The effect of phase separation on the structure and permeability of gelatin–dextran films

The effect of polymer–polymer phase separation on the transport properties of gelatin–dextran films has been studied. In the gelatin–dextran–water system, the phase separation and gel formation do not occur due to the presence of a nonsolvent, but depend entirely on the temperature and the total polymer concentration. It has been found that the permeability of polymer blend films to aqueous solutes can be varied not only by changing the volume ratio of the phases, but also by varying the size of the individual domains of the two phases in the films. Under the conditions of restricted demixing (e.g., after gel formation), the course of the phase separation process can be changed by varying the length of time allowed for unrestricted separation. The two most important parameters affecting the result are the total polymer concentration in the casting solution, and the temperature regime. An exponential dependence of the permeation coefficient on the volume fraction of the solvent in the film is shown.     

Positional and geometric isomer separation of FAME by comprehensive 2-D GC

The technique of comprehensive GC (GC×GC) was applied to the analysis of a standard mixture of FAME. The methodology involved the use of two directly coupled capillary GC columns providing different retention mechanisms, with a pulsing modulator located near their union. The first column was chosen to elute analytes based on b.p. variations, and the second column was based on polarity. Thus, the separation in the two dimensions was orthogonal, since solutes delivered simultaneously to the second column had similar b.p., and the second column separated these primarily on their differentiating mechanisms of polarity. Greater sensitivity of detection and narrower peak widths were obtained; here, peak response increases of about 20-fold were obtained, with pulsed peak widths of about 150 ms. Peaks were displayed in a 2-D contour plot to allow the complexity of the compounds to be seen and their b.p. and polarity properties to be readily recognized. Chromatographic separation of geometric and positional isomers of FAMF in the 2-D space is possible. Since retention can be related to the degree and manner of unsaturation and isomerization, and as peak positions are highly reproducible in the 2-D retention map, this is a useful aid for component identification in the absence of appropriate standards. In this work, two column combinations were used to examine the effects of polarity changes on component separation. Improved quantitation based on FID area measurement was demonstrated. A sample of marine oil gave 49 resolved, identified peaks, with at least an additional 20 peaks resolved but not identified.     

内部热耦合空分塔的节能优化分析

内部热耦合精馏是迄今为止所提出的节能效果最好,而唯一没有商业化的节能技术。将内部热耦合技术用于空分塔,可以带来良好的节能效果。根据低温空气分离过程以及三组分精馏的特点,提出了一种新的内部热耦合空分精馏塔优化模型。在优化模型基础上,对热耦合塔进行了深入的节能优化与分析,并且与常规空分仿真结果进行了比较分析,压缩机能耗下降20.75%,产值增加17.46%,单位产值能耗下降32.53%。内部热耦合空分塔的提取率以及能耗均优于常规热耦合空分塔,节能效果显著。     

Mass transfer and separation criteria for high‐speed countercurrent chromatography

High‐speed countercurrent chromatography (HSCCC) is a versatile technique for preparative separations of a wide variety of solutes. For optimization of operating conditions, prediction of separations, and scale‐up study, a model is needed to describe the effluent concentration profile, which determines the separation efficiency (mass transfer, mixing, and partitioning) and the resolution between peaks. A transfer‐dispersive model is proposed to describe the effluent profile based on the assumption that the retention of a peak is caused by partitioning over two phases, and peak broadening is caused by axial dispersion and mass transfer limitation. In this work, mass transfer was investigated by comparing model simulations to experimental data. One generalized correlation of overall mass transfer coefficients was derived. Based on the correlations of axial dispersion coefficients in our previous work and mass transfer coefficients in this study, the model predicts the elution concentration profile well. Furthermore, separation criteria were proposed to predict the separation of two adjacent solutes, and they were verified using literature data. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Separation of Submicron Particles in Packed Columns – Optimization and Scale-up of the Process

Particle enlargement by heterogeneous condensation and – based on it – separation of submicron particles in packed columns of technical scale are investigated. The activation of submicron particles and droplet growth by heterogeneous condensation is briefly described. Calculations of the droplet growth are performed and compared with experimental results. The enlargement and the separation of submicron particles by cascading packed columns trickled with water which is alternately colder or warmer than the gas is experimentally studied in a technical scale pilot plant consisting of three packed columns with a diameter of 300 mm. Droplet size distributions are measured by means of an optical particle sizer at the outlet of the columns. In order to optimize the separation process, the influence of different parameters on the separation of the submicron particles is investigated. These are the gas and the water temperature, the gas and the water flow rate, and the particle concentration. Moreover, the supersaturation of the air stream in the column is calculated by means of a rate-based nonequilibrium process model as a function of different parameters.     

Modeling of Size Exclusion Parametric Pumping

Abstract

Sephadex G and Biogel P, well-known gels in size exclusion chromatography, show a large change in their elution behaviors as temperature changes. These phenomena were exploited to separate the binary model solutes Blue Dextran 2000 and nickel nitrate. A series of batch size exclusion parametric pumping experiments in the direct thermal mode was carried out previously to separate binary mixtures. In this paper the experimental separations in batch size exclusion parametric pumping are compared with the predictions of both a local equilibrium model and a dispersion model. The dispersion model, which includes an axial dispersion term, gives a better fit of the experimental data. Experimentally obtained adsorption isotherms are used in the dispersion model to predict the separation performance of nickel nitrate in the Sephadex gel column. The resulting simultaneous partial differential equations are solved by quasilinearization of the equations followed by numerical integration. For both models, all parameters were estimated independently.     

三组元全热耦合精馏过程的模拟计算

本文利用Aspen软件对三组分进料全热耦合精馏的分离流程进行设计和模拟,建立了相应的具体计算步骤。首先利用三塔模型把热耦合精馏过程简化为3个单独的简单清晰分割塔,通过简捷法设计和模拟得到塔板数和回流比等初值后进行严格法模拟,得到热耦合精馏的数据和操作条件。然后采用Aspen软件中的RadFrac模型,将三塔模型的模拟初值代入全热耦合模块进行严格模拟。结果表明,采用全热耦合精馏分离C4三组分比传统精馏的直接序列和间接序列节能约为20%。     

Law of substance separation on cross-flow filtration in turbulent flow

Cross-flow filtration is a filtration process for separation of a disperse phase from liquids. Suspension flows tangentially to a membrane and the filtrate is drawn off perpendicular to the direction of flow. Formation of a filter cake on the membrane is thus prevented, reduced, or its composition, modified. The principle of the separation is based on tow opposing effects: on the one hand, the particles are transported by the filtration flux to the membrane where they cause and increase in concentration; on the other hand, concentration differences are again reduced by the turbulence of the cross-flow and by Brownian motion of the particles. The two mechanisms compete with each other and depend upon particle size in different ways. An energetic comparison of the two effects yields the separation law of cross-flow filtration as a steady state solution of the Fokker-Planck equation. The separation law has an exponential form and assigns each particle size a separation probability with which it reaches the membrane. Once on the membrane the particles may form a filter cake, flow through the pores or return to the bulk flow. If the particles remain on the membrane the ranges of layer-free and cake-forming filtration can be calculated from the hydro-dynamic and geometric conditions of the cross-flow filter. Conventional cake filtration is regarded as limiting case. In continuous cross-flow filtration process a low separation probability through the filtration pressure on selection of the filter medium resistance.     

Graft copolymerization of -isopropylacrylamide with 3-(methacryloxy)propyl trimethoxysilane on ultrafine silica and its application in chromatography separation

Thermosensitive core-shell particles were synthesized through graft copolymerization of N-isopropylacrylamide with [ 3-(methacryloxy) propyl]trimethoxysilane (MPT) coupled on the surface of ultrafine silica beads. The copolymerization was carried out using polyvinyl alcohol as a surfactant, water and cyclohexanol as mixed solvent, and 2,2′-azobis(isobutyronitrile) as an initiator. The effect of surfactant concentration and the composition of the mixed solvent on the graft rate were investigated. The structure of modified silica was confirmed by infrared spectra. Differential scanning calorimetry (DSC) has revealed the thermosensitivity of the particles. The thermosensitive particles were used as packing materials of high performance liquid chromatography (HPLC) columns for separating naphthalene derivatives. Satisfactory separation was obtained by controlling the temperature of the column. In contrast, the packing material of silica-MPT has no such separation efficiency due to the lack of thermosensitivity. The effect of the composition of the mobile phase on the separating efficiency was also investigated. The temperature-controlled separation was effective only when the water content was higher than 90% (v/v) in the water-methanol mobile phase. The mechanism for the temperature-controlled separation is attributed to a polarity change of poly(N-isopropylacrylamide) which undergoes volume phase transition on the silica surface as the temperature increases.     

REVERSE OSMOSIS SEPARATION OF GLUCOSE-ETHANOL-WATER SYSTEM BY CELLULOSE ACETATE MEMBRANES

The separation of glucose-ethanol mixed solutes from aqueous solutions was attempted by cellulose acetate membranes of different average pore sizes and pore size distributions at the operating pressure of 6895 kPag (=1000 psig) and at the feed glucose concentration ranging from 2000 to 75000 ppm while maintaining ethanol concentrations at 1/5 to 1/2 of the glucose concentration. Using chosen reference solutes the pore size distribution on the membrane surface was characterized by two normal distributions. It was found that ethanol is attracted to the cellulose acetate membrane material more strongly at the higher glucose concentration in the feed solution, and consequently the separation of ethanol solute is brought down at higher glucose concentrations. These results are attributed to lowering of solubility of ethanol in the solvent when a greater amount of glucose is in the solvent.     

REVERSE OSMOSIS SEPARATION OF GLUCOSE-ETHANOL-WATER SYSTEM BY CELLULOSE ACETATE MEMBRANES

The separation of glucose-ethanol mixed solutes from aqueous solutions was attempted by cellulose acetate membranes of different average pore sizes and pore size distributions at the operating pressure of 6895 kPag (=1000 psig) and at the feed glucose concentration ranging from 2000 to 75000 ppm while maintaining ethanol concentrations at 1/5 to 1/2 of the glucose concentration. Using chosen reference solutes the pore size distribution on the membrane surface was characterized by two normal distributions. It was found that ethanol is attracted to the cellulose acetate membrane material more strongly at the higher glucose concentration in the feed solution, and consequently the separation of ethanol solute is brought down at higher glucose concentrations. These results are attributed to lowering of solubility of ethanol in the solvent when a greater amount of glucose is in the solvent.     

Gel-size dependence of temperature-induced microphase separation in weakly-charged polymer gels

The gel-size dependence of microphase separation in weakly-charged gels of N-isopropylacrylamide (NIPA) and 1-vinylimidazole (VI) copolymers has been investigated using swelling measurement, small-angle neutron scattering (SANS), and dynamic and static light scattering (DLS/SLS). It is known that weakly-charged polymer gels undergo microphase separation in a poor solvent as a result of competing interactions involving hydrophobic attraction versus electrostatic repulsion. The microphase separation is characterized by a scattering maximum in SANS intensity functions of which Bragg spacing, Λ, is around 20-30 nm. However, when gel size was reduced to the order of Λ, no microphase separation was observed. Instead, a typical scattering of isolated spherical particles was clearly observed. On the basis of the experimental evidence, we conclude that microphase separation has its own wavelength independent of gel size, and nanometer-order gels, i.e., nanogels, do not undergo microphase separation.     

Size exclusion chromatography of polyelectrolytes in dimethylformamide

A study of the size exclusion chromatographic behavior of styrene–methacrylic acid and epoxyacrylic polymers has been made. These polymers exhibit strong “ion-exclusion” effects in DMF, similar to that found for water-soluble polyelectrolytes such as sodium polystyrene sulfonate. The addition of lithium bromide, at a concentration of 0.1M, overcomes ion exclusion on a set of silicabased, “deactivated” duPont SEC columns. Calibration of both the duPont columns and a set of styrene–divinyl benzene based columns (μ-Styragel) is complicated by absorption of polystyrene standards in DMF and DMF/salt mobile phases. The absorption of monomeric solutes on the duPont columns in DMF/salt mobile phases is different from that of their corresponding polymers.     

A new approach to fluid separation modelling in the columns equipped with structured packings

An analogy between the flow patterns in real separation columns equipped with structured packing and film flow is used to develop a new modelling approach. The packing is represented as a bundle of channels with identical triangular cross section. The dimensions of the channels as well as their number are derived from the packing geometry. The channel inner surface is wetted by a liquid flowing downwards, whereas the rest of the volume is occupied by a countercurrent vapour flow. Both phases are assumed to be totally mixed at regular intervals, determined by the corrugation geometry of the packing. The mathematical model is based on a set of partial differential equations describing hydrodynamics and mass and heat transport phenomena. These equations are complemented by the conjugate boundary conditions at the phase interface. A numerical solution of the model yields velocity profiles as well as concentration and temperature fields throughout the column. The model is verified using experimental data for a binary distillation in a column equipped with Montz-Pak A3-500.     

A method for steady-state simulation of multistage separation columns involving nonideal systems

A new algorithm is developed for steady-state simulation of multistage separation columns. The algorithm decouples the model equations into two groups. The component-material balance and summation equations are solved simultaneously by the Newton-Raphson method for temperatures and component flow rates in the inner loop. The energy-balance equations are solved in the outer loop to obtain total flow rates. The K-factor is separated into three parts, each representing separately the effect of temperature, composition and apparent volatility. This makes the analytical calculation of the partial derivatives of the K-factors in the Jacobian matrix a simple task. The stability and efficiency of the algorithm is illustrated by solving a variety of problems for distillation, absorber and reboiled absorber columns. The algorithm does not require large storage space.     

Gels as size selective extraction solvents

We have successfully used cross-linked, partially-hydrolyzed, polyacrylamide gels to concentrate solutions of high molecular weight solutes. The gels are sizeselective, concentrating solutes whose diameter exceeds 3 nm. They can be easily regenerated by means of pH-induced changes in gel swelling; this regeneration is consistent with that inferred from existing theories of gel swelling. The resulting separation process is a good alternative to ultrafiltration.     

旋流分离对天然气水合物除砂提纯的影响

针对固态流化开采方法开采海底天然气水合物含砂量大导致开采效率低的问题,提出原位分离工艺,设计了旋流分离装置,基于该装置利用CFD数值模拟方法研究了固相(砂和水合物颗粒)直径、入口浆体流量及浆体中砂浓度对装置分离性能的影响。结果表明,在研究范围内,砂和水合物分离效率大部分高于60%,最高达98.72%,压降大部分低于0.5 MPa,最低至0.03 MPa。砂粒分离效率随固相粒径增大先增大后趋于平稳,随浆体入口流量增大先增大后减小,随砂浓度增大而降低;水合物分离效率随固相粒径增大先增大后趋于平稳,随浆体入口流量增大先增大后减小,随砂浓度增大而降低。溢流口和底流口压降几乎不随固相粒径变化,随砂浓度和浆体入口流量增大而增大。固相粒径、入口流量、砂浓度对分离性能有较大影响,在砂粒径大于20 ?m、水合物粒径大于40 ?m、浆体入口流量约5 m3/h、入口砂浓度不超过25vol%的条件下分离性能良好。     

Calculation of separation columns by nonlinear block successive relaxation methods

A novel technique: nonlinear block successive relaxation (NBSR) method, is proposed to solve the steady-state balance equations describing separation columns. The NBSR methods are a generalization of point relaxation methods frequently used towards solution of elliptic partial differential equations. Aspects of partitioning of the original set of equations into blocks as well as ordering of blocks is discussed. Problems arising in construction of a universal program based on the NBSR methods are presented. A new procedure making use of grouping of equations according to the set of trays is proposed. Aspects of calculation of separation equipments by this procedure is discussed. It is shown that overlapping blocks may essentially improve the convergence properties of the algorithm. The procedure is very simple and can be easily used towards calculation of large separation problems on a small computer. The method described is illustrated on calculation of an absorption column. Application of the NBSR methods to solution of a complex plant is suggested.     

Modeling fluid behavior and droplet interactions during liquid-liquid separation in hydrocyclones

A mechanical separation process in a hydrocyclone is described in which disperse water droplets are separated from a continuous diesel fuel phase. This separation process is influenced by droplet-droplet interaction effects like droplet breakup and coalescence resulting in a change of droplet size distribution. A simulation model is developed coupling the numerical solution of the flow field in the hydrocyclone based on computational fluid dynamics with population balances. The droplet size distribution is discretized and each discrete droplet size fraction is assumed to be an individual phase within a multiphase-mixture model. The droplet breakup and coalescence rates are defined as mass transfer rates between the discrete phases by the aid of user-defined functions. All model equations are solved with the CFD software package FLUENT™. The investigations show the impact of the cyclone geometry on the coupled population and separation dynamics. Cyclone separators with an optimized geometry show less steep velocity gradients increasing the coalescence rates and improving the separation efficiency. The calculated droplet size distributions at the cyclone overflow and at the underflow show good accordance with experimental data. The basic modeling approach can be extended and adapted to other disperse multiphase flow systems.     

Weak gels of fat crystals in oils at low temperatures and their fractal nature

The formation of fat crystal gels in soybean oil has been studied by sedimentation in a low concentration region at 10–25°C. At 10°C, weak gels were formed with 1% crystals, and no gels formed at concentrations of 2–5%. At temperatures of 15–25°C, no gels were formed at concentrations of 1–5%, and samples sedimented. Stronger gels of fat crystals were formed with ∼10% fat crystals at all temperatures examined. Formation of weak gels is a consequence of the fractal nature of fat crystal aggregates and sediments. At low temperature, the interaction is weak. The fractal dimension is then high, and the floc size is large for low crystal concentrations. These large flocs form a three-dimensional network that act as a weak gel and withstand gravitational force. When the temperature is increased, the fat crystal interaction becomes stronger, fractal dimension decreases, and floc size decreases. Smaller flocs have a higher density, pack more easily, and sediment. Similar effects are observed when the concentration of fat crystals is increased at low temperature due to a decrease in floc size.