Electrochemical Reduction System and Methods of Operation Thereof

Abstract

This disclosure provides systems, methods, and apparatus related to electrochemical reduction of gasses. In one aspect, a method includes flowing a gas through a reduction device. The gas is carbon dioxide (CO2) or nitrogen (N2). The reduction device reduces the gas and generates a product stream including the gas, hydrogen (H2), and a chemical. The product stream is flowed through a hydrogen removal device. The hydrogen removal device removes hydrogen from the product stream. The product stream with the hydrogen removed is flowed through the gas reduction device.

Description

BACKGROUND

Ethylene is the largest-volume synthetic organic chemical world-wide, predominantly produced from steam cracking of alkanes. This traditional process of making ethylene generates the greenhouse gas carbon dioxide in significant quantities as a byproduct. In an age of rising temperatures due to increasing CO₂ concentrations in the atmosphere, an alternative, more environmentally friendly process becomes highly desirable. Electrochemical CO₂ reduction is a particularly promising path since it uses CO₂ as a feedstock—rather than generating it as a byproduct—to produce ethylene.

Much progress has been made towards improving the efficiency of electrochemical CO₂ reduction to ethylene, particularly by tuning the microenvironment of Cu catalysts. However, most publications in the recent literature report ethylene concentrations below 10% in electrolyzer outlet streams, even with faradaic efficiencies above 50% and current densities higher than 1 A cm⁻². In many of these reports, ethylene is actually produced at concentrations well below 1%.

To date, ethylene concentrations above 10% have only been achieved by reducing the inlet flow rate of CO₂ significantly. However, this can lead to problematic flow conditions that starve catalytic sites of CO₂, quickly resulting in the hydrogen evolution reaction (HER) dominating over CO₂ reduction, and reducing CO₂ electrolyzer performance. Additionally, current literature would suggest that it is not clear if ethylene concentrations above 40% could ever be reached by further reducing the CO₂ flow rates.

SUMMARY

Described herein is a system that recycles unreacted gas (e.g., N₂ or CO₂) together with products and flows them back into a gas reduction reactor, enabling higher gas conversion rates without decreasing the gas flow rate. In some instances (e.g., when products other than CO are targeted and when the inlet does not contain pure CO₂), faradaic efficiencies for the target product are below 100%. H₂ is also a byproduct, which can impede gas reduction in a looped system if H₂ concentrations surpass a threshold value.

In the system described herein, a hydrogen removal device (e.g., an electrochemical hydrogen pump) is placed in series with a nitrogen reduction reactor or a carbon dioxide reduction reactor, which effectively removes most or all the H₂ from the recycled gas stream. Initial results with a carbon dioxide reduction reactor targeting ethylene as the main product show that ethylene concentrations of at least 10% can be achieved, which is roughly 10 to 20 times higher compared to a single-pass system.

An advantage of the system described herein is that the H₂ byproduct is removed, and so does not impede the conversion of CO₂ or N₂ and accumulation of the targeted C-based product or N-based product. The H₂ (in some instances, high-purity H₂) also may be sold as a separate product.

Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a flow diagram illustrating a method of use of a gas recirculation system.

FIG. 2 shows an example of a schematic illustration of a gas recirculation system.

FIG. 3A shows an example of an experimental CO₂ gas recirculation system comprising a 4 cm² electrochemical CO₂ reduction cell, a 5 cm² electrochemical H₂ pump with proton exchange membrane (PEM), a gas chromatograph (GC), a 4-way valve to open/close the gas loop, a 3-way valve to enable flow of fresh CO₂ into the loop, and a peristaltic pump to move the gases. FIG. 3B shows a more detailed diagram of the experimental CO₂ gas recirculation system.

FIGS. 4A and 4B show the results of a recirculation experiment performed with Au as the CO₂ reduction catalyst, operated at 3 V. FIG. 4A shows the concentration of gases in the recycling loop (in mol %). After 1 h of operation, the loop was closed and after 7.5 h, the flow of fresh CO₂ was stopped. FIG. 4B shows pressure and mass flow rate in the recycling loop.

FIGS. 5A and 5B show the results of a recirculation experiment performed with Cu as the CO₂ reduction catalyst, operated at 4 V. FIG. 5A shows product and CO₂ concentrations over time, indicating a peak C₂H₄ concentration of 8.7% after 3 h of closed loop operation (6 h total operation time). FIG. 5B shows pressure and mass flow rate in the gas loop. The mass flow rate of fresh CO2 was tuned to stabilize the loop pressure. Pressure spikes were due to gas chromatograph injections.

DETAILED DESCRIPTION

Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.

The terms “about” or “approximate” and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be ±20%, ±15%, ±10%, ±5%, or ±1%. The terms “substantially” and the like are used to indicate that a value is close to a targeted value, where close can mean, for example, the value is within 80% of the targeted value, within 85% of the targeted value, within 90% of the targeted value, within 95% of the targeted value, or within 99% of the targeted value.

An alternative way to increase C₂H₄ concentrations in the outlet stream and simultaneously enhance CO₂ utilization is to recirculate the generated fuel stream back into the electrolyzer. However, using a recirculation system will also concentrate any byproducts from CO₂-to-C₂H₄ conversion, such as H₂, which can impede the production of ethylene. Therefore, a looped system for CO₂ reduction that employs a hydrogen pump to remove H₂ from the gas loop was developed, as described herein. While the operation of an H₂ pump may be challenging under conditions of high carbon monoxide concentrations, which effectively poisons the employed Pt catalysts, moving to temperatures above 160° C. can circumvent these poisoning issues, provided appropriate materials are chosen. With this system (described in more detail in the EXAMPLES), a gas stream with a peak ethylene concentration of 9.4% was generated, a value roughly 20 times higher than that achieved using a single-pass system operated under comparable conditions.

With CO₂ reduction, other chemicals can be generated when different catalysts are used in the CO₂ reduction device. Further, a similar setup can be used for a nitrogen reduction system. With a nitrogen reductions system, chemicals that can be generated include ammonia, urea, and hydrazine, depending on the catalyst used.

FIG. 1 shows an example of a flow diagram illustrating a method of use of a gas recirculation system. Starting at block 105 of the method 100, a gas is flowed through a reduction device. The gas is either carbon dioxide (CO₂) or nitrogen (N₂). In some embodiments, the gas is a gas which could be produced by reducing CO₂ or N₂, such as carbon monoxide, for example. The reduction device reduces the gas and generates a product stream that includes the gas, hydrogen (H₂), and a chemical. A gas reduction device may also be referred to as an electrolyzer or an electrochemical reduction device.

A gas reduction device generally includes an anode, a cathode, and an ion exchange membrane. At the cathode, the gas is reduced. At the anode, water is generally oxidized to generate oxygen, but other oxidation reactions, such as the hydrogen oxidation reaction or water oxidation to hydrogen peroxide, are also possible. The cathode and anode include appropriate catalysts for the gas reduction and the water oxidation, respectively. In some embodiments, an anode catalyst for water oxidation comprises iridium, ruthenium, a nickel-containing compound, an iron-containing compound, or a cobalt-containing compound. In some embodiments, when the gas is carbon dioxide, the cathode catalyst for carbon dioxide reduction to carbon monoxide comprises gold, silver, or zinc. In some embodiments, when the gas is carbon dioxide, the cathode catalyst for carbon dioxide reduction to formic acid comprises cadmium, indium, or tin. In some embodiments, when the gas is nitrogen, the cathode catalyst for nitrogen reduction comprises gold or silver (e.g., to generate ammonia) or nickel (to generate hydrazine).

When the method 100 is used to generate a liquid chemical (e.g., formic acid) from CO₂ reduction as opposed to a gaseous chemical, the method improves the production of the liquid chemical. The method 100 would not affect the chemical concentration in the same way as it does when generating a gaseous chemical (i.e., because hydrogen is a gas), but the method would increase CO₂ utilization (i.e., more CO₂ would be reduced by removing H₂ from the recirculated product stream).

The chemical generated by the reduction device depends on the gas flowed through the reduction device. The chemical generated by the reduction device further depends on the catalysts in the reduction device. When the gas is carbon dioxide, the chemical may be a chemical from a group ethylene, ethane, carbon monoxide, methane, propylene. For example, to generate ethylene as the chemical, a reduction device that includes copper as a cathode catalyst and iridium as an anode catalyst may be used. When the gas is nitrogen, the chemical may be a chemical from group ammonia, urea, and hydrazine.

At block 110, the product stream is flowed through a hydrogen removal device. The hydrogen removal device removes hydrogen from the product stream. Is some embodiments, all of the hydrogen or substantially all of the hydrogen is removed from the product stream. In some embodiments, the hydrogen removal device is a device from a group an electrochemical hydrogen pump, a palladium membrane, and a thermal metal hydride adsorption device.

When the hydrogen removal device is an electrochemical hydrogen pump, in some embodiments, the electrochemical hydrogen pump is operated at a temperature of about 150° C. to 180° C., or about 160° C. Operating the electrochemical hydrogen pump at these temperatures aids in preventing CO poisoning of a catalyst in the electrochemical hydrogen pump.

At block 115, the product stream with the hydrogen removed is flowed through the gas reduction device. That is, the product stream with the hydrogen removed is again passed through the gas reduction device. After block 115, the method 100 may continue by repeating blocks 110 and 115.

In some embodiments, the method 100 further comprises prior to flowing the product stream with the hydrogen removed through the gas reduction device, flowing the product stream with the hydrogen removed through an accumulation chamber to remove the chemical from the product stream. In some embodiments, the chemical is removed from the product stream after one to three passes of the product stream though the hydrogen removal device. In some embodiments, the accumulation chamber comprises a substantially gas tight chamber.

In some embodiments, the method 100 further comprises prior to flowing the product stream with the hydrogen removed through the carbon dioxide reduction device, adding additional gas to the product stream with the hydrogen removed. In some embodiments, a first pressure of gas is flowed through the gas reduction device at block 105, and an amount of additional gas is added to the product stream with the hydrogen removed so that the product stream with the hydrogen removed is at the first pressure (e.g., after block 110).

FIG. 2 shows an example of a schematic illustration of a gas recirculation system. As shown in FIG. 2, a system 200 includes a gas reduction device 205 and a hydrogen removal device 210.

An inlet of the gas reduction 205 device is operable to receive a gas, the gas being nitrogen (N₂) or carbon dioxide (CO₂). In some embodiments, the gas is a gas which could be produced by reducing CO₂ or N₂, such as carbon monoxide, for example. The gas reduction device 205 is operable to generate a product stream including the gas, hydrogen (H₂), and a chemical.

An inlet of the hydrogen removal device 210 is operable to receive the product stream from an outlet of the gas reduction device 205. The hydrogen removal device 210 is operable to remove hydrogen from the product stream. An outlet of the hydrogen removal device 210 flows the product stream with the hydrogen removed into the inlet of the gas reduction device 205. In some embodiments, the hydrogen removal device is a device from a group an electrochemical hydrogen pump, a palladium membrane, and a thermal metal hydride adsorption device.

In some embodiments, the system 200 further includes an accumulation chamber 215. The accumulation chamber 215 is operable to remove the product from the product stream. In some embodiments, the accumulation chamber is positioned between the hydrogen removal device 210 and the gas reduction device 205 such that some or all of the chemical is removed from the product stream after hydrogen is removed from the product stream by the hydrogen removal device 210 and prior to flowing the product stream through the gas reduction device 205. In some embodiments, an inlet of the accumulation chamber 215 is operable to receive the product stream with the hydrogen removed from the hydrogen removal device 210 and an outlet of the accumulation chamber 215 is operable to flow the product stream with the hydrogen removed and at least some of the product removed into the inlet of the gas reduction device 205.

The volume of the accumulation chamber 215 determines the volume of the system 200. The volume of the accumulation chamber 215 may be specified based on a downstream process or transportation requirement. The chemical generated by the gas reduction device 205 may be removed from the accumulation chamber 215 when a specified concentration or a specified pressure of the chemical in the accumulation chamber 215 is achieved. In some embodiments, in the operation of the system 200, the accumulation chamber 215 is replaced with a new accumulation chamber containing the gas (i.e., the gas to be reduced by the gas reduction device 205) when the specified concentration or the specified pressure of the chemical in the accumulation chamber 215 is achieved. In some embodiments, the accumulation chamber 215 comprises a vial, a container, or a gas cylinder. The rate of product accumulation and net-pressure buildup inside the accumulation chamber 215 can be controlled by the relative sizes of the inlet and the outlet of the accumulation chamber 215.

In some embodiments, the system 200 further includes a valve 220. The valve 220 is operable to allow for addition of the gas to the product stream with the hydrogen removed prior to flowing the product stream with the hydrogen removed through the gas reduction device 205. In some embodiments, the valve 220 is a 3-way valve or a 4-way valve. In some embodiments, a first pressure of gas is flowed through the gas reduction device (e.g., at block 105 of the method shown in FIG. 1), and an amount of additional gas is added to the product stream with the hydrogen removed so that the product stream with the hydrogen removed is at the first pressure (i.e., at block 115 of the method 100 shown in FIG. 1).

In some embodiments, the system 200 further includes at least one pump (not shown) to pump the gas and the product stream through the system 200. In some embodiments, the system 200 further includes valves to start/stop the flow of gas/product stream in the system 200 or to enable gas/product stream to be added to or taken out of the system 200.

The following examples are intended to be examples of the embodiments disclosed herein, and are not intended to be limiting.

Example

Operation of an Experimental System

CO₂ flows from the gas cylinder through a peristaltic pump and then through the cathode of a CO₂ reduction cell, the anode of a hydrogen pump, and a gas chromatograph until it reaches a 4-way valve where the mixed gas stream is vented. The CO₂ reduction cell was tested with Au and Cu catalysts in the cathode chamber, and generally produced a gas mix of H₂, CO and C₂H₄ (no C₂H₄ with Au). The gas mix from the CO₂ reduction cell outlet then flows into the H₂ pump where H₂ is selectively oxidized, yielding a pure stream of H₂ and a gas mix in the loop which is essentially free of H₂. After air is flushed from the system and the system yields a stable performance, the 4-way valve is turned into recirculation mode, guiding the gas mix from the CO₂ reduction cell outlet back to its inlet. An additional 3-way valve was installed to enable the addition of fresh CO₂ into the closed gas loop, as a way of regulating CO₂ partial pressure in the system.

Example

CO₂ Reduction Cell Materials

A 4 cm² platinized Ti mesh (˜270 μm thick) was coated with 100 nm of Ir (0.23 mg cm⁻²) by sputtering and used as the anode of the cell. For the cathode, 4 cm² large carbon paper (275 μm thick) with a hydrophobic, micro-porous layer was sputtered with either 100 nm of Cu (0.09 mg cm⁻²) or 100 nm of Au (0.19 mg cm⁻²). Selemion AMV (AGC Engineering, New York, NY) membranes (chloride form, ˜100 μm thick) were used to separate anode and cathode. The endplates were machined from polymethylmethacrylate containing straight flow channels for the anode and serpentine flow channels for the cathode compartment. Laser-cut, window frame-shaped silicone pieces served as gaskets. The thickness of the gaskets and the torque of the screws (0.1 N m) determined the cell compression. The electrodes were contacted by 25 μm thick tantalum strips, which were connected to the potentiostat clamps.

Example

H₂ Pump Operating Conditions

A peristaltic pump pushed 1 M KHCO₃ at a flow rate of ˜6 mL min⁻¹ through the anode chamber of the CO₂ reduction cell. KHCO₃ electrolytes were prepared using reagent-grade powder. CO₂ was recirculated using a peristaltic pump and the pump tubing's inner diameter was varied to change the flow rate. The pressure in the gas loop was controlled with a pressure regulator and by adjusting the flow rate of fresh CO₂ entering the loop. A mass flow meter was used to precisely measure the flow rate and pressure in the gas loop. Argon was flowed at 5 sccm to flush the cathode of the hydrogen pump and aid with accurate product detection via gas chromatography. During the heating phase of the H₂ pump, argon was also flowing through the anode side. After the temperature equilibrated, the anode gas flow was changed to H₂ or the outlet of the CO₂ reduction cell. All electrochemical measurements were performed in 2-electrode configuration and cyclic voltammograms were measured with a scan rate of 10 mV s⁻¹.

Example

CO₂ Reduction to CO

An embodiment of gas recycling system (e.g., as shown in FIGS. 3A and 3B) was assembled and tested using an Au catalyst on the cathode of the CO₂ reduction cell. In this configuration the main expected products from CO₂ reduction are H₂ and CO. Since H₂ is removed from the recycled gas stream by the H₂ pump, CO is expected to accumulate over time in the closed loop. An initial test with this system yielded a CO concentration of ˜40% after 6 h of operation, up from 2% when using only single-pass conversion. While this level of product accumulation marks a significant improvement, this experiment also revealed that a large fraction of gas concentrations could not be accounted for. Besides H₂, CO, and CO₂, the only other gas expected in the looped stream is the carrier gas from the gas chromatograph. Since the recycled gas stream flows directly through the sample loop of the gas chromatograph, every injection of the gas chromatograph will push carrier gas into the closed loop when the gas chromatograph valve switches back to the default position. The concentration of the carrier gas in the loop cannot be measured directly by the gas chromatograph but can be estimated by the volume of the sample loop. However, a control experiment with only CO₂ recirculating in the loop revealed that the concentration of carrier gas in the loop can be much larger than expected since the carrier gas in the gas chromatograph is pressurized, leading to a ˜3× higher concentration than initially estimated. Therefore, the standard valve setup of the gas chromatograph was modified to prevent carrier gas from entering the gas loop.

Another experiment was carried out with the modified gas chromatograph valve setup, again targeting CO as the main product with the gas recycling system. Since carrier gas was absent in the recycled gas stream, the CO concentration reached a much higher peak value of 72.5% (FIG. 4A), nearly doubling the concentration compared to the test without the modified gas chromatograph valve setup.

During the first hour of the experiment, the CO concentration equilibrated near 8% using only single-pass conversion, after which the gas loop was closed, explaining the rise in CO concentration over time. After the loop was closed, the pressure in the gas stream was controlled via the flow rate of fresh CO₂ flowing into the loop and set to ˜19 psi (FIG. 4B). After 6.5 h of operation in closed loop mode, the addition of CO₂ was stopped, causing a rapid pressure decrease since the remaining CO₂ in the loop is consumed via reaction to CO and carbonate crossover through the membrane, and produced hydrogen is removed through the H₂ pump. After CO₂ was removed from the loop, a peak CO concentration of 72.5% was achieved at minimal concentrations of H₂.

In this case, the missing gas concentrations may be explained by a gas leak of the system, which allowed air to enter the loop as the loop pressure dropped below ambient pressure (˜14.4 psi). Control experiments showed that the leak was not coming from any of the electrochemical cells, but likely arises from the tubing installed in the peristaltic pump. Other pumps which are specifically designed to be leak-free for gases, such as gas-tight diaphragm pumps, are expected to yield even higher peak CO concentrations. Alternatively, the tubing around the pump could be put into a CO₂ atmosphere, also preventing any air from entering the gas loop. As shown by X-ray photoelectron spectroscopy (XPS) measurements taken before and after this looped experiment, the Au catalyst composition was stable.

Example

CO₂ Reduction to Ethylene

In a separate set of experiments, the potential of the gas recycling loop to concentrate ethylene was examined. For this reason, the Au catalyst on the CO₂ reduction cell's cathode was swapped to a Cu catalyst. Initial tests in single-pass configuration indicate that C₂H₄ concentrations below 0.5% can be expected for gas flow rates of 7 sccm or higher.

Switching from single-pass configuration to gas stream recirculation yielded C₂H₄ concentrations near 1% if no H₂ pump was used. This recycling experiment clearly demonstrated that H₂ accumulates very quickly with an exponential trend in the absence of an H₂ pump, prohibiting the accumulation of C₂H₄. The exponential trend of HER can be explained by the decreasing availability of CO₂ as HER starts to dominate, reducing the chances of CO₂ reduction and further enhancing the rate of HER, resulting in a self-accelerating switch to HER.

Similarly, a separate single-pass experiment was carried out where the CO₂ cathode inlet feed was diluted step-by-step with inert Ar gas. As the concentration of CO₂ was reduced, the total device current increased quickly due to rising HER, with lower concentrations of CO₂ leading to a sharper increase of HER. This test also indicated that higher inlet flow rates enable operation with lower feed concentrations of CO₂ without leading to dominating HER.

As a next step, the hydrogen pump was integrated into the gas recycling loop (e.g., as shown in FIGS. 3A and 3B), and the whole system was operated. The result was a peak C₂H₄ concentration of 4.8%, a value roughly 5× larger than that without integration of the H₂ pump. However, within one hour of operation in closed loop mode, all of the CO₂ in the gas loop was reacted or lost to carbonate crossover through the anion exchange membrane of the CO₂ reduction cell, preventing further product accumulation.

After a recirculation experiment performed with Cu as the CO₂ reduction catalyst, the gas loop was opened and all the accumulated products were flushed out for one hour. Afterwards, the gas loop was closed again at 3 h total operation time with fresh CO₂ constantly flowing into the closed gas loop during this experiment. This enabled longer operation times and higher C₂H₄ concentrations, while keeping the pressure in the loop near atmospheric pressure (FIGS. 5A and 5B).

Due to the longer operation time of the closed loop system, an ethylene concentration of 8.7% was achieved. Interestingly, the concentration of CO also increased over time even though CO is a known intermediate for C₂H₄ generation, suggesting that produced CO is not likely to react further after its desorption. Modification of the catalytic microenvironment in the CO₂ electrolyzer cathode may enhance re-adsorption of CO and its subsequent conversion to C₂H₄, representing a promising pathway to even higher C₂H₄ concentrations.

While for the CO₂ reduction to CO system (FIGS. 4A and 4B), it was beneficial to operate slightly above ambient pressure to prevent air from entering the gas loop, elevated gas pressure is expected to drop the faradaic efficiency for C₂H₄ on Cu catalysts and promote formate generation. For this reason, the pressure was kept near ambient pressure with the Cu-based system, enabling air to enter the gas loop more easily and dilute the formed products while adding the possibility of oxygen reduction reaction as another possible, undesirable side reaction in the CO₂ reduction cell. XPS measurements taken before and after this looped experiment indicated a change in the Cu catalyst composition. Specifically, the relative intensities of the Cu(0/i) and Cu(ii) 2p core levels are shown to switch during operation, with Cu(ii) signals becoming more prominent after CO₂R operation.

The effect of the gas leak in the loop became even more evident during a longer, 24 hour closed loop experiment. After 10 h of operation, increases in ethylene and CO concentration were arrested, indicating that formation of CO₂ reduction products equaled their leak rate, resulting in dropping faradaic efficiencies over time. After the flow of fresh CO₂ was stopped in this longer test, a peak C₂H₄ concentration of 9.4% was reached, only a marginal improvement over the 3 hour test shown in FIGS. 5A and 5B considering the much longer operation time. However, this peak value marks a roughly 20-fold improvement over the single-pass system operated at a similar flow rate. Furthermore, a propylene concentration near 0.5% was also detected during this experiment.

Finally, the peak concentration achieved with the CO₂ reduction cell within the described closed loop system was compared to the same CO₂ reduction cell operated in single-pass configuration at the minimum gas flow rate that maximizes ethylene outlet concentrations. At a much-reduced outlet flow rate of ˜0.8 sccm, the CO₂ reduction cell yielded an C₂H₄ concentration of 7.5%, a value which is lower than with the gas recirculation system even with the present gas leaks. In fact, if inert gases in the closed loop system are ignored (no leaks), the peak C₂H₄ concentration is actually 37.9%, which is 5 times higher than what is possible with the single-pass system operating at a significantly reduced flow rate.

CONCLUSION

Further details regarding the embodiments described herein can be found in T. A. Kistler et al., “A recirculation system for concentrating CO₂ electrolyzer products,” Sustainable Energy Fuels, 2024, 8, 2292-2298, including the Supplementary information, all of which is hereby incorporated by reference.

In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention.

Claims

1. A method comprising: flowing a gas through a reduction device, the gas being carbon dioxide (CO2) or nitrogen (N2), the reduction device reducing the gas and generating a product stream including the gas, hydrogen (H2), and a chemical;flowing the product stream through a hydrogen removal device, the hydrogen removal device removes hydrogen from the product stream; andflowing the product stream with the hydrogen removed through the gas reduction device.

2. The method of claim 1, further comprising: prior to flowing the product stream with the hydrogen removed through the gas reduction device, flowing the product stream with the hydrogen removed through an accumulation chamber to remove the chemical from the product stream.

3. The method of claim 2, wherein the accumulation chamber comprises a substantially gas tight chamber.

4. The method of claim 1, further comprising: prior to flowing the product stream with the hydrogen removed through the carbon dioxide reduction device, adding additional gas to the product stream with the hydrogen removed.

5. The method of claim 4, wherein a first pressure of gas is flowed through the gas reduction device, and wherein an amount of additional gas is added to the product stream with the hydrogen removed so that the product stream with the hydrogen removed is at the first pressure.

6. The method of claim 1, wherein the gas is carbon dioxide, and wherein the chemical is a chemical from a group ethylene, ethane, carbon monoxide, methane, propylene.

7. The method of claim 1, wherein the gas is nitrogen, and wherein the chemical is a chemical from a group ammonia, urea, and hydrazine.

8. The method of claim 1, wherein the hydrogen removal device is a device from a group an electrochemical hydrogen pump, a palladium membrane, and a thermal metal hydride adsorption device.

9. The method of claim 1, wherein the hydrogen removal device is an electrochemical hydrogen pump, and wherein the electrochemical hydrogen pump is operated at a temperature of about 150° C. to 180° C.

10. A system comprising: a gas reduction device, an inlet of the gas reduction device operable to receive a gas, the gas being nitrogen (N2) or carbon dioxide (CO2), and the gas reduction device operable to generate a product stream including the gas, hydrogen (H2), and a chemical; anda hydrogen removal device, an inlet of the hydrogen removal device operable to receive the product stream from an outlet of the gas reduction device, the hydrogen removal device operable to remove hydrogen from the product stream, and an outlet of the hydrogen removal device flowing the product stream with the hydrogen removed into the inlet of the gas reduction device.

11. The system of claim 1, wherein the hydrogen removal device is a device from a group an electrochemical hydrogen pump, a palladium membrane, and a thermal metal hydride adsorption device.

12. The system of claim 1, further comprising: an accumulation chamber, wherein an inlet of the accumulation chamber is operable to receive the product stream with the hydrogen removed from the hydrogen removal device, wherein the accumulation chamber is operable to remove the product from the product stream, and wherein an outlet of the accumulation chamber is operable to flow the product stream with the hydrogen removed and at least some of the product removed into the inlet of the gas reduction device.

13. The system of claim 1, further comprising: a valve, wherein the valve is operable to allow for addition of the gas to the product stream with the hydrogen removed prior to flowing the product stream with the hydrogen removed through the gas reduction device.

14. The system of claim 13, wherein the valve is a 3-way valve or a 4-way valve.

15. The system of claim 1, further comprising: at least one pump to pump the gas and the product stream through the system.