Weiyang Fei

Borate-Catalyzed Carbon Dioxide Hydration via the Carbonic Anhydrase Mechanism

The hydration of CO(2) plays a critical role in carbon capture and geoengineering technologies currently under development to mitigate anthropogenic global warming and in environmental processes such as ocean acidification. Here we reveal that borate catalyzes the conversion of CO(2) to HCO(3)(-) via the same fundamental mechanism as the enzyme carbonic anhydrase, which is responsible for CO(2) hydration in the human body. In this mechanism the tetrahydroxyborate ion, B(OH)(4)(-), is the active form of boron that undergoes direct reaction with CO(2). In addition to being able to accelerate CO(2) hydration in alkaline solvents used for carbon capture, we hypothesize that this mechanism controls CO(2) uptake by certain saline bodies of water, such as Mono Lake (California), where previously inexplicable influx rates of inorganic carbon have created unique chemistry. The new understanding of CO(2) hydration provided here should lead to improved models for the carbon cycle in highly saline bodies of water and to advances in carbon capture and geoengineering technology.

Magnetic titanium dioxide based nanomaterials: synthesis, characteristics, and photocatalytic application in pollutant degradation

Magnetic titanium dioxide based nanocomposites have been gaining increasingly high attention in sustainable environmental protection fields; these materials can integrate the advantages of magnetic recovery and the superior photocatalysis performance of titanium dioxide. However, direct contact between crystalline photoactive titanium dioxide and magnetic iron oxide gives rise to lower photoreactivity than pure titanium dioxide for the pollutant degradation. To overcome the challenge, a number of researches have been done and significant process has been made in this area in recent years. This review primarily focuses on the properties of magnetic particles, structural models, preparation methods and techniques to improve photocatalytic performance of magnetic titanium dioxide based photocatalysts, and aims to provide a systematic overview of the current knowledge of these subjects. Notably, the recently discovered technique coupling graphene into magnetic iron oxide–titanium dioxide system is discussed, which opens a promising future for preparation of magnetic semiconductors with excellent properties. Current challenges and prospects are also proposed at the end of this article. In particular, the examination of corresponding deactivation or regeneration mechanisms should be investigated further, from the point of view of practical applications.

Physical modelling and numerical simulation of velocity fields in rotating disc contactor via CFD simulation and LDV measurement

Velocity fields in a rotating disc contactor (RDC) with single-phase flow have been measured using a Laser Doppler Velocimeter (LDV) and simulated with computational fluid dynamics software. Simulated velocity profiles are in fair agreement with the experimental ones. Both experimental and calculated results show that there exist vortices between adjacent rotating discs and between adjacent stator rings in the flow system. The vortex between stator rings enhances mixing and mass transfer in a compartment, while the vortex between discs is the main factor causing axial mixing. In order to suppress the axial mixing thus enhancing the mass transfer efficiency in the extraction column, a modified rotating disc contactor (MRDC) is proposed. Simulated velocity profiles in the new extraction column have shown that the axial mixing between the discs has been effectively eliminated.

Effects of surface-active agents on mass transfer of a solute into single buoyancy driven drops in solvent extraction systems

Numerical simulation was made of transient mass transfer to a surfactant contaminated buoyancy-driven drop controlled by appreciable resistance in both liquid phases. For this purpose, the momentum equations were formulated and solved in a boundary-fitted orthogonal coordinate system. On the basis of resolved hydrodynamics of the contaminated drop, the transient mass transfer was formulated and solved in the same coordinate system. In order to check the applicability of the numerical scheme, single drop extraction experiments were conducted in a totally closed droplet file column with the terminal effect efficiently eliminated. The MIBK-acetic acid-water system was used with small quantities of SDS (sodium dodecyl sulphate), Triton X-100, or Tween 80 introduced into the continuous phase. For these experimental cases, the flow field and the drag coefficient of a contaminated drop were simulated first. The numerical prediction of the drag coefficient is found in good agreement with the corresponding experimental data. It illustrates that the behavior of a drop approaches that of a rigid sphere and that about 100 times higher bulk concentration of SDS than that of Triton X-100 is required for the same extent contamination of a MIBK drop of the same size. Then the information of the flow field of a contaminated MIBK drop was used in simulating the transient mass transfer of solute into the drop. The resulted extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. Both numerical results and experimental data show that overall mass transfer coefficient of a heavily contaminated drop is only about one third of that in the pure system. This can be explained well by the distribution of the local Sherwood number, which drops down abruptly along the rear stagnant surface. Also the interfacial resistance of adsorbed surfactant was incorporated in the mass transfer model and then estimated by the least square fitting the simulation with data. The numerical results also show that Tween 80 presents obvious interfacial resistance on the acetic acid diffusing across the interface, whereas SDS and Triton X-100 show no interfacial resistance. It is suggested that the numerical simulation can be resorted in some solvent extraction systems containing surfactants to conduct numerical experiments and parametric study

Large Eddy Simulations of Flow Instabilities in a Stirred Tank Generated by a Rushton Turbine

Abstract The aim of this work is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation (LES). The sliding mesh method was used for the coupling between the rotating and the stationary frame of references. The calculations were carried out on the “Shengcao-21C” supercomputer using a computational fluid dynamics (CFD) code CFX5. The flow fields predicted by the LES simulation and the simulation using standard k-ɛ model were compared to the results from particle image velocimetry (PIV) measurements. It is shown that the CFD simulations using the LES approach and the standard k-ɛ model agree well with the PIV measurements. Fluctuations of the radial and axial velocity are predicted at different frequencies by the LES simulation. Velocity fluctuations of high frequencies are seen in the impeller region, while low frequencies velocity fluctuations are observed in the bulk flow. A low frequency velocity fluctuation with a nondimensional frequency of 0.027Hz is predicted by the LES simulation, which agrees with experimental investigations in the literature. Flow circulation patterns predicted by the LES simulation are asymmetric, stochastic and complex, spanning a large portion of the tanks and varying with time, while circulation patterns calculated by the simulation using the standard k-ɛ model are symmetric. The results of the present work give better understanding to the flow instabilities in the mechanically agitated tank. However, further analysis of the LES calculated velocity series by means of fast Fourier transform (FFT) and/or spectra analysis are recommended in future work in order to gain more knowledge of the complicated flow phenomena.

A Study on Stoichiometry of Complexes of Tributyl Phosphate and Methyl Isobutyl Ketone with Lithium in the Presence of FeCl3

Abstract To study the characteristic of liquid-liquid extraction equilibrium of lithium from brine sources, the complexes formed from tributyl phosphate (TBP) and methyl isobutyl ketone (MIBK) with lithium were investigated using FeCl 3 as coextracting agent. Liquid-liquid extraction reaction mechanisms were proposed and the stoichiometry of tetrachloroferrate(III) complex with lithium was obtained by regressing the experimental data. It is found that the stoichiometry of tetrachloroferrate(III) to lithium in the complex is 1 : U1 with either TBP or MIBK as extractant in kerosene. The stoichiometry of the complex of TBP with Li was 1 : U1 and that of MIBK with Li was 2 : U1. The formed complexes of TBP and MIBK with lithium are determined to be LiFeCl 4 ·TBP and LiFeCl 4 2MIBK, respectively, according to the rule of neutralization.

CO2 Absorption Behavior with a Novel Random Packing: Super Mini Ring

Abstract For the purpose of capturing CO2 from flue gas the absorption of CO2 into an aqueous solution of monoethanolamine was measured by using a column packed with a novel packing, Super Mini Ring (SMR). The SMR gave a higher absorption performance relative to pall ring packing due to a larger effective surface area and also reduced the frictional pressure gradient. The absorption mechanism was observed to be mainly gas phase controlling. It was concluded that for the treatment of flue gas the SMR packing could reduce the height of the absorption column by 20% relative to a pall ring packed column.

Liquid Film Characteristics on Surface of Structured Packing

Structured packing is a good candidate for CO2 capture process because of its higher mass transfer efficiency and lower pressure drop. Now, the challenging problem of CO2 capture and storage demands more and more efficiency equipment. The aim of the present study is to investigate the liquid film characteristics under countercurrent gas phase and throw some insight into the enhancing mechanism of mass transfer performance in structuredpacking. A high speed digital camera, non-intrusive measurement technique, was used. Water and air were working fluids. Experiments were carried out for different gas/liquid flow rates and different inclination angles. Thetime-average and instantaneous film widths for each set of flow parameters were calculated. It is shown that the effects of gas phase could be neglected for lower flow rate, and then, become more pronounced at higher flow rate. According to instantaneous film width, three different stages can be distinguished. One is the constant width of liquid film. The second is the slight decrease of film width and the smooth surface. This kind of character will lead toless interfacial area and deteriorate the packing mass transfer performance. For the third stage, the variation of filmwidth shows clearly chaotic behavior. The prediction model was also developed in present work. The predicted and experimental results are in good agreement.

TiO(OH) 2 – highly effective catalysts for optimizing CO 2 desorption kinetics reducing CO 2 capture cost: A new pathway

The objective is to find a new pathway for significant reduction in CO2 capture energy consumption. Specifically, nanoporous TiO(OH)2 was used to realize the objective, which was desired as a catalyst to significantly accelerate the decomposition of aqueous NaHCO3, essentially CO2 desorption – the key step of Na2CO3/NaHCO3 based CO2 capture technologies from overall CO2 energy consumption perspective. Effects of several important factors on TiO(OH)2-catalyzed NaHCO3 decomposition were investigated. The quantity of CO2 generated from 0.238 mol/L NaHCO3 at 65 °C with catalyst is ~800% of that generated without the presence of catalyst. When a 12 W vacuum pump was used for carrying the generated CO2 out of reactor, the total amount of CO2 released was improved by ~2,500% under the given experimental conditions. No significant decrease in the catalytic effect of TiO(OH)2 was observed after five cyclic CO2 activated tests. In addition, characterizations with in-situ Fourier transform infrared spectroscopy, thermal gravity analysis and Brunauer-Emmett-Teller of TiO(OH)2 indicate that TiO(OH)2 is quite stable. The discovery in this research could inspire scientists’ interests in starting to focus on a new pathway instead of making huge effort or investment in designing high-capacity but expensive CO2 sorbent for developing practical or cost-effective CO2 technologies.

Separation characteristics of boron isotopes in continuous annular chromatography

A well designed continuous annular chromatograph (CAC) column was set to study the enrichment of Boron isotopes. The column is 820 mm high and consists of a rotational annulus with an outer diameter of 246 mm and a width of 15 mm. The weak basic resin (Diaion WA21J), the boric acid and water were used as the absorbent, the feed and the eluent respectively. The effects of CAC rotating speed, concentration of boric acid and flow ratio of eluent to feed on the enrichment of 10B were investigated. The concentration of boron isotope was determined by a Thermal Elemental X7 ICP-MS (Thermo Electron Co., USA). It is shown from the experimental results that 10B and 11B can be separated effectively by this CAC column. By fitting the experimental elution profiles based on reliable mathematic models and software the mass transfer coefficient k and adsorption equilibrium constant K values of 10B and 11B in CAC column were estimated. It is clear from this study that the CAC has practical continuous operational capabilities in comparison with fixed batch chromatography and is an effective technology for separating boron isotopes.