abstract

A process for manufacturing isocyanates or polycarbonates comprising the steps of: providing a chlorine stream and carbon monoxide stream; reacting said chlorine stream and said carbon monoxide stream for providing a phosgene stream; cooling the phosgene stream to a temperature at which the phosgene in the phosgene stream is liquid, preferably, to a temperature that is 4 C. less or more than 4 C. less than the boiling point of phosgene, to form a liquid phosgene stream and a gas stream; separating the gas stream and the liquid phosgene stream; removing residual chlorine from the liquid phosgene stream to form a chlorine depleted phosgene stream and reacting the chlorine depleted phosgene stream to form an isocyanate or a polycarbonate.

Claims

1. A process for manufacturing isocyanates comprising the steps of: a) providing a chlorine stream and carbon monoxide stream, wherein the chlorine stream comprises less than 500 ppm bromine; b) reacting said chlorine stream and said carbon monoxide stream for providing a phosgene stream, wherein the mole ratio carbon monoxide in the carbon monoxide stream over chlorine in the chlorine stream is in a range of between 0.900:1.000 to 1.025:1000; c) cooling the phosgene stream to a temperature at which the phosgene in the phosgene stream is liquid, to form a liquid phosgene stream and a gas stream; d) separating the gas stream and the liquid phosgene stream; e) removing residual chlorine from the liquid phosgene stream to form a chlorine depleted phosgene stream; g1) reacting the chlorine depleted phosgene stream with an amine compound to form a corresponding isocyanate compound.

2. A process for preparing polycarbonate compounds comprising the steps of: a) providing a chlorine stream and carbon monoxide stream, wherein the chlorine stream comprises less than 500 ppm bromine; b) reacting said chlorine stream and said carbon monoxide stream for providing a phosgene stream, wherein the mole ratio carbon monoxide in the carbon monoxide stream over chlorine in the chlorine stream is in a range of between 0.900:1.000 to 1.025:1000; c) cooling the phosgene stream to a temperature at which the phosgene in the phosgene stream is liquid, to form a liquid phosgene stream and a gas stream; d) separating the gas stream and the liquid phosgene stream; e) removing residual chlorine from the liquid phosgene stream to form a chlorine depleted phosgene stream; g2) reacting the chlorine depleted phosgene stream to form a polycarbonate compound.

3. The process according to claim 1, further comprising the step f) bringing the separated gas stream from step d) to a second reactor and reacting chlorine and carbon monoxide present in the separated gas stream to form a second phosgene stream.

4. The process according to claim 3, wherein further carbon monoxide is provided to the second reactor.

5. The process according to claim 3, wherein the second phosgene stream flows to a reactor to react with an amine compound to form a corresponding polyisocyanate compound or is used to form a polycarbonate.

6. The process according to any one of the claims 1, wherein the removed residual chlorine of step e) flows back in the chlorine stream of step a).

7. The process according to claim 1, wherein the amine compound comprises diaminodiphenylmethane.

8. The process according to claim 1, wherein the colour of the isocyanate has a Hunterlab Lab colour grade/value L larger than 30.

9. The process according to claim 2, wherein the chlorine depleted phosgene stream reacts with a diol compound, preferably bisphenol A to form a polycarbonate compound.

Description

[0054] The invention is further illustrated by the following drawing.

[0055] FIGS. 1, 2 and 3: Representations of a process flow for making a phosgene stream and separating the phosgene stream to provide a stream that can be used for making isocyanates according to the invention.

[0056] FIG. 1 represents a process flow wherein a carbon monoxide stream 1 and a chlorine stream 2 enter at least one reactor 3 to form a phosgene stream 4. These streams are gas streams. Reactor 3 may optionally be configured to enable generation of steam by making use of the exotherm of the phosgene-forming reaction, as is known in the art, the steam thus produced being therefore available as a heating source for other purposes. The phosgene stream 4 comprises unreacted carbon monoxide, chlorine, phosgene, bromine and bromine monochloride. The amount COBrCl is very low or even non existing due to specific mole ratio carbon monoxide in the carbon monoxide stream over chlorine in the chlorine stream that is used. The phosgene stream is brought to one or more heat exchangers or coolers 5, preferably a condenser, that cools down the gas stream to a temperature at which the phosgene is in its liquid phase. The liquid phosgene stream 7 is separated from the gas stream 6. The liquid phosgene stream now comprises all the bromine species. The liquid phosgene stream is then brought to at least one column 8 that is designed to remove the chlorine from the phosgene, e.g. a stripping column. Column 8 may have a reboiler and/or may have a condenser. The chlorine in the column can e.g. be removed by stripping with carbon monoxide 11 that enters at the bottom of the column 8. The chlorine leaves the column in a stream 10 comprising chlorine and the stripping gas e.g. CO and can at least partly be recycled to make phosgene via the chlorine stream 2, the CO stream 1 or can be fed directly to reactor 3.

[0057] The chlorine depleted phosgene stream 9 now comprises all bromine species and can be used to make isocyanates and/or polycarbonates. The gas stream 6 that is separated from the liquid phosgene stream 7, does not comprise bromine species. The gas stream 6 comprises chlorine, phosgene, carbon monoxide. This stream can be brought to at least one reactor 12, optionally via at least one heat exchanger 17. The reactor 12 is designed for making phosgene. The heat exchanger may be required to get the streams up to temperature again for the reaction in reactor 12. If required further carbon monoxide 14 can be added, which is required to make sure that an excess of carbon monoxide is present. The phosgene stream 13, can be used to make isocyanates and/or polycarbonates.

[0058] FIG. 2 is a drawing representing a flow scheme of another embodiment according to the invention wherein the streams are similar as described in FIG. 1 with the difference that stream 10 comprising chlorine and the stripping gas is fed to the at least one heat exchanger 5, directly or together with stream 4. Since stream 10 will mainly comprise the stripping gas, which is preferably CO, stripping can already occur in the at least one heat exchanger 5. The stripped chlorine gas will then separate from the liquid phase together with the other gasses in stream 6. In case that CO is used as stripping gas, it is possible that stream 14 is no longer required.

[0059] FIG. 3 is a drawing representing a flow scheme of another embodiment according to the invention wherein the streams are similar as described in FIG. 1 with the difference that stream 4 and 7 pass through a cross heat exchanger. This way the warm stream 4 coming from the phosgene reactor is able to warm up stream 7 which allows to perform the stripping in column 8 at a temperature that is higher than the temperature for cooling down in stream 5. This warmer temperature may facilitate the stripping in column 8.