Water treatment in power-to-liquid processes

Abstract

The present invention relates to improved water treatment in power-to-liquid systems and processes, in particular in the conversion of CO2 to hydrocarbons, comprising a reverse water-gas shift reaction for producing synthesis gas.

Description

[0001] Water treatment in power-to-liquid processes

[0002] All documents cited in the present application are incorporated by reference in their entirety into the present disclosure.

[0003] The present invention relates to improved or simplified water treatment in power-to-liquid systems or processes, in particular in the conversion of CO2 to hydrocarbons comprising a reverse water gas shift reaction for the production of synthesis gas.

[0004] State of the art:

[0005] An important question when installing plants for the synthesis of valuable products and / or fuels is often, in addition to the source of carbon, the availability of water for the production of hydrogen.

[0006] In most syntheses, such as methanol synthesis or Fischer-Tropsch synthesis, water is also produced as a byproduct of the reactions. However, this wastewater is not pure; instead, it is contaminated with the products due to their solubilities.

[0007] Methanol synthesis:

[0008] CO2 + 3 H2o CH3OH + H2O

[0009] CO + 3 H2 CH3OH

[0010] Side reaction (water-gas shift - WGS): CO + H2O CO2 + H2

[0011] Fischer-Tropsch synthesis: n CO + (2n + l) H2< > C n H2n+2 + n H2O (alkanes) n CO + (2n) H2«-> C n H2n + n H2O (alkenes) n CO + (2n) H2C n H 2n+iOH + (n - 1) H2O (alcohols) and subsequent oxidation of alcohols to carboxylic acids (with oxygen-containing species such as CO2 or in acidic H2O). Thus, the separated aqueous phase (wastewater) primarily contains alcohols, but also carboxylic acids, which can be explained by the oxygen present in the reaction mixture, either in CO or CO2, as well as by the oxidizing effect of water. In methanol synthesis, it is the product itself, in addition to higher-hydric alcohols, that is contaminated; in Fischer-Tropsch synthesis, these are more likely to be undesirable side reactions, which can lead to the product water being contaminated with concentrations ranging from a few milligrams to a few grams per liter (e.g., 20 mg - 2 g). The exact composition depends on the process conditions and the catalyst used in the process.With cobalt catalysts, the loading of the reaction water is typically lower than with iron-based catalysts; ruthenium-based catalysts likely behave similarly. In Fischer-Tropsch synthesis (FT), the solubility of alkanes, alkenes, and olefins, which is primarily due to van der Waals forces, occurs in the range of a few milligrams. Furthermore, the gases hydrogen and carbon monoxide, and especially carbon dioxide, dissolve in the reaction water. The latter is responsible for the formation of carbonic acid and thus a very low pH value of the water.

[0012] From a wastewater treatment perspective, the wastewater is associated with high BOD (biological oxygen demand) and COD (chemical oxygen demand). These substances can be broken down, for example, in an anaerobic biological stage. However, the low pH value also poses a problem, necessitating neutralization prior to wastewater treatment. Wastewater treatment processes that can be used to make this water suitable for electrolysis include membrane distillation, reverse osmosis, and distillation. All of these processes require energy and therefore reduce the net yield of stored energy in the synthetic fuels.

[0013] The patent literature contains various approaches that deal with the topic of water management:

[0014] CA 3047846 A1 describes a process for the conversion of CO2 and H2 via rWGS and FT, whereby the water produced from the rWGS is used to slak lime. The resulting product water is not recycled into the actual power-to-liquid (PtL) process.

[0015] KR 101152666 Bl and US 9,199,890 B2 disclose the use of separated water from the synthesis and from a subsequent treatment step of the liquid synthesis product in a reformer to generate synthesis gas. Product water from the combustion of undesirable byproducts is also recycled into the reforming process.

[0016] KR 20150104819 A discloses the use of water from the synthesis and hydrotreatment processes in the production of synthesis gas by reforming natural gas (methane); here, no electrolysis is required and the steam is fed into the reforming process.

[0017] AU 2003203442 B2 discloses the use of a combination of a rWGS stage and autothermal reforming of natural gas. The resulting CO2 is recycled, with a portion of the hydrogen required for carbon dioxide reduction coming from the reforming of the resulting naphtha. There is no information on water management.

[0018] US 6,693,138 B2 describes the recycling of CO2 and naphtha into synthesis gas production; water is merely separated.

[0019] US 8,506,910 B2 discloses the recycling of collected water from an RWGS reactor, a subsequent methanol or dimethyl ether synthesis, and a subsequent gasoline synthesis from the methanol / dimethyl ether intermediate to the electrolysis unit. The required water quality is not disclosed. The different qualities of the water from the various steps are not described in detail.

[0020] US 9,227,168 Bl describes a process for seawater electrolysis in which CO2 is extracted from seawater and, together with hydrogen, a fuel is produced from it; here, it is fundamentally assumed that saline water is used in the electrolysis.

[0021] US 10,421,913 B2 from Sunfire envisages the use of water generated from air-based CO2 adsorption for electrolysis.

[0022] WO 2010 / 112982 A1 describes a process for the conversion of CO2 and H2 via rWGS and FT, in which CO2 is recycled to the RWGS and water to produce hydrogen. In plants that initially involve reducing the CO2 to form CO in order to drive the synthesis, the use of a so-called reverse water gas shift (rWGS) reactor is often described, see e.g. WO 2010 / 112982 A1. The process concept is usually as follows: Demineralized water is subjected to electrolysis, followed by rWGS, to which the CO2 is added. In the rWGS, wastewater is produced on the one hand, and CO on the other hand as a product, which is fed into the synthesis of valuable materials (e.g. methanol synthesis or Fischer-Tropsch synthesis). There, in addition to the valuable product, wastewater is also produced.

[0023] In rWGS, water is also produced from the hydrogen used according to the reaction equation CO2 + H2CO + H2O to reduce carbon dioxide. An excess of hydrogen produces synthesis gas (a mixture of CO and H2), which can significantly accelerate the Fischer-Tropsch reaction or the formation of methanol, or, for example, enables the Fischer-Tropsch reaction in the case of cobalt catalysts. Water (hereinafter also referred to as accompanying water) is often used in the feed of the rWGS to prevent the undesirable formation of carbon, see, for example, WO 2019 / 048236 Al.

[0024] In the overall balance of a CO2-based Fischer-Tropsch reaction over a cobalt catalyst, 3 mol of water are initially converted into 3 mol of H2 in electrolysis, of which 1 mol is required to form CO, 1 mol is required to reduce CO to the C building block for hydrocarbons, and one mol is required to form a -(CH2)- synthesis building block. Two mol of hydrogen are thus effectively released as water. If this water could be used to generate hydrogen, the need for demineralized water would be reduced to one-third of the amount required today.To treat normal process water for electrolysis, it is usually softened (using ion exchange, whereby the ion exchanger must be regenerated with NaCl), then subjected to reverse osmosis, and finally either by electrodeionization or directly by ion exchange to remove residual ions to meet the requirements of the electrolysis process, because otherwise, ions in the electrolysis cells block the active centers (Pt or Ni). Therefore, based on the current state of the art, there is still a significant need to improve the current state of the art, particularly with regard to water consumption and the effort involved in reprocessing product water or associated water.

[0025] Task:

[0026] 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.

[0027] In particular, more efficient procedures and devices should be made available.

[0028] Further tasks will become apparent to the person skilled in the art when considering the claims and the following description.

[0029] Solution:

[0030] 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.

[0031] Preferred and particularly advantageous embodiments are presented in the dependent claims and the following description.

[0032] Detailed description of the invention:

[0033] In the context of the present invention, all quantities are to be understood as weights unless otherwise stated.

[0034] For the purposes of the present invention, the term "ambient temperature" means a temperature of 20°C. Unless otherwise stated, temperatures are in degrees Celsius (°C).

[0035] Unless otherwise stated, the reactions or process steps described are carried out at ambient pressure (=normal pressure / atmospheric pressure), ie 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.

[0036] The present invention relates in a first essential aspect to a device for converting CO2 to hydrocarbons comprising a reverse water gas shift reaction for producing synthesis gas, the device comprising:

[0037] A) a water supply, in particular for domestic water;

[0038] B) at least one device for treating the supplied water comprising at least one reverse osmosis device, and optionally a first ion exchange unit and / or a second ion exchange unit;

[0039] C) at least one electrolysis device, preferably selected from a water electrolysis unit or a steam electrolysis unit, which electrolyzes the demineralized water coming from the water treatment device, comprising separate outlets for the oxygen produced and the hydrogen produced;

[0040] D) at least one rWGS device downstream of the electrolysis, which comprises i) in addition to the hydrogen supply line, at least one further supply line for the carbon base containing CO2, ii) at least one further supply line for water vapor, iii) at least one outlet line for the gaseous rWGS product, and iv) at least one waste water outlet line for condensed associated water and reaction water;

[0041] E) at least one synthesis device downstream of the rWGS device, which comprises i) in addition to the supply line for the gaseous rWGS product, at least one outlet for the synthesis product, and ii) at least one waste water outlet;

[0042] F) Optionally, in the event that the electrolysis device is a steam electrolysis unit, an evaporator unit can be provided according to B); wherein the respective rWGS devices and synthesis devices are assigned heating devices for the respectively discharged wastewater, which are configured to degas the respective wastewater at pressures of less than 6 bar, and preferably more than 0.3 bar, and each comprise exhaust gas outlets; the device has a return line for the heated wastewater originating from the at least one synthesis device into the at least one rWGS device; and the device has a return line for the heated wastewater originating from the at least one rWGS device a) partly into the device for treating the supplied water, in particular the reverse osmosis device, and b) partly into the at least one rWGS device.

[0043] In preferred embodiments of the present invention, the heat required to heat the wastewater is obtained by the heating device at least partially, preferably entirely, from the waste heat of the at least one synthesis device. This is preferably achieved through the use of heat exchangers.

[0044] In further preferred embodiments of the present invention, the heating devices are configured to heat the respective wastewater to at least 50°C, in particular at least 70°C and at most 100°C. In alternative embodiments of the present invention, the heating device can also be assigned an evacuation device in its exhaust line to promote degassing. The maximum permissible temperature during heating then results from the vapor pressure of the water. Through this heating, gases dissolved in the respective wastewater are expelled and can then be discharged as exhaust gas. In particular, CO2 is thus expelled and the CO2 content in the wastewater is significantly reduced. In addition, hydrogen and carbon monoxide are outgassed. Volatile dissolved components of hydrocarbons and alcohols from the synthesis wastewater, which can be problematic for side reactions in the rWGS device, can also be removed in this way.In further preferred embodiments of the present invention, the various exhaust gas outlets are combined and combined into a single exhaust gas line. While this is a preferred variant because it simplifies the connection to other systems, this measure is not absolutely necessary.

[0045] In yet further preferred embodiments of the present invention, the at least one synthesis device is configured either to carry out a Fischer-Tropsch synthesis or to carry out a methanol synthesis, preferably including dehydrogenated secondary products, such as preferably dimethyl ether or olefins or oxymethylene ether or aromatics, in particular dimethyl ether or olefins.

[0046] In a second essential aspect, the present invention relates to a process for converting CO? to hydrocarbons comprising a reverse water gas shift reaction for generating synthesis gas, in particular in a device according to the present invention as described above, wherein the process comprises the following steps: a) supplying water, in particular process water; b) treating the supplied water at least by means of reverse osmosis, and optionally by means of a first ion exchanger unit and / or a second ion exchanger unit; c) electrolyzing the demineralized water coming from the water treatment, preferably by means of a water electrolysis unit or a steam electrolysis unit and separately discharging the oxygen produced and the hydrogen produced;d) carrying out an rWGS downstream of the electrolysis, comprising i) supplying hydrogen and supplying carbon base containing CO2, ii) supplying steam, iii) discharging the gaseous rWGS product, and iv) discharging the wastewater, in particular from condensed accompanying water and reaction water; e) carrying out a synthesis downstream of the rWGS, comprising i) supplying gaseous rWGS product and discharging the synthesis product, and ii) discharging the wastewater;f) optionally, in the event that the electrolysis is a steam electrolysis, evaporation can take place after b), wherein the water derived from the rWGS and synthesis is degassed at pressures of less than 6 bar, and preferably more than 0.3 bar, and exhaust gas is discharged in each case, the heated wastewater originating from the at least one synthesis is returned to the at least one rWGS, and the heated wastewater originating from the at least one rWGS is returned a) partly to the treatment of the supplied water, in particular the reverse osmosis, and b) partly to the at least one rWGS.;

[0047] In preferred embodiments of the present invention, the heat required to heat the waste water is obtained at least partially, preferably completely, from the waste heat of the at least one synthesis.

[0048] In further preferred embodiments of the present invention, the respective wastewater is heated, in addition to the pressure reduction, to at least 50°C, in particular at least 70°C and at most 100°C.

[0049] In further preferred embodiments of the present invention, the various exhaust gases are combined and combined to form a single overall exhaust gas, which is preferred but not absolutely necessary.

[0050] In yet further preferred embodiments of the present invention, the at least one synthesis is either a Fischer-Tropsch synthesis or a methanol synthesis, preferably including dehydrated downstream products. The demineralized water coming from the water treatment device or water treatment system is preferably demineralized and free of impurities within the scope of the present invention.

[0051] In the context of the present invention, the carbon base preferably comprises CO2, which can originate from biomass fermentation or gasification, as well as from its removal from industrial processes or the air. In preferred variants of the present invention, the carbon base consists essentially of CO2 and is supplied in particular in gaseous form. Essentially, in this context, means at least 90 vol.%.

[0052] In preferred embodiments of the present invention, the heated wastewater originating from the synthesis or synthesis device is low in hydrocarbon contamination (HC) and has a significantly reduced CO2, H2, and CO content, particularly at the target temperature and optionally reduced pressure. This simplifies the process control of the rWGS device, since disturbances are removed when the synthesis wastewater is recycled as accompanying water for the rWGS device. In some variants of the present invention, in addition to the wastewater originating from the synthesis or synthesis device, deionized water from other sources can optionally be metered into the rWGS device as additional accompanying water. The term "low in" in this context particularly preferably means a reduction in hydrocarbon contamination of >90% compared to the content before the synthesis or synthesis device.

[0053] (Based on the substances present in the water at an exemplary process pressure of 20 bar and 5°C, more than 98% of all substances such as CO, CO2, H2 and Ci-Ce are removed by heating to 50°C and reducing the pressure to 1 bar, for example. Comparing this approach to one with only reducing the pressure (temperature would remain constant at 5°C in this example), the result is a reduction of the components by >90% for CO, CO2 and Ci-Ce. H2 is highly volatile and is already easily expelled at 5°C. A simultaneous reduction in pressure can therefore increase the separation efficiency even further.

[0054] The wastewater from the rWGS or rWGS system is generally free of HC, as the catalysts used there generally allow reforming of the HC components at high temperatures in the presence of associated water. Heating the wastewater from the rWGS system significantly reduces the CO2, H2, and CO content. The reduction in CO2 and CO content allows for use in electrolysis. Contaminants introduced through recirculation, such as particles or inorganic foreign ions, are advantageously retained in the reverse osmosis process. Therefore, recirculation to the reverse osmosis process is the preferred option.

[0055] Last but not least, the present invention relates to the use of the device according to the invention for power-to-liquid processes.

[0056] In the context of the present invention, accompanying water is added as steam to the reactant mixture in the rWGS reactor stage to avoid soot / carbon formed via CO decomposition, Boudouard equilibrium, or the Bosch reaction, or to avoid HC decomposition reactions, even though this adversely affects the equilibrium position. The addition of accompanying water is an integral component of the present invention. The rWGS unit primarily removes residual HC from the synthesis wastewater, making the purification suitable for water electrolysis. The molar ratio of steam to carbon in carbon-containing components is referred to as the S / C (steam-to-carbon) ratio and is at least 0.2, but typically between 0.5 and a maximum of about 1.2. At temperatures of, for example, 700°C to 800°C, the CO2 conversion under elevated pressure (5-30 bar) is typically below 50%.Therefore, the CO2 not converted in the RWGS is recycled either before or after synthesis. This means that twice as much CO2 passes through the rWGS unit as CO is produced. Even with CO conversions of over 90% in the synthesis unit, the water requirement in the rWGS is at least as high as the hydrocarbon-contaminated (HC) product water generated from the synthesis unit at an S / C of 0.5. This product water can therefore be used 100% as accompanying water for steam generation for the RWGS feed because gas components that could cause undesirable parameter deviations in the rWGS are expelled beforehand. According to the solubility equilibrium of CO2 under atmospheric conditions, this only requires a temperature of 50-70°C, which, according to the invention, comes from the synthesis process and optionally from the further processing of the products.

[0057] In the rWGS stage, the HC components contained in the water are converted almost completely (>98%) in a single pass. Because the water condensed from the rWGS is composed of two parts accompanying water vapor and one part reaction water, a single water molecule passes through the rWGS reactor on average twice, meaning the condensate can be considered free of HC components. Thus, the resulting excess rWGS condensate can be used to produce demineralized water, preferably bypassing at least the first stage of ion exchange. For this purpose, only gas must be expelled, in principle similar to the process after the FT reactor. Waste heat can also be utilized here.

[0058] Since reverse osmosis typically separates less than 40% of the raw water, the recycle rate from the rWGS and synthesis steps is more than 60%, thus reducing process water consumption by more than one-third. This also reduces the salt requirement for regenerating the water softener by at least one-third. Wastewater treatment is completely eliminated unless there is a discharge in the water circuit surrounding the rWGS unit. This may be necessary to a limited extent to prevent particles or the concentration of difficult-to-decompose components in the condensate.

[0059] The present invention differs from the prior art in particular by a combination of the following features, which is not known from the prior art:

[0060] Recirculation of synthesis wastewater after heating to at least 50°C, preferably at least 70°C, for the gaseous removal of HC, CO, H2 and CO2 at a maximum pressure of 6 bar, and preferably a minimum pressure of 0.3 bar, or if necessary under reduced pressure.

[0061] Recirculation of the degassed synthesis wastewater into the rWGS stage and thereby co-conversion of remaining HC components from the degassing.

[0062] On average, the synthesis wastewater passes through the rWGS reactor approximately twice due to the recycling of the degassed rWGS wastewater together with degassed synthesis wastewater, thus meeting both the water demand of the overall PtL process and the need for associated water in the rWGS unit.

[0063] Expulsion of H2, CO, CO2 from the wastewater at at least 50°C, preferably 70°C, in the condensate of the rWGS, thereby preventing disruptive gas contributions for the electrolysis and thus reducing the need for process water purification for the PtL process.

[0064] Recirculation of more than 50% and preferably more than 70% or the entire amount of the outgassed rWGS wastewater into the reverse osmosis of the demineralized water production.

[0065] Removal of up to 30 vol.% of the recirculated rWGS wastewater to prevent possible particle load or inorganic foreign ions from the process.

[0066] The devices and methods according to the invention therefore enable significantly more efficient operation compared to the prior art. This is because it makes it possible to remove organic substances from water from the synthesis process without requiring additional expenditures for reducing BOD / COD. At the same time, a significant amount of process water for electrolysis is saved, thus increasing overall process efficiency and significantly reducing the amount of salt required for ion exchange. For applications in water-scarce regions or in offshore plants for the purpose of producing PtL products, a significantly reduced water requirement also represents an energy saving, where salt water would otherwise have to be converted into process water.

[0067] 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:

[0068] No dedicated wastewater treatment is necessary.

[0069] The process water required to remove the BOD / COD in the synthesis water is reduced by at least 30%, depending on the water feed point in the raw water treatment process, or up to a maximum of 70% without discharge, preferably a maximum of 66%. The skilled person can adjust the exact design of the described devices, such as size, wall thicknesses, materials, etc., to the reaction conditions envisaged for a specific reaction, within the scope of their general technical knowledge.

[0070] 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.

[0071] Unless explicitly described, the individual parts of the devices are operatively connected to one another in a customary and known manner.

[0072] 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.

[0073] Flower description:

[0074] The present invention is explained in more detail below with reference to the drawing. The drawing is not to be interpreted as limiting and is not to scale. The drawing is schematic and, furthermore, does not contain all features found in conventional devices. Instead, it is 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.

[0075] Like reference numerals indicate like features in the figure, the description and the claims.

[0076] Figure 1 shows a highly schematically illustrated preferred variant of a device according to the invention. It shows a device for converting CO2 to hydrocarbons, comprising a reverse water-gas shift reaction to generate synthesis gas. The water supply is from the top left, with industrial water or tap water being used in particular. This water enters a device for treating the supplied water, comprising, in the example shown, a first ion exchange unit IT-1, a reverse osmosis device U / O, and a second ion exchange unit IT-2 (the variant comprising IT-1, U / O, IT-1 is a preferred variant according to the invention).From there, the demineralized water VE-W, which is preferably free of impurities (demineralized and free of impurities means, in particular, below the usual detection limits; demineralized water is preferably understood in the standard sense), flows into an electrolysis device EL, which is preferably a water electrolysis unit or a steam electrolysis unit (combinations are also possible). There, the demineralized water VE-W coming from the water treatment device is electrolyzed. The resulting hydrogen is, at least in part, fed into an rWGS device rW, which comprises at least one outlet for the rWGS product and at least one wastewater outlet AW-r.In the variant shown, the outlet for the rWGS product is designed as a direct reactant feed line for a synthesis device SV downstream of the rWGS device rW, so that the rWGS product flows via this line into the synthesis device SV, which comprises at least one outlet for the synthesis product SP and at least one wastewater outlet AW-S. A detailed design of the connection between the RWGS and synthesis unit can also include pressure increase via a compressor and associated further condensation, as well as heat exchangers or other units. The heat exchangers can also be understood as components of the respective units; the precise design of the units can be understood as independent of the design according to the invention.

[0077] Shown in the figure from the bottom left, the device comprises a supply line for carbon base KB, which in the illustration shown leads into the supply line of the rWGS unit.

[0078] In the variant shown, both the rWGS device rW and the synthesis device SV are each assigned a heating device EV for the respective discharged wastewater. The respective discharged water is heated via the heating devices EV to at least 50°C, preferably at least 70°C, in particular at least 70°C and at most 100°C, in order to expel volatile components, in particular CO2, optionally under reduced pressure.

[0079] Furthermore, the essential feature of the invention is evident: the device has a return line for the heated wastewater AW-SV originating from the synthesis device SV into the rWGS device rW, and a return line for the heated wastewater AW-rW originating from the rWGS device rW. The return of the heated wastewater AW-rW originating from the rWGS device rW is divided so that a portion is returned to the reverse osmosis device U / O, and a portion is returned to the rWGS device rW. The division is made according to the water requirement in the rWGS device. Furthermore, a dashed arrow illustrates that additional deionized water can optionally be metered into the rWGS device rW as accompanying water VE-WB, if desired or necessary. This figure also shows that the exhaust gas lines from the heating devices EV are combined, thereby obtaining a total exhaust gas flow.Optionally, a portion of the degassed synthesis water, or ideally a portion of the degassed rWGS wastewater, can be diverted to prevent the accumulation of particles or foreign ions. Since the rWGS wastewater is very clean, diversion is advantageous. Furthermore, all units shown can consist of multiple modules, especially reactors.

[0080] Reference list:

[0081] AW-r wastewater (line) from the rWGS device

[0082] AW-rW wastewater, originally originating from the rWGS device

[0083] AW-S Wastewater (pipe) from the synthesis device

[0084] AW-SV heated wastewater, originally originating from the synthesis device

[0085] EL electrolysis device

[0086] EV heating device

[0087] IT-1 ion exchanger 1

[0088] IT-2 ion exchanger 2

[0089] KB Carbon base (especially CO2) rW rWGS reactor

[0090] SP synthesis product

[0091] SV synthesis device (especially methanol synthesis device or Fischer-T ropsch synthesis device)

[0092] U / O reverse osmosis device

[0093] VE-W demineralized water

[0094] VE-WB accompanying water

[0095] Examples:

[0096] The invention will now be further illustrated with reference to the following non-limiting examples. In each of the experiments, several reactors according to the invention were arranged one above the other to form a multiple reactor arrangement according to the invention.

[0097] Example: Degassing of a FT wastewater by heating at 50°C and ambient pressure

[0098] The following table shows various degassing scenarios. At 50°C, the majority of the components were reduced by more than 90% compared to pure expansion at a separation temperature of 5°C in a cold trap. By further reducing the pressure to 0.3 bar, this reduction could be further increased by around 75%. Thus, by heating, an order of magnitude less CO, H2, and CO2, as well as C1-C8 hydrocarbons, were found in the wastewater from the FT. Starting from this, the concentrations in the liquid phase could be reduced again to one-third by reducing the pressure to negative pressure, so that ultimately only about 3-4 mol% of the normal substance concentrations were contained (reference condition 5°C and ambient pressure). This provided accompanying water for the rWGS reactor, and the risk of side reactions was greatly reduced. The remaining 3-4 mol% were converted in the rWGS by reforming.

Claims

Claims:

1. A device for converting CO2 to hydrocarbons comprising a reverse water gas shift reaction to produce synthesis gas, the device comprising: A) a water supply line, B) at least one device for treating the supplied water comprising at least one reverse osmosis device (U / O), and optionally a first ion exchange unit (IT-1) and / or a second ion exchange unit (IT-2), C) at least one electrolysis device (EL), preferably selected from a water electrolysis unit or a steam electrolysis unit, which electrolyzes the demineralized water (VE-W) coming from the water treatment device, comprising separate outlets for the oxygen produced and the hydrogen produced, D) at least one rWGS device (rW) downstream of the electrolysis, which comprises i) in addition to the hydrogen supply line, at least one further supply line of the carbon base (KB), in particular containing CO2, ii) at least one further supply line of water vapor, iii) at least one outlet for the gaseous rWGS product, and iv) at least one waste water outlet (Aw-r) for condensed associated water and reaction water; E) at least one synthesis device (SV) downstream of the rWGS device (rW), which i) in addition to the supply line of the gaseous rWGS product comprises at least one outlet for the synthesis product (SP), and ii) at least one waste water outlet (AW-S), wherein the respective rWGS devices (rW) and synthesis devices (SV), heating devices (EV) for the respectively discharged Wastewater is assigned, which are configured to degas the respective wastewater at pressures of less than 6 bar, and preferably more than 0.3 bar, and each comprise exhaust gas outlets, the device has a return line for the heated wastewater (AW-SV) originating from the at least one synthesis device (SV) into the at least one rWGS device (rW), and the device has a return line for the heated wastewater (AW-rW) originating from the at least one rWGS device (rW) a) partly into the device for treating the supplied water, in particular the reverse osmosis device (U / O), and b) partly into the at least one rWGS device (rW).

2. Device according to claim 1, characterized in that the heating devices (EV) obtain the heat required for heating the waste water at least in part, preferably completely, from the waste heat of the at least one synthesis device (SV).

3. Device according to claim 1 or 2, characterized in that the heating devices (EV) are configured to heat the respective wastewater, in addition to the pressure reduction, to at least 50°C, in particular at least 70°C and at most 100°C.

4. Device according to claim 3, characterized in that the various exhaust gas discharge lines are brought together and combined into a single exhaust gas line.

5. Device according to one of claims 1 to 4, characterized in that the at least one synthesis device (SV) for carrying out a Fischer-Tropsch synthesis, or for carrying out a methanol synthesis, preferably including dehydrated secondary products, such as preferably dimethyl ether or olefins or oxymethylene ethers or aromatics, in particular dimethyl ether or olefins.

6. A process for converting CO2 to hydrocarbons comprising a reverse water gas shift reaction for generating synthesis gas, in particular in a device according to one of claims 1 to 5, wherein the process comprises the following steps: a) supplying water, in particular process water; b) treating the supplied water at least by means of reverse osmosis (U / O), and optionally by means of a first ion exchange unit (IT-1) and / or a second ion exchange unit (IT-2); c) electrolyzing the demineralized water (VE-W) coming from the water treatment, preferably by means of a water electrolysis unit or a steam electrolysis unit, and separately discharging the oxygen and hydrogen produced;d) carrying out an rWGS downstream of the electrolysis, comprising i) supplying hydrogen and supplying carbon base containing CO2, ii) supplying water vapor, iii) discharging the gaseous rWGS product, and iv) discharging the waste water (AW-r), in particular from condensed associated water and reaction water; e) carrying out a synthesis downstream of the rWGS, comprising i) supplying gaseous rWGS product and discharging the synthesis product (SP), and ii) discharging the waste water (AW-S); f) optionally, in the event that the electrolysis is a steam electrolysis, carrying out an evaporation according to b); wherein; that the water derived from the rWGS and synthesis is degassed at pressures of less than 6 bar, and preferably more than 0.3 bar, and exhaust gas is discharged in each case, the heated wastewater (AW-SV) originating from the at least one synthesis is returned to the at least one rWGS, and the heated wastewater (AW-rW) originating from the at least one rWGS is returned a) partly to the treatment of the supplied water, in particular the reverse osmosis (U / O), and b) partly to the at least one rWGS.

7. A method according to claim 6, characterized in that the heat required for heating the waste water is obtained at least in part, preferably completely, from the waste heat of the at least one synthesis and that the respective waste water, in addition to the pressure reduction, is heated to at least 50°C, in particular at least 70°C and at most 100°C.

8. Method according to claim 6 or 7, characterized in that the various exhaust gases are combined and combined to form a single exhaust gas.

9. Process according to one of claims 6 to 8, in particular according to claim 6, characterized in that the at least one synthesis is a Fischer-Tropsch synthesis or a methanol synthesis, preferably including dehydrated secondary products.

10. Use of the device according to one of claims 1 to 6 for power-to-liquid processes.

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