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991.
Boron is a necessary element for plants that are generally found in the ground and seawater, but it can also be poisonous in large doses. Contamination of water with boric acid or borate ions is a global concern. Due to the absence of the chemical charge that boron possesses, its removal is often difficult. To investigate boron's adsorption characteristics, kinetic, isotherm, and isothermal studies were performed. The adsorption of boron was shown to be a pH-dependent mechanism, with the best results at around pH 9.0. About 47% of the boron from a solution of 50 mg L−1 was removed using 5 g titanium dioxide in 30 min. It was also demonstrated that boron adsorption kinetics increased with temperature, which is best described by the pseudo-second-order kinetic model (R2 > 0.98) and also fits well with Elovich and pseudo-first-order models (R2 > 0.94) at pH 9.0. Equilibrium was reached in about 40 min for all the samples. The film boundary layer diffusion step limits the rate. Experimental results correspond well to the Freundlich isotherm (R2 = 0.95–0.99). Langmuir and Temkin's isotherms also fitted reasonably well (R2 = 0.94–0.98). The Freundlich and Langmuir constants indicate favourable adsorption. The Gibbs free energy (ΔG) values increased negatively (from −11.47 to −15.63 kJ mol−1) with increasing temperature, signifying a feasible and spontaneous process. The enthalpy change (ΔH) value of about 30.35 kJ mol−1 indicated endothermic physical adsorption. The results indicate that titanium dioxide is an excellent and safe adsorbent for the removal of boron from water. 相似文献
992.
Yarong Du Tianxiang Guo Yuhan Geng Runan Zhang Lingfeng Kong Zeng Fan Huining Xiao 《加拿大化工杂志》2023,101(4):1772-1791
The purpose of this work was to investigate the thermodynamic characteristics of carbon dioxide (CO2) adsorption on a promising nitrogen-doped biochar at constant temperature and isopiestic pressure. The biochar was prepared as a CO2 adsorbent based on catalytic pyrolysis of pristine coconut shells using urea as the nitrogen source and moderate temperature ionic liquid as a catalyst. The results showed that CO2 adsorption on the biochar was a spontaneous, dominantly physical, exothermic, and entropy decrement process that could be well described by the slip model and the dual-site Langmuir model. Those thermodynamic parameters, including interface potential, exhibited a series of interesting tendencies with the changes in adsorption temperature and pressure. Under the conditions of 273 K and 100 kPa, the adsorption capacity and the interface potential were 4.6 mmol/g and −16.7 J/g, respectively. And the site energy ranged from 2.57 to 5.13 kJ/mol in the test conditions, which became narrow with increasing temperature. The temperature exhibited positive effects on interface potential, enthalpy change, entropy change, enthalpy change, internal energy change but negative effects on adsorption capacity, Gibbs free energy change, and Helmholtz free energy change. Interestingly, the pressure exhibited the opposite effect trends. The peak pressure with maximum temperature effect at a given temperature and the peak temperature with maximum pressure effect at a given pressure were found to exist for some thermodynamic parameters. These exhibited a different but significantly beneficial perspective to understand the mass and energy transfer during CO2 adsorption on the biochar at constant temperature and isopiestic pressure, which have rarely been reported before. 相似文献
993.
Yuki Nakashima You Zhou Keisuke Tanabe Souhei Arima Kiyoshi Hirao Tatsuki Ohji Norimitsu Murayama Manabu Fukushima 《Journal of the American Ceramic Society》2023,106(2):1139-1148
Silicon nitride (Si3N4) was prepared from silicon by a sintered reaction-bonded silicon nitride method using yttria and magnesia as sintering additives. Post-sintering (PS) of nitrided compacts was carried out at 1850°C under a nitrogen pressure of 1 MPa. Effect of PS time on microstructure and dielectric breakdown strength (DBS) of the prepared Si3N4 ceramics was evaluated. The DBS was measured using specimens with four different thicknesses (0.30, 0.20, 0.10, and 0.05 mm) in order to examine the thickness dependence. The porosity of the sintered Si3N4 decreased by prolonging the PS time, and the full density could be achieved at the PS time of over 6 h. After full densification, rod-like β-Si3N4 grains grew up, and their maximum grain size increased from 45.1 to 154.7 μm by prolonging the PS time from 6 to 48 h. The DBS of the thick Si3N4 substrates (0.30 mm) showed little variation from 35.4 to 47.0 kV/mm, regardless of the PS time. On the other hand, that of the thin ones (0.05 mm) dramatically decreased from 99.5 to 9.8 kV/mm with increased the PS time from 6 to 48 h. Because the DBS sharply decreased at the thin substrate sintered for longer time in which some large-elongated grains might span the substrate thickness-wise throughout, it was inferred that the interface between β-Si3N4 grains and grain boundary phase/intergranular glassy films might be a path of the dielectric breakdown. 相似文献
994.
Hydrate–liquid–vapour (HLV) equilibrium of aqueous clathrates formed from gas mixtures can be complex compared to hydrates formed with single guests. Typically, pressure and temperature are controlled to obtain these data, but for multicomponent systems, it is necessary to control/report more intensive variables, namely, composition. Metastability, manifested as impractically long experimental times, has been reported to be a challenge with some multicomponent systems. We present HLV equilibrium conditions of two ternary gas mixtures: methane + ethane + propane (90:7:3 molar ratio) and methane + propane + carbon dioxide (55:5:40 molar ratio). Conditions varied in the temperature range of 275–285 K and the pressure range of 1.24–4.75 MPa. Experimental standard uncertainties were on average 0.10 K and 0.005 MPa for methane + ethane + propane and 0.19 K and 0.005 MPa for methane + propane + carbon dioxide. Our technique allowed us to bypass the limitations reported in the literature and provided fast, reproducible HLV equilibria for gas-dominated systems. 相似文献
995.
Imane Euldji Aicha Belghait Cherif Si-Moussa Othmane Benkortbi Abdeltif Amrane 《American Institute of Chemical Engineers》2023,69(8):e18115
The purpose of this work was to compare the performance of 7 meta-heuristics algorithms namely: Dragonfly (DA), Ant Lion (ALO), Grey Wolf (GWO), Artificial Bee Colony (ABC), Particle Swarm (PSO), Whale (WAO), and a hybrid Particle Swarm with Grey Wolf (HPSOGWO) optimizers in terms of fine-tuning hyper-parameters of a hybrid quantitative structure property relationships (QSPR)-support vector regression (SVR) for the prediction of molar fraction solubilities of drug compounds in supercritical carbon dioxide (SC-CO2). A dataset of 168 drug compounds, 13 inputs, and 4490 experimental data points was used to achieve the goal. All 7 models were statistically and graphically approved while the HPSOGWO-SVR was found to over-perform with an average absolute relative deviation (AARD) of 0.706% and an AIC of −14,434,249. The model was subjected to an external test (validation) using 160 experimental data points that were not used in the training and the test set. The overall results proved that the obtained model has good predictivity ability and robustness. 相似文献
996.
Valentina Angelici Avincola Elizabeth Opila 《Journal of the American Ceramic Society》2023,106(6):3704-3719
The oxidation behavior of SiC Sylramic fibers coated with chemically vapor deposited Si-doped boron nitride (BN) was investigated at temperatures between 800 and 1200°C in dry and wet O2 atmospheres. Thermogravimetric analysis was used to study the oxidation kinetics of the fiber and the influence of the BN layer and the environment. The morphology and composition of the thermally grown oxide scale was determined posttest by scanning electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry. This study gives new insights into the synergistic effects of BN and water vapor on the oxidation behavior SiC Sylramic fibers. The vulnerability of the BN fiber interphase and the behavior of the fiber under conditions relevant to high-temperature turbine applications are discussed. 相似文献
997.
Spray towers are widely used for controlling air pollution by gases such as SO2, CO2, NOx, and HCl. Results of sulfur dioxide absorption in a spray tower using solutions of 1 g L–1 and 2 g L–1 of hydrogen peroxide are reported. For comparison, a water and sodium hydroxide solution was also used for SO2 abatement. The results indicate that H2O2 may be an important alternative for SO2 removal in spray towers. A set of experimental removal efficiency data was obtained as a function of gas and liquid flow rates. Volumetric mass transfer coefficients (kga) were calculated and an experimental relationship among kga, gas, and liquid flow rates was proposed. As a final experiment, an oxidation process assisted by UV radiation using a 1 g L–1 solution of H2O2 was carried out to speed up the SO2 removal rate. The results obtained in this condition are similar to those achieved with a solution of 2 g L–1 H2O2. 相似文献
998.
Solubility information for CO2 in different ionic liquids, ILs, in part can potentially be used to select a specific IL for the separation of CO2 from hydrocarbon fluids. Unfortunately, not all CO2–IL systems have been experimentally described at similar temperatures and pressures; therefore, a direct comparison of performance by process simulation is not always possible. In the extreme cases, the design of a CO2 separation process may require predicting the CO2–IL equilibria for which there are no available solubility data. To address the need for this information, a semi‐empirical correlation was developed to estimate the dissolution of CO2 in CO2–IL solvent systems. The theoretical COSMO–RS calculation method was used to calculate the chemical potential of CO2 in a wide variety of ILs and the Soave–Redlich–Kwong equation was used to calculate the fugacity coefficient of the CO2 vapour phase. The model was correlated with available literature data, yielding an average error of AAR = 23% and small bias. © 2012 Canadian Society for Chemical Engineering 相似文献
999.
A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fibre membranes was developed considering the permeate pressure build‐up inside the fibre bore and cross flow pattern with respect to the membrane skin. The solution technique provides reliable examination of pressure and concentration profiles along the permeator length (both residue/permeate streams) with minimal effort. The proposed simulation model and scheme were validated with experimental data of gas separation from literature. The model and solution technique were applied to investigate dynamic performance of several membrane module configurations for methane recovery from biogas (landfill gas or digester gas), considering biogas as a mixture of CO2, N2 and CH4. Recycle ratio plays a crucial role, and optimum recycle ratio vital for the retentate recycle to permeate and permeate recycle to feed operation was found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane‐selective or nitrogen‐selective membranes was calculated. © 2012 Canadian Society for Chemical Engineering 相似文献
1000.