CO2 Diffusion Research Articles

Conversion of SOD zeolite into type I porous liquid and preparation of mixed matrix membrane with AO-PIM for efficient gas separation

Low-silica SOD zeolites are among the most promising inorganic materials for mixed matrix membranes (MMMs). However, the gas separation performance is severely hindered by the non-selective voids formed by both the zeolite and polymer membranes, as well as the rigid layer. In this work, SOD-liquid-M2070 PL type I porous liquid was synthesized and subsequently filled into an Amidoxime-functionalized polymer of intrinsic microporosity (AO-PIM) to prepare MMMs. The fillers and MMMs were characterized using FTIR, SEM, TGA, XRD, and gas permeation techniques. SOD-liquid-M2070 PL facilitates the rapid diffusion of CO2 and H2 gas molecules for efficient gas separation. The liquid-like fluidity of SOD-liquid-M2070 PL improves the formation of non-selective pores in the SOD and polymer matrix membranes to enhance gas permeability and selectivity. The CO2, H2 permeability and CO2/N2, H2/N2 selectivity of MMMs composed of 5 wt% SOD-liquid-M2070 PL with optimal filling ratio were increased by 248%, 246%, and 173%, 222%, respectively, compared with pure membranes. It exceeds the 2008 Robeson limit for H2/N2 and approaches much closer to the 2019 Robeson limit for CO2/N2. The field of green environment presents a promising development prospect for low silica SOD zeolite, which exhibits high separation efficiency.

The amine-functionalized alumina captures CO2 directly from the ambient air in the rotating adsorption bed

Global warming presents formidable challenges, prompting the exploration of Direct Air Capture (DAC) as a promising solution. This study employed the ultrasonic impregnation method to load polyethyleneimine (PEI) onto cost-effective millimeter-sized spherical γ-Al2O3 microspheres, thereby preparing an efficient amine-modified adsorbent. Characterization reveals a uniform dispersion of PEI, resulting in an adsorbent with an effective pore structure, enhancing CO2 diffusion. The adsorption experiment combines DAC with high gravity technology, best conditions at a PEI load of 16.37%, high gravity factor of 2.67, and gas flow rate of 30 L/min. Under these conditions, an impressive adsorption capacity of 41.75 mg/g was achieved, marking an increase of 12.11 mg/g compared to the traditional fixed-bed method. The amine efficiency also reaches 0.25. The Freundlich model outperforms the Langmuir model in fitting isotherm curves, suggesting that the experimental data align with the characteristics of a heterogeneous surface and multilayer adsorption. The fitting results of kinetic models further show that RAB's adsorption rate constant has a significantly better fitting value compared to traditional fixed bed methods. The research provides valuable insights for the application and development of DAC technology, enabling new possibilities for future carbon capture and emission reduction efforts.

Green preparation of poly (butylene succinate-co-butylene terephthalate) foam with tunable degradability and mechanical properties by supercritical CO2

Poly (butylene succinate-butylene terephthalate) (PBST) with different chain segments was synthesized by in-situ polycondensation, and foams were prepared by supercritical CO2 foaming. The crystallinity and tensile modulus of PBST increases with the aromatic content, slowing down the diffusion of CO2 and enhancing the dimensional stability of PBST foam. The rheological analysis reveals that a higher temperature of PBST modulus platform is correlated with a higher aromatic content, which is more conducive to the cell stability. The foaming temperature window is 60 - 80 °C at 30% aromatic content, which moves to 160 - 175 °C at 70% aromatic content, and the maximum expansion ratio of PBST foam decreases from 40.7 to 9.8. With the increase of aromatic content from 30% to 70%, there is an obvious improvement in the compressive modulus of PBST foam, from 0.92 MPa to 6.65 MPa, accompanied by a reduction in the weight loss rate of degradation decreased from 10.78% to 3.04% in 10 days. Hence, there is a careful balance between degradability and foamability of PBST foams. Introducing a suitable aromatic content obtained higher strength to improve the cell stability on the premise that the strong degradability can be maintained, which provides an effective strategy to prepare PBST foams with good degradability and favorable mechanical properties.

Study on microscale stress sensitivity of CO2 foam fracturing in tight reservoirs

With huge reserves and wide distribution, tight oil and gas resources are the focus and hotspot of unconventional oil and gas research in recent years. In this paper, firstly, the multi-scale model of CO2 fracturing gas is established by considering the phase evolution characteristics of CO2. Secondly, considering the hydrophilicity of the tight reservoir, a microscale seepage model of CO2 under the adsorption condition of fracturing fluid is proposed. Again, considering the shrinkage effect of dense reservoir matrix, a dynamic coupling model of gas-liquid-solid under CO2 fracturing conditions is established. The results show that: (a) When the volume of the adsorbed layer of CO2 fracturing fluid accounts for 10% of the pore volume and the CO2 concentration is 20%, the fluid transport in the tight reservoir shows significant separation characteristics. (b) More CO2 enters the crude oil after considering the diffusion effect of CO2 body. The influence of CO2 diffusion mechanism on oil recovery should not be neglected. (c) Enhancement of elastic energy is one of the main mechanisms by which CO2 improves oil driving efficiency in tight reservoirs.

Unraveling the evolution of Cathode–Solid electrolyte interface using operando X-ray Photoelectron spectroscopy

Understanding the evolution of the solid electrolyte-electrode interface is currently one of the most challenging obstacles in the development of solid-state batteries (SSBs). Here, we develop an X-ray Photoelectron Spectroscopy (XPS) that allows for operando measurement during cycling. Based on theoretical analysis and the modulated electrode and detector co-grounding mode, the displacement of binding energy can be correlated with the surface electrostatic potential of the material, revealing the charge distribution and composition evolution of the space charge layer between the cathode and the electrolyte. In the investigation of typical LiCoO2 (LCO)/Li6PS5Cl (LPSC)/Li–In batteries, we observed the static potential difference and oxidative decomposition between LPSC and LCO, and the effectiveness of the LiNbO3 coating in reducing potential difference and inhibiting the diffusion of Co and oxidation of S species. Furthermore, our study also revealed that the potential drop between LiNi0·8Co0·1Mn0·1O2 and LPSC is smaller than that of LCO, whilst that between Li3InCl6 and LCO remains near zero. The proposed operando XPS method offers a novel approach for real-time monitoring of interface potential and species formation, providing rational guidance for the interface engineering in SSBs.

Simultaneous impacts of H2 and CO2 transport on NO formations of premixed and diffusion opposed flames fueled by biogas-H2 blends

With the numerical simulation, the transport impacts of H2 and CO2 on the NO formations of premixed and diffusion opposed biogas-H2 flames were isolated quantitatively by using the fictious species method. The combined and individual impacts of H2 and CO2 transport on the NO concentrations, radical pools and critical reactions were compared and investigated comprehensively. The results show that the NO concentration of diffusion flame can be increased steadily with either H2 or CO2 transport, while the NO concentration of the premixed flame can be increased and decreased at fuel-lean and fuel-rich conditions respectively owing to the dominant role of H2 transport in the coupling transport influence. The CO2 transport is confirmed to have the effective influence on the NO formations in the fast reaction zones of the premixed flames based on the convection-diffusion-reaction (CDR) budget analysis, but its effects on the NO concentration are weakened effectively owing to that the NO production in the post-flame zone plays a more dominant role in the NO concentration of the premixed flame. Additionally, the H2 and CO2 transport have the opposite impacts on the major NO production/destruction reactions in the premixed flame but they exert negative or positive effects simultaneously in the diffusion flame. In either premixed or diffusion flame, the H2 and CO2 transport can influence the NO production primarily by affecting the NO/NO2 conversion rate, the thermal route (N + OHNO + H) and the NNH intermediate route (HNO + HH2+NO). Particularly, unlike the CO2 transport effects on the thermochemistry identified in our previous studies, the CO2 transport is found to be relatively insignificant to the NO generation of the premixed biogas-H2 flame. Meanwhile, for the NO production in the diffusion biogas-H2 flame, the CO2 transport effects could account for around 25% of total transport effects of H2 and CO2, suggesting that the CO2 transport should be not neglected when investigating the NO production in the diffusion biogas-H2 flame.

Two-dimensional interfacial enhanced CO2 adsorption performance of porous organic amine solids: Structure-activity relationships and DFT calculations

The utilization of inexpensive and efficient amine-functionalized adsorbents has become a research hotspot in post-combustion capture technology. Meanwhile, the structure of the support and the selection of organic amines are the primary considerations affecting the CO2 adsorption performance. Herein, the novel solid amine adsorbent materials with amine-support interfacial effect were successfully synthesized in this study by loading four organic amines (TETA, TEPA, PEHA, and PEI) onto expanded vermiculite (EVMT) support with the layered structure. The results indicated that EVMT-50TETA exhibited superior CO2 adsorption capacity (132.5 mg/g) along with effective regeneration capability. This was attributed to the unique layered structure of EVMT that facilitates the dispersion of TETA on its surface or between layers as well as the formation of hydrogen bonds between surface functional groups (–OH) and amines to enhance the amine-support interfacial interaction. Furthermore, the minimal volume expansion of TETA during CO2 adsorption enables improved diffusion of CO2 in channels and enhanced accessibility to active sites. DFT calculations show higher binding energies and faster CO2 adsorption-diffusion rates between TETA and EVMT support. In situ DRIFTS experiments revealed that the process of CO2 adsorption followed the zwitterion mechanism, in which the zwitterion can be reversibly deprotonated to form ammonium carbamate and carbamic acid. This study provides comprehensive insights into the supports and amines interfacial effects through systematic investigation, offering both simplified synthesis strategies and profound theoretical support for studying solid amine adsorbents.

Synthesis of amine-pillar[5]arene porous adsorbent for adsorption of CO2 and selectivity over N2 and CH4

A novel amine-modified pillar[5]arene bonded porous silica adsorbent (DETA-P5S) was designed to be applied to dynamic CO2 adsorption and selective separation of CO2 over N2 and CH4 gases mixture. The results demonstrated that reasonable introduction of DETA into the BE-P5 bonded silica support has significantly increased the adsorption capacity of CO2. The DETA-P5S has the optimal adsorption capacity of 9.1 mmol/g with 5 vol% CO2 at 40 °C. The main reason of this increased capacity could be attributed to the enhanced CO2 diffusion into porous adsorbent for its better dispersion in the pores of amine-pillar[5]arene cavity and active site of DETA. Furthermore, the dynamic saturation adsorption capacities of DETA-P5S were 7.11 (0.37) and 6.18 (0.44) mmol/g for CO2/N2 and CO2/CH4, respectively, both the gas mixtures showed high separation selectivity. Simultaneously, the DETA-P5S can maintain outstanding CO2 adsorption capacity after fifteen regeneration cycles. Consequently, the designed DETA-P5S could serve as a promising adsorbent for CO2 capture and storage.

Does stomatal patterning in amphistomatous leaves minimize the CO2 diffusion path length within leaves?

Abstract Photosynthesis is co-limited by multiple factors depending on the plant and its environment. These include biochemical rate limitations, internal and external water potentials, temperature, irradiance and carbon dioxide (CO2). Amphistomatous leaves have stomata on both abaxial and adaxial leaf surfaces. This feature is considered an adaptation to alleviate CO2 diffusion limitations in productive environments as the diffusion path length from stomate to chloroplast is effectively halved in amphistomatous leaves. Plants may also reduce CO2 limitations through other aspects of optimal stomatal anatomy: stomatal density, distribution, patterning and size. Some studies have demonstrated that stomata are overdispersed compared to a random distribution on a single leaf surface; however, despite their prevalence in nature and near ubiquity among crop species, much less is known about stomatal anatomy in amphistomatous leaves, especially the coordination between leaf surfaces. Here, we use novel spatial statistics based on simulations and photosynthesis modelling to test hypotheses about how amphistomatous plants may optimize CO2 diffusion in the model angiosperm Arabidopsis thaliana grown in different light environments. We find that (i) stomata are overdispersed, but not ideally dispersed, on both leaf surfaces across all light treatments; (ii) the patterning of stomata on abaxial and adaxial leaf surfaces is independent and (iii) the theoretical improvements to photosynthesis from abaxial–adaxial stomatal coordination are miniscule (≪1%) across the range of feasible parameter space. However, we also find that (iv) stomatal size is correlated with the mesophyll volume that it supplies with CO2, suggesting that plants may optimize CO2 diffusion limitations through alternative pathways other than ideal, uniform stomatal spacing. We discuss the developmental, physical and evolutionary constraints that may prohibit plants from reaching this theoretical adaptive peak of uniform stomatal spacing and inter-surface stomatal coordination. These findings contribute to our understanding of variation in the anatomy of amphistomatous leaves.

Basal ABA signaling balances transpiration and photosynthesis.

The balance between the CO2 entry for photosynthesis and transpiration water loss is crucial for plant growth, and ABA signaling can affect this equilibrium. To test how ABA balances plant growth and environmental adaptation, we performed molecular genetics studies in the biotech crop Nicotiana benthamiana under well-watered or drought conditions. Studies on ABA signaling in crops are complicated by the multigenic nature of the PYR/PYL/RCAR ABA receptor family and its functional redundancy, which is particularly challenging in polyploid plants. We have generated a pentuple pyl mutant in the allotetraploid Nicotiana benthamiana through CRISPR/Cas9 gene editing. The pentuple mutant is impaired in 2 NbPYL1-like and 3 NbPYL8-like receptors, affecting the regulation of transpiration and several ABA-dependent transcriptional processes. RNA-seq and metabolite analysis revealed that the synthesis of galactinol, an essential precursor for the osmoprotective raffinose family of oligosaccharides, is ABA-dependent and impaired in the mutant under osmotic stress. In contrast, our results show that, under well-watered conditions, partial inactivation of ABA signaling leads to higher CO2 entry and photosynthesis in the mutant than in WT. Photosynthesis analyses revealed an increased CO2 diffusion capacity mediated by higher stomatal and mesophyll conductances, and higher substomatal CO2 concentration in the pentuple mutant. RNA-seq analyses revealed that genes associated with cell wall loosening (e.g., expansins) and porosity were strongly downregulated by ABA in WT. In summary, a partial relief of the ABA control on transpiration mediated by ABA receptors positively affects photosynthesis when water is not limited, at the expense of reduced water use efficiency.

Peanut photosynthesis response to drought can include diffusive and biochemical limitations depending on cultivar.

Photosynthesis, understood as the photosynthetic carbon assimilation rate, is one of the key processes affected by drought stress. The effects can be via decreased CO2 diffusion and biochemical constraints. However, there is still no unified consensus about the contribution of each mechanism to the drought response. This research assessed the underlying limitations to photosynthesis in nine peanut genotypes (Arachis hypogaea L.) with different water strategies (water savers vs water spenders) under progressive drought. Water saver cultivars close the stomata earlier during drought, resulting in decreased transpiration and photosynthesis, which results in less water depletion in the soil, while water spenders maintain the stomata open during drought. In order to test the performance of these genotypes, growth, transpiration per plant, gas exchange measurements, chlorophyll fluorescence and A/Ci response curves were analyzed under drought and well-watered conditions. In general, drought first affected photosynthesis (at the leaf and canopy level) via stomatal closure and then by impacts on chlorophyll fluorescence in all genotypes, but at different intensity levels. The maximum rate of carboxylation and the maximum rate of electron transport, physiological characteristics related to biochemical constraints, were not affected during the onset of drought, but they were decreased at the end of the drought period, with the exception of the PI 493329 genotype that showed higher stomatal conductance due to a bigger root system. The findings presented here highlight the importance of genetic variation in the photosynthetic response of peanut to drought, which should be considered when breeding for future climates.

Spatio-temporal sequence prediction of CO2 flooding and sequestration potential under geological and engineering uncertainties

CO2 injection for subsurface hydrocarbon development not only enhances oil and gas recovery but also enables CO2 sequestration in the subsurface. It is essential to develop effective methods for evaluating the potential of CO2 flooding and sequestration. Despite the existence of methods for predicting the effectiveness of hydrocarbon development using historical production data, insufficient emphasis has been placed on adequately incorporating geological and engineering uncertainty information to enhance prediction accuracy. To address this issue, a novel spatial-temporal ResNet (ST-ResNet) model is proposed for predicting hydrocarbon production, CO2 sequestration volume and CO2 diffusion pattern in the subsurface, which represent the CO2 flooding and sequestration potential. First, high-dimensional reservoir property fields are parameterized using the combined method of principal component analysis and discrete cosine transform (PCA-DCT). Second, the spatial sequence information of various reservoir property fields is extracted with features based on residual neural network (ResNet). Then, the time series information such as dynamic well control parameters is encoded with stacked BiLSTM (SBiLSTM). Specifically, the ST-ResNet model incorporates the above modules to overcome the limitations of collaborative consideration of temporal and spatial information involved in subsurface hydrocarbon development. Comparison between simulation and prediction results on the 2D/3D reservoir model reveals a significant achievement in prediction accuracy by the ST-ResNet model (with R2 and SSIM scores of 0.947, 0.911 and 0.937, 0.922, respectively). In comparison to CNN, LSTM and their combined approach CNN-LSTM, the ST-ResNet model demonstrates an improvement of 3% to 5% in R2, along with reductions of 20% to 30% in MAE and 15% to 25% in RMSE, respectively. These results highlight the superior stability and generalization of the ST-ResNet model. The contribution of this work is to provide a more accurate and efficient prediction tool to guide the integrated development of CO2 flooding and sequestration in subsurface hydrocarbon reservoirs, which facilitates decision-making processes for engineers.

Hydrogen bond unlocking-driven pore structure control for shifting multi-component gas separation function

Purification of ethylene (C2H4) as the most extensive and output chemical, from complex multi-components is of great significance but highly challenging. Herein we demonstrate that precise pore structure tuning by controlling the network hydrogen bonds in two highly-related porous coordination networks can shift the efficient C2H4 separation function from C2H2/C2H4/C2H6 ternary mixture to CO2/C2H2/C2H4/C2H6 quaternary mixture system. Single-crystal X-ray diffraction revealed that the different amino groups on the triazolate ligands resulted in the change of the hydrogen bonding in the host network, which led to changes in the pore shape and pore chemistry. Gas adsorption isotherms, adsorption kinetics and gas-loaded crystal structure analysis indicated that the coordination network Zn-fa-atz (2) weakened the affinity for three C2 hydrocarbons synchronously including C2H4 but enhanced the CO2 adsorption due to the optimized CO2-host interaction and the faster CO2 diffusion, leading to effective C2H4 production from the CO2/C2H2/C2H4/C2H6 mixture in one step based on the experimental and simulated breakthrough data. Moreover, it can be shaped into spherical pellets with maintained porosity and separation performance.

Understanding the Positive Role of Ionic Liquids in CO2 Capture by Poly(ethylenimine).

CO2 capture technology is one of the most important technical methods for significantly mitigating CO2 emissions in a low-carbon context. The recent invention of mixed absorbents comprising poly(ethylenimine) (PEI) and ionic liquids (ILs) provides a novel strategy for efficiently capturing CO2, and this has garnered widespread attention. However, the intermolecular interactions between the IL and other constituents during the CO2 absorption process remain unclear. In this present work, a series of density functional theory (DFT) calculations and molecular dynamics simulations were conducted to investigate the positive role of IL in CO2 capture by PEI. The results showed that the formation of hydrogen bonds between the IL anion and the amino groups of PEI primarily drives the addition of IL to PEI. During the CO2 absorption process, the IL anion not only can absorb CO2 but also exerts a dehydrogenation effect on the amino group of PEI, facilitating enhanced interaction between PEI and CO2. Additionally, the IL substantially reduces the viscosity of PEI, promoting the diffusion of CO2 within the system and enhancing the absorption rate. Based on the information on interaction energy and viscosity, we can easily make theoretical predictions for the optimal proportion of IL to be added. The above results provide fundamental insights to promote the industrial application of the PEI/IL system for CO2 capture.

Skin temperature influence on transcutaneous carbon dioxide (CO2) conductivity and skin blood flow in healthy human subjects at the arm and wrist.

Objective: present transcutaneous carbon dioxide (CO2)-tcpCO2-monitors suffer from limitations which hamper their widespread use, and call for a new tcpCO2 measurement technique. However, the progress in this area is hindered by the lack of knowledge in transcutaneous CO2 diffusion. To address this knowledge gap, this study focuses on investigating the influence of skin temperature on two key skin properties: CO2 permeability and skin blood flow. Methods: a monocentric prospective exploratory study including 40 healthy adults was undertaken. Each subject experienced a 90 min visit split into five 18 min sessions at different skin temperatures-Non-Heated (NH), 35, 38, 41, and 44°C. At each temperature, custom sensors measured transcutaneous CO2 conductivity and exhalation rate at the arm and wrist, while Laser Doppler Flowmetry (LDF) assessed skin blood flow at the arm. Results: the three studied metrics sharply increased with rising skin temperature. Mean values increased from the NH situation up to 44°C from 4.03 up to 8.88 and from 2.94 up to 8.11 m·s-1 for skin conductivity, and from 80.4 up to 177.5 and from 58.7 up to 162.3 cm3·m-2·h-1 for exhalation rate at the arm and wrist, respectively. Likewise, skin blood flow increased elevenfold for the same temperature increase. Of note, all metrics already augmented significantly in the 35-38°C skin temperature range, which may be reached without active heating-i.e. only using a warm clothing. Conclusion: these results are extremely encouraging for the development of next-generation tcpCO2 sensors. Indeed, the moderate increase (× 2) in skin conductivity from NH to 44°C tends to indicate that heating the skin is not critical from a response time point of view, i.e. little to no skin heating would only result in a doubled sensor response time in the worst case, compared to a maximal heating at 44°C. Crucially, a skin temperature within the 35-38°C range already sharply increases the skin blood flow, suggesting that tcpCO2 correlates well with the arterial paCO2 even at such low skin temperatures. These two conclusions further strengthen the viability of non-heated tcpCO2 sensors, thereby paving the way for the development of wearable transcutaneous capnometers.

SAGA1 and SAGA2 promote starch formation around proto-pyrenoids in Arabidopsis chloroplasts

The pyrenoid is a chloroplastic microcompartment in which most algae and some terrestrial plants condense the primary carboxylase, Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) as part of a CO2-concentrating mechanism that improves the efficiency of CO2 capture. Engineering a pyrenoid-based CO2-concentrating mechanism (pCCM) into C3 crop plants is a promising strategy to enhance yield capacities and resilience to the changing climate. Many pyrenoids are characterized by a sheath of starch plates that is proposed to act as a barrier to limit CO2 diffusion. Recently, we have reconstituted a phase-separated "proto-pyrenoid" Rubisco matrix in the model C3 plant Arabidopsis thaliana using proteins from the alga with the most well-studied pyrenoid, Chlamydomonas reinhardtii [N. Atkinson, Y. Mao, K. X. Chan, A. J. McCormick, Nat. Commun. 11, 6303 (2020)]. Here, we describe the impact of introducing the Chlamydomonas proteins StArch Granules Abnormal 1 (SAGA1) and SAGA2, which are associated with the regulation of pyrenoid starch biogenesis and morphology. We show that SAGA1 localizes to the proto-pyrenoid in engineered Arabidopsis plants, which results in the formation of atypical spherical starch granules enclosed within the proto-pyrenoid condensate and adjacent plate-like granules that partially cover the condensate, but without modifying the total amount of chloroplastic starch accrued. Additional expression of SAGA2 further increases the proportion of starch synthesized as adjacent plate-like granules that fully encircle the proto-pyrenoid. Our findings pave the way to assembling a diffusion barrier as part of a functional pCCM in vascular plants, while also advancing our understanding of the roles of SAGA1 and SAGA2 in starch sheath formation and broadening the avenues for engineering starch morphology.

Implementation and Adaptability Analysis of Numerical Simulation for Shale Oil CO2 Huff and Puff

Carbon dioxide (CO2) is being considered for use to enhance oil recovery and resource utilization and storage, with wide technical adaptability. In this paper, a numerical simulation method is used to study the adaptability of CO2 huff and puff in shale reservoirs. A fluid model introduces the nanoconfinement effect and reflects the nanoconfinement effect using the fluid p–T phase diagram. This method uses local grid refinement and changes the permeability near the grid to characterize the reservoir reconstruction volume (SRV) fracture network while considering the CO2 diffusion effect. The results indicate that by using the incremental recovery rate and oil change rate as references, adaptive charts can be obtained for different Kf/Km and oil saturation. When Kf/Km is 1000 and the increase in the CO2 recovery rate reaches 1.5%, the lower limit of oil saturation is 0.54. When Kf/Km is 1000 and the increase in the CO2 recovery rate reaches 2%, the lower limit of oil saturation is 0.57. When the oil saturation is 0.5 and the CO2 huff and puff oil change rate reaches 0.3, the lower limit of Kf/Km is 700. Finally, when the oil saturation is 0.548 and the CO2 huff and puff oil change rate reaches 0.6, the lower limit of Kf/Km is 10. The research results are significant and can guide the design and application of on-site CO2 throughput test plans.

Enhanced oil recovery via dissolution of low molecular weight PDMS in CO2 during immiscible gas injection in matrix-fracture system

Oil recovery in natural fracture reservoirs can be improved by reducing the capillary force during the gravity drainage process in matrix-fracture system. In the current study, a modified gas was generated via dissolution of low molecular weight poly(dimethyl siloxane) (PDMS, average Mw 3780 g/mol, 10000 – 50000 ppm) in CO2 to enhance oil recovery at 50 °C or 70 °C and 3000 psi. Cloud point measurements indicated that PDMS dissolved in CO2 at pressures less than 3000 psi, which was below the minimum miscibility pressure (MMP) of ∼3600 psi at 70 °C determined with the vanishing interfacial technique. The solution density increased from 669.6 kg/m3 for pure CO2 to 780.3 kg/m3 for CO2/PDMS (50000 ppm) at 70 °C and 3000 psi, thereby reducing the density difference between the CO2-rich fluid and crude oil (ρo=865.2 kg/m3) in matrix-fracture system. Also, CO2-oil interfacial tension (IFT) was reduced from 65 to 15 dyn/cm via the dissolution of 50000 ppm PDMS in CO2. Therefore, it led to the CO2 diffusion coefficient increased in both reservoir-fluid saturated porous media and bulk oil scenarios 3–4 fold and 4–7 fold respectively in comparison to pure CO2 injection. These PDMS-induced changes reduced the capillary effects in gas-invaded zone, which consequently led to an increase in oil recovery of 25% points (from 31% to 56%) compared to pure CO2 injection in the case of capillary continuity during gravity drainage tests. For the field-scale, because the PDMS can dissolve in CO2 at pressures and temperatures which are commensurate with CO2 EOR, it is a promising CO2-philic chemical for increasing CO2 density and improving CO2 diffusion coefficient in gas invaded zone compared to conventional CO2 injection.

Carbonation kinetics of calcium-based solids at the centimeter scale for moving bed applications

Countercurrent moving bed reactors were recently proposed to capture CO2 from dispersed sources using calcium materials. Due to disparities with Calcium Looping systems in particle size and solids residence times, additional investigations are required to identify reaction controlling steps and kinetic parameters. This study examines the carbonation reaction of centimeter-scale CaO and Ca(OH)2-derived-CaO pebbles under conditions relevant to moving bed applications. To this end, the impact of carbonation temperature (450–650 °C) and CO2 concentration in the inlet gas (2.5–7.5 %v) was evaluated in TGA, employing particle sizes from 0.26 to 1.65 cm. The obtained results were fitted to a shrinking core model where the rate-determining step is CO2 diffusion through the gas volume that occupies the pores of the solid CaCO3-rich layer formed during carbonation. The experimental findings can be predicted using the effective porosity of the materials as the sole fitting parameter.

Gas diffusion enhanced electrode with ultrathin superhydrophobic macropore structure for acidic CO2 electroreduction

Carbon dioxide (CO2) electroreduction reaction (CO2RR) offers a promising strategy for the conversion of CO2 into valuable chemicals and fuels. CO2RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO2 diffusion due to the absence of hydroxide that facilitates the CO2 diffusion in an acidic environment. Here, we design an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO2RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density (jC2+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$( {j}_{{{{\\rm{C}}}}_{2+}})$$\\end{document} of −1.6 A cm−2 for multicarbon products (C2+), and jC2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {j}_{{{{{{\\rm{C}}}}}}_{2+}}$$\\end{document} of −0.34 A cm−2 when applying dilute 25% CO2. In a highly acidic environment, C2+ formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide.