Process for producing liquid hydrocarbons

Abstract

A process for producing liquid hydrocarbons, the process comprising: providing a first reactant stream comprising water and carbon dioxide; passing the first reactant stream to a first electrolysis unit to form a syngas comprising hydrogen and carbon monoxide; passing the syngas to a hydrocarbon synthesis unit to form a liquid hydrocarbon product and an effluent gas; passing the effluent gas and steam to a deenrichment reactor to form a methane-rich effluent gas; passing the methane-rich effluent gas to the first electrolysis unit to form a gas mixture comprising hydrogen and one or both of carbon monoxide and carbon dioxide; and introducing the gas mixture into the synthesis gas.

Description

Technical Field

[0001] The present invention relates to a method for producing liquid hydrocarbons. Background Art

[0002] Electrolytic hydrogen is increasingly being proposed for the preparation of liquid hydrocarbons, in particular liquid hydrocarbon fuels (so-called e-fuels). Electrolytic hydrogen is used for liquid hydrocarbon synthesis "directly" via a Fischer-Tropsch unit or indirectly via methanol, which is further reacted in a methanol-to-hydrocarbon unit (e.g., a methanol-to-gasoline unit). Waste hydrocarbon by-products are produced during the synthesis of liquid hydrocarbons. Examples thereof are fusel oil in methanol synthesis and LPG and methane in the methanol-to-gasoline process. Methane is also an important by-product of the Fischer-Tropsch process. The combustion of these wastes, for example in a flame steam reformer or a fired heater, is undesirable because it produces CO emissions.

[0003] Xu et al. proposed a method for preparing hydrocarbon fuels using electrolytic hydrogen in "Low carbon fuel production from combined solid oxide CO2 co-electrolysis and Fischer-Tropsch synthesis system:A modelling study", Applied Energy, 242, 2019, 911-918. The method includes converting carbon dioxide and water into carbon monoxide and hydrogen using a solid oxide electrolysis cell (SOEC), followed by conversion of methane and water from the Fischer-Tropsch process to carbon monoxide and hydrogen. The conversion of methane improves the carbon efficiency of the method. However, the C2+ hydrocarbons separated from the Fischer-Tropsch product hydrocarbons are processed, so that the method is still relatively low in carbon efficiency.

[0004] WO2021214214 (A1) discloses a method for operating a solid oxide pool system, wherein an electric current is used to produce hydrogen or synthesis gas from steam or a mixture comprising steam and carbon dioxide in an electrochemical reaction. An additional amount of at least one compound selected from natural gas, methane or another hydrocarbon is added to the steam or mixture for conversion to synthesis gas. Endothermic reforming of the added hydrocarbon is performed by coupling in waste heat from the electrochemical reaction, and an additional amount of at least one compound is added to provide hydrogen to compensate for the degradation effects of the solid oxide pool of the solid oxide pool system, so that the total amount of hydrogen generated by the solid oxide pool system remains constant over time.

[0005] The present invention seeks to address at least some of the problems associated with the prior art or at least provide a commercially acceptable alternative solution thereto. Summary of the Invention

[0006] One aspect of the present disclosure relates to a method of producing liquid hydrocarbons, the method comprising:

[0007] providing a first reactant stream comprising water and carbon dioxide;

[0008] passing the first reactant stream to a first electrolysis unit to form a synthesis gas comprising hydrogen and carbon monoxide;

[0009] passing the synthesis gas to a hydrocarbon synthesis unit to form liquid hydrocarbon products and an effluent gas;

[0010] passing the effluent gas and steam to a reverse enrichment reactor to form a methane-enriched effluent gas;

[0011] passing the methane-enriched effluent gas to the first electrolysis unit to form a gas mixture comprising hydrogen and one or both of carbon monoxide and carbon dioxide; and

[0012] The gas mixture is introduced into the synthesis gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a diagram of a first embodiment of the method according to the present invention;

[0014] Figure 2 is a diagram of a second embodiment of the method according to the invention. DETAILED DESCRIPTION

[0015] The present disclosure relates to a method for producing liquid hydrocarbons, the method comprising:

[0016] providing a first reactant stream comprising water and carbon dioxide;

[0017] passing the first reactant stream to a first electrolysis unit to form a synthesis gas comprising hydrogen and carbon monoxide;

[0018] passing the synthesis gas to a hydrocarbon synthesis unit to form liquid hydrocarbon products and an effluent gas;

[0019] passing the effluent gas and steam to a reverse enrichment reactor to form a methane-enriched effluent gas;

[0020] passing the methane-enriched effluent gas to the first electrolysis unit to form a gas mixture comprising hydrogen and one or both of carbon monoxide and carbon dioxide; and

[0021] The gas mixture is introduced into the synthesis gas.

[0022] Unless expressly indicated to the contrary, each aspect or embodiment as defined herein may be combined with any other aspect or embodiment. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0023] Advantageously, the method of the present invention can produce liquid hydrocarbons in a more carbon-efficient manner compared to prior art methods. Recycling the effluent gas back to the first electrolysis unit ensures that a higher proportion of the carbon content of the first reactant stream is used in the method. Compared to the method of the aforementioned WO2021214214 (A1), including a reverse enrichment unit to convert higher hydrocarbons in the effluent gas recovered from the hydrocarbon synthesis unit into methane, the operation of the electrolysis unit is enhanced without the need to completely convert hydrocarbons into hydrogen and carbon oxides. In addition, there is no need to treat the effluent gas, for example, by combustion, thereby potentially reducing the cost and environmental impact of the method.

[0024] In some prior art methods, methane can be recovered from the effluent gas and subsequently recycled back to the electrolysis unit. Although this can increase the carbon efficiency of the method, the method still loses the carbon content of the C2+ hydrocarbons contained in the effluent gas and needs to process such C2+ hydrocarbons, thereby increasing the environmental impact of the method. In contrast, in the present invention, the C2+ hydrocarbons contained in the effluent gas are converted into methane by being transferred to a reverse enrichment reactor before the effluent gas is transferred to the first electrolysis unit. Therefore, substantially the entire carbon content of the effluent gas can be recycled, which means that the carbon efficiency of the method is increased. In addition, the need for processing the effluent gas is significantly reduced.

[0025] The term "liquid hydrocarbon" has its ordinary meaning in the art. As used herein, the term encompasses substances formed from carbon and hydrogen that are liquid at room temperature and pressure. Hydrocarbons typically include alkanes and typically contain 10 to 20 carbon atoms per molecule. The liquid hydrocarbon product is preferably a liquid hydrocarbon fuel. Examples of liquid hydrocarbon fuels include diesel, gasoline, and jet fuel or kerosene. Such fuels are commercially valuable.

[0026] The method comprises providing a first reactant stream comprising water and carbon dioxide. Water is typically provided in the form of steam. Carbon dioxide can be any carbon dioxide source. For example, carbon dioxide can be a by-product of combustion or a component of a product gas stream produced by partial oxidation, steam reforming or gasification of a carbonaceous material, or carbon dioxide can be separated from air, seawater, landfill gas or methane, or derived from a biological source. Carrying out carbon dioxide recovery from any of these sources can be achieved by known methods.

[0027] The method comprises passing a first reactant stream to a first electrolysis unit to form a synthesis gas comprising hydrogen and carbon monoxide. Electrolysis units are known in the art. A typical electrolysis unit comprises a cathode and an anode. Typically, a co-electrolysis of carbon dioxide and water (typically in the form of steam) occurs at the cathode according to the following reaction:

[0028] CO2+H2O→CO+H2+2O 2-

[0029] Oxygen ions generated at the cathode may be transported to the anode and form molecular oxygen (ie, O 2 ) at the anode.

[0030] As used herein, the term "syngas" or "synthesis gas" may encompass a fuel gas mixture. In the methods of the present invention, syngas comprises hydrogen (i.e., molecular hydrogen H2) and carbon monoxide (i.e., CO). Syngas may comprise other substances such as, for example, carbon dioxide (i.e., CO2).

[0031] The method comprises passing the synthesis gas to a hydrocarbon synthesis unit to form a liquid hydrocarbon product and an effluent gas. Hydrocarbon synthesis units are known in the art. The hydrocarbon product can be recovered from the hydrocarbon synthesis unit. The effluent gas comprises hydrocarbons, typically lower hydrocarbons that do not form a liquid hydrocarbon product. The effluent gas may contain other substances, such as unreacted hydrogen, carbon monoxide and / or carbon dioxide.

[0032] The method comprises passing the effluent gas and steam to a reverse enrichment reactor to form a methane-enriched effluent gas. The effluent gas is preferably heated in heat exchange with synthesis gas upstream of the reverse enrichment reactor. This can reduce the energy requirement of the method.

[0033] The de-enrichment reactor typically includes a bed of de-enrichment catalyst. Suitable de-enrichment reactors and de-enrichment catalysts are known in the art. In the de-enrichment reactor, at least a portion of the C2+ hydrocarbons contained in the effluent gas can be converted into methane. Typically, most of the C2+ hydrocarbons contained in the effluent gas are converted into methane, and more typically, substantially all of the C2+ hydrocarbons contained in the effluent gas are converted into methane. Therefore, the methane-rich effluent gas can also be considered to be a lean C2+ hydrocarbon effluent gas.

[0034] The reverse enrichment reactor can be usefully operated by adiabatic steam reforming of the hydrocarbons contained in the effluent gas. Therefore, it is necessary to supply steam to the reverse enrichment reactor. In addition, in order to satisfactorily steam reform the effluent gas without deactivating the catalyst through carbon formation, a hydrogen source can also be provided to the reverse enrichment reactor.

[0035] The amount of steam introduced into the reverse enrichment reactor can be such that the steam to carbon molar ratio in the feed to the reverse enrichment vessel is from 1:1 to 5:1. The so-called steam to carbon molar ratio refers to the molar ratio of steam to the sum of the carbon-containing components in the feed, which carbon-containing components include hydrocarbons, CO and CO2.

[0036] The feed gas may be passed adiabatically through a bed of reverse enrichment catalyst, such as a particulate nickel catalyst having a nickel content in the range of 30 wt% to 60 wt% (e.g., greater than 40 wt%). Such catalysts are commercially available.

[0037] A hydrogen stream can be fed to the reverse enrichment reactor along with the effluent gas to reliably convert C3-C4 to methane. The hydrogen can be a pure hydrogen stream, or can contain a suitably high hydrogen content to provide hydrogen for reverse enrichment.

[0038] The reverse enrichment reactor is preferably operated at a temperature of 300°C to 650°C and / or at a pressure of 10 bar to 100 bar. In some arrangements, the reverse enrichment reactor can be operated at an inlet temperature in the range of 400°C to 500°C, a steam to carbon molar ratio of 1:1 to 5:1, and an H2 content of at least 0.001 kg H2 per kg of carbonaceous components in the feed. The recommended minimum inlet steam content at an inlet temperature of 400°C is 1.8 kg / kg steam to carbonaceous feed ratio. Operating temperatures above 400°C may require more steam and hydrogen to avoid carbon deposition. Preferably, the inlet temperature is at least 350°C to provide a high reaction rate.

[0039] In some arrangements, the de-enrichment vessel may be operated at a pressure in the range of, for example, 1.0 MPag to 7.0 MPag, preferably 1.5 MPag to 6.6 MPag.

[0040] Where the effluent gas contains olefins which may react exothermically with hydrogen over a reverse enrichment catalyst, a hydrogenation catalyst may be provided upstream of the reverse enrichment catalyst. However, this is generally not necessary unless the olefin level is above, for example, 10 mol%.

[0041] The reverse enrichment reactor produces a methane-rich effluent gas.

[0042] The method includes passing a methane-rich effluent gas to a first electrolysis unit to form a gas mixture comprising hydrogen and one or both of carbon monoxide and carbon dioxide. In the electrolysis unit, methane in the methane-rich effluent gas is converted into hydrogen and one or both of carbon monoxide and carbon dioxide.

[0043] The method comprises introducing the gas mixture into the synthesis gas. The gas mixture may be recovered from the first electrolysis unit before being introduced into the synthesis gas. Alternatively, the gas mixture may be introduced into the synthesis gas within the electrolysis unit.

[0044] Preferably, the first electrolysis unit comprises a solid oxide electrolysis cell (SOEC), which comprises an anode, a cathode and a solid electrolyte membrane arranged between the anode and the cathode. Solid oxide electrolysis cells are known in the art. Solid oxide cells are particularly suitable for (co) electrolysis of water and carbon dioxide at the cathode and / or oxidation of methane at the anode. The solid oxide electrolysis cell consists of a cathode where a reduction reaction is taking place, a solid electrolyte membrane for ion transport and an anode where an oxidation reaction occurs. The solid electrolyte membrane can transport O 2- or H + The catalyst can be deposited together with the cathode or anode to achieve a tandem reaction.

[0045] The first electrolysis unit preferably comprises a stack of solid oxide electrolysis cells. This may enable higher volumes of electrolysis to take place.

[0046] The reactant stream is preferably passed to the first electrolysis unit and includes passing the first reactant stream to a cathode. The cathode material in the solid oxide electrolysis cell may include a Ni or Ag based oxide mixed or supported on yttria stabilized zirconia, or a mixed oxide such as BaCe. 0.2 Zr 0.7 Y 0.1 O 3-δ or La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3-δ In a solid oxide electrolysis cell, co-electrolysis of carbon dioxide and steam can occur at the cathode according to the following reaction:

[0047] At the cathode: CO2+H2O→CO+H2+2O 2-

[0048] Oxygen ions are generated at the cathode along with CO and H2 and transported through the solid oxide electrolyte and react at the anode to produce O2.

[0049] The methane-rich effluent gas is preferably passed to the first electrolysis unit and is preferably passed to the anode. In this case, the hydrocarbons (primarily methane) contained in the methane-rich effluent gas can react with a suitable electrocatalyst at the anode to be oxidized to carbon dioxide and water or partially oxidized to produce carbon monoxide and hydrogen. In this case, the anode preferably comprises an electrocatalyst. Suitable electrocatalysts are perovskites such as lanthanum strontium cobalt ferrite (LSF), gadolinium oxide-doped ceria (GDC), lanthanum strontium cobalt ferrite (LSCF), for example having the formula (La 0.8 Sr 0.2 ) 0.95 MnO3-δ Lanthanum strontium manganate (LSM), lanthanum strontium cobalt manganate (LSCM) and Ni-Sr2Fe 1.5 Mo 0.5 O 6-δ -Ce 0.8 Sm 0.2 O 1.9 Nickel-iron or nickel-copper manganate materials;) and Ni-Cu / LSCM.

[0050] Methane-rich synthesis gas and steam are provided to the anode. Therefore, the anode preferably comprises a steam reforming catalyst. The steam reforming catalyst may suitably comprise nickel and / or PGM based on a suitable catalyst support (such as yttria-stabilized zirconia (YSZ)). The steam reforming catalyst may enable the formation of carbon monoxide and hydrogen. The oxygen ions then transported through the solid oxide electrolyte may react with hydrogen and carbon monoxide to produce water and carbon dioxide at the anode, which may be recycled to the cathode to produce carbon monoxide and hydrogen. In this case, the reaction at the anode may be as follows:

[0051] At the anode; catalysis: CH4+H2O→H2+CO (endothermic)

[0052] In the anode: H2+O 2- →H2O+e - (Exothermic)

[0053] CO+O 2- →CO2+e -

[0054] By oxidizing hydrogen and carbon monoxide at the anode, electricity can also be generated. This improves the overall energy efficiency of the system. In addition, hydrogen oxidation generates heat, which can offset the heat losses in steam reforming, which is an endothermic reaction.

[0055] A proton conducting solid oxide cell (H-SOC) in which the solid electrolyte exhibits proton conductivity may also be used. In this case, a catalyst may be employed at the cathode along with the H-SOC for reforming both methane and carbon dioxide into carbon monoxide and hydrogen. In electrolysis mode, steam is oxidized at the anode to produce H + , which is transported across the solid proton electrolyte membrane, where it reacts in the cathode to produce H2. The H2 can then react with CO2 fed at the cathode to produce CO and H2O. CH4 is fed simultaneously with CO2 at the cathode to produce synthesis gas over a reforming catalyst. Steam can also react with CH4 to further produce synthesis gas at the cathode using a steam reforming catalyst.

[0056] Anode: H2O→2H + +0.5O2

[0057] Cathode: 2H + →H2

[0058] At the cathode catalyst: CO2+H2→CO+H2O

[0059] CO2+CH4→2CO+2H2

[0060] CH4+H2O→CO+H2

[0061] If operated in reverse mode, the cell can also be used to generate electricity if the electricity to operate the electrolysis unit is unavailable. When in fuel cell mode, a reforming catalyst is provided at the anode where CO2 and methane-rich gas are fed. A portion of the hydrogen produced can be oxidized at the anode and produce H+ ions, which are transported via the electrolyte to produce water at the cathode. The benefit of such a system is that electricity and heat can be generated, which can be integrated into the system. Water can be recycled at the anode, where it can be used to prepare additional synthesis gas by reacting with methane over a steam reforming catalyst. In this case, the reaction can be as follows:

[0062] At the anode catalyst: CH4+CO2→2CO+2H2

[0063] CH4+H2O→CO+H2

[0064] In the anode: H2 → 2H +

[0065] In the cathode: 2H + +0.5O2→H2O

[0066] The first electrolysis unit is preferably operated at a temperature of 500° C. to 1000° C., more preferably 700° C. to 900° C. Lower temperatures may result in disadvantageously low levels of hydrolysis. Higher temperatures may reduce the energy efficiency of the process.

[0067] The molar ratio of water or steam to carbon dioxide in the first reactant stream may be from 0.5:1 to 2:1, preferably about 1:1. In addition, steam will be present in the methane-enriched effluent gas recovered from the reverse enrichment reactor. The molar ratio of steam to methane in the methane-enriched effluent gas fed to the first electrolysis unit is preferably in the range of from about 1:1 to 3:1, more preferably from about 2:1 to 3:1.

[0068] In a preferred embodiment, the hydrocarbon synthesis unit comprises a Fischer-Tropsch reactor which converts the synthesis gas into liquid hydrocarbon products, an aqueous stream and an effluent gas.Fischer-Tropsch reactors are known in the art.

[0069] The temperature of the Fischer-Tropsch reactor is preferably between 150°C and 300°C. Lower temperatures may result in the production of unfavourably low levels of liquid hydrocarbons. Higher temperatures may increase the energy cost of the process without significantly increasing the levels of liquid hydrocarbons produced.

[0070] The Fischer-Tropsch reactor preferably comprises a catalyst comprising cobalt, iron and / or ruthenium. Such a catalyst may be particularly effective in catalyzing the Fischer-Tropsch reaction and / or may enable the reaction to be advantageously carried out at low temperatures and / or with high yields.

[0071] The molar ratio of hydrogen to carbon monoxide in the synthesis gas is preferably from 1.8 to 2.2, as this is close to the stoichiometric ratio of the Fischer-Tropsch reaction of about 2.

[0072] The effluent gas preferably comprises C1 to C4 hydrocarbons. Such hydrocarbons are preferably not contained in the liquid hydrocarbons, or are preferably contained in the liquid hydrocarbons only at very low levels. C1, i.e., methane, can be easily converted in the first electrolysis unit. C2, C3, and C4 can be easily converted to methane in the reverse enrichment reactor. The effluent gas may comprise tail gas containing unreacted hydrogen and carbon monoxide, or may be composed of hydrocarbons (e.g., liquefied petroleum gas, i.e., LPG).

[0073] In the case where the hydrocarbon synthesis unit includes a Fischer-Tropsch reactor, passing the synthesis gas to the hydrocarbon synthesis unit (Fischer-Tropsch reactor) preferably includes passing the synthesis gas to a carbon dioxide removal unit to form a carbon dioxide-lean synthesis gas and a carbon dioxide stream, and then passing the carbon dioxide-lean synthesis gas to the hydrocarbon synthesis unit. This can increase the efficiency of the process because no carbon dioxide is used in the Fischer-Tropsch reaction.

[0074] The method preferably further comprises delivering a carbon dioxide stream to the first electrolysis unit. For example, the carbon dioxide stream may be introduced into the first reactant stream before the first reactant stream is delivered to the first electrolysis unit. This may increase the carbon efficiency of the method. The carbon dioxide stream is preferably delivered to the cathode of the first electrolysis unit.

[0075] The method preferably further comprises passing at least a portion of the aqueous stream to the first electrolysis unit in the form of steam. This can reduce the water requirement of the method. For example, the aqueous stream can be introduced into the first reactant stream before the first reactant stream is passed to the first electrolysis unit. The aqueous stream is preferably passed to the cathode of the first electrolysis unit.

[0076] The aqueous stream is preferably at least partially purified before being passed to the first electrolysis unit. For example, hydrocarbons may be removed from the aqueous stream. Impurities such as hydrocarbons may clog the first electrolysis unit and / or poison the catalyst contained in the cathode and / or anode of the first electrolysis unit.

[0077] Preferably, the method further comprises: conveying the liquid hydrocarbon product to an upgrading unit to provide an upgraded liquid hydrocarbon product and waste hydrocarbons; and conveying the waste hydrocarbons and steam to the first electrolysis unit via a reverse enrichment reactor or another reverse enrichment reactor. The upgrading unit may comprise a hydrotreating unit, a hydrotreating unit, a hydrocracking unit, and a fractionation unit. This can produce higher value liquid hydrocarbon products without reducing the carbon efficiency of the method. The waste hydrocarbons can be conveyed to the reverse enrichment reactor before being conveyed to the first electrolysis unit. For example, the waste hydrocarbons can be introduced into the effluent gas before the effluent gas is conveyed to the reverse enrichment reactor. Alternatively, a separate further reverse enrichment reactor can be used in parallel to reverse enrich the waste hydrocarbons. Using the same or parallel reverse enrichment units to reverse enrich the waste hydrocarbons and produce reverse enriched waste hydrocarbon gas protects the first electrolysis unit from clogging by hydrocarbons higher than methane in the waste hydrocarbons. In addition to the enrichment reactor fed with the effluent gas stream, the use of parallel enrichment reactors to enrich the spent hydrocarbons allows the enrichment reactors to operate at different conditions, which better convert the different feeds to methane. The enriched spent hydrocarbons are preferably sent to the anode of the first electrolysis unit.

[0078] In another preferred embodiment:

[0079] The hydrocarbon synthesis unit includes a methanol synthesis unit located upstream of the methanol-to-hydrocarbons unit; and

[0080] The steps of passing the synthesis gas to the hydrocarbon synthesis unit to form liquid hydrocarbon products and an effluent gas include:

[0081] passing the synthesis gas to the methanol synthesis unit to convert the synthesis gas into a methanol stream and a waste gas stream comprising hydrogen;

[0082] passing the methanol stream to the methanol-to-hydrocarbons unit to form a hydrocarbon mixture and the effluent gas; and

[0083] A hydrocarbon fuel product selected from the group consisting of a diesel product, a gasoline product, and a jet fuel product is recovered from the hydrocarbon mixture.

[0084] Methanol synthesis units and methanol-to-hydrocarbon units are known in the art. A methanol-to-hydrocarbon unit may be particularly effective in producing liquid hydrocarbon fuels. A methanol-to-fuel unit may use the Exxon process to generate fuels, wherein methanol is processed into olefins, and the olefins are then oligomerized to obtain a fuel range for gasoline or jet fuel. Recovering at least one of a diesel product, a gasoline product, and a jet fuel or kerosene product from the hydrocarbon mixture may include distillation. Methanol may be formed in a methanol synthesis unit according to the following reaction:

[0085] CO + 2H2 → CH3OH

[0086] CO2+3H2→CH3OH+H2O

[0087] The methanol synthesis unit may comprise a catalyst, preferably a copper-based catalyst. Preferably, the waste gas stream is recycled into the synthesis gas before the synthesis gas is passed to the hydrocarbon synthesis unit. This can improve the carbon efficiency of the process.

[0088] Preferably, the off-gas is passed to a hydrogen recovery unit to increase the hydrogen concentration of the off-gas and form a carbon-containing off-gas before the off-gas is recycled into the synthesis gas; and the method further comprises introducing the carbon-containing off-gas into the off-gas before the off-gas is passed to the de-enrichment reactor. The hydrogen recovery unit may comprise, for example, a membrane hydrogen recovery unit and / or a pressure swing adsorption (PSA) hydrogen recovery unit. Since methanol is formed from carbon monoxide having a H2:CO ratio of 2:1 and carbon dioxide having a H2:CO2 ratio of 3:1, increasing the hydrogen concentration of the off-gas may improve the efficiency of the method. Introducing the carbon-containing off-gas into the off-gas before the off-gas is passed to the de-enrichment reactor may increase the carbon efficiency of the method.

[0089] The synthesis gas preferably sent to the methanol synthesis unit has a stoichiometric number R in the range of 1.95 to 2.15, the stoichiometric number R being defined as R=([H2]-[CO2]) / ([CO2]+[CO]). Such R values ​​may be particularly suitable for methanol synthesis.

[0090] Passing the methanol stream to the methanol-to-fuel reactor preferably includes:

[0091] passing the methanol stream to a methanol distillation unit to form a purified methanol stream and a water stream; and

[0092] The purified methanol stream is sent to a methanol-to-fuel unit.

[0093] This can increase the efficiency of the methanol-to-fuel reaction and / or reduce poisoning of the catalyst used in the methanol-to-fuel reactor. Preferably, the water stream is introduced into the first reactant stream before the first reactant stream is passed to the first electrolysis unit. This can reduce the water demand of the process.

[0094] The process preferably further comprises separating fusel oil from the methanol distillation unit and introducing a fusel oil stream into the effluent gas before passing the effluent gas to the de-enrichment reactor. This can increase the carbon efficiency of the process.

[0095] The process preferably further comprises introducing a water stream into the first reactant stream. This can reduce the water requirement of the process.

[0096] The method preferably further comprises introducing carbon dioxide into the synthesis gas before passing the synthesis gas to the hydrocarbon synthesis unit.As discussed above, additional methanol may be produced from the reaction of carbon dioxide and hydrogen.

[0097] The method preferably further comprises:

[0098] providing a second reactant stream comprising water;

[0099] passing the second reactant stream to a second electrolysis unit to form a hydrogen stream; and

[0100] introducing the hydrogen stream into the synthesis gas before conveying the synthesis gas to the hydrocarbon synthesis unit,

[0101] The second electrolysis unit is operated at a lower temperature than the first electrolysis unit.

[0102] This may enable a portion of the hydrogen in the synthesis gas to be produced at a lower temperature (i.e. in a more energy-efficient manner) than the hydrogen produced in the first electrolysis unit. This may be particularly beneficial when the hydrocarbon synthesis unit requires a higher ratio of hydrogen to carbon monoxide and / or carbon dioxide on a molar basis. This may be the case, for example, when the hydrocarbon synthesis unit comprises a Fischer-Tropsch unit, or comprises a methanol synthesis unit and a methanol-to-fuel unit. The second electrolysis unit may be operated at a temperature below 100°C, typically in the range of 20°C or 30°C to 90°C.

[0103] The second electrolysis unit preferably comprises an alkaline electrolysis unit or a polymer electrolyte membrane (PEM) electrolysis unit. Such electrolysis units are known in the art. Such electrolysis units may be particularly effective when performing electrolysis at such lower temperatures.

[0104] The first electrolysis unit and / or the second electrolysis unit are preferably powered by renewable energy. This can make the method more environmentally friendly.

[0105] Example

[0106] Figure 1A diagram of a first embodiment of a method according to the present invention is shown. A first electrolysis unit 1 powered by renewable energy receives a first reactant stream 2 comprising steam and carbon dioxide. The first electrolysis unit 1 converts the first reactant stream 2 into a synthesis gas 5 comprising hydrogen and carbon dioxide. A second electrolysis unit 3 powered by renewable energy and operated at a lower temperature than the first electrolysis unit 1 receives a second reactant stream 4 comprising water. The second electrolysis unit 3 converts the second reactant stream 4 into a hydrogen stream 6, which is then introduced into the synthesis gas 5. Optionally, a carbon dioxide stream 7 can be introduced into the synthesis gas 5. The synthesis gas 5 is conveyed to a methanol synthesis unit 8 to convert the synthesis gas 5 into a methanol stream 9 and a waste gas stream 10 comprising hydrogen. The waste gas stream 10 is conveyed to a hydrogen recovery unit 11 to increase the hydrogen concentration of the waste gas stream 10 and form a carbon-containing waste gas 12. The hydrogen-rich waste gas stream from the hydrogen recovery unit 11 is then recycled into the synthesis gas 5 before the synthesis gas 5 is conveyed to the methanol synthesis unit 8. The methanol stream 9 is passed to a methanol distillation unit 13 to form a purified methanol stream 14, a water stream 15, and a fusel oil stream 16. The water stream 15 may be treated or passed to the first electrolysis unit 1. The purified methanol stream 14 is passed to a methanol-to-fuel unit 17 to form a liquid hydrocarbon fuel product 18 and an effluent gas 19. The effluent gas 19 is conveyed to the first electrolysis unit 1. Before the effluent gas 19 is passed to a de-enrichment reactor 20, the fusel oil stream 16 is introduced into the effluent gas 19. The de-enrichment reactor 20 contains a de-enrichment catalyst that converts the effluent gas 19 into a methane-enriched effluent gas 21, which is then passed to the first electrolysis unit 1.

[0107] Figure 2 A diagram of a second embodiment of the method according to the present invention is shown. The second embodiment differs from the first embodiment in that, instead of conveying the synthesis gas 5 to a methanol synthesis unit, carbon dioxide is removed from the synthesis gas 5 in a carbon dioxide removal unit 22 to form a carbon dioxide stream 23 and a carbon dioxide-lean synthesis gas 24. The carbon dioxide stream 23 is recycled to the first electrolysis unit 1. The carbon dioxide-lean synthesis gas 24 is then conveyed to a Fischer-Tropsch unit 25, which converts the carbon dioxide-lean synthesis gas 24 into a liquid hydrocarbon product 18, a water-containing stream 26 and an effluent gas 19. After optional purification (not shown), the water-containing stream 26 is conveyed to the first electrolysis unit 1 in the form of steam. The liquid hydrocarbon product 18 is conveyed to a hydrocarbon upgrading unit 27 to provide an upgraded liquid hydrocarbon fuel product 28 and waste hydrocarbons 29. The waste hydrocarbons 29 are then introduced into the effluent gas 19 before the effluent gas 19 is conveyed to the de-enrichment reactor 20.

[0108] Alternatively, the spent hydrocarbons 29 may be mixed with steam and fed to a parallel de-enrichment reactor to form a de-enriched spent hydrocarbon stream that may be fed to the first electrolysis unit 1 .

[0109] The effluent gas from the methane to gasoline unit exhibits the following composition of light gases (methane / ethane), C3 and C4:

[0110]

[0111]

[0112] The effluent gas is sent to a stripping reactor containing a nickel CRG stripping catalyst (Johnson Matthey). The following performance is achieved:

[0113] Feed steam hydrogen Inlet reactor Molar flow kmol / hr 100.0 455.3 3.0 558.4 Mass flow kg / hr 5108.5 8202.5 6.1 13317.2 Steam:Carbon v / v 1.298 pressure -bar 20.0 temperature C 400 Molecular weight 51.085 18.015 2.016 23.850 <![CDATA[H2]]> ％ 0.00 100.00 0.55 <![CDATA[H2O]]> ％ 0.00 100.00 0.00 81.54 methane ％ 6.97 0.00 1.25 Propane ％ 27.36 0.00 4.90 n-butane ％ 59.20 0.00 10.60 1 Propylene ％ 1.00 0.00 0.18 1-Butene ％ 5.47 0.00 0.98

[0114] Entry anti-enrichment Export anti-enrichment Molar flow (wet) kmol / hr 558.4 685.8 Mass flow rate (wet) kg / hr 12765.6 12765.6 Molar flow rate (dry) kmol / hr 103.0 361.8 Mass flow rate (dry) kg / hr 4563.1 6929.2 pressure -bar 20.0 19.3 temperature C 400 468 <![CDATA[H2]]> mol% 0.55 7.37 CO 0.00 0.23 <![CDATA[CO2]]> 0.00 9.46 <![CDATA[H2O]]> 81.54 47.24 methane 3.54 35.70 Propane 5.06 0.00 n-butane 8.31 0.00 1 Propylene 0.19 0.00 1-Butene 0.80 0.00

[0115] This corresponds to:

[0116] Carbonaceous feed = 4557.0 kg / hr

[0117] Steam: Carbon feed = 1.80w / w

[0118] H2: Carbon-containing raw material = 0.015 Nm 3 / kg

[0119] The foregoing detailed description has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations to the presently preferred embodiments illustrated herein will be apparent to those skilled in the art and fall within the scope of the appended claims and their equivalents.

Claims

1. A method for producing liquid hydrocarbons, the method comprising: providing a first reactant stream comprising water and carbon dioxide; passing the first reactant stream to a first electrolysis unit to form a synthesis gas comprising hydrogen and carbon monoxide; passing the synthesis gas to a hydrocarbon synthesis unit to form a liquid hydrocarbon product and an effluent gas; passing the effluent gas and steam to a reverse enrichment reactor to form a methane-enriched effluent gas; passing the methane-enriched effluent gas to the first electrolysis unit to form a gas mixture comprising hydrogen and one or both of carbon monoxide and carbon dioxide; and The gas mixture is introduced into the synthesis gas.

2. The method of claim 1, wherein the liquid hydrocarbon comprises a liquid hydrocarbon fuel, preferably diesel, gasoline, jet fuel or kerosene.

3. The method according to claim 1 or claim 2, wherein the first electrolysis unit comprises a solid oxide electrolysis cell (SOEC) comprising an anode, a cathode, and a solid electrolyte membrane disposed between the anode and the cathode.

4. The method of claim 3, wherein the first electrolysis unit comprises a stack of solid oxide electrolysis cells.

5. The method of claim 3 or claim 4, wherein delivering the first reactant stream to the first electrolysis unit comprises delivering the first reactant stream to the cathode.

6. The method of any one of claims 3 to 5, wherein passing the methane-enriched effluent gas to the first electrolysis unit comprises passing the methane-enriched effluent gas to the anode. The method of claim 6 , wherein the anode comprises a steam reforming catalyst.

8. The method according to any one of claims 3 to 7, wherein the first electrolysis unit is operated at a temperature of 500 to 1000°C, preferably 700 to 900°C.

9. The method of claim 1 or claim 2, wherein the first electrolysis unit comprises a proton-conducting solid oxide cell (H-SOC) in which a catalyst is employed at the cathode for reforming both methane and carbon dioxide to form carbon monoxide and hydrogen.

10. A process according to any preceding claim, wherein the hydrocarbon synthesis unit comprises a Fischer-Tropsch reactor which converts synthesis gas into liquid hydrocarbon products, an aqueous stream and the effluent gas. The method of claim 10 , wherein the effluent gas comprises C1 to C4 hydrocarbons.

12. The method of claim 10 or claim 11, wherein passing the synthesis gas to the hydrocarbon synthesis unit comprises passing the synthesis gas to a carbon dioxide removal unit to form a carbon dioxide-lean synthesis gas and a carbon dioxide stream, and subsequently passing the carbon dioxide-lean synthesis gas to the hydrocarbon synthesis unit.

13. The method of claim 12, further comprising passing at least a portion of the carbon dioxide stream to the first electrolysis unit.

14. The process according to any one of claims 10 to 13, further comprising passing at least a portion of the aqueous stream to the first electrolysis unit in the form of steam, preferably wherein the aqueous stream is at least partially purified before being passed to the first electrolysis unit.

15. The method of any one of claims 10 to 14, further comprising passing the liquid hydrocarbon product to an upgrading unit to provide an upgraded liquid hydrocarbon product and waste hydrocarbons; and The spent hydrocarbons are conveyed to the reverse enrichment reactor or another reverse enrichment reactor and subsequently to the first electrolysis unit.

16. The method according to any one of claims 1 to 9, wherein the hydrocarbon synthesis unit comprises a methanol synthesis unit located upstream of a methanol-to-hydrocarbons unit; as well as The step of passing the synthesis gas to the hydrocarbon synthesis unit to form liquid hydrocarbon products and an effluent gas comprises: passing the syngas to the methanol synthesis unit to convert the syngas into a methanol stream and a waste gas stream comprising hydrogen; passing the methanol stream to the methanol-to-hydrocarbons unit to form a hydrocarbon mixture and the effluent gas; and At least one hydrocarbon fuel product selected from the group consisting of a diesel product, a gasoline product, and a jet fuel product is recovered from the hydrocarbon mixture.

17. The process according to claim 16, wherein the off-gas stream is recycled into the synthesis gas before the synthesis gas is passed to the hydrocarbon synthesis unit.

18. A method according to claim 17, wherein the waste gas stream is passed to a hydrogen recovery unit to increase the hydrogen concentration of the waste gas stream and form a carbon-containing waste gas before the waste gas stream is recycled into the synthesis gas; and the method also includes introducing the carbon-containing waste gas into the effluent gas before the effluent gas is passed to the de-enrichment reactor.

19. The method according to any one of claims 16 to 18, wherein the synthesis gas sent to the methanol synthesis unit has a stoichiometric number R in the range of 1.95 to 2.15, the stoichiometric number R being defined as R = ([H2] - [CO2]) / ([CO2] + [CO]).

20. The method of any one of claims 16 to 19, wherein passing the methanol stream to the methanol-to-hydrocarbons unit comprises: passing the methanol stream to a methanol distillation unit to form a purified methanol stream and a water stream; and conveying the purified methanol stream to the methanol-to-hydrocarbons unit.

21. The method of claim 20, further comprising separating fusel oil from the methanol distillation unit and introducing the fusel oil stream into the effluent gas before passing the effluent gas to the reverse enrichment reactor.

22. The process of claim 20 or claim 21 further comprising introducing the water stream into the first reactant stream.

23. The method of any one of claims 16 to 22, further comprising introducing carbon dioxide into the synthesis gas before passing the synthesis gas to the hydrocarbon synthesis unit.

24. A process according to any preceding claim, wherein the back enrichment reactor comprises a nickel catalyst, preferably a nickel catalyst having a nickel content in the range of 30% to 60% by weight, expressed as NiO, based on the total weight of the catalyst.

25. A process according to any preceding claim, wherein the back enrichment reactor is operated at a temperature of 300 to 650°C and / or at a pressure of 10 to 100 bar.

26. A process according to any preceding claim, wherein the effluent gas is heated upstream of the reverse enrichment reactor in heat exchange with the synthesis gas.

27. The method of any preceding claim, further comprising: providing a second reactant stream comprising water; passing the second reactant stream to a second electrolysis unit to form a hydrogen stream; as well as introducing the hydrogen stream into the synthesis gas before conveying the synthesis gas to the hydrocarbon synthesis unit, wherein the second electrolysis unit operates at a lower temperature than the first electrolysis unit.

28. The method of claim 27, wherein the second electrolysis cell comprises an alkaline electrolysis cell or a polymer electrolyte membrane (PEM) electrolysis cell.

29. A method according to any preceding claim, wherein the first electrolysis unit and / or the second electrolysis unit is powered by a renewable energy source.

Images