Process for preparing isocyanates and polyurethanes with improved sustainability

Abstract

A process is described for preparing at least isocyanates and optionally polyurethanes by synthesizing (1) phosgene (20) from carbon monoxide (21) and chlorine (22), converting (2) the phosgene (20) into diisocyanates (24) and hydrogen chloride (25) with diamines (23), providing a carbon dioxide gas stream (31) and purifying (4) the carbon dioxide gas stream (31) of secondary components, wherein the carbon dioxide is converted by means of an RWGS reaction (6) into carbon monoxide (21) and hydrogen (29), which are used as starting materials for the preparation of polyurethanes, and optionally converting (3) the diisocyanates (24) into polyurethanes (37) with polyether polyols (35a) and / or polyester polyols (35b).

Description

[0001] The invention relates to a process for preparing isocyanates and optionally polyurethanes by synthesizing phosgene from carbon monoxide and chlorine, converting the phosgene into diisocyanates and hydrogen chloride with diamines, optionally converting the diisocyanates into polyurethanes with polyethers and / or polyesters, providing a carbon dioxide gas stream and purifying the carbon dioxide gas stream of secondary constituents, and subsequently converting the carbon dioxide for preparing carbon monoxide for use in the phosgene synthesis.

[0002] The invention also relates to the use of polyurethane-containing waste materials (hereinafter also referred to as "polyurethane material waste") for the preparation of chemical raw materials for the preparation of isocyanates and optionally the subsequent preparation of polyurethanes, wherein carbon dioxide and hydrocarbons and optionally carbon monoxide and hydrogen are generated starting from the polyurethane material waste, for example by pyrolysis, the carbon dioxide is converted into carbon monoxide by means of hydrogen in the so-called reverse water gas shift reaction (hereinafter referred to as RWGS reaction), and the carbon monoxide obtained is converted into isocyanates via phosgene, and the isocyanates can be further processed to form new polyurethane materials.

[0003] The invention relates in particular to a process for the low-emission preparation of isocyanates using the RWGS reaction and providing hydrogen from water electrolysis or from electrolysis for the preparation of chlorine, and to the combustion of a polyurethane-containing material to carbon dioxide using oxygen from water electrolysis and optionally the combustion of pyrolysis residues obtained from the polyurethane-containing material and the use of the carbon dioxide obtained in each case as a starting material for the RWGS reaction.

[0004] Carbon monoxide, preferably produced from waste polyurethane materials, is converted with chlorine into phosgene, which is converted with amines into isocyanates. The isocyanates can be used to produce polyurethane materials again by reaction with polyether polyols or polyester polyols. Thus, part of the value chain is closed. When using CO2 and electricity from renewable energy sources for water electrolysis, polyurethane materials with further improved sustainability can be produced. The intention is to significantly reduce the proportion of fossil carbon in the polyurethane.

[0005] Furthermore, the hydrogen required for the hydrogenation of nitro compounds to amines can be additionally produced by water electrolysis, which can be used to convert phosgene into isocyanates. In the water electrolysis, oxygen is produced as a byproduct at the anode. This oxygen can be used to burn polyurethane-containing waste materials and pyrolysis residues, whereby a high-concentration CO2 waste gas stream is obtained during the combustion and thus CO2 recovery is significantly more economical than when burning polyurethane-containing waste materials with air. However, CO2 from alternative sources (e.g. combustion of other waste materials) can also be used. This CO2 is purified and supplied to the RWGS reaction.

[0006] Polyurethane, also referred to as PU below, is a plastic produced by the polyaddition reaction of a polyol containing at least two hydroxyl groups with a polyisocyanate. Linear polyurethanes are produced using diols and diisocyanates. Crosslinked polyurethanes can be prepared by the reaction of a triisocyanate-diisocyanate mixture with a triol-diol mixture. The properties of PU can vary over a wide range. Depending on the degree of crosslinking and / or the isocyanate component or OH component used, thermosetting plastics, thermoplastics or elastomers are obtained. However, polyurethanes are also used as molding materials for molding, as casting resins (isocyanate resins), as (textile) elastic fibers, polyurethane lacquers and as polyurethane adhesives. Foams can also be prepared very easily from polyurethanes.

[0007] Flexible PU foams are used for a variety of purposes, primarily as soft padding, for example for furniture and car seats, as mattress foam, as carpet backing material, for textile lamination, as cleaning sponges or as filter material.

[0008] PU rigid foams are mainly used for thermal insulation, for example in buildings, cooling units, heat and cold storage devices and in some pipe systems (plastic jacketed composite pipes, flexible composite pipes).

[0009] Other relatively new areas of application for PU foams are found in automotive construction, such as steering wheels, armrests, soft coatings for handles, interior trim, dashboards, sound insulation, crash noise protection (Klapperschutz), seals, clear coatings for wood trim.

[0010] After the useful life of products containing PU materials has expired, they are usually disposed of, i.e. stored in landfills or incinerated in waste incineration plants. So far, it has not been possible to recycle the substances in an economically successful manner, i.e., it has not been possible to obtain the used polyols or polyisocyanates from the PU materials in economical yields.

[0011] One method for the material recovery of PU is glycolysis, in which the carbamate groups are converted into carbamates and polyols with diols.

[0012]

[0013] In addition, amines can be used to convert urethane groups into ureas and polyols.

[0014]

[0015] The object of the present invention is to find a more sustainable process for the production of isocyanates and ultimately also for the production of polyurethanes, including recycling processes and closing of the value chain. To date, the main components for the production of polyurethanes, such as carbon monoxide, hydrogen or the electric current for operating electrolysis (such as water electrolysis and chlor-alkali electrolysis), have been produced from fossil energy carriers. For example, carbon monoxide and hydrogen are usually obtained from natural gas or from coal by means of reforming processes, while chlorine is obtained from electrolysis with electric current produced using fossil fuels such as oil, coal or natural gas.

[0016] The person skilled in the art understands the "sustainability" of a process, using the definition of sustainability created by the United Nations based on the Brundtland Report of the "World Commission on Environment and Development" ("sustainable development"), to mean that by carrying out the process future generations will no longer be able to meet their own needs, in particular with regard to the use of resources, such as fossil raw materials, and in particular with regard to the protection of living space, such as the protection of the Earth's atmosphere, the contribution is as small as possible or even no contribution at all. The object of the present invention is therefore to make the preparation of isocyanates and optionally polyurethanes more sustainable than the preparation methods known from the prior art. It is intended to reduce or even avoid a reduction in the satisfaction of future generations' needs due to the production of isocyanates and thus polyurethanes.

[0017] The object of the present invention is therefore to reduce the use of fossil raw materials as reactants for isocyanate production and optionally also to reduce the use of fossil raw materials to provide energy for isocyanate production. The latter objective is particularly intended to further improve the carbon dioxide balance (carbon footprint) of PU production in order to protect the Earth's atmosphere.

[0018] The subject of the present invention is a process for preparing isocyanates (and optionally polyurethanes) by at least the following steps:

[0019] Phosgene is synthesized from carbon monoxide and chlorine.

[0020] The phosgene is converted into diisocyanate and hydrogen chloride with diamines,

[0021] Provide CO2 gas flow,

[0022] purifying the CO2 gas stream of secondary components, in particular nitrogen oxides, sulfur compounds, dust, water, oxygen and HCl, optionally by means of adsorption, gas scrubbing or catalytic treatment, to obtain purified carbon dioxide,

[0023] Electrolyze water into hydrogen and oxygen.

[0024] A hydrogen stream is provided and fed into the RWGS reaction zone together with a purified CO2 gas stream, and the reactants are converted into a product gas mixture according to the RWGS reaction principle, wherein the product gas mixture consists of water vapor, CO and optional by-products, wherein the by-products are particularly lower hydrocarbons, and methane is particularly preferred.

[0025] Separating water from the product gas mixture as water vapor and recycling this water to the water electrolysis,

[0026] separating unreacted carbon dioxide from the separated gas mixture of the RWGS reaction, in particular by means of an amine wash, and recycling the unreacted carbon dioxide to the RWGS reaction,

[0027] separating off the hydrogen which has not been converted 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 to the hydrogenation of the dinitro compounds for the preparation of diamines as starting materials for diisocyanates,

[0028] The remaining carbon monoxide from the separation is fed to the phosgene synthesis,

[0029] The hydrogen from the water electrolysis, optionally together with unconverted hydrogen from the RWGS reaction, is fed to the hydrogenation of the nitro compounds for the preparation of diamines,

[0030] Separation and purification of the hydrogen chloride formed in the preparation of isocyanates and subsequent hydrogen conversion of the hydrogen chloride as a reaction with oxygen in a thermocatalytic gas phase oxidation to give chlorine and water and / or as an electrochemical oxidation to give chlorine and / or as an electrochemical oxidation to give chlorine and hydrogen by means of HCl membrane electrolysis,

[0031] The chlorine formed previously is supplied to the phosgene synthesis, optionally with addition of fresh chlorine from chlor-alkali electrolysis.

[0032] Here, for the preparation of polyurethane, within the scope of the method according to the invention, a step of reacting diisocyanate with polyether polyol and / or polyester polyol to form polyurethane can be additionally carried out. One embodiment of the method is also suitable as a method for preparing isocyanates and polyurethanes by:

[0033] Synthesis (1) of phosgene (20) from carbon monoxide (21a) and chlorine (22),

[0034] Phosgene (20) is converted (2) into diisocyanate (24) and hydrogen chloride (25) using diamine (23),

[0035] converting (3) a diisocyanate (24) into a polyurethane (37) using a polyether polyol (35a) and / or a polyester polyol (35b),

[0036] Providing a CO2 gas flow (31),

[0037] purifying (4) the CO2 gas stream (31) of secondary components, in particular nitrogen oxides, sulfur compounds, dust, water, oxygen and HCl, optionally by means of adsorption, gas washing or catalytic treatment, to obtain purified carbon dioxide (31a),

[0038] electrolyze (5) water (26) into hydrogen (29) and oxygen (27),

[0039] A hydrogen stream (29a) is provided and fed together with a purified CO2 gas stream (31a) into an RWGS reaction zone and the reactants are converted (6) according to the RWGS principle into a product gas mixture (39), the product gas mixture (39) consisting of water vapor (26b), CO (21) and optionally by-products (32), the by-products (32) being in particular lower hydrocarbons, particularly preferably methane,

[0040] separating (7) the water of the water vapor (26b) from the product gas mixture (39) and recycling the water to the water electrolysis (5),

[0041] separating (8) unreacted carbon dioxide (31b) from the gas mixture (39a) of the RWGS reaction (6) obtained in the separation (7), in particular by means of amine scrubbing, and recycling the unreacted carbon dioxide (31b) to the RWGS reaction (6),

[0042] separating (9) the hydrogen (29a) which has not reacted in the RWGS reaction (6) from the gas mixture (39b) of carbon monoxide (21a) and hydrogen (29c) obtained after the separation (8), in particular using a cold box, and optionally recycling the hydrogen (29c) to the RWGS reaction (6) or feeding the hydrogen (29c) to the hydrogenation (34) of the dinitro compound for the preparation of the diamine (23) as starting material for the diisocyanate (24),

[0043] The remaining carbon monoxide (21a) from the separation (9) is fed to the phosgene synthesis (1),

[0044] The hydrogen (29) from the water electrolysis (5), optionally together with the unreacted hydrogen (29c) from the RWGS reaction (6), is fed to the hydrogenation of the nitro compound (34) for the preparation of (2) diamine (23),

[0045] separation and purification (11) of the hydrogen chloride (25) formed in the isocyanate preparation (2) and subsequent oxidative conversion (18) of the hydrogen chloride (25) as a reaction with oxygen (27) in a thermal catalytic gas phase oxidation (16) to give chlorine (22a) and water (26) and / or as an electrochemical oxidation (12) of the hydrogen chloride (25) to give chlorine (22b) and / or as an electrochemical oxidation (17) of the hydrogen chloride (25) by means of HCl membrane electrolysis (17) to give chlorine (22c) and hydrogen (29),

[0046] The previously formed chlorine (22a, 22b, 22c) is supplied to the phosgene synthesis (1), optionally with addition of fresh chlorine (22d) from chlor-alkali electrolysis (14).

[0047] All the following embodiments and definitions apply equally to the above-described variants of the method according to the invention:

[0048] According to the invention, "lower hydrocarbons" are understood to mean hydrocarbons having 1 to 8 carbon atoms.

[0049] “Amine washing” of the product gas of the RWGS reaction is understood here in particular to mean the washing of the gas mixture according to the principle of chemical adsorption with amines such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) or diglycolamine (DGA), which is known in principle and which already gives a purified gas mixture of high purity at relatively low pressures in an absorption column.

[0050] Those skilled in the art understand "renewable energy" to mean energy coming from a source that will not be exhausted, such as wind, water or solar energy.

[0051] A preferred embodiment of the method according to the invention is characterized in that carbon dioxide produced by the use of polyurethane material waste by combustion and / or by pyrolysis is used for the RWGS synthesis. In this case, it is also preferred to use oxygen obtained from water electrolysis during combustion.

[0052] "Waste polyurethane materials" may be generated by using polyurethanes on the market, wherein the polyurethanes are prepared from the diisocyanates provided by the process of the invention. When such waste polyurethane materials are reused in the RWGS synthesis of the invention, a so-called "closed loop" process is referred to. However, it is of course also possible to utilize waste polyurethane materials in the RWGS synthesis of the invention which originate from polyurethanes which were not prepared from the diisocyanates obtained from the process of the invention.

[0053] A very particularly preferred process is one in which the carbon dioxide for the RWGS synthesis is produced by utilizing polyurethane material waste by combustion in the presence of a gas having an oxygen content (O2) of at least 30% by volume, preferably at least 50% by volume, particularly preferably at least 95% by volume, very particularly preferably at least 99% by volume, most preferably at least 99.5% by volume.

[0054] The oxygen used for the combustion can here again preferably be obtained from water electrolysis.

[0055] The utilization of polyurethane waste is carried out, for example, by pyrolyzing the polyurethane waste at elevated temperature, optionally in the presence of a catalyst, to obtain carbon dioxide, optionally carbon monoxide, optionally hydrogen, optionally a mixture of aliphatic and aromatic low molecular weight hydrocarbons and nitrogen-containing hydrocarbons, and optionally residues of high molecular weight hydrocarbons. Subsequently, the mixture obtained in the pyrolysis is preferably subjected to refining to obtain a gaseous mixture of carbon dioxide, carbon monoxide, hydrogen and other low molecular weight hydrocarbon compounds that are gaseous under standard conditions.

[0056] The combustion of the residues obtained in the pyrolysis and optionally other polyurethane material waste can be carried out in particular with an oxygen-containing gas, in particular with pure oxygen, to give a gas comprising carbon dioxide.

[0057] In a preferred embodiment of the new process, the RWGS synthesis uses carbon dioxide produced by the combustion of polyurethane material waste using oxygen obtained from water electrolysis.

[0058] In another preferred embodiment of the novel process, the water electrolysis and / or electrochemical oxidation is carried out using electric current generated from renewable energy, in particular selected from electric current obtained by utilizing wind power, solar power or hydropower.

[0059] In another preferred embodiment of the novel process, the water electrolysis and / or electrochemical oxidation is carried out using an electric current which is obtained from the feedback energy obtained when burning the spent polyurethane material and / or carrying out the RWGS reaction.

[0060] Another alternative embodiment of the novel process is characterized in that the RWGS reaction is carried out with the aid of electric current generated from renewable energy, in particular selected from electric current obtained by exploiting wind power, solar power or hydropower.

[0061] In another alternative embodiment of the novel process, the heating of the RWGS reaction is carried out by means of feedback energy obtained from the combustion of polyurethane material waste. "Feedback energy" is understood by a person skilled in the art to mean energy, in particular thermal energy, which is taken from one process step of the process according to the invention (optionally converted into another energy form, such as electric current) and introduced again into another process step of the process according to the invention.

[0062] In a preferred variant of the novel process, the heating of the RWGS reaction is carried out by means of the combustion of hydrocarbons from a renewable hydrocarbon production, in particular by means of the combustion of biomethane. Biomethane is understood here to mean methane obtained from biogas obtained by fermentation of biomass. Another particularly preferred variant of the novel process is characterized in that the polyurethane material is recovered as polyurethane material waste after its use and that the polyurethane material waste is burned to generate carbon dioxide, which is used as raw material for purification.

[0063] The oxygen for combustion is preferably obtained from the electrolysis of water.

[0064] By preferably using electric current from renewable energy (preferably from wind, water or solar energy), CO2 emissions in the overall process are further reduced. In a preferred novel process, the hydrogen formed in the water electrolysis is optionally used in the optional refining and / or in the hydrogenation of nitro compounds, wherein the amines obtained in the hydrogenation of nitro compounds can be used for isocyanate preparation. The separated hydrogen optionally obtained in the novel process is preferably used in the hydrogenation of nitro compounds. Amines as isocyanate precursors are thus provided.

[0065] In a particularly preferred embodiment of the process according to the invention, the material cycle is further closed by recycling the polyurethane material after its use as polyurethane material waste and burning the polyurethane material waste to form carbon dioxide and using the carbon dioxide as a starting material in purification.

[0066] When the PU material is recycled after the end of its service life, the commonly used separation methods are used to separate the composite materials in the waste. For example, the PU material is roughly separated automatically or manually, and then mechanically crushed and optionally further separated. The obtained PU material is used as a raw polyurethane material waste for combustion or pyrolysis.

[0067] In the case of combustion, the polyurethane material waste reacts, for example, with pure oxygen O2 produced at the anode as a by-product of the water electrolysis. The reaction heat produced during combustion can be used as feedback energy for producing steam and / or electric current. In particular, the heat can be used for the operation of the pyrolysis and the generated electric current can be used in the electrolysis. This further improves the overall efficiency of the novel method.

[0068] Likewise, the heat generated upon combustion can be used as feedback energy to heat the RWGS reaction, thereby further improving the overall energy efficiency of the new process compared to the prior art.

[0069] The CO2 from the combustion or pyrolysis of polyurethane waste is generated in high concentration and supplied to the purification before further use. This separates out the by-products of the combustion, such as sulfur compounds such as SO2, nitrogen compounds such as NO XAs well as remaining organic matter and dust and other generated compounds resulting from components present in the PU material.

[0070] The combustion of polyurethane material waste with pure oxygen can be carried out, for example, according to the method known as the oxyfuel process in an atmosphere of pure oxygen and CO2 (recycled flue gas). The flue gas produced here is not diluted with the nitrogen contained in the air and consists mainly of CO2 and water vapor. The water vapor condenses easily, thus generating a high-concentration CO2 stream (in the ideal case, the concentration is close to 100%). This CO2 can then be purified and further processed, and optionally also compressed and stored.

[0071] In addition, a portion of the energy obtained when pyrolyzing or burning the polyurethane material waste can be converted into steam or electricity. As previously mentioned, the electricity obtained can be used to run the electrolysis, resulting in a more efficient process with low electrical energy consumption.

[0072] The CO obtained from the combustion gases can be purified according to methods known in principle from the prior art. 2。 This will be exemplarily described below.

[0073] Here, for example, the combustion gas is first purified, the main component of which is CO2. The combustion gas purification is structured in different stages. The specific task of the purification is to provide CO2 free of interfering secondary components for the subsequent RWGS reaction. 2。

[0074] In the first stage, dust is removed from the combustion gases. This can be done with a fabric filter or with an electrostatic filter. Then, any acidic gases present, such as hydrogen chloride formed from chlorine compounds present in the waste, can be removed. For example, an exhaust gas scrubber is used here. Here, the combustion gases are also cooled and freed from other dust and any heavy metals. In addition, the sulfur dioxide gas formed is also separated in a washing circuit and converted into gypsum, for example with slaked lime. The removal of nitrogen compounds from the combustion gases can be carried out, for example, on a catalyst-containing zeolite, or the nitrogen oxides can be converted back into nitrogen and water by adding urea or ammonia. In order to prevent the formation of ammonium salts that would clog the pores of the catalyst, the operation of the catalyst is mostly carried out at temperatures above 320° C. N2 compounds can also be removed by washing with nitric acid or with a catalyst.

[0075] The drying and further purification of the CO2 can be carried out by known conventional methods, for example by treatment with concentrated sulfuric acid.

[0076] In the final purification stage, activated carbon filters are used to remove the remaining organic matter still contained in the combustion gas as well as the last metal residues by means of the activated carbon. For this purpose, for example, dust-like activated carbon can be metered into the combustion or flue gas flow and then deposited again on the fabric filter together with the accumulated pollutants. The used carbon is discharged and supplied for energy utilization (described in principle at: https: / / www.ava-augsburg.de / umwelt / rauchgasreinigung / ).

[0077] The combustion gas is purified to provide CO which can be used as a raw material for the RWGS reaction. 2。

[0078] Optionally, the CO 2 separation can also be carried out with the aid of amine scrubbing with a gas stream having a lower CO 2 concentration.

[0079] In the case of pyrolysis, it is not preferred to supply additional oxygen into the pyrolysis reaction space. The pyrolysis of the used polyurethane material can preferably be carried out as follows:

[0080] The pyrolysis of the polyurethane material is carried out at elevated temperature, optionally in the presence of a catalyst, to obtain optionally carbon dioxide, optionally carbon monoxide, optionally hydrogen, a mixture of aliphatic and aromatic low molecular weight hydrocarbons and nitrogen-containing hydrocarbons, and residues of high molecular weight hydrocarbon compounds,

[0081] optionally refining the resulting mixture of low molecular weight hydrocarbons to obtain a mixture of gaseous and liquid hydrocarbons and a mixture of carbon dioxide and carbon monoxide, hydrogen and other gaseous hydrocarbon compounds, and separating the resulting mixture in a gas separation,

[0082] combusting the residue obtained and optionally further polyurethane material waste with an oxygen-containing gas, in particular with pure oxygen, to obtain a carbon dioxide-containing gas,

[0083] The polyurethane material waste recovered and shredded as described above can be supplied to pyrolysis, wherein the pyrolysis can optionally be carried out with or without a catalyst.

[0084] The fractions produced during pyrolysis are gaseous, liquid and solid, wherein the solid phase is mostly composed mainly of pyrolytic carbon. Preferably, liquid long-chain carbon compounds containing aromatic hydrocarbons such as toluene, benzene and xylene are supplied to the refining process. Here, the compounds can be separated or further converted with hydrogen, preferably hydrogen from water electrolysis, in the refining process, so that propylene and ethylene (as precursors for polyols and polyethers) can also be obtained as a result. Long-chain liquid hydrocarbon compounds can be separated and further processed. Aromatic compounds such as benzene or aniline, or if present, isocyanates, can also be used as raw materials in the corresponding synthesis.

[0085] Furthermore, the pyrolysis can optionally be operated in a manner that produces greater amounts of carbon monoxide and optionally hydrogen. These gases can be separated together with the short-chain hydrocarbon compounds, for example in a refinery, or they can also be separated separately and then supplied to a carbon monoxide-hydrogen separator and used.

[0086] The solid matter produced during pyrolysis consists mostly of carbon. This solid phase can be converted with pure oxygen from water electrolysis. This also produces a highly concentrated CO2 stream, which is supplied for purification.

[0087] Another possibility for preparing high-purity CO2 is to absorb CO2 in an alkaline aqueous solution, for example an aqueous potassium hydroxide solution. Potassium bicarbonate is thus formed, which can then be thermally decomposed into CO2 and potassium hydroxide. The heat generated by pyrolysis or combustion can be used here.

[0088] The purified CO2 is supplied to the RWGS reaction.

[0089] The gas mixture removed from the RWGS reaction is cooled. The reaction water is separated out. This reaction water can be supplied as a raw material to water electrolysis. After the water is separated, the gas is supplied to CO2 separation.

[0090] The CO separation is carried out, for example, by amine scrubbing, wherein the CO is removed and the residual gas consisting of CO and H is supplied to an H / CO gas separation unit. The CO obtained is then supplied to the phosgene synthesis and converted there into phosgene with Cl. The phosgene produced is supplied to the isocyanate preparation. In the isocyanate preparation, the phosgene is converted into isocyanates and hydrogen chloride with amines.

[0091] The hydrogen obtained from water electrolysis or H2 / CO separation can be supplied to the hydrogenation of nitro compounds to amines and thus to the preparation of isocyanates.

[0092] Therefore, an embodiment of the novel process is preferred in which at least a partial stream of carbon monoxide and / or hydrogen from the H2 / CO separation is supplied to the RWGS reaction.

[0093] In a corresponding synthesis, the isocyanates obtained from the isocyanate preparation are converted with polyether polyols or with polyester polyols into the polyurethane materials.

[0094] The novel process can also preferably be operated such that a portion of the polyurethane material waste is fed directly to combustion instead of pyrolysis.

[0095] The hydrogen chloride (HCl) produced in the preparation of isocyanates can be supplied to another HCl recovery unit, such as an HCl membrane or HCl electrolysis with gas diffusion electrodes or catalytic gas phase oxidation. In the case of HCl electrolysis with gas diffusion electrodes or gas phase oxidation, the required O2 can be obtained from water electrolysis.

[0096] The production of chlorine by electrochemical oxidation according to the HCl-ODC electrolysis process (suitable electrolysis cells, see US 6022 634 A, WO03 / 31690 A1), the production of chlorine by HCl diaphragm electrolysis (see EP 1103 636 A1), the production of chlorine by thermal catalytic gas phase oxidation (see WO2012 / 025483 A2), and the production of chlorine by chlor-alkali electrolysis (see WO2009 / 007366 A2) are well known to the person skilled in the art. The contents of the above-mentioned documents relating to the production of chlorine are expressly and completely referenced.

[0097] The PU materials required on the market can then be prepared with isocyanates and polyether polyols and optionally also with polyester polyols. The polyurethanes are used for different applications on the market. After their service life has ended, these materials are supplied to recycling, where the PU materials are separated. The separated materials are then supplied as polyurethane material waste for utilization in the form of pyrolysis and / or combustion.

[0098] As a result, no further fossil raw materials are required for the preparation of isocyanates and polyurethane materials can be produced in an improved sustainable manner.

[0099] The invention is explained in more detail below by way of example with reference to the accompanying drawings.

[0100] in:

[0101] Figure 1 A schematic overview of the entire process is shown, including the RWGS reaction, chlorine production, PU production, use and utilization of the polyurethane material waste produced therefrom to generate CO2 for the RWGS reaction.

[0102] In FIG. 1 , the following reference numerals have the meanings to the right of each:

[0103] 1 Phosgene synthesis

[0104] 2 Preparation of isocyanate

[0105] 3 Polyurethane preparation

[0106] 4 CO2 gas purification

[0107] 5 Water electrolysis

[0108] 6 RWGS reaction (reverse water gas shift reaction)

[0109] 7 Water separation

[0110] 8 CO2 Separation

[0111] 9 H2 / CO separation

[0112] 10 Utilization of polyurethane material waste (38) by pyrolysis (10a) and / or combustion (10b)

[0113] 10a Pyrolysis

[0114] 10b Burning

[0115] 11 HCl gas separation / purification

[0116] 12 Electrochemical oxidation of HCl by means of HCl-SVK electrolysis

[0117] 13 Energy- and steam generation

[0118] 14 Chlor-alkali electrolysis for the production of Cl2

[0119] 15 Current from energy / steam (13)

[0120] 16 Preparation of Cl2 by thermal catalytic gas phase oxidation of HCl (Deacon)

[0121] 17 Preparation of Cl2 by electrochemical oxidation of hydrochloric acid by means of diaphragm electrolysis

[0122] 18 Oxidation of HCl into chlorine as (12) and / or (16) and / or (17)

[0123] 19 hot

[0124] 20 Phosgene

[0125] 21 Carbon monoxide in the gas stream from the RWGS reaction

[0126] 21a Carbon monoxide from H2 / CO separation

[0127] 22 Chlorine selected from 22a and / or 22b and / or 22c

[0128] 22a Chlorine obtained from thermal catalytic gas phase oxidation (16)

[0129] 22b Chlorine from electrochemical oxidation according to the HCl-ODC method (12)

[0130] 22c Chlorine from HCl diaphragm electrolysis (17)

[0131] 22d Chlorine from chlor-alkali electrolysis (14) (preferably with an oxygen-consuming cathode (SVK), supplied with oxygen (27))

[0132] 23 Diamine

[0133] 24 Diisocyanate

[0134] 25 Hydrogen chloride

[0135] 26 Water

[0136] 26b Water

[0137] 27 Oxygen

[0138] 27a Oxygen

[0139] 28 Biogas and / or renewable energy, optionally for heating only

[0140] 28a Electricity from renewable energy

[0141] 29 Hydrogen from water electrolysis

[0142] 29a Hydrogen from water electrolysis for RWGS reaction

[0143] 29b Unconverted hydrogen in the RWGS reaction

[0144] 29c Hydrogen, unconverted, from H2 / CO separation

[0145] 31 CO2 from 10

[0146] 31a Purified CO2

[0147] 31b Unconverted CO2 from CO2 separation

[0148] 32 Byproducts of RWGS reactions

[0149] 33 CO2 from renewable sources

[0150] 34 Hydrogenation of nitro compounds for the preparation of diamines

[0151] 35a Polyether polyol

[0152] 35b Polyester polyol

[0153] 37 Polyurethane material

[0154] 38 Waste containing polyurethane materials for 10 (polyurethane material waste)

[0155] 39 The product gas mixture obtained from the RWGS reaction consists of 21, 26b, CO2, 29b and 32

[0156] 39a 39 with reduced 26b content

[0157] 39b 39a with reduced CO2 content

[0158] 40 Nitro compounds

[0159] 80 37 and / or utilization of polyurethane materials from different sources on the market

[0160] 90 Polyurethane based materials - End of life recycling.

[0161] FIG2 shows a schematic overview of the entire process, including the RWGS reaction, the electrolysis of hydrochloric acid according to the diaphragm method (HCl-DIA) for the production of chlorine, including optional PU production, the use of polyurethane material and the use of the polyurethane material waste obtained therefrom to produce CO for the RWGS reaction. 2。

[0162] The assignment of reference numerals used in FIG. 2 is the same as that defined in FIG. 1 .

[0163] Figure 1 and Figure 2 A closed-loop variant of the process according to the invention is described. Within the scope of one embodiment, as a supply of polyurethane material waste (38), it is of course also possible to use polyurethanes which are not recycled from polyurethane materials (37) in the sense of a closed-loop process, but are directly from fossil sources and not recycled, prepared from toluene-2,4-diisocyanate. In this variant, steps (3), (35a), (35b) and (37) in Figures 1 and 2 can be omitted.

[0164] Example 1

[0165] According to the invention, low-emission toluene diisocyanate (TDI) is produced by means of RWGS, the heating of which is carried out with biogas, the recovery of HCl by means of HCl gas phase oxidation (Deacon), and the provision of H2 by water electrolysis.

[0166] 17.84 t / h of CO2 and 0.81 t / h of H2 are introduced into the RWGS reaction chamber (6) operated at a temperature of 802°C. The resulting product gas mixture (39) is removed from the RWGS reaction, which consists of CO (21), H2O (26b), unreacted CO2 and unreacted H2 (29a) and a by-product (32) which is mainly a small amount of methane and is supplied to the water separation (7), thereby obtaining 7.3 t / h of water. This water (26b) is supplied to the water electrolysis (5). A total of 3.24 t / h of hydrogen are removed from the water electrolysis (5), so that an additional 21.86 t / h of water are added. The remaining gas mixture (39a) from the RWGS is supplied to the CO2 separation (8). The CO2 separation is carried out with the aid of amine washing, wherein the separated CO2 (31b) is supplied to the RWGS reaction again. The energy for separating CO2 from the CO2-amine complex formed is obtained from the water separation (7) of the RWGS gas (39). The gas (39b) freed from CO2 is supplied to the H2 / CO separation (9). For this H2-CO separation, a so-called cold box is used, in which the H2-CO gas mixture is cooled and hydrogen and CO are separated. The separated hydrogen (29c) is supplied to the RWGS (6) again. 11.35 t / h of CO are supplied from the H2-CO separation (9) to the phosgene synthesis (1). Here, CO reacts with 29.79 t / h of chlorine, which is taken from the HCl gas phase oxidation (16). 40.15 t / h of phosgene are taken from the phosgene synthesis (1) and converted into 35.27 t / h of toluene diisocyanate (24) in the isocyanate preparation (2) with 24.73 t / h of toluene diamine 23. The HCl gas (25) thus produced in an amount of 29.59 t / h is supplied to the HCl gas phase oxidation (16) after purification by cryogenic distillation. In the HCl gas phase oxidation (16), the HCl gas is converted into chlorine and H2O at about 300° C. over a catalyst based on ruthenium oxide by oxygen (27). The required oxygen (27) is taken from the water electrolysis (5). For the ring-closing variant of the process according to the invention, the resulting toluene diisocyanate (24) is converted into a polyurethane material (37) in a conventional manner with a polyether polyol (35a) or a polyester polyol (35b).

[0167] After the polyurethane material has been used (80) in various applications on the market, it can be collected and recycled (90) in order to supply the polyurethane material waste (38) thus obtained to a combustion (10b). Here, the combustion is carried out with oxygen (27) obtained from water electrolysis (5), so that a high-concentration CO2 waste gas stream (31) is generated. This CO2 stream (31) is supplied to a CO2 purification (4), where the water originating from the combustion is removed and nitrogen oxides and sulfur oxides are separated. 17.84 t / h of CO2 are then supplied to the RWGS (6). Within the scope of one embodiment, as a supply of polyurethane material waste (38), it is of course also possible to use polyurethane material that is not recycled from polyurethane material (37) in the sense of a closed-loop process, but is directly derived from fossil sources and has not been recycled, which has been prepared from toluene-2,4-diisocyanate. In this variant, it is possible to Figure 1 and Figure 2 The hydrogen (29) is produced in a water electrolysis with a power of 45 MW, using renewable energy. The water electrolysis (5) is an alkaline water electrolysis with a power of 8 kA / m 2 The operation is carried out at a current density of 1.500 MW and a cell voltage of 2 V per electrolysis element. 45 MW and 21.86 t / h of water and 7.3 t / h of water from the H2O separation (7) are supplied. 3.24 t / h of H2 are removed from the water electrolysis.

[0168] The RWGS reaction is carried out at 802°C, a temperature generated by burning biogas.

[0169] By means of the process of the invention, 22% of the carbon present in TDI is replaced by a non-fossil carbon source.The CO2 footprint of phosgene produced from CO and Cl2 is further reduced by using renewable energy in water electrolysis.

[0170] Example 2

[0171] According to the invention, low-emission toluene diisocyanate (TDI) is produced by means of RWGS, the heating of which is carried out with biogas, the recovery of HCl by means of HCl membrane electrolysis, and the provision of H2 for hydrogenation of dinitrotoluene by water electrolysis.

[0172] 17.84 t / h of CO2 and 0.81 t / h of H2 are introduced into the RWGS reaction chamber (6) operated at a temperature of 802°C. The hydrogen here originates from HCl recovery by HCl membrane electrolysis. The resulting product gas mixture (39) is removed from the RWGS reaction, which consists of CO (21), H2O (26b), unreacted CO2 and unreacted H2 (29a) and by-products (32) which are mainly small amounts of methane, and is supplied to water separation (7), where 7.3 t / h of water is obtained. This water (26b) is supplied to water electrolysis (5) in turn. A total of 2.43 t / h of hydrogen is removed from the water electrolysis, whereby 14.56 t / h of water are additionally added. The remaining gas mixture (39a) from the RWGS is supplied to CO2 separation (8). This CO2 separation is carried out with the aid of amine washing, whereby the separated CO2 (31b) is supplied to the RWGS in turn. The energy for separating CO2 from the CO2-amine complex formed is obtained from the water separation (7) of the RWGS gas (39). The gas (39b) freed from CO2 is supplied to the H2 / CO separation (9). For the H2-CO separation, a so-called cold box is used, in which the H2-CO gas mixture is cooled and hydrogen and CO are separated. The separated hydrogen (29c) is supplied to the RWGS (6) again. 11.35 t / h of CO are supplied from the H2-CO separation (9) to the phosgene synthesis (1). Here, CO reacts with 29.79 t / h of chlorine, which is removed from the HCl diaphragm electrolysis (17). 40.15 t / h of phosgene are removed from the phosgene synthesis (1) and converted into 35.27 t / h of toluene diisocyanate (24) in the isocyanate preparation (2) with 24.73 t / h of toluene diamine 23. The HCl gas (25) thus produced in an amount of 29.59 t / h is supplied to the HCl diaphragm electrolysis (17) after purification by cryogenic distillation, absorption in water to form 35% hydrochloric acid, and purification of the hydrochloric acid by means of activated carbon. Chlorine and hydrogen are removed by the HCl diaphragm electrolysis. The hydrogen is purified and supplied to the RWGS. The toluene diisocyanate (24) obtained is converted into a polyurethane material (37) in a conventional manner with a polyether polyol (35a) or a polyester polyol (35b).

[0173] After the polyurethane material is used (80) in various applications on the market, it can be collected and recycled (90) to supply the polyurethane material waste (38) thus obtained to combustion (10b). Here, the combustion is carried out with oxygen (27) obtained from water electrolysis (5), thereby generating a high-concentration CO2 waste gas stream (31). This CO2 stream (31) is supplied to CO2 purification (4), where the water originating from the combustion is removed and nitrogen oxides and sulfur oxides are separated. 17.84 t / h of CO2 are then supplied to RWGS (6).

[0174] Hydrogen (29) is produced in a water electrolysis with a power of 45 MW, using renewable energy. The water electrolysis (5) is an alkaline water electrolysis with 8 kA / m 2 The operation is carried out at a current density of 1.500 MW and a cell voltage of 2 V per electrolysis element. 45 MW and 21.86 t / h of water and 7.3 t / h of water from the H2O separation (7) are supplied. 3.24 t / h of H2 are removed from the water electrolysis.

[0175] RWGS was performed at 802°C, a temperature produced by burning biogas.

[0176] By means of the process of the invention, 22% of the carbon present in TDI is replaced by a non-fossil carbon source.The CO2 footprint of phosgene produced from CO and Cl2 is further reduced by using renewable energy in water electrolysis.

Claims

1. A process for preparing isocyanates and optionally polyurethanes by at least the following steps: Synthesis (1) of phosgene (20) from carbon monoxide (21a) and chlorine (22), Phosgene (20) is converted (2) into diisocyanate (24) and hydrogen chloride (25) using diamine (23), Providing a CO2 gas flow (31), purifying (4) the secondary components of the CO2 gas stream (31) to obtain purified carbon dioxide (31a), electrolyze (5) water (26) into hydrogen (29) and oxygen (27), A hydrogen stream (29a) is provided and fed together with a purified CO2 gas stream (31a) into a RWGS reaction zone and the reactants are converted (6) according to the RWGS principle into a product gas mixture (39) consisting of water vapor (26b), CO (21) and optional by-products (32), separating (7) the water of the water vapor (26b) from the product gas mixture (39) and recycling the water to the water electrolysis (5), separating (8) unreacted carbon dioxide (31b) from the gas mixture (39a) of the RWGS reaction (6) obtained from the separation (7) and recycling the unreacted carbon dioxide (31b) to the RWGS reaction (6), separating (9) the hydrogen (29a) which has not reacted in the RWGS reaction (6) from the gaseous mixture (39b) of carbon monoxide (21a) and hydrogen (29c) obtained after the separation (8), The remaining carbon monoxide (21a) from the separation (9) is fed to the phosgene synthesis (1), The hydrogen (29) from the water electrolysis (5) is fed to the hydrogenation (34) of the nitro compound for the preparation (2) of the diamine (23), separation and purification (11) of the hydrogen chloride (25) formed in the isocyanate preparation (2) and subsequent oxidative conversion (18) of the hydrogen chloride (25) as a reaction with oxygen (27) in a thermal catalytic gas phase oxidation (16) to give chlorine (22a) and water (26) and / or as an electrochemical oxidation (12) of the hydrogen chloride (25) to give chlorine (22b) and / or as an electrochemical oxidation (17) of the hydrogen chloride (25) by means of HCl membrane electrolysis (17) to give chlorine (22c) and hydrogen (29), The chlorine (22a, 22b, 22c) formed previously is supplied to the phosgene synthesis (1).

2. The method according to claim 1, characterized in that It is a process for preparing isocyanates and polyurethanes by: Synthesis (1) of phosgene (20) from carbon monoxide (21a) and chlorine (22), Phosgene (20) is converted (2) into diisocyanate (24) and hydrogen chloride (25) using diamine (23), converting (3) a diisocyanate (24) into a polyurethane (37) using a polyether polyol (35a) and / or a polyester polyol (35b), Providing a CO2 gas flow (31), purifying (4) the secondary components of the CO2 gas stream (31) to obtain purified carbon dioxide (31a), electrolyze (5) water (26) into hydrogen (29) and oxygen (27), A hydrogen stream (29a) is provided and fed together with a purified CO2 gas stream (31a) into a RWGS reaction zone and the reactants are converted (6) according to the RWGS principle into a product gas mixture (39) consisting of water vapor (26b), CO (21) and optional by-products (32), separating (7) the water of the water vapor (26b) from the product gas mixture (39) and recycling the water to the water electrolysis (5), separating (8) unreacted carbon dioxide (31b) from the gas mixture (39a) of the RWGS reaction (6) obtained from the separation (7) and recycling the unreacted carbon dioxide (31b) to the RWGS reaction (6), separating (9) the hydrogen (29a) which has not reacted in the RWGS reaction (6) from the gaseous mixture (39b) of carbon monoxide (21a) and hydrogen (29c) obtained after the separation (8), The remaining carbon monoxide (21a) from the separation (9) is fed to the phosgene synthesis (1), The hydrogen (29) from the water electrolysis (5) is fed to the hydrogenation (34) of the nitro compound for the preparation (2) of the diamine (23), separation and purification (11) of the hydrogen chloride (25) formed in the isocyanate preparation (2) and subsequent oxidative conversion (18) of the hydrogen chloride (25) as a reaction with oxygen (27) in a thermal catalytic gas phase oxidation (16) to give chlorine (22a) and water (26) and / or as an electrochemical oxidation (12) of the hydrogen chloride (25) to give chlorine (22b) and / or as an electrochemical oxidation (17) of the hydrogen chloride (25) by means of HCl membrane electrolysis (17) to give chlorine (22c) and hydrogen (29), The chlorine (22a, 22b, 22c) formed previously is supplied to the phosgene synthesis (1).

3. The method according to claim 1 or 2, characterized in that: Carbon dioxide (31) provided from the utilization (10) of polyurethane material waste (38) by combustion (10b) and / or by pyrolysis (10a) is used for the RWGS synthesis (6).

4. The method according to claim 3, characterized in that The combustion (10b) is carried out using a gas having an oxygen O2 content of at least 30% by volume.

5. The method according to claim 3, characterized in that: The gas has an oxygen O2 content of at least 50% by volume.

6. The method according to any one of claims 1 or 2, characterized in that: The water electrolysis (5) and / or electrochemical oxidation (12, 17) is performed using electric current generated from renewable energy.

7. The method according to claim 1 or 2, characterized in that: The water electrolysis (5) and / or electrochemical oxidation (12, 17) is carried out using electric current obtained from the feedback energy obtained in the combustion of polyurethane material waste and / or in the RWGS reaction.

8. The method according to claim 1 or 2, characterized in that: The RWGS reaction (6) is carried out with the aid of electric current (28) generated from renewable energy.

9. The method according to claim 1 or 2, characterized in that: The heating of the RWGS reaction (6) is carried out with the aid of feedback energy obtained from the combustion of polyurethane material waste (38).

10. The method according to claim 1, characterized in that Additionally included is the conversion (3) of the diisocyanate (24) to the polyurethane (37) using a polyether polyol (35a) and / or a polyester polyol (35b).

11. The method according to claim 1 or 2, characterized in that: The heating of the RWGS reaction (6) is carried out by means of burning hydrocarbons from renewable sources.

12. The method according to claim 1 or 2, characterized in that: The polyurethane material is recovered as polyurethane material waste (38) after its use, and the polyurethane material waste (38) is burned to generate carbon dioxide (31), and the carbon dioxide (31) is used as a raw material in the purification step (4).

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