Simultaneous CO2 Research Articles

Simultaneous CO2 and biogas slurry treatment using a newly isolated microalga with high CO2 tolerance

The fixation of carbon dioxide (CO2) using microalgae is a promising CO2 capture and utilization technology. Microalgae have also been suggested as a potential treatment for biogas slurry (BS). This study screened microalgae capable of tolerating both high CO2 concentrations and BS, assessed their CO2 fixation and pollutant removal capabilities, and evaluated the potential use of the resulting algal biomass. Chlamydopodium sp. HS01, which showed the highest tolerance to 15% CO2 and BS, was selected due to its strong growth, CO2 fixation, and ammonia nitrogen removal abilities. The generated biomass also demonstrated significant potential for bioenergy production. Metabolomics analysis revealed that the lipid composition of HS01 underwent substantial changes under 15% CO2 alone and in combination with BS, likely as a stress adaptation strategy. Overall, HS01 presents high potential for resource utilization of CO2 coupled with actual BS.

Enabling simultaneous CO2 and water vapor removal by MOF-801/Pebax mixed matrix membranes: Molecular simulation and experimental study

Dehydration and CO2 removal are two important gas separation processes. An efficient membrane enabling simultaneous reduction of water vapor and CO2 levels from humid gas streams, such as natural gas and power plant flue gas, may advance these processes. In this study, a water-harvesting metal-organic framework, MOF-801, was synthesized with an average particle size of 120 nm, which was then dispersed in a Pebax matrix to fabricate mixed matrix membranes (MMMs). The potential of the MOF-801 as a filler in MMMs was evaluated for water and CO2 separation from CO2/N2 and CO2/CH4 mixed gas streams. Compared with the neat Pebax membrane, 70% enhancement in the water permeability was achieved for an MMM of 20 wt.% MOF loading at 10 bar with a humid feed composition of CO2/CH4. A considerable CO2/N2 separation factor (108) and CO2 permeability (270 Barrer) were also obtained, exceeding the Robeson upper bound at both dry and humid states. A molecular simulation study was performed to reveal the adsorption sites in the MOF lattice and favorable interactions with gases. Interestingly, competition between gas components close to the Zr atom was observed, which is the favorable site for both CO2 and water. Competitive adsorption was found to be the dominating transport mechanism for the selective transport of CO2 and H2O in MOF-801, revealing the role of MOF-801 in MMMs for CO2 and water vapor separation under both humid and dry conditions.

Simultaneous Photocatalytic CO2 Reduction and H2O Oxidation Under Non-Sacrificial Ambient Conditions.

The utilization of CO2, H2O, and solar energy is regarded as a sustainable route for converting CO2 into chemical feedstocks, paving the way for carbon neutrality and reclamation. However, the simultaneous photocatalytic CO2 reduction and H2O oxidation under non-sacrificial ambient conditions is still a significant challenge. Researchers have carried out extensive exploration and achieved dramatic developments in this area. In this review, we first primarily elucidate the principles of two half-reactions in the photocatalytic conversion of CO2 with H2O, i. e., CO2 reduction by the photo-generated electrons and protons, and H2O oxidation by the photo-generated holes without sacrificial agents. Subsequently, the strategies to promote two half-reactions are summarized, including the vacancy/facet/morphology design, adjacent redox site construction, and Z-scheme heterojunction development. Finally, we present the advanced in situ characterizations and future perspectives in this field. This review aims to provide fresh insights into effectively simultaneous photocatalytic CO2 reduction and H2O oxidation under non-sacrificial ambient conditions.

Carbon Negative Technologies: Carbon Capture, Sequestration, and Conversion

Abstract Carbon dioxide (CO2) capture and storage are now an essential reality that we are required to adapt to address global climate change concerns. Adapting carbon neutrality or carbon negative processes in mainstream energy generation, manufacturing, and transportation is possible using current technologies, albeit with some limitations. Carbon neutral technologies (CNTs) can be seamlessly integrated with existing systems as well as green technologies to ensure that carbon capture gets a boost. On-land and undersea storage are realistic possibilities since there is immense potential to lock atmospheric CO2 using existing technologies. Thermocatalytic, electrochemical, photo(electro)catalytic, and biological – based approaches do offer promising options, but require optimization of different parameters to ensure commercial viability, scalability, and safety. The role of electrochemical process specifically is examined. New directions for further research in the area of electrochemical – driven applications are identified and opportunities in three areas, viz., electrocatalysts design, pilot scale integrated systems, and simultaneous CO2 capture and conversion, are discussed in detail. The global implementation of any CNTs requires dramatic policy shift, unequivocal support from the world governments, public acceptance, backing from industries, and unwavering financial backing from stakeholders to ensure that there is a real chance to address climate change issues.

A stable dual-function lanthanum MOF: Simultaneous CO2 capture and catalysis

Carbon dioxide (CO2) capture has become a hot topic in recent years because of global warming issues. However, most research has focused primarily on gas capture, with limited methods available for achieving both CO2 capture and conversion within a single material. Here, we synthesized FMU-101, a metal-organic framework (MOF) with metal-open sites, through the self-assembly of [1,1′-Biphenyl]-3,3′,5-tricarboxylic acid and lanthanide ions in a solvothermal environment. FMU-101 features hexagonal one-dimensional pores with a diameter of 1.4 nm. The presence of free dimethylamine cations and metal open sites in the channel contributes to its remarkable capability for selectively enriching CO2 from CO2/CH4 mixtures in dynamic breakthrough experiments. Furthermore, the metal-open sites in FMU-101 play a crucial role in CO2 fixation, serving as effective catalytic sites for converting the adsorbed CO2 into high-value chloropropylene carbonate, a versatile chemical intermediate. The segregation and conversion mechanisms were further elucidated through density-functional theory (DFT) calculations and Grand Canonical Monte Carlo (GCMC) simulations, which highlighted the critical role of metal-open sites in CO2 adsorption and transformation.

Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (AuSA), Au clusters (AuC), and a mixed-phase of AuSA and AuC (AuSA+C) on CdS. In addition, we elucidate the synergistic effect of AuSA and AuC in enhancing the photocatalytic performance of CdS substrates for simultaneous CO2 reduction and aryl alcohol oxidation. Specifically, AuSA can effectively lower the energy barrier for the CO2→*COOH conversion, while AuC can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the AuSA and AuC co-loaded CdS show impressive overall photocatalytic CO2 conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g−1 h−1, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of AuSA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.

CO2-selective membrane reactor process for water-gas-shift reaction with CO2 capture in a coal-based IGCC power plant

Integrated gasification combined cycle (IGCC) power plants enable pre-combustion carbon capture to reduce CO2 emissions. Membrane water-gas-shift (WGS) reactors can intensify these processes by converting raw syngas to H2 with simultaneous CO2 capture in one unit. This paper reports process design and techno-economic analysis (TEA) for a membrane reactor (MR) process with a CO2 selective ceramic-carbonate dual-phase (CCDP) membrane for WGS reaction with CO2 capture for a IGCC power plant. The target performance includes CO conversion > 95 %, hydrogen purity > 90 %, CO2 purity > 95 %, and carbon capture > 90 %. Using a commercial catalyst and a CCDP membrane, the MR can achieve the performance target at 750 °C and space velocity of 250 h−1. The outcome of the process design and TEA shows that the CCDP MR has an operating cost of $24 M/year, significantly lower than that for the conventional processes (40 M$/year). However, the MR process has a higher capital cost ($1007 M) than the conventional process ($527 M) because of the higher cost of the CCDP MRs. Modeling analysis shows a MR with higher CO2 permeance can deliver the target at a higher space velocity and lower membrane surface area to catalyst volume ratio, leading to a significantly reduced MR capital costs.

Comprehensive investigation of flue gas component separation and CO2 sequestration in water-saturated porous media of subsurface formation

Flue gas poses subsurface direct storage inefficiency due to its high non-CO2 content, while surface separation, desulfurization and denitrification processes require additional equipment and financial resources. To address these challenges, flue gas subsurface component separation and CO2 sequestration within aquifer were proposed in this paper. CO2 migrates notably slower than N2, leading to the gathering of N2 at gas flooding front and the occurrence of CO2 hysteresis during flue gas filtration within the aquifer. The phenomenon, characterized by gas composition deviations from the original injection mole fractions of N2 and CO2, is referred to as the flue gas component separation. Numerical simulation results indicate that the solubility difference between N2 and CO2 is the primary force driving the separation of components, and the asynchronous filtration velocities of the gas and aqueous phases further promote the separation. Thus, simultaneous N2 separation and CO2 storage can achieve by the optimized gas-water alternate injection, and the efficiencies of N2 separation and CO2 storage are inversely correlated. Increasing N2 mole fraction within the injected flue gas enhances the efficiency of N2 separation, while having a slight effect on CO2 storage. Water vapor in flue gas condenses and integrates into the liquid phase, while O₂ component is produced slightly later than N₂, leading to a marginal reduction in N₂ separation efficiency. The synergistic influences of aquifer temperature and pressure exhibit bidirectionality, stemming from the shift between the dominant factors between CO2 dissolution and gas sweep efficiency. Conditions of relatively lower aquifer temperatures and moderate pressures, particularly in medium permeability aquifers, are more favorable for enhancing N₂ separation and CO₂ storage. This proposal method holds the potential for efficient subsurface separation of flue gas components and concurrent underground storage of CO2, thereby contributing to the reduction of greenhouse gas emissions and mitigation of climate change.

CO2 sequestration by indirect mineral carbonation of serpentine with (NH4)2SO4 as a recyclable extractant

Mineral carbonation with serpentine can offer a sustainable and safe process option for simultaneous CO2 emission reduction and utilization of nature mineral. In this study, a sustainable process for CO2 mineral sequestration was proposed by using serpentine and ammonium sulfate as feedstocks. The mixture of feedstocks was subjected to roasting with temperature ranging from 390°C to 480°C, converting magnesium into the corresponding sulfate. Then, water leaching was employed to dissolve the magnesium sulfate from the roasted samples. Finally, through a mineralization reaction, the corresponding magnesium bicarbonate was generated after sequestrating CO2. Under the optimal roasting-leaching conditions, i.e. roasting temperature of 420ºC, roasting time of 2 hours, and mass ratio of ammonium sulfate/serpentine of 3; leaching temperature of 80ºC, leaching time of 1 hour, and a liquid-to-solid ratio of 1, the magnesium extraction efficiency reached 76 %. Thermodynamics and experimental results demonstrated that during the sulfation roasting process, the products generated during roasting, magnesium sulfate and silicon dioxide, adhered to the surface of the serpentine, thus inhibiting the mass transfer process and impeding the progress of the reaction. However, the liquid-solid reaction facilitated by molten ammonium sulfate and the gas-solid reaction provided by the decomposition of ammonium salts into SO2 played a promoting role in the sulfation roasting reaction. The carbonation of sulfated serpentine results indicated that the optimal CO2 storage capacity can reach 204 kg/t serpentine.

Direct CO2 mineralization and evolution behavior of fine CaCO3 from ammonia-induced phosphogypsum mineral carbonation

The mineral carbonation of phosphogypsum (PG) presents considerable potential for simultaneous CO2 sequestration and high-value utilization of PG. Variations in carbon footprints are crucial for enhancing carbonation efficiency and regulating product formation. This study explores the mechanism of direct CO2 mineralization by PG and the evolution of the resulting product. The results demonstrate that 97.14% of the CaSO4·2H2O in PG can be converted to calcite under conditions including a nitrogen–sulfur molar ratio of 3, a liquid–solid ratio of 6, a CO2 flowrate of 0.4 L/min, and a stirring rate of 800 rpm for 60 min. The carbonation rate exhibits significant variation with time, occurring in three distinct stages. Initially, CO2 reacts with ammonia to form (NH4)2CO3, releasing greater heat. This heat inhibits the dissolution of Ca2+ from PG, resulting in a lower carbonation efficiency, as only a limited amount of Ca2+ reacts with CO32– to preferentially form amorphous CaCO3 (ACC). As CO32– formation reaches equilibrium, the endothermic properties of the reaction between CaSO4 and (NH4)2CO3 promote the dissolution of Ca2+ from PG, further accelerating CO2 mineralization and resulting in significant increases in carbonation efficiency and ACC production. The ACC is rapidly transformed into calcite via a “dissolution-reprecipitation” mechanism. However, the carbonation rate of PG decreases as saturation is approached, mainly resulting from the aggregation of fine CaCO3 particles on the PG surface. As a result, the direct CO2 sequestration process by PG follows a carbon footprint sequence of “CO2–(NH4)2CO3–ACC–calcite”. This study provides significant insights into the mechanisms of direct CO2 mineralization and product evolution and offers a basis for optimizing carbonation processes enhancement and regulating product phases.

Maximizing resource efficiency with dairy and municipal wastewater as nutrient media for Chlorella vulgaris with simultaneous CO2 sequestration

Addressing critical environmental challenges such as greenhouse gas emissions, global warming, and eutrophication demands urgent and innovative solutions. In recent years, microalgae have emerged as a promising avenue for addressing these pressing issues. In this study, the combination of dairy and municipal wastewater is proposed as a culture medium for cultivating microalgae strains capable of sequestering atmospheric CO2. Specifically, the growth of Chlorella vulgaris was investigated using Bold's basal medium, along with varying concentrations of municipal and dairy wastewater, both with and without CO2 supplementation, to assess their CO2 capture potential. Concurrently, the efficiency of chemical oxygen demand (COD), total nitrogen, potassium, and phosphate removal from the wastewater was evaluated. Additionally, the combination of wastewater media with CO2 supplementation yielded the highest CO2 uptake rates, indicating the feasibility of simultaneous CO2 capture during microalgae cultivation. Media composition with 25% municipal wastewater: 75% dairy wastewater supplemented with CO2 demonstrated superior COD elimination with a higher percentage of nutrient removal from wastewater compared to other wastewater proportions. The nutrient removal capacity of aforementioned media also comes in line with high CO2 sequestration rate (13.57 mg L−1 h−1). These findings underscore the potential of utilizing wastewater from diverse sources as a viable culture medium for microalgae cultivation, facilitating concurrent CO2 capture and wastewater treatment.

Evaluation of the Secondary Metabolites and Bioactivity of South African Bulbine Natalensis Under Simultaneous Elevated Carbon Dioxide and Temperatures

The secondary metabolism in medicinal plants are responsible for their protection against environmental factors and the health-promoting benefits they provide to users. The purpose of this study was to assess the responses of the secondary metabolic system of B. natalensis and its influence on the antioxidant and antibacterial activities. The phytochemical analyses, antioxidant and antibacterial assays were conducted from using harvested leaves, underground stems and roots from whole plants exposed to simultaneous elevated CO2 and temperatures over eight days in a heatwave simulation. Most of the phytochemical groups were present in the leaves, however majority of the tested compounds had consistent presence throughout the plants in all treatments. The underground stems possessed a greater total phenolic, tannin and proanthocyanidin contents than the leaves and roots under elevated CO2 and temperatures. The leaves had a comparatively better antioxidant activity from the treatment than control. Overall, there was consistency in the antibacterial activity in both control and experimental conditions. The tannins and phenolics had greater concentrations throughout the plants under elevated conditions overall, which could indicate their leading role in plant defence and the improvement and maintenance of the medicinal activity of B. natalensis. The responses of the plant parts of B. natalensis under elevated CO2 and temperatures provides newfound insights on the physiological roles plant organs play on the overall productivity and medicinal activity of the species.

Hydroxylated TiO2-induced high-density Ni clusters for breaking the activity-selectivity trade-off of CO2 hydrogenation

The reverse water gas shift reaction can be considered as a promising route to mitigate global warming by converting CO2 into syngas in a large scale, while it is still challenging for non-Cu-based catalysts to break the trade-off between activity and selectivity. Here, the relatively high loading of Ni species is highly dispersed on hydroxylated TiO2 through the strong Ni and −OH interactions, thereby inducing the formation of rich and stable Ni clusters (~1 nm) on anatase TiO2 during the reverse water gas shift reaction. This Ni cluster/TiO2 catalyst shows a simultaneous high CO2 conversion and high CO selectivity. Comprehensive characterizations and theoretical calculations demonstrate Ni cluster/TiO2 interfacial sites with strong CO2 activation capacity and weak CO adsorption are responsible for its unique catalytic performances. This work disentangles the activity-selectivity trade-off of the reverse water gas shift reaction, and emphasizes the importance of metal−OH interactions on surface.

Exploring carbon dioxide sequestration in desalination reject brine via NaOH reaction: A kinetics study

Seawater desalination is one of the most sustainable means of water supply in arid and semi-arid regions. Despite its undeniable potential to meet the global water demands, there are several environmental impacts associated with its operation, including the generation of reject brine and the emission of considerable amounts of CO2. Recently, the mineralization of carbon dioxide using desalination reject brine has emerged as a potential solution for simultaneous brine management and CO2 sequestration. In this study, the reaction kinetics of desalination reject brine with CO2 in the presence of NaOH are evaluated. The effect of various operating parameters, such as the temperature, CO2 concentration, NaOH dosage, brine salinity, CO2 flowrates and inert particles volume percent were investigated by varying them within the range of 15–55 °C, 3–20 %, 6–16 g/L, 5–72 g/L, 1–5 L/min and 0–20 %, respectively. The experimental data showed that the overall rate of CO2 conversion is equal to the sum of the rates observed for Ca2+ and Mg2+ carbonation reactions and increases proportionally with the increase in CO2 concentration. The addition of NaOH improved the Ca2+ carbonation reaction rate but had no effect on Mg2+ carbonation reactions within the investigated reaction conditions. Interestingly, increasing brine salinity had a negative effect on the reaction rate, while the change in temperature and inert particles had minimal effect on the overall reaction rate. Analysis of the solid products showed that Hydromagnesite and Calcite were the two major products obtained. Finally, experimental data were used to develop a rate model representing the CO2-Brine-NaOH system. The developed model will assist in successfully predicting the performance of the process and pave the way for efficient brine management and CO2 sequestration.

Alkali activated steel slag – oil composites: Towards resource efficiency and CO2 neutrality

This study describes advances in high-performance construction material development using a minimum of primary resources while enabling simultaneous CO2 sequestration capacities. Two so far unutilized Austrian steel slags were combined with metakaolin and vegetable oil to produce alkali-activated materials exhibiting high compressive and flexural strength of up to 94 MPa and 13 MPa, respectively. This approach enabled a reduction in primary mineral resources of up to 82 wt%, with an average reduction in global warming potential (GWP) of 52 % compared to a traditional high-performance Portland cement material. Oil addition led to the formation of mainly water unsolvable metal soap phases precipitating within the pore spaces without significantly altering the phase assemblage and chemistry of the binder matrix, but further reducing the GWP by 74 %. The (heavy metal) leaching behavior coincides with that of traditional concrete materials and was even further reduced by the addition of oil.

Simultaneous CO2 mineral sequestration and nickel separation from laterite leachate: Thermodynamic and experimental study

Global warming resulting from escalating CO2 emissions and rising nickel demand present dual challenges to the sustainable development. In this study, a process for simultaneous nickel separation and CO2 mineral sequestration was proposed by using the leachate derived from the process of roasting laterite with copperas followed by water leaching. From the thermodynamic study, it was found that nickel can dissolve in the leachate in the form of nickel-ammonium complexes, while magnesium precipitated as carbonates. Furthermore, Eh-pH (potential vs. pH) results demonstrated that the conditions for the formation of nickel-ammonium complexes closely resemble those for magnesium carbonates. Under optimized conditions with the initial solution pH of 10.8, CO32–/Mg molar ratio of 2, reaction temperature of 30 °C, and reaction time of 1 h; over 95 % of Mg and 100 % of Fe can be converted into carbonates or hydroxides, with no more than 1 % Ni loss. Higher pH and CO32–/Mg molar ratios, along with lower temperatures, facilitated the separation of nickel from the magnesium and iron. The phase and microstructure of the precipitates were significantly influenced by the reaction temperature. At 30 °C, the precipitation product was MgCO3·3H2O, exhibiting a microstructure resembling porous spherical flowers; whereas at 80 °C, the precipitated phase was Mg5(OH)2(CO3)4·4H2O, also displaying a microstructure akin to porous spherical flowers. Efficient separation of nickel and magnesium in NH3–(NH4)2CO3-H2O was achieved by leveraging their distinct reaction properties, simultaneously sequestering CO2. This process achieved the maximum selective Ni recovery and CO2emission reduction in one step.

Non-stoichiometric protic ionic liquids for efficient carbon dioxide capture and subsequent conversion under mild conditions

Protic ionic liquids (PILs) have emerged as innovative solvents with significant potential for CO2 capture and transformation, presenting a sustainable alternative to conventional methods which often involve energy-intensive processes or environmentally detrimental chemicals. Herein, a novel strategy for CO2 capture and conversion at mild conditions using non-stoichiometric protic ionic liquids (NPILs) was demonstrated for the first time. These NPILs, employed as sorbents, solvents, and catalysts, were composed of imidazole (Im) and 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) in various ratios. Correlations between the mole ratio of DBU/Im and physicochemical properties such as viscosity, conductivity, thermal stability, and the distribution of neutral and ionic species were systematically investigated. Effects of the absorption temperature and CO2 partial pressure on the absorption capacity were also studied. Different absorption mechanisms, including carbonate and carbamate pathways, were analyzed using FT-IR and NMR spectroscopy. Moreover, the fixed CO2 could be catalytically converted to quinazoline-2,4(1H,3H)-diones under exceptionally mild reaction conditions (1 atm, 50 °C, metal-free process). A plausible reaction mechanism involving simultaneous CO2 activation and substrate activation for the transformation of CO2 into quinazoline-2,4(1H,3H)-diones was verified through NMR spectra. It is believed that the new insights into the CO2 mechanism will facilitate the rational design of functional ionic liquids for CO2 capture, utilization, and storage in the future.

Direct Flue Gas Injection into Ocean for Simultaneous Energy Recovery and CO2 Sequestration in Solid Hydrate Reservoirs

Direct Flue Gas Injection into Ocean for Simultaneous Energy Recovery and CO₂ Sequestration in Solid Hydrate Reservoirs

A red-light-powered silicon nanowire biophotochemical diode for simultaneous CO2 reduction and glycerol valorization

A red-light-powered silicon nanowire biophotochemical diode for simultaneous CO2 reduction and glycerol valorization

Improved Production Rates of Hydrogen Generation and Carbon Dioxide Reduction Using Gallium Nitride with Nickel Oxide Nanofilm Capping Layer as Photoelectrodes for Photoelectrochemical Reaction.

This work investigates the production of hydrogen (H2) and formic acid (HCOOH) through a photoelectrochemical (PEC) approach. Nickel oxide nanofilms prepared by sputtering capped on n-GaN photoelectrodes were employed to achieve simultaneous water photoelectrolysis and CO2 reduction. The study delves into the role of the nickel oxide layer, examining its potential as a catalyst and/or a protective layer. Furthermore, the influence of nickel oxide layer thickness on the performance of the photoelectrodes is explored. In essence, appropriate nickel oxide thickness is beneficial in increasing the photocurrent of the PEC reaction. The observed improvements in photocurrents and, hence, the production rates can be attributed to the functionality of the nickel oxide nanofilm: mitigating the negative influence of surface defects on n-GaN and facilitating the separation of photogenerated electron-hole pairs at the electrolyte/n-GaN interface. Specifically, PEC cells utilizing the 4 nm-thick nickel oxide nanofilms deposited on n-gallium nitride (n-GaN) electrodes demonstrate a significant enhancement in hydrogen and formic acid production rates. These rates were at least 45% higher compared to PECs using bare n-GaN electrodes.