Decrease In Oxygen Concentration Research Articles

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

In vitro study of structural and chemical changes in two reciprocating files after multiple reuses and sterilisation.

To use scanning electron microscopy and energy dispersive X-ray spectroscopy to evaluate the metallurgical-chemical changes of WaveOne Gold (WOG) and R-Motion (RM), after multiple uses. The instruments were divided into groups (n = 8): WOG and RM-control groups, new instruments; WOG1 and RM1; WOG2 and RM2; WOG3 and RM3 after instrumentation of 1, 2 or 3 molars, respectively. Burrs occurred mainly in the control group and after the first use. The RM files were found to have a higher nickel content, which increased during reuse, and a decrease in oxygen content with increasing reuse, in addition to calcium impregnation, which occurred in greater amounts in the corrosion areas in the WOG files. The presence of topographic and chemical changes was demonstrated, indicating that caution should be taken when reusing endodontic instruments to avoid fractures.

Fire zone forefront residual tar combustion characteristics and functional group transformation mechanism: Appling the based on thermogravimetric and in-situ high-temperature FTIR

When preventing spontaneous combustion disasters in extinguished coal fire zones, the influence of the tar re-ignition phenomenon is often overlooked. Therefore, in this study, using thermogravimetric analysis and high-temperature (630 °C) in-situ infrared technology, the combustion reactivity and real-time evolution mechanism of key functional groups for tar were deeply discussed under oxygen-lean conditions. Additionally, a novel two-step baseline drift correction method for spectral graphs at high temperatures is proposed. The results showed that tar combustion could be divided into two stages: pyrolysis-volatilization mass loss and crosslinked structure oxidation combustion. Reduced oxygen concentration limits the violent and stable rapid combustion of tar-crosslinked structures and reduces the re-ignition tendency of tar. Among, with a decrease in oxygen concentration, H (burnout performance), Cb (the reaction ability in the early stage of ignition) and S (overall combustion performance) decreased, while Ti (mass loss endpoint temperature), Th(burnout temperature), and HF (combustion stability) increased. This provides information for the selection of a reasonable process to prevent tar re-ignition. The contents of methylidene and aldehyde carbonyl in tar increased by approximately 2 and 3.7 times, respectively, compared to those of raw coal. In the first thermal decomposition stage of tar, the aromatic hydrocarbons were relatively stable under the action of the structural framework, whereas aliphatic hydrocarbons continued to decrease. Before burnout, a decrease in oxygen concentration increased the crosslinking ability of tar and delayed the tar burnout process. The contents of aromatic hydrocarbons and aldehyde groups are highly sensitive to the evolution of the oxygen concentration. Specifically, the Kubelka–Munk value of the aromatic hydrocarbons increased from 0.015 to 0.10, while that of aldehyde carbonyl groups increased from 0 to 0.23. Additionally, in the early stage of tar combustion, the volatile mass loss was basically not affected by the time-scale effect, and mass loss endpoint residual mass was approximately 48.11 %. In the later stage of tar combustion, owing to the cumulative of time-scale effect, the tar re-ignition tendency increased, H, Cb, and S increased, and HF decreased from 1.388 to 1.098. This research is helpful guiding disaster prevention and control of tar re-ignition in a fire area, which leads to reburning in the surrounding area.

Precise surface machining of fused silica using high stability atmospheric pressure microwave plasma jet with a new internal electrode

Plasma is a promising approach for machining of fused glass substrates. Developing high-performance microwave torch is the core element to ensure the processing accuracy of this technology. In this study, a spline curve-based microwave torch internal electrode structure was proposed, which increased the internal electric field strength by 54 %. The discharge dynamics simulation based on this electrode shows that the plasma is excited at the inner electrode tip and the bottom of the resonant cavity, then it expands to form a linear discharge region and eventually fill the discharge tube. It was revealed by CCD images that with the increase of carrier gas flow rate, turbulent flow state appears in the tail of the jet. OES data shows that microwave Ar plasma can effectively dissociate CF4, and due to the oxidation effect of oxygen, CFx and C2 content decrease significantly with the addition of oxygen. The machining experiment on fused silica shows that the material removal stability of this torch reaches 3.69 %, and the removal rate increases nYarly with dwell time due to thermal effect. Finally, the machining performance of the atmospheric pressure microwave plasma jet was verified by figuring of a planar fused silica surface reducing the form error from 108.1 nm RMS to 16.5 nm RMS.

Fluxes of nitrogen and phosphorus in fouling communities on artificial offshore structures

The number of offshore artificial structures in the North Sea is continuously increasing. Apart from the structures that have been added to the marine environment accidentally (e.g., shipwrecks), structures are also deliberately developed to meet the increasing needs for renewable energy. These structures provide habitat for fouling organisms. The fouling communities vary in abundance and composition based on location, depth, and structure age. Most fouling species filter particles from the water column, changing phytoplankton production and affecting larval settlement success, while releasing ammonium that can fuel phytoplankton growth as well as (pseudo)faeces that enriches the seabed, changing local biogeochemical cycles.Our study used in-situ incubation chambers to investigate oxygen, nitrogen, and phosphate fluxes associated with fouling organisms to improve understanding of these changes in biogeochemical cycles. Divers used incubation chambers (domes) on shipwrecks in the southern North Sea where over 55 years mature fouling communities have established. A series of water samples was collected from each dome during deployment to measure the change in concentration of ammonium, nitrite, nitrate, and phosphate. All fauna enclosed in the domes was collected after each measurement for further analysis.The full macrofauna dataset contained 65 unique species on 4 shipwrecks (25 to 50 species per sample). Abundance ranged from 2187 to 59,427 individuals per sample (683 cm2). On average, a decrease in oxygen concentration of 126 μmol/g ash free dry weight/h was found. The sequential water samples also showed clear changes in nutrient concentration with time in all incubations. The largest changes were observed with high fouling community abundances and biomass. Ammonium, nitrite, and phosphate always increased, with 1.5-to-5-fold increases from start to end of the incubation, while for nitrate both an efflux and influx were measured. Oxygen decreased in all incubations. Mean fluxes (all in μmol per m2 per hour with standard error) were significant for ammonium (945 ± 300), nitrite (80 ± 30), phosphate (61 ± 8), and oxygen (−11,794 ± 3289), but not for nitrate (−206 ± 122). Per gram AFDW, only ammonium (12.7 ± 3.5) and oxygen (−126 ± 48) had fluxes that differed significantly from zero.Compared to average seabed (sandy bottom) oxygen demand and community fluxes from previous studies, the observed fluxes were high. Our findings resembled those from temperate biogenic reef studies. Further data collection across a larger spatial and temporal scale is needed to fully understand offshore structure effects on marine environments.

Effect of background gas composition on the stoichiometry and lithium ion conductivity of pulse laser deposited epitaxial lithium lanthanum tantalate (Li3xLa1/3−xTaO3)

Lithium lanthanum tantalate (Li3xLa1/3−xTaO3, x = 0.075) thin films were grown via pulsed laser deposition using background gas atmospheres with varying partial pressures of oxygen and argon. The background gas composition was varied from 100% to 6.6% oxygen, with the pressure fixed at 150 mTorr. The maximum ion conductivity of 1.5 × 10−6 S/cm was found for the film deposited in 100% oxygen. The ion conductivity of the films was found to decrease with reduced oxygen content from 100% to 16.6% O2 in the background gas. The 6.6% oxygen background condition produced ion conductivity that approached that of the 100% oxygen condition film. The lithium transfer from the target to the film was found to decrease monotonically with decreasing oxygen content in the background gas but did not account for all changes in the ion conductivity. The activation energy of ion conduction was measured and found to correlate well with the measured ion conductivity trends. Analysis of x-ray diffraction results revealed that the films also exhibited a change in the lattice parameter that directly correlated with the ion conduction activation energy, indicating that a primary factor for determining the conductivity of these films is the changing size of the ion conduction bottleneck, which controls the activation energy of ion conduction.

Experimental investigation of the effects of inlet high-swirl air preheating and dilution on kerosene flame

This study investigated the effects of co-flow air swirling on the combustion of Kerosene, as relatively heavy fuel, under preheated and diluted air conditions. Various factors affecting the flame structure, such as preheating temperature, dilution, swirl number, and airflow rate were studied using the upgraded MILD (Moderate or Intense Low-Oxygen Dilution) combustion tester of Sharif University of Technology (SMSTR). This tester, which is symmetrically axial, provides co-flow air with the desired temperature, swirl number, and dilution for a liquid fuel spray burner. The flame characteristics was investigated through direct photography and chemiluminescence. The results show that the stability range significantly increases with the air swirling, while the flame length decreases. Enhancement of combustion quality and more complete combustion of fuel were observed with preheating. Preheating resulted in geometric changes in the appearance of the flame, specially reducing flame lift-off and the front view area in high airflow. A decrease in the air oxygen content causes a general change in the structure of the flame, resulting in a shorter and more lifted one compared to non-diluted condition. The chemiluminescence images of the flame also revealed weaker and more uniform emission pattern with the inlet high-swirl air preheating and dilution. By utilizing around 15 % oxygen content dilution, preheating at around 656 K, and a swirl number of 0.8, the combustion zone exhibited similarities to the MILD combustion mode, suggesting the achievement of MILD combustion. The high swirl concept allowed higher dilution limits (about 12 %) and reduced preheating requirements (approximately 11 %) in achieving the MILD combustion regime compared to the previous study conducted without swirl conditions. In contrast to the non-swirl mode flame, the flame in this study transitioned completely to a MILD-like condition.

Effect of oxide layer state on the photoelectric properties of thermally sensitized PbS thin films

Lead sulfide (PbS) thin films were initially deposited through chemical bath deposition, followed by sensitization in a pure oxygen atmosphere at 600 °C. To investigate the influence of varying oxide layer states on the photoelectric properties of thermally sensitized PbS thin films, the surface oxide layer of the sensitized films was selectively removed using KOH etching. As the etching duration increased, a gradual decrease in surface oxygen content was observed, accompanied by an initial increase and subsequent decrease in detectivity. Notably, the optimum detectivity value (6.92 × 109 cm Hz1/2 W−1) was achieved after 10 s of KOH etching. Our investigation was further supplemented with field emission scanning electron microscopy and X-ray diffraction analyses to gain insights into the impact of the oxide layer state on the photoelectric properties of PbS thin films. Our findings led to the proposal of a dual conduction mechanism for carrier transport within PbS film. In the case of as-grown PbS films, carrier transport primarily occurs via crystal boundary transition. However, after oxygen sensitization, the formation of an oxygen-rich carrier channel at the crystal boundary shifts carrier transport dominance towards crystal boundary transport. The combined influence of both transmission mechanisms serves as a primary driver for the observed changes in the photoelectric properties of PbS films.

Understanding and mitigating temperature-induced agglomeration in silica-based chemical mechanical planarization (CMP) slurry storage

This study explores the impact of temperature on silica particle agglomeration in Chemical Mechanical Planarization (CMP) slurries during storage. Slurries were stored at 15 °C, room temperature, and 45 °C, and analyzed. ATR-FTIR, RAMAN, SEM, zeta potential, and LPC were employed providing qualitative and quantitative data on slurry stability and agglomeration tendencies. Elevated temperature storage significantly increased agglomeration and large particle counts with particle counts value of ∼1.2×107 Part./ml, likely due to water molecule dehydration leading to destabilization. Low-temperature storage also induced agglomeration but to a lesser extent with particle counts the value of ∼4.0×106 Part./ml compared with the RT (∼2.0×106 Part./ml). Short-term storage yielded soft agglomerates with LPC of ∼(2.0–4.0)×106 Part./ml, while long-term high-temperature storage led to hard agglomerates with LPC of ∼3.0×107 Part./ml. The ATR-FTIR and Raman analysis indicate that the spectroscopic features of the original slurry exhibited changes upon variation of storage temperature from RT to 15 and 45 °C. The study also explored the reversibility of agglomeration post-treatment, indicating a potential mitigation pathway. The results demonstrated an inverse relationship between temperature and dissolved oxygen (DO) in silica slurries. For example. the curves depict a decrease in oxygen content from ∼10 ppm at RT to 7 ppm at 45 °C with increasing aging time. A mechanism outlining the temperature and aging-induced agglomeration was proposed, linking temperature fluctuations and thermodynamic aspects to colloidal stability. These findings offer a robust understanding of temperature-induced agglomeration in silica-based CMP slurry storage, paving the way for developing strategies to alleviate these issues and ensuring consistent CMP performance in semiconductor manufacturing.

Gas production analysis for the buffer layer of high‐voltage cross‐linked polyethylene cables

AbstractThe cross‐linked polyethylene insulated cables with corrugated aluminium‐sheathed are widely used in urban power systems. Recently, a new type of power cable fault has emerged, primarily due to defects in the buffer layer. However, there is a notable lack of effective evaluation methods for these defects in high‐voltage (HV) cables. Initially, a theoretical analysis of the gas generation mechanism in the cable buffer layer was conducted, identifying distinct gas products at different stages. Subsequently, the diffusion kinetics of gas within the cable was studied, highlighting the importance of gas in determining the state of the buffer layer. The authors then collected and analysed 60 sets of buffer layer gases from two operational 110 kV HV cables using gas chromatography technology. Combining these results with the findings from on‐site inspections, the characteristic gas components and concentration distribution under various defect conditions were summarised. The results found higher concentrations of CH4 in normal cables and defective cables, while there are higher concentrations of H2, CO and CO2 in defective cables, and the oxygen content decreases. The discoveries made in this research may offer a new approach for assessing the state of the cable buffer layer.

Impact of high-temperature biomass pyrolysis on biochar formation and composition

The development and utilization of biomass play a vital role in reducing fossil fuel dependency and mitigating greenhouse gas emissions. High-temperature pyrolysis provides a promising route for converting biomass into valuable products without tar formation. Kinetic models are essential for understanding biomass pyrolysis processes, aiding reactor design and optimization. In this study, rice husk (RH) and corn straw (CS) are selected, which exhibit significant differences in ash content but are widely present. Pyrolysis is performed using a thermogravimetric analyzer coupled with a mass spectrometer (TGA-MS). The results show a rapid decrease in solid residue oxygen content at elevated temperatures, which stabilized after reaching 900°C, accounting for about 8–10%. MS quantification indicates increased release of H2O and CO during this stage. Fourier transform infrared spectroscopy (FTIR) analysis on the biochar unveils that this phenomenon is attributed to the stretching vibration of C-O bonds and the conversion of -OH groups. The remaining oxygen primarily exists as carbonyl and carboxyl groups. Subsequently, the CRECK-S-B biomass pyrolysis kinetic model is updated, specifically targeting the transformation mechanism of oxygen-containing solids at high temperatures to improve the prediction of biochar yield and elemental composition. The relative error of oxygen content prediction is less than 10%. The accuracy of the model is validated through experimental data and an extensive literature database, leading to the establishment of a comprehensive database. The updated model demonstrates significantly enhanced prediction accuracy for pyrolysis temperatures above 800°C, expanding its applicability range. Moreover, it achieves an accuracy rate exceeding 80% for char yield and elemental content in the temperature range of 200–1000°C, including torrefaction conditions. It provides a theoretical foundation for the effective utilization of high-temperature biochar, offers a novel insight into biomass thermochemical conversion, and contributes to the sustainable development of biomass energy.

Summer heatwaves on the Baltic Sea seabed contribute to oxygen deficiency in shallow areas

Since the early 1980ies, the shallow and brackish Baltic Sea, located in northern Europe, has warmed fastest of all the world’s coastal seas. Hence, the total heat exposure during marine heatwaves increased in frequency and duration, which may have a major impact on the marine ecosystem. We found that marine heatwaves, using two different, commonly used definitions, occurred everywhere on the sea surface since the early 1990s. Periods with sea surface temperatures larger than 20 °C lasting longer than 10 days were particularly numerous in the shallow coastal zone of the southern and eastern Baltic Sea. Furthermore, summer marine heatwaves that reached the seabed mainly occurred in water depths of less than 20 m, where they led to a decrease in oxygen concentration. Since the early 1990s, a positive trend in the expansion of marine heatwaves has been observed on the seabed. The increasing number of marine heatwaves increases the risk of hypoxia events in the coastal zone.

MONITORING AND ANALYSING AIR POLLUTION IN RESIDENTIAL AREAS UNDER THE INFLUENCE OF VEHICLE AND METALLURGICAL PLANT EMISSIONS

Assessment of the level of air pollution in the residential areas of an urbanized city allows to determine the main pollutants contained in the air and allows to adjust or improve the cleaning equipment of emission sources. The purpose of the work: research of the general level of air pollution in the zone of influence of the central road with heavy traffic and an industrial facility on the air quality of residential areas of the city of Kamianske. Methodology. The work used air quality analyzers Benetech GM 8804, Wintact wt 8811, Benetech GM 8806 to determine the presence (concentration) of hydrogen sulfide, carbon monoxide, ammonia, formaldehyde, dust (PM 2.5), combustible gases (LEL). Sampling points were chosen in residential areas: indoors, on the adjacent territory and near the road. Scientific novelty. In the course of research, it was found that the residential area, which is located closer to the industrial facility and to the central part of the city with shopping centers, has relatively higher LEL indicators and lower indicators of oxygen content in the air. The dynamics of changes in air pollution over time are not high. Practical value. Monitoring and analysis of the level of air pollution contributes to the detection of dangerous chemicals in the air of a residential area, the patterns of decreasing oxygen content and the dynamics of changes in the content of combustible gases in the air over time and with a change in the distance to the source of pollution. Results. It was found that the air of residential areas does not contain compounds of hydrogen sulfide, carbon monoxide, ammonia, and formaldehyde sufficient for the measurement range of analytical devices. Traces of dust were detected. Recorded decrease in oxygen content indoors and in atmospheric air near roads. The content of combustible gases (LEL) in the studied premises in most samples is higher than outside.

The Impact of Oxygen Concentration on the Postcuring of 3D-Printed Dental Resin.

This study investigated the impact of reducing the oxygen concentration via nitrogen injection during the postcuring process of 3D-printed dental materials. Resin specimens for dental crown and bridge (15-mm diameter, both 1-mm and 2-mm heights) were 3D-printed and rinsed. Subsequently, the postcuring process was conducted on nine groups categorized according to atmospheric conditions within the curing device (20% [control], 10%, and 5% oxygen) and curing times (10, 15, and 20 minutes). Surface roughness was measured using a gloss meter. Surface polymerization was confirmed through Fourier-transform infrared spectroscopy (FT-IR) analysis, and the flexural strength and elastic modulus of the specimens were measured using a universal testing machine. Water absorption and solubility were determined according to Inernational Organization for Standardization (ISO) standards. All evaluation criteria were statistically analyzed using one-way ANOVA and Tukey's post hoc test based on oxygen concentration. The elastic modulus did not show statistically significant differences in all groups. However, compared to the control group, the flexural strength, degree of conversion, and gloss significantly increased in the groups with decreased oxygen concentrations. Conversely, water solubility and water absorption significantly decreased in a few groups with reduced oxygen concentration. Reducing oxygen concentration through nitrogen injection during the postcuring process of 3D printing enhances the suitability of the dental prosthetic materials. The significant increase in flexural strength can particularly enhance the utility of these materials in dental prosthetics.

Combustion Diagnostics and Emissions Measurements of a Novel Low NOx Burner for Industrial Gas Turbine Operated With CO2 Diluted Methane/Air Mixtures

Abstract While the employment of Exhaust Gas Recirculation (EGR) is a well-established technique in Internal Combustion Engines to limit NOx emissions, its adoption in Gas Turbine engines has not yet found a practical application due to its expensive and complex installation that doesn't justify the emissions reduction when compared to already established DLN combustion technologies. EGR becomes an interesting option in GT engines considering the possibility of increasing the CO2 content of the exhaust gases to improve the efficiency of Carbon Capture and Storage (CCS) units. However, the decrease in oxygen content of the combustion air is extremely challenging in terms of combustion stability and therefore of engine operability. In the present work, a low NOx burner was studied at ambient pressure in a reactive single burner test rig. The burner was fed with methane and characterized in terms of emissions and stability limits at different operating conditions. In addition, the flame position and shape were studied through OH* chemiluminescence imaging together with the flow field thanks to PIV measurements. The effects of CO2 addition on the flame were then investigated at different EGR increasing levels, highlighting the impact of the oxygen content on the combustion reaction intensity. Variations in emissions and burner stability limits in terms of maximum sustainable CO2 content were also studied, to detail the burner operating window. Data have been thoroughly analyzed to gather information on the burner behavior to support the design of new technical solutions capable of ensuring both proper flame stability and low CO and NOx emissions.

Identifying the Causes of Unexplained Dyspnea at High Altitude Using Normobaric Hypoxia with Echocardiography.

Exposure to high altitude results in hypobaric hypoxia, leading to physiological changes in the cardiovascular system that may result in limiting symptoms, including dyspnea, fatigue, and exercise intolerance. However, it is still unclear why some patients are more susceptible to high-altitude symptoms than others. Hypoxic simulation testing (HST) simulates changes in physiology that occur at a specific altitude by asking the patients to breathe a mixture of gases with decreased oxygen content. This study aimed to determine whether the use of transthoracic echocardiography (TTE) during HST can detect the rise in right-sided pressures and the impact of hypoxia on right ventricle (RV) hemodynamics and right to left shunts, thus revealing the underlying causes of high-altitude signs and symptoms. A retrospective study was performed including consecutive patients with unexplained dyspnea at high altitude. HSTs were performed by administrating reduced FiO2 to simulate altitude levels specific to patients' history. Echocardiography images were obtained at baseline and during hypoxia. The study included 27 patients, with a mean age of 65 years, 14 patients (51.9%) were female. RV systolic pressure increased at peak hypoxia, while RV systolic function declined as shown by a significant decrease in the tricuspid annular plane systolic excursion (TAPSE), the maximum velocity achieved by the lateral tricuspid annulus during systole (S' wave), and the RV free wall longitudinal strain. Additionally, right-to-left shunt was present in 19 (70.4%) patients as identified by bubble contrast injections. Among these, the severity of the shunt increased at peak hypoxia in eight cases (42.1%), and the shunt was only evident during hypoxia in seven patients (36.8%). In conclusion, the use of TTE during HST provides valuable information by revealing the presence of symptomatic, sustained shunts and confirming the decline in RV hemodynamics, thus potentially explaining dyspnea at high altitude. Further studies are needed to establish the optimal clinical role of this physiologic method.

Catalytic Upgrading of Rice Straw Bio-Oil via Esterification in Supercritical Ethanol over Bimetallic Catalyst Supported on Rice Straw Biochar

This research explores the enhancement of bio-oil quality through upgrading with the magnetic bimetallic oxide (CuO-Fe3O4) catalysts supported on activated rice straw biochar (AcB). These catalysts were employed in a supercritical ethanol-based upgrading process. Various characterization techniques, including elemental analysis, Fourier transform infrared (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), were utilized to characterize the prepared catalysts. This study revealed significant improvements in the physical characteristics and chemical composition of the bio-oil, with an increase in the heating value (HHV) from 21.3 to 32.1 MJ/kg. Esterification and transesterification were identified as key reactions contributing to this improvement. Notably, the pH of bio-oil increased from 4.3 (raw bio-oil) to 5.63 (after upgrading), signifying reduced acidity. The analysis of the bio-oil’s chemical composition highlighted a decrease in oxygen content and an increase in carbon and hydrogen content. At the optimum conditions, the application of supercritical ethanol proved to be an efficient method for enhancing the bio-oil’s properties. A crucial transformation occurred during the upgrading process and more than 90% of carboxylic acids were converted into esters, primarily ethyl acetate at the optimal conditions. This study has demonstrated the effective enhancement of raw bio-oil from rice straw through the utilization of carbon-based bimetallic oxide catalysts in a supercritical upgrading procedure.

Effect of Inert Species on the Static and Dynamic Stability of a Piloted, Swirl-Stabilized Flame

Abstract Carbon sequestration and utilization has been proposed as a method for decarbonizing high-efficiency industrial gas turbines operating on natural gas fuels for power generation and industrial markets. To increase the efficiency of the carbon removal process from the exhaust stream of the turbine, exhaust gas recirculation (EGR) can be used. EGR recycles a portion of the engine exhaust into the inlet, increasing the concentration of inert species in the exhaust stream to improve the performance and cost-effectiveness of CO2 separation systems. This strategy can, however, reduce the oxygen concentration in the air, leading to changes in flame stabilization in the combustor. In this study, we investigate the effect of air diluted with inert gases of different compositions and the impact that these mixtures have on flame static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variable-length combustor is used to measure the flame behavior for oxygen concentrations of 15–21% by volume. A constant adiabatic flame temperature test matrix is conducted to mimic operation in an industrial gas turbine. High-speed chemiluminescence imaging is used to determine the change in flame shape and dynamics for each gas composition. As the oxygen concentration decreases, the flame lifts from the centerbody, resulting in an aerodynamically stabilized flame at the lowest O2 concentrations. Different compositions of gases result in different flame shapes, where higher levels of N2 in the diluents result in more flame stabilization in the outer recirculation zone as compared to those with higher levels of CO2. The flame oscillation mechanisms also change with oxygen concentration, where the lifted flames at low O2 levels exhibit an ignition/extinction oscillation mode as compared to a vortex-shedding-coupled oscillation mode at high O2 levels where the flame is stabilized on the centerbody. Companion chemical kinetics simulations are used to explain changes in the flame's shape and behavior.

Decrease in Oxygen Concentration for the Fast Start-Up of Partial Nitritation/Anammox without Inoculum Addition

Initiating the partial nitritation and anammox (PN/A) process without inoculation poses a significant challenge. Thus, there is a notable amount of interest in devising a straightforward strategy for the start-up of PN/A. This study demonstrates the feasibility of achieving the rapid start-up of a one-stage PN/A process within a moving-bed sequencing batch biofilm reactor (MBSBBR) by reducing the oxygen concentrations: 3.0 mg O2/L (Stage I), 2.0 mg O2/L (Stage II), and 1.0 mg O2/L (Stage III). The anammox activity was observed 15 days after a gradual decrease in the oxygen concentration and confirmed using a specific anammox activity test (5.9 mg N/gVSS∙h). During Stage III, the average total inorganic nitrogen (TIN) removal efficiency was 60.6%. The relative abundance of planctomycetes, a typical phylum representing anammox microorganisms, increased almost three times from Stage I (2.8%) to Stage III (7.1%). These results demonstrate the potential of a decrease in oxygen concentration for the fast start-up of the one-stage partial nitritation and anammox process without inoculation. The implementation of the studied DO strategy has practical implications for wastewater treatment plant operators, particularly in the start-up of the PN/A processes. Additionally, batch assays allow for the rapid assessment of treatment plant performance, providing real-time insights into its functionality and, thereby, optimizing wastewater treatment practices.

Oxygen Extraction Efficiency and Tolerance to Hypoxia in Sponges

Sponges have always been filter feeders, in contrast to all the other filter-feeding invertebrate groups for which this feeding mode is a secondary adaptation. This study calls attention to this aspect, which explains why sponges are tolerant to hypoxia, but probably not more tolerant than the other filter-feeding invertebrates. The measurement of respiration rates at decreasing oxygen concentrations along with an estimation of the oxygen extraction efficiency in the marine demosponge Halichondria panicea have been used to understand why sponges are tolerant to low oxygen concentrations. It was found that the respiration rate was constant down to about 1.5 mL O2 L−1, which shows that the extraction efficiency increases with a decreasing oxygen concentration. It is argued that the relationship between the filtration rate and oxygen consumption in filter feeders is controlled by the resistance to the diffusion of oxygen across the boundary layer between the feeding current and the tissues of the body. A high tolerance to hypoxia is a consequence of the adaptation to filter feeding, and sponges do not have a special capacity to overcome hypoxic events.