Kinetics of CO₂ Absorption in Concentrated K₂CO₃/PZ Mixture Using a Wetted-Wall Column

Using a K₂CO₃/piperazine (PZ) mixture as a typical phase-change absorbent has promising applicability for carbon dioxide (CO₂) capture in coal-fired power plants that would contribute to low energy consumption for solvent regeneration. In this study, the reaction rate of CO₂ with a concentrated K₂CO₃/PZ mixture was measured in a wetted-wall column. At a CO₂ loading close to saturation absorption, correlative physical parameters were calculated. The effects of operating conditions, including gas flow rate, slurry flow rate, PZ concentration, CO₂ loading, K₂CO₃ mass fraction, and temperature, on the absorption rate of CO₂ were investigated. The results showed that the absorption rate was sensitive to the effects of the gas flow rate and CO₂ loading. The PZ concentration and K₂CO₃ mass fraction also substantially influenced the CO₂ absorption rate. However, minor changes in the CO₂ absorption rate were observed when the slurry flow rate and temperature were increased. On the basis of a pseudo-first-order model, the absorption rate determined in this study was found to be controlled by mass transfer in both the gas film and the liquid film. The results can serve as a useful reference for designing CO₂ removal systems using K₂CO₃/PZ mixtures

Improving the Performance of Hybrid Photoanodes for Water Splitting by Photodeposition of Iridium Oxide Nanoparticles

The efficient coupling between light-harvesting absorbers and cocatalysts allowing for chemical transformation along multielectron pathways is of fundamental importance for the development of solar-fuel-producing photochemical systems. Herein we demonstrate that IrO_<i>x</i> nanoparticles acting as efficient cocatalyst for water oxidation can be photoelectrochemically deposited from hexahydroxoiridate solutions into the porous structure of TiO₂-PH (polyheptazine, “graphitic carbon nitride”) hybrid photoanodes for water photooxidation. As compared to photoanodes loaded with IrO_<i>x</i> by the conventional colloidal deposition method, hybrid photoanodes with photodeposited IrO_<i>x</i> exhibit significantly enhanced dioxygen evolution under long-term irradiation with visible light (λ > 420 nm). Photocurrent transient measurements show that the undesired accumulation of holes in the TiO₂-PH absorber is significantly reduced due to improved coupling between the absorber and the photodeposited cocatalyst. This decreases significantly the recombination rate, leads to more efficient dioxygen evolution, and improves the stability against photocorrosion. Photocurrent measurements under potentiodynamic conditions revealed that at low bias potentials (<0.6 V vs RHE) the photoconversion efficiency of hybrid photoanodes is limited by fast primary back electron transfer and by reduction of Ir­(IV) to Ir­(III). The performance and stability of hybrid photoanodes are also found to be drastically influenced by the solution chemistry (electrolyte composition and pH). The highest photoconversion efficiency was observed in sulfate-based electrolytes at pH ∼6

Kinetics, Thermodynamics, and Mechanism of a Novel Biphasic Solvent for CO₂ Capture from Flue Gas

The main issue related to the deployment of the amine-based absorption process for CO₂ capture from flue gas is its intensive energy penalty. Therefore, this study screened a novel biphasic solvent, comprising a primary amine e.g., triethylenetetramine (TETA) and a tertiary amine e.g., <i>N</i>,<i>N</i>-dimethylcyclohexylamine (DMCA), to reduce the energy consumption. The TETA-DMCA blend exhibited high cyclic capacity of CO₂ absorption, favorable phase separation behavior, and low regeneration heat. Kinetic analysis showed that the gas- and liquid-side mass transfer resistances were comparable in the lean solution of TETA-DMCA at 40 °C, whereas the liquid-side mass transfer resistance became dominant in the rich solution. The rate of CO₂ absorption into TETA-DMCA (4 M, 1:3) solution was comparable to 5 M benchmark monoethanolamine (MEA) solution. Based on a preliminary estimation, the regeneration heat with TETA-DMCA could be reduced by approximately 40% compared with that of MEA. ¹³C NMR analysis revealed that the CO₂ absorption into TETA-DMCA was initiated by the reaction between CO₂ and TETA via the zwitterion mechanism, and DMCA served as a CO₂ sinker to regenerate TETA, resulting in the transfer of DMCA from the upper to lower phase. The proposed TETA-DMCA solvent may be a suitable candidate for CO₂ capture

The TM segments and topology of PeNHX3.

<p>A. The TM helices were analyzed with FFAS03, FUGUE, HMMTOP, and TMHMM. The TM helix numbers are marked at the corresponding regions. The TM boundaries for structure modeling are highlighted in gray. B. The TM topology of PeNHX3. Amino acid residues are colored based on the hydrophobicity scale of Kessel and Ben-Tal (Schushan et al., 2010).</p

Comparison of the four conserved residues in the TM4-TM11 assembly regions of PeNHX3 and EcNhaA.

<p>The cytoplasmic side is at the top and TM12 was omitted for clarity in all panels. The Cα atoms of the four conserved titratable residues in the TM4-TM11 assembly region are shown as spheres. A. The predicated structure of PeNHX3 (light green) is aligned to the crystal structure of EcNhaA (gray) (Hunte et al., 2005). The center of the TM4-TM11 assembly and flanking region is marked by a square. B and C. The marked regions of EcNhaA and PeNHX3.</p

Enabling visible-light water photooxidation by coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids: quantum chemical modeling and photoelectrochemical performance

<div><p>Coordinative incorporation of Co(II/III) cocatalytic sites into organic–inorganic hybrids of TiO₂ and “polyheptazine” (PH, poly(aminoimino)heptazine, melon, or “graphitic carbon nitride”) has been investigated both by quantum chemical calculations and experimental techniques. Specifically, density-functional theory (DFT) calculations (PBE/def2-TZVPP) suggest that Co(II/III) and Zn(II) ions adsorb in nanocavities at the surface of the hybrid PH–TiO₂ cluster, a prediction which can be further confirmed experimentally by ¹⁵N nuclear magnetic resonance in the case of the Zn complex. The absorption spectra of the complexes were characterized by time-dependent DFT calculations, suggesting a change of color upon Co ion binding which can in fact be observed with the naked eye. Hybrid TiO₂–PH photoelectrodes were impregnated with Co(II) ions from aqueous cobalt nitrate solutions. Optical absorption data suggest that Co(II) ions are predominantly present as single ions coordinated within the nitrogen cavities of TiO₂–PH, and any undesired blocking of light absorption is negligible. The cobalt-induced cocatalytic sites can efficiently couple to the holes photogenerated by visible light in TiO₂–PH, leading to complete oxidation of water to dioxygen. Our results indicate that coordinative incorporation of metal ions into well-designed surface sites in the light absorber is sufficient to drive complex multielectron transformations in artificial photosynthetic systems.</p></div

Functional analysis of the conserved residues in the TM4-TM11 assembly region of PeNHX3 (pH profile).

<p>NaCl concentration was kept at 300<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104147#pone-0104147-g006" target="_blank">Figure 6</a>. Asterisks indicate significant difference (P≤0.05; <i>t</i> test).</p

Schematic diagram of the yeast expression constructs for the domain-switch analysis.

<p>(A) The CDS of AtNHX1and PeNHX3, and the C-terminal domain of PeNHX3. (B) The constructs of AtNHX1-PeNHX3-C537 and AtNHX1-PeNHX3-C399. Construct diagrams are not drawn to scale.</p

Zero-Emission Cement Plants with Advanced Amine-Based CO₂ Capture

Decarbonization of the cement sector is essentially required to achieve carbon neutrality to combat climate change. Amine-based CO2 capture is a leading and practical technology to deeply remove CO2 from the cement industry, owing to its high retrofittability to existing cement plants and extensive engineering experience in industrial flue gas decarbonization. While research efforts have been made to achieve low-carbon cement with 90% CO2 removal, a net-zero-emission cement plant that will be required for a carbon neutrality society has not yet been investigated. The present study proposed an advanced amine-based CO2 capture system integrated with a cement plant to achieve net-zero CO2 emission by pushing the CO2 capture efficiency to 99.7%. Monoethanomaine (MEA) and piperazine/2-amino-2-methyl-1-propanol (PZ-AMP) amine systems, which are considered to be the first- and second-generation capture agents, respectively, were detailed investigated to deeply decarbonize the cement plant. Compared to MEA, the advanced PZ-AMP system exhibited excellent energy performance with a regeneration duty of ∼2.6 GJ/tonne CO2 at 99.7% capture, 39% lower than the MEA process. This enabled a low CO2 avoided cost of $72.0/tonne CO2, which was 18process and even 16.2analysis revealed that the zero-emission capture cost of the PZ-AMP system would be further reduced to below$56/tonne CO2 at a $4/GJ steam production cost, indicating its economic competitiveness among various CO2 capture technologies to achieve a zero-emission cement plant

PDEM-based stochastic analysis of a train-track-bridge system using dimension-reduced simulations of turbulent winds and track irregularities

Winds and track irregularities are inherently random in nature, but most of previous work did not fully consider this randomicity in computation of the dynamic response of train-track-bridge system. This study aims to develop an effective framework for stochastic analysis of the wind-train-track-bridge system based on the probability density evolution method. A dimension-reduced simulation scheme is applied since the involved system has high-dimensional random variables. Therefore, the representative samples of turbulent winds and track irregularities can be well expressed with only two random variables. In numerical examples, the accuracy of the framework is verified, and the influences of the mean wind velocity on the random vibration characteristics of the system are investigated. The results show that the dispersion of the lateral displacement of the bridge is larger than the vertical displacement, but both the vertical and lateral accelerations of the bridge have larger dispersions. The existence of lateral wind loads can reduce the dispersion of the lateral wheel–rail interaction forces of the wheel in the leeward direction. Considering the confidence levels of 75%, 85% and 95%, the train can run safely over the bridge in the wind velocity range of 0–25 m/s.</p