CO2 Drop Research Articles

Dynamic link between Neo-Tethyan subduction and atmospheric CO2 changes: insights from seismic tomography reconstruction

Volcanic arc degassing contributes significantly to atmospheric CO2 levels and therefore has a pivotal impact on paleoclimate changes. The Neo-Tethyan decarbonation subduction is thought to have played a major role in Cenozoic climate changes, although there are still no quantifiable restrictions. Here we build past subduction scenarios using an improved seismic tomography reconstruction method and calculate the subducted slab flux in the India–Eurasia collision region. We find remarkable synchronicity between calculated slab flux and paleoclimate parameters in the Cenozoic, indicating a causal link between these processes. The closure of the Neo-Tethyan intra-oceanic subduction resulted in more carbon-rich sediments subducting along the Eurasia margin, as well as continental arc volcanoes, which further triggered global warming up to the Early Eocene Climatic Optimum. The abrupt termination of the Neo-Tethyan subduction due to the India–Eurasia collision could be the primary tectonic cause of the ∼50–40 Ma CO2 drop. The gradual decrease in atmospheric CO2 concentration after 40 Ma may be attributed to enhance continental weathering due to the growth of the Tibetan Plateau. Our results contribute to a better understanding of the dynamic implications of Neo-Tethyan Ocean evolution and may provide new constraints for future carbon cycle models.

Predictors of Neurological Complications of Pediatric Post-Cardiotomy Extracorporeal Life Support.

Post-cardiotomy extracorporeal membrane oxygenation (ECMO) was associated with significant neurological complications affecting the overall outcome. The aim of the work is to determine the incidence and the predictors of neurological events during pediatric extracorporeal life support after cardiac surgery. This is a retrospective study that encompassed all neonates, infants, and children (<18 years of age) who need extracorporeal life support following cardiac surgery between January 2015 and December 2018 at San Donato Hospital, Italy. Data as regards surgical procedure of congenital heart disease, in-hospital mortality, length of ECMO, hospital stay durations, short-term neurological ECMO complications and outcome were analyzed. The sixty-three patients who received post-cardiotomy ECMO, Neurological complications were evident in 31.7% in the form of ischemic stroke in 17.5% and hemorrhagic stroke in 11.1%. By multivariable analysis, the older age of cyanotic cases, the need for a venting cannula, and the rapid CO2 drop in the first 24 h were the most independent risk factors for neurological complications. Prolonged ECMO support and hospital stay duration were associated with neurological sequelae. Neurological complications either ischemic or hemorrhagic strokes were common during pediatric post-cardiotomy ECMO and were significantly related to prolonged ECMO support and hospital stay. Predictors of these neurological sequelae are the older cyanotic cases, the need for a venting cannula, the oxygenator thrombosis, and the rapid CO2 drop in the first 24 h of ECMO.

A dynamic ocean driven by changes in CO2 and Antarctic ice-sheet in the middle Miocene

The middle Miocene climate transition (MMCT), likely triggered by a decrease in atmospheric CO2 concentration and changes in the Earth's orbital configuration, entailed major expansion of the Antarctic ice-sheet and cooling of the global ocean at ~15–13 Ma. By comparing simulations that use boundary conditions representative of 15 and 13 Ma, we assess the response of ocean temperatures and deep ocean circulation to atmospheric CO2 drawdown (from 400 to 200 ppmv) and Antarctic ice-sheet expansion (43 m of sea-level equivalent) during the MMCT by means of the Community Climate System Model version 3. The model simulates a decrease in mean global sea-surface temperature by 1.6 °C across the transition. Individual forcing experiments reveal that surface cooling is fully attributable to the CO2 drop, whereas expansion of the Antarctic ice-sheet tends to cause a slight global warming of the upper ocean. At depth, modelled ocean temperatures decrease by 1.5–2 °C across the MMCT in most regions. While the CO2 effect dominates deep-ocean cooling, about 25–30% is attributable to the expansion of the Antarctic ice-sheet.In the convection regions of the Southern Ocean, the CO2 drawdown causes an increase in salinity through sea ice formation and changes in the precipitation-evaporation balance. This increase in salinity, together with a decrease in surface temperatures, translates into an intensification in Antarctic Bottom Water formation that cools the deep ocean. The contribution of the Antarctic ice-sheet expansion to bottom and deep water cooling occurs through an increase in the surface heat flux from the ocean to the atmosphere, which is linked to intensified cold surface winds blowing off the Antarctic continent.This study suggests that the magnitude of cooling of deep waters across the MMCT inferred from proxy records can be explained by the combined effects of the CO2 decrease and Antarctic ice-sheet expansion. Our surface cooling estimates are generally lower than those indicated by proxies.

Experimental study on thermal effect and gas release laws of coal-polyurethane cooperative spontaneous combustion

This paper presents a research on the kinetics and gas release laws of the cooperative spontaneous combustion of coal-polyurethane binary system by means of thermogravimetric analysis and spontaneous combustion simulation experiments. The coal-polyurethane binary system is more prone than individual samples to combustion. The polyurethane mass fraction has a great influence on the cooperative spontaneous combustion process. As the polyurethane mass fraction rises, the activation energies of oxygen absorption stage and pyrolysis stage decrease. The combustion residues of coal-polyurethane binary system scorches into lumps and the surfaces of the particles become rougher. During spontaneous combustion, the initial release temperatures of the four gases CO2, CO, C2H6 and C2H4 drop as the polyurethane mass fraction increases. The gas release amount of them increases with increasing polyurethane mass fraction. And the amount of CH4 decreases as the polyurethane mass fraction increases. The CO/CO2 ratio with temperature for different polyurethane mass fraction have the same trends. The results of this study have implications concerning polyurethane materials application and fire protection in coal mine.

Experimental determination of walnut shell pyrolysis kinetics in N2 and CO2 via thermogravimetric analysis, fluidized bed and drop tube reactors

A thermogravimetric analyzer (TGA), a fluidized bed reactor (FBR) and a drop tube reactor (DTR) are used to study the effect of reactor type, heating rate and temperature on the pyrolysis of pulverized walnut shell particles in N2 and in CO2. These setups cover a temperature range of 400–1300 K with heating rates of 10−1 to 105 K s−1. The single first-order model in combination with an Arrhenius approach is used to describe the pyrolysis reaction. Derived activation energies for all setups show similar values (Ea,TGA = 71.96 kJ mol−1, Ea,FBR = 68.60 kJ mol−1 and Ea,DTR = 60.83 kJ mol−1), while an increase in the reactor temperature tend to lower the activation energy. Pyrolysis gas compositions in FBR and DTR reveal consistent trends towards lower H2O and higher CO contents with increasing reactor temperature. To evaluate the impact of CO2 on the solid conversion, TGA measurements in CO2 are used to determine gasification kinetics (Ea,g = 214.1 kJ mol−1, Ag = 71.96 s−1). CFD simulations using these kinetics in CO2 drop tube experiments let assume that the changed thermophysical properties of the gas and not the gasification reaction lead to the observed stronger conversion in CO2 compared to N2.

The use of continuous Flow Ventilatory Support for Hypercapnic Respiratory Failure

Our aim was to assess the effectivity of continuous flow ventilatory support (CFVS) in those COPD patients undergoing cardiac surgery who developed hypercapnic respiratory failure.Materials and methods. CFVS was applied in 11 COPD (Stage 2.55±0.52 on average) patients undergoing cardiac surgery, after weaning from «conventional» pressure controlled (PCV) or pressure support ventilation (PSV) mode. All of these patients had hypercapnea with respiratory failure that has been manifested after 15±10 hours after postoperative weaning from ventilator. CFVS was applied using nasotracheal catheter (diameter 5–6 mm) with average inspiratory flow Qin = 26±2,3 l/min while using FiO2 of 0.3–0.35.Results. Only one out of 11 patients failed to recover from hypercapnic respiratory failure using CFVS and had to be intubated instead. Spontaneous ventilation frequency was gradually decreasing from 24.8±3.6 breaths/min to 16±2 breaths/min after initiation of CFVS (P&lt;0.01). Average value of PaO2 before CFVS was 59±7.5 mmHg and rose to 99.6±4.5 mmHg just before CFVS was terminated (P&lt;0.01). PaCO2 before CFVS was measured to be 73.2±7.5 mmHg and dropped to 45.7±4.3 mmHg (P&lt;0.01). CO2 drop was fast in the first 18 hours from CFVS application. Average time for application of CFVS was 3.09±0.9 day.Conclusion. CFVS is an effective and minimally invasive mode of ventilation support that can be used in patients suffering from hypercapnic respiratory failure to avoid the need to intubate trachea and connect the patient to conventional ventilator.

ATHLET extensions for the simulation of supercritical carbon dioxide driven power cycles

Abstract The Fukushima accident reveals the need for additional safety systems for nuclear power plants. One promising option is the supercritical carbon-dioxide (sCO2) heat removal system, which consists of a simple Brayton cycle. This study provides an overview of the extensions and validation of the thermal-hydraulic system code ATHLET for the simulation of sCO2 power cycles, especially with regard to the sCO2 heat removal system. The properties of CO2, heat transfer and pressure drop correlations, as well as compact heat exchanger and turbomachinery modelling are considered.

Coupled climate–carbon cycle simulation of the Last Glacial Maximum atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; decrease using a large ensemble of modern plausible parameter sets

Abstract. During the Last Glacial Maximum (LGM), atmospheric CO2 was around 90 ppmv lower than during the pre-industrial period. The reasons for this decrease are most often elucidated through factorial experiments testing the impact of individual mechanisms. Due to uncertainty in our understanding of the real system, however, the different models used to conduct the experiments inevitably take on different parameter values and different structures. In this paper, the objective is therefore to take an uncertainty-based approach to investigating the LGM CO2 drop by simulating it with a large ensemble of parameter sets, designed to allow for a wide range of large-scale feedback response strengths. Our aim is not to definitely explain the causes of the CO2 drop but rather explore the range of possible responses. We find that the LGM CO2 decrease tends to predominantly be associated with decreasing sea surface temperatures (SSTs), increasing sea ice area, a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a strengthening of the Antarctic Bottom Water (AABW) cell in the Atlantic Ocean, a decreasing ocean biological productivity, an increasing CaCO3 weathering flux and an increasing deep-sea CaCO3 burial flux. The majority of our simulations also predict an increase in terrestrial carbon, coupled with a decrease in ocean and increase in lithospheric carbon. We attribute the increase in terrestrial carbon to a slower soil respiration rate, as well as the preservation rather than destruction of carbon by the LGM ice sheets. An initial comparison of these dominant changes with observations and paleoproxies other than carbon isotope and oxygen data (not evaluated directly in this study) suggests broad agreement. However, we advise more detailed comparisons in the future, and also note that, conceptually at least, our results can only be reconciled with carbon isotope and oxygen data if additional processes not included in our model are brought into play.

Numerical Study on Single Flowing Liquid and Supercritical CO2 Drop in Microchannel: Thin Film, Flow Fields, and Interfacial Profile

Taylor segments, as a common feature in two- or multi-phase microflows, are a strong flow pattern candidate for applications when enhanced heat or mass transfer is particularly considered. A thin film that separates these segments from touching the solid channel and the flow fields near and inside the segment are two key factors that influence (either restricting or improving) the performance of heat and mass transfer. In this numerical study, a computational fluid dynamics (CFD) method and dense carbon dioxide (CO2) and water are applied and used as a fluid pair, respectively. One single flowing liquid or supercritical CO2 drop enclosed by water is traced in fixed frames of a long straight microchannel. The thin film, flow fields near and within single CO2 drop, and interfacial distributions of CO2 subjected to diffusion and local convections are focused on and discussed. The computed thin film is generally characterized by a thickness of 1.3~2.2% of the channel width (150 µm). Flow vortexes are formed within the hydrodynamic capsular drop. The interfacial distribution profile of CO2 drop is controlled by local convections near the interface and the interphase diffusion, the extent of which is subject to the drop size and drop speed as well.

High speed spin coating in fabrication of Pebax 1657 based mixed matrix membrane filled with ultra-porous ZIF-8 particles for CO2/CH4 separation

Modified ultra-porous ZIF-8 particles were used to prepare novel ZIF-8/Pebax 1657 mixed matrix membranes (MMMs) on PES support for separation of CO2 from CH4 using spin coating method. TEM and SEM were used to characterize modified ZIF-8 particles. SEM was also used to investigate the morphology of synthesized MMMs. The MMMs with thinner selective layer showed higher CO2 permeability and lower CO2/CH4 selectivity in permeation tests compared to MMMs with thicker selective layer. The plasticization was recognized as the main reason for rise in CO2 permeability and drop in CO2/CH4 selectivity of thinner MMMs. The gas sorption results showed that the high permeability of CO2 in MMMs is mainly due to the high solubility of this gas in MMMs, leading to high CO2/CH4 solubility selectivity for MMMs. The fractional free volume and void volume fraction of MMMs increased as the thickness of membrane decreased. Applying higher mixed feed pressures and permeation tests temperatures resulted in increase in CO2 permeability and decrease in CO2/CH4 selectivity. At highest testing temperature (60 °C), the CO2 permeability of synthesized MMMs with thinner selective layer remarkably increased.

The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition

The continental scale initiation of the Antarctic ice sheet at the Eocene-Oligocene boundary (Eocene-Oligocene transition (EOT), 34 Ma) is associated with a global reorganization of the climate. If data studies have assessed the precise timing and magnitudes of the ice steps, modeling studies have been unable to reproduce a transient ice evolution during the Eocene-Oligocene transition in agreement with the data. Here we simulate this transition using general circulation models coupled to an ice sheet model. Our simulations reveal a threshold for continental scale glaciation of 900 ppm, 100 to 150 ppm higher than previous studies. This result supports the existence of ephemeral ice sheets during the middle Eocene, as similar CO2 levels (900–1000 ppm) have been reached episodically during this period. Transient runs show that the ice growth is accurately timed with EOT-1 and Oi-1, the two δ18O excursions occurring during the transition. We show that CO2 and orbital variations are crucial in initiating these steps, with EOT-1 corresponding to the occurrence of low summer insolation, whereas Oi-1 is controlled by a major CO2 drop. The two δ18O steps record both ice growth and temperature, representing some 10–30 m eustatic sea level fall and 2–4°C cooling at EOT-1 and 70 ± 20 m and 0–2°C for Oi-1. The simulated magnitude of the ice steps (10 m for EOT-1 and 63 m for Oi-1) and the overall cooling at various locations show a good agreement with the data, which supports our results concerning this critical transition.

Glacial CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; cycle as a succession of key physical and biogeochemical processes

Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that have led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. The computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve in time: changes in sea surface temperatures and in the volume of bottom water of southern origin control atmospheric CO2 during the glacial inception and deglaciation; changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.

An analysis of liquid CO2 drop formation with and without hydrate formation in static mixers

AbstractThe formation process of CO2 drops in various types of Kenics Static Mixers was analyzed from the perspective of energy dissipation in the mixer, focusing on the formation of drop surfaces. Experimental studies on CO2 drop formation were conducted under varying temperatures, pressure, and flow rates, with and without hydrate formation. Analysis of the CO2 drop size and distribution at several locations within the static mixer was conducted, as of pressure drop in the mixer, to determine dissipation energies. In all the experimental conditions, by considering the surface energy for hydrate formation, the energy required for the formation of CO2 drops correlated well with total energy dissipation by mixer flow, which is represented by a pressure drop along the mixer. This process has important applications to the formation of liquid CO2 for ocean disposal as a countermeasure to global warming. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Impact of strong deep ocean stratification on the glacial carbon cycle

During the Last Glacial Maximum, the climate was substantially colder and the carbon cycle was clearly different from the late Holocene. According to proxy data deep oceanic δ13C was very low, and the atmospheric CO2 concentration also reduced. Several mechanisms have been proposed to explain these changes, but none can fully explain the data, especially the very low deep ocean δ13C values. Oceanic core data show that the deep ocean was very cold and salty, which would lead to enhanced deep ocean stratification. We show that such an enhanced stratification in the coupled climate model CLIMBER‐2 helps get very low deep oceanic δ13C values. Indeed the simulated δ13C reaches values as low as −0.8‰ in line with proxy data evidences. Moreover it increases the oceanic carbon reservoir leading to a small, yet robust, atmospheric CO2 drop of approximately 10 ppm.

Dissolution of CO2 Drops and pH Change in CO2 Ocean Storage

The dissolution rate of CO2 drops with CO2 hydrate films was investigated to estimate the environmental impacts of the ocean storage of CO2. The diameter of dissolving CO2 drops was measured and compared with that from a theoretical model, where the mass transfer coefficient is provided by Ranz-Marshall's equation to involve the effect of water flow on the dissolution rate. The pH in ambient water around the drops was also measured to obtain the CO2 concentration in ambient water, which is also incorporated into the model. The dissolution rate of the CO2 drop was obtained from both the model and the experimental results. The experimental dissolution rate was enhanced by an increase in flow velocity similar to the predicted rate; however, the experimental dissolution rate was lower than that predicted. Moreover, the difference between the experimental and predicted dissolution rates became higher due to an increase in flow velocity.

Parameterization of drag and dissolution of rising CO2 drops in seawater

In this work the dynamics and dissolution of a hydrate‐covered CO2 drop were studied, using a numeric model and data from one of very few CO2 experiments performed in the real ocean. A theory including the standard drag curve of rigid spheres was shown not to fit the observed drop rise velocity. However, a drag parameterization supported by numerous laboratory experiments with gas bubbles provides a good match of the observed rise velocity of a liquid CO2 drop covered with hydrate. The results confirm laboratory results showing that shape is a key factor determining the CO2 drop dynamics. We also found that hydrate reduces the mass transfer of the observed drop by a factor of 2, which is compatible with laboratory experiments. Numerical experiments with different drop sizes showed that the choice of drag parameterization has a significant impact on the estimated vertical distribution of dissolved CO2.