Conversion of carbon dioxide to synthesis gas with water

Abstract

The present invention relates to a method for producing methanol via synthesis gas produced by combining electrolysis of a water feedstock for producing a stream containing hydrogen and electrolysis of a carbon dioxide-rich stream for producing a stream containing CO and CO 2 wherein the synthesis gas has a molar ratio of CO / CO 2 greater than 2. The present invention also relates to a method for producing synthesis gas by one-through co-electrolysis of a feed gas stream combining CO 2 and steam in a SOEC unit.

Description

Technical Field

[0001] The present invention relates to a method for producing synthesis gas from a carbon dioxide-rich stream (a stream rich in carbon dioxide) and a water feedstock by electrolysis, where the synthesis gas is further converted to methanol, synthetic fuel, substitute natural gas (SNG). The synthesis gas can also be further converted to higher alcohols, i.e., C1-C5 alcohols.

Background Art

[0002] Currently, producing methanol from H 2 and CO 2 is often inefficient and problematic. For example, in the case of synthesis gas, it is a H 2 and CO 2 -rich gas, usually produced by steam reforming of hydrocarbon feedstocks such as natural gas. In the case of methanol synthesis, if the CO 2 to CO ratio in the synthesis gas is high, the methanol conversion reactor becomes larger and the downstream purification process becomes more expensive.

[0003] For the purpose of producing methanol, it is known to electrolyze water to generate H 2 and mix it with CO 2 to form synthesis gas. Therefore, a known method for producing methanol is to obtain a water feedstock, convert it to H 2 by electrolysis, mix it with another CO 2 -rich stream and compress it to form a synthesis gas with a molar ratio of H 2 / CO 2 of about 3. This synthesis gas is converted to methanol (CH 2 + CO 2 = CH 3 OH + H 2 O, CO + 2H 2 = CH 3 OH according to the reactions of 3H 3It is passed to a conventional methanol loop that includes conversion to OH). The resulting feed methanol stream is purified by distillation, enriched in methanol, and at least 98% by weight of methanol and another water stream are produced.

[0004] US2007045125A1 discloses a method for synthesizing syngas from carbon dioxide and water obtained from air or other available carbon dioxide sources using a sodium-conductive electrochemical cell. Syngas is also produced by co-electrolyzing carbon dioxide and steam in a solid oxide electrolysis cell. The produced syngas can be further processed and ultimately converted into liquid fuels suitable for transportation and other applications. This cited document does not even mention, at least, the use of a solid oxide electrolysis unit for converting CO 2 to a specific mixture of CO and CO 2 .

[0005] US20090289227A1 includes recovering carbon dioxide from an industrial process that generates a waste stream containing more carbon dioxide than the amount of carbon dioxide present in the starting materials of the industrial process, a method of utilizing waste. This method further includes producing hydrogen using renewable energy resources, and producing hydrocarbon materials using the produced hydrogen and the recovered carbon dioxide. Carbon dioxide can be converted to CO by electrolysis, and water can be converted to hydrogen by electrolysis. This cited document does not even mention, at least, the use of a solid oxide electrolysis unit for converting CO 2 to a specific mixture of CO and CO 2 2 .

[0006] ​US20180127668A1 discloses a renewable fuel generation system including a carbon dioxide capture unit for extracting carbon dioxide from air in the atmosphere, a carbon dioxide electrolyzer for converting carbon dioxide into carbon monoxide, a water electrolyzer for converting water into hydrogen, and a synthetic fuel generator for converting the carbon monoxide generated by the carbon dioxide electrolyzer and the hydrogen generated by the water electrolyzer into fuel. The fuel produced can be synthetic gasoline and / or synthetic diesel. Carbon dioxide is converted to CO 2 via electrochemical conversion of CO (electrochemical conversion of CO), which refers to any electrochemical process in which carbon dioxide, carbonate, or bicarbonate is converted to another chemical substance at any stage of the process. Thus, this cited reference does not mention at least the use of a solid oxide electrolysis unit for the conversion of CO 2 and the conversion of CO 2 to a specific mixture of CO and CO 2 .

[0007] Kuengas, Rainer, “Review - Electrochemical CO2 reduction for CO production: Comparison of Low. And High-Temperature Electrolysis Technologies”; Journal of The Electrochemical Society, 2020, 167 044508 provides a review of state-of-the-art low-temperature, molten carbonate, and solid oxide electrolyzers for CO production.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Literature

[0009]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The patent application WO PCT / EP2021 / 086999 jointly filed by the applicant of the present application discloses a method and a system for producing synthesis gas from a carbon dioxide-rich stream and a water feedstock, and the synthesis gas is further converted to methanol by methanol synthesis. A feed stream consisting of hydrogen is generated by the electrolysis of water, and a feed stream consisting of CO and CO 2 is generated by the one-through electrolysis of carbon dioxide. The feed streams are combined into a synthesis gas with a CO / CO 2 molar ratio of 0.2 to 0.6.

Means for Solving the Problems

[0011] By combining and using the electrolysis process for both water supply and CO 2 supply, it is possible to form a more reactive synthesis gas for subsequent methanol conversion and / or the production of hydrocarbon products, such as synthetic fuels. As a result, the size of the reactor, e.g., the size of the methanol converter, is reduced, the production of water is reduced, and it has been found that at least the carbon footprint is not significantly reduced. Furthermore, savings in hydrogen consumption, especially for methanol conversion, are also achieved. Other related advantages will become apparent from the following embodiments.

[0012] Thus, in a first aspect, the present invention is a method for producing methanol comprising the following steps: a) providing a first CO 2 -rich stream and passing it through a first electrolysis unit to produce a first stream containing CO and CO 2 ; separating from the first stream containing CO and CO 2 - a second stream containing CO and CO 2 - and a second CO 2 -rich stream; and reusing the second CO 2 -rich stream in the electrolysis unit; b) providing a water feedstock and passing it through a second electrolysis unit to produce a stream containing H 2 ; c) combining the second stream containing CO and CO 2 with the stream containing H 2 to form synthesis gas; d) converting the synthesis gas to methanol; wherein the second stream containing CO and CO 2 has a CO / CO 2 molar ratio greater than 2.

[0013] Reusing the second CO 2 -rich stream in the first electrolysis unit means that in step a), the electrolysis is not carried out in a once-through electrolysis unit.

[0014] The first CO 2 -rich stream is understood to be a stream mainly containing CO 2 , for example, 99 volume% (vol.%) or more of CO 2 .

[0015] CO and CO 2 ​​The first stream containing is converted in the first electrolysis unit to a first CO 2 -rich stream, so it will be understood that it is a mixture containing CO and CO 2 .

[0016] As used herein, the term "thereby" means that electrolysis is carried out in the electrolysis unit, whereby at least a part of carbon dioxide is converted to CO with the help of an electric current, for example.

[0017] As used herein, the term "comprising" can also be construed as "comprising only", i.e., "consisting of".

[0018] Therefore, the present invention can convert a part of CO 2 to CO and convert this together with H 2 and the remaining CO 2 to methanol by methanol synthesis. Thereby, compared with the prior art, an excellent synthesis feed for producing methanol can be obtained. The solution provided by the present invention is neutral with respect to power consumption because the power required for CO generation by electrolysis can be subtracted from the power required for H 2 generation by electrolysis. Furthermore, the amount of catalyst in the downstream methanol synthesis, i.e., in the methanol conversion reactor, is further reduced. The excellent synthesis gas reduces both the operating cost (OPEX) and the capital cost (CAPEX).

[0019] In one embodiment, the synthesis gas has a module M = (H 2 -CO 2 ) / (CO + CO 2 ) in the range of 1.95 to 2.10 and a molar ratio of CO / CO 2 greater than 2.

[0020] The synthesis gas used for methanol production is usually described by the module M. This is because when M = 2, the synthesis gas is suitable for the methanol reaction. M = (H 2 -CO 2 ) / (CO + CO2 ) It will be understood that it is calculated in mol% (molar concentration). In a typical synthesis gas for methanol production, for example, a synthesis gas produced by steam reforming, the synthesis gas contains some excess hydrogen that results in a module slightly above 2, for example 2.05 or 2.10. In the present invention, preferably, M is greater than 2, for example 2.05 or 2.10. Thereby, the size of the corresponding conversion unit, such as the size of the methanol synthesis reactor (methanol reactor), is further significantly reduced. Furthermore, a significant saving in electrolysis power consumption is achieved.

[0021] In this specification, the terms "preferably" or "preferred" are used interchangeably with the terms "optionally" or "optional", that is, with any embodiment.

[0022] Furthermore, for example, CO 2 - In the once-through electrolysis of a rich stream, when operating with a molar ratio of CO / CO 2 above 0.6, the CO content in the gas becomes high, so there is a risk of carbon formation. However, in the present invention, the molar ratio of CO / CO 2 in the effluent gas at the outlet of the electrolysis unit in step a), that is, the first stream containing CO and CO 2 is maintained below 0.6 to avoid the risk of carbon formation. This effluent gas is recycled to the inlet of the first electrolysis unit with a second CO 2 - rich stream and separated into a CO-rich product gas with a molar ratio of CO / CO 2 above 2, that is, a second stream containing CO and CO 2 .

[0023] The higher the molar ratio of CO / CO 2 , the better. For example, the molar ratio of CO / CO 2 in the synthesis gas in the second stream containing CO and CO 2 is 4 or 6 or 8 or 10 or 20 or greater than them. Thereby, 3H 2 +CO 2 =CH 3 OH+H2 Rather than the reaction of O, CO + 2H 2 = CH 3 By the reaction of OH, excellent synthesis gas is generated to promote methanol synthesis downstream, and at the same time, the risk of carbon formation in the first electrolysis unit of step a), that is, the first electrolysis unit supplied with the carbon dioxide-rich stream, can be avoided.

[0024] Therefore, in one embodiment, the first stream containing CO and CO 2 has a CO / CO molar ratio 2 of 0.6 or less, for example in the range of 0.2 to 0.6.

[0025] In one embodiment, the first CO 2 -rich stream is produced by passing a carbon dioxide-feed stream, preferably carbon dioxide from an external source, through a CO 2 -cleaning unit for removing impurities such as Cl, sulfur, Si, As.

[0026] Thereby, the protection of downstream units, especially subsequent electrolysis, is ensured. For example, even a small amount of COS can cause problems. Usually, the amount of COS in industrial CO 2 is below the detection limit, but in one example, COS has been measured in the range of 10 - 20 ppb, which is sufficient to have a harmful effect on the electrolysis unit, and as a result, the electrolysis unit deteriorates rapidly.

[0027] In one embodiment, when the CO content in the synthesis gas is less than 0.5 mol%, H 2 O corresponding to 1.5 - 3 mol% in the synthesis gas is added to the synthesis gas. Therefore, when the CO 2 content is <0.5 mol% (less than 0.5 mol%), H 2 O corresponding to 1.5 - 3 mol% is added to the synthesis gas. That is, in this embodiment, the CO content in the synthesis gas is less than 0.5 mol%, and H 2 O corresponding to 1.5 - 3 mol% in the synthesis gas is added to the synthesis gas. That is, in this embodiment, the CO content in the synthesis gas is less than 0.5 mol%, and H 2 O corresponding to 1.5 - 3 mol% in the synthesis gas is added to the synthesis gas. 2O is added to the synthesis gas.

[0028] The synthesis gas for methanol conversion contains CO, CO 2 and H 2 mixture, and H 2 O. When the content of CO 2 is less than 0.5 mol%, by adding H 2 O in the synthesis gas to 1.5 - 3%, it becomes possible to more offset the influence when the necessary CO 2 for methanol synthesis is insufficient. The molar ratio of CO to CO 2 in the synthesis gas is more than 2, and the higher the better, but since at least the presence of CO 2 is necessary for methanol synthesis, it is often desirable to suppress the CO 2 content rate in the synthesis gas to a level not less than 0.5 mol%. The addition of water enables the generation of CO 2 by the water - gas shift reaction: CO + H 2 O = H 2 + CO 2 . According to the present invention, it becomes easy to produce pure CO, and instead of adding CO 2 , water is added.

[0029] When producing methanol, if producing methanol from CO 2 and H 2 , it costs much more than the methanol feed gas containing H 2 , CO, and CO 2 . The reaction from CO 2 is CO 2 + 3H 2 = CH 3 OH + H 2 O, CO + 2H 2 = CH 3 OH, and forms water compared to the resulting reaction and the reaction from CO. The water generated as a result has a negative impact on the performance of the catalyst, and CO 2If the concentration is too high, for example, 90%, the catalyst capacity increases by more than 100%. Also, since all water is removed by distillation, a large amount of energy is required for methanol purification.

[0030] Including the energy for evaporating water, the energy for electrolyzing water and electrolyzing carbon dioxide is approximately the same. Therefore, from the perspective of energy, generally, when aiming to produce methanol from water and CO 2 it is not very important which of water electrolysis and carbon dioxide electrolysis is carried out.

[0031] According to the present invention, the first electrolysis unit for generating the first stream containing CO and CO 2 is preferably a solid oxide electrolysis cell unit, hereinafter also referred to as SOEC-CO 2 (electrolysis of CO 2 via SOEC).

[0032] In one embodiment, when performing CO 2 electrolysis in step a), the step of separating the first stream containing CO and CO 2 includes passing this stream through a CO concentration unit, for example, a pressure swing adsorption unit (PSA), to generate the second stream containing CO and CO 2 and the second CO 2 -rich stream.

[0033] The second stream containing CO and CO 2 from the CO concentration unit, for example, the PSA unit, is rich in CO (CO-rich), with a molar ratio of CO / CO 2 greater than 2, for example, containing more than 99% CO. The second CO 2 -rich stream is drawn from the PSA at low pressure and thus compressed and recycled to the first electrolysis unit.

[0034] The electrolysis of CO 2 to CO in step a) is preferably at a molar ratio of CO / CO 2 greater than 2., particularly high - purity CO, e.g., 99.9995% CO, for generating a second stream containing CO and CO 2 is composed of the following five sections, namely: a supply system, electrolysis, compression, purification (CO enrichment), e.g., purification by PSA including recycle compression, polishing.

[0035] The CO enrichment unit may be a membrane unit.

[0036] In one embodiment, providing a first CO 2 -rich stream and passing it through a first electrolysis unit to generate a first stream containing CO and CO 2 , and supplying a water feedstock and passing it through a second electrolysis unit to generate a stream containing H 2 are carried out separately, i.e., each step is carried out in the corresponding electrolysis unit, as shown in the attached Figure 1.

[0037] Higher efficiency is achieved when converting syngas to methanol. When co - electrolysis is carried out, i.e., when the first and second electrolysis units are the same, there may be some methane formation because hydrogen and carbon monoxide may react. In methanol production, methane is inert, so there is a decrease in efficiency associated with methane formation.

[0038] Furthermore, by separately performing the electrolysis of carbon dioxide and the electrolysis of water, it becomes easier to optimize the SOEC stack of the corresponding electrolysis unit and the two different manufacturing processes.

[0039] In one embodiment, step a) includes bypassing (circling around) a part of the first CO 2 -rich stream before passing it through the first electrolysis unit, preferably a solid oxide electrolysis unit (SOEC - CO 2 ).

[0040] Thereby, the molar ratio CO / CO of the first stream containing CO and CO 2 2 ​Flexibility during adjustment increases, and at the same time, miniaturization of the solid oxide electrolysis cell unit becomes possible compared to the case where no bypass is provided. For example, mainly CO 2 in the first CO 2 -rich stream that is bypassed is preferably used for recycling after separating the second CO 2 -rich stream, and is combined with the stream flowing out of the first electrolysis unit and the feed stream containing H 2 such that syngas with a molar ratio of CO / CO 2 >2 and a module M = (H 2 -CO 2 ) / (CO + CO 2 ) of 1.95 to 2.10, preferably 2.05 or 2.10, is produced as shown in FIG. 1.

[0041] In one embodiment, the first electrolysis unit is a solid oxide electrolysis unit (also referred to herein as an SOEC-CO 2 or SOEC-CO 2 unit), and the second electrolysis unit for generating a stream containing H 2 is an alkaline / polymer electrolyte membrane electrolysis unit, i.e., an alkaline and / or PEM electrolysis unit, or a solid oxide electrolysis cell unit (SOEC unit).

[0042] By combining the electrolysis of CO 2 via SOEC (SOEC-CO 2 ) with the electrolysis of water via alkaline / PEM electrolysis, the electrolysis power is further reduced compared to the prior art that uses only the electrolysis of water via alkaline / PEM electrolysis without performing the electrolysis of CO 2 .

[0043] Furthermore, when the electrolysis of H 2 O to H 2 is based on liquid water (such as alkaline / PEM), the latent heat of vaporization of water is saved.

[0044] SOEC-CO 2, Alkaline / PEM electrolysis units are well known in the art, and in particular, alkaline / PEM electrolysis is known. For example, in the applicant's WO2013 / 131778, SOEC-CO 2 is described. The specific combination of SOEC-CO 2 and alkaline / PEM electrolysis is readily available and is also less expensive than other combinations of electrolysis units.

[0045] In particular, in SOEC-CO 2 , CO 2 is converted to a mixture of CO and CO 2 at the fuel electrode, i.e., the cathode. Also, at the oxygen electrode, i.e., the anode, air is often used as the flushing gas and oxygen is generated simultaneously. Thus, CO and O 2 are formed on both sides of the electrolytic cell.

[0046] The present invention enables the conversion of 1 mole of CO 2 to CO, thereby reducing the required H 2 for the conversion to methanol by up to 1 mole, which is again described here: CO + 2H 2 = CH 3 OH; CO 2 + 3H 2 = CH 3 OH + H 2 O.

[0047] Therefore, each time 1 mole of CO 2 is converted to 1 mole of CO, 1 mole of hydrogen 2 is required less. This leads to a significant saving in hydrogen consumption.

[0048] In certain embodiments, H 2The second electrolysis unit for generating a feed stream containing is a solid oxide electrolysis cell unit. Thus, both the first and second electrolysis units are solid oxide electrolysis cell units (SOEC units). Any of these electrolysis units preferably operates in a temperature range of 700 to 800 °C, thereby enabling operation in a common system for cooling the stream, and thus enabling integration of the process units. Further, when SOEC is used for both the electrolysis of CO 2 and the electrolysis of H 2 to H 2 O based on steam, energy for distilling the generated CH 3 OH to H 2 O is saved.

[0049] Operation of the SOEC unit at such a high temperature (700 to 800 °C) offers advantages compared to alkaline / PEM electrolysis, which operates in a much lower temperature range, i.e., 60 to 160 °C. Such advantages include, for example, in relation to CO 2 electrolysis, reduction of operating costs due to a low cell voltage and reduction of equipment costs due to a high current density.

[0050] In one embodiment, the water feedstock includes steam generated from other steps of the method, such as steam generation or downstream distillation. In other words, the method of the present invention can further include the step of producing steam from other steps of the method.

[0051] Thereby, for example, steam generated in a downstream process can be reused instead of requiring, for example, steam export, thus improving the energy efficiency of the process. Also, in the concentration or purification of methanol or the like by distillation, water is also generated, and this water can advantageously be reused as part of the raw water.

[0052] It can be understood that liquid water cannot be passed through the SOEC unit and steam cannot be passed through the alkaline / PEM unit. In other words, the SOEC unit operates with liquid water (water), and the alkaline / PEM unit operates with steam.

[0053] Also, if surplus steam is available, it will be understood that overall savings can be achieved when using a water (steam) SOEC for the production of H 2 . In SOEC, evaporation energy is saved, but this does not apply when using surplus steam with lost condensation heat for power generation. In particular, when the final product is raw methanol, for example, if the raw methanol is produced according to the applicant's US4520216, i.e., the methanol - gasoline route (TiGAS), and the raw tanol is converted to other transportation fuels such as gasoline or jet fuel, or if synthesis gas is used as substitute natural gas (SNG), surplus steam becomes available.

[0054] In one embodiment, the carbon dioxide feed stream or the first carbon dioxide - rich stream includes carbon dioxide from an external source, for example, from the upgrading of biogas or a fossil - fuel - based synthesis gas plant.

[0055] As an external source, there is the upgrading of biogas as described above. Biogas is a renewable energy source that can be used for heating, electricity, and many other operations. Biogas can be cleaned and improved to natural - gas standards when it becomes biomethane. Biogas mainly consists of methane (CH 4 ) and carbon dioxide (CO 2 ), and usually contains 60 - 70% methane. Up to 30%, or 40% of biogas is carbon dioxide. Typically, this carbon dioxide is removed from the biogas and discharged into the atmosphere in order to further process the methane - rich gas or supply it to the natural - gas network. According to the method of the present invention, the removed CO 2 is utilized to produce more synthesis gas (syngas).

[0056] Examples of fossil fuel-based syngas plants include natural gas-based syngas plants for gasoline production (TiGAS), i.e., for the GTL (Gas-to-Liquid) process, or natural gas-based syngas plants for methanol production, where CO 2 is extracted from the waste heat section or the flue gas from the calcination heating and is utilized to produce more syngas by the method according to the present invention.

[0057] Other external sources include thermal power plants and waste incinerators.

[0058] In an embodiment according to the first aspect of the present invention, the electric power required in the step of electrolysis of the carbon dioxide-rich stream or the water feedstock is supplied, at least in part, by a renewable energy source such as wind energy or solar energy, or, for example, by hydroelectric power generation. Thereby, since fossil fuels are not used for the generation of the electric power required for electrolysis, a more sustainable, i.e., "more environmentally friendly" method (process) and system (plant) approach is achieved. Optionally, power can also be supplied from a nuclear heat source.

[0059] In one embodiment, the step of converting syngas to methanol includes passing the syngas through a methanol synthesis reactor in the presence of a catalyst to produce a raw methanol stream, and the step optionally further includes a distillation step of the raw methanol stream to produce a water stream and a separate methanol stream having at least 98% by mass of methanol.

[0060] The molar ratio of CH 3 OH / H 2 O in the raw methanol stream according to the present invention is 1.2 or more, for example 1.3 or more, because the syngas for methanol synthesis is more reactive than in the case where only water electrolysis is used for conventional methanol synthesis or hydrogen production. In conventional methanol synthesis, a molar ratio of CH 3 OH / H 2A raw methanol product having O is produced, which means the production of a significant amount of water that needs to be separated downstream. Thus, the present invention further enables the produced raw methanol to have a much lower water content, for example, at least 20% or at least 30% less water on a molar basis, compared to conventional methanol synthesis. Thereby, for example, the amount of water carried in the process can be reduced, along with a reduction in the size of equipment such as piping, and the cost of downstream water separation can be reduced by enabling much simpler and cost-effective distillation for the purification of methanol. Furthermore, since the catalyst performance in the methanol synthesis reactor is also easily affected by water, the amount of catalyst and the reactor size can be further significantly reduced.

[0061] Methanol technologies including a methanol synthesis reactor and / or a methanol synthesis loop are well known in the art. Thus, a common practice in the art is to carry out methanol conversion in a once-through methanol conversion process or to recycle the unconverted synthesis gas separated from the reaction effluent and dilute the fresh synthesis gas with the recycle gas. Typically, the latter results in a so-called methanol synthesis loop (referred to interchangeably as a methanol loop herein) with one or more reactors connected in series or parallel. For example, the serial synthesis of methanol is disclosed in US5827901 and US6433029, and the parallel synthesis is disclosed in US5631302 and EP2874738B1.

[0062] The method of the present invention preferably does not perform steam reforming of a hydrocarbon feed gas such as natural gas for producing synthesis gas. Since steam reforming, for example, conventional steam methane reforming (SMR) or autothermal reforming (ATR), is a large-scale and energy-intensive process, an operation without performing steam reforming for producing synthesis gas enables a significant reduction in the scale and operating cost of the plant, as well as significant energy savings. In addition, compared with SMR, in the electrolysis unit, the production capacity can be easily changed (linear scaling of cost proportional to size) by removing or adding an electrolysis unit. This usually does not apply to SMR and the like.

[0063] As a second aspect, the present invention also relates to a method for producing synthesis gas useful for various downstream applications.

[0064] Therefore, a method for producing synthesis gas is provided, including the following: i) providing a first CO 2 -rich stream, providing a water feedstock, combining it with the first CO 2 -rich stream to form a combined feed gas stream, passing the combined feed gas stream through an electrolysis unit, and generating the synthesis gas containing CO, CO 2 and H 2 ; wherein the synthesis gas has a module M = (H 2 -CO 2 ) / (CO + CO 2 ) in the range of 1.95 to 2.10, or a molar ratio of H 2 / CO of 1.95 - 2.10; wherein i) is carried out by one-through co-electrolysis, i.e., a one-through operation, in an electrolysis unit such as a solid oxide electrolysis cell unit (SOEC unit); and wherein the one-through co-electrolysis is carried out in a solid oxide electrolysis cell unit, and the method includes bypassing a part of the first CO 2 -rich stream before passing it through the solid oxide electrolysis cell unit.

[0065] Thus, for example, co-electrolysis in a once-through type SOEC unit is carried out by adding steam to carbon dioxide (the first CO 2 -rich stream) in front of the SOEC unit in order to generate all or part of the H 2 O by electrolysis of H 2 O together with electrolysis of CO 2 . Thereby, due to the once-through operation, even when the molar ratio CO / CO 2 is higher than 0.6, the desired CO / CO 2 ratio can be achieved without the risk of carbon formation due to the presence of H 2 O and H 2 . Furthermore, instead of providing a separate water feedstock introduced separately into the SOEC unit, the water feedstock which is steam is directly combined with the first CO 2 -rich stream, for example, steam is added thereto, providing a simple solution with less piping.

[0066] In an embodiment according to a second aspect of the present invention, the synthesis gas has a molar ratio CO / CO 2 greater than 0.2, for example from 0.2 to 0.6, or more, for example greater than 1 or 2, or a molar ratio CO / CO 2 greater than 2, for example a molar ratio CO / CO 2 greater than 2. Thus, in a particular embodiment according to a second aspect of the present invention, the synthesis gas has a molar ratio CO / CO 2 greater than 2.

[0067] The advantages associated with avoiding the risk of carbon formation at a high CO / CO 2 molar ratio, i.e. greater than 0.6, for example 1 or 2, or a large molar ratio, for example 10, outweigh the disadvantage of forming methane during co-electrolysis by reaction of hydrogen and carbon monoxide in this second aspect of the present invention. In the case of downstream methanol production, methane is inert, so there is an efficiency loss associated with the generation of methane, but in the case of downstream production of methane such as substitute natural gas or synthetic natural gas (SNG), the generation of methane in co-electrolysis would actually be advantageous.

[0068] For example, compared with introducing a first electrolysis unit for generating CO from a first CO 2 and a second electrolysis unit for generating H from a water raw material (water or steam), a simpler process and plant for producing syngas are provided. 2

[0069] By performing a one-through operation such as an SOEC unit, the reuse of syngas becomes unnecessary. Therefore, at least a recycle compressor is unnecessary, and related valves, pipes, and control systems are also unnecessary. Associated operating costs such as the power required for the compressor and the maintenance of the recycle compressor and other equipment (valves, pipes, etc.) are saved. Furthermore, a CO concentration unit, for example, a PSA unit, is also unnecessary, and the process and plant for producing syngas can be significantly simplified.

[0070] Similar to the first aspect of the present invention, the term "comprising" can also be interpreted as "comprising only", that is, "consisting of".

[0071] Similar to the first aspect of the present invention, the terms "preferably" or "preferred" are used interchangeably with the terms "optionally" or "any", that is, any embodiment.

[0072] In an embodiment according to the second aspect of the present invention, the syngas has a molar ratio CO / CO of 0.2 to 0.6 2 and the method further includes the following: ii) Subjecting the syngas to a reverse water gas shift step (rWGS step).

[0073] Therefore, one-through co-electrolysis is carried out in a state where the molar CO / CO ratio in the syngas is 0.6 or less, preferably 0.2 to 0.6, in order to avoid the risk of carbon formation. Then, after optionally adding hydrogen, the endothermic rWGS reaction CO 2 +H 2 2 =CO+H 2Via O, a desired CO / CO 2 ratio, for example, a desired molar ratio of CO / CO 2 >2, the rWGS step is carried out.

[0074] In certain embodiments, the rWGS is carried out in an electrically heated WGS reactor (e-rWGS reactor). Since the e-RWGS reactor in step ii) is also powered, separate from the SOEC unit of step i), the carbon footprint of the process is thereby kept low. Details of the e-RWGS are described in the applicant's WO2021110806.

[0075] According to a second aspect of the invention, the one-through co-electrolysis is carried out in a solid oxide electrolysis cell unit, and the method comprises bypassing a part of the first CO 2 -rich stream before passing it through the solid oxide electrolysis cell unit (SOEC-unit). A part of the first CO 2 -rich stream that is not bypassed is combined into the stream to produce a combined feed gas stream to the SOEC-unit as shown in FIG. 2.

[0076] This, as in the first aspect of the invention, increases the flexibility in adjusting the molar ratio of CO / CO 2 in the syngas, and at the same time enables downsizing of the solid oxide electrolysis cell unit compared to the case where no bypass is provided.

[0077] In embodiments according to the second aspect of the invention, the method further comprises: iii) converting the syngas to methanol, synthetic fuel by Fischer-Tropsch synthesis (FT synthesis), or methane, for example, substitute natural gas (SNG).

[0078] Thereby, various useful products can be obtained from the syngas, all of which can be regarded as renewable products or electric fuels, i.e., e-fuels. The molar ratio of H 2Syngas with an H2 / CO ratio of about 2 is suitable for producing synthetic fuels (synfuels), such as jet fuel and diesel, by FT synthesis. When M is about 2 and the molar ratio CO / CO 2 >2, for example about 10 or more, the syngas is suitable for methanol production. Syngas can also be converted to SNG by a methanation reaction in which carbon dioxide and hydrogen react to produce methane and water: CO 2 +4H 2 ₂O=CH 4 ₄+2H 2 ₂O.

[0079] In certain embodiments, the method includes converting syngas to methanol, and when the CO 2 content in the syngas is less than 0.5 mol%, H 2 ₂O corresponding to 1.5 - 3 mol% of the syngas is added to the syngas. Thus, when the CO 2 content is <0.5 mol (less than 0.5 mol%), H 2 ₂O corresponding to 1.5 - 3 mol% is added to the syngas. That is, in this embodiment, the CO 2 content in the syngas is less than 0.5 mol%, and H 2 ₂O corresponding to 1.5 - 3 mol% of the syngas is added to the syngas.

[0080] As described in connection with the first aspect of the present invention, typically, syngas for methanol conversion includes a mixture of CO, CO 2 and H 2 ₂, as well as a mixture of H 2 ₂O. When the CO 2 content is less than 0.5 mol% (mol%), adding H 2 ₂O such that the H 2 ₂O content in the syngas is 1.5 - 3% can more offset the effect when sufficient CO 2 cannot be obtained. The molar ratio of CO to CO 2 in the syngas is 2 or more, and the higher this ratio, the better, but for methanol synthesis, at least CO 2Since the presence of is necessary, it is often desirable to keep the CO content in the synthesis gas from falling below 0.5 mol%. The addition of water enables the production of CO by the water-gas shift reaction: CO + H 2 O = H 2 + CO. 2 2 2

[0081] As related to the first aspect of the present invention, also in this second aspect of the present invention, the first CO 2 -rich stream is assumed to be produced by passing a carbon dioxide feed stream, preferably carbon dioxide from an external source, through a CO 2 -washing unit for removing impurities such as Cl, sulfur, Si, As; this is to ensure the protection of downstream units, here especially the subsequent once-through SOEC unit. For example, even a small amount of COS can cause problems. Usually, the amount of COS in industrial CO 2 is below the detection limit, but in some cases, COS has been measured in the range of 10 - 20 ppb, which is sufficient to have a harmful effect on the electrolysis unit, and as a result, the electrolysis unit deteriorates rapidly.

[0082] In a third aspect of the present invention, a method for producing higher alcohols and methane is also provided.

[0083] Accordingly, a method for producing alcohol (wherein the alcohol is at least one of C1 - C5 alcohols) or a method for producing methane, including the following steps, is also provided: a) Supplying a first CO 2 -rich stream and passing it through a first electrolysis unit to generate a first stream containing CO and CO 2 ; From said first stream containing CO and CO 2 : - a second stream containing CO and CO 2 ; and - separating a second CO 2 -rich stream ;​​ and reusing the second CO 2 -rich stream in the first electrolysis unit; b) supplying a water feedstock and passing it through a second electrolysis unit to generate a stream containing H 2 ; c) combining the second stream containing CO and CO 2 with the stream containing H 2 to form synthesis gas; d) converting the synthesis gas into the alcohol or the methane, such as substitute natural gas (SNG); wherein the second stream containing CO and CO 2 has a CO / CO 2 molar ratio greater than 2.

[0084] The alcohol is, for example, ethanol (C2 alcohol), propanol (C3 alcohol), butanol (C4 alcohol), or a combination thereof.

[0085] The methane is supplied, for example, as substitute natural gas (SNG).

[0086] It will be understood that any of the embodiments of the first aspect of the invention and the associated advantages related to one-through co-electrolysis applicable embodiments may be combined with the second aspect of the invention, or vice versa. Further, any of the embodiments of the first aspect of the invention and the associated advantages may be combined with the third aspect of the invention, or vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] FIG. 1 shows a schematic method and system for producing synthesis gas and further converting it into methanol according to an embodiment of the first aspect of the invention.

[0088] FIG. 2 shows a schematic method and system for producing synthesis gas and further converting it into useful products according to an embodiment of the second aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0089] Referring to FIG. 1, a carbon dioxide feed stream such as carbon dioxide from an external source is passed through a CO 2 - washing unit (not shown) to remove impurities and produce a first CO 2 - rich stream 1, 1', 1'', which is then passed through a first electrolysis unit 10, for example, a SOEC - CO 2 unit, i.e., a SOEC unit for CO 2 - electrolysis. This electrolysis unit 10' is powered by a sustainable energy source such as wind energy or solar energy, thereby appropriately having a molar ratio of CO / CO of 0.6 or less to avoid the risk of carbon formation 2 and producing a first stream 3 containing CO and CO 2 . This stream is separated, for example, via a PSA unit (not shown), into a second stream 5 containing CO with a molar ratio of CO / CO 2 > 2 and CO 2 , and a second CO 2 - rich stream 7 that is recycled to the electrolysis unit 10. Separately, a water feedstock 9 passes through a second electrolysis unit 12, such as a PEM electrolysis unit or a SOEC unit, powered by a sustainable source at 12'. Both streams 5 and 11, compared to the prior art, have a module M=(H 2 - CO 2 ) / (CO + CO 2 ) of, for example, 2.05 or 2.10, and at the same time a molar ratio of CO / CO 2 > 2, and are combined into a more reactive synthesis gas stream 13 that is very suitable for downstream conversion to methanol. As shown in the figure, a part 1'' of the first CO 2 - rich stream 1 can bypass the first electrolysis unit 10. The synthesis gas 13 enters a methanol section, for example, a methanol loop 14, as is well known in the art, thereby having a molar ratio of CH 3 OH / H 2 O compared to the prior art where the ratio is typically about 1 3 OH / H2 The raw methanol stream 15 having O of 1.3 or more, i.e., at least 30% less water, is converted. Then, the water in the raw methanol stream 15 is more preferably removed by a downstream distillation apparatus (not shown), and this stream is purified or concentrated in methanol. The downstream section 14 may also be a section where the syngas 13 is converted to at least one of higher alcohols, i.e., C1-C5 alcohols such as ethanol. Also, the downstream section 14 can be a section for converting the syngas 13 to methane, for example SNG.

[0090] Next, referring to FIG. 2, a carbon dioxide feed stream, for example, carbon dioxide from an external source, is passed through a CO 2 - washing unit (not shown) to remove impurities and produce a first CO 2 - rich stream 101, 101', 101''. A water feedstock, here in particular steam 109, is added and a combined feed gas stream is formed, and this gas stream is passed through a once-through type SOEC unit 110 powered by a sustainable power source 110' such as wind power or solar energy. Thereby, once-through co-electrolysis is performed to produce a syngas stream 105. By the once-through co-electrolysis, a desired molar ratio of CO / CO 2 in the syngas, for example >2, is obtained without the risk of carbon formation due to the presence of H 2 O and H 2 in the gas. As shown in the figure, a part 101'' of the first CO 2 - rich stream 101 can bypass the once-through SOEC unit 110. The syngas 105 or 107 enters a downstream section 120 such as a methanol section for producing methanol as shown in FIG. 1, a Fischer-Tropsch section for producing synthetic fuels such as jet fuel and diesel, or a section for converting the syngas to methane, for example SNG.

Claims

1. a) Providing a first CO ２ - rich stream and passing it through a first electrolysis unit to produce a first stream containing CO and CO ２ ; CO and CO ２ from the first stream containing -CO and CO ２ a second stream containing, and - Second CO ２ - Rich flow a step of separating; and Second CO ２ - Reusing the rich stream in the first electrolysis unit; b) providing a water supply raw material and passing it through a second electrolysis unit to generate a stream containing H ２ ; c) Combining the second stream containing CO and CO ２ with the stream containing H ２ to form synthesis gas; d) a step of converting the syngas into the methanol; A method for producing methanol, comprising: Here, the second stream containing CO and CO ２ has a molar ratio of CO / CO ２ greater than 2 the method.

2. The synthesis gas has a module M = (H ２ -CO ２ ) / (CO + CO ２ ) in the range of 1.95 to 2.10, and a molar ratio CO / CO ２ greater than 2, the method according to claim 1.

3. CO and CO ２ A first stream containing is in a molar ratio CO / CO in the range of 0.6 or less, for example 0.2 to 0.6 ２ The method according to any one of claims 1 to 2, having.

4. The first CO ２ -rich stream removes carbon dioxide from the carbon dioxide feed stream, preferably from an external source, of impurities such as Cl, sulfur, Si, As, for CO ２ - The method according to any one of claims 1 to 3, which is produced by passing through a cleaning unit.

5. CO in synthesis gas ２ When the content rate is less than 0.5 mol%, H corresponding to 1.5 to 3 mol% in the synthesis gas ２ O is added to the synthesis gas, and the method according to any one of claims 1 to 4.

6. In step a), CO ２ When performing electrolysis, the step of separating the first stream containing CO and CO ２ is to pass this stream through a CO enrichment unit, for example, a pressure swing adsorption unit (PSA), to produce the second stream containing CO and CO ２ and the second CO ２ -rich stream, the method according to any one of claims 1 to 5.

7. First CO ２ - providing a rich stream and passing it through a first electrolysis unit to produce a first stream containing CO and CO ２ ; and Providing a water supply raw material and passing this through a second electrolysis unit to generate a stream containing H ２ The method according to any one of claims 1 to 6, wherein the steps are carried out separately.

8. Step a) includes bypassing a part of the first CO ２ -rich stream before passing it through the first electrolysis unit, according to any one of claims 1 to 7. ２ -rich stream before passing it through the first electrolysis unit, according to any one of claims 1 to 7.

9. The first electrolysis unit is a solid oxide electrolysis unit, and the second electrolysis unit for generating a stream containing H ２ is an alkali / polymer electrolyte membrane electrolysis unit, i.e., an alkali and / or PEM electrolysis unit; or a solid oxide electrolysis cell unit, according to any one of claims 1 to 8.

10. The method according to any one of claims 1 to 9, wherein the water feedstock comprises steam generated from other steps of the method, such as steam generation or downstream distillation.

11. The step of converting syngas into methanol comprises passing the syngas through a methanol synthesis reactor in the presence of a catalyst for generating a raw methanol stream, and the step optionally further comprises a distillation step of the raw methanol stream for generating a separate methanol stream having a water stream and at least 98% by mass of methanol. The method according to any one of claims 1 to 10.

12. i) Provide a first CO ２ -rich stream, provide a water feedstock, combine it with the first CO ２ -rich stream to form a combined feed gas stream, pass the combined feed gas stream through an electrolysis unit to produce the synthesis gas containing CO, CO ２ and H ２ ; A method for producing syngas, comprising: Here, the synthesis gas has a module M = (H ２ -CO ２ ) / (CO + CO ２ ) in the range of 1.95 to 2.10, or a molar ratio of H ２ / CO of 1.95 - 2.10; wherein i) is carried out by one-through co-electrolysis; and i) is implemented by one-through co-electrolysis; and Here, the one-through co-electrolysis is carried out in a solid oxide electrolysis cell unit, and the method includes bypassing a part of the first CO ２ -rich stream before passing it through the solid oxide electrolysis cell unit. the method.

13. The method according to claim 12, wherein the synthesis gas has a molar ratio CO / CO of 0.2 to 0.6, and the method comprises ２ having, and the method is ii) the syngas is fed into a reverse water gas shift step (rWGS step), optionally into an electrically heated WGS reactor (e-rWGS reactor). The method further comprising.

14. iii) converting the syngas into methanol, or synthetic fuel via Fischer-Tropsch synthesis (FT synthesis), or methane, such as substitute natural gas (SNG). The method according to claim 12 or 13, further comprising.

15. comprising converting syngas to methanol, and when the CO content in the syngas is less than 0.5 mol%, adding H2O corresponding to 1.5 to 3 mol% in the syngas to the syngas, the method according to claim 14. ２ When the content is less than 0.5 mol%, H2O corresponding to 1.5 to 3 mol% in the syngas is added to the syngas. ２ The method according to claim 14.

16. A method for producing an alcohol, wherein the alcohol is at least one of C1-C5 alcohols, or a method for producing methane, comprising: a) providing a first CO ２ - rich stream and passing it through a first electrolysis unit to produce a first stream containing CO and CO ２ ; CO and CO ２ from the first stream containing: -CO and CO ２ a second stream containing, and - Second CO ２ - Rich flow a step of separating; And then, reuse the second CO ２ - rich stream in the first electrolysis unit; b) Supplying a water supply raw material, passing this through a second electrolysis unit to generate a stream containing H ２ ; and c) combining the second stream containing CO and CO ２ with the stream containing H ２ to form synthesis gas; d) a step of converting the syngas into the alcohol or the methane, such as substitute natural gas (SNG); comprising Here, the second stream containing CO and CO ２ has a molar ratio of CO / CO ２ greater than 2 the method.

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