Application of the combined CFD and swarm intelligence for optimization of baffles number in a mixer-settler

Process optimization in a mixer-settler is of great importance. Optimization algorithm of particle swarm optimization is one of the evolutionary algorithms to solve optimization problem which is used in many fields. In this study, the optimal condition is calculated in finite volume method in terms of the number of baffles, inlet velocity of fluid, and impeller speed in a mixer-settler with a specific dimension that can be extended to industrial dimensions using the PSO algorithm and the numerical solution of Navier-Stokes equations and k-ε standard.     

Influence of the Presence of CO2 in the Feed of an Indirect Heating TSA Process for VOC Removal

This work deals with an experimental study of an indirect temperature swing adsorption process for VOC removal from air or for gas purification. A 1 m long and 70 mm diameter column with an internal heat exchanger has been filled with Ambersorb 600 carbonaceous adsorbent. This column is equipped with sensors to measure temperature at several points inside the bed, as well as the inlet and outlet gas concentration, pressure, temperature and mass flow. In a first step, CO₂ or ethane/dry nitrogen mixtures were used to simulate a single VOC in air, with different concentrations (350 ppm, 1% and 10%). As a first results very effective gas purification was obtained and an advantage of this process is the high pollutant concentration during the regeneration phase. Experiments were performed with various ethane/CO₂ mixtures. The influence of the presence of CO₂ on the ethane concentration breakthrough curves and on the ethane concentration during regeneration is reported. The IAS theory was used, as a first approach, to predict the adsorbed pollutants amount. Relatively good prediction is obtained with a maximum error in the order of 10%. An energy balance study is reported as well.     

Power consumption and gas—liquid dispersion in turbulently agitated vessels with vertical dual-array tubular coil baffles

In this work vertical dual-array tubular coil baffles arranged in groups of four, six or eight were investigated and the results compared with those from four planar baffles. The baffle coefficients for a single phase, along with the power consumption and gas hold-up in the gas-liquid phase of a system with the various baffle configurations for single and triple Rushton turbines are presented. Measurements were carried out using a dish-bottom vessel with an inner diameter of 0.29 m. Two ambient-temperature media were used as the liquid phase, namely, tap water and a 0.5 M Na₂SO₄ aqueous solution, representing coalescent and non-coalescent liquids, respectively. The results of the single-phase experiment revealed the coil baffles to have lower power numbers; when the baffle coefficient is ≥ 0.12, the mixing efficiency is the same as that for four planar baffles. The power consumption experiment using the gas-liquid phase showed that installing coil baffles prevented a large power draw in all types of media. In addition, the power draw characteristics are affected by the media. It was found that, because of the low K_B number, flooding occurred more readily with coil baffles than with planar baffles. Gas-liquid dispersion experiments in an air-water system indicated that, at a low gas flow-rate, the gas hold-up values of the coil baffles were almost 60 % higher than those of the conventional four baffles. However, this phenomenon was not observed in the Na₂SO₄ aqueous solution because of the existence of dead zones in viscous liquids. Finally, all the data from the power consumption and gas hold-up experiments on the gas-liquid phase were correlated.     

Ultimate resolution in open tubular columns

The expression for the resolution function, R, in terms of operating parameters for open tubular columns has been extended to include inlet contributions to the peak variance. Subsequent optimization has revealed the existence of optima in the column radius, the stationary phase thickness and the diffusion coefficient ratio in the stationary and mobile phases-in addition to the well-known optimum in the flow velocity. This implies that R at optimum becomes R=f(K)L^0.6V_i^?0.2, i.e. a function only of the column length, L, the inlet volume, V_i, and the concentration distribution coefficient, K. For given K, L and V_i all other parameters such as retention time and pressure drop can thus be directly computed. The information is finally consolidated in the form of contour diagrams. The text itself is cast in the form of a science fantasy.     

Crystal growth of polyethylene from dilute solution: Growth kinetics of {110} twins and diffusion-limited growth of single crystals

We have studied the growth kinetics of {110} twins and single crystals of polyethylene in dilute solution of tetrachlorethylene. In terms of {110} twins, we succeeded in obtaining twins without {100} sectors, using a relatively high molecular weight fraction M_w > 10⁴. It is confirmed that the growth is enhanced at the reentrant corner of the twins, and the enhanced growth face inclines to the {110} face because of consecutive generation of steps at the corner. These facts are strong evidence for nucleation-controlled growth of single crystals. The growth rates and obliquity are measured at various supercoolings and concentrations. From consideration of kinetics of steps on the growth face, the following rates and velocity are independently determined from the experimental data: nucleation rate on a flat face, velocity of step propagation, and generation rate of steps at the reentrant corner. The supercooling dependence strongly supports regime II growth. The results on concentration dependence show that the velocity of steps is proportional to concentration over the whole range examined, and the nucleation rate is independent of it in the usual range and becomes proportional to it in the lower range. This concentration dependence of nucleation rate is attributed to the density of adsorbed polymer on the growth face. From this evidence, it is suggested that the rate of travel of steps is limited by volume diffusion of solute polymer, whereas the growth face is saturated with adsorbed polymer at ordinary concentrations. This contradictory situation could be explained by the hypotheses that the saturation density is rather low and that surface diffusion of adsorbed polymer is much slower than volume diffusion of solute polymer. The lower limit of the rate of folding is also determined for the first time from the velocity of step propagation. As regards the single crystals, it is found that the habit maintains a lozenge shape with sharpened points, even at very high supercooling (δT < 50°C) if the concentration is very dilute. Diffusion-limited growth is verified for the first time at the higher supercoolings, where the growth rate is almost independent of supercooling. The growth rate becomes almost equivalent to the velocity of steps determined in the experiments with twins, and this fact will support the accuracy of the evaluation of the step velocity. The order of magnitude of the growth rate obtained agrees with the value which is calculated from the balance between the flux of solute polymer to the growth face and the rate of growth of single crystals.     

Adiabatic compressibility of tetraethylammonium tetrafluoroborate solutions in propylene carbonate

The density and ultrasound propagation velocity for Et₄NBF₄ solutions in propylene carbonate were determined in a concentration range of 0.01–0.8 mol/kg at 283.15, 298.15, and 308.15 K. Apparent molar compressibilities and volumes of the studied electrolyte in solvent were calculated. Solvation numbers and molar adiabatic compressibilities of solvate complexes were determined using the isoentropic compression method. These quantities indicated weak solvation of tetraethylammonium tetrafluoroborate in propylene carbonate in the range of concentrations practically used in ionistors.     

Intricate relation between the content and interactive roles of β‐cyclodextrin in fixing the characteristics of conducting polyaniline composites

This work is an investigation of the influence of β‐cyclodextrin (CD) on the synthesis and characteristics of conducting polyaniline composites (PCDs). In a systematic way, this influence was studied with two different approaches for five PCDs: (1) increasing the initial CD content under identical preparation conditions (three composites: PCD1, PCD2, and PCD3) and (2) using the same initial CD content (as in PCD2) under different preparation conditions (two composites: PCD4 and PCD5). The quite unexpected order of the electrical conductivity (PCD2 < PCD3 < PCD1 < PCD4 < PCD5), the IR and ultraviolet–visible spectroscopy features, and the scanning electron microscopy characteristics (the particle size decreased from PCD1 to PCD3 but increased for PCD4 and PCD5) all exposed and confirmed the markedly different physicochemical characteristics associated with the two groups of composites. PCD5 remained unique among the five (prepared in i‐PrOH–H₂O–acid; the other four were prepared in H₂O–acid). Differences in the characteristics existed within the group also. The development of all these characteristics in an unrelated order was found to originate from the amount of CD in its two roles as encapsule and dopant toward polyaniline. The interrelation between the content and roles of CD was, however, intricate in combination with the experimental conditions employed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 281–294, 2006     

Improved oxygen delivery in a continuous-roller-bottle reactor

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k_La values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.     

Intermolecular/interionic interactions in l-leucine-, l-asparagine-, and glycylglycine-aqueous electrolyte systems

Ultrasonic velocity and density values have been measured for ternary systems (amino acid/di-peptide + salt + water): l-leucine/l-asparagine/glycylglycine each in 1.5 M aqueous solutions of NaCl or NaNO₃ or KNO₃ used as solvents for several concentrations of amino acids/di-peptide at different temperatures in the range of 298.15-323.15 K. The ultrasonic velocity values have been found to increase with increase in amino acids/di-peptide concentration and temperature in all the systems. The increase in ultrasonic velocity with increase in concentration has been discussed in terms of electrostatic interactions occurring between terminal groups of zwitterions (NH₄⁺ and COO⁻) and Na⁺, K⁺, Cl⁻, NO₃⁻ ions. The interactions of water dipoles with cations/anions and with zwitterions have also been taken into consideration. It has been observed that the ion-zwitterion and ion-dipole attractive forces are stronger than those of ion-hydrophobic repulsive forces. These interactions comprehensively introduce the cohesion into solutions under investigation. The cohesive forces are further enhanced on successive increases in solute concentration. Using ultrasonic velocity and density data, the parameters such as isentropic compressibility (κ_s), change (Δκ_s) and relative change (Δκ_s/κ₀) in isentropic compressibility, specific acoustic impedance (Z) and relative association (RA) have been computed. The isentropic compressibility values decrease with increase in the concentration of solutes as well as with temperature. The decrease in κ_s values with increase in concentration of l-leucine, l-asparagine and glycylglycine in 1.5 M aqueous solutions of NaCl, NaNO₃ and KNO₃ have been explained in terms of an increase in the number of incompressible molecules/zwitterions in solutions and the formation of compact zwitterions-water dipole and zwitterions-ions structures in solutions. The decrease in κ_s values with increase in temperature has been attributed to the corresponding decrease of κ_relax. (relaxational part of compressibility)_, which is dominant over the corresponding increase of κ_∞ (instantaneous part of compressibility). The trends of variations of Δκ_s, Δκ_s/κ₀, Z and RA with change of concentration and temperature have also been interpreted in terms of various intermolecular/interionic interactions existing in the systems.     

Experimental investigations of liquid flow in pipe with flat internal baffles

Liquid flow in a tubular reactor with flat internal baffles of various widths was investigated. On the basis of the laser Doppler anemometry (LDA) measurements, the main flow parameters, i.e. the mean and fluctuating velocity components and turbulent kinetic energy (TKE) were determined. The investigations demonstrated that the insertion of baffles into a pipe and a change in their width caused a generation of liquid stream whirls, induced liquid recirculation loops and intensified the flow considerably. The results can be useful in describing turbulent flow in tubular reactors with baffles and in optimising their design.     

Research into the simultaneous removal process of H2S and PH3 by Cu–Fe–Ce composite metal oxide adsorbent

In this study, a Cu–Fe–Ce composite metal oxide adsorbent was synthesized by chemical precipitation method to simultaneously remove H₂S and PH₃. The effects of reaction temperature, oxygen content, gas inlet concentration and gas hourly space velocity (GSHV) were studied. The DRIFTS results showed that excessive oxygen and high reaction temperature lead to excessive conversion of H₂S, which competed with adsorption–oxidation of PH₃, and it was not conducive to simultaneous removal of H₂S and PH₃, and it was found that high concentration of H₂S was more likely to cause deactivation of the adsorbent than PH₃. GHSV affected the contact time between the adsorbent and the gas and affected the removal effect. The BET results showed that a larger specific surface area was more conducive to gas adsorption, and thus had a better removal effect. The XPS results showed that the deactivation of the adsorbent was due to the formation of sulfur-containing and phosphorus-containing substances.

     

An automatic optosensing device for the simultaneous determination of resveratrol and piceid in wines

For the first time, a spectrofluorimetric method is reported for the simultaneous determination of resveratrol (RVT) and piceid (PCD), two stilbenes showing diverse interesting physiological and biochemical attributes, as well as a wide range of health benefits ranging from cardioprotection to chemoprevention. The method makes use of a multicommutated flow-through optosensor in which the resolution of RVT and PCD is accomplished by means the sequential arrival of their photoproducts, on-line generated by UV-irradiation, to the detection area. This is possible due to the different kinetic behaviour of these latter on a solid support (C₁₈ silica gel) filling a minicolumn placed before the detector. The measurement in solid-phase of the photochemically induced fluorescence of the photoproducts (λ_ex: 257 nm/λ_em: 382 nm) is used as analytical signal for monitoring both compounds. The method has been applied to the analysis of RVT and PCD in wines and requires a previous solid-phase extraction (SPE) using Bakerbond C₁₈ cartridges. This pretreatment and the use of a solid-support in both the minicolumn and the flow-cell of the detector allow the determination of RVT and PCD by external calibration. Detection limits (DLs) are 9.3 and 12.6 ng mL⁻¹ for RVT and PCD, respectively. Commercial red and white wine samples have been analysed and the results obtained have been satisfactorily validated by high-performance liquid chromatography (HPLC).     

Influence of Plasma Regimes and Catalysts on Ethanethiol Oxidation

Plasma oxidation of ethanethiol in air was investigated using three plasma regimes: surface dielectric pulsed corona discharge, surface dielectric barrier discharge and pulsed corona discharge (PCD) in the plasma reactor. Catalytic plasma degradation of ethanethiol was also performed on the singular or binary metals doped ?èCAl₂O₃. The ethanethiol removal rate increased with increasing energy density but energy efficiency was first increased and then decreased with increasing energy density under three various types of discharges. PCD plasma required the lowest energy density at the similar ethanethiol removal performance compared with the other two plasma discharges. The main intermediate by-products of ethanethiol oxidation by plasma are CH₃CHO, HCHO, CO and CO₂. The sum of these intermediate products selectivities is 19?C43?%, implying that some other intermediates containing carbon were undetermined. When using PCD plasma combined with catalysts, ethanethiol removal rate and energy efficiency were all evidently improved. The maximum energy efficiency was achieved about 200?g kWh^?1 using Fe?CMn/?èCAl₂O₃ assisted PCD plasma, which was about 4.4 times when using PCD plasma alone. The mechanism of ethanethiol oxidation is also discussed.     

Surface and electrocatalytic properties of well-defined and vicinal RuO2 single crystal faces

The kinetics of Cl₂ evolution from concentrated NaCl solutions on the (110) and (230) faces of RuO₂ single crystals has been investigated by determining the Tafel slope, the stoichiometric number and the reaction orders with respect to Cl^– and H⁺. The experimental parameters suggest that the mechanism is presumably similar to that put forward earlier by Krishtalik [51] for RuO₂ layers, but a step common to oxygen evolution, like the case of polycrystalline samples, is present only with the (230) face. Reasons for this difference and for the apparent lower activity of the (110) face with respect to the (230) are discussed. A detailed analysis of the surface behavior of the two faces in Cl^– free acid and alkaline solutions has also been carried out by cyclic voltammetry.Dedicated to Professor G. Horanyi on the occasion of his 70th birthday     

Analysis of preparation of TiO<Subscript>2</Subscript> particles by diffusion flame reactor for photodegradation of phenol and toluene

TiO₂ nanoparticles were produced in the diffusion flame reactor, and the size and anatase/rutile content of TiO₂ were examined by a Particle Size Analyzer and X-ray diffraction, respectively. Increase in fuel/O₂ ratio, initial concentration of TiCl₄ or total gas flow rate causes the larger particle size and the higher rutile composition. The photocatalytic activities of TiO₂ powders were tested on the decompositions of phenol and toluene in the aqueous solution under UV irradiation. The degradation rate increases as the TiO₂ particle size decreases and as the initial concentration of phenol or toluene increases. The photodegradation rate of phenol by TiO₂ particles is higher than that of toluene at the same process conditions. The computational method was used to simulate the gas temperature, velocity and species mass fractions inside the diffusion flame reactor during synthesis of TiO₂ nanoparticles. The measured and simulated temperature results were compared on several positions above the burner and both of them show good agreements. The typical contours of TiCl₄, TiO₂ mass fractions and gas velocities in flame reactor were presented.     

Visualization and quantification of chaotic mixing for helical-type micromixers

The paper presents a micro mixer structures fabricated by an interesting technique of embedded twisted threads in polydimethylsiloxane (PDMS), which is polymerized and cured. After removing the threads carefully, the remaining channel structure is studied concerning the flows and mixing characteristics. Three-, four-, and six-strand-helical fluid microchannels (d _h ?=?100?μm, L?=?3?mm) with a specified helix angle (θ?=?22°) were used to conduct the experiments. The electroosmotic flow, inlet velocity, local velocity at specified positions, and sample concentration distribution along a downstream direction were measured via microparticle image velocimetry and laser-induced fluorescence techniques, respectively. Local mixing efficiency and mixing length were obtained at very low Reynolds numbers (≤0.0242) and low Peclet numbers (≤65.8). Results show that four-strand micromixer has the best mixing performance. Finally, a correlation of mixing length with Pe was developed, which might be applicable to a microbiomedical device design.     

Catholyte‐Free Electrocatalytic CO2 Reduction to Formate

Electrochemical reduction of carbon dioxide (CO₂) into value‐added chemicals is a promising strategy to reduce CO₂ emission and mitigate climate change. One of the most serious problems in electrocatalytic CO₂ reduction (CO₂R) is the low solubility of CO₂ in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO₂ reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm^?2, despite the decrease in CO₂ solubility. Furthermore, a significantly high formate concentration of 41.5 g L^?1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm^?2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.     

固定床反应器上挤条小晶粒TS-1催化丙烯环氧化反应

采用纳米TS-1母液作为晶种, 在四丙基溴化铵(TPABr)-乙胺廉价水热体系中, 合成出晶粒尺寸为600 nm×400 nm×250 nm的小晶粒钛硅分子筛(TS-1), 用挤条法将其成型, 得到的挤条小晶粒TS-1被用于催化固定床反应器中的丙烯环氧化反应. 采用X射线衍射(XRD)光谱, 傅里叶变换红外(FT-IR)光谱, 紫外-可见(UV-Vis)漫反射光谱及氮气物理吸附对挤条成型的小晶粒TS-1进行表征, 并对丙烯环氧化的最优反应条件进行考察. 其中所考察的条件包括: 反应温度, 压力, 丙烯/H₂O₂摩尔比(n(C₃H₆)/n(H₂O₂)), 丙烯、甲醇及H₂O₂的质量空速(WHSV), 以及NH₃·H₂O浓度. 在所考察的范围内, 温度对环氧丙烷(PO)收率的影响较小, 当反应压力为2.0 MPa, n(C₃H₆)/n(H₂O₂)为4时, 可以得到最高的PO收率. 当丙烯、甲醇及H₂O₂的空速分别为0.93、2.5及0.25 h^-1时, PO在产物中的含量最高. 较低的NH₃·H₂O浓度对高PO收率更有利. 在优化的反应条件下, 对比不同晶粒大小TS-1的催化性能, 并考察了挤条小晶粒TS-1的长期运转性能, 连续反应1000 h, H₂O₂转化率及PO选择性仍能维持在95%以上.     

超低浓度甲烷在Cu/γ-Al2O3催化颗粒流化床中的燃烧特性

采用流化床燃烧技术,使用自制Cu/γ-Al₂O₃颗粒作为催化剂床料,实验研究了超低浓度甲烷在流化床中催化燃烧时床层温度(450~700℃)、流化风速比ω(1.5~4)、进气甲烷体积分数(0.3%~2%)等对甲烷燃烧效率的影响。结果表明,床层温度是影响甲烷催化燃烧反应的关键因素,甲烷的转化率随着床层温度的升高而增加;床层温度达到650℃时,甲烷含量低于1%的超低浓度甲烷其转化率超过95%,继续提高床层温度至700℃且控制流化风速比ω≤2可以实现甲烷的完全转化;甲烷转化率随着流化风速和进气甲烷浓度的增加而降低,当ω>3.5时,温度对甲烷转化的影响减弱,未燃烧的甲烷含量增大。动力学实验发现,床层温度较低时,催化反应受动力学控制,测得催化反应的活化能E_a为1.26×10⁵J/mol,反应级数m为0.73,当温度t>450℃时,扩散作用影响显著,反应级数增大。     

矿化剂对水热法改性氢氧化镁晶体的影响

近几年来,氢氧化镁作为一种无机阻燃剂由于其具有制备条件相对温和,生产工艺简单且产品与自然环境友好等特点,在研究及生产活动方面备受关注且得到了长足的发展[1～4].目前采用氢氧化钠法进行反应一水热制备高分散阻燃级氢氧化镁的工艺路线已经比较成熟[5～8].然而,不利的是,氢氧化钠偏高的价格导致了产品的制造成本较高.而采用石灰法制备氢氧化镁阻燃剂具有价格低廉的特点,引起了人们的关注.