Eiji Iritani

Upward Dead-End Ultrafiltration of Binary Protein Mixtures

Abstract Upward dead-end ultrafiltration of aqueous solutions of mixtures of bovine serum albumin (BSA) and egg white lysozyme was conducted using membranes which are almost completely retentive for BSA but permeable for lysozyme. The dependence of lysozyme rejection and the filtration flux rate on pH and the addition of salts has been investigated. The experimental data obtained in this study clearly demonstrate that the electrostatic interactions between dissimilar molecules may control the solute rejection and the filtration rate in upward ultrafiltration of binary protein mixtures. For instance, the BSA and lysozyme molecules have opposite electric charges at pH 7. Consequently, lysozyme rejection is large because both molecules within the filter cake pack more tightly due to heterocoagulation. On the other hand, the BSA and lysozyme molecules have the same electric charge at pH 4. Thus, lysozyme is rejected by the filter cake of the retained BSA molecules due to repulsive electrostatic interactions b...

Flux decline behavior in dead-end microfiltration of protein solutions

Constant pressure microfiltration of solutions of the protein bovine serum albumin (BSA) has been studied in a batch filtration cell without stirring. Flow resistance increased dramatically with time compared with the initial membrane resistance while most of the solutes passed through the membrane. The variation of the filtration flux rate with time during extended filtration periods could not be analysed by a unique blocking filtration law. The long-term decline in the filtration rate was accurately described by considering the variation of the value of the exponent i in the general characteristic form of the blocking filtration laws. It was found that the value of i continued to decrease with the progress of filtration. In addition, the effects on the filtration rate due to the solution pH, the filtration pressure, the fluid solute concentration, and the membrane type were described based on the general characteristic form of the blocking filtration laws.

A Review on Modeling of Pore-Blocking Behaviors of Membranes During Pressurized Membrane Filtration

Pore blocking is one of the critical factors governing the overall performance of membrane filtration systems. Pore blockage leads to a large resistance to filtration, giving rise to a sharp decline in the filtrate flux rate under constant pressure conditions and a severe increase in the pressure for operation under constant flux conditions during membrane filtration. In membrane filtration work, blocking filtration laws are widely used to interpret the membrane fouling in membrane filtration. This article presents a systematic review on the theoretical developments of mechanistic models related to the blocking filtration laws for describing the membrane fouling in membrane filtration. Equations for constant pressure and constant flux separations in the interstices of a membrane and on the surface are reported for the filtrate flow of Newtonian and power-law non-Newtonian fluids. The blocking filtration laws are useful also in the evaluation of the reduced pore size, maximum filtrate volume, and fouling potential. Moreover, the combined models are reviewed for a more complete, rigorous description of complicated behaviors of membrane fouling in which more than one mechanism operating successively or simultaneously is controlled.

Influence of protein adsorption on flow resistance of microfiltration membrane

Abstract It is well known that the flow resistance and sieving property of a membrane change when protein adsorption, which is a specific interaction between the protein and membrane, occurs within the pores. The influence of the protein adsorption on the membrane hydraulic permeability was examined using bovine serum albumin (BSA) as the model protein and a nitrocellulose microfiltration membrane. The Kozeny—Carman equation, which has been applied to the laminar flow in a granular bed, was employed for the description of the flow property of the tortuous pore membranes. The flow resistance of the membrane after BSA adsorption was well evaluated from the reduced porosity due to the protein adsorption in the pores. Also, the equivalent diameter of the pore space of both the clean and preadsorbed membranes was evaluated by introducing the expression for the hydraulic mean diameter. Furthermore, it was found that a more significant protein adsorption at around the isoelectric point brings about a larger increase of the flow resistance of the preadsorbed membrane.

Analysis of dead-end ultrafiltration based on ultracentrifugation method

Abstract In order to clarify the internal structures of the filter cake formed in protein ultrafiltration, ultracentrifugation experiments were conducted. The local specific flow resistance at the various solution concentrations was determined by the sedimentation velocity technique. The porosity was related to the solute compressive pressure by the high-speed sedimentation equilibrium technique. A method has been developed for evaluating the internal structures in the cake on the basis of a compressible cake resistance model using ultracentrifugation data. The decline in the filtration rate in dead-end ultrafiltration was accounted for by considering the internal structures of the compressible cake. The properties of the cake were determined from ultrafiltration experiments in which a filter was subjected to a sudden reduction in its filtration area. The results accorded well with the calculations. This study revealed that the filtration behavior of ultrafiltration can be accurately described by a compressible cake resistance model.

Measurements and evaluation of concentration distributions in filter cake formed in dead-end ultrafiltration of protein solutions

Abstract To clarify the internal structures of the filter cake formed on the membrane surface in protein ultrafiltration, a method has been developed for measuring the variations of protein concentration across the filter cake on the basis of the principle of inclined ultrafiltration, where the membrane was inclined and a large amount of filter cake was formed, and the results were compared with the calculations based on a compressible cake filtration model, which explicitly took the non-homogeneity and the compressibility of the filter cake into account. The experimental results obtained from ultrafiltration of bovine serum albumin (BSA) solutions under constant pressure conditions clearly demonstrated that the filter cake tended to have a much more compact structure at the membrane in comparison with a relatively loose condition at the surface. It was also found that the thickness of the filter cake formed on the membrane increased as the filtration progressed. Further, the effects of pH and the solute concentration in the feed solution on the structure of the filter cake have been examined experimentally. The measured concentration distributions accorded well with the calculated results based on a compressible cake filtration model. This study revealed that the dynamic deposition behaviors of the protein molecules in dead-end ultrafiltration could be accurately described by a compressible cake filtration model.

Effects of pH and solvent density on dead-end upward ultrafiltration

Abstract Upward ultrafiltration experiments, in which the filtrate flow is in the opposite direction of gravity, were conducted under a constant pressure of 98 kPa, using a dead-end filter. The filtration characteristics were studied using a protein (bovine serum albumin) solution of 0.6 wt.% to determine the effects of the solvent environment such as pH and the density of the solvent. A dynamically balanced rate of filtration can be obtained by this newly developed technique. This filtration rate ranges from 3.0 × 10 −4 cm/sec to 1.04 × 10 −3 cm/sec depending on the pH of the solution, with a distinct minimum near the isoelectric point (ca. 5.1). The results obtained from downward ultrafiltration experiments conducted by a batchwise filter having a sudden reduction in its filtration area show that a very compact gel-cake with an average porosity of 0.902, which is not exfoliated easily, forms on the membrane surface at the isoelectric pH. The dynamically balanced filtration rate in upward ultrafiltration is shown to be largely determined by the density of the solvent. A method was developed for determining the buoyant density of protein solutes on the basis of the results of upward ultrafiltration experiments performed at different values of the density of the solvent; a value of about 1.27 g/cm 3 was obtained for bovine serum albumin.

Effects of electric field on dynamic behaviors of dead-end inclined and downward ultrafiltration of protein solutions

Abstract The effects of a direct current electric field on the transient and dynamically balanced filtration rate in dead-end inclined and downward ultrafiltration were explored under constant pressure using protein (bovine serum albumin) solution. It is found that, in downward electro-ultrafiltration, the dynamically balanced filtration rate q e is directly proportional to the electric field strength E . Also, in inclined electro-ultrafiltration, q e increases with E above the critical electric field strength E c . However, q e becomes invariant below E c . The model was developed to describe the processes occurring during inclined and downward electro-ultrafiltration, and it accounted well for the variation in filtration rate with time.

Separation of binary protein mixtures by ultrafiltration

Ultrafiltration of aqueous solutions of mixtures of bovine serum albumin(BSA) and egg white lysozyme was conducted using membranes which were almost completely retentive for BSA, but permeable for lysozyme, in order to investigate the factors influencing the filtration rate and the lysozyme rejection. The experimental data obtained in this study clearly demonstrate that the electrostatic interactions between dissimilar molecules may control the filtration rate and solute rejection in ultrafiltration of binary protein mixtures to a significant degree. It is also shown that increasing the shear stress acting on the membrane causes an increase in the lysozyme rejection, resulting in a reduced fractionation efficiency, and that ultrasonic irradiation is quite effective for fractionation of binary protein mixtures. Furthermore, the properties of the filter cake formed on the retentive membranes in downward dead-end ultrafiltration of binary protein mixtures have been studied in a batchwise filter which has a sudden reduction in its filtration area. In the pH range where both proteins are electropositive, the filter cake becomes loose and wet, thus reducing the flow resistance, while the cake becomes compact and dry in the pH range where the two proteins have opposite electrical charges.

Fractionation Characteristics of Binary Protein Mixtures by Ultrafiltration

ABSTRACT Ultrafiltration (UF) of mixtures of bovine serum albumin (BSA) and egg white lysozyme was conducted using membranes which were almost completely retentive for BSA but permeable for lysozyme. The experimental data have clearly demonstrated that the separation properties of binary protein mixtures are largely influenced by the hydrodynamics above the membrane, the solution environment, and the adsorption of the protein solutes within the membrane. In particular, it must be noted that the increase of the shear stress acting on the membrane surface improves the filtration rate, but causes the increase of the lysozyme rejection, resulting in a reduction in the fractionation efficiency. Furthermore, the effects of ultrasonic irradiation on the UF properties have been tested experimentally. Although the filtration rate was enhanced significantly by ultrasonic irradiation, the lysozyme rejection remained unchanged. The results showed that ultrasonic irradiation is quite effective for protein fractionation.