Commercial Microfiltration Research Articles

Transfer characterization of charged particles through charged conductive membrane via dialysis process

In this work the effects of applied electrical charge on mechanism and transfer rate of charged particles through conductive membrane have been elucidated. Another individual parameter which plays a vital role in assigning mechanism and rate of transport is absolute concentration. This is independent from the effect of concentration gradient which is the driving force for mass transfer. In the experimental section, the transfer of sodium dodecyl sulphate (SDS) micelles through charged membrane was investigated. The membrane consisted of a commercial microfiltration (GVHP) membrane as the support coated with a conductive polymer i.e. polypyrrole. A wide range of electrical charges (voltages) were applied on the surface of the conductive membrane. The electrical charge qualitatively and quantitatively influences the mass transfer rate. The difference between transport mechanisms of charged particles at low and high concentrations is more evident in the presence of electrical surface charge. In summary, initial feed concentration, electrical charge and their interactions affect the transport rate and mechanism.

Electrospun cellulose nanofiber as affinity membrane

The objective of this work is to study the feasibility of applying cellulose nanofiber membrane prepared by electrospinning as affinity membrane. Cellulose acetate (CA) solution (0.16 g/ml) in a mixture solvent of acetone/DMF/trifluoroethylene (3:1:1) was electrospun into nonwoven fiber mesh with the fiber diameter ranging from 200 nm to 1 μm. The CA nanofiber mesh was heat treated under 208 °C for 1 h to improve structural integrity and mechanical strength, and then treated in 0.1 M NaOH solution in H 2O/ethanol (4:1) for 24 h to obtain regenerated cellulose (RC) nanofiber mesh, which was used as a novel filtration membrane in this work. The RC nanofiber membrane was further surface functionalized with Cibacron Blue F3GA (CB), a general affinity dye ligand for separation of many biomolecules. The material's chemical and physical properties were studied by SEM, DSC and ATR-FTIR. Water filtration properties of the novel RC membrane were studied and compared with a commercial micro-filtration membrane. The CB derived RC nanofiber membrane has a CB content of 130 μmol/g, and capture capacity of 13 mg/g for bovine serum albumin (BSA) and 4 mg/g for bilirubin. The membrane showed reusability after regeneration with elution buffer. Dynamic adsorption of BSA on the nanofiber membrane was studied by breakthrough curve measurements.

Selection of microporous hydrophobic membranes for use in gas/liquid contactors: An experimental approach

Contactors equipped with hydrophobic porous membranes were widely tested and operated in different separation processes. New applications, e.g. concentration of fruit juice or air conditioning, require a reliable separation of the two contacting phases at a higher level as for common applications in order to avoid product pollution by the liquid absorbent. The application of coated membranes as a liquid tight semipermeable barrier offers the best prerequisites in order to meet this requirement. Because the dense layer of such membranes acts as an additive transport resistance its thickness has to be as thin as possible which requires porous support membranes with the porosity profile of ultrafiltration membranes. Are such support membranes suitable for the application in gas/liquid contactors? In order to find an answer to this question at first a model gas/liquid contactor arrangement was installed and experimentally proved. Applying this arrangement the water vapor permeability of membrane types with ultrafiltration separation characteristics was determined. At the model development a well characterized hollow fiber with microfiltration properties was used. The results show that neglecting the temperature polarization would result in underestimated membrane permeability values. Hence the temperature polarization arising during the absorption process was determined experimentally. By taking the temperature polarization into consideration the calculated membrane permeabilities were in good accordance to literature data. Using this simple model different structured poly(ether imide) hollow fiber membranes with ultrafiltration separation profile were characterized with respect to the water vapor permeability. The results document that these ultrafiltration membranes provide equivalent or even distinctly higher permeabilities than commercial microfiltration membranes. The better performance is related to the asymmetric structure of these membranes. On basis of the obtained results it can be concluded that membranes with ultrafiltration separation profile – which are coatable with a thin coating layer – should be suitable for the preparation of effective contactor membranes without risk of remarkable losses in performance in comparison with uncoated microfiltration membranes. Furthermore the morphology of these membrane types can be tailored to special contactor applications, which require high heat transfer (e.g. osmotic distillation) or low heat transfer (e.g. membrane distillation).

Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd–Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H 2 permeation measurement. Commercial microfiltration ceramic membrane were coated with γ-Al 2O 3-based layer by the sol–gel method and used as substrate of Pd and Pd–Ag alloy film. Both the as-prepared membranes were shown to be He gas-tight at room temperature with a thickness of <1 μm. Permeation results showed that H 2 permeation through these composite membranes is mainly dominated by the surface chemistry of H 2 on or/and in the membranes. The membranes exhibited a high permeation rate of H 2 and a H 2/N 2 permselectivity of higher than 60 in the optimized operation conditions .

Determination of ζ-Potential by Measuring Electroosmotic Flux in an Alternating Electric Field and Its Applications in the Study of Membrane Fouling

A new method for determining the ζ-potential of a membrane or other porous media is proposed in which an alternating electric field is applied in the measurement of the electroosmotic flux. Determination of the apparent ζ-potential of commercial microfiltration membranes was conducted under different alternating frequencies. An increase in the magnitude of ζ-potential is obtained as a result of increased alternating frequency. A dramatic change of the apparent ζ-potential was observed when the membrane was soaked for 24 hours in a solution containing bovine serum albumin (BSA). The magnitude of the ζ-potential approached zero at pH 4.9, which indicated the adsorption of BSA on the membrane surface. When the membrane sample was soaked for 24 hours in a BSA solution containing PEG 4000, a substantial increase in the magnitude of the ζ-potential compared to that in the BSA solution was obtained. In some cases the apparent ζ-potential obtained in the BSA-PEG 4000 solution was up to that obtained in the BSA-free solution. This demonstrated the shielding function of PEG 4000 as described elsewhere. The ζ-potential was shown to be a sensitive indicator of membrane fouling caused by protein adsorption.

Theoretical Analysis of the Effect of Membrane Morphology on Fouling during Microfiltration

Previous studies of membrane fouling have often employed one of the classical blocking laws to describe the variation of filtrate flux with time. However, these models implicitly assume that the membrane has straight-through noninterconnected pores, even though most commercial microfiltration and ultrafiltration membranes have a highly interconnected pore structure. We have developed a theoretical model for the effects of pore blockage on the fluid velocity and pressure profiles within membranes having different interconnected pore structures assuming Darcy flow in the porous membrane. Model calculations are in good agreement with filtrate flux data obtained during protein microfiltration using membranes with very different pore morphologies. The results clearly demonstrate that the membrane pore connectivity has a significant influence on the flux decline due to the possibility for fluid to flow around the pore blockage, an effect which has been ignored in previous studies.

Microcentrifuge‐Based Method for Measuring Water‐Holding of Protein Gels

ABSTRACTA method developed to measure water‐holding properties of protein gels provides high precision and expanded analysis. A cylindrical gel sample was placed in an inner cell (which at its base contained a filter membrane) of a commercial microfiltration unit. The unit was then spun in a horizontal rotor microcentrifuge. Rates of water loss and degree of compression were determined. The rate of water loss could be modeled as the summation of two exponential decay functions. Degree of compression correlated with held‐water. Gel rehydration ability and microstructure were used to study effects of centrifugal compression on gel structure.

Microfiltration membranes, cross-flow transport mechanisms and fouling studies

Microfiltration membranes have been used, in dead-end mode, in gas purification, wine clarification and medical-product sterilization applications. The same types of membrane have been tested even in the cross-flow mode of operation (CFMF), but with less success. Especially a great effort has been made to apply CFMF in the downstream processing of biotechnological applications, like cell harvesting and cell-debris removal. It is recognized that a great deal remains to be done in developing membranes suitable for the cross-flow mode of operation, in such a way that biofouling, seeming to be the main reason hindering the progress of the method, will be minimized. In this paper we will present a literature review we have carried out about the state of the art of microfiltration membranes; their types, methods of preparation and characterization, commercial and potential applications, and theoretical models. Understanding the mechanisms of the transport as well as the phenomena leading to fouling seems to be another prerequisite for the further development of cross-flow microfiltration. This need addresses to the necessity of carrying out studies at a basic level, using well characterized membranes and testing substances. In this paper, we will also present and discuss results, which we have until now obtained, about the performance of selected commercial microfiltration membranes in terms of flux decline and retention properties under varying experimental conditions of transmembrane pressure and circulation velocity. The feed is a model dispersion containing two kind of components: typical biopolymer like BSA protein and silica particles of a size 600-800 nm. These particles were used in order to simulate microorganism, as providing, the size apart, the possibility of varying surface modification. Besides flux decline and pure water flux recovery data, electron microscopy is used in order to study the prevailing fouling mechanisms.