Steady-state CO Research Articles

Can the Rate of a Catalytic Turnover Be Altered by Ligands in the Absence of Direct Binding Interactions?

Second sphere coordination effects ubiquitous in enzymatic catalysis occur through direct interactions, either covalent or non-covalent, with reaction intermediates and transition states. We present herein evidence of indirect second sphere coordination effects in which ligation of water/alkanols far removed from the primary coordination sphere of the active site nevertheless alter energetic landscapes within catalytic redox cycles in the absence of direct physicochemical interactions with surface species mediating catalytic turnovers. Density functional theory, in situ X-ray absorption and infrared spectroscopy, and a wide array of steady-state and transient CO oxidation rate data suggest that the presence of peripheral water renders oxidation half-cycles within two-electron redox cycles over μ3-oxo-bridged trimers in MIL-100(M) more kinetically demanding. Communication between ligated water and the active site appears to occur through the Fe-O-Fe backbone, as inferred from spin density variations on the central μ3-oxygen 'junction'. Evidence is provided for the generality of these second sphere effects in that they influence different types of redox half-cycles or metals, and can be amplified or attenuated through choice of coordinating ligand. Specifically in the case of MIL-100(M) materials, the Cr isostructure can be made to kinetically mimic the Fe variant by disproportionately hindering oxidation half-cycles relative to the reduction half-cycles. Kinetic and spectroscopic inferences presented here significantly expand both the conceptual definition of second sphere effects as well as the palette of synthetic levers available for tuning catalytic redox performance through chemical ligation.

Micro-Scale Lattice Boltzmann Simulation of Two-Phase CO2–Brine Flow in a Tighter REV Extracted from a Permeable Sandstone Core: Implications for CO2 Storage Efficiency

Deep saline permeable sandstones have the potential to serve as sites for CO2 storage. However, unstable CO2 storage in pores can be costly and harmful to the environment. In this study, we used lattice Boltzmann (LB) simulations to investigate the factors that affect steady-state CO2–brine imbibition flow in sandstone pores, with a focus on improving CO2 storage efficiency in deep saline permeable sandstone aquifers. We extracted three representative element volumes (REVs) from a digital rock image of a sandstone core and selected a tighter REV in the upper subdomain so that its permeability would apparently be lower than that of the other two based on single-phase LB simulation for further analysis. The results of our steady-state LB simulations of CO2–brine imbibition processes in the tighter REV under four differential pressures showed that a threshold pressure gradient of around 0.5 MPa/m exists at a differential pressure of 200 Pa, and that higher differential pressures result in a greater and more linear pressure drop and stronger channelization after the flow are initiated. Furthermore, we conducted simulations over a range of target brine saturations in the tighter REV at the optimal differential pressure of 400 Pa. Our findings showed that the relative permeability of CO2 is greatly reduced as the capillary number falls below a certain threshold, while the viscosity ratio has a smaller but still significant effect on relative permeability and storage efficiency through the lubrication effect. Wettability has a limited effect on the storage efficiency, but it does impact the relative permeability within the initial saturation range when the capillary number is low and the curves have not yet converged. Overall, these results provide micro-scale insights into the factors that affect CO2 storage efficiency in sandstones.

Information fusion of stationary, mobile, and wearable consumer-grade sensors to confidently estimate bedroom ventilation rates

This study adds to the body of research investigating ventilation rates measured in residential dwellings. Using open-source Consumer-Grade Sensors (CGS), we measure Carbon Dioxide (CO2) to estimate ventilation rates under one of three conditions: CO2build-up when bedrooms were initially occupied, steady-state CO2 during the latter half of participants’ sleep episodes, and CO2decay after participants wake and vacate their bedroom. We do not ask participants to record their bedroom occupancy, but use information fusion to identify nightly occupied periods by cross-referencing home addresses to GPS measurements provided by their smartphones during sleep episodes identified by Fitbit wearable fitness trackers. We estimate 106 ventilation rates during build-up conditions which ranged from 0.04–1.36 h−1, 242 ventilation rates under steady-state conditions spanning 0.17–2.49 h−1, and 39 ventilation rates from decay conditions over a range of 0.06–1.05 h−1. In addition, we used occupied periods alongside times when GPS confirmed participants were away from home to label Indoor Air Quality (IAQ) data, and to train a Multi-Layer Perceptron (MLP) to classify occupancy based on CO2 and Total Volatile Organic Compound (TVOC) measurements. Using periods classified as occupied with at least 90% confidence, we estimated 116 additional steady-state ventilation rates spanning 0.25–2.49 h−1. Our results are consistent with more traditional and costly sensing approaches, and we conclude that information fusion of CGS is effective in measuring IAQ, detecting occupancy, and estimating ventilation rates.

Effect of Outdoor Temperature on Performance of All-air Wall Induction Unit in a Four-bed Hospital Ward

The prototype all-air wall induction unit (IU) has the characteristics of displacement ventilation (DV) and windless air supply, which is considered ideal for hospital ward usage. The outdoor temperature, however, will affect its ventilation and thermal performance. This study conducted a full-scale experiment. IUs are vertically installed in the four corners of the experiment room, which is furnished as a Japanese hospital ward. An outdoor climate simulation chamber (OCSC) is installed on one side of the room to simulate the external window and sill under different outdoor temperature conditions. CO2 is generated from the room’s one point, representing pollutants emitted by a patient. The room’s steady-state temperature and CO2 concentration distribution are analyzed under different outdoor temperatures (in OCSC) and air supply conditions. The IU maintained a comfortable thermal environment under all experimental conditions. In terms of ventilation performance, downward airflow undermines concentration stratification in midwinter. The DV stabilizes when the temperature difference between inside and outside air becomes less than 10 °C while using the double-pane window in winter. Conversely, upward airflow strengthens the DV in the summer. In addition, a sufficient supply rate is recommended to keep concentrations and temperatures above the patients’ breathing zone.

Light and carbon limited photosynthesis of Chlorella sorokiniana

Carbon dioxide (CO2) and light are essential for high photosynthetic rates of microalgal cultures. Microalgal photosynthetic behavior at low CO2 concentrations has not been revealed yet at the same level of detail as leaf photosynthesis. In the present study, we investigated the short-term photosynthetic response of suspended Chlorella sorokiniana to limiting light intensity and CO2 concentration. We used a novel CO2-based photosynthesis monitor originating from leaf research but equipped with an aquatic chamber sparged with CO2 enriched air. Photosynthesis was measured by employing a steady-state CO2 mass balance over the chamber. Light and carbon response curves were determined under constant pH, temperature, dissolved oxygen, light intensity or dissolved carbon dioxide. We determined the volumetric mass transfer coefficient of the aquatic chamber to accurately convert gaseous CO2 partial pressure into aqueous CO2 concentration to evaluate the CO2 response measurements.Light response measurements on dilute algal cultures revealed a high photosynthetic capacity on a time scale of minutes which by far exceeded the average CO2 uptake on a time scale of hours (cell growth). Light response measurements with dense and fully absorbing cultures provided accurate insight into the response of microalgal mass culture to changing incident irradiance, including the efficiency of photosynthesis of the algal culture as a whole. CO2 response measurements demonstrated severe CO2 limitation at dissolved CO2 levels of <20 μM giving a concrete target for optimization of CO2 supply in large-scale cultivation systems. Measurements at a background of either 21 % O2 (air) or 2 % O2 indicated the existence of photorespiration in Chlorella. Moreover, the magnitude of photorespiration first increased and then decreased again while reduced dissolved CO2 levels, indicating the activation of a carbon concentrating mechanism at low CO2. Simultaneous measurement of the quantum yield of PSII linear electron transport (ϕPSII) and CO2 uptake revealed the transition of CO2 limited photosynthesis towards light-limited photosynthesis.

Mechanistic Insights on the Low-Temperature Oxidation of CO Catalyzed by Isolated Co Ions in N-Doped Carbon

Isolated cobalt ions on nitrogen-doped carbon (Co–N–C) catalyze CO oxidation at temperatures as low as 196 K, but the active site and mechanism for this reaction remain elusive. In this work, steady-state CO oxidation around 273 K over Co–N–C revealed nearly first-order behavior in both CO and O2 as well as a negative apparent activation energy. Isotopic transient analysis of the reaction confirmed a rapid turnover frequency and low surface coverage of adsorbed intermediates leading to CO2 (<10% of the Co). Results from kinetics experiments combined with quantum chemical calculations and molecular dynamics simulations are consistent with a reaction path involving weak adsorption of CO onto Co ions followed by a low barrier for the CO-assisted activation of weakly adsorbed O2. This proposed mechanism for dioxygen activation does not involve a redox cycle with the transition-metal ion and may be important in other low-temperature catalytic reactions involving O2.

Effect of quenching region characteristics on the performance of two-region porous inert medium burners at low-power operation

Although the effects of quenching and combustion regions on the performance of two-region porous inert medium (PIM) burners are different, only the combustion regions have received the utmost consideration. This study focuses on quenching regions by exploring the effect of varying their characteristics on the performance of PIM burners operated at low powers (1–5 kW). Therefore, the axial real-time temperature distributions and the steady-state CO– and NOx-emissions due to the combustion of wide ranges of well-premixed LPG-air mixtures within a well-designed PIM burner were measured. To vary the quenching region characteristics, two different materials of alumina and cordierite and three different thicknesses of the alumina material were used. The combustion stability limits were extracted from the measured stable temperature distributions and presented as a function of the applied power. Both the lower and higher stability limits decayed toward lower excess air ratios. However, the higher limit decayed at a faster rate, thereby causing the modulation ability of the excess air ratio to shrink continuously, which limited the burner’s adaptability and capacity. Meanwhile, using the alumina material instead of the cordierite improved the entire lower stability limit by at least 0.1. Conversely, using the cordierite material improved the higher stability limit by 0.1, but only for the two lower powers of 1 and 2 kW. In addition, increasing the alumina material’s thickness from 13 to 20 mm enhanced the whole modulation ability by 0.2, where each limit was entirely improved by 0.1. Therefore, these findings emphasize the effects of quenching region characteristics on the performance of two-region PIM burners, revealing the importance of optimizing this region during their design for actual practical applications. Finally, except for the CO-emission at 1 and 2 kW, outstanding insignificant CO– and NOx-emissions were observed.

Application of the rapid leaf A-Ci response (RACiR) technique: examples from evergreen broadleaved species.

Using steady-state photosynthesis-intercellular CO2 concentration (A-Ci) response curves to obtain the maximum rates of ribulose-1,5-bisphosphate carboxylase oxygenase carboxylation (Vcmax) and electron transport (Jmax) is time-consuming and labour-intensive. Instead, the rapid A-Ci response (RACiR) technique provides a potential, high-efficiency method. However, efficient parameter settings of RACiR technique for evergreen broadleaved species remain unclear. Here, we used Li-COR LI-6800 to obtain the optimum parameter settings of RACiR curves for evergreen broadleaved trees and shrubs. We set 11 groups of CO2 gradients ([CO2]), i.e. R1 (400-1500ppm), R2 (400-200-800ppm), R3 (420-20-620ppm), R4 (420-20-820ppm), R5 (420-20-1020ppm), R6 (420-20-1220ppm), R7 (420-20-1520ppm), R8 (420-20-1820ppm), R9 (450-50-650ppm), R10 (650-50ppm) and R11 (650-50-650ppm), and then compared the differences between steady-state A-Ci and RACiR curves. We found that Vcmax and Jmax calculated by steady-state A-Ci and RACiR curves overall showed no significant differences across 11 [CO2] gradients (P > 0.05). For the studied evergreens, the efficiency and accuracy of R2, R3, R4, R9 and R10 were higher than the others. Hence, we recommend that the [CO2] gradients of R2, R3, R4, R9 and R10 could be applied preferentially for measurements when using the RACiR technique to obtain Vcmax and Jmax of evergreen broadleaved species.

Experimental study and CFD modelling of four-bed hospital ward with all-air wall induction unit for air-conditioning

This study focuses on a prototype all-air wall induction unit. While maintaining the non-reheating and power saving conveying characteristics of the induction systems, this unit is water pipe free and has a low air supply velocity, and is therefore suitable for application in hospital wards. However, its ventilation and thermal performance have not been sufficiently investigated for further improvement. Thus, this study performs a full-scale experiment in which induction units are vertically installed in the ward's four corners. CO2 is generated to represent pollutants from a sample patient, and the steady-state temperature and CO2 concentration distribution are measured and analyzed under different supply conditions. Moreover, computational fluid dynamics (CFD) modeling methods are proposed and validated for this unit. The results show that the wall induction system can maintain a normalized concentration near the hospital beds that are away from the pollution source of less than 0.7 by producing displacement ventilation (DV). Supplying the air from the bottom half of the wall corner with a low supply rate while the bed is surrounded by a curtain can halve the CO2 concentration in the occupied zone by improving the efficiency of the DV. The vertical distribution of room temperature ranges from Δ3 °C to Δ4 °C depending on the supply volume, which is considered acceptable in the ward usage. Furthermore, in the ward CFD simulation, the accuracy of the Standard k-ϵ (SKE) model with specific heat transfer boundaries has been proved to be nearly identical to the low-Reynolds calculation results.

Photosynthetic upgrading of biogas from anaerobic digestion of mixed sludge in an outdoors algal-bacterial photobioreactor at pilot scale

Anaerobic digestion can biotransform the biodegradable fraction of sewage sludge into biogas, while the symbiotic action of algal-bacterial consortia can remove both the CO2 and H2S from biogas and nutrients from digestate. A 100 L anaerobic digester operated at 20 days of retention time coupled with a 180 L high-rate algal pond (HRAP) engineered to upgrade the biogas and treat the liquid fraction of the pilot digester was optimized along four operational stages: (I) operation with a greenhouse during winter; (II) operation without greenhouse; (III) process supplementation with NaHCO3; (IV) process supplementation with Na2CO3. The biogas produced was composed of 63.7 ± 2.9% CH4, 33.7 ± 1.9% CO2, 0.5 ± 0.3% O2 and 1.6 ± 1.1% N2. An average methane productivity of 324.7 ± 75.8 mL CH4 g VSin−1 and total COD removals of 48 ± 20% were recorded in the digester. The CH4 concentration in the biomethane gradually decreased to 87.6 ± 2.0% and 85.1 ± 1.3% at the end of stage I and II, respectively, attributed to the loss of inorganic carbon in the HRAP. The supplementation of NaHCO3 and Na2CO3 mediated an increase in the CH4 content to 90.4 ± 1.5 and 91.2 ± 0.7% in stages III and IV, respectively. Steady state CO2 removals of 90% and 88% in stages I and II, and 95.7 and 97.6% in stages III and IV, respectively, were recorded. A constant biomass productivity of 22 g m−2 d−1, set by daily harvesting 26.5 g dry algal-bacterial biomass from the bottom of the settler, was maintained concomitantly with a complete removal of the N and P supplied via centrate.

Permeability of Bituminous Coal to CH4 and CO2 Under Fixed Volume and Fixed Stress Boundary Conditions: Effects of Sorption

Permeability evolution in coal reservoirs during CO2-enhanced coalbed methane (ECBM) production is strongly influenced by swelling/shrinkage effects related to sorption and desorption of CO2 and CH4, respectively. Recent research has demonstrated fully coupled stress–strain–sorption–diffusion behavior in small samples of cleat-free coal matrix material exposed to a sorbing gas. However, it is unclear how such effects influence permeability evolution at the scale of a cleated coal seam and whether a simple fracture permeability model, such as the Walsh elastic asperity loading model, is appropriate. In this study, we performed steady-state permeability measurements, to CH4 and CO2, on a cylindrical sample of highly volatile bituminous coal (25 mm in diameter) with a clearly visible cleat system, under (near) fixed volume versus fixed stress conditions. To isolate the effect of sorption on permeability evolution, helium (non-sorbing gas) was used as a control fluid. All flow-through tests reported here were conducted under conditions of single-phase flow at 40°C, at applied Terzaghi effective confining pressures of 14–41 MPa. Permeability evolution versus effective stress data were obtained under both fixed volume and fixed stress boundary conditions, showing an exponential correlation. Importantly, permeability (κ) obtained at similar Terzaghi effective confining pressures showed κhelium &amp;gt; κCH4 &amp;gt;&amp;gt; κCO2, while κ-values measured in the fixed volume condition were higher than those in the fixed stress case. The results show that permeability to CH4 and CO2, under in situ conditions where free swelling of rock is not possible, is strongly influenced by the coupled effects of 1) self-stress generated by constrained swelling, 2) the change in effective stress coefficient upon sorption, 3) sorption-induced closure of transport paths independently of poroelastic effect, and 4) heterogeneous gas penetration and equilibration, dependent on diffusion. Our results also show that the Walsh permeability model offers a promising basis for relating permeability evolution to in situ stress evolution, using appropriate parameter values corrected for the effects of stress–strain–sorption.

Machine learning-aided optimization of coal decoupling combustion for lowering NO and CO emissions simultaneously

Decoupling combustion technology enables significant suppression of NOx and CO emissions from solid fuel combustion, but calls for optimizing reactor structure to make full use of its superiority. Taking a coal stove as an example, three different network models were established and trained to predict the steady-state NO and CO emissions from coal decoupling combustion well. The two GRU-DNN models have higher prediction accuracy and better generalization ability than the DNN model, but they both need to be fed with complex sequence data, leading to long training and response time to new inputs. The DNN model with simple fuel properties and structural parameters as the inputs was used to forecast the steady-state NO and CO emissions from various coal-stove combinations with acceptable accuracy, so facilitating the optimization of stove structure and further coal decoupling combustion to lower the NO and CO emissions simultaneously.

Nitric oxide contributes to cerebrovascular shear-mediated dilatation but not steady-state cerebrovascular reactivity to carbon dioxide.

Cerebrovascular CO2 reactivity (CVR) is often considered a bioassay of cerebrovascular endothelial function. We recently introduced a test of cerebral shear-mediated dilatation (cSMD) that may better reflect endothelial function. We aimed to determine the nitric oxide (NO)-dependency of CVR and cSMD. Eleven volunteers underwent a steady-state CVR test and transient CO2 test of cSMD during intravenous infusion of the NO synthase inhibitor NG -monomethyl-l-arginine (l-NMMA) or volume-matched saline (placebo; single-blinded and counter-balanced). We measured cerebral blood flow (CBF; duplex ultrasound), intra-arterial blood pressure and . Paired arterial and jugular venous blood sampling allowed for the determination of trans-cerebral NO2- exchange (ozone-based chemiluminescence). l-NMMA reduced arterial NO2- by ∼25% versus saline (74.3±39.9 vs. 98.1±34.2nM; P=0.03). The steady-state CVR (20.1±11.6nM/min at baseline vs. 3.2±16.7nM/min at +9 mmHg ; P=0.017) and transient cSMD tests (3.4±5.9nM/min at baseline vs. -1.8±8.2nM/min at 120 s post-CO2 ; P=0.044) shifted trans-cerebral NO2- exchange towards a greater net release (a negative value indicates release). Although this trans-cerebral NO2- release was abolished by l-NMMA, CVR did not differ between the saline and l-NMMA trials (57.2±14.6 vs. 54.1±12.1ml/min/mmHg; P=0.49), nor did l-NMMA impact peak internal carotid artery dilatation during the steady-state CVR test (6.2±4.5 vs. 6.2±5.0% dilatation; P=0.960). However, l-NMMA reduced cSMD by ∼37% compared to saline (2.91±1.38 vs. 4.65±2.50%; P=0.009). Our findings indicate that NO is not an obligatory regulator of steady-state CVR. Further, our novel transient CO2 test of cSMD is largely NO-dependent and provides an in vivo bioassay of NO-mediated cerebrovascular function in humans. KEY POINTS: Emerging evidence indicates that a transient CO2 stimulus elicits shear-mediated dilatation of the internal carotid artery, termed cerebral shear-mediated dilatation. Whether or not cerebrovascular reactivity to a steady-state CO2 stimulus is NO-dependent remains unclear in humans. During both a steady-state cerebrovascular reactivity test and a transient CO2 test of cerebral shear-mediated dilatation, trans-cerebral nitrite exchange shifted towards a net release indicating cerebrovascular NO production; this response was not evident following intravenous infusion of the non-selective NO synthase inhibitor NG -monomethyl-l-arginine. NO synthase blockade did not alter cerebrovascular reactivity in the steady-state CO2 test; however, cerebral shear-mediated dilatation following a transient CO2 stimulus was reduced by ∼37% following intravenous infusion of NG -monomethyl-l-arginine. NO is not obligatory for cerebrovascular reactivity to CO2 , but is a key contributor to cerebral shear-mediated dilatation.

The stability of cerebrovascular CO2 reactivity following attainment of physiological steady-state.

What is the central question of this study? During a steady-state cerebrovascular CO2 reactivity test, do different data extraction time points change the outcome for cerebrovascular CO2 reactivity? What is the main finding and its importance? Once steady-state end-tidal pressure of CO2 and haemodynamics were achieved, cerebral blood flow was stable, and so cerebrovascular CO2 reactivity values remained unchanged regardless of data extraction length (30 vs. 60s) and time point (at 2-5min). This study assessed cerebrovascular CO2 reactivity (CVR) and examined data extraction time points and durations with the hypotheses that: (1) there would be no difference in CVR values when calculated with cerebral blood flow (CBF) measures at different time points following the attainment of physiological steady-state, (2) once steady-state was achieved there would be no difference in CVR values derived from 60 to 30s extracted means, and (3) that changes in would not be associated with any changes in CVR. We conducted a single step iso-oxic hypercapnic CVR test using dynamic end-tidal forcing (end-tidal , +9.4 ± 0.7mmHg), and transcranial Doppler and Duplex ultrasound of middle cerebral artery (MCA) and internal carotid artery (ICA), respectively. From the second minute of hypercapnia onwards, physiological steady-state was apparent, with no subsequent changes in end-tidal , or mean arterial pressure. Therefore, CVR measured in the ICA and MCA was stable following the second minute of hypercapnia onwards. Data extraction durations of 30 or 60s did not give statistically different CVR values. No differences in CVR were detected following the second minute of hypercapnia after accounting for mean arterial pressure via calculated conductance or covariation of mean arterial pressure. These findings demonstrate that, provided the stimulus remains in a steady-state, data extracted from any minute of a CVR test during physiological steady-state conditions produce equivalent CVR values; any change in the CVR value would represent a failure of CVR mechanisms, a change in the magnitude of the stimulus, or measurement error.

Metamorphic CO2 emissions from the southern Yadong-Gulu rift, Tibetan Plateau: Insights into deep carbon cycle in the India-Asia continental collision zone

Extensional rift systems provide important pathways for the release of large amounts of deeply-sourced CO2 into the atmosphere. Continental rifting zones (e.g., East African rift) are thus invoked to be important for understanding the links between CO2 outgassing and global climate change associated with continental breakup. However, deeply-sourced CO2 emissions from extensional rift systems in continental collision zones remain poorly understood. Here, we focus on hydrothermal CO2 emissions from the southern segment of the Yadong-Gulu rift (YGR), the largest extensional rift in southern Tibetan Plateau, aiming at delineating rift-related CO2 emissions from the India-Asia continental collision zone. In-situ measurements of diffuse soil CO2 emissions indicate that average soil CO2 fluxes from the Kangbu, Mengzha, and Chaduo hydrothermal fields are 40, 700, and 255 g m−2 d−1, respectively. Combined with average soil CO2 fluxes (20–437 g m−2 d−1) from central and northern YGR, we speculate a relatively steady-state CO2 degassing pattern for the entire rift. The magnitude of soil CO2 fluxes of the YGR is higher than that of representative areas of the East African rift system. Evidence from 3He/4He reveals a pure crustal origin for CO2-bearing fluids in southern YGR, while the involvement of mantle CO2 is recognized in the central and northern rift segments. We suggest that metamorphic decarbonation of crustal rocks at variable depths is the primary cause for CO2 origin in southern YGR, which differs from the magma‑carbonate interaction model of central and northern YGR. Ternary mixing calculation based on He-CO2 systematics of hydrothermal gases indicates dominant contributions from carbonate rocks to total carbon inventory, with mantle CO2 contributions absent in southern YGR but discernible in northern YGR. The characteristic high proportions of crustal CO2 (>90%) distinguish the YGR from extensional rifts fed primarily by mantle CO2 in continental rifting zones. Our results reveal a crustal-scale carbon cycle in accretionary wedge of the India-Asia continental collision zone, together with magmatic front setting of the central and northern YGR, outlining a transect of the rift-related CO2 emissions across continental collision zones. This would contribute to better understanding the role of continental assembly in deeply-sourced CO2 emissions and global carbon budget.

Performance and Durability of the Zr-Doped CaO Sorbent under Cyclic Carbonation–Decarbonation at Different Operating Parameters

The effect of cyclic carbonation–decarbonation operating parameters on Zr-doped CaO sorbent CO2 uptake capacity evolution is examined. It is revealed that the capacity steady state value increases with the decrease in the carbonation temperature, CO2 concentration in the gas flow upon carbonation and with the increase in the heating rate from the carbonation to the decarbonation stages. The rise in decarbonation temperature leads to a dramatic decrease in the sorbent performance. It is found that if carbonation occurs at 630 °C in the gas flow containing 15 vol.% CO2 and decarbonation is carried out at 742 °C, the sorbent shows the highest values of the initial and steady state CO2 uptake capacity, namely, 10.7 mmol/g and 9.4 mmol/g, respectively.

Emission rate of carbon dioxide while sleeping.

Humans emit carbon dioxide (CO2 ) as a product of their metabolism. Its concentration in buildings is used as a marker of ventilation rate (VR) and degree of mixing of supply air, and indoor air quality (IAQ). The CO2 emission rate (CER) may be used to estimate the ventilation rate. Many studies have measured CERs from subjects who were awake but little data are available from sleeping subjects and the present publication was intended to reduce this gap in knowledge. Seven females (29±5years old; BMI: 22.2±0.8kg/m2 ) and four males (27±1years old; BMI: 20.5±1.5kg/m2 ) slept for four consecutive nights in a specially constructed capsule at two temperatures (24 and 28°C) and two VRs that maintained CO2 levels at ca. 800ppm and 1700ppm simulating sleeping conditions reported in the literature. The order of exposure was balanced, and the first night was for adaptation. Their physiological responses, including heart rate, pNN50, core body temperature, and skin temperature, were measured as well as sleep quality, and subjective responses were collected each evening and morning. Measured steady-state CO2 concentrations during sleep were used to estimate CERs with a mass-balance equation. The average CER was 11.0±1.4 L/h per person and was 8% higher for males than for females (P<0.05). Increasing the temperature or decreasing IAQ by decreasing VR had no effects on measured CERs and caused no observable differences in physiological responses. We also calculated CERs for sleeping subjects using the published data on sleep energy expenditure (SEE) and Respiratory Quotient (RQ), and our measured CERs confirmed both these calculations and the CERs predicted using the equations provided by ASHRAE Standard 62.1, ASHRAE Handbook, and ASTM D6245-18. The present results provide a valuable and helpful reference for the design and control of bedroom ventilation but require confirmation and extension to other age groups and populations.

Ventilation Assessment by Carbon Dioxide Levels in Dental Treatment Rooms

It is important for dental care professionals to reliably assess carbon dioxide (CO2) levels and ventilation rates in their offices in the era of frequent infectious disease pandemics. This study was to evaluate CO2 levels in dental operatories and determine the accuracy of using CO2 levels to assess ventilation rate in dental clinics. Mechanical ventilation rate in air change per hour (ACHVENT) was measured with an air velocity sensor and airflow balancing hood. CO2 levels were measured in these rooms to analyze factors that contributed to CO2 accumulation. Ventilation rates were estimated using natural steady-state CO2 levels during dental treatments and experimental CO2 concentration decays by dry ice or mixing baking soda and vinegar. We compared the differences and assessed the correlations between ACHVENT and ventilation rates estimated by the steady-state CO2 model with low (0.3 L/min, ACHSS30) or high (0.46 L/min, ACHSS46) CO2 generation rates, by CO2 decay constants using dry ice (ACHDI) or baking soda (ACHBV), and by time needed to remove 63% of excess CO2 generated by dry ice (ACHDI63%) or baking soda (ACHBV63%). We found that ACHVENT varied from 3.9 to 35.0 in dental operatories. CO2 accumulation occurred in rooms with low ventilation (ACHVENT ≤6) and overcrowding but not in those with higher ventilation. ACHSS30 and ACHSS46 correlated well with ACHVENT (r = 0.83, P = 0.003), but ACHSS30 was more accurate for rooms with low ACHVENT. Ventilation rates could be reliably estimated using CO2 released from dry ice or baking soda. ACHVENT was highly correlated with ACHDI (r = 0.99), ACHBV (r = 0.98), ACHDI63% (r = 0.98), and ACHBV63% (r = 0.98). There were no statistically significant differences between ACHVENT and ACHDI63% or ACHBV63%. We conclude that ventilation rates could be conveniently and accurately assessed by observing the changes in CO2 levels after a simple mixing of household baking soda and vinegar in dental settings.

Syngas production from ethanol dry reforming using Cu-based perovskite catalysts promoted with rare earth metals

This paper reports about the production of syngas from dry reforming of ethanol (EDR) upon LaCuO3 and CeCuO3 catalysts that were prepared by using citrate sol-gel method. EDRs were run with fresh catalyst at each varied variable and 42 L/gcat/h of feed in a tubular reactor under atmospheric pressure. At equal feed pressure of reactants, steady state CO2 conversion increased exponentially from 700 to 800 °C while H2 and CO yields were increasing differently in sigmoid trend rendering H2/CO ratios to drop linearly from 1.7 to 1.0. However, these reaction results except the latter are otherwise when ethanol-CO2 ratio was increased (reducing CO2 pressure) at 750 °C. A minimum H2/CO ratio was evidenced at the ethanol-CO2 ratio of 1.48. LaCuO3 catalyst was more superior in producing syngas owing to its relatively low reduction temperature, high surface area and crystallinity, many active sites, good surface morphology and many C–O, C–H and hydroxyl groups.

Ru-M (M = Fe or Co) Catalysts with high Ru surface concentration for Fischer-Tropsch synthesis

Ru-Co/Al2O3 and Ru-Fe/Al2O3 have been prepared by the reduction-deposition method. This approach favours the interaction between Ru and Fe or Co in the final catalysts, while increasing surface enrichment of Ru. Their performance for the Fischer-Tropsch Synthesis (FTS) has been evaluated in a fixed bed reactor. Ru-Co/Al2O3 displays the highest activity in the series, doubling the steady-state CO conversion rate of a Ru/Al2O3 catalyst with 3 times higher Ru loading. Ru-Fe/Al2O3 displays higher initial CO conversion and -CH2- productivity than Ru/Al2O3, but its activity declines during operation reaching lower conversion rates than Ru/Al2O3. In addition to CO2, Ru-Fe/Al2O3 produces oxygenated products, mainly alcohols. To a lesser extent, the formation of oxygenates over Ru-Co/Al2O3 and Ru/Al2O3 is also observed, and ascribed to the small crystallite size of the Ru particles. The evolution of CO2 during time on stream indicates that Fe is segregated to the surface of this catalyst during the FTS.