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Transmembrane Pressure (transmembrane + pressure)
Selected AbstractsTandem dialyzers with dual monitors to meet Kt/V targetsHEMODIALYSIS INTERNATIONAL, Issue 1 2005N. Sridhar Objective:,A large body mass and/or a poorly functioning vascular access predispose to inadequate Kt/V. Double dialyzers in parallel and tandem have been shown to enhance Kt/V to levels recommended by K/DOQI. We experienced difficulties with unintended excessive ultrafitration (UF), positive transmembrane pressure (TMP)-triggered pump stoppage, need for large volume saline infusion (inflating Kt/V), and a high incidence of clotting of the second dialyzer in tandem. Since blood and dialysate flow rates are higher in the tandem configuration, Kt/V should be theoretically higher. We developed a technique of using the tandem configuration with two monitors in which all the UF could be limited to the second dialyzer, the TMP of the two dialyzers independently controlled, TMP reversal eliminated, and saline infusion and unintended UF minimized. Methods:,3 large male patients with AV grafts (AVG) and 2 with tunneled catheters (TC) had 7 treatments (with Kt/V and URR calculated using the stop-flow technique in the last 5) sessions of each of single, double parallel, and tandem configurations. Blood (Qb) and dialysate-flow (Qd) were halved with Y-connectors in the parallel configuration. Qb through both dialyzers and Qd through the second were controlled with the first monitor and Qd (TMP set to near zero) through the first dialyzer controlled with the second monitor using recirculating saline through its blood pump (with the "venous" pressure adjusted using an air-filled syringe) in the tandem configuration. The patient's blood did not circulate through the blood-pump of the first machine. Qd was 500 ml/min through each dialyzer in the single and tandem and 250 ml/min in the parallel configurations. Processed blood volume (dialysis time) was exactly 85 L with AVG and 60 L with TC. Heparin dosage was constant. ANOVA, 2 × k tables, and Neuman-Keuls test were used in analyzing data. Results:,Mean Kt/V (%URR) increased from 1.15 (62) with single to 1.35 (68) with parallel (p < 0.02) and 1.48 (71) with tandem (p < 0.001) dialyzers in patients with AVG but not TC [1.05 (58), 1.02 (55), and 1.25 (64) with single, parallel, and tandem, respectively]. Tandem dialyzers met targets for URR (p < 0.001) and Kt/V ( p < 0.05) more frequently than parallel with AVG but not TC. Conclusions:,Tandem dialyzers with 2 monitors are more successful than parallel dialyzers in delivering target Kt/V and URR when Qb is not compromised. [source] Ultrafiltration of industrial waste liquors from the manufacture of soy protein concentratesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Andrés Moure Abstract Protein-containing waste liquors from the manufacture of soy protein concentrates were processed by ultrafiltration to recover soluble protein using three different membranes (with molecular weight cut-offs of 10, 30 and 50 kDa). Operating at 20 °C under reversible conditions, the experimental data of the normalized permeate flux (NPF) obtained at various transmembrane pressures were well described by a model reported in the literature. For each membrane and transmembrane pressure, the values of the parameters involved in the model were calculated. Operating at selected transmembrane pressures, protein rejections of 0.705, 0.747 and 0.637 were determined for the 10, 30 and 50 kDa membranes, respectively. Operation with the 10 kDa membrane at temperatures in the range 30,50 °C and operation with the 30 or 50 kDa membranes at 40 or 50 °C resulted in hysteresis. Copyright © 2006 Society of Chemical Industry [source] Measurement and prediction of the ultrafiltration of whey proteinAICHE JOURNAL, Issue 7 2004M. Davey Abstract Ultrafiltration of proteins and other compressible material is characterized by a significant transmembrane pressure and is often limited by the formation of a fouling layer. This study examines the compressive rheology of such fouling layers. A model is proposed that can be used to predict the performance of filtration processes where there is significant pressure drop across the clean membrane and the filtration rate is limited by fouling during the filtration cycle. The information required for the model can in principle be obtained from simple centrifuge tests and the clean membrane pressure drop. The model can be used to optimize the cycle times, pressures, and other operating parameters of the ultrafiltration process. The model was tested on the ultrafiltration of whey protein concentrate and shown to describe the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1431,1437, 2004 [source] A ceramic microfiltration tube membrane dispersion extractorAICHE JOURNAL, Issue 2 2004G. G. Chen Abstract Although the phase-free membrane extraction process has shown many advantages over the traditional extraction, the process is still at the experimental stage. On the other hand, in a new extractor a microfiltration membrane is used as a dispersion medium. The mass-transfer performance of the new extractor was tested with 30% TBP (in kerosene),nitric acid,H2O as an experimental system. The overall mass-transfer coefficient and the equipment efficiency were calculated with the concentrations of the inlet and outlet. The extractor was designed and constructed with two special inner elements for improving the performance further. The effects of the transmembrane pressure, the continuous-phase flow rate, and the geometric parameters of the inner elements on the mass-transfer performance, as well as on the flux of the dispersion phase, are discussed. The experimental results showed that very higher efficiency was reached. The inner elements could improve the mass-transfer performance greatly by changing the two-phase contact status. The results suggested that the mass-transfer process could be completed quickly while the drop size was in the range of micrometers. In addition, the flux of the dispersed phase was mainly influenced by the transmembrane pressure, not by the equipment structures, inner elements, and the continuous-phase flow rate. The new extractor can be operated with very higher efficiency and higher flux, and the efficiency can be predicted with a cubic polynomial. © 2004 American Institute of Chemical Engineers AIChE J, 50: 382,387, 2004 [source] Design Considerations for Plate and Frame Ultrafiltration Modules by Computational Fluid Dynamics Analysis,THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2006Mauro M. Dal-Cin Abstract Pressure and flow maldistributions were studied in a full-scale industrial plate and frame ultrafiltration module, operating in a Z flow pattern, for the recovery of used motor oils. Solutions were obtained using (1) a three-dimensional solution of the Navier-Stokes equation using computational fluid dynamics and (2) Bernoulli's equation and a momentum balance in one dimension. Fluid decelerations and accelerations generated pressure increases and decreases in the distributor and collector, respectively, biasing the flow distribution to the last channel. Several modifications to the original design were evaluated; the most effective was larger distributor and collector diameters, which greatly improved the uniformity of the flow distribution and transmembrane pressure, and reduced the overall pressure drop in a bank. A variable diameter distributor and collector module was designed using the 1-D model. Flow distribution was significantly improved but also yielded an undesirable overall higher pressure drop and a pressure maldistribution in the bank. The maldistribution of the main inlet manifold to the distributors in the first bank was strongly dependent on the module design. The flow distribution across the width of a channel became uniform within a short distance, essentially eliminating the need to consider this design aspect any further. Flows at the bank outlets, and hence inlets of the following bank, showed uniform lateral distribution in all cases, suggesting that future modelling work can be limited to a fraction of the module width, based on symmetry, in order to gain computational efficiency. On a étudié les mauvaises distributions de pression et d'écoulement dans un module d'ultrafiltration à plateaux et à cadres à l'échelle industrielle, fonctionnant dans un schéma d'écoulement en Z, pour la récupération des huiles de moteurs usées. Des solutions ont été obtenues avec (1) une solution tridimensionnelle de l'équation de Navier-Stokes utilisant la mécanique des fluides par ordinateur, et (2) l'équation de Bernoulli et un bilan de quantité de mouvement unidimensionnel. Les décélérations et accélérations de fluide entraînent des augmentations et diminutions de pression dans le distributeur et le collecteur, respectivement, ce qui fausse la distribution d'écoulement dans le dernier canal. On a évalué plusieurs modifications du concept original; la plus efficace sont des diamètres de distributeur et de collecteur plus larges, qui permettent d'améliorer grandement l'uniformité de la distribution d'écoulement et la pression transmembranaire, et qui réduisent la perte de charge globale dans une batterie. Un module de distributeur et de collecteur de diamètres variables a été conçu au moyen du modèle 1D. La distribution d'écoulement est significativement améliorée mais cause une perte de charge globale plus grande indésirable et une mauvaise distribution de pression dans la batterie. La mauvaise distribution du manifold d'entrée principal vers les distributeurs dans la première batterie est fortement dépendante de la conception du module. La distribution d'écoulement dans toute la largeur d'un canal devient uniforme sur une courte distance, éliminant essentiellement le besoin d'approfondir cet aspect de la conception. L'écoulement en sortie de batteries et donc à l'entrée des batteries suivantes montre une distribution latérale uniforme dans tous les cas, ce qui suggère que le travail de modélisation futur peut se limiter à une fraction de la largeur du module, pour des raisons de symétrie, pour gagner de l'efficacité numérique. [source] Scaleable purification process for gene therapy retroviral vectorsTHE JOURNAL OF GENE MEDICINE, Issue 4 2007Teresa Rodrigues Abstract Background Retroviral vectors (RVs) constitute one of the preferred gene therapy tools against inherited and acquired diseases. Development of scaleable downstream processes allowing purification under mild conditions and yielding viral preparations with high titer, potency and purity is critical for the success of clinical trials and subsequent clinical use of this technology. Methods A purification process for murine leukaemia virus (MLV)-derived vector supernatants was developed based on membrane separation and anion-exchange chromatography (AEXc). Initial clarification of the vector stocks was performed using 0.45 µm membranes followed by concentration with 500 kDa molecular weight cut-off (MWCO) membranes; further purification was performed by AEXc using a tentacle matrix bearing DEAE functional ligands. Finally, concentration/diafiltration was performed by 500 kDa MWCO membranes. To validate final product quality the process was scaled up 16-fold. Results Optimization of microfiltration membrane pore size and ultrafiltration transmembrane pressure allowed the recovery of nearly 100% infectious particles. Further purification of the RVs by AEXc resulted in high removal of protein contaminants while maintaining high recoveries of infectious vectors (77 ± 11%). Up-scaling of the process resulted in high titer vector preparations, 3.2 × 108 infectious particles (IP)/ml (85-fold concentration), with an overall recovery reaching 26%. The process yielded vectors with transduction efficiencies higher than the starting material and more than 99% pure, relative to protein contamination. Conclusions The combination of membrane separation and AEXc processes results in a feasible and scaleable purification strategy for MLV-derived vectors, allowing the removal of inhibitory contaminants thus yielding pure vectors with increased transduction efficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Artificial neural network modeling of O2 separation from air in a hollow fiber membrane moduleASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008S. S. Madaeni Abstract In this study artificial neural network (ANN) modeling of a hollow fiber membrane module for separation of oxygen from air was conducted. Feed rates, transmembrane pressure, membrane surface area, and membrane permeability for the present constituents in the feed were network input data. Output data were rate of permeate from the membrane, the amount of N2 in the remaining flow, and the amount of O2 in the permeate flow. Experimental data were obtained from software developed by Research Institute of Petroleum Industry (RIPI). A part of the data generated by this software was confirmed by experimental results available in literature. Two third of the data were employed for training ANNs. Based on different training algorithms, radial basis function (RBF) was found as the best network with minimum training error. Generalization capability of best RBF networks was checked by one third of unseen data. The network was able to properly predict new data that incorporate excellent performance of the network. The developed model can be used for optimization and online control. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Enzyme recovery during gas/liquid two-phase flow microfiltration of enzyme/yeast mixturesBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2002Muriel Mercier-Bonin Abstract The effect of a gas/liquid two-phase flow on the recovery of an enzyme was evaluated and compared with standard crossflow operation when confronted with the microfiltration of a high-fouling yeast suspension. Ceramic tubular and flat sheet membranes were used. At constant feed concentration (permeate recycling) and transmembrane pressure, the results obtained with the tubular membrane were dependent on the two-phase flow pattern. In comparison with single-phase flow performances at the same liquid velocity, the enzyme transmission was maintained at a high level with a bubble flow pattern but it decreased by 70% with a slug flow, whatever the flow rate ratio. Identical results were obtained with flat sheet membranes: for the highest flow rate ratio, the enzyme transmission was reduced by 70% even though the permeate flux was improved by 240%. During diafiltration experiments with the tubular membrane, it was found that a bubble flow pattern led to a 13% higher enzyme recovery compared to single-phase flow conditions, whereas with a slug flow the enzyme recovery was strongly reduced. With bubble flow conditions, energy consumption was minimal, confirming that this flow pattern was the most suitable for enzyme recovery. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 610,621, 2002. [source] Mimic of a large-scale diafiltration process by using ultra scale-down rotating disc filterBIOTECHNOLOGY PROGRESS, Issue 2 2010Guijun Ma Abstract Ultra scale-down (USD) approach is a powerful tool to predict large-scale process performance by using very small amounts of material. In this article, we present a method to mimic flux and transmission performance in a labscale crossflow operation by an USD rotating disc filter (RDF). The Pellicon 2 labscale system used for evaluation of the mimic can readily be related to small pilot and industrial scale. Adopted from the pulsed sample injection technique by Ghosh and Cui (J Membr Sci. 2000;175:5-84), the RDF has been modified by building in inserts to allow the flexibility of the chamber volume, so that only 1.5 mL of processing material is required for each diafiltration experiment. The reported method enjoys the simplicity of dead-end mode operation with accurate control of operation conditions that can mimic well the crossflow operation in large scale. Wall shear rate correlations have been established for both the labscale cassette and the USD device, and a mimic has been developed by operating both scales under conditions with equivalent averaged shear rates. The studies using E. coli lysate show that the flux vs. transmembrane pressure profile follows a first-order model, and the transmission of antibody fragment (Fab,) is independent of transmembrane pressure. Predicted flux and transmission data agreed well with the experimental results of a labscale diafiltration where the cassette resistance was considered. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] An Integrated Process for Mammalian Cell Perfusion Cultivation and Product Purification Using a Dynamic FilterBIOTECHNOLOGY PROGRESS, Issue 4 2002Leda R. Castilho In the present work, a dynamic filter was employed to develop an integrated perfusion/purification process. A recombinant CHO cell line producing a human anti-HIV IgG was employed in the experiments. In the first part of this work, the dynamic filter was fitted with conventional microfiltration membranes and tested as a new external cell retention device for perfusion cultivations. The filter was connected to a running perfusion bioreactor and operated for approximately 400 h at an average cell concentration of 10 million cells mL,1, whereby cell viability remained above 90% and no problems of sterility were experienced. In the second part of this work, the dynamic filter was employed to simultaneously carry out cell separation and product purification, using membrane adsorbers containing Protein A affinity ligands. An automated system was built, which integrated the features of an automated perfusion bioreactor and of a liquid chromatography system. The IgG was continuously adsorbed onto the affinity membranes and was periodically recovered through elution cycles. After connection of the filter, the system was operated for approximately 300 h, whereby three elution cycles were carried out. No progressive increase in transmembrane pressure was observed, indicating no membrane fouling problems, and the IgG was recovered practically free of contaminants in a 14-fold concentrated form, indicating that the integrated, one-step perfusion/purification process developed during this work is a promising alternative for the production of biologicals derived from mammalian cells. [source] Ultrafiltration of industrial waste liquors from the manufacture of soy protein concentratesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Andrés Moure Abstract Protein-containing waste liquors from the manufacture of soy protein concentrates were processed by ultrafiltration to recover soluble protein using three different membranes (with molecular weight cut-offs of 10, 30 and 50 kDa). Operating at 20 °C under reversible conditions, the experimental data of the normalized permeate flux (NPF) obtained at various transmembrane pressures were well described by a model reported in the literature. For each membrane and transmembrane pressure, the values of the parameters involved in the model were calculated. Operating at selected transmembrane pressures, protein rejections of 0.705, 0.747 and 0.637 were determined for the 10, 30 and 50 kDa membranes, respectively. Operation with the 10 kDa membrane at temperatures in the range 30,50 °C and operation with the 30 or 50 kDa membranes at 40 or 50 °C resulted in hysteresis. Copyright © 2006 Society of Chemical Industry [source] Predictive membrane transport model for nanofiltration processes in water treatmentAICHE JOURNAL, Issue 6 2001Shih-Chieh Tu A membrane transport model was developed for prediction and simulation of membrane filtration (nanofiltration) dynamics with reference to permeate flux. It incorporates important phenomenological aspects of membrane transport, such as concentration polarization and gel layer formation, and illustrates the concentration of solutes as foulants in the mass-transfer boundary layer on the membrane surface. Membrane filtration tests using tannic acid as a model organic compound were designed for investigating permeate fluxes, as well as solute concentration profiles for permeates and concentrates. Membrane performance experiments were conducted under various operation conditions by varying several parameters including solute concentrations, transmembrane pressures, and reject flow rates. The tests showed that the NF-45 membrane composed of polypiperazine amide was more susceptible to organic fouling by tannic acid than the NF-70 membrane made of cross-linked aromatic polyamide. These observations were supported by surface-potential measurements that demonstrated higher negative surface charges and greater hydrophilicity for the NF-70 membrane in the presence of tannic acid. The predictive capability of the membrane transport model was evaluated using the results from membrane filtration tests. Model sensitivity studies were conducted to obtain information on effects of various input parameters pertaining to operating conditions and fluid-dynamic regimes. [source] | |||||||||||||