In this work, K2CO3-containing composite materials were synthesized based on a mesoporous zirconia aerogel prepared by an epoxide-assisted sol-gel method using supercritical drying in ethanol. The ...porous ZrO2 was impregnated with an aqueous solution of potassium carbonate to obtain composite materials with K2CO3 weight content ranging from 9 to 29 wt%. All the composites were tested in the process of CO2 absorption from the air with a relative humidity of 25% followed by thermal desorption at 200 °C. The samples after the CO2 absorption step were characterized by Fourier transform infrared spectroscopy and X-ray diffraction methods. Among the materials studied, the composite sorbent containing 23 wt% K2CO3 demonstrated the highest dynamic CO2 absorption capacity (4.6 wt%) in the temperature-swing absorption (TSA) cycles. The results indicate that a certain part of K2CO3 loaded into zirconia mesopores forms surface species which do not actively participate in the CO2 absorption and desorption processes. For the composite K2CO3/ZrO2 material with the optimal K2CO3 loading, CO2 absorption capacity is higher compared to the values obtained for K2CO3/γ-Al2O3 composite sorbents studied under the same conditions. Taking into account that this material demonstrates stable CO2 absorption capacity values in the consecutive TSA cycles and needs a relatively low temperature for regeneration, it should be considered for application in Direct Air Capture units.
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•A zirconia aerogel was prepared by a sol-gel method using supercritical drying.•K2CO3/ZrO2 composite materials were prepared by a dry impregnation method.•CO2 capture from ambient air was studied using K2CO3/ZrO2 composite sorbents.•The composite containing 23 wt % of K2CO3 showed the highest CO2 uptake of 4.6 wt%.•The materials after CO2 absorption were studied by XRD and ATR-FTIR methods.
To improve the stability of high temperature CO2 absorbent for sorption enhanced reforming applications yttria supported CaO were synthesized using two methods: calcination of mixed salt precursors ...and wet impregnation of yttria support. According to XRD data, CaO does not interact with the yttria matrix. However, introduction of CaO drastically changes the morphology of primary yttria particles. Increase in CaO concentration results in gradual plugging of the smaller pores and sintering of yttria support. The CO2 absorption uptake in recarbonation-decomposition cycles increases with increase in CaO content and reach 9.6 wt % at CaO content of 19.9 wt %. CaO recarbonation extent varies from 49 to 77%. CaO/Y2O3 absorbents are extremely stable under overheating and maintain their capacity in long series of decomposition-recarbonation cycles even after calcination at 1350 °C. The novel material resists moisture and retains its strength during storage in the air. According to tests, CaO/Y2O3 can be considered as a promising CO2 absorbent for fixed bed sorption enhanced hydrocarbons reforming.
Measurements of the production of forward jets from transversely polarized proton collisions at s=500 GeV conducted at the Relativistic Heavy Ion Collider (RHIC) are reported. Our measured jet cross ...section is consistent with hard scattering expectations. Our measured analyzing power for forward jet production is small and positive, and provides constraints on the Sivers functions that are related to partonic orbital angular momentum through theoretical models.
The evolution of sorptive and textural properties of CaO-based sorbents during repetitive sorption/regeneration cycles has been mathematically simulated. The proposed model takes into account the ...morphology of nascent CaO, sorbent sintering physics and CO2 sorption kinetics. The results show that the model is in good agreement with the experimental data for real sorbents and predicts the dependence of the recarbonation extent on the number and duration of the sorption/regeneration cycles well. The model obtained allows predicting the change of the textural properties of the sorbent (e.g. the values of specific surface area and mean pore size) during the sorption/regeneration cycles.
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•A new model of evolution of CaO-based sorbent properties in cycles is proposed.•Model is based on sintering physics, CO2 capture kinetics and CaO morphology.•Model predicts the CaO recarbonation extent on the number and duration of cycles well.•Model predicts the changing of CaO specific surface area and pore size during cycling.
Yttrium oxide has promising characteristics such as chemical stability and a porous structure for various high-temperature applications in catalysis and chemical engineering. The prediction of the ...structural properties of Y2O3 presents a computational challenge.
In this study, we implemented a phase-field approach to obtain a precise description of the Y2O3 sintering process over a wide range of temperatures. In the phase-field method, the microstructure is described by a system of continuous variables that model Y2O3 crystallites, where the microstructure interfaces have a finite width over which the material transfers.
The experiments on stepwise sintering process were carried out and the obtained data on the textural and morphological properties of Y2O3 particles were used to calibrate and validate the numerical model. The evolution of the specific surface area and pore volume for the pores ranging from 3 to 70 nm and the rate of growth of Y2O3 crystallites during sintering of Y2O3 grains were effectively predicted. The obtained model indicates that a stepwise increase in the calcination temperature from 600 to 900 and 1200 °C decreases the surface area of the materials from 54 to 15 and 5 m2/g, respectively.
This study can be used to predict the textural properties of yttrium oxide during the sintering of porous ceramics and for the exploitation of catalyst systems.
•K2CO3/Y2O3 sorbent is suggested for direct CO2 capture from air.•CO2 absorption capacity is about 28mg/g for TSA cycles with Treg<300°C.•Absorption uptake decreases drastically down to 10mg/g in TSA ...cycles with Treg⩾300°C.•Phase composition and texture of the sorbent differ before and after TSA cycling.
Carbonate–bicarbonate looping was tested for direct CO2 capture from air using a composite sorbent K2CO3/Y2O3. The phase composition, the porous structure and the texture of the composite sorbent were characterized by means of X-ray diffraction, mercury intrusion and scanning electron microscopy methods. The thermal properties of the sorbent were additionally studied by X-ray diffraction in situ and thermogravimetry methods. CO2 absorption from air and desorption experiments were performed in a continuous-flow system. The effect of regeneration temperature on CO2 uptake was investigated. It was shown that CO2 absorption uptake from air is about 28mg (CO2)/g in temperature swing absorption cycles within regeneration temperature range of 150–250°C. However, the increase of the regeneration temperature up to 300°C results in gradual decrease of the absorption uptake down to 10mg (CO2)/g. The XRD pattern of the cycled sample contains a set of reflections that cannot be assigned to any known potassium- or yttrium-containing crystalline phase. The new phase, which is thermally stable up to 460°C, accumulates potassium ions and is, probably, responsible for the sorbent capacity decay.
The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high ...temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong vortical structure that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity. However, no experimental indications of fluid vorticity in heavy ion collisions have yet been found. Since vorticity represents a local rotational structure of the fluid, spin-orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark-gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions. (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. These data provide experimental access to the vortical structure of the nearly ideal liquid created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.
Global polarization of Λ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at √SNN = 200 GeV, with no significant difference between Λ and Λ¯. These new ...results reveal the collision energy dependence of the global polarization together with the results previously observed √SNN = 7.7 – 62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy.
The Λ (Λ¯) hyperon polarization along the beam direction has been measured in Au+Au collisions at sNN=200 GeV, for the first time in heavy-ion collisions. The polarization dependence on the ...hyperons' emission angle relative to the elliptic flow plane exhibits a second harmonic sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction, expected due to elliptic flow. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum (pT) dependence at pT greater than 1 GeV/c. The magnitude of the signal is about 5 times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, the kinematic vorticity calculations in the blast-wave model tuned to reproduce particle spectra, elliptic flow, and the azimuthal dependence of the Gaussian source radii measured with the Hanbury Brown–Twiss intensity interferometry technique reproduce well the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the polarization signal.
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•A new model for the evolution of CaO-based sorbent properties in sorption/regeneration cycles is proposed.•The model takes into account the morphology of a sorbent and its surface ...sintering.•The model predicts the recarbonation extent of sorbents during initial cycles.•The contributions of volume and surface sintering mechanisms are estimated.
A new model describing the evolution of sorptive and textural properties of a CaO-based sorbent during repetitive sorption/regeneration cycles has been developed. The proposed model considers the morphology of nascent monodisperse CaO and the sintering of sorbent grains upon the assumption of the surface mass-transfer mechanism. In addition, the obtained model allows predicting the change in the textural properties of the sorbent (e.g. the values of specific surface area and mean pore size) during the sorption/regeneration cycles. The obtained results show that the model of surface sintering is well applicable to the description of the decay of the sorbent sorption capacity in initial several cycles, while the previously developed model of the volume sintering provides good prediction of this decay only after several cycles. It can be assumed that during the cycling, the sintering of the sorbent switches from the surface to the volume regime.
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