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Rare earth elements (REEs) are critical materials due to their utilization in high-flux magnets for wind turbines and electric motors. Purification and recycling of REEs are vital for maintaining their supply. This work explores and models nanofiltration (NF) followed by diafiltration for concentrating La3+ and polishing monovalent ions from the concentrated solution. Highly negative monovalent-ion rejections greatly enhance this polishing step, and proton concentrations decrease 3–4 orders of magnitude in 2.4 cell volumes of diafiltration. Studies with rotating membranes give a controlled, uniform boundary layer above the membrane to enable estimation of salt and ion permeances at various feed compositions. Insertion of these permeances in the solution-diffusion-electromigration model yields trends in ion rejections as a function of composition, solution flux, and boundary layer thickness. Simulated rejections of monovalent ions become much more negative with lower solution fluxes (up to a point) and higher ratios of La3+ to monovalent ions. La3+ rejections are much higher in the rotating membrane than in a stirred cell where the diffusion boundary layer is thicker and nonuniform. The combination of NF and diafiltration provides concentrated La3+ with a molar purity of 99 % when starting with equimolar mixtures of La3+ and Na+. Acid removal from La3+ solutions via diafiltration could prove useful for subsequent separations among REEs or other transition metals. [Display omitted] • Diafiltration efficiently polishes La3+ from Na+ or H+ due to negative rejection. • Uniform boundary layers on rotating membranes enable estimation of permeances. • The solution-diffusion-electromigration model gives trends in ion rejections. • Negative monovalent-ion rejections depend on flux, composition, and boundary layers. • Diafiltration yields 99 % La3+ from equimolar Na+ and La3+. [ABSTRACT FROM AUTHOR]

As a result of distinctive nanopores of two-dimensional material, graphene oxide (GO) has emerged as a new-generation membrane for high performance water separation. However, GO-based composed membrane applied to dye desalting gains less attention. A series of novel ultrathin and stable polydopamine/graphene oxide (PGO) membranes has been successfully fabricated via intercalation polymerization of dopamine using triple vacuum filtration. The polymerized dopamine (PDA) via intercalation polymerization in the interspace between the lamellar layers is used to simultaneously improve the stability of GO film and rapid passage of ions. The high permeation of pure water of as-prepared PGO membranes is investigated through adjusting the thickness (9–126 nm) of modified layers. In addition, the values decrease from 24.2 to 0.65 L m−2 h−1 bar−1 with increasing the layer. With the ultrafast ion transport and dyes rejection under cross-flow condition, the stability PGO membranes show a good capability for desalination dyes and concentration of dye (11.6 times of the initial dye solution). • A series of novel ultrathin and stable polydopamine/graphene oxide (PGO) nanofiltration membranes was successfully fabricated via intercalation polymerization of dopamine using triple vacuum filtration. • The intercalation polymerization method was applied to raise the stability of the GO film and increased the interspace of the lamellar layer which resulting in high permeation of pure water and ions. • The stability PGO membranes give an excellent capability for desalination dyes under the long-time testing, which show 99.6% rejection of methyl blue and 28.0% for Na 2 SO 4 , respectively. • The diafiltration process along with the mathematic simulation for preparation of digital inkjet printing dye were exploited. The result showed that the concentration of experiment date for dye was consist with the simulation date and obtain concentrated dye with 11.6 times. [ABSTRACT FROM AUTHOR]

Abstract Nanofiltration was studied for detoxification of lignocellulose hydrolysates obtained in harsh conditions. A hemicellulosic hydrolysate obtained from sulfuric acid steam explosion of wheat straw and presenting very low pH (= 1) and high osmotic pressure (28 bar) was studied and 8 inhibitory compounds were followed, among which 4 phenolic compounds. Several polymeric nanofiltration membranes were compared for separation performances and permeabilities; DK membrane (GE Osmonics) proved suitable with high rejection of sugars (> 99%) and lower rejections of inhibitors. Acetic acid and furfural were quasi-fully transmitted whereas the rejection of compounds ranked as follow: HMF (5-hydroxymethyl-furfural) < coumaric acid < levulinic acid < vanillin < ferulic acid < syringaldehyde with values of 40%, 50%, 60%, 80%, 90% and 98%, respectively, at a permeate flux of 14 L h−1 m−2. Diafiltration was carried out at a transmembrane pressure of 26 bar until 3 DV (Diafiltration Volume) to complete detoxification, and continuous and sequential-dilution modes were compared. Thanks to the permeability of the membrane to the monovalent form of sulfuric acid HSO 4 -, effective transmembrane pressure was increased and pH reached 2. At 3 DV, both modes showed removal performances between 92% (acetic acid and furfural) and 25% (syringaldehyde). Irreversible fouling was observed, leading to 30% permeability loss after diafiltration. Highlights • Detoxification of hemicellulosic hydrolysate by nanofiltration was investigated. • Hydrolysate has a very low pH (pH = 1) and a high osmotic pressure (28 bar). • Phenolic compounds behavior was highlighted. • Continuous and sequential-dilution diafiltrations were compared. • HSO 4 - transmission allowed pH to increase and osmotic pressure to decrease. [ABSTRACT FROM AUTHOR]

Polyethylene oxide stabilized nanoparticles are becoming increasingly important as a means of delivering and targeting therapeutics. Processing and purifying these nanomedicines has become increasingly important. Ultrafiltration studies were performed on sterically-stabilized nanoparticle systems formed by Flash NanoPrecipitation and charge-stabilized latexes formed by emulsion polymerization for the purposes of concentration-diafiltration process optimization and characterization of membrane fouling. The nanoparticle systems were compared against similar studies done on bovine serum albumin to elucidate the mechanisms of stabilization and membrane fouling based on hydrodynamic models. As the only scalable method for the precise concentration and purification of nanoparticle systems, these studies provide guidance on achieving the desired specifications for different nanoparticle sizes, geometries and surface chemistries as opposed to typical protein ultrafiltration that is routinely employed in the biotechnology industry. [ABSTRACT FROM AUTHOR]

A novel particle classification system based on the integration of classification and diafiltration, both of which utilize cross-flow microfiltration under high flow rate, was successfully developed. In this system, particles could be classified into two fractions, one of which was smaller than pores of the membrane and collected as permeate and another collected as retentate. Diafiltration was then conducted to completely remove the smaller particles contained in the retentate to obtain another fraction consisting of larger particles. Importantly, classification and diafiltration should be conducted under cross-flow microfiltration at a high flow rate because the sufficiently large hydrodynamic lift force attributed to the cross-flow microfiltration operation keeps the membrane surface clean so it can act as a sieve. To show the effectiveness of our particle classification system, we demonstrated stable classification and continuous diafiltration for 26 h of bi-dispersed suspensions containing particles with diameters of 0.6 and 1.5 µm and polydispersed suspensions with particle diameters of 0.1–3 µm. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membranes have been used previously for the recovery of dyes, salts, and water from textile wastewaters with high salinity. However, commercially available NF membranes have a high rejection for divalent salts (i.e., Na 2 SO 4 ), substantially reducing the salt recovery and membrane flux when treating textile wastewater containing Na 2 SO 4 . In this study, a tight ultrafiltration membrane (UH004, Microdyn-Nadir) was proposed to fractionate the dye and Na 2 SO 4 in the textile wastewater. The UH004 membrane with a molecular weight cutoff of 4700 Da provided complete passage of monovalent salts, with little rejection of Na 2 SO 4 . This significantly increases the filtrate flux that can be achieved with high-salinity wastewater since osmotic pressure and concentration polarization effects are minimized. Furthermore, the retention behavior of four different dyes was evaluated to determine the efficiency of this membrane process. This tight ultrafiltration membrane offered the high retention for direct dyes (i.e., direct red 80, direct red 23, and Congo red) and reactive blue 2. For instance, the UH004 membrane yielded >98.9% rejection for all of the dyes at a pressure of 4 bar even in the presence of 60 g L −1 Na 2 SO 4 . Subsequently, an ultrafiltration-diafiltration process was designed to separate a dye/Na 2 SO 4 aqueous mixture with 98% desalination efficiency and greater than 97% dye recovery after 5 diavolumes. These results clearly demonstrate that tight ultrafiltration membranes can be a stand-alone alternative to NF membranes for the effective fractionation of dye and Na 2 SO 4 in the direct treatment of high-salinity textile wastewater. [ABSTRACT FROM AUTHOR]

In order to improve bioethanol production by yeast fermentation of lignocellulosic hydrolysates, sugar/inhibitor separation by nanofiltration was studied on a bench-scale unit equipped with a spiral-wound membrane. Therefore, a model solution containing 3 sugars and 4 inhibitors was treated with two previously selected membranes (NF270 from DOW Filmtec and DK from GE Osmonics). Both membranes led to high sugar rejection, especially at high permeate flux (>90% for glucose and arabinose and >85% for xylose). Although its water permeability was smaller, DK membrane was preferred for its higher transmission of the inhibitors, especially for the largest ones (vanillin and 5-hydroxymethyl furfural), ensuring a better detoxification level. Diafiltration was applied to improve sugar purity of the treated hydrolysate. With a diavolume equivalent to 1.25 times that of the feed, acetic acid concentration was divided by 5 and brought back to concentrations lower than 1 g L −1 . A simulation model was proposed to predict the diavolume to apply, depending on the initial concentrations. Finally, processed hydrolysates were tested for the fermentation ability with a Pichia stipitis species. Fermentation tests showed that diafiltration followed by concentration led to retentates as fermentable as an equivalent pure sugars solution. [ABSTRACT FROM AUTHOR]

The performances of hyaluronic acid (HA) purification (yield, purity, permeate flow rate and productivity) in a semi-synthetic medium composed of salts, proteins/peptides by diafiltration through a 100 kDa PES membrane were studied over 10 diavolumes (DV). The HA purity went from 3% to almost 100% with a yield in the retentate close to 100% at the end of the process. The permeate flow rate showed a peculiar trend due to the influence of charged microsolutes. DF mass balance applied to three groups of solutes (HA, peptides/proteins and charged microsolutes) allowed a good prediction of HA yield and purity in the course of DF. An equation of the permeate flux based on limit flux equation, correlations between mass transfer coefficient mineral concentration and mineral mass balance was proposed to predict the process productivity. Eventually, a methodology based on these equations was proposed to predict HA yield, purity and productivity. The methodology was validated with an actual Streptococcus zooepidemicus broth. Differences between calculations and experimental performances in term of yield, purity and productivity never exceeded 10%. [ABSTRACT FROM AUTHOR]

In the textile industry, high salinity waste streams are a challenge urging for the recovery and purification of dyes and salts (e.g., NaCl), requiring a treatment going beyond the classical filtration by e.g., reverse osmosis to produce pure water. In this work, two commercial loose nanofiltration (NF) membranes (Sepro NF 6 and NF 2A, Ultura) are proposed to fractionate dye/salt aqueous mixtures. It was observed that both NF membranes have a salt rejection <33.3% in solutions with 0.1–40.0 g L −1 of NaCl at 6 bar. Furthermore, both membranes have >99.6% retention of direct dyes (direct red 80, direct red 23, and congo red), even though 40.0 g L −1 NaCl is present, indicating salt addition has no obvious impact on the dye retention. The combination of a low salt rejection and a high dye rejection indicates the feasibility for the reuse of salt from fractionation in forward osmosis and bipolar membrane electrodialysis. Application of diafiltration for an aqueous mixture containing direct red 80 (1000 ppm) and NaCl (~20 g L −1 ) by both membranes demonstrates that above 95% of NaCl is removed from aqueous mixture, and <0.9 g L −1 NaCl remains after the addition of pure water with a volume factor of 4.0 in the feed solution. At the premise of excellent diafiltration performance, concentration as the post-treatment for dye recovery expectedly indicates direct red 80 is concentrated by a factor of 4.0 for both membranes while keeping the salt concentration with a very slight increase. Over 99.9% dye retention in both diafiltration and concentration procedures yields a very high recovery since <0.045% of dye is permeated. These results indicate that loose nanofiltration membranes have potential for dye/salt fractionation. [ABSTRACT FROM AUTHOR]

Abstract: Glucose and enzyme in a high concentration enzymatic hydrolysis suspension were separated using hollow fiber cross-flow diafiltration. The operating condition effects on the filtration performance are discussed. Over 86% of the enzymes were retained using a 10kDa polysulfone membrane. Most glucose molecules penetrated through the membrane into the filtrate. The major filtration resistances are due to the cake formation on the membrane surface and enzyme blocking in the membrane pores in addition to the appreciable virgin membrane resistance. The cake mass is correlated with the drag force ratio tangential to the filtration directions and the average specific cake filtration resistance is expressed as a power-function of the transmembrane pressure with a cake compressibility of 0.3. The empirical equation related the resistances due to internal membrane fouling to the operating conditions established by conducting experimental data regression. The filtration flux can be estimated accurately by substituting the results calculated using the empirical equations into the basic filtration equation. An increase in cross-flow velocity or transmembrane pressure leads to higher filtration flux. The filtration flux increases ca 2-fold as the cross-flow velocity increases from 0.3 to 1.5m/s under a transmembrane pressure of 60kPa. The filtration flux increases over 3-fold as the transmembrane pressure increases from 20 to 100kPa. Two kinds of modified operating methods are used to improve the filtration flux. A pulse feeding method may increase the filtration flux by 25%, while the step-increase pressure method improves the filtration flux by over 34%. Forming a thin cake under low pressure in the early filtration period has great potential to significantly mitigate membrane pore blocking and enhance filtration flux. [Copyright &y& Elsevier]

A number of Single Pass Tangential Flow Filtration (SPTFF) systems have recently been commercialized for inline concentration of monoclonal antibodies and other biotherapeutics, both to resolve bottlenecks in existing processes and as part of the development of integrated continuous downstream processes. The objective of this study was to examine the design and optimization of SPTFF modules using a previously developed mathematical model for the filtrate flux and pressure drop that specifically accounts for the concentration dependence of the antibody viscosity and osmotic pressure as well as the variation of the flow rate and antibody concentration with the position in the long pathlength SPTFF device. Model simulations were performed to examine the effects of channel width, length, and cassette staging (number of parallel cassettes in each stage) on SPTFF performance. The concentration factor (conversion) was greatest for a long thin channel configuration, but this also caused very large feed-side pressure drops. The use of cascade configurations, with a greater number of parallel channels near the feed inlet, significantly reduced the pressure drop but with a corresponding increase in total membrane area. A key factor governing the SPTFF performance was the increase in viscosity of the antibody solution at high conversion. These results provide important insights into the design and optimization of SPTFF systems for monoclonal antibody processing. [Display omitted] • Model developed for SPTFF accounting for axial variation in pressure/flux. • Model simulations in good agreement with experiments using monoclonal antibody. • Model used to analyze/optimize design of SPTFF module for target application. • Design calculations specifically account for module geometry and configuration. • Long thin channels provide greatest volume reduction but at cost of high pressure drop. [ABSTRACT FROM AUTHOR]

Abstract: This paper studies the problem of economically oriented optimal operation of an ultrafiltration/diafiltration process that is designed to reduce the initial volume of a given process liquor and to eliminate impurities from the product solution in a batch setup. This theoretical investigation focuses on applications where the permeate flux is given by the well-known limiting flux model and the rejections of micro-solute and macro-solute are assumed to be zero and one, respectively. Unlike previous approaches to the problem, we consider a complex economical objective that accounts for the total operational costs involving both the cost of consumed diluant and processing time-related costs. The optimization problem is formulated as a multi-objective optimal control problem and it is solved using the analytical approach that exploits Pontryagin's minimum principle. We prove that economically optimal control strategy is to perform a constant-volume diafiltration step at a given, optimal macro-solute concentration. This constant-volume diafiltration step is preceded and followed by ultrafiltration or pure dilution steps that force the concentrations at first to arrive to the optimal macro-solute concentration and at last to arrive to the desired final concentrations. By taking into account the unit prices of both processing time and utilized diluant, we provide a practical algebraic formula that allows decision makers to evaluate the optimal starting point of the constant-volume diafiltration step and to adapt it when considered prices change. Finally, we demonstrate the applicability and achievable benefit of the here presented approach on an industrial-scale case study using literature data. [Copyright &y& Elsevier]

Abstract: This work addresses the optimal control strategy of diafiltration buffer utilisation in discontinuous membrane processes that are designed to fulfil the twin aims of concentration and fractionation. The problem of optimal process operation is formulated using a general membrane response model that encounters concentration-dependent flux and rejections. We consider two problems, operation time minimisation and diluant consumption minimisation, and we apply theory of optimal control and derive necessary conditions of optimality. Through selected case studies from the literature, we demonstrate how to apply the proposed methodology to determine optimal time-dependent wash-water feeding policy. The analytical results are confirmed by numerical computations, using numerical methods of dynamic optimisation. The presented methodology allows decision makers to analyse suboptimality of conventional diafiltration strategies in terms of processing time and diluant consumption. Results show that depending on the complexity of the membrane response model, it may be attractive to implement optimal trajectory. [Copyright &y& Elsevier]

Abstract: This study examines a generalized ultrafiltration/diafiltration process that is designed to reduce the initial volume of a given process liqueur and to eliminate impurities from the product solution. This theoretical investigation focuses on applications where the permeate flux is given by the gel polarization model. The goal of this paper is to use optimal control theory to determine optimal time-varying diluant addition that minimizes treatment time. We propose a diafiltration model in a dimensionless form with normalized model equations in order to determine general features of optimal diluant utilization strategy. Based on the model, we formulate the optimal control problem and apply the theory of optimal control exploiting the Pontryagin’s minimum principle. We confirm the analytical results by numerical computations using numerical methods of dynamic optimization. We prove that optimal control strategy is to perform a constant-volume diafiltration step at optimal macro-solute concentration that guarantees maximal removal of micro-solute at any time instant. This constant-volume diafiltration step is preceded and followed by optional ultrafiltration or pure dilution steps that force the concentrations at first to arrive to the optimal macro-solute concentration and at last to arrive to the desired final concentrations. Finally, we provide practical optimization diagrams that allow decision makers to determine the optimal diluant control of a given separation task. [Copyright &y& Elsevier]

Abstract: This paper investigates the membrane purification and fractionation of a mixture containing the homologous series of cyclodextrins CD6 to CD60 obtained by enzymatic conversion of starch. Three commercial polyamide thin film composite NF and UF membranes (HL, GH and GK from GE-Osmonics) were used for this purpose. In a first step, a binary mixture composed of glucose and heptacyclomaltose (β-cyclodextrin, CD7) was filtered to examine the separation performance of the studied membranes. A mathematical model based on mass balance was proposed for the simulation of the discontinuous diafiltration process assuming that the membrane separation performance is based on a sieving mechanism. A three stage diafiltration cascade (in retentate configuration) was then selected to fractionate the CD6–CD60 crude mixture. The experimental composition of the obtained permeate and retentate solutions in the targeted fractions (glucose, CD6–CD8, CD9–CD21, CD22–CD60) fit well with the predicted data indicating that membrane process enables purification and fractionation of the homologous series of large ring CDs. Some discrepancies were however observed implying that other mechanisms such as coupled transport also took place. The most striking effect was the presence of glucose in the GK retentate possibly as a result of the formation of inclusion complexes with the large ring CDs. [Copyright &y& Elsevier]

Abstract: Increased titers from 2 to 10mg/ml represents a major future challenge for recovery of desirable proteins during downstream processing. Pressure-driven microfiltration using synthetic membranes, due to its advantages such as speed, no phase change, no additives, selectivity and competitive economics, will be among several unit processes that will be considered to help attain this goal. Microfiltration in the biotechnology industry currently involves either removing soluble host cell protein while retaining larger insoluble particles like insoluble bodies or separating soluble recombinant protein from cells which are larger than the membrane pore-size. Such a step usually falls at the interface of upstream cell-culture/fermentation and downstream polishing steps. Hence, there is a need to rapidly optimize this step to meet time-lines for drug development and for new challenges such as those listed above. Using basic mass balance equations for batch concentration and diafiltration, we offer a simple and useful methodology to optimize a membrane filtration process. The process is similar to that used earlier for ultrafiltration. The main goals in any microfiltration application are high yield and low processing time, as enhancement in purity is implicit in the choice of membrane pore-size and chemical composition. An optimization diagram for predicting yield of the desired protein and processing time for microfiltration applications is developed by incorporating experimental parameters like observed sieving coefficient of protein, concentration factor and number of diavolumes. As a demonstration of the methodology, an optimization diagram was developed for the filtration of E. coli cell lysate containing inclusion bodies of a recombinant protein which enabled rapid determination of the two parameters (concentration factor and number of diavolumes) and optimization of membrane microfiltration processes for a given combination of sieving coefficient, membrane pore-size, and solute. [Copyright &y& Elsevier]

Abstract: A comprehensive modeling approach is proposed for the dynamic simulation and operation optimization of batch diafiltration processes. We provide a unified technology for water utilization control that addresses generality versus special cases. A rigorous dynamical model of the diafiltration process with concentration-dependent rejections of solutes is developed. We determine the optimal time-dependent profile of the diluant flow for the entire process using dynamic optimization methods. The results show that optimal process operation needs not to be any of the conventional diafiltration concepts. The presented optimization technique is a useful tool for improving the performance of a membrane diafiltration process. [Copyright &y& Elsevier]

Abstract: Liquors from the aqueous processing of Eucalyptus wood were diafiltered through a nanofiltration ceramic membrane, and experimental data concerning the time-course of flux and concentrations of the different compounds present in the medium (monosaccharides, oligosaccharides, oligosaccharide substituents and other non-volatile compounds) were determined. A mathematical model based on a combination of osmotic pressure and an additional in-series resistance provided a quantitative interpretation of experimental data. [Copyright &y& Elsevier]

Abstract: The optimization of the cleaning process, aiming to recover the permeate flux, and diafiltration as a means to obtain and purify soybean lecithin, were analyzed in this study as a means of delaying the decrease in permeate flux during the ultrafiltration (UF) of vegetable oils and their derivatives. It also aimed to maximize the exploration of the use of this type of technology during the processing steps. Thus the influence of the transmembrane pressure, cross flow velocity, and the opening of the permeate valve during the cleaning process (hexane circulation) of a ceramic membrane with a permeation area of 0.2m2 and a pore diameter of 0.01mm in a pilot unit with a processing capacity of 40L, was studied. Four different operational cleaning conditions, associating combinations of pressure (0.5–2.0bar) and velocity (1.0–5.0ms−1), as well as the influence of opening the permeate valve, were studied. Also the production and purification of soybean lecithin was carried out by diafiltration of the retentates derived from the UF of the miscella, resulting in a product with about 90% of acetone insoluble matter. The most favorable cleaning condition was associated with a low pressure (0.5bar) and elevated velocity (5.0ms−1), with which it was possible to recover the permeate flux in about 85min. [Copyright &y& Elsevier]

Abstract: A mathematical frame for modeling batch and semi-batch membrane filtration processes is provided. The approach followed in this work uses the feed concentrations as a basis for the calculations, rather than the concentration factor. A practical computational algorithm is proposed. Our method hands separately the design equations describing the engineering aspects of batch and semi-batch systems and the models of mass transfer through the membrane. Thus, different methods can be applied to compute the permeate flux and rejection without having to modify the general framework. In particular, we present an empirical approach to characterize the membrane separation behavior based on a minimal number of experiments. Moreover, we consider irreversible thermodynamics models and a transport model based on the extended Nernst–Planck equations. Finally, various batch and semi-batch nanofiltration operations are carried out with an organic/electrolyte binary test solution to validate the proposed algorithms. [Copyright &y& Elsevier]

Improved characterization techniques, which address knowledge gaps related to the interfacial processes that govern solute–solute selectivity and the performance of membranes in complex multi-component feed streams, are necessary to advance membrane processes. In this study, guided by the tools of data science, a diafiltration apparatus is developed to inform material and process design by rapidly characterizing membrane performance over a broad range of feed solution compositions. The apparatus doses a fixed-concentration diafiltrate solution into a stirred cell to achieve a predetermined change in the retentate concentration. Here, using an 80 mM potassium chloride (KCl) diafiltrate solution, it was shown that membrane performance, within a 5 mM to 80 mM KCl phase space, could be probed five times more quickly with one diafiltration experiment (8 h) than with an experimental campaign using traditional filtration processes (47 h). Additionally, the synergy between data analytics and instrumentation led to the incorporation of an inline conductivity probe that monitored the real-time retentate concentration. This additional information provided key insights to distinguish between the mechanisms that govern membrane separations (e.g., discriminating between adsorption or rejection based separations) and allowed for the membrane transport coefficients to be determined accurately. Ultimately, incorporating the appropriate governing phenomena identified a single set of self consistent transport parameters for commercial NF90 membranes. [Display omitted] • Synergy between data analytics and instrumentation enables innovative device design. • DATA allows for the evaluation of membrane performance over a wide concentration range. • Diafiltration experiments run five times faster than traditional experiments. • An inline conductivity probe directly measures the retentate concentration. • Modeling the appropriate physics identifies a single set of self-consistent parameters. [ABSTRACT FROM AUTHOR]

Abstract: A simple numerical technique is presented for batch membrane filtration design. The underlying model accounts for variable solute rejection coefficients, and it has a modular structure which permits to easily describe the batch process involving different arrangements of the three typical basic steps: pre-concentration, dilution mode and final concentration. The experimental design required to set up the model is discussed, together with the necessary sampling procedure. In order to validate the technique, multi-step nanofiltration experiments were carried out using a binary test solution containing organic and inorganic substances. The objective of the process is to remove the electrolyte from the solution and concentrate the organic component. The predictions for the multi-step process performances were found to be in good agreement with the experimental results. Finally, optimum-search techniques for the overall multi-step process are discussed, considering economical aspects and technological demands. The presented optimization procedure can be useful to find the optimum pre-concentration and dilution factors for a membrane plant with a defined module configuration and membrane area. [Copyright &y& Elsevier]

For traditional separation processes there are widely available process design methodologies for scale-up and optimisation. However, there is an increasing need for such a rational approach to membrane separation processes, identifying at an early stage operating limits and process options. Such predictive models will reduce development risk and time, thus promoting the wider use of membrane technology in process industries such as pharmaceutical manufacture. Design methods exist that have been verified experimentally at the laboratory scale for simple aqueous solutions. There is now a need for the application of the existing theoretical and experimental methods to separations of real industrial interest.In this paper we demonstrate this philosophy by describing the rationale for modelling the performance of membrane nanofiltration (NF) used in the isolation of N-acetyl-d-neuraminic acid (Neu5Ac) an industrially important example of an equilibrium-controlled biotransformation reaction. The chemoenzymatic synthesis of Neu5Ac is already achieved at large scale and its derivatives are important as precursors for a range of antiviral drugs such as the commercially available anti-influenza agent 4-guanidino-Neu5Ac-2-en (zanamivir, Relenza™). The separation involves the removal of pyruvate from the process stream, which is complicated by the fact that Neu5Ac and pyruvate have similar pKa values.A systematic study of the rejection of the components involved in the separation was carried out, firstly as individual components and then as mixtures. Excellent agreement between the calculated and experimental rejections of the solutes and ions was observed for batch nanofiltration. A membrane charge isotherm was developed from the experimental data for use in the theoretical process modelling.A comparison was made between a full model and a linearised model based upon the extended Nernst–Planck equation and the difference between the two was considered small. Subsequently, the linearised model was used for prediction of a diafiltration process to remove pyruvate and excellent agreement was achieved when allowing for the variation in effective membrane charge density as the pyruvate concentration in the solution changed as a function of time. [Copyright &y& Elsevier]

Recent studies have demonstrated that membrane ultrafiltration can be used to separate proteins with very similar size, but these investigations have been performed with model binary mixtures. This study examined the use of a two-stage tangential flow filtration system for the purification of both α-LA and β-LG from whey protein isolate. Separation was achieved using 100 and 30 kDa membranes in series, with the buffer concentration and filtration velocity for each stage adjusted to give optimal separation. Two purification strategies were examined: one using the 100 kDa membrane followed by the 30 kDa and one with the reverse order. In both cases, the α-LA purification was greater than 10-fold at 90% yield. The recovery of β-LG was more challenging since it was obtained in the permeate from one stage and the retentate from the other. The results provide important insights into the development of staged membrane systems for the purification of complex protein mixtures. [Copyright &y& Elsevier]

Athermal solvent exchange from one organic synthesis step to the next step is highly desirable in bulk pharmaceutical manufacturing due to the thermally labile nature of the active intermediates. Diafiltration (DF) was employed using methanol as the solvent needed in the next synthesis step to drastically reduce the concentration of ethyl acetate used as the solvent in the previous synthesis step. Ethyl acetate was reduced to the level of a low concentration impurity in methanol by both batch and continuous DF using solvent resistant nanofiltration membranes MPF-50 and MPF-60; the latter has a high rejection of around 96% for the solute, erythromycin, representing an active intermediate. Nanofiltration-based diafiltration for exchanging the solvent methanol for ethyl acetate was demonstrated. The membrane rejection of the solute needs to be higher. Membrane compaction has to be considered in the design of the process for both membranes. [Copyright &y& Elsevier]

Nanofiltration (NF) of a model sugar solution and a commercial galacto-oligosaccharide mixture has been studied with a cross-flow filtration unit in an attempt to investigate the significance of the operating parameters and evaluate a possible purification process. The pressure, feed concentration and filtration temperature effects were studied in experiments carried out in full recycle mode of operation. The rejection factors of the sugar components present in the solutions increased with increasing pressure due to increased solvent flux and also compaction of the membranes (e.g. rejection factor increased from 0.10 to 0.42 for fructose), with this effect being greater for the low molecular weight sugars in the solutions. Increasing the total sugar concentration of the feed caused a decrease to the rejections of the sugars (e.g. from 0.58 to 0.43 for glucose). Increasing the filtration temperature caused a decrease to the observed rejections of the low molecular weight sugars of the solutions (e.g. from 0.72 to 0.48 for fructose). Continuous diafiltration (CD) purification using NF-CA-50 membranes (at 25 °C) and DS-5-DL membranes (at 60 °C), gave yield values of 14–18% for the monosaccharide, 59–89% for the disaccharide and 81–98% for the trisaccharide (oligosaccharide), respectively. The study clearly demonstrates the potential of cross-flow nanofiltration in the purification of oligosaccharide from mixtures containing contaminant monosaccharides. [Copyright &y& Elsevier]

In this article, the permeation experiments by using a NF membrane were carried out for single component solutions of inorganic electrolytes (NaCl, KCl, MgCl2, Na2SO4 and MgSO4) and neutral organic solutes (glycerin, glucose, sucrose and raffinose) and a mixture solution of NaCl and glucose or sucrose. The effects of applied pressure and feed concentration and the coupling interaction between glucose or sucrose and NaCl on the separation performance (observed rejection and permeation flux) were investigated for single and mixture solutions, respectively. NF45 membrane is a negative charged membrane with the molecular weight (MW) cut-offs of about 300 Da, and it is available for the separation of saccharides or bivalent anion electrolytes and univalent anion electrolytes. An overall diafiltration process with a batch-wise mode was simulated for a model solution of soybean whey wastewater containing some saccharides and salts (such as NaCl), and the feasibility of the concentration of oligosaccharides and the removal of salts was also discussed. [Copyright &y& Elsevier]

Graphene-based materials have been used for fabricating organic solvent nanofiltration membranes due to their excellent mechanical properties and chemical stability in organic solvents. However, graphene membranes exhibit low organic solvent permeation properties due to the large molecular size of the organic solvent molecules and their strong interactions with the graphene surface. Herein, a nanoporous graphene membrane was fabricated to enhance organic solvent permeation. Nanopores were generated on the basal plane of graphene by rapid thermal annealing of graphene oxide. The size of the nanopores was also tuned from micropores to nanopores by adjusting the activation temperatures. The optimized nanoporous graphene membrane showed ultrafast isopropyl alcohol permeance up to 295 Lm−2h−1bar−1 and a sharp molecular weight cut-off of 616 Da. The membrane showed excellent stability and diafiltration performance under cross-flow filtration with a separation factor of around 1000 for dye molecules mixed in isopropyl alcohol. [Display omitted] • Nanopores were easily generated by rapid thermal annealing of graphene oxide. • The pore structure can be controlled by adjusting the thermal activation temperatures. • Mixed organic molecules can be precisely separated by both dead-end or cross-flow filtration. [ABSTRACT FROM AUTHOR]

Single Pass Tangential Flow Filtration (SPTFF) enables continuous ultrafiltration and diafiltration for inline concentration and buffer exchange in downstream bioprocessing of monoclonal antibody (mAb) products. However, the high conversion in SPTFF modules leads to large variations in local flow rate, protein concentration, and transmembrane pressure drop, significantly complicating the design of effective SPTFF modules/processes. In this study, a recent concentration polarization model for the filtrate flux in protein ultrafiltration that accounts for protein-protein interactions has been extended to the analysis of SPTFF, specifically including the effects of the mAb and membrane properties as well as the long path-length. Model calculations are in good agreement with experimental data for the filtrate flux and pressure drop in two commercial SPTFF systems with very different module geometries. The model was then used to analyze the design of SPTFF processes for inline mAb concentration, providing additional insights into the underlying physical phenomena governing the performance and optimization of SPTFF modules for bioprocessing. [Display omitted] • Model developed for SPTFF accounting for axial variation in pressure/flux. • Model includes key protein properties of viscosity and osmotic pressure. • Experiments performed with monoclonal antibody in several SPTFF modules. • Flux and pressure data in very good agreement with model simulations. • Model used to analyze/optimize design of SPTFF module for target application. [ABSTRACT FROM AUTHOR]

Looking at current trends within downstream processing (DSP) of high value bioproducts, it shows that there are ongoing efforts in replacing batch processes by continuous variants. However, a unit procedure which still lacks a simple and compact continuous variant is diafiltration. Here, we present such a single piece of diafiltration equipment achieving continuous buffer exchange of up to 99.90%. The device is composed of a 3D-printed single pass diafiltration (SPDF) module containing two commercial ultrafiltration membranes. While the retentate is flowing through a narrow channel between the two membranes, the channels above and below can supply diafiltration buffer or remove permeate solution. The obtained results illustrate systematically the vulnerability of the device to the effect of concentration polarization at the membrane surface, and that this problem can be strongly reduced using an alternating direction of diafiltration buffer perfusion through the membranes as process inherent backflush. By this, a quasi-stationary operation could be obtained during continuous diafiltration, making the device an interesting option for in-process buffer exchange. Image 1 • Single-pass diafiltration using a 3D-printed membrane module. • Buffer exchange 99.90% achieved with 14.4 diavolumes. • Counter-current operation mode strongly improved the degree of buffer exchange. • Alternating perfusion of the membranes reduced the phenomena of concentration polarization. [ABSTRACT FROM AUTHOR]