Influence of electrostatic interactions in electrophoretic membrane contactors

In electrophoretic separators, a porous membrane is used to put into contact two flowing liquids between which an electrically driven mass transfer takes place. As far as charged solutes are concerned, the mass transfer can be affected by electrostatic interactions taking place at the membrane solution interface. The influence of these interactions on the solvent and solute transfer is investigated by associating a theoretical and an experimental work, carried out with buffered solutions of different solutes, chosen with respect to their size or electrical charge. Experimental variations of the electroosmotic flux as well as those of the solute concentrations are used to get the values of the characteristic parameters involved in the model. Results obtained with binary solutions are then compared to those obtained with single-solute solutions so as to point out the mass transfer limitation

Study of the mass transfer phenomena involved in an electrophoretic membrane contactor

Electrophoretic separators, in which a porous membrane is used as a contactor, offer the possibility to scale up electrophoresis as well as to extend the field of application of electrodialysis to fractionate polyamino acids, peptides or small proteins for instance. This paper deals with the study of the mass transfer mechanisms involved in such electroseparation processes. On one hand, a theoretical approach is carried out. The different contributions to the mass transfer are considered in order to establish a relationship providing the solute concentration as function of the main parameters of the system, i.e. the operating conditions and the membrane, buffer and solute characteristics. In this expression, a partition coefficient is used to represent the interactions taking place at the membrane–solution interface. Then, an experimental study is performed with different representative solutes using a prototype apparatus in order to determine the dependence of the solvent and solute transfer with respect to the operating and physicochemical parameters of the system. The experimental results show the existence of a limiting electro-osmotic flux, the origin of which is explained. Then the partition coefficient is determined for any set of conditions by fitting the variations of the solute concentration calculated by the model with experimental ones. The dependence of the partition coefficient with respect to the solute and buffer characteristics, together with that of the transmission coefficient obtained during filtration experiments, shows that the main limitation with respect to the mass transfer is due to electrostatic interactions taking place at the membrane–solution interface

The electrophoretic membrane contactor: A mass-transfer-based methodology applied to the separation of whey proteins

In the electrophoretic membrane contactor (EMC), a porous membrane is used to establish a contact across two flowing liquids between which an electrically driven mass transfer takes places. In this work, a methodology is proposed to select the best operating conditions to separate biomolecules in an EMC. Single-solution experiments were coupled with a theoretical approach to predict the influence of the process parameters (pH, membrane MWCO) on the separation factor.This methodology was applied to the separation of wheyproteins, α-lactalbumin and β-lactoglobulin, which are known to be difficult to separate. Experiments were first carried out with single synthetic protein solutions at different pH values (4.8, 6 and 8) using cellulose acetate membranes of either 30 or 100 kDa molecular weight cut-off. The experimental work was associated with a theoretical approach to study the mass transfer mechanisms. The parameters used in the model were calculated from the experimental variations of the solute and solvent transfer. The dependence of these parameters on the operating conditions gives the extent of electrostatic repulsion and provides information on the steric effect with respect to separation performance.The model was then used to calculate the separation factor for various operating conditions in order to determine the best ones (pH and membrane) for fractionation. Using the results, fractions enriched in α-lactalbumin and in β-lactoglobulin were obtained at pH 4.8 with the 100 kDa membrane

On the Endogeneity of Inflation Targeting: Preferences Over Inflation

Over the last quarter of a century, inflation targeting has become a popular monetary regime. Nevertheless, empirical evaluations of IT have shown contradictory results. Part of the reason is that IT in and of itself constitutes an endogenous decision and thus needs to be properly instrumented. In this paper, we show that preferences over inflation constitute a crucial determinant of IT: countries exhibiting greater inflation aversion are more likely to adopt IT.Inflation targeting, Monetary Policy, Monetary Regimes

Fluorescence spectroscopy applied to the optimisation of a desalting step by electrodialysis for the characterisation of marine organic matter

The isolation and characterisation of marine dissolved organic matter (DOM) are still not readily achieved today. The study of this chemically complex material is particularly difficult, especially as it is hindered by the high salinity of seawater. It is therefore essential to develop a method in which a sufficient quantity of marine organic matter can be collected for structural analyses. Reverse osmosis (RO) is often used for the concentration of DOM from freshwaters, due to the fact that DOM is not modified during RO and that DOC recoveries are high (about 80%). Unfortunately, RO cannot be used directly to isolate marine DOM,since both salts and organic matter are concentrated during the process. Therefore, marine samples have to be desalted before their concentration by RO. Our aim was to develop a desalting step of seawater by electrodialysis (ED), whilst minimising DOM modifications and losses. The process was first developed with small volumes (2 L) of artificial and Mediterranean seawater and was then applied to larger volumes.We showed that 20 L of Mediterranean seawater could be rapidly desalted (in less than 7 h) and, by monitoring the quality of DOM in desalted subsamples collected during ED using spectrofluorometry, that the quality of DOM was not significantly modified. It was concluded that desalted samples were still representative of the initial seawater samples. It should be noted, however, that care has to be taken in choosing the ratio of the volume of water to be desalted over the membrane surface area in order to limit DOM modifications and losses. Electrodialysis efficiently removed up to 75% of the salts present in the seawater samples whilst recovering most of unaltered DOM. ED and RO could then be combined in order to isolate, concentrate and characterise marine organic matter

Modelling the microfiltration of lactic acid fermentation broths and comparison of operating modes

clarification of fermentation broths by cross-flow microfiltration. Microfiltration experiments conducted under constant transmembrane pressure and under constant permeate fluxes (higher and lower than the critical flux) were represented by the resistance in series model in which the membrane resistance, the adsorption resistance, the bacteria cake resistance and the soluble compounds concentration polarisation resistance were taken into account. The different operating modes were compared in terms of two industrial interest criteria: the productivity and fouling rates. Higher productivities were obtained during constant transmembrane pressure runs whereas the lowest fouling rate was observed during the run conducted with a constant permeate flux lower than the critical flux. However, this fouling was mainly due to adsorption and solute components concentration polarisation. Key words

Influence of the ionic composition on the diffusion mass transfer of saccharides through a cation-exchange membrane

Recent studies have pointed out that the presence of salts can change significantly the membrane process performances because of the resulting modification of the neutral solutes transfer through the membrane. The influence of the ionic composition on the transfer of neutral solutes through membranes could be explained by a modification of the membrane properties, due to electrostatic effects, by a modification of the solute radius, likely due to its dehydration induced by the electrolyte, or more probably by a combination of both. This study deals with the investigation of the mechanisms governing the mass transfer of neutral species through an ion-exchange membrane used in electrodialysis, CMX, with a focus on the role of ions. The mass transfer of various saccharides (xylose,glucose and sucrose) as well as the solvent transfer in different electrolytic solutions (NaCl,NH 4Cl, CaCl 2 and MgCl 2) was studied in a diffusion regime. A specific procedure has been used to dissociate the solvent or solute fluxes variations due to the modifications of the solute properties and of the membrane material induced by the electrolyte. The results showed that the transfer modification is mainly due to the influence of the electrolyte on the membrane properties, which is fixed by the membrane soaking. A quantitative correlation has been established between the solvent and solute transfer and the hydration number of the membrane counterion. In presence of electrolyte, the saccharide mass transfer increased but the impact of the presence of electrolyte is much less than the one of membrane soaking. However, in this case, a relationship has been also established between the increase of the saccharide mass transfer and the cation hydration state

Introduction of nanofiltration in a production process of fermented organic acids

Nanofiltration in a production process of fermented organic acid

Investigation of nanofiltration as a purification step for lactic acid production processes based on conventional and bipolar electrodialysis operations

Nanofiltration was investigated for usability in a specific lactic acid production process based on conventional and bipolar electrodialysis operations. Industrial fluids, corresponding to two potential integration levels and coming from an existing installation, were investigated. The commercially available DK nanofiltration membrane was used and performances in terms of lactate/lactic acid recovery rate and purification efficiency are reported. Nanofiltration was able to efficiently remove magnesium and calcium ions from a sodium lactate fermentation broth before its concentration and conversion by electrodialysis (first potential integration level). Maximum impurities rejections and lactate recovery were obtained at maximum transmembrane pressures. Mg2+ and Ca2+ rejections were 64±7 and 72±7%, respectively and lactate recovery rate reached 25±2 molm−2 h−1 for P = 20 bar. Sulfate and phosphate ions were also partially removed from the broth (40% rejection). At the invert, chloride ions were negatively retained by the membrane and were consequently more concentrated in the permeate. Nanofiltration also led to a nearly total decolouration of the fermentation broth. On the other hand, sulfate and phosphate rejections obtained from the filtration of a converted broth containing the lactic acid under its neutral form (second potential integration level) were also satisfactory, i.e. 47±5 and 51±5%, respectively. High recovery rates were observed in that case, i.e. 48±2 molm−2 h−1 at 20 bar. It indicated that NF could also be used as final purification step in the process

Elaboration in Dependent Type Theory

To be usable in practice, interactive theorem provers need to provide convenient and efficient means of writing expressions, definitions, and proofs. This involves inferring information that is often left implicit in an ordinary mathematical text, and resolving ambiguities in mathematical expressions. We refer to the process of passing from a quasi-formal and partially-specified expression to a completely precise formal one as elaboration. We describe an elaboration algorithm for dependent type theory that has been implemented in the Lean theorem prover. Lean's elaborator supports higher-order unification, type class inference, ad hoc overloading, insertion of coercions, the use of tactics, and the computational reduction of terms. The interactions between these components are subtle and complex, and the elaboration algorithm has been carefully designed to balance efficiency and usability. We describe the central design goals, and the means by which they are achieved