Patent Application
20250188624
Ethylene glycol, an essential ingredient in antifreeze, polyester fibers, and plastic bottles, held a market size of 31.9 MMt in 2022. The prevailing production approach involves ethylene oxidation to ethylene oxide under elevated temperature and pressure (200-300° C., 1.5-2.5 MPa), which is subsequently hydrolyzed to produce ethylene glycol at 120-250° C. and 1-4 MPa. The production of ethylene glycol leads to over 46 million tonnes of CO2 emissions annually. A substantial portion of these emissions stems from the production of ethylene—primarily via oil cracking—and the overoxidation during the synthesis of ethylene glycol.
Methods and systems for the electrosynthesis of an oxidized product (e.g., ethylene glycol) from a hydrocarbon (e.g., ethylene) are provided. In the present methods and systems, electrosynthesis of the oxidized product is coupled with CO2 capture in a catholyte, which may be subsequently released.
The methods and systems are illustrated below primarily by reference to oxidation of a specific hydrocarbon, ethylene, to ethylene glycol. Briefly, although other electrochemical processes have been developed for ethylene glycol manufacturing, they are impeded by challenges like ethylene overoxidation and low current density. The present methods and systems are illustrated in greater detail in the Examples below, which describe a single-electrolyzer system configured to couple chloride-mediated ethylene glycol electrosynthesis with carbon capture. First, the Examples describe experiments in which the role of pH gradients across membranes in regulating anodic ethylene partial oxidation is delineated. Next, experiments are presented which highlight how these pH gradients can be exploited for carbon capture and optimization of anodic partial oxidation conditions. Leveraging this knowledge, tin-doped ruthenium oxide catalysts were developed that enable selective ethylene partial oxidation under a near-neutral pH. Surprisingly, the integrated approach attains up to 94% Faradaic efficiency for ethylene glycol production along with 92% carbon capture efficiency when CO2 concentrations vary between 1% and 10% in a feeding gas stream containing 20% O2 and 70-79% N2. Operating at a full cell voltage of 1.8 V and a current density of 100 mA cm−2, the system requires only 6.9 GJ/tonne of energy to produce one tonne of ethylene glycol while capturing 0.75 tonnes of CO2. This is a marked reduction from the conventional 22.6 GJ. The cradle-to-grave life cycle assessment reveals a tenfold carbon footprint reduction to 0.11 tonnes CO2-eq/tonne with oil-cracking ethylene. Further integration of CO2 electroreduction will result in a negative carbon footprint of −2.06 tonnes CO2-eq per tonne. Given that global ethylene production accounts for 260 million tonnes of CO2 emissions annually—approximately 0.8% of global emissions—the single-electrolyzer integrated system provides a transformative solution for both emission reduction and value-added chemical production.
A method for electrolyzing a hydrocarbon is provided that comprises (a) delivering a cathode feed comprising CO2 to a cathode in contact with a catholyte; (b) delivering an anode feed comprising a hydrocarbon to an anode in contact with an anolyte; and (c) generating hydroxide in the catholyte to dissolve CO2 therein, while oxidizing the hydrocarbon in the anolyte, by generating a potential difference between the cathode and the anode.
An electrolyzer for electrolyzing a hydrocarbon is provided, the electrolyzer comprising: a cathode in contact with a catholyte, the cathode comprising a catalyst that generates hydroxide in the catholyte to dissolve CO2 therein upon generation of a potential difference between the cathode and an anode in electrical communication with the cathode; the anode in contact with an anolyte that dissolves a hydrocarbon therein, the anode comprising a catalyst that induces oxidation of the hydrocarbon in the anolyte upon generation of the potential difference between the cathode and the anode; a cathode feed inlet configured to deliver a cathode feed comprising CO2 to the cathode; and an anode feed inlet configured to deliver an anode feed comprising the hydrocarbon to the anode.
Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.
Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.
The present methods are based on paired electrochemical reactions induced within an electrolyzer that facilitate CO2 capture in a catholyte and oxidation, including selective oxidation, of a hydrocarbon in an anolyte. In a basic embodiment, a method for electrolyzing a hydrocarbon comprises delivering a cathode feed to a cathode in contact with a catholyte, the cathode feed comprising CO2; delivering an anode feed to an anode in contact with an anolyte, the anode feed comprising a hydrocarbon; and generating hydroxide (OH−) in the catholyte to dissolve CO2 therein, while oxidizing the hydrocarbon in the anolyte. The method may further comprise releasing CO2 gas from the catholyte while producing an oxidation product from the anolyte.
The composition of the catholyte, which is generally a liquid, is selected to facilitate the dissolution of CO2 (from the cathode feed) therein. The dissolution of the CO2 in the catholyte need not be perfect (i.e., 100%), but generally a substantial amount of the CO2 is incorporated into the liquid catholyte. The catholyte is also selected to enable formation of the hydroxide therein via a reduction reaction taking place at the cathode, as further described below. The catholyte is further selected to enable formation of a carbonate therein, e.g., by providing a species that forms the carbonate with the dissolved CO2. The catholyte may comprise (or consist of) water and a suitable salt. This salt may comprise the carbonate-forming species as well as a redox mediator for the partial oxidation of the hydrocarbon in the anolyte, as further described below. A suitable salt is an alkali metal halide salt, e.g., NaCl. The sodium cations can form Na2CO3 while the chlorine anions can be oxidized at the anode and serve as an effective redox mediator for partial oxidation of the hydrocarbon. However, other alkali metals (e.g., potassium) and other halides (e.g., bromide) may be used. The concentration of the salt in the catholyte may be adjusted as desired, e.g., to maximize CO2 dissolution, maximize Faradaic efficiency and specificity, etc. Illustrative amounts are provided in the Examples, below. Components which may be excluded from the catholyte include those described below with respect to the anolyte, as well as an aldehyde (e.g., formaldehyde).
The cathode comprises a catalyst. Various catalysts that catalyze the reduction reaction at the cathode to generate the hydroxide during operation of the disclosed electrolyzers may be used, desirably with high Faradaic efficiency and specificity for hydroxide production. Generally, the reduction reaction is the oxygen reduction reaction. Desirably, the production of H2O2 is minimized. This includes the catholyte being free of H2O2, including during operation of the disclosed electrolyzers. In addition, the hydrogen evolution reaction at the cathode is desirably minimized. This includes the hydrogen evolution reaction not occurring at the cathode during operation of the disclosed electrolyzers. Illustrative catalysts that may be used include supported platinum catalysts (e.g., Pt/C) and iron-single-atom catalysts, the synthesis of which is described in the Examples, below. Other illustrative catalysts include those comprising Ni, Fe, Ru, Mn, and combinations thereof.
As noted above, the cathode feed comprises CO2 to be captured in the catholyte as described above. Generally, the cathode feed also comprises O2 which may be provided together with CO2 as a gas mixture. Other gases may be present, e.g., N2. The amounts of CO2 (and O2, if present) being fed may be adjusted as desired, e.g., to maximize Faradaic efficiency and specificity. Illustrative amounts are provided in the Examples below. For example, the CO2 may be present in the cathode feed at an amount of at least 1% by volume, at least 2% by volume, at least 4% by volume, at least 6% by volume, at least 8% by volume, or in a range between any of these values, including from 1% to 10% by volume. In embodiments, the cathode feed comprises air, including air enriched with CO2 at any of the disclosed amounts. In embodiments, the cathode feed consists of air, or CO2 and one or more of O2 and N2.
The composition of the anolyte, which is also generally a liquid, is selected to facilitate the dissolution of the hydrocarbon (from the anode feed) therein. The dissolution of the hydrocarbon in the anolyte need not be perfect (i.e., 100%), but generally a substantial amount of the hydrocarbon is incorporated into the liquid anolyte. The anolyte is also selected to enables oxidation of the hydrocarbon via an oxidation reaction taking place at the anode. This oxidation reaction may involve the redox mediator noted above, i.e., anions which are oxidized at the anode to induce partial oxidation of the hydrocarbon to form an oxidation intermediate in the anolyte. Partial oxidation of a hydrocarbon is distinguished from full or complete oxidation of the hydrocarbon to CO2 and H2O. Suitable redox mediators include halides (e.g., Cl−) although other halides and other redox mediators may be used. The anolyte may comprise (or consist of) water and any of the salts described above. Additive(s) may be included, e.g., to facilitate hydrocarbon dissolution. The concentration of the salt (and additive(s), if present) in the anolyte may be adjusted as desired, e.g., to maximize hydrocarbon dissolution, maximize Faradaic efficiency and specificity, etc. Illustrative amounts are provided in the Examples, below. The composition of the anolyte and the catholyte may be the same or they may be independently selected. Components which may be excluded from the anolyte include those described above with respect to the catholyte, as well as an alcohol (e.g., methanol).
The anode comprises a catalyst. Various catalysts that catalyze the oxidation reaction at the anode (which may be the oxidation of the redox mediator as noted above), desirably with high Faradaic efficiency and specificity (including towards formation of the oxidation intermediate of the selected hydrocarbon). The catalyst also desirably exhibits high stability under acidic pH (e.g., below about 3). In embodiments, the catalyst is a mixed oxide catalyst comprising at least two transition metals, e.g., those selected from Ru, V, W, Mn, and Sn. The transition metal selection and relative amounts may be adjusted as desired, e.g., to maximize Faradaic efficiency and specificity. In embodiments, the mixed oxide catalyst is RuMOx, wherein M is selected from V, W, Mn, and Sn. As demonstrated in the Examples, below, the mixed oxide catalyst RuSnOx, in which Sn is incorporated into the RuO2 structure, was found to significantly improve the Faradaic efficiency towards ethylene chlorohydrin (an oxidation intermediate) as well exhibit enhanced stability at low pH. (See
As noted above, the anode feed comprises the hydrocarbon to be oxidized. A variety of hydrocarbons may be used. The hydrocarbon may be an olefin, e.g., ethylene, propylene, butene. In other embodiments, the hydrocarbon is an alkane, e.g., methane. The hydrocarbon may be unsubstituted, i.e., consisting of carbon and hydrogen and no heteroatoms. A single type of hydrocarbon or multiple, different types of hydrocarbons may be used. The amount of hydrocarbon in the anode feed may be adjusted analogous to the components of the cathode feed. In embodiments, the anode feed consists of the hydrocarbon to be oxidized, e.g., one or more unsubstituted olefins, unsubstituted alkanes.
As noted above, the present methods comprise generating hydroxide in the catholyte while oxidizing the hydrocarbon in the anolyte. This is accomplished by generating a potential difference between the cathode and the anode (which are in electrical communication with one another) sufficient to induce the reduction and oxidation reactions described herein. In this way, the electrochemical reactions are paired with one another and occur essentially simultaneously in the same electrolyzer. For this reason, the electrolyzer in which these paired electrochemical reactions are being carried out may be referred to as a “single-electrolyzer.” As described above, the hydroxide may be generated via the oxygen reduction reaction and a carbonate may be formed in the catholyte. The hydrocarbon may be oxidized via a mediated partial oxidation reaction to form an oxidation intermediate in the anolyte.
The present methods may further comprise releasing CO2 gas from the catholyte that had been incorporated therein, which may be accompanied by producing an oxidized product from the anolyte. The CO2 gas release and production of the oxidized product may be accomplished by combining a portion of the catholyte and a portion of the anolyte to induce a reaction between the carbonate (from the catholyte) and the oxidation intermediate (from the anolyte) that produces the CO2 gas and the oxidation product. The oxidation product may depend upon a pH of the combined catholyte and anolyte. Using ethylene chlorohydrin as an illustrative oxidation intermediate, the pH of the combined catholyte and anolyte may be tuned to provide ethylene glycol (at approximately neutral pH) or ethylene oxide (at more alkaline pH). Thus, the conditions (including the pH) under which the catholyte and the anolyte are combined may selected to provide a desired yield/selectivity of a desired oxidation product. The present methods may further comprise recovering the oxidation product from the combined catholyte and anolyte. The released CO2 gas may be sequestered, if desired.
The present methods are carried out using an electrolyzer comprising (or consisting of) the cathode, the catholyte, anode, and the anolyte, each of which has been described above. The cathode and the anode are in electrical communication with each other such that the potential difference sufficient to induce the reduction and oxidation reactions described above may be generated therebetween. Various electrolyzer configurations may be used, comprising components and using arrangements typical of electrolyzers. The electrolyzer may be configured for continuous flow operation, i.e., involving continuously flowing catholyte and anolyte as well as continuous (or periodic) removal of portions of the catholyte and the anolyte. A separator may be included in the electrolyzer to separate the catholyte and the anolyte, e.g., an ion exchange membrane or a passive separator. In embodiments, an ion exchange membrane is used. In embodiments, the ion exchange membrane is a cation exchange membrane capable of allowing cations to pass therethrough while inhibiting the passage of hydroxide. In embodiments, the cathode, the anode, and the separator (e.g., ion exchange membrane) are configured to form a membrane electrode assembly (MEA), wherein the cathode is in direct contact with one side of the separator and the anode is in direct contact with an opposing side of the separator. The electrolyzers described herein are also encompassed by the present disclosure, which may be a component of an electrolyzer system. The electrolyzer system may further comprise a feed electrolyzer for providing the hydrocarbon to be oxidized, e.g., a feed electrolyzer configured to provide ethylene from the electrochemical reduction of CO2. Other components that may be included in any of the disclosed electrolyzers include gas diffusion layers; flow field plates; a power source, etc.
In addition to the potential difference under which the present methods are carried out, other conditions such as temperature and pressure may be selected as desired, e.g., to maximize CO2 dissolution, maximize hydrocarbon dissolution, maximize Faradaic efficiency and specificity (at the cathode and/or anode), etc. However, in embodiments, the present methods are carried out at room temperature and atmospheric pressure. Depending upon the selected hydrocarbon, higher temperatures and/or pressures may be used. The conditions used during the combining of the catholyte and the anolyte may be the same as used during the electrochemical reactions or they may be independently selected.
An illustrative electrolyzer and method of electrolyzing a hydrocarbon using the electrolyzer is shown in
Other electrolyzers and methods for electrolyzing other hydrocarbons are also encompassed. In embodiments, the present methods and systems are configured to oxidize propylene to propylene glycol, propylene oxide, or both (including via a propylene halohydrin oxidation intermediate). In embodiments, the present methods and systems are configured to oxidize butene to butenediol or butanediol (including via a butene halohydrin oxidation intermediate). In embodiments, the present methods and systems are configured to oxidize methane to methanol (including via a halomethane oxidation intermediate).
The present methods and systems may be characterized by various properties including CO2 capture efficiency (e.g., at least 85%, at least 90%, at least 95%, or a range of between any of these values) and Faradic efficiency (e.g., at least 90%, at least 92%, at least 94%, or a range of between any of these values) towards a desired oxidation product (e.g., ethylene glycol from ethylene). These values may refer to specific operating conditions, e.g., from 1% to 10% by volume CO2, 20% by volume O2, balance N2 in the cathode feed; a full cell voltage of 1.8 V; and a current density of 100 mA cm−2.
The terms “selective,” “specificity,” and the like refer to the percentage of a reactant (e.g., any of the disclosed hydrocarbons) that goes toward the desired product (e.g., any of the disclosed oxidation intermediates or oxidation products). The selectivities/specificities referenced herein may be at least 90%, at least 95%, at least 98%, 100%, or a range of between any of these values. This includes the present methods achieving a selectivity/specificity of any of these values in the conversion of ethylene to ethylene glycol.
In a typical synthesis of N-doped carbon, a 400 mL methanol solution containing 9.04 g of Zn(NO3)2·6H2O was poured into another 400 mL methanol solution containing 10.507 g of 2-methylimidazole, while stirring quickly. The mixture was stirred for 2 minutes and then kept in a stable condition for 1 day without further stirring. Afterward, the white precipitates were collected by centrifugation, washed with methanol three times, and dried in a vacuum oven at 70° C. To obtain N-doped carbon, the synthesized zeolitic imidazolate framework (ZIF-8) powders were ground and then subjected to heat treatment at 900° C. for 1 hour under Ar purging conditions in a tube furnace. Subsequently, 200 mg of N-doped carbon was dispersed in 40 mL of H2O and sonicated it for 20 minutes. Then, 1 mL of Fe(NO3)3 solution (prepared by dissolving 269.3 mg of iron nitrate in 10 mL of H2O) was added to the dispersion and subjected to an additional 20 minutes of sonication, followed by continuous stirring for 24 hours. After filtration, the resulting precipitate was rinsed with deionized water and dried in a vacuum oven overnight. In the final step, the dried sample was pyrolyzed in the tube furnace at 1000° C. for 2 hours under an Ar atmosphere.
Morphological characterization of the synthesized sample was performed by using a Transmission electron microscopy (TEM, JEOL JEM-2100F) at an acceleration voltage of 200 kV. High angle annular dark field-scanning TEM (HAADF-STEM) and energy dispersive spectroscopy (EDS) analysis were obtained in the JEOL JEM-2100F (JEOL) microscope. X-ray photoelectron spectroscopy (XPS) data was measured by NEXSA G2 (Thermo Fisher Scientific). X-ray absorption near-edge spectroscopy (XANES) and Extended X-ray absorption fine structure (EXAFS) were performed at Pohang Accelerator Laboratory (PAL) 8C beamline.
The electrocatalytic performance for the oxygen reduction reaction (ORR) was evaluated using a rotating disk electrode (RDE, Pine Instrument) system within a three-electrode setup. The counter electrode and reference electrode employed were a glassy carbon rod and Ag/AgCl electrode, respectively. The working electrode was a 5 mm (0.19625 cm2) glassy carbon disk electrode. All potentials are reported relative to the reversible hydrogen electrode (RHE), determined by measuring the equilibrium potential of hydrogen oxidation/evolution under H2-saturated electrolyte using a Pt electrode. The catalyst ink was prepared by mixing the catalyst with Nafion ionomer (5 wt %, Ion Power) and 2-isopropanol (Sigma-Aldrich). The catalyst loading of the Fe—N—C catalyst was 0.2 mg cm−2, while that of the commercial 40 wt % Pt/C catalyst (Johnson Matthey) was 0.05 mg cm−2, respectively. ORR activity was measured using linear scan voltammetry at a rotation speed of 1600 rpm, a scan rate of 10 mV s−1, in an O2-saturated 0.1 M KOH electrolyte. The capacitance arising from non-Faradaic effects was compensated for by measurements conducted under Ar-saturated conditions, and iR-correction was applied.
A titanium felt (Fuel cell store) was first cleaned using acetone and then etched in a boiling 10% oxalic acid (98%, Sigma-Aldrich) solution for half an hour to serve as the electrode substrate. To fabricate RuSnOx-coated Ti felt, a painting solution with a Ru:Sn molar ratio of 50:50 was created by dissolving ruthenium (III) chloride hydrate (99.9%, Sigma-Aldrich) and tin (II) chloride hydrate (98%, Sigma-Aldrich) in isopropanol. This solution was applied to the pre-treated titanium substrate using an airbrush. Subsequently, the coated samples were dried at 100° C. for 10 minutes in an oven and then sintered at 450° C. for 1 hour in a furnace.
The rotating ring-disk electrode (RRDE) setup was used to differentiate the current densities for the oxygen evolution reaction and the chloride oxidation reaction. In order to quantify chloride oxidation rates during the electrolysis process, an RRDE setup featuring a platinum ring electrode and a glassy carbon disk electrode was utilized. The potential of Pt ring electrode was fixed at 0.95 V, which enabled the accurate quantification of active chlorine species at the ring through their reduction back to Cl−. The collection efficiency for these active chlorine species was denoted as NI, which was determined by the electrode area. Based on these parameters, the partial current density for chloride oxidation was subsequently calculated by iCER=iRing/NI. In a typical RRDE test, 5 mg of catalyst was added to 1 ml of isopropyl alcohol and 20 μl of Nafion ionomer (5%; Fuel cell store) and sonicated for 1 h to obtain a well-dispersed catalyst ink. For electrode preparation, 16 μl of catalyst ink was drop-cast onto the glassy carbon disk electrode, resulting in a catalyst loading of 0.4 mg cm−2, and then dried at room temperature before usage. A graphite electrode and an Ag/AgCl electrode were used as the counter and reference electrode, respectively. The rotation rate was set to 2,500 r.p.m.
The ethylene partial oxidation was tested using a membrane electrode assembly-based electrolyzer with an active area of 1 cm2. The cell incorporated a ruthenium-based mixed oxide as anodic catalyst. A reinforced cation-exchange membrane from Dongyue was used to separate the cathodic and anodic chamber. The lab-synthesized iron-single atom catalyst or 40% Pt on Vulcan XC72 (Fuel cell store) were used as catalysts for oxygen reduction reaction and carbon capture. 1 M NaCl was fed as the electrolyte on both sides. Various concentrations of CO2 were fed to the cathodic gas chamber with 20% oxygen and nitrogen was used as balanced gas. Ethylene was fed to the anodic gas chamber for ethylene partial oxidation. A constant volume (25 ml) of catholyte and anolyte were circulated through the electrolyzer at a stable flow rate of 10 ml min−1 controlled by two peristaltic pumps. The capture efficiency was measured in the flue gas of cathodic chamber by GC injection. After one hour of electrolysis, the anolyte samples were collected to measure the ethylene chlorohydrin formation. Then the anolyte was mixed with catholyte, to measure the ethylene glycol formation and CO2 regeneration. Liquid products were analyzed by NMR spectrometry using DMSO as internal standard via a pre-saturated water suppression method. A typical procedure to prepare an NMR sample was to add 0.1 ml 0.008 M DMSO in D2O standard and 0.4 ml D2O to 0.1 ml liquid sample.
To evaluate the local pH at the interface of the catalyst and the membrane in the membrane electrode assembly, a pH-sensitive dye, LysoSensor Green DND 189 (LSG), was affixed to the membrane and an in-situ photoluminescence study was executed. UV light at 365 nm was used to collect fluorescence emissions via a spectrometer (Ocean Optics, QE Pro). The dyes were calibrated using solutions of varying pH levels (1-7) to determine their fluorescence, with 100 μM of the dyes dissolved in the solutions. LSG demonstrated fluorescence emission between 500 nm and 575 nm at a pH range of 1-6. Consequently, alterations in pH at the membrane interface can be examined by monitoring the peak shifts of the pH-sensitive dyes.
The in-situ kinetics NMR study was carried out using a 400 MHz Bruker Avance III HD Nanobay system. The ethylene chlorohydrin obtained from the electrochemical chloride-mediated ethylene partial oxidation was collected, which was then subjected to alkaline and neutral conditions by introducing stoichiometric amounts of sodium hydroxide and sodium bicarbonate. Post-electrolysis ethylene chlorohydrin solution with a pH of 1.5 was used for the control experiment. Dimethyl sulfoxide in deuterium water was used as internal standard. The one-dimensional 1H spectrum was acquired every two minutes to monitor the hydrolysis of ethylene chlorohydrin employing water suppression via a pre-saturation method.
In this Example, all DFT calculations were performed with periodic slab models using the Vienna ab initio simulation package (VASP). The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was used. The projector-augmented wave (PAW) method was utilized to describe the electron-ion interactions, and the cut-off energy for the plane-wave basis set was 520 eV. All the configurations were optimized using a force-based conjugate gradient algorithm. The D3 correction method was used to correct the long-range dispersion interactions between the adsorbates and catalysts. Dipole correction was also considered to correct the electrostatic interaction resulted from the periodic images.
Ethylene partial oxidation was conducted via a chloride-mediated mechanism in which ethylene is converted to ethylene chlorohydrin facilitated by hypochlorous acid from anodic chloride oxidation (see
In the zero-gap setup, the anode is in direct contact with the membrane, while the three-compartment configuration positions a 5 mm gap in between. After applying 100 mA cm−2 for 30 minutes, a stark pH gradient across the membrane was observed, with the anolyte at pH 1.5 and the catholyte at pH 11.7. To determine the local pH at the catalyst-membrane interface in the membrane electrode assembly, a pH-sensitive dye, LysoSensor Green DND 189 (LSG), was anchored onto the membrane and an in-situ photoluminescence study was conducted. Results indicated a near-neutral pH of 5-6 on the surface of the membrane facing anode, contrasting with the anolyte bulk pH of 1.49 (data not shown). This was determined to be due to the undesired back-migration of hydroxide ions stemming from the extensive pH gradient.
The local pH affects the ethylene partial oxidation by altering the thermodynamics of chloride oxidation and oxygen evolution. The equilibrium potentials are 1.229 V vs. RHE for oxygen evolution and 1.358+0.059 pH V vs. RHE for chloride oxidation. Meanwhile, chloride oxidation involves only two electron transfers and has a more favorable kinetics than oxygen evolution reaction. Thus, acidic environments favor chloride evolution, while neutral conditions favor oxygen evolution. This was validated by the Rotating Ring-Disk Electrode (RRDE) measurements (
The inventors had the insight that coupling CO2 capture with ethylene oxidation, instead of hydrogen evolution, could benefit the overall device efficiency by regulating the anodic microenvironment for ethylene partial oxidation. Specifically, coupling CO2 capture at the cathode could capitalize on the OH− generated at the gas diffusion interface (convert to (bi) carbonate), mitigate the overpotential induced by pH gradient, and suppress the hydroxide back-migration.
Iron-single-atom catalysts (denoted as Fe—N—C) were used as cathodic catalysts. Notably, the Fe—N—C catalysts exhibit a CO2 capture efficiency of 92.7% in a feeding stream composed of 10% CO2, 20% O2, and 70% N2, with an overpotential comparable to commercial 40 wt % Pt/C. Gas chromatography and NMR analysis revealed no detectable byproducts, indicating the absence of competing reactions, such as hydrogen evolution or CO2 electroreduction. The CO2 capture-ethylene oxidation device displayed a substantial two-unit decrease in the catholyte's pH and a reduction in the full cell voltage by 1.3 V. (See
To further enhance the selectivity of ethylene partial oxidation, a secondary transition metal was introduced into RuO2 to form mixed oxide catalysts. The transition metals, tin, vanadium, magnesium, and tungsten, were selected based on their ionic radii, closely matching that of Ru4+. This resemblance facilitated their incorporation into the RuO2 rutile crystal lattices to form a solid solution, according to the Hume-Rothery rule. Moreover, incorporating a “valve metal” can stabilize the ruthenium cation within the tetragonal rutile crystal structure, significantly enhancing stability in acidic oxygen evolution reactions. A series of RuMOx (M=V, W, Mn, Sn) catalysts were synthesized using a hydrothermal method. Characterization using X-ray photoelectron spectroscopy (XPS) (
To elucidate how Sn doping improves the thermodynamic stability and catalytic activity of RuO2, Density Functional Theory (DFT) calculations were first used to generate a bulk Pourbaix diagram (not shown). The reaction conditions (pH=5 and U=1.71 V) were set based on findings from in-situ photoluminescence and RRDE experiments. Under these conditions, the Pourbaix energy of RuO2 (ΔGpbx(RuO2)) was determined to be 1.30 eV. This value indicates that the energy of RuO2 was 1.30 eV higher than the thermodynamically stable species RuO4. Simultaneously, under the same conditions, ΔGpbx (RuSnOx) was calculated to be 0.80 eV, indicating the energy of RuSnOx was only 0.80 eV above the thermodynamically stable species RuO4+SnO2. Therefore, the lower ΔGpbx value of RuSnOx signifies its enhanced thermodynamic stability compared to RuO2 under chloride oxidation conditions. DFT calculations were further performed to compare the chloride oxidation energetics on the (110) surfaces of both RuO2 and RuSnOx with a 10Clc1Oc termination, using the two-step Volmer-Heyrovsky mechanism (data not shown). From these, the overpotentials of RuO2 and RuSnOx were calculated to be 0.16 V and 0.09 V, respectively. These results indicated the catalytic activity of RuSnOx was enhanced by incorporating Sn into the RuO2 structure.
This Example reveals that the present integrated system offers a significant advantage over traditional methodologies. Specifically, the system can sequester 0.75 tonnes of CO2 for every tonne of ethylene glycol produced while requiring only 6.9 GJ of energy. Conventional ethylene glycol production and carbon capture consume 20.0 GJ/tonne of ethylene glycol and 3.5 GJ/tonne of CO2. Consequently, conventional methods require 22.6 GJ for comparable results. (See
Additional information, including additional experimental data and figures is found in U.S. provisional patent application No. 63/607,143 that was filed Dec. 7, 2023, the entire contents of which are incorporated herein by reference.
In a typical synthesis of N-doped carbon, a 400 mL methanol solution containing 9.04 g of Zn(NO3)2·6H2O was poured into another 400 mL methanol solution containing 10.507 g of 2-methylimidazole, while stirring quickly. The mixture was stirred for 2 minutes and then kept in a stable condition for 1 day without further stirring. Afterward, the white precipitates were collected by centrifugation, washed with methanol three times, and dried in a vacuum oven at 70° C. To obtain N-doped carbon, the synthesized zeolitic imidazolate framework (ZIF-8) powders were ground and then subjected to heat treatment at 900° C. for 1 hour under Ar purging conditions in a tube furnace. Subsequently, we dispersed 200 mg of N-doped carbon in 40 mL of H2O and sonicated it for 20 minutes. Then, 1 mL of Fe(NO3)3 solution (prepared by dissolving 269.3 mg of iron nitrate in 10 mL of H2O) was added to the dispersion and subjected to an additional 20 minutes of sonication, followed by continuous stirring for 24 hours. After filtration, the resulting precipitate was rinsed with deionized water and dried in a vacuum oven overnight. In the final step, the dried sample was pyrolyzed in the tube furnace at 1000° C. for 2 hours under an Ar atmosphere.
Morphological characterization of the synthesized sample was performed by using Transmission electron microscopy (TEM, JEOL JEM-2100F) at an acceleration voltage of 200 kV. High-angle annular dark field-scanning TEM (HAADF-STEM) and energy dispersive spectroscopy (EDS) analysis were obtained in the JEOL JEM-2100F (JEOL) microscope. X-ray photoelectron spectroscopy (XPS) data was measured by NEXSA G2 (Thermo Fisher Scientific). X-ray absorption near-edge spectroscopy (XANES) and Extended X-ray absorption fine structure (EXAFS) were performed at the Pohang Accelerator Laboratory (PAL) 8C beamline.
The electrocatalytic performance for the oxygen reduction reaction (ORR) was evaluated using a rotating disk electrode (RDE, Pine Instrument) system within a three-electrode setup. The counter electrode and reference electrode employed were a glassy carbon rod and an Ag/AgCl electrode, respectively. The working electrode was a 5 mm (0.19625 cm2) glassy carbon disk electrode. All potentials are reported relative to the reversible hydrogen electrode (RHE), determined by measuring the equilibrium potential of hydrogen oxidation/evolution under an H2-saturated electrolyte using a Pt electrode. ORR activity was measured using linear scan voltammetry at a rotation speed of 1600 rpm, and a scan rate of 10 mV s−1, in an O2-saturated 0.1 M KOH electrolyte. The capacitance arising from non-Faradaic effects was compensated for by measurements conducted under Ar-saturated conditions, and iR-correction was applied.
To fabricate RuSnOx-coated Ti electrode, titanium felt is treated in 0.5 M oxalic acid (98%, Sigma-Aldrich) at 80° C. for 30 minutes and washed by DI water and dry in the vacuum oven. A painting solution of 0.02 mM ruthenium chloride hydrate (99.9%, Sigma-Aldrich) and 0.02 mM tin chloride hydrate (98%, Sigma-Aldrich) in isopropanol was prepared with a Ru:Sn molar ratio of 1:1. This solution was applied to the pre-treated titanium substrate using an airbrush with a loading of 2 mg cm−2. The loading is determined by measuring the mass difference. Subsequently, the coated samples were dried at 100° C. for 10 minutes in an oven and then sintered at 450° C. for 1 hour in a furnace. For cathode, the catalyst ink was prepared by mixing the catalyst with Nafion ionomer (5 wt %, Ion Power) and isopropanol (Sigma-Aldrich). The catalyst loading of the Fe—N—C catalyst was 2 mg cm−2. The catalysts were sprayed onto Ag-sputtered porous PTFE membrane using a spray gun as a gas diffusion electrode. Ag/PTFE gas diffusion layer was prepared by sputtering a 300 nm thick Ag layer onto a PTFE membrane (average pore size of 450 nm) using an Ag target (99.99%) at a rate of 1 Å s−1.
The rotating ring-disk electrode (RRDE) setup is used to differentiate the current densities for the oxygen evolution reaction and the chloride oxidation reaction. In order to quantify chloride oxidation rates during the electrolysis process, we utilize an RRDE setup featuring a platinum ring electrode and a glassy carbon disk electrode. The potential of the Pt ring electrode is fixed at 0.95 V, which enables the accurate quantification of active chlorine species at the ring through their reduction back to Cl−. The collection efficiency for these active chlorine species is denoted as NI, which is determined by the electrode area. Based on these parameters, the partial current density for chloride oxidation can subsequently be calculated by
In a typical RRDE test, 5 mg of catalyst was added to 1 ml of isopropyl alcohol and 20 μl of Nafion ionomer (5%; Fuel cell store) and sonicated for 1 h to obtain a well-dispersed catalyst ink. For electrode preparation, 16 μl of catalyst ink was drop-cast onto the glassy carbon disk electrode, resulting in a catalyst loading of 0.4 mg cm 2, and then dried at room temperature before usage. A graphite electrode and an Ag/AgCl electrode were used as the counter and reference electrode, respectively. The rotation rate is set to 2500 r.p.m.
Ethylene Partial Oxidation Coupled with Carbon Capture
The ethylene partial oxidation was first tested using a MEA-based electrolyzer with an active area of 1 cm2. The cell incorporated a ruthenium-based mixed oxide as the anodic catalyst. A reinforced cation-exchange membrane (DF2807, Dongyue Polymer Material., Ltd.) was used to separate the cathodic and anodic chambers. The lab-synthesized iron-single atom catalysts or 40% Pt on Vulcan XC72 (Fuel cell store) were used as catalysts for oxygen reduction reaction and carbon capture. 1 M NaCl is fed as an electrolyte on both sides. After switching to the ethylene oxidation paired with carbon capture, the anode remains in direct contact with the membrane, while a 2 mm microfluidic channel (Supplementary
To evaluate the local pH at the interface of the catalyst and the membrane in the MEA, we affixed a pH-sensitive dye, LysoSensor Green DND 189 (LSG), to the membrane and executed an in-situ photoluminescence study. We employed UV torch at 385 nm to collect fluorescence emissions via a spectrometer (Ocean Optics, QE Pro). The dyes were calibrated using solutions of varying pH levels (1-7) to determine their fluorescence, with 100 μM of the dyes dissolved in the solutions. And PL spectra of the standards were collected in a cuvette using a spectrometer (Ocean Optics, QE Pro), fiber-coupled UV LED (Ocean Optics), and a cuvette holder (ocean optics). LSG demonstrated fluorescence emission between 500 nm and 575 nm at a pH range of 1-7. Consequently, alterations in pH at the membrane interface can be examined by monitoring the peak shifts of the pH-sensitive dyes.
The in-situ kinetics NMR study is carried out using a 400 MHz Bruker Avance III HD Nanobay system. The ethylene chlorohydrin obtained from the electrochemical chloride-mediated ethylene partial oxidation was collected, which was then subjected to alkaline and neutral conditions by introducing stoichiometric amounts of sodium hydroxide and sodium bicarbonate. We used post-electrolysis ethylene chlorohydrin solution with a pH of 1.5 as our control experiment. Dimethyl sulfoxide in deuterium water is used as an internal standard. The one-dimensional 1H spectrum was acquired every two minutes to monitor the hydrolysis of ethylene chlorohydrin employing water suppression via a pre-saturation method.
In this work, all DFT calculations were performed with periodic slab models using the Vienna ab initio simulation package (VASP). The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was used. The projector-augmented wave (PAW) method was utilized to describe the electron-ion interactions, and the cut-off energy for the plane-wave basis set was 520 eV. All the configurations were optimized using a force-based conjugate gradient algorithm. We employed the D3 correction method proposed by Grimme et al. to correct the long-range dispersion interactions between the adsorbates and catalysts. Dipole correction was also considered to correct the electrostatic interaction resulting from the periodic images. The crystal orbital Hamilton population (COHP) analysis was performed using the Lobster 5.1.0 package.
In this study, we used in-situ photoluminescence to explore the electrochemical interface in the chloride-mediated ethylene oxidation, and we found the environment to be near-neutral at the membrane/anode interface, as a result of a pronounced pH gradient across the membrane. This observation highlights a trade-off, in this first attempt at implementing a membrane electrode assembly for anodic chloride-mediated ethylene oxidation, between ethylene oxidation FE and internal resistance (this latter contributing to a high full cell voltage). We thus explored using the process of CO2 capture on the cathodic side to consume OH− and mitigate undesired hydroxide counter-migration. Previous studies used pH gradients for electrochemical carbon capture—often relying on organic redox-active mediators or bipolar membranes. The former is limited to low current densities (<10 mA cm−2) and sensitivity to oxygen; while the latter relies on bipolar membranes and solid electrolytes, with the best reported full cell voltage of 1.9 V at 100 mA cm−2. The present study instead takes advantage of the pH gradient in ethylene oxidation using a cation-exchange membrane-based microfluidic electrolyzer for carbon capture, and operates at 1.8 V and 100 mA cm−2. We further developed tin-doped RuO2 that favors *Cl adsorption over *OH, shifting the selectivity towards chloride-mediated ethylene under near-neutral environment in the paired electrolyzer and achieve a 94% FE for chloride-mediated ethylene oxidation. For cathodic carbon capture, it demonstrates a 91% carbon capture efficiency in a 10% CO2 stream and captures 0.75 tonnes of CO2 per tonne of EG produced. This configuration lowers the total energy consumption of the system to 12.7 GJ/ton EG (with 6.6 GJ attributed to the electrolysis step), compared to 22.6 GJ/ton EG for traditional methods. Meanwhile, this approach offsets the carbon footprint of the fossil fuel-derived ethylene feedstock, leading to an estimated carbon intensity of 0.13 tonCO2 eq/tonEG, compared to the 1.2 tonCO2 eq/tonEG global average for ethylene glycol today.
In initial studies, we fabricated a zero-gap MEA electrolyzer; our purpose was to study and improve the ethylene partial oxidation reaction using a chloride-mediated mechanism. We provide NaCl electrolyte on each side, i.e. the initial catholyte and initial anolyte are each NaCl. We used RuO2 for chloride-mediated ethylene partial oxidation at the anode, and obtained an encouraging full cell voltage of 2.7 V at 100 mA cm 2; this compared to the 4.5 V observed in the conventional three-compartment flow cell. The cathodic reaction with which we paired the anodic process was the hydrogen evolution reaction, for which we used Pt/C as the catalyst. Unfortunately, the Faradaic efficiency (FE) was only 42% towards ethylene chlorohydrin in the MEA configuration.
We noted that the local pH at the anode catalyst is expected to impact the relative rates of the desired chloride oxidation for mediated ethylene oxidation versus the undesired oxygen evolution reaction. In our studies, we used the neutral electrolyte NaCl. During the electrolysis, the catholyte is expected to alkalify and the anolyte to acidify as Na+ transport across the cation exchange membrane and the reduction reaction produces OH−, while chloride oxidation yields hydrochloric acid and hypochlorous acid.
It would be important to evaluate the actual local pH at the membrane-anode interface, operando. After we operated the device for 30 minutes continuously, the bulk pH of the anolyte descended to 1.5 (measured using a pH meter). To study the local pH at the membrane-anode interface, we used in situ photoluminescence based on a pH-sensitive dye anchored onto the membrane. After subtracting the background from the spectra collected during the in-situ photoluminescence experiment, we found that the local pH at the membrane-anode interface is in the range 5-6.
We noted the large [OH−] gradient across the membrane: this could potentially lead to OH− diffusion, from cathode to anode, and could account for the local alkalinity on the anode side of the membrane.
This possibility motivated us to study pH effects on the anodic ethylene oxidation. Rotating ring-disc electrode (RRDE) measurements in pH 1 vs. pH 6 showed that, in acidic conditions, the desired chloride oxidation reaction in mediated ethylene oxidation is the predominant reaction. In contrast, at pH 6, OER overtakes chloride oxidation. We propose that competitive adsorption occurs between hydroxide and chloride ions on the catalyst surface, and that—in the presence of a high local [OH−] concentration—hydroxide adsorption leads to oxygen evolution.
A Route to Decrease Local pH on the Anode: Using CO2 Capture to Consume OH−
We contemplated whether a cathodic reaction—an alternative to HER-might serve as a “sink” for OH−, whose undesired counter-migration we posited was leading to the competitive adsorption between hydroxide and chloride ions on the anode catalyst. Better yet, we looked for an application that took advantage of, and consumed, this local flux of OH− on the cathodic side of the membrane.
CO2 capture appeared to be a promising such reaction: it would benefit from OH− generation, leading to carbonate formation in the catholyte; and would consume OH− and thus limit the diffusive flux across the membrane.
We implemented the ORR reaction to produce OH− using iron single-atom catalysts (Fe—N—C), and proceeded to estimate, experimentally, the CO2 capture efficiency: the ratio of {OH− consumed to convert CO2 into carbonate} to {the number of cathodically-generated hydroxide ions} (Methods). While the anode is in direct contact with membrane, we introduced ˜2 mm microfluidic channel between cathode and membrane to prevent salt precipitation.
We achieved a CO2 capture efficiency of 91% at current density of 100 mA cm−2. This was obtained when we used a gas feed stream composed of 10% CO2, 20% O2, and 70% N2. Gas chromatography and 1H nuclear magnetic resonance (NMR) spectroscopy revealed no detectable hydrogen or CO2 reduction products—an expected result given that the oxygen reduction reaction is more favorable than CO2 electroreduction/hydrogen evolution reaction.
When comparing ethylene oxidation paired with carbon capture versus hydrogen evolution in a microfluidic electrolyzer, introducing CO2 into the cathode gas inlet led to a pH of 11.4 instead of 13.7 in the prior case of HER. Pairing ethylene partial oxidation on the anode with ORR for CO2 capture on the cathode decreased the full cell voltage by over 1 V. When comparing the full cell voltage of ethylene oxidation coupled with ORR, both with and without carbon capture, we observed a decrease in cell voltage when carbon capture was implemented. This decrease can be attributed to a reduction in the pH gradient across the membrane, which in turn reduces the associated Nernst loss. Most strikingly, the FE for anodic ethylene partial oxidation increased from 40% to 71%, consistent with the hypothesis that using OH−—with the goal of lowering [OH−] supply on the cathode side of the membrane, and thus lowering the pH gradient at the membrane interface-improved local conditions on the anode towards ethylene partial oxidation.
Since even the improved FE of 71% left considerable room for improvement, we pondered whether the catalyst could be better designed to prefer chloride oxidation over oxygen evolution under near-neutral condition. We used DFT to study CIER vs. OER selectivity of RuO2 (110) and RuMOx (110) (M=V, W, Sn) by calculating the Gibbs free energy of chlorine (ΔG*O→*OCl) and hydroxyl (ΔG*O→*OOH) adsorption at pH 5. We find a nearly linear scaling relationship between ΔG*O→*OCl and ΔG*O→*OOH; and further find dopants have a more pronounced effect on *OH over *Cl. Specifically, Sn doping slightly increases ΔG*O→*OCl but significantly raises ΔG*O→*OOH, shifting selectivity from OER to CIER, making RuSnOx the most promising candidate for CIER at a near-neutral pH. RuSnOx is also projected to decrease Pourbaix energy and increase stability during chloride oxidation.
Experimentally we synthesized candidate catalysts using a hydrothermal method. Within the family considered in DFT, RuMOx (M=Sn, V, W), RuSnOx exhibited the highest ECSA-normalized chloride oxidation partial current density in rotating ring-disc electrode (RRDE) screening. We further tested the RuMOx for chloride-mediated ethylene oxidation at a constant potential of 1.8 V vs RHE. RuSnOx had a FE of 94% for ethylene chlorohydrin production, the highest among catalysts evaluated. When we analyzed the gaseous product using gas chromatography, we observed no measurable CO2, indicating that overoxidation of ethylene was substantially avoided in chloride-mediated ethylene partial oxidation. We conducted cyclic voltammetry studies in a non-chloride electrolyte. There are no appreciable differences with vs. without ethylene; and no ethylene oxidation products were detected in the liquid electrolyte. These findings suggest that ethylene oxidation occurs through a chloride-mediated pathway in the solution rather than directly on the catalyst surface. 13C-labeled ethylene was applied to investigate any 1,2 dichloroethane formation. The 13C-NMR results suggest that 2-chloroethanol is the only product of chloride-mediated ethylene oxidation.
We sought to understand, with the aid of in-situ X-ray Absorption Spectroscopy (XAS), the chemical origins of the increased operating stability of RuSnOx relative to RuO2. Across the wide range of applied anodic potentials from 1.0 to 1.8 V, ruthenium in RuSnOx is in a lower oxidation state than it is in RuO2 under the same operating conditions. The addition of Sn thus appears to militate against over-oxidation known to contribute to the degradation of RuO2.
We turned to in-situ Surface Enhanced Raman Spectroscopy (SERS) to study the binding energy of chloride ions, anticipating that this as a result of change in electronic structure and might correlate with the chloride oxidation activity. Cl adsorption on RuSnOx (271 and 335 cm−1) is shifted to a lower wavenumber compared to that observed on RuO2 (274 and 348 cm−1), indicating a weaker *Cl binding on RuSnOx relative to RuO2.
The influence of dopants on catalytic performance was further elucidated by analyzing the p-band center of the Oc site. This showed a linear correlation between p-band center and ΔG*O→*OCl. This suggests that Sn doping shifts the p bands away from the Fermi level, thereby weakening *Cl adsorption. A similar trend was observed with Bader charge analysis, where more negatively charged Oc sites in RuSnOx make it less likely to accommodate electrons from Cl−, thus reducing the adsorption strength of *Cl on Oc. Crystal orbital Hamilton population (COHP) analysis accords with this picture, for it shows a stronger Ru—Oc bond in RuSnOx, characterized by a shorter bond length and a lower integrated COHP value, this linked to weaker Oc—Cl binding.
We integrated chloride-mediated ethylene oxidation with carbon capture in a cation-exchange membrane-based microfluidic electrolyzer (
To produce ethylene glycol and release the captured CO2, we mixed—outside the electrolyzer—the post-carbon capture catholyte with the anolyte. This led to hydrolysis of ethylene chlorohydrin to ethylene glycol accompanied by the regeneration of CO2 and sodium chloride. The regenerated CO2 was measured using a water displacement method. Ethylene glycol production rates ranged from 180 μmol h−1 cm−2 at 10 mA cm−2, accompanied by 94% FE; to 1600 μmol h−1 cm−2 at 100 mA cm−2 at 85% FE and CO2 was regenerated at 4-118 ml h−1 cm−2. In-situ kinetic NMR showed that 95% conversion was achieved from {ethylene chlorohydrin and sodium carbonate} to {ethylene glycol and CO2}. Active chlorine species were not detected in the liquid products nor in the regenerated CO2 stream. Extending the hydrolysis time to 6 hours increased the overall conversion to 99%. We tested the integrated system at 100 mA cm−2 for 15 hours, finding that the voltage remained in the range 1.85-1.89 V, that the FE to EG remained above 81%, and that the carbon capture efficiency was stable in the range 89-92%. High-resolution TEM characterization and EDS mapping of RuSnOx were carried out, these data indicating that morphology is retained following stability tests.
In light of ratio among the rates measured above, the system will, for every tonne of ethylene glycol produced, capture 0.75 tonnes of CO2 (
Traditionally, the production of one ton of ethylene glycol results in the emission of 1.2 tons of CO2, with 0.8 tons arising from naphtha cracking to produce ethylene and 0.4 tons from ethylene overoxidation. When coupled with thermal naphtha cracking for ethylene production, the system contributes a gross negative CO2 emission component of 0.71 ton/ton EG, assuming CO2 sequestration. If we assume low-carbon-intensity wind electricity 2.86 kgCO2 eq/GJ for the electrosynthesis, this leads to an estimated net cradle-to-grave carbon intensity of 0.13 tonCO2 eq/tonEG, compared to the 1.2 tonCO2 eq/tonEG global average for ethylene glycol today. Techno-economic analysis suggests that the coupled system has the potential to produce ethylene glycol at an estimated ˜$520/tonEG compared to today's market price of $800-$1200/tonEG. The production cost breakdown of the base case suggests that feedstock, along with compression, separation, and sequestration, are the major contributors, followed by the electrolysis.
In this study, we demonstrated an electrochemical method for ethylene glycol production coupled with carbon capture in a single electrolyzer. The in-situ photoluminescence analysis revealed that the pH gradient across the electrolyzer membrane created a near-neutral microenvironment at the membrane-catalyst interface that adversely impacts ethylene oxidation efficiency. Seeking to address this, we integrated carbon capture at the cathode to mitigate OH− diffusion and developed a tin-doped ruthenium oxide catalyst to enhance ethylene oxidation selectivity. In-situ XAS, SERS coupled with DFT calculations suggest that tin doping increases the stability and activity of RuSnOx by tuning the oxidation state of ruthenium and promoting *Cl adsorption over *OH, thereby shifting selectivity towards chloride-mediated ethylene oxidation. The optimized system achieves 94% ethylene glycol FE and 91% carbon capture efficiency in a 10% CO2 stream. The integrated system requires 12.7 GJ of energy per tonne ethylene glycol produced and captures 0.75 tonnes of CO2, compared to the traditional 22.6 GJ. A cradle-to-gate analysis indicates that this approach can lower the carbon intensity of ethylene glycol production from fossil fuel-derived ethylene to 0.13 tonnes CO2 eq per tonne EG.
The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more.”
If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.
The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described to explain the principles of the disclosure and; as practical applications of the disclosure, to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents.
In recognition of the inherent nature of electrochemical processes, throughout the present disclosure, terms and phrases such as “absence,” “free,” “does not comprise,” “does not occur,” etc. encompass, but do not require a perfect absence of the referenced entity.
The term “type” as used herein refers to chemical formula such that a single type means the same chemical formula and different type means different chemical formula. Similarly, use of “more” as in “one or more” refers to use of different types of the relevant entity. Terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.
The present application claims priority to U.S. provisional patent application No. 63/607,143 that was filed Dec. 7, 2023, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63607143 | Dec 2023 | US |
