New robust and efficient liquid membranes for conductive vial electromembrane extraction of acids with low to moderate hydrophilicity in human plasma.

The current paper reports two new, robust, and efficient conditions for electromembrane extraction of acidic substances from human plasma. Two systems were developed based on eutectic solvents: A1 ("A" for acid) comprised dodecyl methyl sulfoxide and thymol in 1:2 ratio (w/w) as liquid membrane, while A2 used [6-methylcoumarin:thymol (1:2)]:2-nitrophenyl octyl ether in 2:1 ratio (w/w). The performance of A1 and A2 was characterized by extraction of 31 acidic model analytes (pharmaceutical drugs and nutrients) spiked into 100 µL human plasma diluted 1:1 (v/v) with phosphate buffer pH 7.4. The acceptor solution was 50 mM NH4HCO3 buffer pH 10.0, and extraction was performed at an agitation rate of 750 RPM. Voltage and extraction time were 30 V for 30 min and 10 V for 20 min for A1 and A2, respectively. Under optimal conditions, A1 extracted analytes with 1.8 ≤ log P ≤ 6.0 with an average recovery (R) of 85.1%, while A2 extracted in a range of 0.5 ≤ log P ≤ 6.0 with an average recovery of 79.9%. Meanwhile, extraction current was low at 9 and 26 µA, respectively, which is indicative of good system robustness. Using UHPLC-MS/MS analysis of the acceptor solution, repeatability of the A1 and A2 methods was determined to be 2.8-7.7% and 3.3-9.4% for R > 40%, matrix effects were 82-117% and 84-112%, respectively, and linear calibration curves were obtained. The performance and compatibility with human plasma represent a major improvement over previous state-of-the-art liquid membranes for acidic analytes, namely 1-octanol.

A review of greener approaches for rare earth elements recovery from mineral wastes.

The use of rare earth elements (REE) in many various fields, including high-tech products, increases the demand for these materials day by day. The production of REE from primary sources has expanded in response to increasing demand; however, due to its limited, a more sustainable supply is also started to offer for the REE demand by using secondary sources. The most commonly used metallurgical method for REE recovery is hydrometallurgical processes. However, it has some disadvantages, like pyrometallurgical methods. In the review, studies of the environmental impacts of REE production from primary sources and life cycle assessments of products containing REE were investigated. According to the results, it has been seen that those studies in the literature in which hydrometallurgical methods have changed to more environmentally friendly approaches have begun to increase. In this review, mine wastes, which are secondary sources, were defined, conventional methods of recovery of rare earth elements were discussed, greener approaches to the recovery of REE from these sources were comprehensively examined and studies in the literature were evaluated. Furthermore, it was stated that there are limited studies on green approaches and REE recovery from mineral wastes and that this field is developing with an emphasis on the current outlook and future perspectives.

Emulsion Liquid Membranes Based on Os-NP/n-Decanol or n-Dodecanol Nanodispersions for p-Nitrophenol Reduction.

Membrane materials with osmium nanoparticles have been recently reported for bulk membranes and supported composite membrane systems. In the present paper, a catalytic material based on osmium dispersed in n-decanol (nD) or n-dodecanol (nDD) is presented, which also works as an emulsion membrane. The hydrogenation of p-nitrophenol (PNP) is carried out in a reaction and separation column in which an emulsion in the acid-receiving phase is dispersed in an osmium nanodispersion in n-alcohols. The variables of the PNP conversion process and p-aminophenol (PAP) transport are as follows: the nature of the membrane alcohol, the flow regime, the pH difference between the source and receiving phases and the number of operating cycles. The conversion results are in all cases better for nD than nDD. The counter-current flow regime is superior to the co-current flow. Increasing the pH difference between the source and receiving phases amplifies the process. The number of operating cycles is limited to five, after which the regeneration of the membrane dispersion is required. The apparent catalytic rate constant (kapp) of the new catalytic material based on the emulsion membrane with the nanodispersion of osmium nanoparticles (0.1 × 10-3 s-1 for n-dodecanol and 0.9 × 10-3 s-1 for n-decanol) is lower by an order of magnitude compared to those based on adsorption on catalysts from the platinum metal group. The advantage of the tested membrane catalytic material is that it extracts p-aminophenol in the acid-receiving phase.

Efficiency, Kinetics and Mechanism of 4-Nitroaniline Removal from Aqueous Solutions by Emulsion Liquid Membranes Using Type 1 Facilitated Transport.

4-Nitroaniline (4NA) is a common organic pollutant that is released into the environment during the manufacture and processing of a wide variety of industrial products. This article describes the use of an emulsion liquid membrane process to remove 4NA from aqueous solutions using a type 1 facilitated transport mechanism. Optimization of the removal process was carried out by analyzing the efficiency of 4NA removal from the feed phase and the initial apparent feed/membrane fluxes and permeabilities under different experimental conditions. The kinetics of the removal process was analyzed using a simplified mass transfer model involving an empirical mass transfer coefficient calculated from experimental data, assuming that the concentrations of 4NA in the external aqueous phase and in the internal w/o emulsion are uniform. The results show that there is a very good fit between the experimental and model data and that the variation in the values of the overall mass transfer coefficients with the experimental conditions coincides with that of the removal efficiency mentioned above. The transport mechanism was studied by identifying the rate-controlling step of the removal process, using models described for adsorption processes, due to the strong parallelism between the transport mechanisms in adsorption and emulsion liquid membrane processes.

Modelling and Comparative Analysis of Different Methods of Liquid Membrane Separations.

This article is devoted to a brief review of the modelling of liquid membrane separation methods, such as emulsion, supported liquid membranes, film pertraction, and three-phase and multi-phase extraction. Mathematical models and comparative analyses of liquid membrane separations with different flow modes of contacting liquid phases are presented. A comparison of the processes of conventional and liquid membrane separations is carried out under the following assumptions: mass transfer is described by the traditional mass transfer equation; the equilibrium distribution coefficients of a component passing from one of the phases to another are constant. It is shown that, from the point of view of mass transfer driving forces, emulsion and film pertraction liquid membrane methods have advantages over the conventional conjugated extraction stripping method, when the mass-transfer efficiency of the extraction stage is significantly higher than the efficiency of the stripping stage. The comparison of the supported liquid membrane with conjugated extraction stripping showed that when mass-transfer rates on the extraction and stripping sides are different, the liquid membrane method is more efficient, while when they are equal to each other, both processes demonstrate the same results. The advantages and disadvantages of liquid membrane methods are discussed. The main disadvantages of liquid membrane methods-low throughput and complexity-can be overcome by using modified solvent extraction equipment to carry out liquid membrane separations.

Extraction of Copper from Sulfuric Acid Solutions Based on Pseudo-Liquid Membrane Technology.

Pseudo-liquid membranes are extraction devices in which a liquid membrane phase is retained in an apparatus consisting of two interconnected chambers while feed and stripping phases pass through the stationary liquid membrane phase as mobile phases. The organic phase of the liquid membrane sequentially contacts the aqueous phases of the feed and stripping solutions in the extraction and stripping chambers, recirculating between them. This extraction separation method, called multiphase pseudo-liquid membrane extraction, can be implemented using traditional extraction equipment: extraction columns and mixer-settlers. In the first case, the three-phase extraction apparatus consists of two extraction columns connected at the top and bottom by recirculation tubes. In the second case, the three-phase apparatus consists of a recycling close-loop, which includes two mixer-settler extractors. In this study, the extraction of copper from sulfuric acid solutions in two-column three-phase extractors was experimentally studied. A 20% solution of LIX-84 in dodecane was used as the membrane phase in the experiments. It was shown that the extraction of copper from sulfuric acid solutions in the apparatuses studied was controlled by the interfacial area in the extraction chamber. The possibility of the purification of sulfuric acid wastewaters from copper using three-phase extractors is shown. To increase the degree of extraction of metal ions, it is proposed to equip two-column three-phase extractors with perforated vibrating discs. To further increase the efficiency of extraction using the pseudo-liquid membrane method, it is proposed to use multistage processes. The mathematical description of multistage three-phase pseudo-liquid membrane extraction is discussed.

Recent Advances in Poly(Ionic Liquid)-Based Membranes for CO2 Separation.

Poly(ionic liquid)-based membranes have been the subject of intensive research in the last 15 years due to their potential for the separation of CO2 from other gases. In this short review, different types of PIL-based membranes for CO2 separation are described (neat PIL membranes; PIL-IL composite membranes; PIL-polymer blend membranes; PIL-based block copolymer membranes, and PIL-based mixed matrix membranes), and their state-of-the-art separation results for different gas pairs (CO2/N2, CO2/H2, and CO2/CH4) are presented and discussed. This review article is focused on the most relevant research works performed over the last 5 years, that is, since the year 2017 onwards, in the field of poly(ionic liquid)-based membranes for CO2 separation. The micro- and nano-morphological characterization of the membranes is highlighted as a research topic that requires deeper study and understanding. Nowadays there is an array of advanced structural characterization techniques, such as neutron scattering techniques with contrast variation (using selective deuteration), that can be used to probe the micro- and nanostructure of membranes, in length scales ranging from ~1 nm to ~15 µm. Although some of these techniques have been used to study the morphology of PIL-based membranes for electrochemical applications, their use in the study of PIL-based membranes for CO2 separation is still unknown.

Comparative Study of 4-Aminophenol Removal from Aqueous Solutions by Emulsion Liquid Membranes Using Acid and Basic Type 1 Facilitations: Optimisation and Kinetics.

The molecule 4-aminophenol (4AP) is recognised as a serious environmental pollutant that enters the environment during the manufacture and processing of a variety of industrial processes and through the degradation of some pharmaceutical products. This paper describes a comparative study of 4AP removal from aqueous solutions by emulsion liquid membranes using acid and basic type 1-facilitated transports. The results are explained by analysing the stripping process through both the different relative acid/basic strength of the hydroxyl and amine groups of the 4AP molecule and the hydrogen-bonding capacity with water of the ionisation products generated by the reaction of 4AP with HCl or NaOH. To optimize the 4AP removal process, the influence of different experimental conditions (stripping agent concentration in the product phase, surfactant concentration in the membrane phase, stirring rate, feed phase/emulsion phase volume ratio, product phase/membrane phase volume ratio and emulsification rate and time) were studied. The kinetics of the removal process has been analysed by fitting the experimental results to first order, second order and the Behnajady and Avrami models. The Behnajady model presents an excellent fit, allowing to calculate both the initial removal rate and the maximal removal conversion. Optimal conditions of the removal process obtained through these parameters are in full agreement with those obtained from the experimental study.

Three- and Multi-Phase Extraction as a Tool for the Implementation of Liquid Membrane Separation Methods in Practice.

To promote the implementation of liquid membrane separations in industry, we have previously proposed extraction methods called three- and multi-phase extraction. The three-phase multi-stage extraction is carried out in a cascade of bulk liquid membrane separation stages, each comprising two interconnected (extraction and stripping) chambers. The organic liquid membrane phase recycles between the chambers within the same stage. In multi-phase extraction, each separation stage includes a scrubbing chamber, located between the extraction and stripping chambers. The three- and multi-phase multi-stage extraction technique can be realized either in a series of mixer-settler extractors or in special two- or multi-chamber extraction apparatuses, in which the convective circulation of continuous membrane phase between the chambers takes place due to the difference in emulsion density in the chambers. The results of an experimental study of the extraction of phenol from sulfuric acid solutions in the three-phase extractors with convective circulation of continuous membrane phase are presented. Butyl acetate was used as an extractant. The stripping of phenol from the organic phase was carried out with 5-12% NaOH aqueous solutions. The prospects of using three-phase extractors for wastewater treatment from phenol are shown. An increase in the efficiency of three-phase extraction can be achieved by carrying out the process in a cascade of three-phase apparatuses.

Obtaining and Characterizing the Osmium Nanoparticles/n-Decanol Bulk Membrane Used for the p-Nitrophenol Reduction and Separation System.

Liquid membranes based on nanoparticles follow a continuous development, both from obtaining methods and characterization of techniques points of view. Lately, osmium nanoparticles have been deposited either on flat membranes, with the aim of initiating some reaction processes, or on hollow fiber membranes, with the aim of increasing the contact surface with the phases of the membrane system. This paper presents the obtainment and characterization of a liquid membrane based on osmium nanoparticles (Os-NP) dispersed in ndecanol (nDol) for the realization of a membrane system with a large contact surface between the phases, but without using a liquid membrane support. The dispersion of osmium nanoparticles in n-decanol is carried out by the method of reducing osmium tetroxide with 1-undecenoic acid (UDA). The resulting membrane was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy analysis (EDAX), thermoanalysis (TG, DSC), Fourier transform infra-red (FTIR) spectroscopy and dynamic light scattering (DLS). In order to increase the mass transfer surface, a design for the membrane system was realized with the dispersion of the membrane through the receiving phase and the dispersion of the source phase through the membrane (DBLM-dispersion bulk liquid membrane). The process performance was tested for the reduction of p-nitrophenol (pNP) from the source phase, using sodium tetra-borohydride (NaBH4), to p-aminophenol (pAP), which was transported and collected in the receiving phase. The obtained results show that membranes based on the dispersion of osmium nanoparticles in n-decanol can be used with an efficiency of over 90% for the reduction of p-nitrophenol and the separation of p-aminophenol.