WO2025078241A1 - Water-management for electrolysis-related reverse water-gas shift processes - Google Patents

Abstract

The present invention relates to improved water purification in power-to-liquid systems and processes, which are based on reverse water-gas shift reaction in conjunction with the electrolysis of water in order to provide hydrogen, as a result of the controlled use of an additional at least one ion exchanger and/or at least one gase-phase filtering device.

Description

Water management for reverse water gas shift processes associated with electrolysis

All documents cited in the present application are incorporated by reference in their entirety into the present disclosure.

The present invention relates to improved water purification in power-to-liquid systems or processes based on reverse water gas shift reaction in conjunction with water electrolysis for synthesis gas production from carbon dioxide and hydrogen.

State of the art:

Electrolysis is used in many processes to produce synthetic fuels or chemicals from renewable electricity, known as the power-to-liquid process. In these electrolysis processes, water is first split into hydrogen and oxygen using renewable electricity. The hydrogen is then used to reduce CO2 and, via appropriate synthesis, convert it into methanol, ethanol, other higher-value alcohols, and liquid hydrocarbons or their derivatives. In some processes, a partial reduction of the CO2 to CO2 is first forced via a reverse water gas shift reaction (rWGS), as some synthesis catalysts, such as cobalt-containing systems, are unable to activate CO2 directly as a molecule. The first step is therefore to produce a synthesis gas (a mixture of CO2, _H2 , and residual CO2). From a thermodynamic perspective, the reverse water gas shift reaction requires temperatures of at least 400°C, and preferably even above 700°C, to prevent side reactions such as the formation of methane or carbon. In almost all process variants of the reverse water gas shift reaction, steam is added to prevent the formation of solid carbon. The water used for evaporation must meet high quality standards, as the catalysts of both the water gas shift reaction and those of the subsequent synthesis catalysts are sensitive to impurities. Impurities include primarily chlorides and Fluorides, as well as other anions. The removal of carbonate formers, i.e., the cations magnesium and calcium, is also important for the formation of solid deposits on the surfaces of recuperative heat exchangers or electrical heating systems for water evaporation. Since electrolysis has similar water quality requirements, it is obvious that both electrolysis and rWGS are supplied with (almost) identical water. In such cases, normal drinking water is often first softened (to remove magnesium) and then freed of most of its ions via reverse osmosis. In electrodeionization, a combination of electrodialysis and ion exchange, residual amounts of conductive salt ions (e.g., sodium and chloride) that are harmful to the electrolysis are removed. Particularly in electrolysis with a polymer electrolyte, a high proportion of water is discharged from the electrolysis process to prevent accumulation on the membranes, meaning only a fraction of the water is used to generate hydrogen. To ensure the highest possible utilization rate of the treated water, the return water is often continuously treated using ion exchangers. The ion exchanger is usually located in a water storage tank, i.e., it operates alongside the water cycle rather than within it. The water quality obtained in this way is, according to current knowledge, sufficient to ensure long-term operation of the electrolysis system.

However, despite extensive cleaning measures, silicon dioxide has been proven to deposit in the hot areas of the rWGS reactor during operation of the rWGS, despite the extensive cleaning measures. Silicates or free silicon present in drinking water are only partially removed by the cleaning process described above. For example, in a corresponding setup with a storage tank, a concentration of around 0.2 mg/L of silicon was repeatedly detected in the tank. Since similar silicon values were also found in the return flow from the electrolysis, the removal of water via the electrolysis does not lead to a depletion, but rather to an increase in the concentration of silicates. Furthermore, the silicates do not deposit in the evaporation process (i.e., in/at the evaporator) upstream of the rWGS, but are transported to the rWGS in the form of siloxanes (formed with hydrocarbons from the return of unconverted synthesis gas from the synthesis step) and are deposited as SiC both in the hot zones and on the catalyst of the rWGS reactor. It has been proven that the catalyst is deactivated, build-up of SiC layers in heat exchange zones and, in extreme cases, can even lead to blockage of channel structures within structured reactors for rWGS.

Descriptions of water purification can be found, for example, in the leaflets "Keeping the water ultrapure inside electrolyzers challenges and solutions" or "Water treatment for green hydrogen" from Eurowater - a Grundfoss Company.

US 2019/0359894 A1 or DE 697 21 814 T2 can also be cited as state of the art.

There is therefore great interest in providing devices and methods to remove silicon or silicon compounds from the water cycle of power-to-liquid systems based on water electrolysis and connected rWGS as far as possible.

In this respect, based on the known state of the art, there is still a considerable need to improve the current state of the art.

Task:

The object of the present invention was therefore to overcome the disadvantages of the prior art described above and to provide devices and methods which no longer have these problems, or at least only to a considerably lesser extent, and in particular enable improved removal of silicon or silicon compounds from the water cycle in power-to-liquid systems which are based on water electrolysis and have connected rWGS.

Further tasks will become apparent to the person skilled in the art when considering the claims and the following description.

Solution:

These and other objects which will become apparent to the person skilled in the art from the present description are achieved by the subject matter presented in the independent claims. Preferred and particularly advantageous embodiments are presented in the dependent claims and the following description.

Detailed description of the invention:

In the context of the present invention, all quantities are to be understood as weights unless otherwise stated.

In the context of the present invention, the term "ambient temperature" means a temperature of 20°C. Unless otherwise stated, temperatures are in degrees Celsius (°C).

Unless otherwise stated, the reactions or process steps listed are carried out at ambient pressure (=normal pressure/atmospheric pressure), i.e. at 1013 mbar.

Pressure specifications within the scope of the present invention, unless otherwise stated, mean absolute pressure specifications, ie x bar means x bar absolute (bar _a ) and not x bar gauge.

The present invention is based on the fact that at least one additional purification stage or at least one additional purification step of the water treated by means of a deionization step according to the prior art is provided between the water storage tank and before introduction into the rWGS.

A first subject of the present invention is accordingly a device for converting CO2 to hydrocarbons comprising a reverse water gas shift reaction for generating synthesis gas, wherein the device comprises: a water supply line, in particular for tap water, at least one device for treating the water comprising at least one of a softening device, a reverse osmosis device, an electrodeionization device, preferably, but not necessarily (depending on the initial quality of the supplied water), all three, at least one water storage tank connected downstream of the device for treating the water with a connected ion exchanger unit, which can comprise several individual ion exchangers and which is configured in particular for continuous water treatment, at least one rWGS device, at least one evaporator device which is connected upstream of the at least one rWGS device and evaporates water originating from the water storage tank before it is introduced into the at least one rWGS device, at least one electrolysis device which is preferably configured to be operated with electricity from renewable energies and which, in some variants, is preferably operated at least partially, in particular completely, with water originating from the water storage tank, wherein the device is configured such that at least a portion of the hydrogen generated in the at least one electrolysis device is fed into the at least one rWGS device(s), wherein the at least one electrolysis device is controlled in preferred embodiments of the present invention such that the complete amount of hydrogen required for the rWGS originates from the at least one electrolysis device, thus no additional hydrogen source is required, optionally, in preferred embodiments of the present invention, at least one mixing device for mixing the hydrogen originating from the at least one electrolysis device and the water vapor introduced into the at least one rWGS device, wherein this at least one mixing device is connected upstream of the at least one rWGS device, at the water vapor inlet into the at least one rWGS device or within the at least one rWGS device, is arranged, in preferred variants designed as a multi-way valve or as described in DE 10 2017 120 814, there for example Figures 1 or 2, optionally at least one return for water discharged from the at least one electrolysis device into the water storage tank, wherein the return optionally comprises a degassing device, this return is preferably implemented in particular in electrolysis with a polymer electrolyte and serves to avoid accumulation on the membranes.

In contrast to the prior art, the device according to the invention comprises at least one additional device which is arranged between the at least one water storage tank and the water gas inlet into the at least one rWGS device. It is also important that this at least one additional device is separated from one or all of the ion exchanger units assigned to this water tank by at least one water storage tank.

The at least one additional device according to the invention is a) at least one ion exchange device, b) at least one gas phase filter device, or c) at least one ion exchange device, and at least one

Gas phase filter device, wherein the at least one gas phase filter device is arranged downstream of the at least one ion exchange device).

In preferred embodiments of the present invention, liquid water flows through the ion exchange device and gaseous water or a gas mixture containing gaseous water (containing one or more of H ₂ , CO ₂ , CO and optionally short-chain hydrocarbons) flows through the gas phase device.

In preferred embodiments of the present invention, the at least one ion exchange device is arranged between the at least one water storage tank and the at least one evaporator device upstream of the water gas inlet into the at least one rWGS device.

In further preferred embodiments of the present invention, the at least one ion exchange device comprises two or more individual ion exchangers, which are particularly interconnected such that water can flow through them sequentially, in parallel, or individually. In some variants, all ion exchangers can be blocked simultaneously; this then either blocks the water supply to the rWGS, or a diversion around or through the ion exchange device allows the water to be directed to the rWGS without further treatment through the ion exchange device.

In further embodiments of the present invention, it is preferred if at least the last individual ion exchanger through which the water flows is an acidic ion exchanger. It is further preferred if the ion exchanger through which the fluid flows first is a basic ion exchanger and the ion exchanger through which the fluid flows next is an acidic ion exchanger, and the ion exchangers are flowed through in this order. In particularly preferred variants of the present invention, the individual ion exchangers are also combination ion exchangers or double exchanger cartridges consisting of two acidic subunits or individual cartridges, or a basic cartridge (subunit) arranged first in the flow direction and an acidic cartridge (subunit) arranged last in the flow direction, the latter arrangement (basic first, acidic last) being particularly preferred. Most preferably, according to the invention, two or more individual ion exchangers are arranged in the ion exchange device according to the invention, each of which is a double exchanger cartridge (double combination ion exchanger), comprising first a basic ion exchanger cartridge (basic subunit) in the flow direction and last an acidic ion exchanger cartridge (basic subunit) in the flow direction.

Commercially available ion exchange resins are typically supplied in the form of round beads. Examples of basic ion exchange resins include Lewatit® ASB 1 P, a high-quality, gel-like, strongly basic (Type I) anion exchange resin produced from a crosslinked styrene-divinylbenzene polymer. An example of a strongly acidic ion exchange resin is Lewatit® C 249, a gel-like cation exchanger with a heterodisperse particle size distribution based on a styrene-divinylbenzene copolymer. Lewatit® C 249 can be used both in single-filter circuits and as a cation component in mixed beds. Lewatit® ASB 1 and Lewatit® C 429 are commercially available examples of ion exchange resins that can be used (preferably) in the context of the present invention; similar products from other manufacturers are known to those skilled in the art.

Instead of double exchanger cartridges (combination ion exchangers), other multiple cartridges, for example, triple, quadruple, or quintuple exchanger cartridges (triple, quadruple, or quintuple combination ion exchangers), can of course also be used, although it is usually more economical to use double exchanger cartridges (double combination ion exchangers). It should be noted that, within the scope of the present invention, the term "cartridge" should not be interpreted as limiting cartridges in the true sense. Although it is often useful for practical reasons (e.g., interchangeability), Cartridges or cartridge-like containers are used, but individual ion exchangers with corresponding subunits but not designed in a cartridge-like manner serve the same purpose. Corresponding designs of ion exchangers, including multiple ion exchangers, are known to those skilled in the art.

Furthermore, it is preferred within the scope of the present invention if the at least one gas phase filter device is arranged between the at least one evaporator device upstream of the rWGS and the water gas inlet into the at least one rWGS.

In further preferred embodiments of the present invention, the at least one gas-phase filter device comprises two or more individual gas-phase filters, which are preferably interconnected such that water can flow through them sequentially, in parallel, or individually. In some variants, all gas-phase filters can be blocked simultaneously; this then allows either the water supply to the rWGS to be blocked, or a diversion around or through the gas-phase filter device allows the water to be directed to the rWGS without further treatment through the gas-phase filter device.

Within the scope of the present invention, it is preferred if the at least one gas-phase filter device comprises an alumina filter or aluminosilicate filter, or an alumina filter and aluminosilicate filter. It is further preferred if the gas-phase filter device is configured to operate at temperatures between 200°C and 400°C.

Furthermore, the present invention relates to a process for removing silicon and silicon compounds from the water circuit of a device for converting CO2 to hydrocarbons, comprising a reverse water gas shift reaction for generating synthesis gas.

It is preferred if this method is operated with a device according to the invention, in particular as described above (and further below). For the method according to the invention, the device on which it is operated comprises at least: a water supply line, in particular for tap water, at least one device for treating the water, comprising at least one of a softening device, a reverse osmosis device, an electrodeionization device, preferably, but not necessarily (depending on the initial quality of the supplied water), all three, at least one water storage tank connected downstream of the device for treating the water, with a connected ion exchanger unit, which may comprise several individual ion exchangers, wherein the device is configured in particular for continuous water treatment, at least one rWGS device, at least one evaporator device connected upstream of the at least one rWGS device and evaporates water originating from the water storage tank before being introduced into the at least one rWGS device, at least one electrolysis device, which is preferably configured to be operated with electricity from renewable energies, and is preferably operated at least partially, in particular completely, with water originating from the water storage tank, wherein the device is configured such that at least part of the hydrogen generated in the at least one electrolysis device is converted into the at least one rWGS device(s) is conducted, wherein the at least one electrolysis device is controlled in preferred embodiments of the present invention such that the complete amount of hydrogen required for the rWGS originates from the at least one electrolysis device, i.e. no additional hydrogen source is required, optionally, in preferred embodiments of the present invention, at least one mixing device for mixing the hydrogen originating from the at least one electrolysis device and the water gas introduced into the at least one rWGS device, wherein this at least one mixing device is arranged upstream of the at least one rWGS device, at the water gas inlet into the at least one rWGS device or within the at least one rWGS device, in preferred Variants designed as a multi-way valve or as described in DE 10 2017 120 814, there for example Figures 1 or 2, optionally at least one return for water discharged from the at least one electrolysis device into the water storage tank, wherein the return comprises a degassing device, this return is preferably implemented in particular in electrolysis with a polymer electrolyte and serves to avoid accumulation on the membranes.

What is essential for the method according to the invention is that, in contrast to the prior art, it comprises:

A) additionally arranging between the at least one water storage tank (WV) and the water gas inlet into the at least one rWGS device a) at least one ion exchange device, b) at least one gas phase filter device, or c) at least one ion exchange device and at least one

Gas phase filter device, wherein these are separated from the ion exchange unit associated therewith at least by the at least one water storage tank, and wherein the at least one gas phase filter device is arranged downstream of the at least one ion exchange device; and

B) Passing the water coming from the at least one water storage tank through the at least one ion exchange device or through the at least one gas phase filter device, or through the at least one ion exchange device and the at least one gas phase filter device, and separating silicon or silicon compounds or silicon and silicon compounds from the water passed through in the device(s).

In preferred embodiments of the process according to the invention, the ion exchange device is flowed through by liquid water and the gas phase device is flowed through by gaseous water or a gas mixture containing gaseous water (containing one or more of H ₂ , CO ₂ , CO and optionally short-chain hydrocarbons). Furthermore, the preferred embodiments mentioned above for the device are also applicable analogously to the method according to the invention.

Last but not least, the present invention relates to the use of at least one ion exchange device, at least one gas phase filter device, or at least one ion exchange device and at least one gas phase filter device for separating silicon, silicon compounds, or silicon and silicon compounds from the water circuit of devices for converting CO2 to hydrocarbons, comprising a reverse water gas shift reaction for generating synthesis gas and further comprising an electrolysis device, in addition to any ion exchange units that may be assigned to the water storage tank(s) in the device.

The first fundamental possibility for achieving the objectives underlying the present invention therefore consists in the installation of at least one additional ion exchange device before the water is introduced into the rWGS. The connection of this ion exchange device can be carried out in a conventional and known manner. A preferred embodiment of the present invention is one in which the ion exchange device comprises two separate ion exchangers; one possible (but not the only possible) variant of this is illustrated in Figure 5.

This preferred embodiment of the invention with two or more separate ion exchangers has the advantage, for example, that if one ion exchanger has to be removed for regeneration, continuous operation is still possible because the second stage continues to operate. The connection of the separate ion exchangers chosen in the preferred embodiment of the invention, in that they can be selectively connected in series or parallel and, in particular, can also be switched on or off individually or together, allows sufficient water quality to be ensured by one of the two ion exchangers (or, if there are more than one, the ones that are not switched off). This type of connection allows, for example, one (not switched off) ion exchanger to be operated (i.e., to allow water to flow through it) and to capture silicon and/or silicon compounds, while the second ion exchanger acts as a police filter (redundancy system). It is further preferred if, within the ion exchange device, downstream of each individual ion exchanger, which is preferably a double ion exchanger with, in the direction of flow, first a basic subunit and then an acidic subunit, a measuring device is arranged which is associated with the ion exchanger and measures the conductivity of the flowing fluid, the silicon concentration in the flowing fluid, or both.

The silicon concentration is measured, for example, using silica analyzers, which can precisely monitor the Si content in the fluid (feed water) and the fatigue of ion exchangers. These analyzers are preferably based on standard colorimetric measurement methods, particularly the so-called heteropolyblue method.

If the silicon concentration after an ion exchanger reaches 50 ppb, preferably 35 ppb, particularly preferably 25 ppb, and especially 10 ppb, this is an indicator that the ion exchanger should be replaced. Accordingly, in preferred variants, upon detection of a silicon concentration of 50 ppb, preferably 35 ppb, particularly preferably 25 ppb, and especially 10 ppb, the respective (monitored/measured) ion exchanger is replaced, particularly during ongoing operation, with a second (or more) ion exchangers in the ion exchange device ensuring or taking over silicon removal. One method for detecting (or the absence of) silicon on solids, for example, catalysts in subsequent reaction steps, is energy-dispersive analysis in a microprobe apparatus.

The conductivity is measured, for example, using standard (commercially available) conductivity measuring devices.

The conductivity of the fluid (feed water) is measured and a change in conductivity is recorded, which is an indicator of decreasing ion exchange capacity. If the conductivity measurement after an ion exchanger reaches a value change of 0.5 pS/cm or more, preferably 0.4 pS/cm or more, particularly preferably 0.3 pS/cm or more and in particular 0.2 pS/cm or more, this is an indicator that the ion exchanger should be replaced. In preferred variants, if a conductivity change of 0.5 pS/cm or more, preferably 0.4 pS/cm or more, particularly preferably 0.3 pS/cm or more and in particular 0.2 pS/cm or more, is detected, the respective (monitored/measured) ion exchanger is replaced, in particular in the ongoing operation, during which a second (or more) ion exchangers in the ion exchange device ensure or take over the silicon removal.

Particularly preferred within the scope of the present invention are measuring devices which measure conductivity.

In the context of the present invention, it has surprisingly been shown that, in particular, the measurement of (small) conductivity changes is an effective means of preventing a breakdown of silicon because it is economical and practically easy to implement.

In this embodiment, the use of acidic ion exchangers is particularly possible. It is preferred if the respective ion exchange device and/or the respective individual ion exchangers contain a series connection of basic and acidic ion exchangers (or subunits) to further improve the retention of silicon and silicon compounds. A purely basic stage is less preferred, since basic ion exchangers can cause undesirable entrainment of cations.

The second principle possibility to solve the problems underlying the present invention consists in the installation of an additional gas phase filter device downstream of the evaporator and before the introduction of the water (vapor) into the rWGS.

This embodiment is preferably based on a similar interconnection of individual gas-phase filters as the additional at least one additional ion exchange device just described; thus, two or more gas-phase filters are arranged in series or parallel in the device, which can be switched on or off individually or together.

Ideally, in this embodiment of the invention, the separation of silicon and silicon compounds takes place on aluminum oxides or aluminosilicates, which in particular also enable strong reactive adsorption of siloxanes at temperatures between 200-400°C.

In this respect, the separation can be carried out in the steam stream or in the mixture of different feed compositions (H2+CO2+H2O, H2+H2O, or CO2+H2O or conceivable combinations with recycled gas not converted in the synthesis). If the CO2 also contains siloxanes from a fermentation process of biomass or residues, the purification can be carried out as a process combination (in the stream CO2+H2O).

The third principal possibility for achieving the objects underlying the present invention consists in the installation of an additional ion exchange device, as described in detail above, before the water is introduced into the rWGS and an additional gas phase filter device, as described in detail above, downstream of the additional ion exchange device, in which case it is preferred that an evaporator device is arranged between the two additional devices in order to evaporate the water.

The devices and methods according to the invention provide several significant advantages over the prior art, some, but not all, of which are the following:

Higher CO2 to CO conversions and, consequently, lower _H2 /CO through the prevention of Si deposition on the catalyst surface. Si deposits were detected without downstream purification. Deposits were also detected in the heat exchange zones of the rWGS reactors.

Improvements in _H2 /CO are visible. No more significant increase in pressure loss, as was the case without post-cleaning.

Improved removal of silicon and/or silicon compounds from the water cycle.

Easy to integrate into existing systems (by interposing into existing pipe connections).

Longer lifetime of devices for converting CO2 to hydrocarbons comprising a reverse water gas shift reaction to produce synthesis gas.

The person skilled in the art can, insofar as these are not explicitly described in this description, determine the exact design of the devices described, such as size, wall thicknesses, materials, etc., to suit the reaction conditions envisaged for a specific reaction within the scope of his general technical knowledge. If, in the description of the devices according to the invention, parts or the entire device are marked as "consisting of", this is to be understood as referring to the essential components mentioned. Self-evident or inherent parts such as lines, valves, screws, housings, measuring devices, storage containers for reactants/products, etc. are not excluded.

Unless explicitly described, the individual parts of the devices are operatively connected to one another in a manner customary and known in the art.

The various embodiments of the present invention, for example - but not exclusively - those of the various dependent claims, can be combined with one another in any desired manner, provided that such combinations do not contradict one another.

Figure description:

The present invention is explained in more detail below with reference to the drawings. The drawings are not to be interpreted in a limiting manner and are not to scale. The drawings are schematic and, furthermore, do not contain all features that conventional devices have, but are reduced to the features essential to the present invention and its understanding; for example, screws, connections, etc. are not shown or are not shown in detail. The same reference numerals indicate the same features in the figures, the description, and the claims. Explanatory passages that do not only refer directly to the respective figure are accordingly not limited to this, but are to be understood within the context of the entire disclosure.

Figure 1 shows a state-of-the-art circuit for water treatment with electrolysis starting from drinking or tap water W, often also called city water, including the option for rWGS. It can be seen that drinking water is extracted and fed to the treatment. The treatment in this figure is carried out using three consecutive steps: softening EH, reverse osmosis U/O and electrodeionization ED (each of which Wastewater A can arise). However, not all three steps always take place or not all three devices are always present. The treated water is then fed into the water storage tank WV, from where it is passed on to the electrolysis unit EL or the rWGS rW. As can be seen, the water storage tank WV is assigned its own ion exchange unit IT, which is intended to ensure that the water circulated between the electrolysis unit EL and the water storage tank WV is continuously freed of unwanted impurities. This circulation is only indicated in the figure; in particular, the return flow RI from the electrolysis unit EL is shown, with a deaerator EG assigned to this return flow RI. As can also be seen, water is taken from the water storage tank WV and fed to the rWGs rW. Since the rWGS is advantageously fed with gaseous water or a gas mixture containing gaseous water (containing one or more of _H2 , CO2, CO and optionally short-chain hydrocarbons), an evaporator V is arranged between the water storage tank WV and the rWGS rW, which evaporates the (fully demineralized) water VE before it is fed to the rWGS rW as steam D. As further indicated, the rWGS rW is also fed with a gas mixture containing _CO2 or CO2. The problem with such prior art devices is that the water fed to the rWGS rW (as steam D) may still contain too many impurities, in particular silicon and/or silicon compounds. In addition, it is illustrated that hydrogen _H2 originating from the electrolysis EL is fed into the rWGS rW. Finally, the right-hand edge of the figure illustrates that the electrolysis device EL is supplied with electricity C, preferably generated from renewable energy sources, and that the rWGS rW is passed on to a synthesis S, for example, a Fischer-Tropsch process, from which the product Pr is then derived. In addition to the product Pr, residues are also produced, some of which are recycled as recycle stream Re—shown here, only as an example, directly into the RWGS rW and/or into the CC stream (fed to the rWGS)—and some of which are or can be derived as purge stream Pu (and discarded or otherwise processed).

Figure 2 illustrates one possible ion exchanger variant of the present invention. The device shown here corresponds in its basic structure to that described in Figure 1. However, it should be noted that the present invention is not limited 1:1 to such devices. In contrast to Figure 1, here An ion exchange device F is now arranged between the water storage tank WV and the evaporator V. This means that the water coming from the water storage tank WV is further purified before evaporation by the ion exchanger(s) present in the ion exchange device F. Because the additional ion exchange device F arranged according to the invention is separated from the ion exchange unit IT assigned to it by the water storage tank WV, the additional ion exchange device F arranged according to the invention does not represent a simple extension of the ion exchange unit IT, but is an independent device which, surprisingly, shows a higher purification performance than if the ion exchange unit IT had been enlarged (for example, doubled).

Figure 3 illustrates one possible gas phase filter variant of the present invention. The device shown here corresponds in basic structure to that described in Figure 1. However, it should be noted that the present invention is not limited 1:1 to such devices. In contrast to Figure 1, a gas phase filter device GF is arranged between the evaporator V and the rWGS rW. This means that the water coming from the water storage tank WV is further purified after evaporation by the gas phase filter(s) present in the gas phase filter device GF. Surprisingly, this variant also shows a higher purification performance than if the ion exchange unit IT had been enlarged (e.g., doubled). In addition, it is also illustrated here that the supply of CO2 or a CO2-containing gas mixture can take place not only in the rWGS rW, but also (alternatively or additionally) in the gas phase filter device GF.

Figure 4 illustrates one possible combination of the ion exchanger variant with the gas phase filter variant of the present invention. The device shown here corresponds in its basic structure to that described in Figure 1. However, it should be noted that the present invention is not limited 1:1 to such devices. In contrast to Figure 1, here, on the one hand, an ion exchanger device F is arranged between the water storage tank WV and the evaporator V, and on the other hand, a gas phase filter device GF is arranged between the evaporator V and the rWGS rW. In addition, it is also illustrated here that the CO2 or a CO2-containing gas mixture can be fed not only into the rWGS rW, but also (alternatively or additionally) into the gas phase filter device GF. Here, the water coming from the water storage tank WV is further purified by two different, additional devices. This variant results in a further significant improvement in the purity of the water fed into the rWGS rW.

Figure 5 illustrates a possible circuit for purification downstream of the water storage tank WV using an ion exchanger device F, with the flow direction running from left to right (along the intersection lines). The illustration shows a sequence of two individual ion exchangers F-1 and F-2 or F-2 and F-1, which represent preferred variants according to the invention; however, more individual ion exchangers can also be arranged (both in series and in parallel, or switchably in series and/or in parallel), or even just one ion exchanger F-1 (depending, among other things, on the dimensioning of the system and the contamination of the water with silicon or silicon compounds). These alternatives are not illustrated in Figure 5, since in this case the flow directions can be changed (at least in part).

In the variants according to the invention illustrated in Figure 5, the water coming from the tank enters the circuit from the left (see arrow) and leaves the circuit again on the right (see arrow). The water can be cleaned either via open VB-1, VB-3 and VB-8 serially in the sequence of ion exchangers F-1 and F-2 or with open VB-4, VB-2 and VB-6 in the sequence F-2 to F-1. In the circuit shown from F-2 to F-1, the water flows from 1-2 via VB-2 to F-1 and from there via VB-6 towards the outlet (i.e. to the rWGS). The other valves are closed. The flow direction within the circuit variant shown is always from the left inlet to the right outlet.

Figure 6 shows a circuit diagram for possible connections of the additional gas-phase filter device according to the invention. The circuit diagram shows variants according to the invention that have the same basic structure as shown in Figure 5. The only difference is that gas, rather than liquid, is passed through the gas-phase filter device, and that two gas-phase filters G1 and G2 are now present instead of ion exchangers. Figure 7 shows the measured pressure drop and the pressure drop change for the operation of a state-of-the-art rWGS reactor in which no silicon was removed as a function of time.

Figure 8 shows the pressure curve and the pressure change for the operation of an rWGS reactor operated according to the invention, in which silicon was removed (by means of an ion exchange device), as a function of time.

In general, however, the recycle stream or streams Re can not only be fed directly into the RWGS rW and/or into the CO ₂ stream (supplied to the rWGS) as indicated in the figures, but can also be fed back in at various points in the process, for example (but not exclusively) into the hydrogen stream coming from the electrolysis device EL, which is preferred in some variants of the present invention.

It may, for example, be sensible to combine CO2 and _H2O so that silicon can come via the feeds (silicates/silica in the _H2O and siloxanes in the _CO2 ). The combination of _H2O + _{H2 + recycle stream separate from CO2 may also be sensible so as to prevent coke formation. The possible variations as to where the recycle stream can be fed back in and which other stream can be mixed with which stream first are correspondingly diverse. The option of H2O or H2O + CO2 via the} gas phase filter is a preferred option according to the invention. For example (which is not shown in Figure 1) hydrogen (from the electrolysis device EL) can be added to the fluid mixture upstream of the gas phase filter. From a process engineering perspective, it usually makes the most sense if the _CO2 is also passed through the gas phase filter because _CO2 can contain siloxanes (a source of _SiO2 ).

Reference list:

A Wastewater (stream)

C Electricity (especially from renewable energies)

D Steam (stream)

ED electrodeionization (device) EC degassing device

EH water softening device

EL electrolysis (device)

F ion exchange device (according to the invention, comprising F-1 and optionally F-2, F-3...)

F-l ion exchanger (part of the additional ion exchange device F according to the invention)

F-2 ion exchanger (part of the additional ion exchange device F according to the invention)

GF gas phase filter device

G-l Gas phase filter (part of the additional, inventive

Gas phase filter device (GF)

G-2 Gas phase filter (part of the additional, inventive

Gas phase filter device (GF)

IT ion exchange unit (assigned to the water storage tank)

1-1 Measuring device

1-2 Measuring device

Pr product (stream)

Pu Purge(-current)

Re Recycle(-electricity)

RI return rW (device for) reverse water gas shift reaction

S (downstream of the rWGS) synthesis (for example Fischer

Tropsch)

U/O reverse osmosis (device)

V Evaporator (device)

VE VE water (electricity)

VB-1 to VB-9 valve

W Water

WV water storage tank

Examples:

The invention will now be described with reference to the following non-limiting

Example further explained. An rWGS reactor was operated according to the state of the art—without the inventive water treatment supplement—coupled with a Fischer-Tropsch synthesis including the recycling of residual gas to the rWGS reactor at approximately 750°C and a total pressure of 7 bar. 0.2 mg/Si was detected in the line upstream of the evaporator.

Figure 7 shows the pressure loss (dp - in bar) and the pressure loss change (dp/dt) for the operation of the state-of-the-art rWGS reactor as a function of time (t - in hours).

The consequence of the presence of silicon was a pressure drop increase of approximately 0.05 bar/h and an absolute pressure drop increase of approximately 1.4 bar over a period of approximately 28 hours during steady-state operation (according to the dashed vertical line in the figure; the system was started up with an increase in throughput through the rWGS reactor before this line). Energy-dispersive analysis using a microprobe apparatus detected between 0.3 and 1 mass percent silicon in the nickel catalyst used in this example in the rWGS reactor. No silicon was present in the fresh catalyst.

Accordingly, an rWGS reactor according to the present invention—with the inventive addition of two individual ion exchangers connected in series in an ion exchange device—was then operated, coupled with a Fischer-Tropsch synthesis including the recycling of residual gas to the rWGS reactor at approximately 750°C and a total pressure of 7 bar. No silicon was found in the line upstream of the evaporator.

Figure 8 shows the pressure curve (dp - in bar) and the pressure change (dp/dt) for the inventive operation of the rWGS reactor as a function of time (t - in hours). The consequence of the absence of silicon is that no increase in pressure loss occurs over the period of approximately 95 hours in steady-state operation (after the second dashed vertical line in the figure). Between the first two dashed vertical lines, a similar operating point as in Figure 7 was approached; after the second dashed line, the throughput through the reactor is increased again by approximately 20%. With increased throughput, the water demand increases and would result in an even faster increase in pressure loss if silicon were present in the water. would be present; however, this is not the case. Nevertheless, no silicon was found on the catalyst.

It is clear from this comparison that the inventive approach achieves significant technical advantages, in particular enabling longer system stability and thus longer continuous operation without downtime.

Claims

Device for converting CO2 into hydrocarbons comprising a reverse water gas shift reaction for generating synthesis gas, the device comprising: a water supply line, at least one device for treating the water comprising at least one of a softening device (EH), a reverse osmosis device (U/O), an electrodeionization device (ED), at least one water storage tank (WV) connected downstream of the device for treating the water and having a connected ion exchange unit (IT), at least one rWGS device (rW), at least one evaporator device (V) connected upstream of the at least one rWGS device (rW) and evaporating water originating from the water storage tank (WV) before being introduced into the at least one rWGS device (rW), at least one electrolysis device (EL), which is optionally operated at least partially, in particular completely, with water originating from the water storage tank (WV), the device being configured such that at least a portion of the water in the at least one electrolysis device (EL) is fed into the at least one rWGS device(s), optionally at least one return for water discharged from the at least one electrolysis device (EL) into the water storage tank (WV), wherein the return comprises a degassing device (EG), characterized in that additionally, and separated by at least the at least one water storage tank (WV) from the ion exchange unit (IT) assigned to it, between the at least one water storage tank (WV) and the water gas inlet into the at least one rWGS device (rW) is arranged: a) at least one ion exchange device (F), b) at least one gas phase filter device (GF), or c) at least one ion exchange device (F), and at least one gas phase filter device (GF), wherein the at least one gas phase filter device (GF) is arranged downstream of the at least one ion exchange device (F). 2. Device according to claim 1, characterized in that the at least one ion exchange device (F) is arranged between the at least one water storage tank (WV) and the at least one evaporator device (V) connected upstream of the water gas inlet into the at least one rWGS device (rW). 3. Device according to claim 1 or 2, characterized in that the at least one ion exchange device (F) comprises two or more individual ion exchangers (F-1, F-2), which are preferably connected in such a way that they can be flowed through one after the other, in parallel or individually. 4. Device according to claim 3, characterized in that at least the last individual ion exchanger through which the ion exchanger flows is an acidic ion exchanger, preferably that the first ion exchanger (F-1) is a basic ion exchanger and the second ion exchanger (F-2) is an acidic ion exchanger and the ion exchangers are flowed through in this order, or that the first ion exchanger (F-1) and the second ion exchanger (F-2) are each made up of two ion exchanger subunits, the first being a basic ion exchanger subunit and the second being an acidic ion exchanger subunit and the ion exchangers (F-1, F-2) are flowed through in this order. 5. Device according to one of claims 1 to 4, characterized in that the at least one gas phase filter device (GF) is arranged between the at least one water gas inlet into the rWGS upstream Evaporator device (V) and the water gas inlet into which at least one rWGS (rW) is arranged. 6. Device according to one of claims 1 to 5, characterized in that the at least one gas phase filter device (GF) comprises two or more individual gas phase filters (G-1, G-2), which are preferably connected in such a way that they can be flowed through successively, in parallel or individually. 7. Device according to one of claims 1 to 6, characterized in that the at least one gas phase filter device (GF) comprises aluminum oxide filters or aluminosilicate filters or aluminum oxide filters and aluminosilicate filters, and is preferably configured to be operated at temperatures between 200°C and 400°C. 8. A method for removing silicon and silicon compounds from the water circuit of a device for converting CO2 to hydrocarbons, comprising a reverse water-gas shift reaction to generate synthesis gas, preferably a device according to one of claims 1 to 7, in particular a device according to claim 1, wherein the device comprises: a water supply line, at least one device for treating the water, comprising at least one of a softening device (EH), a reverse osmosis device (U/O), an electrodeionization device (ED), at least one water storage tank (WV) connected downstream of the water treatment device with a connected ion exchange unit (IT), at least one rWGS device (rW), at least one evaporator device (V) connected upstream of the at least one rWGS device (rW) and evaporating water originating from the water storage tank (WV) before it is introduced into the at least one rWGS device (rW), at least one electrolysis device (EL), which is optionally operated at least partially, in particular completely, with water originating from the water storage tank (WV), wherein the device is configured such that at least a portion of the hydrogen generated in the at least one electrolysis device (EL) is fed into the at least one rWGS device(s), optionally at least one return line for water discharged from the at least one electrolysis device (EL) into the water storage tank (WV), wherein the return line comprises a degassing device (EG), characterized in that the method comprises: A) additionally arranging, at least by the at least one water storage tank (WV) separated from the ion exchange unit (IT) assigned thereto, between the at least one water storage tank (WV) and the water gas inlet into the at least one rWGS device (rW) of a) at least one ion exchange device (F), b) at least one gas phase filter device (GF), or c) at least one ion exchange device (F) and at least one gas phase filter device (GF), wherein the at least one gas phase filter device (GF) is arranged downstream of the at least one ion exchange device (F); B) Passing the water coming from the at least one water storage tank (WV) through the at least one ion exchange device (F) or through the at least one gas phase filter device (GF), or through the at least one ion exchange device (F) and the at least one gas phase filter device (GF), and separating silicon or silicon compounds or silicon and silicon compounds from the water passed through therein. 9. Use of at least one ion exchange device (F), at least one gas phase filter device (GF), or at least one Ion exchange device (F) and at least one gas phase filter device (GF) for separating silicon, silicon compounds, or silicon and silicon compounds from the water circuit of devices for converting CO2 to hydrocarbons, comprising a reverse water gas shift reaction for generating synthesis gas and further comprising an electrolysis device, in addition to any ion exchange units assigned to the water storage tank(s) (WV) in the device.