CO2 Bubbles Research Articles

High ebullitive, millennial‐aged greenhouse gas emissions from thermokarst expansion of peatland lakes in boreal western Canada

AbstractMethane (CH4) and carbon dioxide (CO2) emissions from small peatland lakes may be highly sensitive to climate warming and thermokarst expansion caused by permafrost thaw. We studied effects of thermokarst expansion on ebullitive CH4 and CO2 fluxes and diffusive CH4 fluxes from a peatland thaw lake in boreal western Canada. Ebullitive CH4 fluxes from the thaw edge (236 ± 61 mg CH4 m−2 d−1) were double and quadruple that of the stable lake edge and center, respectively. Modeled diffusive CH4 fluxes did not differ between the thawing and stable edges (~ 50 mg CH4 m−2 d−1) but were double that of the center. Radiocarbon (14C) analysis of CH4 and CO2 bubbles from the thaw edge was older (~ 1211 and 1420 14C yr BP) than from the stable edge and the center (modern to ~ 102 and 50 14C yr BP, respectively). Incubations indicated that deep, old peat sediment was more labile along the thaw edge than in the center. While our study suggested increase CH4 emissions partly derived from millennial‐aged carbon along the thaw edge, accounting for these emissions only increased the estimated total lake CH4 emissions by ~ 10%, which is a much smaller contribution than measured from thermokarst lakes in yedoma regions. Our study suggests that it is important to account for landscape history and lake types when studying the processes that govern the sensitivity of lake greenhouse gas emissions to climate change.

Review and Perspectives on CO2 Bubble Dynamic Characteristics in Different Liquids during Carbon Capture, Utilization, and Storage Process

Carbon dioxide (CO2) bubbles are common during carbon capture, utilization, and storage (CCUS) processes and have many impacts on water conservancy machinery, metallurgy, and the chemical industry. To explore the dynamic characteristics of CO2 bubbles in different liquids in CCUS, the motion mechanism of CO2 bubbles was integrated, and the effects of different liquid characteristics and different external conditions on the dynamic characteristics of CO2 bubbles were classified and summarized. At the same time, the research progress of numerical simulation on CO2 bubble dynamics is reviewed. Therefore, approaches and methods that can be further explored in theoretical analysis, experimental research, and numerical simulation of CO2 bubble dynamics are proposed, which can provide reference and guidance for engineering practice, especially CCUS technologies.

The DIC carbon isotope evolutions during CO2 bubbling: Implications for ocean acidification laboratory culture

Ocean acidification increases pCO2 and decreases pH of seawater and its impact on marine organisms has emerged as a key research focus. In addition to directly measured variables such as growth or calcification rate, stable isotopic tracers such as carbon isotopes have also been used to more completely understand the physiological processes contributing to the response of organisms to ocean acidification. To simulate ocean acidification in laboratory cultures, direct bubbling of seawater with CO2 has been a preferred method because it adjusts pCO2 and pH without altering total alkalinity. Unfortunately, the carbon isotope equilibrium between seawater and CO2 gas has been largely ignored so far. Frequently, the dissolved inorganic carbon (DIC) in the initial seawater culture has a distinct 13C/12C ratio which is far from the equilibrium expected with the isotopic composition of the bubbled CO2. To evaluate the consequences of this type of experiment for isotopic work, we measured the carbon isotope evolutions in two chemostats during CO2 bubbling and composed a numerical model to simulate this process. The isotopic model can predict well the carbon isotope ratio of dissolved inorganic carbon evolutions during bubbling. With help of this model, the carbon isotope evolution during a batch and continuous culture can be traced dynamically improving the accuracy of fractionation results from laboratory culture. Our simulations show that, if not properly accounted for in experimental or sampling design, many typical culture configurations involving CO2 bubbling can lead to large errors in estimated carbon isotope fractionation between seawater and biomass or biominerals, consequently affecting interpretations and hampering comparisons among different experiments. Therefore, we describe the best practices on future studies working with isotope fingerprinting in the ocean acidification background.

A mathematical model for single CO2 bubble motion with mass transfer and surfactant adsorption/desorption in stagnant surfactant solutions

Gas absorption into a liquid is an effective means of reducing the emission of environmentally unfavorable gases. The efficiency of the gas absorption is determined by the gas–liquid mass transfer. In this study, a mathematical model coupling gas–liquid mass transfer and surfactant adsorption/desorption with CO2 bubble motion in a bubble column is proposed. The kinetics of surfactant adsorption and desorption on the bubble surface are represented by two model parameters. To obtain the model parameters, we measured the eccentricity, rising velocity and volume of bubbles in a diameter range of 1.96–0.59 mm in stagnant surfactant solutions using high-speed photography. The instantaneous mass transfer coefficient is derived from the variation of the bubble volume with time. The effect of the accumulation of surfactant on the bubble shape, rising velocity, and mass transfer coefficient is discussed. The mathematical model is able to calculate the variation trends of the CO2 bubble diameter and rising velocity with an initial bubble diameter d less than 2 mm in surfactant solutions, which are consistent with the experimental results.

Irradiance penetration distribution and flashing light frequency simultaneously affected with microalgal cell absorption and CO2 bubble scattering in a raceway pond

In order to investigate light penetration and flashing light frequency for microalgal cell-CO2 bubble culture system in a raceway pond, user-defined function for CO2 mass transfer and bubble scattering models coupled with discrete ordinates radiation model were adopted to clarify simultaneous effects of microalgal cell absorption and CO2 bubble scattering. Light intensity along the microalgal suspension depth attenuated more rapidly with increased biomass concentration, decreased bubble generation diameter, increased CO2 gas content and incident light intensity. Ratio of light zone decreased from 81.13 % to 20.00 % when biomass concentration increased from 0 to 0.4 g/L because of light absorption and shading effects of microalgae. When bubble generation diameter increased from 0.1 to 1.6 mm, ratio of light zone increased from 37.95 % to 42.64 %, while microalgal flashing light cycle first decreased to a valley of 1.81 s at 0.8 mm and then increased. Local light intensity in the upper layers was more enhanced due to lots of CO2 bubbles gathering and reflecting more light with decreased bubble diameter and increased gas content. Light attenuated more rapidly in microalgal suspension with decreased bubble generation diameter and increased CO2 gas content because of increased bubble diffraction coefficient and contact area. When initial CO2 volume fraction increased from 0.02 to 0.2, flashing light frequency of microalgal cells decreased from 0.55 to 0.29 Hz and light zone time ratio φ decreased from 36.90 % to 18.40 %. At a biomass concentration of 0.1 g/L and a bubble flow rate of 0.1 m/s, the maximum light penetration and microalgal growth rate was achieved when bubble diameter, incident light intensity and gas content were optimally at 0.8 mm, 200 W/m2 and 0.02, respectively. This work provides data support and theoretical guidance for photobioreactor design and optimization of light energy utilization.

Surfactant in a Polyol-CO2 Mixture: Insights from a Classical Density Functional Theory Study.

Silicone-polyether (SPE) surfactants, made of a polydimethyl-siloxane (PDMS) backbone and polyether branches, are commonly used as additives in the production of polymeric foams with improved properties. A key step in the production of polymeric foams is the nucleation of gas bubbles in the polymer matrix upon supersaturation of dissolved gas. However, the role of SPE surfactants in the nucleation of gas bubbles is not well understood. In this study, we use classical density functional theory to investigate the effect of an SPE surfactant on the nucleation of CO2 bubbles in a polyol foam formulation. We find that the addition of an SPE surfactant leads to a ∼3-fold decrease in the polyol-CO2 interfacial tension at the surfactant's critical micelle concentration. Additionally, the surfactant is found to reduce the free energy barrier and affect the minimum free energy pathway (MFEP) associated with CO2 bubble nucleation. In the absence of a surfactant, a CO2-rich bubble nucleates from a homogeneous CO2-supersaturated polyol solution by following an MFEP characterized by a single nucleation barrier. Adding a surfactant results in a two-step nucleation process with reduced free energy barriers. The first barrier corresponds to the formation of a spherical aggregate with a liquid-like CO2 core. This spherical aggregate then grows into a CO2-rich bubble (spherical aggregate with a vapor-like CO2 core) of a critical size representing the second barrier. We hypothesize that the stronger affinity of CO2 for PDMS (than polyether) stabilizes the spherical aggregate with the liquid-like CO2 core, leading to a lower free energy barrier for CO2 bubble nucleation. Stabilization of such an aggregate during the early stages of the nucleation may lead to foams with more, smaller bubbles, which can improve their microstrustural features and insulating abilities.

Evaluation of CO2 absorption characteristics of low-cost Al2O3/MeOH nanoabsorbent using porous Nickel foam for high efficiency CO2 absorption system

This study proposes an effective strategy to enhance the capturing of CO2 using the Al2O3 nanoparticle-enhanced methanol absorbents with the porous metal foam, which requires no additional energy or operating cost. To investigate CO2 absorption performance, the viscosity and surface tension of Al2O3/MeOH nanoabsorbent under various conditions were measured. Moreover, the behavior of the CO2 bubble and absorption processes was analyzed. As a result, a CO2 mole fraction in the absorbents increased up to 379% when operating pressure increased to 1 MPa and it also increased up to 488% when a concentration of 0.1 wt% Al2O3 nanoparticles was added to the MeOH absorbent. Besides, when 0.1 wt% Al2O3/MeOH nanoabsorbent and porous Ni foam were used, CO2 absorption increased up to 503% compared to pure MeOH without the porous Ni foam. It was concluded that a hybrid system using Al2O3 nanoparticles and porous Ni foam significantly enhanced CO2 absorption due to the hydrodynamic and forced bubble-breaking mechanisms.

Violent Groundwater Eruption Triggered by a Distant Earthquake

AbstractIt is now well established that earthquakes cause various hydrogeological responses at distances thousands of kilometers from the epicenter. What remains unexplained is the large amplitude and intensity of some responses. Following the 2004 Mw 9.1 Sumatra earthquake, groundwater 3,200 km from the epicenter erupted violently from a well and formed a water fountain reaching a height exceeding 60 m. We model the relevant processes by combining tidal analysis of groundwater level with numerical simulations using a two‐dimensional finite‐element model. We suggest that the eruption resulted from a combination of factors, including a rapid increase of crustal permeability and runaway CO2 exsolution and bubble nucleation induced by the passage of seismic waves. Our results may have implications for some engineering applications such as oil production and CO2 sequestration, and the eruption of hydrothermal features such as geysers.

Effect of the number of hydroxyl groups of CO2-triggered surfactants on capability and performance in CO2-stimulated response

This paper reports the synthesis and characterization of three CO2-triggered surfactants (S-0, S-2, S-4) containing different number of hydroxyl groups. The impact of the hydroxyl groups on S-0, S-2, and S-4 was investigated by observing the morphological appearance, conductivity, and pH after CO2 bubbling. The surface tension of the three CO2-triggered surfactants decreased from S-0 to S-2 then to S-4, meaning surface tension decreasing with increasing the number of hydroxyl groups. The interfacial tension results showed that surfactants with more hydroxyl groups can better reduce the interfacial tension at a given pH. The pKa and micromorphology results revealed different degree of protonation of the CO2-triggered surfactants by CO2 in water, causing variations in their aggregation patterns. Molecular simulations revealed that increasing the number of hydroxyl groups increases the thickness of the hydration layer. And S-4 with a thicker hydration layer will more likely form a complex network structure than S-0 and S-2 with a thinner hydration layer. The new surfactants utilize a simple and mild approach to synthesis; solving problems such as insolubility and phase separation through the introduction of hydroxyl groups. The study serves as a guide to the application of CO2-trigger surfactant solutions.

Adsorption characteristics of six bisphenol compounds on magnetic three-dimensional nitrogen-doped carbon nanomaterials and their use in effervescent reaction-assisted dispersive microextraction

Herein, we successfully prepared magnetic Co/Ni-based N-doped 3D carbon nanotubes and graphene nanocomposites (CoNi@NGC) using a simple high-temperature calcination method. The CoNi@NGC nanocomposites were used as adsorbents to study their adsorption performances and underlying kinetic mechanisms for six types of bisphenol compounds (BPs) in water. They were also used as extractants, and acid-base effervescent tablets were used to enhance extractant dispersion with the aid of vigorous CO2 bubbling. Thus, a novel pretreatment method was developed, denoted effervescent reaction-assisted dispersive solid-phase microextraction (ER-DSM), which was combined with high performance liquid chromatography-fluorescence detection (HPLC-FLD) to rapidly quantify trace-level BPs in several drinks. The morphology and structure of the CoNi@NGC adsorbent were characterized in detail using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption and desorption (BET-BJH), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The CoNi@NGC nanocomposites were successfully doped with N and exhibited large specific surface areas (109.42 m2/g), abundant pores, and strong magnetic properties (17.98 emu/g).Key parameters were rigorously optimized to maximize the adsorption performance of CoNi@NGC, including adsorbent dosage, solution pH, temperature, and time. Under the constant conditions of pH=7, 5 mg of CoNi@NGC, initial BP concentrations of 5 mg/L, and 5 min of shaking at 298 K, the adsorption percentages of bisphenol M (BPM) and bisphenol A (BPA) reached respective maxima of 99.01% and 98.21%. Remarkably, those of bisphenol Z (BPZ), BPA, and BPM reached almost 100% after 90 min. The adsorption between the BPs and CoNi@NGC was mainly governed by hydrogen bonds, electrostatic interactions, and π-π conjugation. The entire adsorption process was consistent with Freundlich adsorption and a quasi-second-order kinetic equation, representing spontaneous adsorption. Via integration with HPLC-FLD, ER-DSM was used to rapidly extract and analyze trace-level BPs in six types of boxed drinks. Critical factors were optimized individually, including the type of eluent and elution time and volume, which influenced the enrichment effect. Under the optimized extraction conditions (pH=7, 5 mg CoNi@NGC, elution with 2 mL acetone for 6 min), the limits of detection and quantification of the novel extraction method were 0.06-0.20 and 0.20-0.66 μg/L, respectively. The intra- and inter-day precisions spanned the ranges 1.44%-4.76% and 1.69%-5.36%, respectively, and the recoveries in the actual samples were in the range 82.4%-103.7%. Moreover, the respective residual levels of BPA and BPB in peach juice samples were 2.09 and 1.37 μg/L. Regeneration studies revealed that the CoNi@NGC adsorbent could be reused at least five times, which significantly reduced the cost of evaluation. In summary, compared to other methods, this method displays the advantages of a high sensitivity, rapid extraction, and environmental friendliness, thereby exhibiting considerable potential for use in conventional monitoring of trace-level BPs in food matrices.

A Numerical Evaluation of the Lorentz Force Effect on CO2 Bubble Flow in the Aluminum Reduction Cell

A Numerical Evaluation of the Lorentz Force Effect on CO2 Bubble Flow in the Aluminum Reduction Cell

Study on CO2 bubble growth and detachment in liquid steel induced by thermal decomposition reaction with physical modeling

The bubbles have been widely applied in industrial processing, including steelmaking. Recently, industrial trials of natively generated bubbles via decomposition reactions have been successfully adopted in steel refining and inclusion removal. The refining efficiency was proved to be outstanding due to the small bubble sizes and the subsequent satisfying dynamic conditions. However, the bubble behaviors, including growth and detachment, are still not thoroughly clarified due to the strict requirements for observation conditions. Therefore, the growth and detachment behavior of the bubbles generated by decomposition reactions were carefully observed with physical modeling and shadow imaging method. The detachment sizes of the bubbles were extracted accordingly. Based on the statistical data on the detachment bubble sizes, a traditional nozzle flow model was modified for the prediction of the bubble detachment size in decomposition reactions. This work provides the foundation for further studies on the interaction mechanism between the natively generated bubbles and the impurities in liquid steel in terms of inclusion removal.

Effect of N2 and CO2 bubbles on gas volume fraction and flow pattern in a quasi-2D bubble column by shadow imaging

This study reports the effect of N2 and CO2 bubbles on dilute to dense gas-liquid two-phase bubbly flow. A shadowgraph imaging technique captured bubble images at a high spatiotemporal resolution. The recordings of bubble images allow us to compute gas fraction distribution. It requires challenging segmentation and gas-liquid interface detection approaches in image processing. Hence a novel gas contour characterization technique has been introduced in this study that analyses light intensity per pixel for quantifying the effect of local gas volume fraction. The dominant gas structure and repetitive gas pattern have also been determined here using Fourier transform-based power spectral density and 2D cross-correlation functions, respectively. Gas-liquid flow regimes of dissolved CO2 bubbles are found quite different than that of N2 bubbles. The plausible reasons are that gas fraction distribution at the sparger region may inhibit bubble coalescence and the positive surface charge of CO2 bubbles acts as a barrier to the interface deformation.

Kinetic Study on Reduction of FeO in a Molten HIsarna Slag by Various Solid Carbon Sources

To investigate the reduction behaviour of different reductants such as charcoal (CC), thermal coal (TC), and carbon black (CB) with HIsarna slag, a series of isothermal reduction experiments were performed in a vertical tube resistance furnace (VTF), coupled with a Quadrupole mass spectrometer (QMS) at 1450 °C, 1475 °C and 1500 °C. The results confirm that the highest overall reduction rate was achieved by CC, followed by TC and CB. The reduction mechanism between FeO containing molten slag and the selected carbonaceous materials is determined by studying the morphology of the water quenched samples at the intervals of 1.5, 3 and 5 minutes, using optical and scanning electron microscopes. The results reveal that the overall reaction is controlled by two main mechanisms: (1) nucleation and growth of CO bubbles, proceeded by the gaseous intermediates CO and CO2; and (2) diffusion of FeO in the molten slag. The initial reduction period in which chemical reaction control is dominant, can be described by the Avrami–Erofeev model, whereas the final period is described by the three-dimensional diffusion model.

Study on the process intensification of superaerophobic materials to improve CO2 mass transfer efficiency

Chemical absorption is the most widely used method in capturing CO2 from flue gas, in which the gas-liquid mass transfer process is the control step of the absorption rate; the spherical structure and easy flow characteristics of bubbles in the liquid phase affect the gas-liquid mass transfer efficiency. This study carefully examines the effect of superaerophobic surfaces on the mass transfer efficiency of CO2 bubbles on both dynamic and static behaviors. The results show that the 0.5 mol/L MDEA solution can absorb CO2 bubbles within 70 s when the CA (Contact Angle) of the superaerophobic surface bubbles reaches more than 150°. However, after contacting the superaerophilic substrate, the mass transfer area between the gas and liquid phases increases instantly and the CO2 bubbles burst rapidly and form a gas film within 18 ms. After that, the absorption saturation time of the absorption tower using superaerophilic packing is 25% less than that using untreated packing. Therefore, the superaerophilic packing can significantly increase the gas-liquid contact area and the mass transfer efficiency.

Encapsulated salts in velvet worm slime drive its hardening

Slime expelled by velvet worms entraps prey insects within seconds in a hardened biopolymer network that matches the mechanical strength of industrial polymers. While the mechanic stimuli-responsive nature and building blocks of the polymerization are known, it is still unclear how the velvet worms’ slime hardens so fast. Here, we investigated the slime for the first time, not only after, but also before expulsion. Further, we investigated the slime’s micro- and nanostructures in-depth. Besides the previously reported protein nanoglobules, carbohydrates, and lipids, we discovered abundant encapsulated phosphate and carbonate salts. We also detected CO2 bubbles during the hardening of the slime. These findings, along with further observations, suggest that the encapsulated salts in expelled slime rapidly dissolve and neutralize in a baking-powder-like reaction, which seems to accelerate the drying of the slime. The proteins’ conformation and aggregation are thus influenced by shear stress and the salts’ neutralization reaction, increasing the slime’s pH and ionic strength. These insights into the drying process of the velvet worm’s slime demonstrate how naturally evolved polymerizations can unwind in seconds, and could inspire new polymers that are stimuli-responsive or fast-drying under ambient conditions.

CO2 entrapment using 1–hexyl‐3–methyl‐imidazolium room temperature ionic liquids with multi-walled carbon nanotubes

Multi-walled carbon nanotube (MWCNT) enhanced 1–hexyl‐3–methyl‐imidazolium cation-based room temperature ionic liquids (RTILs) with different anions were investigated for CO2 capture. Besides, the viscosity, surface tension, and thermal stability of the samples were also investigated. Moreover, the behavior of CO2 bubbles captured and analyzed. Among various pristine RTILs, [HMIM][Tf2N] exhibited better CO2 capture capability compared to other ionic liquids; hence, MWCNT/[HMIM][Tf2N] nanoparticle enhanced ionic liquids (NEILs) were prepared and tested for CO2 absorption. As a result, the highest CO2 absorption capability or pressure reduction was observed at the pressure and MWCNT nanoparticles concentration of 1 MPa and 0.05 wt%, respectively. At the system pressure of 0.35, 0.6, and 1 MPa, the CO2 absorption capacities of 16.17%, 23.13%, and 31.30% were obtained at the temperature of 20 oC, 50 oC, and 20 oC, respectively, for 0.05 wt% MWCNT/[HMIM][Tf2N] NEIL. Furthermore, it was deduced that the effect of pressure and MWCNT nanoparticle concentration was superior to the temperature effect on the CO2 absorption capability of MWCNT/[HMIM][Tf2N] NEILs.

(Invited) Elucidating the Hydrodynamic Behavior of Multi-Species Gas Bubbles in an Electrochemical Solvent Regenerator for Direct Air Capture

Direct Air Capture (DAC) is very significant to bolstering the global drive towards net negative emissions. DAC technologies/plants have emerged in recent years, with the regeneration of the capture solvent used in the process being the major bottleneck of most aqueous technologies. [1] Leveraging electrochemical principles has offered a potential opportunity to simplify the entire solvent regeneration process and potentially reduce its overall capture cost, compared to traditional approaches. The electrochemical approach also offers the benefit of direct integrating clean energy, and also eliminating the high thermal energy requirements of typical methods.[2] Despite these potentials, the complex three-phase (solid-liquid-gas) interaction on the electrode surface pose a significant impediment to this electrochemical approach for DAC. The evolution of gas bubbles in electrochemical cells are well-known to contribute to energy losses in such reactors, from previous studies. [3],[4],[5] Gas bubbles have been shown to influence ohmic overpotentials in electrochemical reactors and studies have shown that the energy demand for water electrolysis can be reduced by 10-25 percent if the formation of gas bubbles is suppressed. [6],[7] However, the evolution of gas bubbles in electrochemical systems remains a complicated issue requiring further investigation. This study advances previous work by investigating the simultaneous evolution of CO2 gas bubbles along with O2/H2 gas bubbles in an electrochemical reactor for DAC. Gas bubbles are infamous for their ability to cover the active area of electrodes, limiting the transport of reactive species to the electrode surface, thus, increasing cell resistance. In this work, we explore changes in the polarization and hydrodynamics behavior of gas bubbles in the electrolyzer used for DAC solvent regeneration owing to the evolution of CO2 bubbles from pH swing, and the implications of the additional CO2 bubble formation to electrode surface coverage. By using a high-speed camera, we observe that bubbles coverage appears to be larger at the edges of the electrodes, and that the orientation of the electrodes influence bubble coalescence and detachment rate. We also employ different cell designs to mitigate the impact of bubble surface coverage towards reducing cell resistance. References Sabatino, A. Grimm, F. Gallucci, M. Van Sint Annaland, G. J. Kramer, M. Gazzani, Joule, 5(8), 2047-2076 (2021).Gao, A. Omosebi, R. Perrone, K. Liu, Journal of The Electrochemical Society (2022).H. Li, Y. J. Chen, Scientific Reports, 11(1), 1-12 (2021).F. Swiegers, R. N. L.Terrett, G. Tsekouras, T. Tsuzuki, R. J. Pace, R. Stranger, Sustainable Energy & Fuels, 5(11), 3004–3004 (2021).Zhao, H. Ren, L. Luo, Langmuir, 35(16), 5392-5408 (2019).Mazloomi, N. B. Sulaiman, H. Moayedi, International Journal of Electrochemical Science, 7(4), 3314-3326 (2012).C. Wang, C. Y. Chen, Electrochimica Acta, 54(15), 3877-3883 (2009).

Modelling the Electrochemical Reduction of CO2 Under Gas-Liquid Channel Flow

Electrochemical reduction of CO2 using renewable energy sources is a promising avenue for sustainable production of bulk chemicals. The feasibility of electrochemical CO2 conversion has been demonstrated at lab scale, leading researchers to propose several reactor designs. However, CO2 electrolysis in aqueous systems is severely limited by mass transfer leading to performance parameters insufficient for industrial application. A strategy to enhance mass transfer is to actively introduce CO2 as a gas flow, while keeping diffusion paths between reactants and catalyst short, by separating the gas flow from the liquid electrolyte through a gas diffusion electrode. However, flooding, salt formation, or drying out of the gas diffusion electrode are common problems and present a major obstacle towards commercialisation. A promising reactor concept that enhances mass transfer without the complexity of a gas diffusion electrode is a structured reactor operated under gas-liquid Taylor flow: gas–liquid flow consisting of elongated bubbles in micro- or milli-channels. While this is a proven concept to enhance mass transfer for heterogeneous catalysis in flow cells, literature on this approach for electrochemical processes is scarce and the effect of process conditions on the reactor performance are poorly understood.In this work, we propose a tubular cell design, inspired from the field of fuel cells, for CO2 electrolysis with a zero-gap membrane electrode assembly. We further, develop a simple analytical model revealing how reactor performance in terms of faradaic efficiency and current density is governed by the key features of Taylor flow. These features film thickness, bubble velocity, and volume fraction of CO2 bubbles over aqueous electrolyte, for a given cathode potential.We find that the film thickness and the volume ratio of CO2/electrolyte fed to the reactor significantly affect the limiting current density and the faradaic efficiency. Additionally, we find industrially relevant performance with faradaic efficiencies (> 90 %) at current densities of up to 500 mA cm-2, when operating the reactor at elevated pressure beyond 5 bar. This demonstrates the general potential of this reactor concept to overcome mass transfer limitations in the field of electrolysis. We compare our predictions with numerical simulations, showing good agreement for a large window of operation conditions, illustrating when the simple predictive expressions for the current density and faradaic efficiency can be applied. We will discuss the importance of including interdependencies on the reactor scale to assess the economic viability of a reactor design and presents a tool to evaluate reactor design choices. We expect that the simple predictive expressions are instrumental in guiding experimental studies and reactor design choices, taking into account both technical and economic considerations.

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system