A new approach to continuous emulsion polymerization

The application of a continuous Couette-Taylor vortex reactor to continuous emulsion polymerization was studied. First, the mixing characteristics of the reactor were examined by the stimulus-response method. It was found that the reactor performance was similar to that of a continuous flow reactor consisting of more than 60 well-stirred tanks in series if the reactor was properly designed and operated near the critical Taylor number. It was also demonstrated by a comparison of the particle size distributions of the latexes produced in a batch reactor and in the continuous Couette-Taylor vortex reactor that the continuous reactor could produce latex particles with fairly narrow size distribution. Furthermore, since no stirrer is involved, this continuous reactor is suited for the purpose of avoiding coagulation of latex particles that are very sensitive to mechanical shear.     

Measurements and modelling of free-surface turbulent flows induced by a magnetic stirrer in an unbaffled stirred tank reactor

Measurements and numerical simulations of turbulent flows with free-surface vortex in an unbaffled reactor agitated by a cylindrical magnetic stirrer are presented. Measurements of the three mean and fluctuating components of the velocity vector are made using a laser Doppler velocimetry in order to characterise the flow field at different speeds of the stirrer. A homogeneous Eulerian-Eulerian multiphase flow model coupled with a volume-of-fluid method for interface capturing is applied to determine the vortex shape and to compute the turbulent flow field in the reactor. Turbulence is modelled using a second-moment differential Reynolds-stress transport (RST) model, but for some cases the k-ε/k-ω based shear-stress transport (SST) model is also used. The predictions obtained using the ANSYS CFX-5.7 computational fluid dynamics code are compared with the images of the vortex and the measured distributions of mean axial, radial and tangential velocities and turbulent kinetic energy. The predicted general shape of the liquid free-surface is in good agreement with measurements, but the vortex depth is underpredicted. The overall agreement between the measured and the predicted axial and tangential velocities obtained with the RST model is good. However, the radial velocity is significantly underpredicted. Predictions of the turbulent kinetic energy yield reasonably good agreement with measurements in the bulk flow region, but discrepancy exists near the reactor wall where this quantity is underpredicted. The SST model predictions are generally of the same quality as those of the RST model, with the latter model providing better predictions of the tangential velocity distribution.     

A COUNTER CURRENT EXPERIMENT FOR THE SEPARATION OF TRIVALENT ACTINIDES AND LANTHANIDES BY THE SETFICS PROCESS

ABSTRACT

The SETFICS process, a variation of TRUEX process, was developed for the recovery of Am and Cm from acidic waste solution and the separation of actinides (III) and light lanthanides. The process uses the general TRUEX solvent as the extracting reagent and a DTPA-sodium nitrate solution for selective stripping of actinides(III). The basic flow sheet is composed of four steps: extraction-scrubbing; acid stripping; actinide(III) stripping; and lanthanide stripping.

To demonstrate the usefulness of the SETFICS process, a counter current experiment was conducted using a real TRUEX product solution. Americium and curium were successfully recovered with a solution of 0.05 M DTPA-4 M NaNO₃ (pH 2.0). Although the actinide(III) product solution contained Sm and Eu, the decontamination factor of ¹⁴⁴Ce/²⁴¹Am was 72, and most of the light lanthanides, specifically La, Ce, Pr, Nd, were removed. At least 80 % of the lanthanides were separated from the Am and Cm end products. In order to minimize the acidity in the actinide(III) stripping step, the nitric acid which extracted with the trivalent metals was previously removed with a solution of 0.5 M NaNO₃ (pH 2.0) in the “acid stripping” step.     

Performance of the monolithic stirrer reactor: applicability in multi-phase processes

The novel monolithic stirrer reactor is a promising replacement for a conventional slurry reactor in multi-phase reactions. In this reactor monolithic structures are used as stirrer blades, creating a catalytic stirrer. The most important advantage of the monolithic stirrer reactor is the easy catalyst handling. The influences of different parameters on the performance of the monolithic stirrer reactor in the selective hydrogenation of 3-methyl-1-pentyn-3-ol were investigated. The decreasing catalyst layer thickness with increasing cell density proved to be beneficial for the performance of the monolithic stirrer reactor. An increasing stirrer speed caused an increase in the activity because of the higher flow through the monolith channels and the improved gas–liquid mass transfer. If the length of the monolithic stirrer blades was smaller than 0.03 m the performance of the monolithic stirrer was enhanced.     

Mixing and micromixing times in the forced vortex region of unbaffled mixing devices

Unbaffied mixing devices are characterized by a very particular hydrodynamics. A well defined depression in the liquid surface is formed, resulting from the combined vortex established in the liquid. The combined vortex is composed of one central Forced Vortex Region (FVR) and one annular free vortex region. Because the FVR behaves like a confined mixing zone, this region inside an unbaffled mixing device appears to be quite interesting to carry out certain chemical reactions. In this paper the influence of operating conditions on the mixing time of two reagent feed streams arriving continuously in the FVR of unbaffled mixing devices is investigated. Process parameters investigated are?: stirrer speed, reagent flow rates and feed pipe position. Mixing time correlations are established, which are useful for the scale‐up of this reactor.     

Effect of liquid circulation in the draft-tube reactor on precipitation of calcium carbonate via carbonation

Precipitation of calcium carbonate was carried out in a draft-tube reactor by mechanical agitation of calcium hydroxide solution with carbon dioxide. The circulation of a reactive mixture was created by gas flow and a stirrer. It was observed that a higher circulation decreased the precipitation time and improved CO₂ consumption. A higher circulation velocity of liquid contributed to smaller calcium carbonate particles at the end of precipitation.     

Electrochemical denitrification of metal-finishing wastewater: Influence of operational parameters

Experimental results are presented for the electrolytic ChemDen (Chemical-Denitrification) process which was designed to investigate the effect of operational parameters on the nitrate (NO₃⁻) removal from metal-finishing wastewater. The parameters included electrode materials, electrode gap, reducing agent, hydraulic retention time (HRT) and recycle ratio in the single electrolytic ChemDen reactor for lab-scale tests. The removal efficiency of nitrate is based upon a non-biological process which consists of chemical and electrolytic treatment. Results showed that removal efficiency of nitrate was highest when the zinc (Zn) electrodes were used for both anode and cathode. In the case of insoluble electrode, combining Pt anode with Ti cathode provided great improvement of nitrate removal. For the Pt-Ti electrode combination, increasing electrode gap tended to increase removal efficiency of nitrate significantly. However, no further increase in the nitrate removal was observed when the electrode gap was longer than 10mm. Using sulfamic acid and Zn metal powder as reducing agents for the electrolytic ChemDen reaction, highest nitrate removal was achieved when the mole ratio of Zn: sulfamic acid: nitrate was 1.2: 1: 1. Remarkable improvement in the nitrate removal was also observed with increasing HRT from 10 to 30 min, while the effectiveness was limited when HRT was increased to 60 min. Recycling in electrolytic ChemDen reactor affected nitrate removal positively because it could improve both dispersion and reuse of Zn metal powder as reducing agent in the reactor. Recycling effects were thought to be associated with increasing surface reactivity of the Zn metal powder in the electrolytic ChemDen reactor.     

流体中气泡微细化与分散过程的数值模拟

采用CFD商用软件模拟了搅拌加喷吹情况下溶池中流场和相的分布.对比分析了水模型内单相流和两相流时液面和轴向迹线图、矢量图和相分布图,重点考察了中心搅拌和偏向搅拌对漩涡和相分布的影响规律.模拟结果表明,中心搅拌模式下在搅拌桨轴附近形成很大的漩涡,偏心时虽然也有漩涡形成,但偏离轴心.两相流偏心搅拌模式下由于漩涡较小且偏离轴心,有利于气体的分散;偏心搅拌与中心搅拌相比可以抑制漩涡在几何中心的形成,有利于气体的分散和气泡的细化,同时偏心搅拌也可以有效地抑制水模底部的死区.研究结果对喷气机械搅拌装置的设计具有参考价值.     

CFD analysis of interphase mass transfer and energy dissipation in a milliliter-scale stirred-tank reactor for filamentous microorganisms

A newly developed stirred tank bioreactor for the cultivation of filamentous microorganisms on a milliliter-scale was investigated by means of computational fluid dynamics (CFD). The applied paddle impeller has an asymmetric shape and thus creates a complex liquid vortex in an unbaffled reactor. Size and shape of the formed gas–liquid interface were simulated applying CFD because they cannot be measured experimentally. As expected, higher stirrer speeds correspond to deeper vortices and larger interfacial areas. CFD simulations confirmed stirrer functionality at high liquid viscosities. Volumetric oxygen mass transfer coefficients (k_La) were estimated based on the simulated interfaces. Comparison with experimental data showed good agreement. Simulated maximum energy dissipations were in the same order of magnitude as experimental data at varying stirrer speeds. In contrast to these findings, simulated power characteristics showed significant deviations if compared to measured data. One reason may be the challenging turbulence modeling of two-phase flows with strong streamline curvature and the mostly transitional flow regime. Another reason could be the demanding measurement of very small stirrer torques.     

第三分散相液滴增强气体吸收的一维非稳态非均相传质模型

A model for one-dimensional unsteady heterogeneous mass transfer was developed based on Danckwerts’ surface renewal theory in order to describe the mass transfer enhancement of absorption process for a slightly soluble gas in a gas-liquid-liquid system. The model accounts for the mass transfer resistance within the dispersed phase and the effect of emulsion viscosity on mass transfer. An analytical solution for enhancement factor was obtained by Laplace domain transformation. The absorption rates of carbon dioxide in the dodecane-in-water and castor oil-in-water systems were measured in a thermostatic reactor, and the enhancement factors were calculated at different volume fractions of dispersed phase and stirrer speeds. The model predictions agree well with the experi-mental data.     

A Double Liquid Membrane System for the Removal of Actinides and Lanthanides from Acidic Nuclear Wastes

Abstract

Supported liquid membranes (SLM), consisting of an organic solution of n-octyl(phenyl)-N, N-diisobutylcar-bamoylmethylphosphine oxide (CMPO) and tributyl-phos-phate (TBP) in decalin are able to perform selective separation and concentration of actinide and lantha-nide ions from aqueous nitrate feed solutions and synthetic nuclear wastes.

In the membrane process a possible strip solution is a mixture of formic acid and hydroxylammonium formate (HAF). The effectiveness of this strip solution is reduced and eventually nullified by the simultaneous transfer through the SLM of HNOs which accumulates in the strip solution. A possible way to overcome this drawback is to make use of a second SLM consisting of a primary amine which is able to extract only HNO₃ from the strip solution.

In this work the results obtained by experimentally studying the membrane system: synthetic nuclear waste/CMPO-TBP membrane/HCOOH-HAF strip solution/ primary amine membrane/NaOH solution, are reported. They show that the use of a second liquid membrane is effective in controlling the HN0₃ concentration in the strip solution, thus allowing the actinide and lanthanide ions removal from the feed solution to proceed to completion.     

Inorganic Precipitated Silica Gel. Part 2: Fragmentation by Mechanical Energy

Precipitated silica (SiO₂) is industrially produced by mixing a silicate solution with acid in a semi‐batch process. Polycondensation of monomeric silica leads to the formation of particles which aggregate and eventually form a particulate gel. However, this is instantly fragmented by the mechanical energy input caused by the stirrer. Shrinkage and compaction of these fragments lead to the final product aggregates. It is the aim of this study to enable tailoring of the structure and size of these product particles via the process parameters. In the present paper this is achieved by varying the stirrer speed. It can be shown that there is an analogy between the behavior of the gel and that of highly viscous liquids. Unexpectedly, however, the fragment size can not be reversibly controlled by the power input. The influence of the process parameters on the strength of the gel has been described in the first part of this series [1].     

水泥专用丁苯胶乳的工业放大试验

研究了水泥专用丁苯胶乳从2m3中试聚合釜到20m3工业规模聚合釜的放大过程。结果表明:采用单位体积功率与搅拌桨的叶端剪切速率相结合的放大准则,能够在20m3工业聚合釜重现2m3中试聚合釜的反应结果。以38→48→40r/min变搅拌转速的操作方式可以制得平均粒径为110~120nm、粒径分布指数为0·050~0·065和化学稳定性及机械稳定性优异的水泥专用丁苯胶乳。     

过氧化氢异丙苯分解绿色工艺 ?I.催化剂性能

对不同类型磺酸树脂催化剂进行比较,筛选出活性较高的磺酸树脂CT–175,用于过氧化氢异丙苯(CHP)分解工艺. 湿基树脂催化剂可采用丙酮脱水, 液固比为40 ml/g时, 经80 min, 脱水率接近100%. 研究表明,机械搅拌对树脂催化剂破碎有很大的影响,因此,反应器中不宜有机械搅拌装置. 另外,树脂催化活性与其在反应过程中吸附的Na+含量有重要关系,当树脂中Na+含量达到0.03%(w)时,需要再生. 适宜的再生条件是常温、3.5%(w)硫酸水溶液,可使Na+脱除95%.     

Experimental and numerical study of turbulent mixing in a model of a polymerization reactor

In this study the turbulent mixing in a model of a polymerization reactor is analyzed experimentally and numerically. The model corresponds to a zone of an autoclave reactor equipped with a stirrer. Two different configurations of the stirrer, with different arrangement of the paddles, have been considered. The mixing process has been monitored by following the time-evolution of injections of a passive scalar through the different inlets of the model. The time-evolution of the mixing quality in a laboratory scale model of the reactor has been measured using water and the Planar Laser Induced Fluorescence (PLIF) technique. Numerical simulations of the flow and of the mixing processes were carried out and results of the evolution of the mixing are compared successfully with measurements. The mixing processes are dominated by the flow topology generated by the rotation of the stirrer. Superimposed to the tangential flow, secondary flows divide the length of the reactor in different zones. It has been found that macro mixing in each individual zone is a relatively fast process and that the mixing rates within each zone are very similar. However, the mixing rate between different zones is a relatively slow process.     

Large-eddy simulation of the turbulent free-surface flow in an unbaffled stirred tank reactor

This article deals with the large-eddy simulation (LES) of a complex turbulent free-surface flow in an unbaffled mixing tank reactor. The free-surface vortex generated in such a configuration is captured using a front-tracking method, while the stirrer is modelled with an immersed boundary condition technique. Comparisons of mean and fluctuating velocities show good agreement with both theory and experimental laser Doppler velocimetry measurements. The study of mean and instantaneous hydrodynamics points out several interesting features, especially coherent structures, which may have a strong impact on mixing in the reactor. Finally, Reynolds stresses analysis confirms the high anisotropy of turbulence throughout the tank.     

亚硝酸盐对厌氧产酸耦合反硝化工艺的影响

以木薯酒精废水为碳源,通过批次实验研究了亚硝酸盐对厌氧产酸耦合反硝化系统的影响。结果表明,投加600 mg·L^-1 后的最终产酸量与空白反应器相差不大,但是投加相同浓度亚硝酸盐后产酸受到严重抑 制,最终产酸量仅为空白反应器的1.8%。而硝酸盐还原过程中厌氧产酸受到抑制可能是由于反硝化中间产物亚硝酸盐的存在,低投加量的亚硝酸盐即可对厌氧产酸产生强烈的抑制作用并具有持续性,且对各产酸组分的影响作用：正丁酸>丙酸>乙酸。随着 的降低,亚硝酸盐的还原率由74.9%降低至22.2%。当游离亚硝酸（free nitrous acid, FNA）浓度为0.05 mg·L^-1以上时,亚硝酸盐还原几乎被完全抑制（90%以上）。此外,随着 的增加,反硝化所占的比例逐渐减小,而DNRA过程（dissimilatory nitrate reduction to ammonium,异化硝酸盐还原为铵）逐渐占优势。     

Vibrational Damage to a Bio-Reactor

On a methane reactor with a diameter of 29 m and a total height of 16 m, vibrational damage running into millions occurred after three years of operation. It was proved that the damage resulted from vibrations of the stirrer and the surrounding guiding pipe. The reason for the damage was an incorrect calculation of the eigenfrequency of both the stirrer and guiding pipe where the damping of the medium water as well as the effect of the constructive restraints were ignored.     

Improvement of the mechanical and thermal properties of silica‐filled polychloroprene vulcanizates prepared from latex system

In this work, well‐dispersed silica suspension having excellent storage stability was prepared by using an ultrasonic probe. The obtained silica suspension and curatives were added into the polychloroprene (CR) latex for preparing silica‐filled CR latex compounds having various silica loadings. Then, the silica‐filled CR vulcanizates were prepared via a dipping process. The thermal and mechanical properties of the dipped CR vulcanizates containing silica dispersed by using an ultrasonic probe were compared with those of the dipped CR vulcanizates containing silica dispersed by using a mechanical stirrer. By using thermogravimetric analysis, it could be seen that thermal resistance of the dipped CR films having silica prepared by ultrasonic probe is greater than that prepared by using the mechanical stirrer. This result corresponds well with their tensile strength after aging in the hot‐air oven. In addition, modulus, tensile strength, and tear strength of the vulcanizates prepared from CR latex compounds containing silica prepared by using the ultrasonic probe are obviously greater than those prepared by using the mechanical stirrer, especially at high silica loading. This is because the silica prepared using the ultrasonic probe is uniformly distributed and dispersed throughout the CR matrix, as can be observed in the scanning electron microscope micrographs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and investigation of sodium alginate nanocapsules by different microemulsification devices

Numerous techniques of preparation have been reported for the encapsulation of the core material, but the microemulsion technique is the most effective and commonly used for encapsulation. In this article, three microemulsification devices including ultrasonic stirrer, labo ratory reactor, and mechanical stirrer were used to produce the alginate nanocapsules containing peppermint oil. The effect of different parameters on surface morphology, mean particle size, and size distributions were investigated. The results indicated that the ultrasonic stirrer is the best device to make the nanocapsules containing essential oils prepared by microemulsion method, so that the size of nanocapsules prepared by ultrasonic stirrer was about 56 nm. Also, the results of GC‐MS, FTIR, and TGA show that quantities of the remaining compounds in nanocapsules prepared by ultrasonic stirrer are higher than other devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41904.