Electrical Field-Flow Fractionation in a Rigid Membrane Channel

Abstract

Experimental problems associated with the previous flexible membrane system of electrical field-flow fractionation (EFFF) are first reviewed. The potential advantages of an effective EFFF system are then discussed and compared to those of electrophoresis. The general theory of EFFF is briefly stated, and the possible means for evaluating electrical field strength in the fractionating channel are discussed.

Results are presented for protein components showing that retention follows the predicted behavior with variations in field strength. Furthermore, retention becomes theoretically predictable in numerical magnitude with the aid of an internal standard. The determining parameter for this calculable retention is the ratio D/μ, where D is the diffusion coefficient and μ is mobility. The results show that D/μ becomes a measurable parameter using this system.

Preliminary efforts to induce the retention of denatured proteins and polystyrene beads are shown to be unsuccessful for entirely independent reasons.     

Reverse osmosis separations for some alcohols and phenols in aqueous solutions using aromatic polyamide membranes

The performance of aromatic polyamide membranes for reverse osmosis separations of eight alcohol and four phenol solutes in dilute aqueous solutions has been studied. The Taft polar parameter σ^* for the solutes studied were in the range of ?0.3 to 1.388. Positive solute separations were obtained for each one of the solutes. In the σ^* value range of ?0.3 to 0, data on PR/PWP ratio scattered close to 1, and solute separation decreased with increase in σ^*. For the phenol solutes, PR/PWP ratio decreased and solute separation increased with increase in σ^*. The results are interpreted on the following basis. The aromatic polyamides are more nonpolar than cellulose acetates. In the σ^* range of ?0.115 to ?0.3, solute separation is governed primarily by polar interactions; in this range, solute transport parameter D_AM/Kδ is well correlated by the expression D_AM/Kδ = C^* exp (ρ^*σ^*). The solute separation for ethyl and methyl alcohol solutes (σ^* = ?0.1 and 0, respectively) is reduced by the nonpolar character of the membrane material. Positive solute separation for each of the phenolic solutes is due to preferential sorption of solute at the membrane-solution interface caused by both the nonpolar character of the membrane material and acidity of the solutes.     

Fluid Flow Characteristics of String Reactors Packed with Spherical Particles

A hydrodynamic investigation of three geometries of string pellet reactors filled with spheres was conducted. Two geometries were circular spiral channels, while the third was a straight horizontal square channel. Stimulus‐response experiments provided data for residence time distribution analysis from which Pe numbers and liquid holdup were deduced. Flow regimes and transitions were determined from visual observations through the transparent tube wall. For the whole range of the experimental conditions applied in this work and for all reactors, the ratio of gas to liquid velocities, V_g/V_l, is a controlling parameter for Pe number, holdup, and pressure drop.     

Meso-scale structures of bidisperse mixtures of particles fluidized by a gas

Flow characteristics of bidisperse mixtures of particles fluidized by a gas predicted by the mixture based kinetic theory of [Garzó et al., 2007a] and [Garzó et al., 2007b] and the species based kinetic theory model of Iddir and Arastoopour (2005) are compared. Simulations were carried out in two- and three-dimensional periodic domains. Direct comparison of the meso-scale gas-particle flow structures, and the domain-averaged slip velocities and meso-scale stresses reveals that both mixture and species based kinetic theory models manifest similar predictions for all the size ratios examined in this study. A detailed analysis is presented in which we demonstrate when the species based theory of Iddir and Arastoopour (2005) will reduce to a mathematical form similar to the mixture framework of [Garzó et al., 2007a] and [Garzó et al., 2007b] . We also find that the flow characteristics obtained for bidisperse mixtures are very similar to those obtained for monodisperse systems having the same Sauter mean diameter for the cases examined; however, the domain-averaged properties of monodisperse and bidisperse gas-particle flows do demonstrate quantitative differences. The use of filtered two-fluid models that average over meso-scale flow structures has already been described in the literature; it is clear from the present study that such filtered models are needed for coarse-grid simulations of polydisperse systems as well.     

Comments on “Thermal shock resistance of yttria-stabilized zirconia with Palmqvist indentation cracks” by G. Fargas,D. Casellas,L. Llanes,M. Anglada [J. Eur. Ceram. Soc. 23 (2003) 107–114]

In a recent paper, Fargas et al. [Fargas, G., Casellas, D., Llanes, L. and Anglada, M., Thermal shock resistance of yttria-stabilized zirconia with Palmqvist indentation cracks. J. Eur. Ceram. Soc., 2003, 23, 107–114] make use of the Vickers indentation technique to characterise the thermal shock resistance of brittle materials exhibiting the Palmqvist indentation crack system. They claim that their approach can provide a measurement of Hasselman's R⁗ thermal shock resistance parameter. It is here demonstrated that the obtained parameter is in fact different from R⁗. In parallel, it is shown that a previously developed approach, which is both consistent with the concepts of R⁗ and of the critical quenching temperature difference, ΔT_C, can be used in the case of the Y-TZP ceramics of Fargas et al. This approach also allows an estimation of the maximum thermal stresses and of the coefficient of heat transfer at the fluid–solid interface as a function of the quenching temperature difference.     

Experimental studies on extrudate swell behavior of PS and LLDPE melts in single and dual capillary dies

Extrudate swell behavior of polystyrene (PS) and linear low‐density polyethylene (LLDPE) melts was investigated using a constant shear rate capillary rheometer. Two capillary dies with different design configurations were used, one being a single flow channel and the other being a dual flow channel. A number of extrudate swell related parameters were examined, and used to explain the discrepancies in the extrudate swell results obtained from the single and dual flow channel dies, the parameters including output rate and output rate ratio, power law index, wall shear rate, wall shear stress, melt residence time, pressure drop induced temperature rise, flow channel position relative to the barrel centerline, and the flow patterns. It was found in this work that the power law index (n value) was the main parameter to determine the output rate ratio and the extrudate swell between the large and small holes for the dual flow channel die: the greater the n value the lower the output rate ratio and thus decreased extrudate swell ratio. The differences in the extrudate swell ratio and flow properties for PS and LLDPE melts resulted from the output rate ratio and the molecular chain structure, respectively. The extrudate swell was observed to increase with wall shear rate. The discrepancies in the extrudate swell results from single and dual dies for a given shear rate were caused by differences in the flow patterns in the barrel and die, and the change in the melt velocities flowing from the barrel and in the die to the die exit. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1713–1722, 2003     

Efficient separation of (R)‐(‐)‐mandelic acid biosynthesized from (R,S)‐mandelonitrile by nitrilase using ion‐exchange process

BACKGROUND: (R)‐(‐)‐Mandelic acid (R‐MA) is an important intermediate and chiral regent with broad uses. An efficient method for the separation of R‐MA from the bioreaction mixture with high yield is of great importance, thus, the main objective of this work is to investigate the recovery of R‐MA using an ion‐exchange process. RESULTS: The equilibrium isotherms for the separation of R‐MA by resin HZ202 were obtained in the pH range 5.0–9.0 and temperature range 25–35 °C. The equilibrium data are well fitted by the Langmuir isotherm. Batch kinetic experiments showed that the mobility of R‐MA^? in solution was rapid and the R‐MA^?/OH^? ion‐exchange process reached equilibrium after about 60 min. Adsorption kinetics were analyzed by a linear driving force mass‐transfer model, yielding good prediction of the kinetic behavior. In fixed bed column experiments, the breakthrough curves of R‐MA from the solution on resin HZ202 were determined at different flow rates and R‐MA was eluted with different concentrations of HCl. A favorable breakthrough curve and optimal eluant concentration were obtained. The results were used for the separation of R‐MA biosynthesized from (R,S)‐mandelonitrile with nitrilase, and separation was successfully achieved with above 90% recovery yield. CONCLUSION: Resin HZ202 presents favorable behavior for the recovery of R‐MA, in terms of capacity, kinetics, affinity, and susceptibility to regeneration. The results of this study provide an efficient method for R‐MA recovery from bioreaction mixture and could potentially be used in industry. Copyright © 2010 Society of Chemical Industry     

REVIEW OF REVERSE OSMOSIS MEMBRANES AND TRANSPORT MODELS

After a brief introduction to membrane processes in general, and the reverse osmosis process in particular, the structure and properties of membranes and membrane transport theory are described. The mechanism of salt rejection and transport properties of membranes are discussed in detail. Solubility, diffusivity, and permeability of membranes to solutes and solvents are reviewed critically and compared with each other. Special attention is given to two particular types of membranes, cellulose acetate (CA) and aromatic polyamide (AP) membranes, which are often used for water desalination.

The major portion of this article is devoted to the review and discussion of membrane transport theory with application to the reverse osmosis and ultrafiltralion processes. It is shown that the solvent flux can be represented reasonably well by linear models such as the solution-diffusion model (Lonsdale, et al., 1965). The contribution of pore flow to the solvent flux is small. The solute flux, however, is not linearly dependent on the driving forces and one has to solve the differential equation of transport within the membrane which results in models such as the Spiegler-Kedem (1966) or the finely-porous (Merten, 1966) models. When the wall Peclet number is small, Pe_w =uτδ/D_sw ?1, (D_sw = bD_e one can linearize the nonlinear models. This requirement is not satisfied in most practical cases. Furthermore, the pore flow has significant effect on the solute flux equation and thus it can not be neglected.

The ambiguities that exist in the literature concerning the types of fluxes are discussed. The fluxes used in models derived from irreversible thermodynamics are purely diffusive (concentration and pressure diffusion) and they do not contain any convective effects; whereas the experimentally observed fluxes are the total fluxes with respect to the membrane which consist of a diffusive flux and a convective flux. A new model, based on irreversible thermodynamics, is derived which includes a convective term.

A membrane model is especially useful when the transport coefficients which define the model are not functions of the driving forces, i.e., pressure and concentration gradients. The coefficients in the solution diffusion and sotution-diffusion-imperfection (Sherwood, et al., 1967) models are functions of both pressure and concentration, while the coefficients in the Kedem-Katchalsky (1958) model are relatively insensitive to pressure and concentration. The nonlinear model of Spiegler-Kedem (1966) further improves the Kedem-Katchalsky model.     

Non-Newtonian Flow for Retention Control in Field-Flow Fractionation

Abstract

Retention in field-flow fractionation (FFF) can be altered and controlled by the introduction of different kinds of velocity profiles in the FFF channel. Here we propose the use of non-Newtonian fluid flow to manipulate retention in FFF. The flexible, three parameter Ellis equation, describing non-Newtonian behavior, is used to derive the dependence of retention ratio R on the dimensionless mean solute layer thickness λ. Numerical calculations show the way in which changes in the parameters of the Ellis equation change the velocity profile in the channel and therefore the shape of the R versus λ functions.     

Reverse osmosis separation of amino acids in aqueous solutions using porous cellulose acetate membranes

Polar and steric effects together govern the reverse osmosis separation of amino acids in single-solute aqueous solution systems. The solute transport parameter for the completely ionized aliphatic amino acids (with no additional polar groups other than one ? NH₂ and one ? COOH) in the pK₁ range of 4.03 to 1.71 can be represented as a function of pK₁ and the steric parameter ΣE_s. The latter parameter has a relatively greater influence with respect to the separation of zwitter ions. The effect of the polar parameter pK₁ on solute separation increases with increase in the concentration of the ionic species R⁺ (or decrease in the concentration of the ionic species R^?) in the feed solution. The effect of the presence of additional polar groups in the amino acid molecule is to increase its basicity. Experiments with p-aminobenzoic acid solutions indicate that the undissociated acid is preferentially sorbed at the membrane–solution interface. With respect to both aliphatic and aromatic amino acid ions, solute separation is in the order R^? > R^± > R⁺ for the cellulose acetate membrane material studied.     

Friction factor-Reynolds number relationship for laminar flow of non-Newtonian fluids in open channels of different cross-sectional shapes

The effect of channel shape on the friction factor-Reynolds number relationship for laminar, open channel flow of three non-Newtonian fluids was investigated. For each channel shape, the data can be described by a general relationship, f=K/Re where f is the Fanning friction factor and Re is the appropriate Haldenwang et al. (2002) Reynolds number corresponding to the flow curve model used to describe the non-Newtonian behaviour exhibited by the test fluid. The K values were found to be 14.6 for triangular channels with a vertex angle of 90°, 16.2 for semi-circular channels, 16.4 for rectangular channels and 17.6 for trapezoidal channels with 60° sides. These K values were found to be in line with those reported by Straub et al. (1958) and Chow (1959) for open channel flow of Newtonian fluids as opposed to the assumption made by Haldenwang et al., 2002, Haldenwang et al., 2004 of using a constant value of 16 based on the pipe flow paradigm for all channel shapes.     

A study on the determination of burning velocities of LFG and LFG-mixed fuels

Numerical and experimental studies on the determination of burning velocities of landfill gas (LFG) fuel and LFG-mixed fuel with LPG have been conducted. The propriety of numerical results is inspected for the adopted GRI-v2.11 and two C3 reaction mechanisms separately developed by Sung et al. and Qin et al. The predicted burning velocities using the C3 reaction mechanism suggested by Sung et al. are in good agreement with the present and previous experimental data. Based on numerical results, the correlation formula of maximum burning velocities of LFG fuel and LFG-mixed fuel with LPG is proposed as a function of the blending percentage of CH₄ and LFG at Φ=1.0. In addition, the correlations of burning velocities of LFG fuel and LFG-mixed fuel with LPG are obtained over a wide range of equivalence ratio. The proposed correlation formulas of burning velocities for LFG fuel and LFG-mixed fuel with LPG are quite well in accord with numerical results.     

Simulation of particles and gas flow behavior in a riser using a filtered two-fluid model

Flow behavior of gas and particles is predicted by a filtered two-fluid model by taking into the effect of particle clustering on the interphase momentum-transfer account. The filtered gas–solid two-fluid model is proposed on the basis of the kinetic theory of granular flow. The subgrid closures for the solid pressure and drag coefficient (Andrews et al., 2005) and the solid viscosity (Riber et al., 2009) are used in the filtered two-fluid model. The model predicts the heterogeneous particle flow structure, and the distributions of gas and particle velocities and turbulent intensities. Simulated solids concentration and mass fluxes are in agreement with experimental data. Predicted effective solid phase viscosity and pressure increase with the increase of model constant c_g and c_s. At the low concentration of particles, simulations indicate that the anisotropy is obvious in the riser. Simulations show the subgrid closures for viscosity of gas phase and solid phase led to a qualitative change in the simulation results.     

Three‐dimensional isothermal simulation of PP melt flow in laminating‐multiplying elements based on the finite element method

The laminating‐multiplying element (LME) with a high aspect ratio used in coextrusion process is highly desired since it has useful applications for the preparation of multilayer sheets or membranes. In this article, the flow behaviors of a polymeric melt through a high aspect ratio LME channel was simulated by the finite element method and verified by a coextrusion process. The results showed that the velocity Y distortion in LME lead to the interface deformation and the interface deformation can be improved by reducing the velocity Y gradient via decreasing the inlet flow rate or increasing the wall slip. POLYM. ENG. SCI., 59:973–981, 2019. © 2019 Society of Plastics Engineers     

Synthesis and characterization of chitosan‐graft‐poly(acrylic acid)/nontronite hydrogel composites based on a design of experiments

A 2^4–1 fractional factorial design was used to evaluate the effect of some parameters, such as the acrylic acid (AA)/chitosan (CTS) molar ratio, crosslinker concentration, initiator concentration, and filler concentration, in the swelling capacity of superabsorbent hydrogel composites based on CTS‐graft‐poly(acrylic acid) and nontronite clay. The data from wide‐angle X‐ray scattering and Fourier transform infrared spectroscopy confirmed the syntheses of the hydrogel composites. Main and interaction effects were analyzed by analysis of variance, F tests, and p values. We found that the AA/CTS and crosslinker were the most influential effects in the evaluated response. The proposed statistical model presented a high coefficient of determination (R² = 0.985). In addition to the swelling kinetics, the effects of pH and salt for the both compositions (with and without filler), which presented the best water uptake, were evaluated. Both hydrogels showed responsive behavior in relation to the pH and the salt solution, presenting good potential for application as devices in the controlled release of solutes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Comparison of optimal and model cascades for the separation of multicomponent mixtures at arbitrary stage enrichments

A method in which the model-matched abundance ratio (R) cascade to be designed at given concentrations of the target component in the product and waste streams is optimized using the parameter M*, defined as the half-sum of the values of the mass numbers of the target and reference components, is proposed. The comparison between the overall characteristics of the R cascade optimized using the parameter M* and minimal-total-flow cascade shows that they are close to each other. The conclusion that the parameters of the optimized R cascade for separating multicomponent isotope mixtures are reasonable to use as the initial approximation in determining the optimal parameters of multistage separation cascades with a given concentration of the lightest or heaviest target component in output streams is made     

Frequency distributions of breaking load,tenacity, and ratio of cell wall thickness to ribbon width for single cotton fibers

Analysis of the frequency distributions of breaking load, tenacity, and ratio of cell wall thickness to ribbon width (C/R) for single cotton fibers in this study has indicated that they can all be represented by β-distributions. This suggests that a parallel model of element configurations exists in which there is a uniform distribution of elemental strengths in single cotton fibers before as well as after slack mercerization. In the case of breaking load and tenacity, the distributions are positively skewed and the skewness decreases on slack mercerization, suggesting that quite a few potentially weak places have been either completely removed or at least strengthened. The changes in C/R ratio on slack mercerization for cottons having a range of maturity have been examined and discussed. The dependence of properties such as breaking load, tenacity, and linear density on cell wall to ribbon width ratio (C/R) have also been studied.     

Scale-up of mixing in gassed multi-turbine agitated vessels

A mixing model previously developed for the determination of mixing time in gassed tanks stirred by multiple Rushton turbines (Vasconcelos et al., 1995) was verified for the additional scales of 0.39, 0.56 and 0.72 m vessel diameter. It is now shown that the single adjusted parameter previously required by the model, the air-induced axial velocity parameter v_ax, is scale-independent with an invariant value of 7 × 10^?2 m/s. Model simulations, with tank and turbine diameters and the number of stages as the only required parameters, deviate 5% on average from the experimentally determined mixing time t_0.05. The model is thus a valuable tool for scale-up of this type of vessels.     

Estimation of solubility parameter components of solutes and polymers using heat of vaporization and heat of sorption of solutes

In a recent study, a two‐dimensional solubility parameter model was used to correlate the heat of solution for solutes ranging from n‐alkanes to alcohols, dissolved in isotatic polypropylene (PP), poly(ethyl ethylene) (PEE), and poly(dimethylsiloxane) (PDMS). When literature data of solubility parameter components of solutes were used, the correlation had some scattering for solutes with low values of cohesive energy density. In this study, the components of solubility parameters of solutes and polymers were estimated from cohesive energy and heat of sorption of solutes. Good correlation was obtained for the specific heat of sorption (ΔU_sorp/V) for solutes ranging from n‐alkanes to alcohols, and PDMS had a polar component as previously estimated. Free volume effect in solution process may be the source of a small systematic deviation from the model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009