METHOD FOR ISOCYANATE AND POLYURETHANE PRODUCTION WITH IMPROVED SUSTAINABILITY

Abstract

The invention relates to a method for producing isocyanates and optionally polyurethanes by at least: synthesising (1) phosgene (20) from carbon monoxide (21) and chlorine (22); reacting (2) phosgene (20) with diamines (23) to form diisocyanates (24) and hydrogen chloride (25); providing a carbon dioxide gas flow (31); and cleaning (4) the carbon dioxide gas flow (31) of additional components, wherein the carbon dioxide is converted by means of an RWGS reaction (6) to form carbon monoxide (21) and hydrogen (29), which are used as raw materials for the polyurethane production, as well as optionally reacting (3) the diisocyanates (24) with polyether polyol (35a) and/or polyester polyol (35b) to form polyurethanes (37).

Claims

1.-12. (canceled)

13. A process for producing isocyanates and optionally polyurethanes by at least the following steps: synthesizing phosgene from carbon monoxide and chlorine, reacting phosgene with diamines to form diisocyanates and hydrogen chloride, providing a CO.sub.2 gas stream, purifying the CO.sub.2 gas stream of secondary constituents, in particular of nitrogen oxides, sulfur compounds, dust, water, oxygen and HCl optionally by means of adsorption, gas scrubbing or catalytic treatment to obtain a purified carbon dioxide, electrolyzing water to hydrogen and oxygen, providing the hydrogen stream and feeding together with the purified CO.sub.2 gas stream into an RWGS reaction zone and reacting the reactants according to the principle of the RWGS to form a product gas mixture consisting of water vapor, CO, and any by-products, in particular lower hydrocarbons, particularly preferably methane, separating off the water of the water vapor from the product gas mixture and recycling the water to the water electrolysis, separating off unreacted carbon dioxide from the gas mixture of the RWGS reaction obtained from the separation, in particular by means of amine scrubbing, and recycling the unreacted carbon dioxide to the RWGS reaction, separating off the hydrogen that has not reacted in the RWGS reaction from the gas mixture of carbon monoxide and hydrogen obtained after the separation, in particular using a cold box, and optionally recycling the hydrogen to the RWGS reaction or feeding the hydrogen into the hydrogenation of dinitro compounds for the production of diamines as feedstock for the diisocyanate, feeding the remaining carbon monoxide from the separation into the phosgene synthesis, feeding the hydrogen from the water electrolysis, optionally together with unreacted hydrogen from the RWGS reaction, into the hydrogenation of nitro compounds for the production of diamines, separating off and purifying the hydrogen chloride formed in isocyanate production and subsequent oxidative reaction of the hydrogen chloride in the form of a reaction in a thermocatalytic gas-phase oxidation with oxygen to chlorine and water and/or in the form of an electrochemical oxidation of the hydrogen chloride to chlorine and/or in the form of an electrochemical oxidation of the hydrogen chloride to chlorine and hydrogen by HCl diaphragm electrolysis, supplying the previously formed chlorine to the phosgene synthesis, optionally alongside feeding in fresh chlorine from a chloralkali electrolysis.

14. The process as claimed in claim 13, wherein the process is a process for producing isocyanates and polyurethanes comprising: synthesizing phosgene from carbon monoxide and chlorine, reacting phosgene with diamines to form diisocyanates and hydrogen chloride, reacting the diisocyanates with polyether polyol and/or polyester polyol to form polyurethanes, providing a CO.sub.2 gas stream, purifying the CO.sub.2 gas stream of secondary constituents, optionally by means of adsorption, gas scrubbing or catalytic treatment to obtain a purified carbon dioxide, electrolyzing water to hydrogen and oxygen, providing the hydrogen stream and feeding together with the purified CO.sub.2 gas stream into an RWGS reaction zone and reacting the reactants according to the principle of the RWGS to form a product gas mixture consisting of water vapor, CO, and any by-products, separating off the water of the water vapor from the product gas mixture and recycling the water to the water electrolysis, separating off unreacted carbon dioxide from the gas mixture of the RWGS reaction obtained from the separation, in particular by means of amine scrubbing, and recycling the unreacted carbon dioxide to the RWGS reaction, separating off the hydrogen that has not reacted in the RWGS reaction from the gas mixture of carbon monoxide and hydrogen obtained after the separation, and optionally recycling the hydrogen to the RWGS reaction or feeding the hydrogen into the hydrogenation of dinitro compounds for the production of diamines as feedstock for the diisocyanate, feeding the remaining carbon monoxide from the separation into the phosgene synthesis, feeding the hydrogen from the water electrolysis, optionally together with unreacted hydrogen from the RWGS reaction, into the hydrogenation of nitro compounds for the production of diamines, separating off and purifying the hydrogen chloride ormed in isocyanate production and subsequent oxidative reaction of the hydrogen chloride in the form of a reaction in a thermocatalytic gas-phase oxidation with oxygen to chlorine and water and/or in the form of an electrochemical oxidation of the hydrogen chloride to chlorine and/or in the form of an electrochemical oxidation of the hydrogen chloride to chlorine and hydrogen by HCl diaphragm electrolysis, supplying the previously formed chlorine to the phosgene synthesis, optionally alongside feeding in fresh chlorine from a chloralkali electrolysis.

15. The process as claimed in claim 13, wherein carbon dioxide provided from the utilization of polyurethane material waste by burning and/or by pyrolysis is used for the RWGS synthesis.

16. The process as claimed in claim 15, wherein the burning is carried out using gas having a content of oxygen gas (O.sub.2) of 30% by volume.

17. The process as claimed in claim 15, wherein the gas has a content of oxygen gas (O.sub.2) of at least 50% by volume.

18. The process as claimed in claim 13, wherein the water electrolysis and/or the electrochemical oxidation is performed using electricity generated from renewable energy.

19. The process as claimed in claim 13, wherein the water electrolysis and/or the electrochemical oxidation are performed using electricity from feedback energy obtained from burning polyurethane material waste and/or from performing the RWGS reaction.

20. The process as claimed in claim 13, wherein the RWGS reaction is performed using electricity generated from renewable energy.

21. The process as claimed in claim 13, wherein the RWGS reaction is heated by means of feedback energy obtained from burning polyurethane material waste.

22. The process as claimed in claim 13, wherein the process additionally comprises reacting the diisocyanates with polyether polyol and/or polyester polyol to form polyurethanes.

23. The process as claimed in claim 13, wherein the RWGS reaction is heated by burning hydrocarbons from renewable sources.

24. The process as claimed in claim 13, wherein the polyurethane material is, after having been used, recycled as polyurethane material waste and that the polyurethane material waste is burned to form carbon dioxide and the carbon dioxide used as feed material in the purification step.

Description

[0098] The invention is elucidated in more detail hereinbelow and by way of example with reference to the figures.

[0099] In the figures:

[0100] FIG. 1 shows a schematic overview of the overall process comprising the RWGS reaction, chlorine production, PU production, use, and utilization of the polyurethane material waste therefrom to afford CO.sub.2 for the RWGS reaction

[0101] In FIG. 1, the following reference numbers have in each case the meaning shown on the right:

[0102] 1 Phosgene synthesis

[0103] 2 Isocyanate production

[0104] 3 Polyurethane production

[0105] 4 Purification of CO.sub.2 gas

[0106] 5 Water electrolysis

[0107] 6 RWGS reaction (reverse water-gas shift reaction)

[0108] 7 Water separation

[0109] 8 CO.sub.2 separation

[0110] 9 H.sub.2/CO separation

[0111] 10 Utilization of polyurethane material waste (38) through pyrolysis (10a) and/or burning (10b)

[0112] 10a Pyrolysis

[0113] 10b Burning

[0114] 11 HCl gas separation/purification

[0115] 12 Electrochemical oxidation of HCl by HCl—ODC electrolysis

[0116] 13 Power and steam generation

[0117] 14 Chloralkali electrolysis for production of Cl.sub.2

[0118] 15 Electricity from energy/steam (13)

[0119] 16 Cl.sub.2 production through thermocatalytic gas-phase oxidation (Deacon) of HCl

[0120] 17 Cl.sub.2 production through electrochemical oxidation of hydrochloric acid by diaphragm electrolysis

[0121] 18 Oxidative conversion of HCl to chlorine gas in the form of (12) and/or (16) and/or (17)

[0122] 19 Heat

[0123] 20 Phosgene

[0124] 21 Carbon monoxide in the gas stream from the RWGS reaction

[0125] 21a Carbon monoxide from the H.sub.2/CO separation

[0126] 22 Chlorine gas selected from 22a and/or 22b and/or 22c

[0127] 22a Chlorine gas from thermocatalytic gas-phase oxidation (16)

[0128] 22b Chlorine gas from electrochemical oxidation according to the HCl—ODC process (12)

[0129] 22c Chlorine gas from HCl diaphragm electrolysis (17)

[0130] 22d Chlorine from chloralkali electrolysis (14) (preferably with oxygen-depolarized cathode (ODC) with supply of oxygen (27))

[0131] 23 Diamines

[0132] 24 Diisocyanates

[0133] 25 Hydrogen chloride

[0134] 26 Water

[0135] 26b Water

[0136] 27 Oxygen

[0137] 27a Oxygen

[0138] 28 Bio-natural gas and/or renewable energy, optionally only for heating

[0139] 28a Electricity from renewable energy

[0140] 29 Hydrogen from water electrolysis

[0141] 29a Hydrogen from water electrolysis for the RWGS reaction

[0142] 29b Hydrogen that is unreacted in the RWGS reaction

[0143] 29c Hydrogen, unreacted, from the H.sub.2/CO separation

[0144] 31 CO.sub.2 from 10

[0145] 31a Purified CO.sub.2

[0146] 31b Unreacted CO.sub.2 from CO.sub.2 separation

[0147] 32 By-products from the RWGS reaction

[0148] 33 CO.sub.2 from renewable sources

[0149] 34 Hydrogenation of nitro compounds for diamine production

[0150] 35a Polyether polyol

[0151] 35b Polyester polyol

[0152] 37 Polyurethane material

[0153] 38 Waste containing polyurethane material (polyurethane material waste) for 10

[0154] 39 Product gas mixture from the RWGS reaction consisting of 21, 26b, CO.sub.2, 29b, and 32

[0155] 39a 39 with decreased content of 26b

[0156] 39b 39a with decreased content of CO.sub.2

[0157] 40 Nitro compounds

[0158] 80 Use of 37 and/or of polyurethane material from different commercial source

[0159] 90 Polyurethane-based materials—end-of-life recycling

[0160] FIG. 2 shows a schematic overview of the overall process comprising the RWGS reaction, hydrochloric acid electrolysis according to the diaphragm process (HCl—DIA) for chlorine production, including optional PU production, use of the polyurethane material, and utilization of polyurethane material waste therefrom to afford CO.sub.2 for the RWGS reaction.

[0161] The assignment of the reference numbers used in FIG. 2 is as defined for FIG. 1.

[0162] FIG. 1 and FIG. 2 illustrate the closed-loop variant of the process of the invention. It is of course possible in one embodiment to use, as a polyurethane material waste (38) feed, also polyurethane material that has been produced not from recycled polyurethane material (37) in the sense of a closed-loop process, but from toluene-2,4-diisocyanate that originated directly from feedstocks from fossil sources without recycling. In this variant, steps (3), (35a), (35b), and (37) are to be deleted in FIG. 1 and FIG. 2.

EXAMPLE 1

[0163] Low-emission production according to the invention of toluene diisocyanate (TDI), CO production by RWGS, heating thereof with bio-natural gas, HCl recycling by means of HCl gas-phase oxidation (Deacon), and provision of H.sub.2 from a water electrolysis

[0164] Into an RWGS reaction chamber (6) operated at a temperature of 802° C. was introduced 17.84 t/h of CO.sub.2 and 0.81 t/h of H.sub.2. The product gas mixture (39) resulting from the RWGS reaction, which consisted of CO (21), H.sub.2O (26b), unreacted CO.sub.2, and also unreacted H.sub.2 (29a), as well as by-products (32), mainly small amounts of methane, was withdrawn and supplied to a water separation (7), affording 7.3 t/h of water. This water (26b) is returned to the water electrolysis (5). A total of 3.24 t/h of hydrogen was taken from the water electrolysis (5), which meant that an additional 21.86 t/h of water was added. The remaining gas mixture (39a) from the RWGS was supplied to a CO.sub.2 separation (8). The CO.sub.2 separation was effected by amine scrubbing, wherein the separated CO.sub.2 (31b) was recycled to the RWGS reaction. The energy for the CO.sub.2 separation from the CO.sub.2-amine complex formed was obtained from the separation of water (7) from the RWGS gases (39). The gas freed of CO.sub.2 (39b) was supplied to the H.sub.2/CO separation (9). For the H.sub.2/CO separation, a so-called cold box was employed, in which the H.sub.2/CO gas mixture was cooled and hydrogen and CO were separated. The separated hydrogen (29c) was returned to the RWGS (6). 11.35 t/h of CO from the H.sub.2/CO separation (9) was supplied to a phosgene synthesis (1). Here, the CO reacted with 29.79 t/h of chlorine taken from an HCl gas-phase oxidation (16). 40.15 t/h of phosgene was taken from the phosgene synthesis (1) and reacted in an isocyanate production step (2) with 24.73 t/h of toluenediamine 23 to give 35.27 t/h of toluene diisocyanate (24). This gave rise to 29.59 t/h of HCl gas (25) which, after purification by low-temperature distillation, was supplied to an HCl gas-phase oxidation (16). In the HCl gas-phase oxidation (16), the HCl gas was reacted with oxygen (27) to form chlorine and H.sub.2O at approx. 300° C. over a ruthenium oxide-based catalyst. The oxygen (27) required was taken from the water electrolysis (5). For the closed-loop variant of the process of the invention, the toluene diisocyanate (24) obtained was reacted in a conventional manner with polyether polyols (35a) or polyester polyols (35b) to form polyurethane material (37).

[0165] After use of the polyurethane material in various commercial applications (80), it could be collected and recycled (90) in order to burn (10b) the polyurethane material waste (38) resulting therefrom. Burning was here realized with oxygen (27) from the water electrolysis (5), resulting in the formation of a highly concentrated CO.sub.2 offgas stream (31). This CO.sub.2 stream (31) was supplied to a CO.sub.2 purification (4) in which water originating from combustion and nitrogen oxides and sulfur oxides were removed. 17.84 t/h CO.sub.2 was thereafter supplied to the RWGS (6). It is of course possible in one embodiment to use, as a polyurethane material waste (38) feed, also polyurethane material that has been produced not from recycled polyurethane material (37) in the sense of a closed-loop process, but from toluene-2,4-diisocyanate that originated directly from fossil sources without recycling. In this variant, steps (3), (35a), (35b), and (37) are to be deleted in FIG. 1 and FIG. 2. The hydrogen (29) was generated in a water electrolysis with a power of 45 MW in which renewable energy was used. The water electrolysis (5) was an alkaline water electrolysis operated with a current density of 8 kA/m.sup.2 and a cell voltage of 2 V per electrolysis element. Supplied to this were 45 MW and 21.86 t/h of water plus 7.3 t/h of water from H.sub.2O separation (7). 3.24 t/h of H.sub.2 was taken from the water electrolysis.

[0166] The RWGS reaction was operated at 802° C., the temperature was generated by burning bio-natural gas.

[0167] Through the process of the invention, 22% of the carbon present in the TDI was replaced from a non-fossil carbon source. The use of renewable energy in the water electrolysis allowed the CO.sub.2 footprint of the phosgene produced from CO and Cl.sub.2 to be further reduced.

EXAMPLE 2

[0168] Low-emission production according to the invention of toluene diisocyanate (TDI), CO production by RWGS, heating thereof with bio-natural gas, HC1 recycling by means of HCl diaphragm electrolysis, and provision of H.sub.2 for the hydrogenation of dinitrotoluene from a water electrolysis

[0169] Into an RWGS reaction chamber (6) operated at a temperature of 802° C. was introduced 17.84 t/h of CO.sub.2 and 0.81 t/h of H.sub.2. The hydrogen originated from HCl recycling by HCl diaphragm electrolysis. The product gas mixture (39) resulting from the RWGS, which consisted of CO (21), H.sub.2O (26b), unreacted CO.sub.2, and also unreacted H.sub.2 (29a), as well as by-products (32), mainly small amounts of methane, was withdrawn and supplied to a water separation (7), affording 7.3 t/h of water. This water (26b) was returned to the water electrolysis (5). A total of 2.43 t/h of hydrogen was taken from the water electrolysis, which meant that an additional 14.56 t/h of water was added. The remaining gas mixture (39a) from the RWGS was supplied to a CO.sub.2 separation (8). The CO.sub.2 separation was effected by amine scrubbing, wherein the separated CO.sub.2 (31b) was recycled to the RWGS. The energy for the CO.sub.2 separation from the CO.sub.2-amine complex formed was obtained from the separation of water (7) from the RWGS gases (39). The gas freed of CO.sub.2 (39b) was supplied to the H.sub.2/CO separation (9). For the H.sub.2/CO separation, a so-called cold box was employed, in which the H.sub.2/CO gas mixture was cooled and hydrogen and CO were separated. The separated hydrogen (29c) was returned to the RWGS (6). 11.35 t/h of CO from the H.sub.2/CO separation (9) was supplied to a phosgene synthesis (1). Here the CO reacted with 29.79 t/h of chlorine taken from an HCl diaphragm electrolysis (17). 40.15 t/h of phosgene was taken from the phosgene synthesis (1) and reacted in an isocyanate production step (2) with 24.73 t/h of toluenediamine 23 to give 35.27 t/h of toluene diisocyanate (24). This gave rise to 29.59 t/h of HCl gas (25) which, after purification by low-temperature distillation, absorption in water to form 35% hydrochloric acid, and purification of the hydrochloric acid using activated carbon, was supplied to an HCl diaphragm electrolysis (17). Chlorine and hydrogen were taken from the HCl diaphragm electrolysis. The hydrogen was purified and supplied to the RWGS. The toluene diisocyanate (24) obtained was reacted in a conventional manner with polyether polyols (35a) or polyester polyols (35b) to form polyurethane material (37).

[0170] After use of the polyurethane material in various commercial applications (80), it can be collected and recycled (90) in order to burn (10b) the polyurethane material waste (38) resulting therefrom. Burning was here realized with oxygen (27) from the water electrolysis (5), resulting in the formation of a highly concentrated CO.sub.2 offgas stream (31). This CO.sub.2 stream (31) was supplied to a CO.sub.2 purification (4) in which water originating from combustion and nitrogen oxides and sulfur oxides were removed. 17.84 t/h CO.sub.2 was thereafter supplied to the RWGS (6).

[0171] The hydrogen (29) was generated in a water electrolysis with a power of 45 MW in which renewable energy was used. The water electrolysis (5) was an alkaline water electrolysis operated with a current density of 8 kA/m.sup.2 and a cell voltage of 2 V per electrolysis element. Supplied to this were 45 MW and 21.86 t/h of water plus 7.3 t/h of water from H.sub.2O separation (7). 3.24 t/h of H.sub.2 was taken from the water electrolysis.

[0172] The RWGS was operated at 802° C., the temperature was generated by burning bio-natural gas.

[0173] Through the process of the invention, 22% of the carbon present in the TDI was replaced from a non-fossil carbon source. The use of renewable energy in the water electrolysis allowed the CO.sub.2 footprint of the phosgene produced from CO and Cl.sub.2 to be further reduced.