Efrem Curcio

Membrane Distillation and Related Operations—A Review

Abstract Membrane contactors represent an emerging technology in which the membrane is used as a tool for inter phase mass transfer operations: the membrane does not act as a selective barrier, but the separation is based on the phase equilibrium. In principle, all traditional stripping, scrubbing, absorption, evaporation, distillation, crystallization, emulsification, liquid‐liquid extraction, and mass transfer catalysis processes can be carried out according to this configuration. This review, specifically addressed to membrane distillation (MD), osmotic distillation (OD), and membrane crystallization (MCr), illustrates the fundamental concepts related to heat and mass transport phenomena through microporous membranes, appropriate membrane properties, and module design criteria. The most significant applications of these novel membrane operations, concerning pure/fresh water production, wastewater treatment, concentration of agro food solutions, and concentration/crystallization of organic and biological solutions, are also presented and discussed.

Human hepatocyte functions in a crossed hollow fiber membrane bioreactor.

An important challenge in liver tissue engineering is the development of bioartificial systems that are able to favour the liver reconstruction and to modulate liver cell behaviour. A crossed hollow fiber membrane bioreactor was developed to support the long-term maintenance and differentiation of human hepatocytes. The bioreactor consists of two types of hollow fiber (HF) membranes with different molecular weight cut-off (MWCO) and physico-chemical properties cross-assembled in alternating manner: modified polyetheretherketone (PEEK-WC) and polyethersulfone (PES), used for the medium inflow and outflow, respectively. The combination of these two fiber set produces an extracapillary network for the adhesion of cells and a high mass exchange through the cross-flow of culture medium. The transport of liver specific products such as albumin and urea together with the transport of drug such as diazepam was modelled and compared with the experimental metabolic data. The theoretical metabolite concentration differed 7.5% for albumin and 5% for urea with respect to experimental data. The optimised perfusion conditions of the bioreactor allowed the maintenance of liver functions in terms of urea synthesis, albumin secretion and diazepam biotransformation up to 18 days of culture. In particular the good performance of the bioreactor was confirmed by the high rate of urea synthesis (28.7 microg/h 10(6) cells) and diazepam biotransformation. In the bioreactor human hepatocytes expressed at high levels the individual cytochrome P450 isoenzymes involved in the diazepam metabolism. The results demonstrated that crossed HF membrane bioreactor is able to support the maintenance of primary human hepatocytes preserving their liver specific functions for all investigated period. This device may be a potential tool in the liver tissue engineering for drug metabolism/toxicity testing and study of disease pathogenesis alternatively to animal experimentation.

Integrated membrane operations for seawater desalination

Reverse osmosis is widely applied to water desalination because of the relatively low cost of the process. Besides the well defined role that this technology plays in the desalination scenario, in the last years, from all over the world, demand for lower costs and higher quality of water has been advanced. Integrated membrane processes represent an attractive opportunity because of the synergic effects that can be reached, the simplicity of these units, and the possibility of advanced levels of automatisation and remote control. Moreover, the integration of different membrane units represents an interesting way for reaching the process intensification goals due to the possibility of overcoming the limits of the single units and, thus, to improve the performance of the overall operation.

Photothermal Membrane Distillation for Seawater Desalination

Thermoplasmonic effects notably improve the efficiency of vacuum membrane distillation, an economically sustainable tool for high-quality seawater desalination. Poly(vinylidene fluoride) (PVDF) membranes filled with spherical silver nanoparticles are used, whose size is tuned for the aim. With the addition of plasmonic nanoparticles in the membrane, the transmembrane flux increases by 11 times, and, moreover, the temperature at the membrane interface is higher than bulk temperature.

Recovery of fumaric acid by membrane crystallization in the production of L-malic acid

Abstract A study on redesigning traditional crystallizers by using microporous hydrophobic membranes and, in particular, the realization of a separation unit aiming to recover the unreacted fumaric acid leaving a biocatalytic membrane reactor for the production of l -malic acid is presented. The development of two main conceptual aspects of this operation are analysed: one concerning the transport of matter and energy through membrane, other the physical and chemical phenomena that occur during crystallization. From experimentally determined particle size distributions and induction time measurements, the parameters of a set of equations describing both heterogeneous and secondary nucleation processes, as well as growth rate, have been evaluated. Finally, population balance equation has been applied in order to predict the evolution of CDS in time.

Potential of brackish water and brine for energy generation by salinity gradient power-reverse electrodialysis (SGP-RE)

In the present work, a salinity gradient power-reverse electrodialysis (SGP-RE) unit was tested for the production of electrical energy by exploiting the chemical potential of real brackish water and exhaust brine from a solar pond. A cross-flow SGP-RE module (REDstack B.V.), equipped with AEM-80045 and CEM-80050 membranes specifically developed by Fujifilm Manufacturing Europe B.V. within the EU-funded project REAPOWER (“Reverse Electrodialysis Alternative Power Production”), was able to generate a maximum power density (expressed in W m−2 membrane pair – MP) of 3.04 W m−2 MP when operated with pure NaCl aqueous solutions (0.1 M in low concentration compartment – LCC, 5 M in high concentration compartment – HCC) at 20 °C and at a recirculation rate of 20 L h−1. However, a drastic reduction to 1.13 W m−2 (−63%) was observed when feeding the SGP-RE unit with artificial multi-ion solutions mimicking real brackish water and exhaust brine. Further experimental activity allowed to identify Mg2+ ion as responsible for the significant increase in stack resistance and consequent depletion in SGP-RE performance. Therefore, specific softening treatments of the real solutions should be considered in order to maintain the process efficiency at practical level.

Membrane crystallization of macromolecular solutions

Crystal growth is the critical step in determining the protein X-ray crystal structure. Hundreds, or even thousands, of crystallization trials must often be performed on a target macromolecule and, unfortunately, less than 1% of them typically yield promising results. Many macromolecules are reluctant to crystallize and, usually, their crystalline arrangement is not good enough to provide diffraction data at a resolution sufficient to establish structure-function correlation. The history of macromolecular crystallization emphasizes the importance of new observations and ideas that are useful in initiating more systematic studies using novel techniques and creative approaches. On this basis an innovative methodology, the membrane crystallization, has been introduced in order to promote the formation of macromolecular crystals. Lysozyme crystals, produced by removing the solvent (in vapour phase) from the protein solution by using microporous hydrophobic membrnaes, showed a good structural quality suitable for successive X-ray diffraction analysis.

Oxygen mass transfer in a human tissue-engineered trachea.

On June 2008, the first human tissue-engineered trachea replacement was performed using decellularized (de-antigenised) cadaveric donor trachea, seeded with recipient epithelial cells on the internal surface of the graft and mesenchymal stem-cell-derived chondrocytes on the external. During the follow-up, cytological analysis at 4 postoperative days showed a migration of the stem-cells derived chondrocytes from the outer to the inner surface of the first 2 cm of the graft length. With the aim to rationalize these clinical findings, and under the hypothesis that cellular migration is driven by the oxygen gradients developing from the external part of the construct (exposed to O(2) deficiency) towards the better oxygenated epithelial region, an accurate computational model of oxygen transport in the trachea engineered construct was developed and solved using finite element method (FEM). Results confirm that critical limitation to oxygen transport prevalently occurs from proximal to middle section, within the first 2.8 cm of longitudinal length, in good agreement with experimental observation. In the proximal section, recognized as the most critical part of the engineered construct, the severe O(2) mass transfer limitation causes a drastic reduction of the diffusive flux within a distance of 650 microm. At cell density of 1 x 10(7)cells/cm(3), the 30% c.a of the total section area is under oxygen deficiency (O(2) partial pressure below the critical threshold of 38 mmHg). Along the whole tracheal construct, the Thiele modulus ranges within 2.3 and 3.7 in the external chondrocyte compartment, confirming thus the importance of the mass transfer limitation to oxygen diffusion rate. In general, the efficiency of the O(2) transport reduces considerably in the region close to proximal section.

Antisolvent membrane crystallization of pharmaceutical compounds

This article describes a modification of the conventional membrane crystallization technique in which a membrane is used to dose the solvent/antisolvent composition to generate supersaturation and induce crystallization in a drug solution. Two operative configurations are proposed: (a) solvent/antisolvent demixing crystallization, where the solvent is removed in at higher flow rate than the antisolvent so that phase inversion promotes supersaturation and (b) antisolvent addition, in which the antisolvent is dosed into the crystallizing drug solution. In both cases, solvent/antisolvent migration occurs in vapor phase and it is controlled by the porous membrane structure, acting on the operative process parameters. This mechanism is different than that observed when forcing the liquid phases through the pores and the more finely controllable supersaturated environment would generate crystals with the desired characteristics. Two organic molecules of relevant industrial implication, like paracetamol and glycine, were used to test the new systems. Experiments demonstrated that, by using antisolvent membrane crystallization in both configurations, accurate control of solution composition at the crystallization point has been achieved with effects on crystals morphology.

Energetics of protein nucleation on rough polymeric surfaces.

Metropolis Monte Carlo (MC) algorithm of the two-dimensional Ising model is used to study the heterogeneous nucleation of protein crystals on rough polymeric surfaces. The theoretical findings are compared to those obtained from classical nucleation theory (CNT), and to experimental data from protein model hen egg white lysozyme (HEWL) crystallized on poly(vinylidene fluoride) or PVDF, poly(dimethylsiloxane) or PDMS and Hyflon homemade membranes. The reduction of the activation energy for the nucleation process on polymeric membranes, predicted to occur at increasing surface roughness, results in a nucleation kinetics that is many orders of magnitude faster than in homogeneous phase. In general, MC stochastic dynamics offers the unique opportunity to investigate the effects of collective molecular aggregation at site level on the nucleation rate and, consequently, allows to identify optimal morphological and structural properties of polymeric membranes for a fine control of the crystallization kinetics.