Method for isocyanate and polyurethane production with improved sustainability

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 CO2 gas stream,
• purifying the CO2 gas stream of secondary constituents to obtain a purified carbon dioxide,
• electrolyzing water to hydrogen and oxygen,
• providing the hydrogen stream and feeding together with the purified CO2 gas stream as reactants into a reverse water-gas shift reaction (RWGS) reaction zone and reacting the reactants according to a principle of the RWGS reaction 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 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,
• feeding the remaining carbon monoxide from the separation into the phosgene synthesis,
• feeding the hydrogen from the water electrolysis 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.