Low CO2 Partial Pressure Research Articles

Screening tests of new hybrid solvents for the post-combustion CO2 capture processby chemical absorption

This study focused on the screening of new hybrid solvents (mixture of a chemical (usually an amine) and a physical (ether, alcohol, etc.) solvent) for the post-combustion CO2 capture process by chemical absorption. Such scrubbing solutions aim at combining the advantages of the two components, namely: a low regeneration energy and a high absorption capacity of the physical solvent at intermediate CO2 partial pressures, a better absorption performances of the chemical solvent at low CO2 partial pressures and also high absorption kinetics due to chemical reactions with CO2. The innovative aspect of our approach was based on the use of acetals as physical components of the hybrid solvent. The purpose of our study was to characterize and compare these new hybrid solvents in terms of absorption and regeneration performances using two types of screening tests. Different blended solutions (composed of a conventional amine such as monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP)) and an acetal compound such as 2,5,7,10-tetraoxaundecane (TOU) were tested. Regarding the absorption performances, a double stirred cell reactor was used to compare the absorption efficiencies of the solvents at 298 K. It was observed that the addition of the acetal compound improves significantly the absorption efficiencies, especially at the beginning of the batch absorption test, namely at low CO2 loadings of the solution. Meanwhile, regeneration tests were performed using a regeneration cell allowing to compare the regeneration efficiency of the solvents at fixed heating power (600 W). The higher cyclic capacities and better regeneration efficiencies with acetals base solvents were also highlighted. Globally, this work confirms through this first step that new hybrid solvents, composed of amine(s) and acetal, could be a very promising alternative to classical solvents.

Dissolution of dehydroxylated lizardite at flue gas conditions: I. Experimental study

The direct mineralization of flue gas CO2 yields serviceable carbonates, thus combining CO2 utilization with its permanent storage. Such a process requires the rapid dissolution of a magnesium or calcium source at lean operating conditions. Motivated by its worldwide abundance, we have studied the dissolution kinetics of a lizardite-type serpentine that was 75% dehydroxylated by thermal pretreatment to maximize its reactivity. A continuous stirred liquid and gas flow-through setup was designed to perform far-from-equilibrium dissolution experiments at moderate temperatures (30°C⩽T⩽120°C),lowCO2 partial pressures (0.1bar⩽pCO2⩽2bar), using two different particle size fractions, and using a mineral acid instead of CO2 to vary the solution pH. Dissolution was measured to be non-stoichiometric and did not reach steady state within 10h. Up to 83% of the magnesium (Mg) and 72% of the silicon (Si) dissolved within the first 100min, where the dissolution rate for both Mg and Si increased with temperature and pCO2. This fast stage was followed by a period with much reduced dissolution rates. The key observations are rationalized with regard to the physical morphology and chemical properties of the thermally activated mineral, and discussed in view of the design of a process that combines CO2 capture and storage by mineralization.

Unusual Small Subunit That Is Not Expressed in Photosynthetic Cells Alters the Catalytic Properties of Rubisco in Rice

Rubisco small subunits (RbcSs) are encoded by a nuclear multigene family in plants. Five RbcS genes, OsRbcS1, OsRbcS2, OsRbcS3, OsRbcS4, and OsRbcS5, have been identified in rice (Oryza sativa). Among them, the amino acid sequence of OsRbcS1 differs notably from those of other rice RbcSs. Phylogenetic analysis showed that OsRbcS1 is genetically distant from other rice RbcS genes and more closely related to RbcS from a fern and two woody plants. Reverse transcription-PCR and promoter β-glucuronidase analyses revealed that OsRbcS1 was not expressed in leaf blade, a major photosynthetic organ in rice, but was expressed in leaf sheath, culm, anther, and root central cylinder. In leaf blade of transgenic rice overexpressing OsRbcS1 and leaf sheath of nontransgenic rice, OsRbcS1 was incorporated into the Rubisco holoenzyme. Incorporation of OsRbcS1 into Rubisco increased the catalytic turnover rate and Km for CO2 of the enzyme and slightly decreased the specificity for CO2, indicating that the catalytic properties were shifted to those of a high-activity type Rubisco. The CO2 assimilation rate at low CO2 partial pressure was decreased in overexpression lines but was not changed under ambient and high CO2 partial pressure compared with nontransgenic rice. Although the Rubisco content was increased, Rubisco activation state was decreased in overexpression lines. These results indicate that the catalytic properties of Rubisco can be altered by ectopic expression of OsRbcS1, with substantial effects on photosynthetic performance in rice. We believe this is the first demonstration of organ-specific expression of individual members of the RbcS gene family resulting in marked effects on Rubisco catalytic activity.

Low rank coal – CO2 gasification: Experimental study, analysis of the kinetic parameters by Weibull distribution and compensation effect

Gasification is generally considered as the most effective for low rank coal exploitation and CO2 gasification offers the advantage of upgrading an environmentally detrimental gas. Isothermal CO2 gasification tests of Greek low rank coal were performed in a tubular fixed bed reactor, to study the effect of the various reaction conditions. Greek lignite was quite reactive with CO2, resulting in high conversions even at short reaction times, while the obtained chars remained reactive after devolatilisation, as the continuous increase of conversion indicated. Conversion was very sensitive to temperature due to both pyrolysis and C–CO2 reactions, and for the granulometries studied (up to 1000 μm) the gasification rate was independent of particle size. CO2 partial pressure affected the gasification rate at low CO2 partial pressures, since the reactivity of lignite remained high (conversion ∼85% w/w daf) even for 0.25 atm CO2 partial pressure. The presence of CO retarded the reaction and the gasification rate decreased rapidly as the concentration of CO increased. The first order Volume Reaction Model (VMR) adopted was proven quite effective in describing the experimental results. Experimental results showed that the activation energy (E) varied with time, passing through a wide maximum between 10 and 15 min. The pre-exponential factor (k0) follows the behaviour of the activation energy, however, it exhibits a more sharp maximum at the same time region. The variations of the kinetic parameters with time could be attributed to the different nature of carbon atoms gasified and the changes of the number of active collisions, as the gasification reaction proceeds. As the gasification reaction advanced the Arrhenius parameters (E and k0) increased or decreased simultaneously, exhibiting a compensation effect. The probability density function (pdf) of the Weibull distribution was employed successfully to depict the variations of the kinetic parameters, E and k0.

CO2-induced shift in microbial activity affects carbon trapping and water quality in anoxic bioreactors

Microbial activity is a potentially important yet poorly understood control on the fate and environmental impact of CO2 that leaks into aquifers from deep storage reservoirs. In this study we examine how variation in CO2 abundance affected competition between Fe(III) and SO42--reducers in anoxic bioreactors inoculated with a mixed-microbial community from a freshwater aquifer. We performed two sets of experiments: one with low CO2 partial pressure (∼0.02atm) in the headspace of the reactors and one with high CO2 partial pressure (∼1atm). A fluid residence time of 35days was maintained in the reactors by replacing one-fifth of the aqueous volume with fresh medium every seven days. The aqueous medium was composed of groundwater amended with small amounts of acetate (250μM), phosphate (1μM), and ammonium (50μM) to stimulate microbial activity. Synthetic goethite (1mmol) and SO42- (500μM influent concentration) were also available in each reactor to serve as electron acceptors. Results of this study show that higher CO2 abundance increased the ability of Fe(III) reducers to compete with SO42- reducers, leading to significant shifts in CO2 trapping and water quality. Mass-balance calculations and pyrosequencing results demonstrate that SO42- reducers were dominant in reactors with low CO2 content. They consumed 85% of the acetate after acetate consumption reached steady state while Fe(III) reducers consumed only 15% on average. In contrast, Fe(III) reducers were dominant during that same interval in reactors with high CO2 content, consuming at least 90% of the acetate while SO42- reducers consumed a negligible amount (<1%). The higher rate of Fe(III) reduction in the high-CO2 bioreactors enhanced CO2 solubility trapping relative to the low-CO2 bioreactors by increasing alkalinity generation (6X). Hence, the shift in microbial activity we observed was a positive feedback on CO2 trapping. More rapid Fe(III) reduction degraded water quality, however, by leading to high Fe(II) concentration.

Pathophysiology of white-nose syndrome in bats: a mechanistic model linking wing damage to mortality

White-nose syndrome is devastating North American bat populations but we lack basic information on disease mechanisms. Altered blood physiology owing to epidermal invasion by the fungal pathogen Geomyces destructans (Gd) has been hypothesized as a cause of disrupted torpor patterns of affected hibernating bats, leading to mortality. Here, we present data on blood electrolyte concentration, haematology and acid-base balance of hibernating little brown bats, Myotis lucifugus, following experimental inoculation with Gd. Compared with controls, infected bats showed electrolyte depletion (i.e. lower plasma sodium), changes in haematology (i.e. increased haematocrit and decreased glucose) and disrupted acid-base balance (i.e. lower CO2 partial pressure and bicarbonate). These findings indicate hypotonic dehydration, hypovolaemia and metabolic acidosis. We propose a mechanistic model linking tissue damage to altered homeostasis and morbidity/mortality.

CO2 Solubility in a Mixture Absorption System of 2-Amino-2-methyl-1-propanol with Ethylene Glycol

A mixture system of sterically hindered amine 2-amino-2-methyl-1-propanol (AMP) with ethylene glycol (EG) was developed. The solubility of CO2 in mixture solutions of AMP–EG was measured at temperatures from 303.2 to 353.2 K and partial pressures of CO2 from 5 to 120 kPa. The concentration of AMP ranged from 0.4 to 1.0 mol/L. A model based on a zwitterion mechanism concerned with parameters independent of temperature and ion strength was derived, which could fit the experimental data very well. The calculated heat of absorption of CO2 in AMP–EG solution showed a decline compared to that in AMP–H2O solution. Comparing the solubilities of CO2 in different solvents with the same chemical absorber AMP, we found that the solvent has a significant influence on the solubility of CO2. Two possible aspects make contributions to the influence: deprotonation process and ion strength. The study of the influence of the solvent provides guidance for a reasonable selection and good design of the absorption process for CO2. Compared to AMP–DEG and AMP–TEG solutions, the loading of CO2 in AMP–EG solution is higher especially at lower partial pressure of CO2; the viscosity of AMP–EG solution is also lower. Compared to AMP–H2O solution, AMP–EG solution has higher circular loading of CO2 while the temperature changes especially at lower desorption temperature.

Comparison study on strategies to prepare nanocrystalline Li2ZrO3-based absorbents for CO2 capture at high temperatures

A comparison study has been conducted on the strategies for synthesizing nanocrystalline Li2ZrO3 and K- doped Li2ZrO3 absorbents for CO2 capture at high temperatures, including solid-state and liquid-phase meth- ods, citrate route, and starch-assisted sol-gel method combined with freeze-drying technique. The absorption properties, including uptake rate and absorption capacity, of synthesized absorbents were investigated by thermo- gravimetric analysis (TGA) at different CO2 partial pressures. The nanosized Li2ZrO3 crystals synthesized by the citrate route exhibit a faster uptake and a higher, nearly stoichiometric absorption capacity than those synthesized by the solid-state and liquid-phase methods. The doping of K into Li2ZrO3 can significantly improve the uptake rate of CO2, especially at low CO2 partial pressures. For the synthesis of K-doped Li2ZrO3, the citrate route has poor reproducibility and scalability, whereas the starch-assisted sol-gel method combined with freeze-drying technique is reproducible and easily scaled up, and the thus synthesized absorbents possess excellent CO2 capture properties.

Facilitated transport by amine-mediated poly(vinyl alcohol) membranes for CO2 removal from natural gas

The drive toward greater application of membrane has resulted in its rapid development in natural gas processing industry. In this work, amine-mediated membranes were tailored for CO2 removal from CO2/CH4 stream. The effects of various parameters such as amine concentration, microporous support, feed pressure and composition were examined to study the permeation behavior of pure and mixed gases. Generally, CO2 transport through the DEA-PVA membranes was higher than that of MEA-PVA membranes for approximately 70%. The membrane containing 15 wt% DEA and 35 wt% MEA revealed higher permselectivity. CO2 permeance enhancement of amine-PVA membranes in comparison with neat PVA membrane, confirmed that CO2-amine reaction was the dominant transport mechanism. Additionally, with increasing feed pressure, CO2/CH4 permselectivity decreased due to carrier saturation. However, lower partial pressure of CO2 was in favor of reaction mechanism in pure and mixed gas tests. On the other hand, CH4 is not significantly affected by feed pressure confirming that solutiondiffusion is the governing transport mechanism. Additionally, PTFE support with higher wettability showed better performance (18%) regardless of amine type, concentration and feed pressure. DEA-PVA membrane has exhibited good stability during 2 weeks, unlike MEA-impregnated membrane, which was probably due to carrier degradation over time. POLYM. ENG. SCI., 54:1268–1279, 2014. V C 2013 Society of Plastics Engineers

CO2 Capture at High Temperature and Low Concentration on Li4sio4 Based Sorbents

Solid sorbents based on lithium orthosilicate (Li4SiO4) have shown promise for CO2 capture at high temperature. Improved sorption properties can be obtained by appropriate doping. In this study, different promoted Li4SiO4-based sorbents were prepared by addition of potassium carbonate and binary/ternary alkali (Li, K and Na) carbonate eutectic mixtures. The CO2 sorption properties of the sorbents were investigated by thermal gravimetric analysis (TGA) at different temperatures in the range between 500 and 600 °C and at low CO2 partial pressure (0.04 atm). The results showed that all the promoters used noticeably improved the CO2 sorption capacity in comparison to no-promoted Li4SiO4. At the optimum sorption temperature of 580 °C, Li4SiO4 with addition of 30 wt% of K2CO3 showed the best CO2 adsorption proprieties with sorption capacities of 230 mg CO2/g sorbent corresponding to a conversion of about 80 %. Besides this sample maintained its original capacity during multiple CO2 sorption/desorption cycles.

Alkali promoted lithium orthosilicate for CO2 capture at high temperature and low concentration

In this study, lithium orthosilicate (Li4SiO4) based sorbents containing different amounts of alkali carbonates (K2CO3, Na2CO3), binary (K2CO3/Li2CO3, Na2CO3/Li2CO3) and ternary (K2CO3/Na2CO3/Li2CO3) eutectic mixtures were prepared and characterized by X-ray diffraction and scanning electron microscopy. The CO2 adsorption properties of the sorbents were investigated by thermogravimetric analysis (TGA) at low CO2 partial pressure (0.04atm) and temperatures between 500 and 600°C. The durability of the selected sorbents was investigated by multiple CO2 adsorption/desorption cycles. The results showed that all the promoters used noticeably improved the CO2 uptake rate and sorption capacity in comparison to no-promoted Li4SiO4. At the optimum sorption temperature of 580°C, Li4SiO4 with addition of 30wt% of K2CO3 or Na2CO3 showed the best CO2 adsorption proprieties with sorption capacity of 230mg CO2/g sorbent corresponding to a Li4SiO4 conversion of about 80%. But, the addition of Na2CO3 caused sintering during multiple sorption/desorption cycles reducing significantly the sorption capacity within the defined sorption time. Whereas, the sample with addition 30wt% K2CO3 maintained its original capacity during 25 CO2 sorption/desorption cycles, showing an excellent cyclic stability.

CO2 capture using particulate silica aerogel immobilized with tetraethylenepentamine

A high capacity CO2 sorbent was developed using high porosity hydrophilic and hydrophobic silica aerogel impregnated with tetraethylenepentamine (TEPA). Aerogel sorbents were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, and nitrogen adsorption porosimetry for confirming the TEPA loadings and examining the residual porosity after modification. The aerogel sorbents appear to shrink during the drying step of amine impregnation while the surface chemistry of the support is altering the TEPA distribution within the pores. The adsorption performance was tested under pure and low CO2 partial pressure conditions at 75°C where the hydrophilic aerogel sorbents outperformed the hydrophobic sorbents. The 80wt.% TEPA loaded hydrophilic sorbent achieved the largest capacity of 6.1mmol/g in pure CO2 while also attaining 3.5mmol/g under a dry 10% CO2/Ar stream. The sorbent also showed excellent cyclic stability having a working CO2 sorption capacity of 5.1mmol/g over 10 cycles.

Adsorption of CO2, moisture and ethanol at low partial pressure using aminofunctionalised silica aerogels

Common applications for CO2 adsorption require the removal of CO2 at high partial pressures. Hence, a number of adsorbents have already been optimised for this task. Nonetheless, new fields for CO2 adsorption at low partial pressure are emerging, like the removal of CO2 from atmosphere or enclosed inhabited environments in submarines, space crafts or aircraft. One way to increase the energetic efficiency of the latter application would be to use tailor made adsorbents in the closed loop environmental control systems able to remove all desired species in one adsorption step. First off all these adsorbents should feature a high adsorption capacity at low CO2 partial pressures. Furthermore, the adsorbents should allow regeneration at low temperatures, have the ability to work in moist conditions and adsorb small amounts of VOCs like ethanol. In this work, the ability of silica aerogels functionalised with a mono- and a tri-aminosilane to fulfil the desired requirements was investigated. Both adsorption of pure components and adsorption from gas mixtures were used to characterise the adsorbents. The aerogels showed a high CO2 adsorption capacity at low partial pressure (250Pa) despite a decreasing specific surface area due to functionalisation. In presence of humidity an increase in the CO2 adsorption capacity takes place. Both types of amino-functionalised aerogels are able to adsorb water, ethanol and CO2 simultaneously. The aerogels could be regenerated in an air flow at 70°C and a mild vacuum (25,000Pa) with negligible losses in adsorption capacity. Thus, functionalised silica aerogel possesses properties for an application as adsorbents in a closed loop environmental control system.

Porous materials with optimal adsorption thermodynamics and kinetics for CO2 separation

The energy costs associated with the separation and purification of industrial commodities, such as gases, fine chemicals and fresh water, currently represent around 15 per cent of global energy production, and the demand for such commodities is projected to triple by 2050 (ref. 1). The challenge of developing effective separation and purification technologies that have much smaller energy footprints is greater for carbon dioxide (CO2) than for other gases; in addition to its involvement in climate change, CO2 is an impurity in natural gas, biogas (natural gas produced from biomass), syngas (CO/H2, the main source of hydrogen in refineries) and many other gas streams. In the context of porous crystalline materials that can exploit both equilibrium and kinetic selectivity, size selectivity and targeted molecular recognition are attractive characteristics for CO2 separation and capture, as exemplified by zeolites 5A and 13X (ref. 2), as well as metal-organic materials (MOMs). Here we report that a crystal engineering or reticular chemistry strategy that controls pore functionality and size in a series of MOMs with coordinately saturated metal centres and periodically arrayed hexafluorosilicate (SiF(2-)(6)) anions enables a 'sweet spot' of kinetics and thermodynamics that offers high volumetric uptake at low CO2 partial pressure (less than 0.15 bar). Most importantly, such MOMs offer an unprecedented CO2 sorption selectivity over N2, H2 and CH4, even in the presence of moisture. These MOMs are therefore relevant to CO2 separation in the context of post-combustion (flue gas, CO2/N2), pre-combustion (shifted synthesis gas stream, CO2/H2) and natural gas upgrading (natural gas clean-up, CO2/CH4).

In the mitochondrial CMSII mutant of Nicotiana sylvestris photosynthetic activity remains higher than in the WT under persisting mild water stress

Photosynthetic responses to persisting mild water stress were compared between the wild type (WT) and the respiratory complex I mutant CMSII of Nicotiana sylvestris. In both genotypes, plants kept at 80% leaf-RWC (WT80 and CMSII80) had lower photosynthetic activity and stomatal/mesophyll conductances compared to well-watered controls. While the stomatal conductance and the chloroplastic CO2 molar ratio were similar in WT80 and CMSII80 leaves, net photosynthesis was higher in CMSII80. Carboxylation efficiency was lowest in WT80 leaves both, on the basis of the same internal and chloroplastic CO2 molar ratio. Photosynthetic and fluorescence parameters indicate that WT80 leaves were only affected in the presence of oxygen. Photorespiration, as estimated by electron flux to oxygen, increased slightly in CMSII80 and WT80 leaves in accordance with increased glycerate contents but maximum photorespiration at low chloroplastic CO2 was markedly lowest in WT80 leaves. This suggests that carbon assimilation of WT80 leaves is impaired by limited photorespiratory activity. The results are discussed with respect to a possible pre-acclimation of complex I deficient leaves in CMSII to drive photosynthesis and photorespiration at low CO2 partial pressure.

Solubility of Carbon Dioxide in Aqueous 2-(2-Aminoethylamine)ethanol (AEEA) Solution and Its Mixtures with N-Methyldiethanolamine/2-Amino-2-methyl-1-propanol

Solubility measurements of carbon dioxide (CO2) in aqueous 2-(2-aminoethylamino)ethanol (AEEA, 15 wt %), AEEA + N-methyldiethanolamine (MDEA, 5, 10 wt %), and AEEA + 2-amino-2-methyl-1-propanol (AMP, 5, 10 wt %) solutions as CO2 absorbents were performed at CO2 partial pressure from (0.8 to 800) kPa and temperatures of (303, 313, and 323) K. With increasing the MDEA/AMP amount to AEEA, CO2 loading of the absorbents decreased, while the absorption rate increased. At low CO2 partial pressure (< 30 kPa), the loading of AEEA + AMP was higher than that of AEEA + MDEA, while at high CO2 partial pressure (> 100 kPa), the loading of AEEA + AMP was lower than that of AEEA + MDEA at the same concentration. Furthermore, the absorption rate was in the order AEEA + AMP > AEEA + MDEA > AEEA.

Carbon nanotube modified carbon composite monoliths as superior adsorbents for carbon dioxide capture

Carbon composite monoliths were prepared from a commercial phenolic resin mixed with just 1 wt% of carbon nanotubes (CNTs) followed by carbonization and physical activation with CO2. The products possess a hierarchical macroporous–microporous structure and superior CO2 adsorption properties. In particular, they show the top-ranked CO2 capacity (52 mg CO2 per g adsorbent at 25 °C and 114 mmHg) under low CO2 partial pressures, which is of more relevance for flue gas applications. This matches or exceeds those of carbons produced by complex chemical activation and functionalization. Our study demonstrates an effective way to create narrow micropores through structural modification of carbon composites by CNTs.

A Study of Mass Transfer Kinetics of Carbon Dioxide in (Monoethanolamine + Water) by Stirred Cell

The gas phase resistance in a stirred cell was investigated to understand and avoid its influence on the measurement of the reaction kinetics. To validate the influence of gas phase resistance and the experimental conditions of pseudo first order reaction for Monoethanolamine (MEA) + CO2 system, low CO2 partial pressure under various inert gas pressure were employed for CO2 the absorption into 0.5, 1, 3 and 3.6M MEA solutions with H2O and ethyleneglycol as solvents, respectively. The absorption was investigated with the stirred cell based on a fall-in-pressure technique.

Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid

The processes responsible for the highly explosive events at Merapi, Central Java, Indonesia have been investigated through a petrological, mineralogical and geochemical study of the first-stage tephra and pyroclastic flows sampled in October and November 2010, and second-stage ash sampled shortly after the 5–6th November 2010 paroxysmal subplinian eruption. Several chemical and physical parameters suggest that the magma assimilated calc-silicate xenoliths derived from the surrounding carbonate-bearing crust (Javanese limestone). The bulk volcanic samples have highly radiogenic 87Sr/86Sr (0.70571–0.70598) ratios that approach the compositional field of material similar to the calc-silicate xenoliths. The 2010 plagioclase phenocrysts from the pyroclastic flow and tephra reveal anorthite cores (up to An94–97) with low FeO contents (≤0.8wt.%), and 18O enrichment (6.5‰ δ18O). The major and trace elements of the silicic glasses and phenocrysts (plagioclase, low-Al augite and titanomagnetite), the Sr-isotopic compositions of the bulk samples and plagioclases erupted in 2010 can be explained by complete digestion of the 1998 and 2006 calc-silicate xenoliths. The bulk assimilation proceeded through binary mixing between a calcic melt (representing Crustal Assimilant, CaO up to 10.5wt.% and CaO/Al2O3 up to 1.2) and the deep source hydrous K-rich melt. Similarly to the 1998 and 2006 calc-silicate xenolith composition, the 2010 Crustal Assimilant is enriched in Mn (MnO up to 0.5wt.%), Zn, V, and Sc contents. In contrast, the hydrous K-rich melt is enriched in volatiles (Cl up to 0.37wt.% and bulk H2O+CO2 up to 5±1wt.%), Al2O3, TiO2 and REE contents, consistent with its derivation from deep source. This hydrous K-rich melt may have been saturated with an aqueous Cl-rich fluid at about 200MPa, a pressure consistent with the level of the crustal assimilation. We estimated that the pre-eruptive basaltic andesite magma assimilated from 15 to 40wt.% of the calc-silicate crustal material, corresponding to introduction of additional 0.19 to 2.1Mt of CO2 to the magma. Experimental leaching of the ash samples documents the release of an aqueous fluid enriched in Cl, Na, Ca, Cd, Sb and Zn during the paroxysmal subplinian eruption. The paroxysmal eruption may have been produced by saturation of the pre-eruptive basaltic andesite magma with hybrid aqueous carbonic NaCl–HCl-rich fluid due to bulk assimilation creating elevated partial pressure of CO2 at shallow crustal conditions of about 200MPa. In contrast, mildly explosive block-and-ash flows (typical Merapi-type) may result from selective assimilation of the carbonate-bearing xenoliths and lower CO2 partial pressure that may not lead to explosive degassing.

Prospective crossover comparison between NAVA and pressure control ventilation in premature neonates less than 1500 grams

Neurally adjusted ventilatory assist (NAVA) synchronizes spontaneous respiratory effort with mechanical ventilation. Electrodes detect the electrical activity of the diaphragm (Edi) and transmit this information to the ventilator, allowing the patient to determine their own respiratory rate (RR), peak pressures, and inspiratory and expiratory times in synchrony with the ventilator. The objective of this study was to evaluate if premature neonates ventilate as effectively on NAVA as compared to pressure control ventilation (PCV). Five ventilated neonates were enrolled (gestational age 25-29 weeks). Each neonate was ventilated on NAVA for 4 h, then switched to PCV for another 4 h. The cycle was repeated three times. Ventilatory parameters were averaged every 30 min to collect eight time points for each ventilatory mode. Data were analyzed using the mixed effects model procedure, utilizing the least-squares means (P<0.05). When compared to PCV, neonates ventilated with NAVA had lower peak inspiratory pressures (PIP), fraction of inspired oxygen (FiO2), transcutaneous PCO2 Edi peak and RR. There was an increase in expiratory tidal volume (TV), compliance and Edi minimum. Despite lower PIP and RR, partial pressure of CO2 (PCO2) was lower when ventilated on NAVA. There was no difference in mean airway pressure. Premature neonates ventilated with NAVA required less PIP, FiO2 and RR to achieve lower PCO2 and better compliance compared with PCV.