Residence Time Of CO2 Research Articles

Optimizing macroalgal biochar-based catalysts for monophenols recovery during wood dust catalytic pyrolysis: A comparative study using response surface methodology and artificial neural network

This study aimed to explore the optimization of macroalgal biochar-based catalysts (MBBCs) for enhanced monophenolic production in biomass pyrolysis. By utilizing response surface methodology (RSM) and artificial neural network (ANN), key variables in the activation process during preparation of MBBCs were identified including activation temperature, activator ratio, and CO2 residence time. The results showed that the ANN model, with an R2 of 0.9816, accurately predicted optimal catalyst activation conditions, closely matching the experimentally determined optimal conditions (ENPC800-1:2–30). The bio-oil yield decreased under ENPC800-1:2–30 catalyst, but the monophenolic content increased significantly, reaching a relative content of 60 %, with a total concentration of phenol, cresols, and ethylphenol amounting to 35.54 mg/gbio-oil. The present study revealed significant changes in non-condensable gas composition, including increased hydrogen and carbon monoxide which aid in enhancing their energy applications. Thus, the optimized MBBCs greatly help in improving the bio-oil and non-condensable gas quality and thereby providing vital insights over sustainable chemical production through biomass pyrolysis.

Synergistic treatment of digested wastewater with high ammonia nitrogen concentration using straw and microalgae

Microalgae as a promising approach for wastewater treatment, has challenges in directly treating digested piggery wastewater (DPW) with high ammonia nitrogen (NH4+-N) concentration. To improve the performance of microalgae in DPW treatment, straw was employed as a substrate to form a straw-microalgae biofilm. The results demonstrated that the straw-microalgae biofilm achieved the highest NH4+-N removal rate of 193.2 mg L−1 d−1, which was 28.8 % higher than that of culture system without straw. The final NH4+-N concentration in the effluent met the discharge standard of 5 mg L−1. Furthermore, the total organic carbon (TOC) released from straw facilitated bacterial proliferation and the secretion of extracellular polymeric substances (EPS). The EPS and TOC increased the suspension viscosity and surface tension, thereby enhancing the residence time of CO2 in the liquid phase and promoting CO2 fixation. This study presented a novel method for the biological treatment of high-ammonia–nitrogen DPW.

Dry reforming process using microwave plasma generator with high carbon dioxide conversion efficiency for syngas production

The proposed CO2 reforming solution has improved CO2 conversion efficiency by developing a new double helix type plasma generator (DHTPG) to preheat the discharge gas and increase residence time of CO2 at DHTPG. In addition, injecting CH4 independently allows for a stable increase in the temperature of the CO2 plasma in the microwave plasma generator compared with other conventional methods. To verify the performance of the DHTPG, we experimentally investigated the distribution of the plasma gas temperature using an enthalpy probe system as a function of the specific energy input, which is a key parameter for understanding the mechanisms of CO2 reforming of CH4. We performed the CO2 reforming of CH4 using the newly designed plasma generator and a comparative analysis of its characteristics with those of other plasma generators. Without catalyst materials, our method significantly enhanced the CO2 conversion efficiency to 91.4 % with an energy efficiency of 67 % at a specific energy input of 245 kJ/mol. The main advantage of our method is an increase in energy-consumption selectivity, in which the energy injected through the plasma decomposes CO2 rather than CH4. In addition, it reduces the energy required to stably maintain the plasma to improve energy efficiency.

Enhanced carbon dioxide fixation of Chlorella vulgaris in microalgae reactor loaded with nanofiber membrane carried iron oxide nanoparticles

To improve the CO2 dissolution and carbon fixation in the process of microalgae capturing CO2 from flue gas, a nanofiber membrane containing iron oxide nanoparticles (NPsFe2O3) for CO2 adsorption was prepared, and coupled with microalgae utilization to achieve carbon removal. The performance test results showed that the largest specific surface area and pore size were 8.148 m2 g−1 and 27.505 Å, respectively, when the nanofiber membrane had 4% NPsFe2O3. Through CO2 adsorption experiments, it was found that the nanofiber membrane could prolong the CO2 residence time and increase CO2 dissolution. Then, the nanofiber membrane was used as a CO2 adsorbent and semifixed culture carrier in the Chlorella vulgaris culture process. The results showed that compared with the group without nanofiber membrane (0 layer), the biomass productivity, CO2 fixation efficiency and carbon fixation efficiency of Chlorella vulgaris with 2 layers of membranes increased by 1.4 times.

Intensification of supercritical fluid in the extraction of flavonoids: A comprehensive review

The utilization of highly toxic, expensive, and eco-unfriendly organic solvents for the extraction process has been replaced by carbon dioxide (CO2) in its supercritical state. The most significant advantage of supercritical CO2 extraction is after the extraction process there was no trace amount of solvent present in extracted compounds since the residual CO2 can be easily depressurized and vented. Supercritical CO2 attracts interest because of its high compressibility, non-toxic, non-flammable, and physiological compatibility. This insight is a compilation of research works related to flavonoids extraction using a supercritical fluid. The significant parameters that affect the extraction process are temperature, pressure, solvent flow rate, and extraction time. These are the adjustable parameters that were optimized predominantly to improve the yield of the flavonoids extraction. The density of supercritical CO2 is attained by tuning temperature and pressure. The addition of co-solvents enhances the extraction of polar compounds. The residence time of CO2 in the extractor should be sufficient such that the solute reaches the saturation conditions in the fluid phase. This review article will give immense knowledge on the insights about the parameter that needs to be determined to scale up the extraction process.

Tangential Flue Gas Recirculation (TFGR) technique for enhancement of radiation characteristics and reduction of NOx emission in natural gas burners

Experiments were carried out to find out the effect of different TFGR ratios on flame characteristics, pollutant emission, temperature, luminosity, IR radiation and total radiation of natural gas flames. A spiral duct connected tangentially to the furnace inlet linked the furnace to the chimney. A centrifugal fan was installed on the spiral duct to suck the combustion products and a spiral duct back-draft round damper was installed to adjust the FGR volume flow rate. The optical properties of the flame were studied for visible and IR wavelengths by a TES-1332 A digital luminance meter, a BOMEM FTIR and IR flame photography. Also, the total radiation of flame was determined by an SBG01 heat flux sensor. Furthermore, an S type thermocouple was used to measure the flame temperature. The results indicate that TFGR changes the nonluminous natural gas flame to a luminous flame by the dissociation of the recirculated CO2 to CO. TFGR enhances the tangential momentum of flame and generates a voluminous flame, increases the heat transfer area of flame and eliminates the hot-spot region in the core of flame, which decrease the axial flame temperature and thermal corrosion. Furthermore, the concentration and residence time of CO2 and H2O, as the most important radiative species of natural gas flames, increase in the flame reaction zone, which results in the enhancement of the IR emissivity and the radiation heat transfer of natural gas flame. Finally, although the TFGR increases the concentration of CO emission to a level lower than the standard level, it causes natural gas burners to emit significantly less dangerous NOx.

Distribution and Transport of CO2 in Hydrated Hyperbranched Poly(ethylenimine) Membranes: A Molecular Dynamics Simulation Approach.

Hyperbranched poly(ethylenimine) (HB-PEI) has been distinguished as a promising candidate for carbon dioxide (CO2) capture. In this study, we investigate the distribution and transport of CO2 molecules in a HB-PEI membrane at various hydration levels using molecular dynamics (MD) simulations. For this, model structures consisting of amorphous HB-PEI membranes with CO2 molecules are equilibrated at various hydration levels. Under dry conditions, the primary and secondary amines are highly associated with CO2, indicating that they would participate in CO2 capture via the carbamate formation mechanism. Under hydrated conditions, the pair correlations of CO2 with the primary and secondary amines are reduced. This result suggests that the carbamate formation mechanism is less prevalent compared to dry conditions, which is also supported by CO2 residence time analysis. However, in the presence of water molecules, it is found that the CO2 molecules can be associated with both amine groups and water molecules, which would enable the tertiary amine as well as the primary and secondary amines to capture CO2 molecules via the bicarbonate formation mechanism. Through our MD simulation results, the feasibilities of different CO2 capture pathways in HB-PEI membranes are demonstrated at the molecular level.

Carbon Dioxide in Taal Volcanic Lake: A Simple Gasometer for Volcano Monitoring

AbstractWe report here an increase in the amount of carbon dioxide in Taal lake during the year preceding the January 2020 eruption. Starting in February 2019, the CO2 emissions from the lake increased from background value (700 t day−1) to a flux close to 2,400 t day−1 at the time of the eruption. We show that the lake acts as a highly sensitive gasometer where CO2 (aq) reflects the balance between CO2 supplied to the lake (by hot springs) and CO2 lost by diffusion at air‐water interface. The lake waters are extremely enriched in dissolved carbon dioxide with pCO2 values as high as 0.35 atm (350,000 ppmV) equivalent to a CO2 (aq) of 9.32 mmol l−1. The residence time of CO2 in the lake is around 1 week which allows for fast detection of change in magma degassing and makes carbon dioxide a very promising tool for volcano monitoring.

The Role of Synthetic Biology in Atmospheric Greenhouse Gas Reduction: Prospects and Challenges.

The long atmospheric residence time of CO2 creates an urgent need to add atmospheric carbon drawdown to CO2 regulatory strategies. Synthetic and systems biology (SSB), which enables manipulation of cellular phenotypes, offers a powerful approach to amplifying and adding new possibilities to current land management practices aimed at reducing atmospheric carbon. The participants (in attendance: Christina Agapakis, George Annas, Adam Arkin, George Church, Robert Cook-Deegan, Charles DeLisi, Dan Drell, Sheldon Glashow, Steve Hamburg, Henry Jacoby, Henry Kelly, Mark Kon, Todd Kuiken, Mary Lidstrom, Mike MacCracken, June Medford, Jerry Melillo, Ron Milo, Pilar Ossorio, Ari Patrinos, Keith Paustian, Kristala Jones Prather, Kent Redford, David Resnik, John Reilly, Richard J. Roberts, Daniel Segre, Susan Solomon, Elizabeth Strychalski, Chris Voigt, Dominic Woolf, Stan Wullschleger, and Xiaohan Yang) identified a range of possibilities by which SSB might help reduce greenhouse gas concentrations and which might also contribute to environmental sustainability and adaptation. These include, among other possibilities, engineering plants to convert CO2 produced by respiration into a stable carbonate, designing plants with an increased root-to-shoot ratio, and creating plants with the ability to self-fertilize. A number of serious ecological and societal challenges must, however, be confronted and resolved before any such application can be fully assessed, realized, and deployed.

CFD simulations of rotary BOF slag carbonation kiln reactor with cyclone flow

Rotary kiln reactors play an important role in improving the mechanical properties and usability of basic oxygen furnace slag through a carbonation process. The performance of such reactors is critically dependent on the residence time of the CO2 gas used to promote the carbonation reaction. Accordingly, the present study proposes a rotary kiln reactor in which the residence time is increased by arranging the inlet and outlet pipes obliquely to the reactor centerline; thereby producing a cyclone flow structure within the reactor tube. The optimal geometry parameters and rotational speed of the kiln are determined using the robust Taguchi experimental method. The CO2 residence time in the optimized kiln is then evaluated by means of computational fluid dynamics simulations. It is shown that the residence time increases from 63.587 s in a standard (non-cyclone-flow) rotary kiln to 105.815 s in the optimized rotary kiln; corresponding to a performance improvement of 66.4%.

Study of Thermal Stability of Hydrotalcite and Carbon Dioxide Adsorption Behavior on Hydrotalcite-Derived Mixed Oxides Using Atomistic Simulations.

Hydrotalcites (HTlcs) or layered double hydroxides (LDHs) have been used in a wide range of applications such as catalysis, electrochemical sensors, wastewater treatment, and carbon dioxide (CO2) capture. In the current study, molecular dynamics simulation was employed to investigate carbon dioxide adsorption behavior on amorphous layered double oxides (LDOs) derived from LDHs at elevated temperatures. The thermal stability of LDHs was first examined by heating the sample up to T = 1700 K. Radial distribution functions confirmed the structural evolution upon heating and the obtained structures were in good agreement with experiments, where periclase was confirmed to be the stable phase in the recrystallized mixed oxides above T = 1200 K. Further, CO2 adsorption was studied as a function of amorphous HTlc-derived oxide composition, where static and dynamic atomistic measures have been employed to characterize the CO2 adsorption behavior. The simulation results showed that the CO2 dynamic residence time on LDH-derived LDOs was sensitive to the Mg/Al molar ratio and the average amount of residence time of CO2 on the surface of LDOs reached maximum when the Mg/Al molar ratio was equal to 3.0. Meanwhile, the activation energy for diffusion also showed local maximum when the Mg/Al molar ratio was 3.0, suggesting that this particular ratio of Mg/Al mixed oxides possessed the highest CO2 adsorption capacity. This is consistent with experimental results. Examination of the binding between CO2 and mixed oxides revealed that both magnesium and oxygen in amorphous LDOs contributed to CO2 adsorption. Further analysis suggested that the interaction between Mg–O and O(LDO)–C were the most important interactions for the physisorption of CO2 on amorphous surface and different CO2 adsorption behavior on different Mg/Al molar ratio surfaces was directly related to their amorphous local structure.

The process intensification of CO2 absorption in Hilbert fractal reactor fabricated by a 3D printer

ABSTRACT CO2, as a major greenhouse gas, contributes greatly to the global warming. Increasing the efficiency of CO2 capture and utilization has becomea worldwide challenge. In the present research, Hilbert fractal reactor was fabricated via 3D printing technology for process intensification of ethanolamine (MEA) CO2 absorption. The performance of the Hilbert fractal reactor was investigated and compared to the serpentine reactor. For constant gas and liquid flow rates, the CO2 removal efficiency, the absorption rate, and the assumption of MEA increased with increasing concentration of MEA. In the comparison with the serpentine reactor, the CO2 removal efficiency in Hilbert fractal reactor is higher than that in the serpentine reactor at the relative low gas flow rate. The continuous bending in the Hilbert fractal reactor enhances the shear stress of the fluids, and the gas phase is segregated into the small bubbles which significantly increase the interface mass transfer. Under the relative high gas flow rate, the residence time of CO2 is short and the flow pattern in Hilbert reactor turns into the annular flow which adverse to CO2 absorption rate, and the advantage of Hilbert fractal reactor over serpentine reactor becomes negligible. The maximum CO2 removal efficiency of 57% was obtained in Hilbert fractal reactor.

Oxygen isotope anomaly in tropospheric CO2 and implications for CO2 residence time in the atmosphere and gross primary productivity

The abundance variations of near surface atmospheric CO2 isotopologues (primarily 16O12C16O, 16O13C16O, 17O12C16O, and 18O12C16O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, and stratospheric photochemistry. Oxygen isotopes, in particular, are affected by the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO2 biogeochemical cycles, Δ17O (=ln(1 + δ17O) − 0.516 × ln(1 + δ18O)) provides an alternative constraint on the strengths of the associated cycles involving CO2. Here, we analyze Δ17O data from four places (Taipei, Taiwan; South China Sea; La Jolla, United States; Jerusalem, Israel) in the northern hemisphere (with a total of 455 measurements) and find a rather narrow range (0.326 ± 0.005‰). A conservative estimate places a lower limit of 345 ± 70 PgC year−1 on the cycling flux between the terrestrial biosphere and atmosphere and infers a residence time of CO2 of 1.9 ± 0.3 years (upper limit) in the atmosphere. A Monte Carlo simulation that takes various plant uptake scenarios into account yields a terrestrial gross primary productivity of 120 ± 30 PgC year−1 and soil invasion of 110 ± 30 PgC year−1, providing a quantitative assessment utilizing the oxygen isotope anomaly for quantifying CO2 cycling.

Supercritical carbon dioxide extraction of Calendula officinalis: Kinetic modeling and scaling up study

The extraction of marigold (Calendula officinalis) oleoresin with supercritical carbon dioxide SCCO2 was carried out in a small scale extraction vessel (2.7×10−4m3) studying different extraction pressures (14, 24 and 34MPa) and different flow rates (15, 30 and 45gmin−1) at 313K. Then, using semi-empirical engineering scaling criteria (constant solvent lineal velocity or constant solvent residence time) and the Broken and Intact Cell (BIC) model, the scaling up to larger extraction vessels (1.35×10−3m3 and 5.16×10−3m3) was theoretically investigated.According to the BIC model, by keeping constant the CO2 residence time in the different size vessels a good reproduction of the kinetic behavior should be obtained. Nevertheless, experimental results did not confirm model predictions, and in fact none of the scaling criteria studied resulted adequate in the marigold supercritical extraction scaling up. Thus, using all the experimental overall extraction curves obtained, a new specific correlation was developed between the Schmidt number (Sc), CO2 mass flow, bed geometry and the supercritical mass transfer coefficients kYA with a good fit (R2=0.9767) for scaling up the supercritical extraction of marigold.

Supercritical CO<sub>2</sub> extraction of oil and omega-3 concentrate from Sacha inchi (<em>Plukenetia volubilis</em> L.) from Antioquia, Colombia

Sacha inchi (Plukenetia volubilis L.) seeds were employed for oil extraction with supercritical CO2 at laboratory scale. The supercritical extraction was carried out at a temperature of 60 °C, pressure range of 400–500 bars and CO2 flow of 40–80 g/min. The maximum recovery was 58% in 180 min, favored by increasing the residence time of CO2 in the extraction tank. Subsequently, the process was evaluated at pilot scale reaching a maximum recovery of 60% in 105 min, with a temperature of 60 °C, pressure of 450 bars and CO2 flow of 1270 g/min. The fatty acid composition of the oil was not affected for an extraction period of 30–120 min. The Sacha inchi oil was fractionated with supercritical CO2 to obtain an omega-3 concentrate oil without finding a considerable increase in the proportion of this compound, due to the narrow range in the carbon number of fatty acids present in the oil (16–18 carbons), making it difficult for selective separation.

Scrutinizing the carbon cycle and CO2 residence time in the atmosphere

Climate scientists presume that the carbon cycle has come out of balance due to the increasing anthropogenic emissions from fossil fuel combustion and land use change. This is made responsible for the rapidly increasing atmospheric CO2 concentrations over recent years, and it is estimated that the removal of the additional emissions from the atmosphere will take a few hundred thousand years. Since this goes along with an increasing greenhouse effect and a further global warming, a better understanding of the carbon cycle is of great importance for all future climate change predictions. We have critically scrutinized this cycle and present an alternative concept, for which the uptake of CO2 by natural sinks scales proportional with the CO2 concentration. In addition, we consider temperature dependent natural emission and absorption rates, by which the paleoclimatic CO2 variations and the actual CO2 growth rate can well be explained. The anthropogenic contribution to the actual CO2 concentration is found to be 4.3%, its fraction to the CO2 increase over the Industrial Era is 15% and the average residence time 4years.

Vaccinium meridionale Swartz Supercritical CO₂ Extraction: Effect of Process Conditions and Scaling Up.

Vaccinium meridionale Swartz (Mortiño or Colombian blueberry) is one of the Vaccinium species abundantly found across the Colombian mountains, which are characterized by high contents of polyphenolic compounds (anthocyanins and flavonoids). The supercritical fluid extraction (SFE) of Vaccinium species has mainly focused on the study of V. myrtillus L. (blueberry). In this work, the SFE of Mortiño fruit from Colombia was studied in a small-scale extraction cell (273 cm3) and different extraction pressures (20 and 30 MPa) and temperatures (313 and 343 K) were investigated. Then, process scaling-up to a larger extraction cell (1350 cm3) was analyzed using well-known semi-empirical engineering approaches. The Broken and Intact Cell (BIC) model was adjusted to represent the kinetic behavior of the low-scale extraction and to simulate the large-scale conditions. Extraction yields obtained were in the range 0.1%–3.2%. Most of the Mortiño solutes are readily accessible and, thus, 92% of the extractable material was recovered in around 30 min. The constant CO2 residence time criterion produced excellent results regarding the small-scale kinetic curve according to the BIC model, and this conclusion was experimentally validated in large-scale kinetic experiments.

Cenozoic mean greenhouse gases and temperature changes with reference to the Anthropocene.

Cenozoic greenhouse gases (GHG) variations and warming periods underscore the extreme rates of current climate change, with major implications for the adaptability and survivability of terrestrial and marine habitats. Current rise rate of greenhouse gases, reaching 3.3ppm CO2 per year during March 2015-2016, is the fastest recorded since the Paleocene-Eocene Thermal Event (PETM) when carbon release to the atmosphere was about an order of magnitude less than at present. The ice core evidence of concentration of (GHG) and temperatures in the atmosphere/ocean/cryosphere system over the last 740 kyr suggests that the rate of rise in GHG over the last ~260 years, CO2 rates rising from 0.94 ppm yr-1 in 1959 (315.97 ppm) to 1.62 ppm yr-1 in 2000 (369.52 ppm) to 3.05 ppm yr-1 in 2015 (400.83 ppm), constitutes a unique spike in the history of the atmosphere. The reliance of pre-740 kyr paleoclimate estimates on multiple proxies, including benthic and plankton fossils, fossil plants, residual organic matter, major and trace elements in fossils, sediments and soils, place limits on the resolution of pre-upper Pleistocene paleoclimate estimates, rendering it likely recorded mean Cenozoic paleoclimate trends may conceal abrupt short-term climate fluctuations. However, as exemplified by the Paleocene-Eocene thermal maximum (PETM) and earlier GHG and temperature spikes associated with major volcanic and asteroid impact events, the long-term residence time of CO2 in the atmosphere extends the signatures of abrupt warming events to within detection limits of multiple paleoproxies. The mean post-1750 temperature rise rate (approximately ~0.0034°C per yr, or ~0.008°C per yr where temperature is not masked by sulfur aerosols) exceeds those of the PETM (approximately ~0.0008-0.0015°C per yr) by an order of magnitude and mean glacial termination warming rates (last glacial termination [LGT] ~ 0.00039; Eemian ~0.0004°C per yr) by near to an order of magnitude. Consistent with previous interglacial peaks an increasing likelihood of collapse of the Atlantic Meridional Ocean Circulation is threatening a severe stadial event.

A new model to estimate CO2 coal gasification kinetics based only on parent coal characterization properties

A new mathematical model is proposed for the estimation of CO2 gasification kinetics of different rank coals and ash contents. There are no previous reports on the determination of the conversion rate or even residence time of CO2 or steam gasification based on coal characterization and for a wide range of ash content. This new approach can be used to infer the residence time and other parameters required for reactor design and operation optimization of newly mined coals or coal mixtures used as feedstock.The coal micropore surface area and the alkaline content determined by the ash composition were proved to be the most significant variables influencing the gasification rate. These variables were correlated to formulate a semi-empirical expression based on the Arrhenius equation. An equation to infer residence time, independent of the kinetic model, is also presented.The new equation is important in understanding the catalytic effect of the alkaline content in the temperature range where the chemical reaction is the controlling step. It can also be used as the corresponding term of the chemical reaction in a gas–solid kinetic model when working at higher temperatures. This new approach is valid, if there is not loss of alkali and alkaline earth metals due to sublimation or melting, which results in a glassy slag structure. The proposed model has direct industrial application in simulation of gasifiers’ performance with the knowledge of only coal characterization properties.

Four decades of multiyear targets in energy policy: aspirations or credible commitments?

A look at the past 40 years of U.S. energy policy provides ample evidence of volatility, including rapidly changing budgets, moving targets, and shifting incentives. Changing policy too often is a serious criticism because systemic inertia—for example, due to the long lifetimes of capital stock and to the atmospheric residence time of CO2—implies a need for persistence in order to achieve social goals. Further, a pattern of failing to meet objectives may reduce the credibility of future targets, and thus reduce the incentives for investment and behavioral change. But changing policy has benefits as well: it allows for adaptive management, experimentation, policy learning, and assimilation of new information. Assembling data on the effectiveness, duration, and ambition of 63 energy policy initiatives with targets ≥5 years, we find: targets were met 64–77% of the time; median duration to target was 12 years; and median rate of change was 2% per year. Significant predictors of success in meeting targets are enforcement, duration, and ambition. These determinants are robust across multiple specifications and definitions of ambition and success. We find a significant decline in ambition over time. Binding targets are much more likely to be met than nonbinding ones, but discretionary clauses completely offset the effect of enforceable penalties on the likelihood of target attainment. WIREs Energy Environ 2014, 3:522–533. doi: 10.1002/wene.116This article is categorized under: Energy Policy and Planning > Economics and Policy Energy Policy and Planning > Climate and Environment