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The performance of hollow fiber membrane contactor for CO2 removal using MEA-based nanofluid was experimentally evaluated. Different types of nanoparticles, including Al2O3, Fe3O4, and functionalized MWCNT in this study. The influence of various operating conditions including gas and absorbent flow rates, absorbent concentration, and nanofluid characteristics on separation performance was thoroughly examined. The results showed that compared to conventional amine solvents, the nanofluid absorbents significantly enhance CO2 absorption performance. In comparison to the base fluid, the mass transfer coefficient was raised by 320, 120, and 40% for 0.15 wt% MWCNT, Al2O3 and Fe2O3, respectively. The MWCNT showed much more compliance with amine solvents due to its carboxyl functional groups and higher surface area which make it more stable in a strong polar mixture. The study underscores the importance of stability, viscosity, and shear stress of nanofluids as key parameters affecting CO2 absorption performance. [ABSTRACT FROM AUTHOR]

A new landfill-gas-to-biomethane process prescribing decarbonation/desulfurization via gas–liquid membrane contactors and siloxane absorption using Selexol are presented in this study. Firstly, an extension for an HYSYS simulator was developed as a steady-state gas–liquid contactor model featuring: (a) a hollow-fiber membrane contactor for countercurrent/parallel contacts; (b) liquid/vapor mass/energy/momentum balances; (c) CO2/H2S/CH4/water fugacity-driven bidirectional transmembrane transfers; (d) temperature changes from transmembrane heat/mass transfers, phase change, and compressibility effects; and (e) external heat transfer. Secondly, contactor batteries using a countercurrent contact and parallel contact were simulated for selective landfill-gas decarbonation/desulfurization with water. Several separation methods were applied in the new process: (a) a water solvent gas–liquid contactor battery for adiabatic landfill-gas decarbonation/desulfurization; (b) water regeneration via high-pressure strippers, reducing the compression power for CO2 exportation; and (c) siloxane absorption with Selexol. The results show that the usual isothermal/isobaric contactor simplification is unrealistic at industrial scales. The process converts water-saturated landfill-gas (CH4 = 55.7%mol, CO2 = 40%mol, H2S = 150 ppm-mol, and Siloxanes = 2.14 ppm-mol) to biomethane with specifications of CH4MIN = 85%mol, CO2MAX = 3%mol, H2SMAX = 10 mg/Nm3, and SiloxanesMAX = 0.03 mg/Nm3. This work demonstrates that the new model can be validated with bench-scale literature data and used in industrial-scale batteries with the same hydrodynamics. Once calibrated, the model becomes economically valuable since it can: (i) predict industrial contactor battery performance under scale-up/scale-down conditions; (ii) detect process faults, membrane leakages, and wetting; and (iii) be used for process troubleshooting. [ABSTRACT FROM AUTHOR]

Hydrogen is an industrial raw material both for the production of chemicals and for oil refining with hydrotreating. It is the subject of increasing attention for its possible use as an energy carrier and as a flexible energy storage medium. Its production is generally accomplished in Steam Methane Reforming (SMR) plants, where a gaseous mixture of CO and H2, with a limited number of other species, is obtained. The process of production and purification generates relevant amounts of carbon dioxide, which needs to be removed due to downstream process requirements or to limit its emissions to the atmosphere. A work by IEAGHG focused on the study of a state-of-the-art Steam Methane Reforming plant producing 100 kNm3/h of H2 and considered chemical absorption with MethylDiEthanolAmine (MDEA) solvent for removing carbon dioxide from the PSA tail gas in a baseline scheme composed of the absorber, one flash vessel and the regeneration column. This type of process is characterized by high energy consumption, in particular at the reboiler of the regeneration column, usually operated by employing steam, and modifications to the baseline scheme can allow for a reduction of the operating costs, though with an increase in the complexity of the plant. This work analyses three configurations of the treatment section of the off gas obtained after the purification of the hydrogen stream in the Pressure Swing Adsorption unit with the aim of selecting the one which minimizes the overall costs so as to further enhance Carbon Capture and Storage in non-power industries as well. [ABSTRACT FROM AUTHOR]

The production of hydrogen from residual biomass represents a sustainable alternative to integrate the production of renewable hydrogen in coming years. This work shows the results obtained during an experimental campaign dedicated to analysing the performance of a downdraft gasifier of about 100 kW t fed with woody biomass and oxy-steam mixtures. With suitable oxygen-steam ratios it was possible to produce a syngas with a hydrogen content higher than 40%vol, with a cold gas efficiency of more than 80%. The experimental syngas composition is used as input of a numerical model, created in Aspen Plus® and dedicated to evaluating the performance of the plant section for the pure H 2 -production. The numerical analysis highlighted the possibility of obtaining approximately 5% by mass of hydrogen with respect to the biomass used, also evidencing how the correct use of thermal waste and residues makes the whole plant (gasifier plus hydrogenizer) independent on heat supply. • Woody biomass oxy-steam gasification has been analysed in a real-scale downdraft gasifier. • Oxy-steam gasification confirmed to be effective in increasing hydrogen yield in the syngas. • The optimum equivalence ratio and steam/biomass mass ratio have been determined. • A H 2 production plant has been conceived and analysed to exploit the produced syngas. • The study evidenced the possibility of obtaining a hydrogen/biomass mass ratio of 5%. [ABSTRACT FROM AUTHOR]

Alternative solvents based on aqueous solutions of amino acids have been recently developed as possible substitutes for Mono Ethanol Amine (MEA) for CO2 removal from flue gas streams. The potassium taurate solvent has the advantages of degradation resistance, low toxicity and low energy requirements for its regeneration. With any type of solvent, CO2 removal applied to a power production plant decreases the revenues obtained from selling electricity because of the energy requirements. Operating the CO2 removal section in flexible mode avoids significant effects on the profits of the power plant, while accomplishing environmental regulations. This work is the first journal paper focusing on the application in flexible mode of the potassium taurate system for treating a flue gas stream from a 500 MW coal-fired power plant. Techno-economic evaluations are performed to determine the best operating conditions considering the variation in the electricity demand and its price, and different values of carbon tax. In the summer period, with high electricity prices and demands, carbon tax values between 45 EUR/tCO2 and 60 EUR/tCO2 favor CO2 absorption in the flexible mode, without periods of full CO2 emissions during the day. [ABSTRACT FROM AUTHOR]

CO2 capture experiments were carried out in a small-scale bubble column reactor using alkaline solutions of sodium hydroxide. The results of the experiments show that a higher NaOH content in the liquid phase and elevated CO2 concentrations in the gas mixture led to a higher CO2 removal efficiency. A mathematical model was developed to describe the CO2 absorption as a function of CO2 gas inlet and OH- concentrations at low CO2 and OH- concentrations. The CO2 uptake at high OH- concentrations (high pH) was accurately predicted by the model, whereas the CO2 uptake at lower OH- concentrations could not be predicted with the same accuracy. [ABSTRACT FROM AUTHOR]

Available data on amine‐based sorbents used for the direct air capture (DAC) process were gathered and analyzed to identify the correlations between various aspects of these sorbents and the operating conditions they are used in. It is demonstrated that a moderately high temperature (∼ 50 °C) can help with higher CO2 capture capacity. The effect of sorbent preparation method on its activity and stability was studied. Also, the influence of amine groups and support choice on amine efficiency and CO2 capture capacity was discussed. The DAC process conditions proved to play a major role in determining the optimal sorbent. An outlook for characteristics to be sought for in future DAC sorbents for CO2 removal is proposed. [ABSTRACT FROM AUTHOR]

Understanding the response of the Indian summer monsoon (ISM) onset to CO2 forcing is of utmost importance for rain‐fed agriculture and water management. In this study, we utilized an idealized symmetric CO2 removal scenario from the sixth phase of the Coupled Model Intercomparison Project to analyze the reversibility of monsoon onset. The results show that ISM onset is reversible but exhibits strong asymmetry: it undergoes minimal changes during the ramp‐up phase, but experiences rapid postponement as the CO2 begins to decline; Eventually, it is delayed more than 1 week when the CO2 concentration is restored to the initial level. To investigate the possible underlying mechanisms, we decomposed the climate response to CO2 forcing into the fast and slow processes. Notably, it is the enhanced slow response, which is driven by long‐term sea surface temperature (SST) changes, that dominates the asymmetric response of ISM onset. This slow response delays the ISM onset by strengthening near‐surface poleward land‐sea moist static energy contrast, thereby weakening the lower‐tropospheric monsoonal circulation. Based on the atmospheric component model simulations, we found that both the uniform SST change and patterned SST changes in the slow response contribute to the delay of ISM onset, but the latter plays a dominant role. Our results emphasize the importance of thoroughly assessing regional hydrological cycle features when designing the CO2 removal pathways. Plain Language Summary: The 2015 Paris Agreement set a target to limit global warming to 2°C by the end of the 21st century, with a preference for achieving 1.5°C. Meeting this temperature goal requires the atmospheric CO2 concentration to peak in this century and then start declining. It is crucial to understand whether the changes in the regional hydrological cycle can be reversed when we reach the global mean temperature goal. This study focuses on examining the responses of the Indian summer monsoon (ISM) onset to idealized CO2 removal (CDR) forcing, in which the atmospheric CO2 concentration decreases symmetrically after increasing. Under the symmetric CDR pathway, the ISM onset displays reversible yet asymmetric evolution, it significantly delays when the CO2 concentration returns to the pre‐industrial level. This asymmetric response is attributed to the slow process of the climate system driven by long‐term sea surface temperature change, which leads to the delay in ISM onset by weakening the lower‐tropospheric circulation and, consequently, the precipitation. The slow response lags behind the evolution of CO2 concentration and plays a dominant role in the global mean surface temperature change during the ramp‐down phase. Understanding these mechanisms is essential for addressing climate change challenges and the impacts on regional monsoonal systems. Key Points: The idealized symmetric CO2 removal forcing leads to a reversible but asymmetric Indian summer monsoon (ISM) onsetThe delayed onset of ISM during the ramp‐down period is primarily dominated by the asymmetric and lagged slow process, which is associated with the long‐term sea surface temperature changeThe slow process delays the ISM onset by enhancing the near‐surface poleward land‐sea moist static energy contrast, which subsequently weakens the monsoonal circulation [ABSTRACT FROM AUTHOR]

Carbon capture and sequestration from a stationary source comprises four distinct engineering processes: separation of CO2 from the other flue gases, compression, transportation, and injection into the chosen storage site. An analysis of the thermodynamic and transport properties of CO2 shows that dissolving this gas in seawater at depths more than 600 m is, most likely, an optimal long-term storage method; and that for transportation, the CO2 must be in the denser supercritical state at pressures higher than 7.377 MPa. The separation, compression, transportation, and injection processes require significant energy expenditures, which are determined in this paper using realistic equipment efficiencies, for the cases of two currently in operation coal power plants in Texas. The computations show that the total energy requirements for carbon removal and sequestration are substantial, close to one-third of the energy currently generated by the two power plants. The cost analysis shows that two parameters - the unit cost of the pipeline and the discount factor of the corporation - have a very significant effect on the annualized cost of the CCS process. Doubling the unit cost of the pipeline increases the total annualized cost of the entire CCS project by 36% and increasing the discount rate from 5% to 15% increases this annualized cost by 32%. [ABSTRACT FROM AUTHOR]

The accumulation of uncollected fly ash from flue gas in post-combustion CO2 capture processes is a significant concern in current coal-fired power plants due to its potential impact on the performance of CO2 absorbent and absorption towers. In order to determine the effect of fly ash on the mass transfer performance of CO2 absorption into monoethanolamine (MEA) and diethanolamine (DEA) aqueous solutions, experimental studies were carried out using a small-sized packed tower equipped with θ-ring random packing. These studies were conducted under various operating parameters, including solution temperature, liquid/gas ratio (L/G), packing height, and fly ash concentration. The results show that the effect of fly ash on the outlet CO2 concentration was primarily observed during the initial stages of the experimental process. Moreover, the presence of fly ash leads to a reduction in the volumetric overall mass transfer coefficient (KGav) when using MEA and DEA solution, and increasing the fly ash concentration further exacerbates this negative impact. However, the effect of fly ash on the reduction in KGav is not significantly related to its chemical composition but rather depends on the operational parameters. With increasing solution temperature, liquid/gas ratio (L/G), and packing height, the KGav values for different solutions exhibit an upward trend. The negative effect of fly ash on KGav remains relatively stable for MEA as solution temperature and packing height increase. Compared to MEA, fly ash has a greater negative effect on DEA solution under the same experimental conditions. The analysis reveals that the detrimental effect of fly ash on KGav primarily stems from its ability to alter the distribution state of the absorption liquid within the packed tower. [ABSTRACT FROM AUTHOR]

Recent model projections and many research results along the world suggest that forests could be significant carbon sinks or sources in the future, contributing in such a way to global warming mitigation. Conversion of coppice forest to high forest may play an important role towards this direction. However, the most effective way for this to succeed is questionable. This study examines the long-term effect of different intensity thinning (light 10% of the volume removal every 5–10 years, moderate 15%, and heavy 20%) on biomass, and on all the carbon pool categories (according to IPCC), as well as the accumulation rates, in a 77-year-old oak ecosystem, which has been subjected to conversion from coppice to high forest through repeating thinning since 1973. The research included numerous field tree measurements, and a systematic sampling of standing and fallen dead wood, litter, and surface soil up to 50 cm depth. Data analysis shows that heavy and moderate thinning result in a greater accumulation of carbon in the aboveground ecosystem pools, especially in living biomass, with an average annual rate of 1.62 Mg C ha−1 carbon accumulation in living aboveground tree biomass, resulting in a carbon pool of 125.04Mg C ha−1 at the age of 77 years. Dead wood volume was found low in all thinning treatment with significant differences between the thinning intensities. Litter carbon pool was also affected by moderate and heavy thinning, while soil carbon was unaffected by the treatments. The findings could contribute on climate change mitigation actions if they are adopted in forest management plans of similar types of forest ecosystems; a periodical thinning application of removal ca. 20% of wood volume is suggested. [ABSTRACT FROM AUTHOR]

The process of membrane gas separation is a technique of increasing interest in industrial applications. In many cases, the membrane gas separation process can replace or support commonly used technologies for gas mixtures separation, such as adsorption, absorption or cryogenic distillation. One of the areas in which the research on the development and implementation of new types of membranes is particularly intensive is the technology of CO2 removal from mixtures containing also CH4 or N2. The need to extract CO2 from these mixtures results from economic, legal, ecological and technological reasons. A solution that can improve the process properties of membranes is the development of heterogeneous membranes. Heterogeneous membranes are structures consisting of a polymeric continuous phase and an organic or inorganic dispersed phase. The presence of additives can improve both the permeability of the membrane and its selectivity, as well as the mechanical properties. However, in addition to developing a new material and examining its properties, it is also necessary to propose a method for manufacturing membranes from these materials on an industrial scale and to determine their process properties based on tests on gas mixtures. For this purpose, heterogeneous capillary membranes obtained by dip coating method were developed. PEBAX® 2533 copolymer and additives such as SiO2, zeolitic imidazolate frameworks (ZIF-8) or PSS-octaphenyl substituted (POSS-Ph) were used to produce them. The permeability and selectivity of the developed membranes were determined on the basis of tests using pure gases (CH4, CO2 and N2), as well as gas mixtures (CO2/CH4 and CO2/N2). The process conditions used in the research, that is, feed pressure and temperature, were determined on the basis of the authors' previous research [1] and mathematical-statistical analysis. On the basis of the conducted tests, the usefulness of the produced composite capillary membranes for conducting the process of separating gas mixtures in which CO2 is one of the components has been proven. [ABSTRACT FROM AUTHOR]

As the urgency to limit global warming has intensified, negative emissions technology such as direct air capture and carbon sequestration are increasingly considered in climate mitigation scenarios. When Iceland opened the commercial-grade direct air carbon capture and storage (DACCS) facility in 2021, this marked a breakthrough for DACCS technology as a scalable climate mitigation solution. This study investigates the adoption of DACCS in Iceland and the potential for diffusion into other contexts as a global decarbonization solution. We implement expert interviews to analyze the adoption of technology, and to identify the various requirements of scaling DACCS into local and global contexts. Using inductive thematic analysis, we characterize the diverging perspectives on the role of carbon dioxide removal as a climate mitigation solution and also identify pathways toward technology upscaling at national, regional, and global scales. Despite the successful technology demonstration of DACCS, we find that experts hold different mental models of climate mitigation generally, characterized as "nature vs. technology." We also find that experts clearly articulate the necessary conditions for the diffusion of DACCS more broadly, including explicit regulatory measures as guardrails against a "license to pollute" as well as bilateral governance structures that include financial investment. Finally, we find that the importance of public acceptance of the technology was noted among all expert groups. Limited data exist on the acceptance of DACCS paired with renewable energy and this is a future research recommendation. [ABSTRACT FROM AUTHOR]

Ocean iron fertilization (OIF) aims to remove carbon dioxide (CO2) from the atmosphere by stimulating phytoplankton carbon‐fixation and subsequent deep ocean carbon sequestration in iron‐limited oceanic regions. Transdisciplinary assessments of OIF have revealed overwhelming challenges around the detection and verification of carbon sequestration and wide‐ranging environmental side‐effects, thereby dampening enthusiasm for OIF. Here, we utilize five requirements that strongly influence whether OIF can lead to atmospheric CO2 removal (CDR): The requirement (a) to use preformed nutrients from the lower overturning circulation cell; (b) for prevailing iron‐limitation; (c) for sufficient underwater light for photosynthesis; (d) for efficient carbon sequestration; (e) for sufficient air‐sea CO2 transfer. We systematically evaluate these requirements using observational, experimental, and numerical data in an "informed back‐of‐the‐envelope approach" to generate circumpolar maps of OIF (cost‐)efficiency south of 60°S. Results suggest that (cost‐)efficient CDR is restricted to locations on the Antarctic Shelf. Here, CDR costs can be <100 US$/tonne CO2 while they are mainly >>1,000 US$/tonne CO2 in offshore regions of the Southern Ocean, where mesoscale OIF experiments have previously been conducted. However, sensitivity analyses underscore that (cost‐)efficiency is in all cases associated with large variability and are thus difficult to predict, which reflects our insufficient understanding of the relevant biogeochemical and physical processes. While OIF implementation on Antarctic shelves appears most (cost‐)efficient, it raises legal questions because regions close to Antarctica fall under three overlapping layers of international law. Furthermore, the constraints set by (cost‐)efficiency reduce the area suitable for OIF, thereby likely reducing its maximum CDR potential. Key Points: Iron fertilization efficiency is constrained mainly by carbon transfer efficiency into Antarctic Bottom Water and air‐sea CO2 exchangeIron fertilization could cost below 100 US‐Dollar per tonne CO2 on Antarctic shelves but may be much more expensive off shelves(Cost‐)efficient Iron Fertilization is restricted to relatively small parts of the Southern Ocean that are protected by international law [ABSTRACT FROM AUTHOR]

Stenotrophomonas maltophilia has been demonstrated herein to reduce CO2 without any cofactor, photon or hydrogen (H2) addition during reaction. S. maltophilia reduces 13CO2 into 13C-labeled formate in batch mode. Two intracellular enzymes are curently being considered for their ability to catalyze the CO2 reduction reaction: a Fe-nitrogenase and a formate dehydrogenase (FeS-FDH). The reaction was intensified by implementing the bacteria in an electrolysis cell continuously fed with CO2. In this configuration, CO2 removal reached up to 25% v/v at 30°C and atmospheric pressure.

Abstract In combination with dramatic and immediate CO2 emissions reductions, net‐negative atmospheric CO2 removal (CDR) is necessary to maintain average global temperature increases below 2.0°C. Many proposed CDR pathways involve the placement of vast quantities of organic carbon (biomass) on the seafloor in some form, but little is known about their potential biogeochemical impacts, especially at scales relevant for global climate. Here, we evaluate the potential impacts and durability of organic carbon storage specifically within deep anoxic basins, where organic matter (OM) is remineralized through anaerobic processes that may enhance its storage efficiency. We present simple biogeochemical and mixing models to quantify the scale of potential impacts of large‐scale OM addition to the abyssal seafloor in the Black Sea, Cariaco Basin, and the hypersaline Orca Basin. These calculations reveal that the Black Sea in particular may have the potential to accept biomass storage at climatically relevant scales with moderate changes to the geochemical state of abyssal water and limited communication of that impact to surface water. Still, all of these systems would require extensive further evaluation prior to consideration of megatonne‐scale CO2 sequestration. Many key unknowns remain, including the partitioning of breakdown among sulfate‐reducing and methanogenic metabolisms and the fate of methane in the environment. Given the urgency of responsible CDR development and the potential for anoxic basins to reduce ecological risks to animal communities, efforts to address knowledge gaps related to microbial kinetics, benthic processes, and physical mixing in these systems are critically needed.

Abstract Understanding the response of the Indian summer monsoon (ISM) onset to CO2 forcing is of utmost importance for rain‐fed agriculture and water management. In this study, we utilized an idealized symmetric CO2 removal scenario from the sixth phase of the Coupled Model Intercomparison Project to analyze the reversibility of monsoon onset. The results show that ISM onset is reversible but exhibits strong asymmetry: it undergoes minimal changes during the ramp‐up phase, but experiences rapid postponement as the CO2 begins to decline; Eventually, it is delayed more than 1 week when the CO2 concentration is restored to the initial level. To investigate the possible underlying mechanisms, we decomposed the climate response to CO2 forcing into the fast and slow processes. Notably, it is the enhanced slow response, which is driven by long‐term sea surface temperature (SST) changes, that dominates the asymmetric response of ISM onset. This slow response delays the ISM onset by strengthening near‐surface poleward land‐sea moist static energy contrast, thereby weakening the lower‐tropospheric monsoonal circulation. Based on the atmospheric component model simulations, we found that both the uniform SST change and patterned SST changes in the slow response contribute to the delay of ISM onset, but the latter plays a dominant role. Our results emphasize the importance of thoroughly assessing regional hydrological cycle features when designing the CO2 removal pathways.

● Simultaneous H2S and CO2 removal from biogas is studied.● Renewable absorbent from biogas slurry is used in membrane contactor.● More than 98% of H2S can be removed by membrane absorption.● The impurities have less influence on H2S removal efficiency. Upgrading biogas into biomethane not only improves the biogas utilization as vehicle fuel or natural gas substitute, but also reduces the greenhouse gases emissions. Considering the principle of engineering green energy process, the renewable aqueous ammonia (RAA) solution obtained from biogas slurry was used to remove H2S and CO2 simultaneously in the hollow fiber membrane contactor. RAA was mimicked in this study using the ammonia aqueous solution mixed with some typical impurities including ethanol, acetic acid, propionic acid, butyric acid and NH4HCO3. Compared with the typical physical absorption (i.e., pure water) removing 48% of H2S from biogas, RAA with 0.1 mol·L−1 NH3 could remove 97% of H2S. Increasing the NH3 concentration from 0.1 to 0.5 mol·L−1 could elevate the CO2 absorption flux from 0.97 to 1.72 mol·m−2·h−1 by 77.3%. Among the impurities contained in RAA, ethanol has a less impact on CO2 absorption, while other impurities like CO2 and acetic acid have significant negative impacts on CO2 absorption. Fortunately, the impurities have a less influence on H2S removal efficiency, with more than 98% of H2S could be removed by RAA. Also, the influences of operating parameters on acid gases removal were investigated to provide some engineering suggestions.

Hydrogen is an industrial raw material both for the production of chemicals and for oil refining with hydrotreating. It is the subject of increasing attention for its possible use as an energy carrier and as a flexible energy storage medium. Its production is generally accomplished in Steam Methane Reforming (SMR) plants, where a gaseous mixture of CO and H2, with a limited number of other species, is obtained. The process of production and purification generates relevant amounts of carbon dioxide, which needs to be removed due to downstream process requirements or to limit its emissions to the atmosphere. A work by IEAGHG focused on the study of a state-of-the-art Steam Methane Reforming plant producing 100 kNm3/h of H2 and considered chemical absorption with MethylDiEthanolAmine (MDEA) solvent for removing carbon dioxide from the PSA tail gas in a baseline scheme composed of the absorber, one flash vessel and the regeneration column. This type of process is characterized by high energy consumption, in particular at the reboiler of the regeneration column, usually operated by employing steam, and modifications to the baseline scheme can allow for a reduction of the operating costs, though with an increase in the complexity of the plant. This work analyses three configurations of the treatment section of the off gas obtained after the purification of the hydrogen stream in the Pressure Swing Adsorption unit with the aim of selecting the one which minimizes the overall costs so as to further enhance Carbon Capture and Storage in non-power industries as well.

Alternative solvents based on aqueous solutions of amino acids have been recently developed as possible substitutes for Mono Ethanol Amine (MEA) for CO2 removal from flue gas streams. The potassium taurate solvent has the advantages of degradation resistance, low toxicity and low energy requirements for its regeneration. With any type of solvent, CO2 removal applied to a power production plant decreases the revenues obtained from selling electricity because of the energy requirements. Operating the CO2 removal section in flexible mode avoids significant effects on the profits of the power plant, while accomplishing environmental regulations. This work is the first journal paper focusing on the application in flexible mode of the potassium taurate system for treating a flue gas stream from a 500 MW coal-fired power plant. Techno-economic evaluations are performed to determine the best operating conditions considering the variation in the electricity demand and its price, and different values of carbon tax. In the summer period, with high electricity prices and demands, carbon tax values between 45 EUR/tCO2 and 60 EUR/tCO2 favor CO2 absorption in the flexible mode, without periods of full CO2 emissions during the day.

Model predictive control (MPC) is used in the CO2 removal process in the Subang field to improve its control performance. MPC is used to maintain the CO2 concentration at the sweet gas output by controlling the feed gas pressure (PIC-1101), makeup water flow rate (FIC-1102), and amine flow rate (FIC-1103). The empirical model applied to MPC to represent the process model is the auto-regressive exogenous (ARX) model. The ARX model is compared with the first order plus dead time (FOPDT) model based on the root mean square error (RMSE) between the model and the actual process, then MPC parameters are tuned which include sampling time (T), prediction horizon (P) and control horizon (M) to control for the three variables. Improved control performance is measured based on the integral square error (ISE). The results show that the ARX model is the best model for the CO2 removal process with an RMSE value of 35%-91% smaller than the FOPDT model. The optimal control parameters Prediction Horizon (P), Control Horizon (M) and Sampling Time (T) in the CO2 removal process are 75, 25 and 1 on PIC-1101, 25, 10 and 1 on FIC-1102, and 30, 25 and 1 on FIC-1103. The MPC-ARX (MPC using ARX model) can improve the control performance of 33% in the servo control and 6-56% on the regulatory control. However, not all of them showed an increase in control performance improvement from previous studies even though they had used the best model (ARX). This is due to the MPC parameter setting that is not yet appropriate, so it needs to be retuning.

As the urgency to limit global warming has intensified, negative emissions technology such as direct air capture and carbon sequestration are increasingly considered in climate mitigation scenarios. When Iceland opened the commercial-grade direct air carbon capture and storage (DACCS) facility in 2021, this marked a breakthrough for DACCS technology as a scalable climate mitigation solution. This study investigates the adoption of DACCS in Iceland and the potential for diffusion into other contexts as a global decarbonization solution. We implement expert interviews to analyze the adoption of technology, and to identify the various requirements of scaling DACCS into local and global contexts. Using inductive thematic analysis, we characterize the diverging perspectives on the role of carbon dioxide removal as a climate mitigation solution and also identify pathways toward technology upscaling at national, regional, and global scales. Despite the successful technology demonstration of DACCS, we find that experts hold different mental models of climate mitigation generally, characterized as “nature vs. technology.” We also find that experts clearly articulate the necessary conditions for the diffusion of DACCS more broadly, including explicit regulatory measures as guardrails against a “license to pollute” as well as bilateral governance structures that include financial investment. Finally, we find that the importance of public acceptance of the technology was noted among all expert groups. Limited data exist on the acceptance of DACCS paired with renewable energy and this is a future research recommendation.

Upgrading biogas into biomethane not only improves the biogas utilization as vehicle fuel or natural gas substitute, but also reduces the greenhouse gases emissions. Considering the principle of engineering green energy process, the renewable aqueous ammonia (RAA) solution obtained from biogas slurry was used to remove H2S and CO2 simultaneously in the hollow fiber membrane contactor. RAA was mimicked in this study using the ammonia aqueous solution mixed with some typical impurities including ethanol, acetic acid, propionic acid, butyric acid and NH4HCO3. Compared with the typical physical absorption (i.e., pure water) removing 48% of H2S from biogas, RAA with 0.1 mol·L-1 NH3 could remove 97% of H2S. Increasing the NH3 concentration from 0.1 to 0.5 mol·L-1 could elevate the CO2 absorption flux from 0.97 to 1.72 mol·m-2·h-1 by 77.3%. Among the impurities contained in RAA, ethanol has a less impact on CO2 absorption, while other impurities like CO2 and acetic acid have significant negative impacts on CO2 absorption. Fortunately, the impurities have a less influence on H2S removal efficiency, with more than 98% of H2S could be removed by RAA. Also, the influences of operating parameters on acid gases removal were investigated to provide some engineering suggestions. [ABSTRACT FROM AUTHOR]

The operational and economic constraints suffered by amine solvents for CO2 removal have motivated the research on an alternative solvent with better performance and cost-effectiveness. Amino acid salt (AAS) has been identified as an interesting green solvent, an alternative to commercial amine solvents. The present work evaluated the physicochemical and CO2-solubility properties of potassium L-cysteine (K-CYS), a naturally occurring amino-acid-based solvent for CO2 removal from natural gas. Its physicochemical properties, including density, viscosity, and refractive index, were measured at different temperatures ranging between 298.15 and 333.15 K and a concentration range of 5 to 30 wt.%. Based on the experiment, all properties were found to decrease with increasing temperature and increase with increasing concentration. The experiments also demonstrated a significant reduction of CO2 loading from 2.4190 to 1.1802 mol of CO2/mol of K-CYS with increasing solvent concentration from 10 to 30 wt% at 313.15 K and 20 bar (g). [ABSTRACT FROM AUTHOR]

One of the most mature technologies for removal of carbon dioxide from gaseous streams is chemical absorption and aqueous solutions of alkanolamines are employed, with Monoethanolamine (MEA) considered the benchmark solvent. However, its volatility and toxicity and the need for a lot of energy for regeneration made research focus on possible solvents that can perform the desired treatment of gaseous streams while reducing production and operating costs and the environmental impact, to be considered as substitutes. The process based on amino acid aqueous solutions, one type of these new solvents, has the advantage of an improved sustainability and, as the one employing aqueous solutions of potassium taurate, can also benefit of the enhancement due to the reaction of precipitation. In this work a rigorous rate-based model, built in the commercial process simulator ASPEN Plus®, properly customized for the representation of the system, is used to carry out a detailed process design for the CO 2 removal section of a NGCC plant by an aqueous solutions of potassium taurate, for which no previous papers on the topics have been found in the literature. The scheme is optimized and the performances of the process are evaluated for different targets of CO 2 removal. [Display omitted] • CO 2 removal in NGCC power plant is studied. • An aqueous solution of potassium taurate solvents is considered. • Simulations are performed in ASPEN Plus® customized for representing the system. • Design based on a techno-economic analysis is carried out. [ABSTRACT FROM AUTHOR]

In this study, hydrogen was recovered and purified by using a membrane contactor unit from CO2-rich gas without the use of any basic chemicals such as amines. The membrane operational parameters were adjusted to achieve high CO2 removal and H2 recovery. The effects of gas flow rate, pressure, gas composition (CO2/H2 ratio), pressure difference between liquid and gas, and gas/liquid ratio on CO2 removal and H2 recovery were investigated. Depending on the gas flow rate, the contact time between gas and liquid could be controlled, changing the absorption amounts of CO2 and H2. Regarding gas composition, an increase in the CO2/H2 ratio from 0.25 to 1 boosted H2 recovery. Furthermore, increasing the CO2/H2 ratio above 1 (from 1 to 3) generally reduced H2 recovery from 98.7% to 83%. Additionally, supplementation with the optimal amount of additive enhanced CO2 removal and H2 recovery. Thus, using a membrane contactor system results in high CO2 removal (82.7–93.5%) and H2 recovery (91.5–98.7%). Moreover, H2 production and separation can be performed in one system, implying that CO2 removal can be performed more efficiently by the membrane contactor. This study offers a new and promising route for producing high-purity H2 while removing CO2. [ABSTRACT FROM AUTHOR]

Natural gas processing is currently facing economic and environmental challenges due to abrupt changes in oil prices and the development of an alternate source of energy. Therefore it is essential to optimize the processing unit to make it profitable and environmentally friendly. Sustainable optimization of an industrial natural gas treatment plant is carried out using the NSGA-II algorithm for the methyl diethanol amine (MDEA) process to optimize CO 2 removal along with payback period and damage index. This multi-objective optimization study includes seven decision variables such as temperature and pressure of feed gas, feed flow rate, temperature and pressure of regenerator feed, lean amine temperature, and MDEA concentration. Three separate two-objective optimization study problems are developed and applied for retrofitted case and base case studies. Two different ProMax models are developed and validated the model by using actual plant data. All the retrofitted cases and base cases are solved and the Pareto optimal fronts are obtained. Trade-offs between different objectives are illustrated for all the problems. The lean vapor compression process can facilitate maximum H 2 S removal of 99.75% and maximum CO 2 removal of 98.52% simultaneously by maintaining a DI value of 476. TOPSIS method is used to rank and find the best optimal solution. Optimization study for uncertain CO 2 concentration (4%mole) in the feed gas is also analyzed and compared with normal feed conditions. The machine learning approach is used to obtain the predictions of selected objective functions for all the problem cases using the decision tree method. [Display omitted] [ABSTRACT FROM AUTHOR]

Energy may be generated in large quantities from fossil fuels, but this comes with environmental concerns. Thus, renewable resources like biogas, comprising carbon dioxide and methane, should be used alone or in combination with fossil fuels to mitigate the environmental footprints of energy generation systems. In this study, a new concept of hybrid solvent was presented, which combines 1-octyl-3-methylimidazolium tetrafluoroborate with aqueous mono diethanolamine for biogas upgrading process to provide high purity (≥ 99 wt%) and recovery (≥ 99 wt%) of biomethane. The process was simulated in ASPEN Plus® V.11. The thermodynamic framework was validated against experimental data, and rigorous regression was conducted to obtain binary parameters. To establish the efficacy of the suggested hybrid solvent, three scenarios were studied by altering the concentration of ionic liquid (5–20 wt%) linked with amine and compared to aqueous mono diethanolamine as the base case (50 wt%). The results showed that a hybrid solvent with 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate could increase CH4 purity to 99% (mol%). The hybrid solvent led to an energy saving of 64.94% compared to the amine-based system. Thermodynamic irreversibilities showed that 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate improved exergy efficiency by 54% over the amine-based procedure. Environmentally, the hybrid solvent system also achieved a higher capture rate (99%) and lower emissions (0.017 kW/kmol). Comparing the economic prospects, 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate saved 56% on total capital cost, making it competitive from an investment perspective.

Carbon dioxide removal (CDR) is expected to play a critical role in reaching net zero CO _2 and especially net zero greenhouse gase (GHG) emissions. However, the extent to which the role of CDR in counterbalancing residual emissions can be reduced has not yet been fully quantified. Here, we use a state-of-the-art integrated assessment model to develop a ‘Maximum Sectoral Effort’ scenario which features global emissions policies alongside ambitious effort across sectors to reduce their gross GHG emissions and thereby the CDR required for offsets. We find that these efforts can reduce CDR by over 50% globally, increase both the relative and absolute role of the land sink in storing carbon, and more evenly distribute CDR contributions and associated side-effects across regions compared to CO _2 pricing alone. Furthermore, the lower cumulative CO _2 and nonCO _2 emissions leads to earlier and lower peak temperatures. Emphasizing reductions in gross, in addition to net emissions while disallowing the substitution of less durable CDR for offsets can therefore reduce both physical and transition risks associated with high CDR deployment and temperature overshoot.

The accumulation of uncollected fly ash from flue gas in post-combustion CO2 capture processes is a significant concern in current coal-fired power plants due to its potential impact on the performance of CO2 absorbent and absorption towers. In order to determine the effect of fly ash on the mass transfer performance of CO2 absorption into monoethanolamine (MEA) and diethanolamine (DEA) aqueous solutions, experimental studies were carried out using a small-sized packed tower equipped with θ-ring random packing. These studies were conducted under various operating parameters, including solution temperature, liquid/gas ratio (L/G), packing height, and fly ash concentration. The results show that the effect of fly ash on the outlet CO2 concentration was primarily observed during the initial stages of the experimental process. Moreover, the presence of fly ash leads to a reduction in the volumetric overall mass transfer coefficient (KGav) when using MEA and DEA solution, and increasing the fly ash concentration further exacerbates this negative impact. However, the effect of fly ash on the reduction in KGav is not significantly related to its chemical composition but rather depends on the operational parameters. With increasing solution temperature, liquid/gas ratio (L/G), and packing height, the KGav values for different solutions exhibit an upward trend. The negative effect of fly ash on KGav remains relatively stable for MEA as solution temperature and packing height increase. Compared to MEA, fly ash has a greater negative effect on DEA solution under the same experimental conditions. The analysis reveals that the detrimental effect of fly ash on KGav primarily stems from its ability to alter the distribution state of the absorption liquid within the packed tower.

Over the Amazon region, rainfall-induced changes to CO _2 pathways significantly impact humans and multiple ecosystems. Its resilience is of vital importance, and idealized CO _2 removal experiments indicate that declining trends in rainfall amounts are irreversible and exhibit a deficiency when the CO _2 concentration returns to the pre-industrial level. The irreversible decline in Amazon rainfall is mainly due to the weakened ascent, further led by two main causes. (1) Enhanced tropospheric warming and a wetter atmospheric boundary layer over the tropics during CO _2 removal generate a strong meridional gradient of temperature and specific humidity; driven by prevailing northeasterly winds, negative moist enthalpy advection occurs, which in turn weakens the ascent over the Amazon and results in anomalous drought. (2) The enhanced radiative cooling of atmospheric column. Driven by the negative lapse-rate feedback, the outgoing longwave radiative flux increases in the clear-sky atmosphere. As a result, the anomalous diabatic descent generates to maintain the energy balance of the atmospheric column. This result implies that the symmetric removal of CO _2 does not guarantee full recovery of regional precipitation.

This study explored the consequences of allocating commitments to remove CO2 to countries according to their responsibility for human-made climate change based on historical (cumulative) CO2 emissions from fossil fuel use and industry. The 'carbon debt' to be restored through CO2 removal was calculated as the remaining carbon budget for warming by 2 °C minus emissions until 2100. The study included the remaining carbon budget from the recent literature and scenarios for greenhouse gas emissions. This experiment showed that industrialized countries would need to take on the biggest share of CO2 removal if the calculation of historical emissions starts with the industrial era. If accounting instead starts with the global negotiations on climate policy in 1990, however, developing countries would have to take on the largest commitment for CO2 removal. Given this scheme and with the aim of settling the carbon debt over two decades with equal annual efforts, the eight countries with the largest shares of historical emissions would have to take on annual CO2 removal efforts from 1 to 12 Gt CO2. These CO2 removal commitments would imply substantial efforts for many countries but nevertheless depend on the choice of a fairness principle and calculation method to render this operational. [ABSTRACT FROM AUTHOR]

With the increasing impact of climate change, carbon emissions and removals have become major issues. Forests are major carbon pools, and forest fires are an essential part of the carbon cycle. This study introduces a model for estimating the detailed actual CO2 removal in burned forests using burn severity and tree survivability. Actual CO2 removal was estimated from empirical yield tables without using the standard carbon removal provided by the national inventory. The primary CO2 calculation method followed the guidelines of the International Panel on Climate Change. The burn severity was mapped using Sentinel-2 multispectral instrument data, and the survivability of each forest type was estimated according to burn severity. The survivability was applied to the pre-fire CO2 removal of each forest to estimate post-fire CO2 removal. In our case study, the burned forest area was 1,034 ha, and the CO2 removal before the fire was 8,615.3 t/year. After the fire, removal decreased by 81.2% to 1,618.4 t/yr. In particular, the decrease in coniferous forests was high, more than 86%. The lack of survivability data on burned trees was a major limitation of our study. Systematically accumulating field monitoring data of post-fire forests will be necessary for future research and could serve as a reference for devising immediate countermeasures against forest fires. [ABSTRACT FROM AUTHOR]

The efficiency of a novel synthetic zeolite (Ze) prepared from stone cutting sludge and a natural zeolite (clinoptilolite, Cp) as the support of TiO2 photocatalyst was examined for the CO2 removal under solar irradiation using a designed parabolic trough collector (PTC). The used samples were characterized using XRF, BET, SEM/EDS, and XPS analyses. The enhanced sunlight irradiation obtained by PTC increased the performance of CO2 photocatalytic removal. The maximum CO2 adsorption by TiO2–Ze and TiO2–Cp composites was 21.1% and 28.4% which increased to 61.8% and 78.9% under sunlight irradiation, respectively. The efficiency of zeolite–TiO2 composites for CO2 removal was approximately two times higher than zeolites and TiO2 alone. The performance of TiO2–Ze-coated composite with lower use of photocatalyst for CO2 adsorption and photocatalytic removal was better than that of powder one. Regeneration of TiO2–Ze using NaOH solution improved its removal efficiency. The adsorption behavior of CO2 on TiO2–Ze composite was well described by the Langmuir isotherm and the pseudo-first-order kinetic model. This work promises CO2 reduction using natural and synthetic zeolite as an efficient photocatalyst support under solar irradiation. [ABSTRACT FROM AUTHOR]

Applying microalgae is a valuable strategy for CO2 removal, wastewater treatment, and biofuel production leading to valuable biomass production. However, the major challenge of biodiesel production by microalgae is achieving high lipid content while maintaining high biomass productivity. To do so, optimizing microalgal cultivation conditions is necessary. A novel two-stage process for increasing lipid productivity employing Chlorella vulgaris was introduced. The effect of three parameters; CO2 concentration (0.04–15.00% (v/v)), aeration rate (50–150 mL min−1), and photobioreactor diameter (7–14 cm), on microalgae growth, CO2, and nutrient removal in the first cultivation stage was studied. The effect of disconnecting CO2 aeration on the lipid content was then studied in the second cultivation stage. The results suggest that the maximum cell concentration (1.73 g L−1) is related to cultivation in a 10.5 cm diameter photobioreactor fed with 7.52% (v/v) CO2 concentration and 100 mL min−1 flow rate. The CO2 removal rate of the latter photobioreactor was 100% after 7 days. Although significantly affected the growth and lipid content, the studied parameters had no obvious effect on the nutrient removal. The highest lipid content was 32.85 wt.% and the lipid content of microalgae increased up to 61.24 wt.% by detaching CO2 aeration, a sign of the feasibility of using the proposed two-stage process for commercialization of biodiesel production by microalgae. The lipid produced by this strategy seems promising for biodiesel production according to American and European standards. [ABSTRACT FROM AUTHOR]

Energy may be generated in large quantities from fossil fuels, but this comes with environmental concerns. Thus, renewable resources like biogas, comprising carbon dioxide and methane, should be used alone or in combination with fossil fuels to mitigate the environmental footprints of energy generation systems. In this study, a new concept of hybrid solvent was presented, which combines 1-octyl-3-methylimidazolium tetrafluoroborate with aqueous mono diethanolamine for biogas upgrading process to provide high purity (= 99 wt%) and recovery (= 99 wt%) of biomethane. The process was simulated in ASPEN Plus® V.11. The thermodynamic framework was validated against experimental data, and rigorous regression was conducted to obtain binary parameters. To establish the efficacy of the suggested hybrid solvent, three scenarios were studied by altering the concentration of ionic liquid (5-20 wt%) linked with amine and compared to aqueous mono diethanolamine as the base case (50 wt%). The results showed that a hybrid solvent with 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate could increase CH4 purity to 99% (mol%). The hybrid solvent led to an energy saving of 64.94% compared to the amine-based system. Thermodynamic irreversibilities showed that 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate improved exergy efficiency by 54% over the amine-based procedure. Environmentally, the hybrid solvent system also achieved a higher capture rate (99%) and lower emissions (0.017 kW/kmol). Comparing the economic prospects, 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate saved 56% on total capital cost, making it competitive from an investment perspective. [ABSTRACT FROM AUTHOR]

Objective The CO2 absorption process under high gravity environment is simulated so as to provide guidance for the optimization of experimental process parameters. Methods An Aspen Plus calculation model for CO2 absorption using NaOH alkaline solution under high gravity was established, and the influence factors on the CO2 removal rate were investigated. Results While the high gravity reactor was equivalent to a conventional packed tower through the equivalent conversion method, the influence of sodium hydroxide mass fraction, solution feed rate and pressure on the CO2 removal rate were similar to that of the high gravity laboratory value, but the simulated value was only about 1/2 of the experimental value. The corrected simulation results were close to the experimental values, and the average deviation was only 0. 77%. Conclusions The established CO2 absorption model under high gravity environment is accurate and reliable, which can provide some directional guidance for subsequent experiments. [ABSTRACT FROM AUTHOR]

Memsorb™ (DMF Medical, Halifax, Canada) is a novel device based upon membrane oxygenator technology designed to eliminate CO2 from exhaled gas when using a circle anesthesia circuit. Exhaled gases pass through semipermeable hollow fibers and sweep gas flowing through these fibers creates a diffusion gradient for CO2 removal. In vivo Memsorb™ performance was tested during target-controlled closed-circuit anesthesia (TCCCA) with desflurane in O2/air using a Zeus IE® anesthesia workstation (Dräger, Lübeck, Germany). Clinical care protocols for using this novel device were guided by in vitro performance results from a prior study (submitted simultaneously). After IRB approval, written informed consent was obtained from 10 ASA PS I–III patients undergoing robot-assisted radical prostatectomy. TCCCA targets were 39% inspired O2 concentration (FIO2) and 5.0% end-expired desflurane concentration (FETdes). Minute ventilation (MV) was adjusted to maintain 4.5–6.0% FETCO2. The O2/air (40% O2) sweep flow into the Memsorb™ was manually adjusted in an attempt to keep inspired CO2 concentration (FICO2) ≤ 0.8%. The following data were collected: FIO2, FETdes, FICO2, FETCO2, MV, fresh gas flow (FGF, O2 and air), sweep flow, and cumulative desflurane usage (Vdes). Vdes of the Zeus IE®—Memsorb™ combination was compared with historical Vdes observed in a previous study when soda lime (DrägerSorb 800 +) was used. Results are reported as median and inter-quartiles. A combination of manually adjusting sweep flow (26 [21,27] L/min) and MV sufficed to maintain FICO2 ≤ 0.8% and FETCO2 ≤ 6.0%, except in one patient in whom the target Zeus IE® FGF had to be increased to 0.7 L/min for 6 min. FIO2 and FETdes were maintained close to their targets. Zeus IE® FGF after 5 min was 0 [0,0] mL/min. Average Vdes after 50 min was higher with Memsorb™ (20.3 mL) compared to historical soda lime canister data (12.3 mL). During target-controlled closed-circuit anesthesia in patients undergoing robot-assisted radical prostatectomy, the Memsorb™ maintained FICO2 ≤ 0.8% and FETCO2 ≤ 6.0%, and FIO2 remained close to target. Modest amounts of desflurane were lost with the use of the Memsorb™. The need for adjustments of sweep flow, minute ventilation, and occasionally Zeus IE® FGF indicates that the Memsorb™ system should preferentially be integrated into an automated closed-loop system. [ABSTRACT FROM AUTHOR]

Soda lime-based CO2 absorbents are safe, but not ideal for reasons of ecology, economy, and dust formation. The Memsorb™ is a novel CO2 removal device that uses cardiopulmonary bypass oxygenator technology instead: a sweep gas passes through semipermeable hollow fibers, adding or removing gas from the circle breathing system. We studied the in vitro performance of a prototype Memsorb™ used with a Zeus IE® anesthesia machine when administering sevoflurane and desflurane in O2/air mixtures. The Zeus IE® equipped with Memsorb™ ventilated a 2L breathing bag with a CO2 inflow port in its tip. CO2 kinetics were studied by using different combinations of CO2 inflow (VCO2), Memsorb™ sweep gas flow, and Zeus IE® fresh gas flow (FGF) and ventilator settings. More specifically, it was determined under what circumstances the inspired CO2 concentration (FICO2) could be kept < 0.5%. O2 kinetics were studied by measuring the inspired O2 concentration (FIO2) resulting from different combinations of Memsorb™ sweep gas flow and O2 concentrations, and Zeus IE® FGFs and O2 concentrations. Memsorb™'s sevoflurane and desflurane waste was determined by measuring their injection rates during target-controlled closed-circuit anesthesia (TCCCA), and were compared to historical controls when using a soda lime absorbent (Draegersorb 800+) under identical conditions. With 160 mL/min VCO2 and 5 L/min minute ventilation (MV), lowering the sweep gas flow at any fixed Zeus IE® FGF increased FICO2 in a non-linear manner. Sweep gas flow adjustments kept FICO2 < 0.5% over the entire Zeus IE® FGF range tested with VCO2 up to 280 mL/min; tidal volume and respiratory rate affected the required sweep gas flow. At 10 L/min MV and low FGF (< 1.5 L/min), even a maximum sweep flow of 43 L/min was unable to keep FICO2 ≤ 0.5%. When the O2 concentration in the Zeus IE® FGF and the Memsorb™ sweep gas flow differed, FIO2 drifted towards the sweep gas O2 concentration, and more so as FGF was lowered; this effect was absent once FGF > minute ventilation. During sevoflurane and desflurane TCCCA, the Zeus IE® FGF remained zero while agent usage per % end-expired agent increased with increasing end-expired target agent concentrations and with a higher target FIO2. Agent waste during target-controlled delivery was higher with Memsorb™ than with the soda lime product, with the difference remaining almost constant over the FGF range studied. With a 5 L/min MV, Memsorb™ successfully removes CO2 with inflow rates up to 240 mL/min if an FICO2 of 0.5% is accepted, but at 10 L/min MV and low FGF (< 1.5 L/min), even a maximum sweep flow of 43 L/min was unable to keep FICO2 ≤ 0.5%. To avoid FIO2 deviating substantially from the O2 concentration in the fresh gas, the O2 concentration in the fresh gas and sweep gas should match. Compared to the use of Ca(OH)2 based CO2 absorbent, inhaled agent waste is increased. The device is most likely to find its use integrated in closed loop systems. [ABSTRACT FROM AUTHOR]