Effect Of Transmembrane Pressure Research Articles

Insight into the transport of hexane–solute systems through tailor-made composite membranes

This work presents composite membranes comprising poly(acrylonitrile) (PAN) as the support and polydimethylsiloxane (PDMS) as the selective top layer. For sunflower oil/hexane and polyisobutylene (PIB)/hexane, the permeation characteristics of these membranes for various feed concentrations and pressures are studied. For each system, the effect of transmembrane pressure upon the flux and retention of the PAN/PDMS composite membrane is investigated. Osmotic phenomena similar to those of aqueous systems are observed and interpreted using the van’t Hoff equation. The hexane flux increases linearly with the applied pressure and the solution-diffusion model seems to describe satisfactory the aspects of its transport to these systems. The hexane permeability decreases with the increase of the feed concentration. Its normalization by the viscosity inside the swollen membrane (according to the Stokes–Einstein diffusion phenomenon) and the swelling degree of the membrane results in a constant value quantifying the hexane transport independent of the solute present in the feed mixture. The flux of the solute (oil or PIB) increases linearly with the applied pressure as well, especially at low feed concentrations when the membrane swelling is higher, indicating coupling of solute transport to solvent flux. For the same feed solution concentration, the effect of flux coupling (solvent-induced solute dragging) decreases with the molecular weight of the solute. Ultimately, when the applied pressure increases; the increase of hexane flux is much higher than the corresponding solute (oil or PIB) flux resulting to an increase of the membrane retention.

Study of fouling mechanism in pineapple juice clarification by ultrafiltration

The flux behavior of ceramic and polysulfone membranes was examined during cross-flow ultrafiltration (UF) of depectinized pineapple juice. The effects of transmembrane pressure (TMP) and temperature on membrane fouling have been evaluated. The observed flux decay was modeled using a modified form of the differential equation used to describe classical dead-end filtration process. The mechanism of fouling during the cross-flow ultrafiltration was identified by estimation of the parameters model according to a nonlinear regression optimization procedure. Analysis of the results revealed that hollow fiber membrane separation process is controlled by a cake filtration mechanism and a pore blocking fouling mechanism controls ceramic tubular membrane. The model parameter k was modeled as a temperature and transmembrane pressure function for each combination juice-membrane. The main physical chemistry properties of pineapple juice were evaluated in order to determine the condition that supply the highest permeated flux and best clarified juice.

CROSSFLOW FILTRATION OF BRINE FROM CUCUMBER FERMENTATION+

Due to environmental concerns, pickle companies are considering ways of reclaiming the brine obtained fromcucumber fermentation. The removal of microbial cells is crucial in use of the brine in finished pickle products. The effectsof transmembrane pressure (41 to 166 kPa), feed flow rate (7.8 to 15.5 L/min), pore size (500,000 NWCO and 0.2 .m), andcell concentration (optical density of 0.171 to 1.170 at 640 nm) on permeate flux during the crossflow filtration of brineobtained from bulk fermentation of cucumber were studied. Results indicate that the microfiltration membranes exhibited alarge flux decline during the first 15 min of operation when challenged with the fermentation brine. The net decline inpermeate flux increased with transmembrane pressure, flow velocity, pore size, and cell concentration. Filtration throughfilter pore size of 0.2 .m or smaller effectively removed the microbial cells present in the brine. Only the transmembranepressure significantly affected the resistance of the cake formed at the filter surface. From the results obtained from the study,it is possible to use microfiltration to filter sediments and microbial cells from brine obtained from cucumber fermentation.

Membrane fouling during cross-flow microfiltration of Polyporus squamosus fermentation broth

The application of microfiltration to biological systems is hindered by membrane fouling that results in a decrease in the filtrate flux and solute transmission with time. In this work, the effects of transmembrane pressure, cross-flow feed velocity, biomass structure and feed composition, on membrane fouling during cross-flow microfiltration of Polyporus squamosus fermentation broth, were investigated. The results of cross-flow trials with 0.2 μm aluminum oxide membrane showed the existence of the optimal operation transmembrane pressure and cross-flow velocity, in respect of membrane fouling, for examined range of operation conditions. It was noticed that the process of membrane fouling was moved from a predominantly surface layer phenomenon to internal membrane fouling as the cross-flow velocity was increased. Comminution of the fungal biomass prior to microfiltration to reduce particle size showed a beneficial effect on the transient flux. The steady-state flux and the transmission of solutes were not significantly affected by the biomass comminution. The observations of the filtrate flux and the transmission of solutes indicated a decrease in the rate of fouling with decreasing content of soluble components with large molecular weights in the feed.

Separation of the protease enzymes of Bacillus licheniformis from the fermentation medium by crossflow ultrafiltration

The separation from fermentation medium of extracellular serine alkaline protease (SAP) enzyme produced by Bacillus licheniformis was investigated using a crossflow ultrafiltration system. SAP was separated from the high molecular weight neutral protease (NP) and amylase (AMY) enzymes and from the low molecular weight organic acids and amino acids in a crossflow ultrafiltration system with 30 000 Da and 10 000 Da MWCO polysulfone membranes, respectively. The effects of transmembrane pressure (TMP), recirculation velocity (v), and initial enzyme concentration (CE) on the permeate flux, on the activities of SAP, NP and AMY enzymes, and on the recovery of SAP were investigated. High permeate flux was obtained at high recirculation velocity and TMP, but at low initial enzyme concentration. SAP enzyme recovery and activity measured in the system also showed alterations with hydrodynamic conditions. The best operation conditions for the separation of SAP from NP and AMY were TMP = 20 kPa, v = 0.50 ms−1 and CE = 0.28 gdm−3. The separation of SAP from the organic and amino acids was best performed at TMP = 100 kPa, v = 0.33 ms−1 and CE = 0.40 gdm−3. © 2000 Society of Chemical Industry

Membrane ultrafiltration in a tubular module with a steel rod inserted concentrically for improved performance

Rising fluid velocity in the tubular-membrane module by inserting concentrically a steel rod has two conflicting effects. One, the decrease in resistance to permeation due to reduction in concentration polarization, is good for ultrafiltration, while the other, the decrease in average transmembrane pressure due to increase in friction pressure loss, is bad for ultrafiltration. It appears, therefore, that proper adjustment of fluid velocity as well as proper arrangement of the annular size of flow channel with a specified volumetric feed rate, might effectively suppress any undesirable resistance to permeation while still preserving an effective transmembrane pressure and thereby lead to improved performance of membrane ultrafiltration. It was found that considerable improvement in permeate flux is obtainable by employing such a modified tubular module rather than using the open tubular module without an inner tube. The enlargement of power consumption for fluid flow due to the insertion of an inner tube has been also discussed. The improved performance has been checked at same hydraulic dissipated power.

Separation of the protease enzymes ofBacillus licheniformis from the fermentation medium by crossflow ultrafiltration

The separation from fermentation medium of extracellular serine alkaline protease (SAP) enzyme produced by Bacillus licheniformis was investigated using a crossflow ultrafiltration system. SAP was separated from the high molecular weight neutral protease (NP) and amylase (AMY) enzymes and from the low molecular weight organic acids and amino acids in a crossflow ultrafiltration system with 30 000 Da and 10 000 Da MWCO polysulfone membranes, respectively. The effects of transmembrane pressure (TMP), recirculation velocity (v), and initial enzyme concentration (CE) on the permeate flux, on the activities of SAP, NP and AMY enzymes, and on the recovery of SAP were investigated. High permeate flux was obtained at high recirculation velocity and TMP, but at low initial enzyme concentration. SAP enzyme recovery and activity measured in the system also showed alterations with hydrodynamic conditions. The best operation conditions for the separation of SAP from NP and AMY were TMP = 20 kPa, v = 0.50 ms−1 and CE = 0.28 gdm−3. The separation of SAP from the organic and amino acids was best performed at TMP = 100 kPa, v = 0.33 ms−1 and CE = 0.40 gdm−3. © 2000 Society of Chemical Industry

Demulsification of water-in-oil emulsion by using porous glass membrane

The hydrophilic porous glass membranes were used to demulsify water-in-oil emulsion, and demulsification efficiency can reach more than 96.2%. Effects of pore size of the membrane, transmembrane pressure and volumetric ratio of oil phase to internal aqueous phase in the emulsion on demulsification were investigated. It was found that pore size of membrane and transmembrane pressure can significantly affect demulsification efficiency. The smaller the pore size of the membrane, the better the demulsification efficiency. However, smaller pore size of the membrane has to be exerted a greater transmembrane pressure in order to make internal aqueous phase enter the membrane pore. Correspondingly, effect of transmembrane pressure on permeation flux of the droplets was also studied. In addition, recovered-oil phase by the demulsification were reused five times to extract cadmium from simulated aqueous waste. The results indicated that the extracting efficiency could arrive at 96.5%.

Modelling and simulation of membrane fouling in batch ultrafiltration on pilot plant

In order to control membrane fouling, a batch ultrafiltration was used to study the reduction in membrane permeability in turbulent flow. A model of the process was developped on pilot plant as function of time, taking into account the non uniformities in flow, cake deposits along the length of the channel. The model predictions compared to the experimental results for ultrafiltration of bentonite solutes shows a good agreement. The effect of transmembrane pressure on the filtration has been studied.

Membrane ultrafiltration in multipass hollow-fiber modules

Rising fluid velocity in the fiber tubes of a hollow-fiber module has two conflicting effects. One, the decrease in resistance to permeation due to reduction in concentration polarization, is good for ultrafiltration, while the other, the decrease in average transmembrane pressure due to increase in frictional pressure loss, is bad for ultrafiltration. It appears, therefore, that proper adjustment of fluid velocity as well as proper arrangement of the number of fiber passes in a hollow-fiber module of fixed total hollow fibers, might effectively suppress the undesirable resistance to permeation while still preserving an effective transmembrane pressure and thereby lead to improved performance of membrane ultrafiltration. It was found that considerable improvement in ultrafiltration is obtainable by employing a multipass hollow-fiber membrane module rather than using the one with only single fiber pass and with the same total fibers, especially for a dilute solution ultrafiltered with low volumetric flow rate and under high transmembrane pressure.

Pressure effects in cross-flow microfiltration of suspensions of whole bacterial cells

The effect of Trans-Membrane Pressure (TMP) on permeate flux during cross-flow microfiltration of bacterial cell suspensions in tubular ceramic membranes is studied experimentally. Continuous filtration experiments with suspensions of whole bacterial cells (Mycobacterium M156) show a dramatic permeate flux decline with increasing TMP. During the very early stages of the filtration process, a linear relationship between permeate flux and TMP is observed, suggesting an initial surface sorption of cells on the membrane surface. At longer times, the permeate flux vs. TMP data exhibit a critical pressure beyond which the permeate flux declines with increasing trans-membrane pressure. This is interpreted in terms of the formation of a compressible cake, whose permeability can be described through the Carman-Kozeny equation.

Selective Strontium Removal from a Sodium Nitrate Aqueous Medium by Nanofiltration - Complexation

In aqueous medium, selective complexation increases the ionic separation by nanofiltration. The combination of nanofiltration and complexation can be applied to the nuclear effluents treatment. To separate radioelements from a sodium salt medium, poly(acrylic acid) is associated to the FILMTEC NF 70 membrane. Effects of transmembrane pressure, pH, ligand concentration and ionic strength on salts retention are described, and the complexation constants are estimated. Finally, to reach the objectives, a strontium two - stages concentration by nanofiltration - complexation with a control of retentate salinity is investigated in a nonactive solution case.

Microfiltration of oil‐in‐water emulsions

Effects of transmembrane pressure and membrane pore size on the microfiltration of oil‐in‐water emulsions are reported. A model for calculating the critical pressure required to force the entry of an oil drop into a membrane pore is formulated based on the Young‐Laplace equation and serves as the basis for analyzing the rejection of emulsified materials by microfiltration membranes. This critical pressure appears to be a reasonable predictor of the operating pressure at which oil drops are no longer rejected by the membrane and their penetaration leads to membrane fouling.

Membrane performance with plug screw feeder pressate: operating conditions and membrane properties

Membrane performance can be significantly affected by operating conditions. The effects of transmembrane pressure and cross flow velocity are discussed for various membranes during ultrafiltration of a pulp mill effluent. The effluent contained suspended solids, colloidal particles such as resin and fatty acids and materials with a wide molecular weight distribution. This effluent had severe membrane fouling characteristics, the nature of which complicated interpretation of the results. A variety of commerically available membranes made with different polymers and pore sizes were evaluated. Permeation experiments were performed using thin-channel, flat sheet, test cells. Cross-flow velocities varied from 0.4 to 1.2 m/s and the transmembrane pressure from 345 to 1,035 kPa. Flux decline occurred by several mechanisms and the selection of the membrane material, pore size and the operating conditions determined the relative contribution of these mechanisms. A modified series resistance model using flux loss ratios qualitatively explained changes in membrane performance under different operating conditions.

PILOT-SCALE ULTRAFILTRATION OF CONCENTRATED PROTEIN PRECIPITATE SUSPENSIONS: THE EFFECT OF CONCENTRATION AND FLUID DYNAMICS

Abstract The effects of transmembrane pressure (TMP) and trans-cartridge pressure drops on the concentration of protein precipitate suspensions are evaluated in a hollow fibre device. A sharp decline in the filtrate flux occurs above a critical concentration, the value of which depends on the hydrodynamic operating conditions, and this is shown to coincide with the system entering a state of pressure-independent flux, commonly known as “gel polarization”. The effect of TMP, cross-flow velocity and concentration on the onset of pressure independence are examined in more detail in a series of nitrations carried out at constant concentration. Increasing cross-flow velocity enhanced fluxes for a given TMP in accordance with the standard film model, but increasing concentration was found unexpectedly to enhance fluxes at relatively low concentrations. Two possible explanations for this are discussed; one depends on the interaction of the large protein precipitate aggregates with the soluble protein and one on ...

Metal Recovery from Wastewater Using Membranes

This paper outlines the requirements for metal recovery from wastewater, with particular reference to electroplating. The technical features of three alternative membrane processes are described. Nanofiltration is shown to separate ionic species on the basis of coulombic interactions or hydrated ion size, which leads to either a ‘charge' pattern or a ‘hydration' pattern of rejection. These rejection patterns provide ion selectivity. Ultrafiltration (UF), coupled with ion-complexing polymers or ion exchange resin, also provides efficient removal of metal ions, at high flux. The effectiveness of the UF-resin process is considerably increased as the resin size is decreased. Solvent extraction in a Liquid Membrane Contactor (LMC), which is based on microporous hollow fibre modules with aqueous and organic phases circulating through the shell or fibre lumens, achieves high fluxes of metal ions. A limitation of the LMC is the need to avoid phase leakage. The factors governing the critical displacement pressure and the effective transmembrane pressure are discussed. An LMC with a high packing density of fibres in the shell is preferred. Finally, the paper discusses criteria for selection of ‘user friendly' technologies for the electroplating industry. The membrane technologies, particularly in combined form, score highly except in terms of simplicity. This aspect needs further development.

Cross flow filtration of RNA extracts by hollow fiber membrane

AbstractThe feasibility of using ultrafiltration to concentrate RNA was investigated. Ultrafiltration flux and solute retentivity were affected by membrane cut‐off and inlet pressure.The RNA can be concentrated by selecting a hydraulically permeable membrane (PM 30) and then operating the system at a sufficiently high pressure (2.07 · 105 Nm−2) and a high recirculation rate (150 cm−1). The use of this procedure was limited to a high‐flux regime. However, a very high retentivity of macrosolute was achieved. The effect of transmembrane pressure on the apparent mass transfer coefficient in the “gel polarization model” was discussed and related to ultrafiltration flux.

Cross-flow filtration as a method of separating fungal cells and purifying the polysaccharide produced

Cross-flow filtration (CFF) has been investigated as a method of separating filamentously growing fungal cells and purifying the polysaccharide produced. The effects of transmembrane pressure, module geometry (e.g. channel height or tube diameter), tangential feed velocity and cell as well as polysaccharide concentration are discussed. Apart from these experiments, influences by the recirculation pump used are shown.

RBC membrane instability for large pipette deformation. A theoretical approach.

Under conditions of high pressure difference micropipette aspiration experiments show a "pinch-off" phenomenon as observed by RAND /31/. In a very recent paper, MEIER et. al /9/ have reported about new data obtained with a modern electronic technique under moderate mechanical load. We have theoretically analysed the conditions necessary to form such a instability. In our approximations we have investigated the effective transmembrane pressure difference which is given both by the true pressure drop, determined by the hydrodynamic flow through a small gap between the cell tongue and the pipette wall and the interaction between the tongue and the wall, as well as by the nonisotropic part of the membrane tension. When the membrane tongue is long enough (greater than 3Rp) we have found a condition for the loss of membrane stability in a point where a minimum of the effective transmembrane pressure drop occurs. An expression for it and the vesicle size are given.

Estimation of compaction and fouling effects during membrane processing of cottage cheese whey

Effects of transmembrane pressure on membrane performance and permeate flux were studied using pure water and cottage cheese whey. The transmembrane pressure was varied from 0·8 to 30 bar and the temperature was maintained at 21 ± 1°C. Mechanical deformation and compression of the ultrafiltration membrane used (MW cut-off 25 000 daltons) were considered to be the main factors responsible for the non-linearity of the relationship between processing pressure and water permeate flux rate. During membrane processing of cottage cheese whey, a further deviation from linearity was observed, possibly due to the effect of membrane fouling. Assuming that compaction effects were dependent only on the transmembrane pressure applied and not on the type of liquid being processed, compaction effects appeared to exceed fouling markedly in the pressure range 4–30 bar. Fouling and compaction effects were of the same order at pressures below 3 bar. In spite of the compaction phenomena, no substantial change in total solids flux was observed in membrane processing of cottage cheese whey.