A thermally integrated method for liquid fuel production using solid oxide electrolyzers

Abstract

Fuel production from low oxygen electricity and from carbon dioxide by using a solid oxide electrolysis cell (SOEC) and Fischer-Tropsch is shown. Fischer-Tropsch is an exothermic reaction and can be used to generate steam. Steam generated from a Liquid Fuel Production (LFP) reactor system in which the Fischer-Tropsch reaction occurs is used as feed to the SOEC. The high temperature of the steam improves the overall efficiency of the electrolysis system. The integration of LFP steam improves the electrolysis efficiency as the heat of vaporization for liquid water does not need to be provided by the electrolyzer.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 372,384, filed March 8, 2022, the entire contents of which are hereby incorporated by reference herein.

[0002] [Field of the Invention] The electrolyzer is thermally integrated with a liquid fuel production process to produce liquid hydrocarbon fuels from hydrogen and carbon monoxide produced in a solid oxide electrolyzer. [Background technology]

[0003] The increase in the global atmospheric carbon dioxide concentration is linked to global climate change. The combustion of fossil fuels in various engines produces atmospheric carbon dioxide. Concerns over climate change have led to a major shift in society towards renewable or low carbon electricity. This has also led to increased efforts to decarbonize the transport sector of the economy. As a result, the use of electric vehicles powered by renewable electricity is increasing to facilitate the decarbonization of the transport sector. Heavy transport and aviation are among the most carbon intensive transport sectors. Efficient and economical production of low carbon fuels such as diesel fuel and sustainable aviation fuel could significantly reduce carbon dioxide emissions from the heavy transport and aviation sectors. Summary of the Invention

[0004] Fuel production from low carbon electricity and carbon dioxide is demonstrated using a solid oxide electrolysis cell (SOEC). Figure 1 shows an integrated method for producing liquid fuels. Fischer-Tropsch is an exothermic reaction and can be used to generate steam. Steam generated from a Liquid Fuel Production (LFP) reactor system in which the Fischer-Tropsch reaction occurs is used as feed to the solid oxide electrolysis cell. The high temperature steam improves the efficiency of the entire electrolysis system. This steam improves the efficiency of the electrolysis since the heat of vaporization for liquid water does not need to be provided from the electrolyzer.

[0005] [Description of Related Art] Some prior patent applications that discuss the production of fuels and chemicals from carbon dioxide and low carbon fuels include U.S. Patent Application No. 17 / 300,259, U.S. Patent Application No. 17 / 300,260, U.S. Patent Application No. 17 / 300,262, and U.S. Patent Application No. 16 / 873,561, each of which is incorporated by reference in its entirety, but each of which does not specifically discuss methods of integration with a Solid Oxide Electrolyzer (SOE).

[0006] Cinti et al. (Reference 1) discuss the integration of fuel production with SOECs, but do not discuss the thermal integration process and associated efficiency improvements presented in this patent application. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 shows an integrated process for liquid fuel production. [Diagram 2] FIG. 2 shows a multi-tubular fixed-bed liquid fuel production reactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] FIG. 1 shows an integrated process for liquid fuel production. Unit 1 is a solid oxide electrolyzer (SOE) or solid oxide electrolysis cell (SOEC). Unit 1 is a high temperature electrolyzer operating at temperatures between 550° C. and 900° C. The SOEC operates at or near atmospheric pressure. Higher pressure operation is possible with improved stack sealing. In the SOEC, electricity is supplied to the system to drive the electrochemical reaction. In this SOEC, the electricity used is low carbon electricity including electricity generated from wind, solar, nuclear or hydroelectric power. The SOEC includes a cathode and an anode along with an electrolyte. The reactants are supplied to the SOE cathode, which is the electrode where the reduction takes place. The anode is the electrode where oxygen is obtained.

[0009] In a SOEC, water is split into hydrogen and oxygen ions at the cathode. The oxygen ions diffuse across a ceramic membrane to produce oxygen at the anode by recombination of the oxygen ions using heat and the electrochemical gradient as driving forces; see Equation 1 below. If carbon dioxide is also supplied, co-electrolysis occurs and the carbon dioxide is reduced to produce carbon monoxide at the cathode and oxygen at the anode; see Equation 2 below.

[0010] [ka] [ka]

[0011] ΔH0 is the energy (enthalpy) required for the reaction at standard temperature of 25°C. Both reactions are endothermic and require the addition of energy to drive them to completion. ΔH is adjusted for the operating temperature of the SOEC. Note that Equation 1 is for gaseous water or steam as the feedstock. If water is in the liquid state, then ΔH0=285.84 kJ / mol.

[0012] Equation 3 shows the relationship between enthalpy and Gibbs free energy. Gibbs free energy is the electrical work that depends on the reversible potential between the cell electrodes (E rev , Equation 4). Entropy is supplied in the form of heat. Energy balance is obtained when the irreversible heat losses are equal to the heat demand, and is called thermoneutrality (E tn )

[0013]

number

number

number

[0014] The efficiency of an SOEC (Equation 6) is the ratio of the chemical energy leaving the system in terms of enthalpy to the externally supplied electrical energy (E e ) is calculated as the ratio between

[0015]

number

[0016] Here, E e is the electrical energy input equal to the current (z × F) multiplied by the working potential E. The efficiency is equal to 1 under thermoneutral conditions where all electrical energy and relative heat losses are converted to chemical energy.

[0017] As seen in FIG. 1, the cathode of the SOEC unit 1 is fed by a feed stream 1 made up of carbon dioxide. The feed stream 1 is mixed with a recycled product stream 5 containing water vapor (steam) produced as part of the heat management / steam system of the liquid fuel production reactor unit 4. This becomes the cathode feed stream. Additional steam can also be added to make a mixed cathode feed stream. These additional streams can optionally contain hydrogen. Hydrogen is useful as a co-feed to keep the cathode in reducing mode. Hydrogen can be recycled from the product of the SOEC cathode or produced in other areas of the facility including hydrogen produced in a hydrocarbon reforming unit from light hydrocarbons produced in unit 4. Additionally, light hydrocarbons produced in unit 4 (LFP) can also be part of the cathode feed.

[0018] The material of the fuel electrode (cathode) is Ni-doped YSZ. However, high partial steam pressure and low partial hydrogen pressure at the Ni-YSZ interface often cause nickel oxidation, leading to catalyst degradation. Hydrogen in the cathode feedstock helps to overcome this problem. Instead of or in addition to Ni-YSZ as the cathode material, there are perovskite types of lanthanum strontium manganese (LSM) and lanthanum strontium manganese chromate (LSCM) that can be used instead of or in combination with Ni-YSZ.

[0019] At the anode side, oxygen ions are generated in Equation 1 and Equation 2. In SOEC, it is beneficial to use a sweep gas on the anode to sweep the anions (and oxygen gas) away from the anode. Feed stream 2 in FIG. 1 is the flow of sweep gas going to the anode. The sweep gas can be chosen from several gases. The sweep gas can be chosen from air or steam. Product stream 1 is an oxygen rich gas with an oxygen content above that of air in case air is used as the sweep gas. The anode material can be chosen from a number of materials including lanthanum strontium manganate (LSM), Gd doped CeO2 impregnated LSM, neodymium nickelate or combinations thereof.

[0020] The electrolyte used in SOECs is a dense ionic conductor composed of ZrO2 doped with 8 mol% Y2O3 (also known as YSZ). Zirconia dioxide is used due to its high strength, high melting point (about 2700°C) and excellent corrosion resistance. Other electrolyte materials include scandia stabilized zirconia (ScSZ), ceria-based electrolytes, or lanthanum gallate materials. All materials can be used separately or in combination.

[0021] Product stream 2, or the hot product of the cathode, comprises hydrogen and carbon monoxide. This product stream leaves the cathode at the operating temperature of the SOEC, 550° C. to 900° C. This product stream can be used to heat the incoming feed stream of the cathode via a feed / product heat exchanger. This cathode feed stream comprises steam and carbon dioxide.

[0022] Product Stream 1 is the hot anode product stream containing oxygen or oxygen-enriched sweep gas. This product stream leaves the cathode at the SOEC operating temperature of 550° C. to 900° C. This product stream can be used to heat Feed Stream 2 or the incoming anode feed via a feed / product heat exchanger.

[0023] The cooled product stream 2 or cathode product comprises syngas. The steam goes to unit 2 or syngas conditioning unit. The syngas conditioning block is actually a collection of many unit operations. This includes additional cooling, water removal, hydrogen to carbon monoxide ratio adjustment, carbon dioxide removal, and compression to increase pressure to unit 4 (the LFP reactor). This results in product stream 3, which is the feed stream for the LFP, comprising syngas with a hydrogen to carbon monoxide molar ratio of 1.5 to 2.5, or more preferably 2.0 to 2.2. Besides the hydrogen and carbon monoxide in product stream 2, other components are likely to be present in this stream, including unreacted carbon dioxide, unreacted hydrogen, and water. The water is removed in a flash drum. The removed water becomes product stream 7 in FIG. 1 and can be optionally recycled to liquid water that can be mixed into feed stream 3.

[0024] If the hydrogen to carbon monoxide ratio in the syngas conditioning unit feed is greater than 2.2, excess hydrogen can be removed from this stream by known hydrogen removal systems such as pressure swing adsorption (PSA), hydrogen membranes, or other methods. This excess hydrogen-containing stream can be recycled to the front end of the process for addition to the combined feed of unit 1 and the SOEC cathode. If the hydrogen to carbon monoxide ratio is less than 2.0, additional hydrogen can be produced by the water gas shift reaction (Equation 7).

[0025] [ka]

[0026] A catalytic reactor can be used to convert a portion of the CO into additional hydrogen if necessary to meet syngas composition specifications.

[0027] Removal of carbon dioxide in the syngas is useful since it serves as a diluent in downstream processing. Carbon dioxide removal can be accomplished by any of a number of different processes including: 1) amine absorbents, 2) rectisol or methanol absorbents, 3) other physical absorbents such as solexol, and 4) cryogenic CO2 fractionation. The captured and removed CO2 becomes a CO2 stream that can be sent back to the front end of the process for addition to feed stream 1.

[0028] The operating pressure of the SOEC is near atmospheric pressure. The LFP reactor, Unit 4, operates at a pressure of 250 psig to 450 psig. The syngas conditioning block, Unit 2, contains the syngas compressor. This is a multi-stage compressor system with interstage cooling.

[0029] Unit 2 produces product stream 3 which is the feed stream to Unit 4. Unit 4 is a Liquid Fuel Production (LFP) reactor. Figure 2 shows the details of the LFP reactor. A feed stream of LFP containing hydrogen and carbon monoxide enters the LFP reactor. The LFP reactor is a multi-tubular fixed bed reactor that enables the Fischer-Tropsch (FT) reaction of Equation 8.

[0030] [ka]

[0031] The FT reaction is exothermic, releasing a standard enthalpy of reaction of 165 kJ per mole of CO converted. The high heat of reaction makes temperature control of the FT reactor critical. Without control, an increase in temperature in the reactor will lead to increased methane production and catalyst deactivation. Therefore, temperature control is important. Ideally, the temperature of the FT reactor is maintained between 200°C and 240°C.

[0032] The multi-tubular fixed bed reactor of Figure 2 aids in temperature control of the FT reactor. Syngas is fed to this reactor, split, and passed through a tubular catalytic reactor (unit 6 in Figure 2). The syngas reactor produces a mixture containing primarily alkanes, alkenes, and alcohols, as shown by the FT reaction (equation 8). A mixed hydrocarbon product stream 6 exits the tubular reactor.

[0033] Feed stream 3, which includes liquid water, is fed to unit 3 (FIG. 1). This stream can optionally include water separated from unit 2, a syngas conditioning unit. Unit 3 includes water purification, water treatment, and water pumping. Purification can include reverse osmosis or other purification systems. Water treatment can include chemical addition, deionization, etc. The water is pumped to a pressure of 100 psig to 300 psig, preferably about 200 psig, to produce product stream 4. Product stream 4, which is pressurized and water-treated cooling water, is fed to unit 5, which is the boiler portion of the shell-and-tube reactor. The tubular catalytic reactor is surrounded by the boiler of unit 5 (FIG. 2). The heat of reaction provides the heat to vaporize the liquid water into steam. In some embodiments of the present invention, a mixture of steam and liquid water is fed to unit 5, which can make some of the liquid water into additional steam. In some embodiments, the mixture of steam and liquid leaves unit 5. A steam drum is used to separate the water and steam. The liquid water is recycled as feed to the boiler of Unit 5. The steam produced in the boiler of Unit 5, product stream 5 steam, is sent back to the front end and mixed with feed stream 1 to provide the feed to the SOEC, Unit 1. The liquid water to steam ratio is typically about 0.5, but can range from 0.2 to 0.7.

[0034] The hydrocarbon products from the LFP reactor are further processed downstream of the LFP reactor in Unit 4. Water is also produced in the FT reaction (Equation 8). Water can be removed from the FT product stream via a flash drum. The recovered water can also be recycled back to the liquid water treatment in Unit 3 in Figure 1. Light hydrocarbons are also separated from the LFP hydrocarbon products, which are primarily alkanes and alkenes with carbon numbers 1 to 5. The desired C5-C 23 The product of the LFP reactor containing hydrocarbons can be further processed in a separation system. The separation system can include distillation. The desired C5-C 23 The products can be used for gasoline blendstocks, diesel fuel, jet fuel, or as low carbon chemicals that can replace chemicals derived from petroleum or natural gas. In one embodiment, the LFP products are sent to a series of fractionators and used to produce high cetane diesel fuel with tunable flash points between 32°C and 50°C (90°F and 122°F) and stabilized naphtha (potential gasoline blendstocks or chemical feedstocks). The basic setup for these columns includes the following:

[0035] A) Wax Stripper: This unit uses steam to recover fuel range components from waxy materials. The overhead fuel range components and steam are sent to the main fractionator and the stripped wax is sent to heated storage for sale. The wax stripper is a column with no condenser or reboiler, operates at about 170°C (340°F) and has a pressure of 2.75 barg (40 psig), sufficient for the overhead vapor to enter the main fractionator column.

[0036] B) Main Fractionator: This column separates the raw fuel into naphtha and diesel range components to control the diesel flash point. This column contains a high pressure (HP) steam heated reboiler and an external condenser that uses three phase separation to remove absorbed water and steam from the wax stripper feed.

[0037] C) Optionally, a naphtha stabilizer controls the Reid vapor pressure (RVP) to a specification of 8 psia. The stabilizer includes a low pressure (LP) steam reboiler and an integrated knockback water-cooled condenser.

[0038] D) Optionally, a diesel cold stream / kerosene vacuum column adjusts the pour point of the diesel for sale in cold weather and / or produces a kerosene fraction. The feed is heated to 300°C (570°F). The column has 20 stages and the overhead condenser pressure is 6 psia. The kerosene fraction is used as a component of jet fuel. Under certain conditions, the kerosene fraction may meet ASTM specifications (ASTM D7566) for use as jet fuel.

[0039] In one embodiment of the present invention, the kerosene fraction of the LFP product does not meet all of the ASTM D7566 specifications for use as jet fuel, which may in some circumstances be higher than diesel fuel. To meet the specifications for use as jet fuel or Sustainable Aviation Fuel (SAF), the LFP product or a fraction of the LFP product, such as LFP kerosene or LFP light diesel, may need to be hydrotreated. Hydrotreating involves hydrotreating the C9-C kerosene produced in the LFP reactor. 15 The LFP process involves the hydroisomerization of alkanes. The LFP product, or a fraction of this product, is pressurized and mixed with a stream containing hydrogen. The hydrogen can be produced from the electrolysis of water, from the reforming of natural gas, or from the gasification of waste or biomass. The hydrogen is preferably low carbon hydrogen.

[0040] The combined stream containing hydrogen and at least a portion of the LFP product is then heated and fed to a hydrotreating reactor, which operates at high pressure, greater than 100 psig, but generally less than 2000 psig. The hydrotreating reactor operates at a temperature between 250° C. and 400° C. The effluent from the hydrotreating reactor is cooled before entering a high temperature separator, where gases and liquids are separated in the high temperature and low temperature separators.

[0041] The hydrocarbon products from the hot and cold separators are sent to a fractionation section where the light ends and hydrocarbon products are separated. The fractionation system may include a wax stripper and a main fractionator, as well as a naphtha stabilizer and a kerosene vacuum column. The fractionator operates such that the kerosene stream meets ASTM D7566 specifications and is useful as a sustainable aviation fuel (SAF).

[0042] The following examples illustrate several aspects of the present invention.

[0043] [Example 1] In this example, 1000 mol / s of liquid water and 500 mol / s of carbon dioxide are fed to the SOEC. 800 mol / s of hydrogen and 400 mol / s of carbon monoxide are produced. Using the amount of heat required for the reactions of Equation 1 and Equation 2 with liquid water as the feedstock, the minimum power demand for the SOEC stack can be calculated. In this example, the minimum power requirement is 401.3 MW.

[0044] [Example 2] In this example, 1000 mol / s steam produced in the boiler of LFP reactor unit 5 is fed to the SOEC instead of the liquid water in Example 1. 800 mol / s hydrogen and 400 mol / s carbon monoxide are produced in the SOEC. The amount of heat required for the reactions of Equation 1 and Equation 2 using steam as the feedstock can be used to calculate the minimum power demand for the SOEC. In this example, the minimum power requirement is 360.4 MW.

[0045] Table 1 shows the improvement of Example 2 over Example 1. It shows that the use of steam saved 40.9 MW of power and improved the power required for the SOEC by 10.2%.

[0046] The amount of steam generated in the LFP reactor boiler significantly reduces the feed water required for the SOEC. Table 2 below highlights the overall process improvement. With a single pass CO conversion of 50% in the LFP reactor, the released reaction heat is equal to 33.0 MW. This reaction heat can generate 745.4 mol / s of steam from water. The remaining 245.3 mol / s required for the SOEC can be partially provided by recycling unconverted steam.

[0047] [Table 1]

[0048] [Table 2]

[0049] [References] Reference 1 G. Cinti, A. Baldinelli, A. Di Michele, and U. Desideri, Applied Energy 162 (2016) 308-320. “Integration of Solid Oxide Electrolyzer and Fischer-Tropsch: A sustainable pathway for synthetic fuel” (Integration of solid oxide electrolysers with Fischer-Tropsch: A sustainable route for synthetic fuels) Reference 2 U.S. Patent Application No. 17 / 300,259 Reference 3 U.S. Patent Application No. 17 / 300,260 Reference 4 U.S. Patent Application No. 17 / 300,262 Reference 5 U.S. Patent Application No. 16 / 873,561

Claims

1. 1. A method for producing a liquid fuel, comprising: a. a first electrolysis feed stream comprising steam is fed to a solid oxide electrolyzer; b. a second electrolysis feed stream comprising carbon dioxide is fed to the solid oxide electrolyzer; c. low carbon electricity is used in said solid oxide electrolyzer to produce a first electrolysis product stream comprising a mixture of hydrogen and carbon monoxide and a second electrolysis product stream comprising an oxygen-enriched sweep gas; d. cooling the first electrolysis product stream to a temperature less than 200° C. to produce a cooled syngas stream; e. feeding the cooled syngas stream to a syngas conditioning block to produce a syngas conditioned product stream comprising hydrogen and carbon monoxide, the hydrogen to carbon monoxide molar ratio being between 2.0 and 2.2 and having a pressure between 250 psig and 400 psig; f. feeding the syngas conditioned product stream to a liquid fuel production reactor in which an exothermic chemical reaction is capable of converting hydrogen and carbon monoxide into liquid fuel production reactor products comprising liquid hydrocarbons comprising alkanes having 5 to 23 carbon atoms; g. The liquid fuel production reactor comprises: i. A tubular fixed bed catalytic reactor, in which ii. a steam boiler is surrounded by the tubular fixed bed catalytic reactor, the boiler is filled with a mixture of steam and liquid water, and heat can be removed from the tubular fixed bed catalytic reactor by boiling the liquid water, and the boiler produces medium pressure steam; h. At least a portion of the medium pressure steam is used as the first electrolysis feed stream. method.

2. 10. The method of claim 1, wherein the solid oxide electrolyzer operates at a temperature of from 550°C to 900°C.

3. 10. The method of claim 1, wherein the solid oxide electrolyzer operates at atmospheric pressure.

4. 2. The method of claim 1, wherein the solid oxide electrolytic cell comprises a cathode, the cathode being Ni-doped NSZ.

5. The solid oxide electrolytic cell includes an anode, the anode being made of lanthanum strontium manganate, Gd-doped CeO impregnated with lanthanum strontium manganate, ２ 10. The method of claim 1, wherein the metal is selected from the group consisting of neodymium nickelide, ... and combinations thereof.

6. 2. The method of claim 1, wherein carbon dioxide removal occurs in the cooled syngas stream fed to the syngas conditioning block.

7. 10. The method of claim 1, wherein the liquid hydrocarbons comprising alkanes having from 5 to 23 carbon atoms are further processed in a separation system.

8. 10. The method of claim 1, wherein the liquid hydrocarbons are sent to successive fractionators used to produce high cetane diesel fuel and stabilized naphtha.

9. 10. The method of claim 1, wherein the syngas conditioning block includes a syngas compressor, the syngas compressor being a multi-stage compressor system with inter-stage cooling.

10. 10. The method of claim 1, wherein light hydrocarbons are separated from said liquid hydrocarbons comprising alkanes having 5 to 23 carbon atoms and used for gasoline blend stocks, diesel fuel, or jet fuel.

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