Susana Luque

Fouling and retention of nanofiltration membranes

Abstract Nanofiltration membranes retain substances with molar masses higher than ∼300 g/mol and multivalent ions. The retention characteristics depend much on how much free volume there is in the membranes, which can for some membranes be related to the flux. In this study, fouling and retention of four different nanofiltration membranes (NF40, NTR-7450, NTR-7410 and NTR-7250) were followed using different model substances. It could be seen that multivalent salts were retained better than small organic substances, but retention was much depending on the pH. As nanofiltration membranes have characteristics of both ultrafiltration as well as reverse osmosis membranes, their fouling characteristics are also rather individual. The tighter membranes foul less. Multivalent salts foul mostly only when together with organic compounds, e.g., lignosulfonate containing calcium fouls more than if it contains sodium as counterion. Maize starch containing small amounts of protein fouls more than potato starch. The NTR-7250 membranes could be modified by chloride ions at high pH to give better flux without loss of retention. Anionic model substances were retained better and fouled less due to charge repulsion effects especially at high pH

Mass transfer correlations in membrane extraction: Analysis of Wilson-plot methodology

Mass transfer correlations have been obtained for the past eight decades by the Wilson-plot method which has proved to be suitable for systems operating in steady-state conditions and where the only variable is the fluid velocity. In this work, this methodology is evaluated by using a membrane extraction process with a hollow-fiber membrane contactor as a case study. Taking into consideration the currently available mathematical tools, alternative methods to obtain mass transfer correlations are proposed and discussed. The proposed one-step calculation methodology proved to be a most suitable approach, leading to a drastic reduction in the errors associated with the estimated parameters. Additionally, improvements were observed when accounting for the partition coefficient variation.

Recovery of phenol from aqueous solutions using hollow fibre contactors

The purpose of this study is to characterise recovery of phenol from an aqueous solution using a hydrophobic polypropylene membrane contactor. The effects of temperature and hydrodynamics on the overall mass transfer coefficient were determined. Integration of the extraction and stripping stages was also carried out thereby allowing removal of more than 99% of the original phenol, while the organic phase is simultaneously regenerated.

A new coiled hollow-fiber module design for enhanced microfiltration performance in biotechnology

The microfiltration performance of a novel membrane module design with helically wound hollow fibers is compared with that obtained with a standard commercial-type crossflow module containing linear hollow fibers. Cell suspensions (yeast, E. coli, and mammalian cell cultures) commonly clarified in the biotechnology industry are used for this comparison. The effect of variables such as transmembrane pressure, particle suspension concentration, and feed flow rate on membrane performance is evaluated. Normalized permeation fluxes versus flow rate or Dean number behave according to a heat transfer correlation obtained with centrifugal instabilities of the Taylor type. The microfiltration performance of this new module design, which uses secondary flows in helical tubes, is significantly better than an equivalent current commercial crossflow module when filtering suspensions relevant to the biotechnology industry. Flux and capacity improvements of up to 3.2-fold (constant transmembrane pressure operation) and 3.9-fold (constant flux operation), respectively, were obtained with the helical module over those for the linear module.

A comparative study of reverse osmosis and freeze concentration for the removal of valeric acid from wastewaters

Abstract The recovery of valeric (n-pentanoic) acid from a synthetic aqueous solution simulating a wastewater stream in nylon manufacturing has been carried out using freeze concentration and reverse osmosis as separation processes. The concentration of valeric acid in aqueous solutions was in the range of 0.5–25 g/L. Reverse osmosis was carried out at 20 and 40°C and at a transmembrane pressure in the range of 1.3 to 6.0 MPa. The feed flow rate was 2 m/s in all the experiments. Although no membrane fouling was observed under the experimental conditions tested, a strong interaction of the acid with the membrane was noticeable. Rejections of the order of 90% were observed at 20°C, while values below even 50% were found at 40°C. The optimum performance for freeze concentration was determined, the best conditions being −10°C of subcooling temperature and 1012 kg/hm of feed flow. A model based on the heat transfer balance allows to predict the rate of ice crystallization. An economic analysis reveals that although freeze concentration consumes as much as five times the energy of reverse osmosis, which is compensated by the high costs of membrane replacement in reverse osmosis.

Removal of valeric acid from wastewaters by membrane contactors

Membrane contactors, providing a non-dispersive extraction technique, were used for the removal of valeric (n-pentanoic) acid from synthetic aqueous solutions simulating an industrial wastewater from polymer manufacturing. Amberlite LA-2 (secondary amine) in toluene was chosen as the extraction system. Equilibrium conditions were determined and mechanistically modelled for different extractant concentrations allowing the further calculation of mass transfer coefficients. The influence of the hydrodynamics of both the aqueous and organic phases on the overall mass transfer coefficient, calculated through two proposed methods, was studied. The integration of extraction and backextraction was also carried out, allowing a further acid removal with lower extractant concentrations.

Comparison of ultra- and microfiltration in the presence and absence of secondary flow with polysaccharides, proteins, and yeast suspensions

The purpose of this research was to show that controlled centrifugal instabilities—Dean vortices—produced by solutions and suspensions from typical biotechnology applications flowing through curved tubes can be used to reduce concentration polarization and/or fouling in pressure‐driven ultrafiltration (UF) and microfiltration (MF) processes. Experiments were conducted to (i) evaluate the ultrafiltration performance of hollow fiber membranes in linear and helical configurations with dextran (low fouling) and bovine serum albumin (high fouling) solutions and (ii) compare the performance of linear and helical coiled UF hollow fiber modules with that of similar MF modules using bakers and beer yeast (Saccharomyces cerevisiae) suspensions as feed. Both constant transmembrane pressure (TMP) and constant permeation flux (J) experiments were utilized here. The membrane material was polyether sulfone. For the ultrafiltration experiments, the helical module performed consistently better than the linear module with dextran T500 and BSA solutions, resulting in performance improvements (helical versus linear) from 20 to 200% and up to 85%, respectively. For the comparative experiments between UF and MF, the helical module again performed better than the linear module for low concentration bakers yeast suspensions (0.5–1% dry wt). At constant TMP, the flux improvements for UF were 30–120%, while at constant J, the capacity or loading was 4.5 times higher for the UF as compared to the MF membrane. At high beer yeast concentrations (5.1–6.8% dry wt), although flux improvements were not observed between the linear and helical modules for UF, the UF fluxes were 72% higher than that obtained with MF. Also, for MF, with the same high beer yeast concentrations, the helical module exhibited 30–90% higher fluxes than that obtained with the linear module. At constant flux (117–137 L m−2 h−1) and intermediate bakers yeast concentrations (0.65–2.7% dry wt), 10–20 times the capacity was obtained for the helical over the linear module. Yeast cells were the dominant foulant. For constant UF flux (70 L m−2 h−1) experiments at high beer yeast concentrations ((4.3–7.7) × 107 cells/mL or 5.1–6.8% dry wt), the capacity (loading) for the helical module was 10 times that of the linear module. Again, the yeast cells were the dominant foulant. A new mass‐transfer correlation for ultrafiltration of dextran T500 solutions for laminar flow in a helical hollow fiber module was obtained, viz. Sh = 0.173Re0.55Sc0.33(a/Rc) 0.07.

Enhanced membrane filtration of wood hydrolysates for hemicelluloses recovery by pretreatment with polymeric adsorbents

In this study adsorption of foulants from birch and pine/eucalyptus wood hydrolysates on two polymeric adsorbents was studied aiming to reduce the membrane fouling. The effect of the pretreatment of hydrolysate on polyethersulphone membrane performance was studied in dead-end filtration experiments. Adsorption pretreatment improved significantly filtration capacity and decreased membrane fouling. Especially high-molecular weight lignin was efficiently removed. A multistep adsorption pretreatment was found to reduce the amount of adsorbent required. While large adsorbent amount was shown to increase flux in filtration, it was found also to cause significant hemicellulose losses.

Simulation of integrated extraction and stripping processes using membrane contactors

A mathematical model has been developed to simulate the performance of an integrated extraction-stripping process based on the use of hollow fiber contactors. The model allows one to predict the time-dependent concentration profiles of the two phases involved in an individual extraction or stripping process, or of the three phases involved in an integrated extraction-stripping process (two aqueous phases — feed and stripping — and one organic phase). The model includes as parameters operating conditions such as the initial concentrations, volumes and flowrates, distribution coefficients and overall mass transfer coefficients.

Industrial Applications of Porous Ceramic Membranes (Pressure‐Driven Processes)

Publisher Summary This chapter discusses the industrial applications of porous ceramics membranes. Pressure-driven membrane processes are among the most mature membrane technologies. They are used for liquid separations and are generally classified into four categories: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), andmicrofiltration (MF). Pressure-driven membrane processes at present have high industrial impact, with a market constantly growing. They are used in a wide range of separation processes and are considered among the best available technologies (BAT), in the European Union environmental recommendations because they present several advantages with respect to other separation processes. The main applications of RO are found in the desalination of brackish and seawater; the production of ultrapure water (electronic industry); concentration of food juice, sugars, and milk; and in the treatment of wastewater. The performance of the ceramic membrane-based systems depends on the separation and permeation properties of the membrane as well as its mechanical integrity. These properties depend on the selective top layer and on the support system on which the active separation layer is coated. Therefore, pore size, porosity, surface roughness, and mechanical properties—all are important parameters.