Liquid Membrane Separation Processes Research Articles

Lactic Acid Extraction from Aqueous Systems by Emulsion Liquid Membrane Separation Process Using Statistical Experimental Design

Box-Behnken design was utilized to obtain optimized process condition for maximizing lactic acid extraction efficiency and initial extraction rate by emulsion liquid membrane (ELM) process. A mixture of tri-n-octylamine and tri-n-decylamine (1:1, v/v) was employed as carrier in membrane phase of ELM for synergic facilitated lactic acid transport. The effect of different process parameters like lactic acid concentration in feed, sodium carbonate concentration in internal phase, carrier fraction, treatment ratio, phase ratio, stirring speed and contact time has been investigated. Extraction efficiency of 98.5% and 9.36 × 10−9 mol/cm2.sec, initial extraction rate were found under optimized conditions of process parameters.

Separation and recovery of critical metal ions using ionic liquids

Separation and purification of critical metal ions such as rare-earth elements (REEs), scandium and niobium from their minerals is difficult and often determines if extraction is economically and environmentally feasible. Solvent extraction is a commonly used metal-ion separation process, usually favored because of its simplicity, speed and wide scope, which is why it is often employed for separating trace metals from their minerals. However, the types of solvents widely used for the recovery of metal ions have adverse environmental impact. Alternatives to solvent extraction have been explored and advances in separation technologies have shown commercial establishment of liquid membranes as an alternative to conventional solvent extraction for the recovery of metals and other valuable materials. Liquid membrane transport incorporates solvent extraction and membrane separation in one continuously operating system. Both methods conventionally use solvents that are harmful to the environment, however, the introduction of ionic liquids (ILs) over the last decade is set to minimize the environmental impact of both solvent extraction and liquid membrane separation processes. ILs are a family of organic molten salts with low or negligible vapour pressure which may be formed below 100 °C. Such liquids are also highly thermally stable and less toxic. Their ionic structure makes them thermodynamically favorable solvents for the extraction of metallic ions. The main aim of this article is to review the current achievements in the separation of REE, scandium, niobium and vanadium from their minerals, using ILs in either solvent extraction or liquid membrane processes. The mechanism of separation using ILs is discussed and the engineering constraints to their application are identified.

Integrated use of liquid membranes and membrane contactors: Enhancing the efficiency of L-L reactive separations

Separation processes combining facilitated transport membranes and membrane contactors offer several advantages such as the ability of liquid membranes to promote the uphill transport of target species by the coupling between mass transfer and chemical reaction, together with the benefits of using membrane contactors: large interfacial area, non-dispersive contact and independent flow of the fluid phases that can play an important role in process intensification. In this work, computer simulation techniques using previously validated mathematical models which take into account mass transfer and chemical reaction are employed: (i) to design the integration of liquid contactors in an already existing electroplating process and (ii) to quantify the degree of intensification provided by liquid membrane separation processes through the definition of suitable intensification indexes such as productivity/size ratio and modularity. The methodology has been illustrated through two different real applications in the context of surface treatment industry which were extensively analyzed in previous works: (i) the regeneration of trivalent chromium passivation baths by the on-site continuous removal of zinc and iron trap ions derived from the electroplating process and, (ii) the treatment of spent pickling hydrochloric acid generated in the hot-dip galvanizing process, with the aim of recovering the valuable zinc.

Recent progress in supported liquid membrane technology: stabilization and feasible applications

Supported Liquid Membranes (SLMs) have been widely studied as feasible alternative to traditional processes for separation and purification of various chemicals both from aqueous and organic matrices. This technique offers various advantages like active transport, possibility to use expensive extractants, high selectivity, low energy requirements and minimization of chemical additives. SLMs are not yet used at large scale in industrial applications, because of the low stability. In the present paper, after a brief overview of the state of the art of SLM technology the facilitated transport mechanisms of SLM based separation is described, also introducing the small and the big carrousel models, which are employed for transport modeling. The main operating parameters (selectivity, flux and permeability) are introduced. The problems related to system stabilization are also discussed, giving particular attention to the influence of membrane materials (solid membrane support and organic liquid membrane (LM) phase). Various approaches proposed in literature to enhance SLM stability are also reviewed. Modification of the solid membrane support, creating an additional layer on membrane surface, which acts as a barrier to LM phase loss, increases system stability, but the membrane permeability, and then the flux, decrease. Stagnant Sandwich Liquid Membrane (SSwLM), an implementation of the SLM system, results in both high flux and stability compared to SLM. Finally, possible large scale applications of SLMs are also reviewed, evidencing that if the LM separation process is opportunely carried out (no production of byproducts), it can be considered as a green process.

An overview of the mathematical modelling of liquid membrane separation processes in hollow fibre contactors

AbstractLiquid membranes have traditionally been employed for liquid/liquid mass transfer and have found applications in industrial, biomedical and analytical fields as well as in hydrometallurgical processes, wastewater treatment and remediation of polluted groundwater. However, in spite of the known advantages of liquid membranes, there are few examples of industrial application. The development of reliable mathematical models and design parameters (mass transport coefficients and equilibrium or kinetic parameters associated with the interfacial reactions) is a necessary step for design, cost estimation, process optimisation and scale‐up. This work reports an overview of the different approaches that have been proposed in the literature to the mathematical modelling of liquid membrane separation processes in hollow fibre contactors providing, at the same time, a useful guideline to characterise the mass transport phenomena and a tool for the optimal design and intensification of separation processes. Copyright © 2009 Society of Chemical Industry

Non-Newtonian conversion solves problems of stability, permeability, and swelling in emulsion liquid membranes

Our recent experiments have proved the effectiveness of non-Newtonian conversion of the membrane in emulsion liquid membrane separation processes, with regard to simultaneously enhanced stability, retained – or improved – permeability, and reduced swelling. These findings for Type 1 (non-carrier) systems are now extended here to two new solutes with a variety of membrane formulations to demonstrate the generality of this approach. There are grounds for optimism in the proposed extension of this new procedure to Type 2 (carrier-containing) membranes, despite their unique stability problems.

A new solution to emulsion liquid membrane problems by non‐Newtonian conversion

AbstractEmulsion liquid membrane separation processes remain excessively vulnerable to one or more of four major problems. Difficulties lie in developing liquid membranes that combine high levels of both stability and permeability with acceptably low levels of swelling and ease of subsequent demulsification for membrane and solute recovery. This article provides a new technique for simultaneously overcoming the first three problems, while identifying physical indications that the proposed solution may have little adverse effect on the fourth problem (demulsification) and may even alleviate it. Numerous benefits of optimized conversion of the membrane phase into suitable non‐Newtonian form are identified, their mechanisms outlined, and experimental verifications provided. These include increased stability, retained (or enhanced) permeability, reduced swelling, increased internal phase volume, and increased stirrer speeds. The highly favorable responsiveness of both aliphatic and aromatic membranes to the new technique is demonstrated.

Extraction and Stripping Characteristics of Ni(II) with Di(2-ethylhexyl)Phosphoric Acid under a High Electrostatic Field

Recently, a new liquid membrane separation process called ESPLIM (Electrostatic Pseudo-Liquid Membrane) was proposed. This process is characterized by the simultaneous extraction and stripping in a single tank, in which the aqueous phase is dispersed in the organic phase under a high electrostatic field. To obtain a fundamental knowledge of the applicability of ESPLIM to recover metal values from the leach solution, it is useful to study the characteristics of extraction and stripping, separate(y. In this study, the effect of various factors on the extraction of Ni(II) with di(2-ethylhexyl)phosphoric acid from NiSO 4 -CH 3 COONa aqueous solution and the stripping of the extracted Ni(11) with HCl aqueous solution was investigated separately under a high electrostatic field. The main results are as follows

Metal ion transport through microemulsion liquid membranes

Reversed micelles of AOT and C 12EO 4 are used as mobile carriers to transport metal ions between two liquid-liquid interfaces. For this purpose w/o microemulsions are replacing classical liquid membranes separating two aqueous compartments, one “source” compartment containing the solute to be transported and one “receiving” compartment in which ion transfer can be monitored. Two types of detection have been used: UV-visible absorption (picrate transport) and atomic absorption (Ni 2+ transport). Different parameters influencing the transport rate are examined: nature and composition of the microemulsion, nature of the salt (anion effect), pH of the receiving phase. The transport mechanism is shown to be different for the C 12EO 4 and the AOT systems and models are proposed for the interfacial transfer step. Coupled transport experiments are also reported in which two different carriers are operating in the liquid membrane: reversed micelles and extractant molecules (crown-ethers or Kelex 100). Synergy effects for metal ion transport have been found in some cases but not in others. These results are discussed in terms of diffusion of the carriers in the stagnant layers. They provide useful guides for further investigations concerning the development of liquid membrane separation processes based on microemulsion systems.

Use of additives to enhance the selectivity of liquid surfactant membranes

This study is aimed at attempting to improve both the selectivity and the permeation rates for the separation of 1-methylnaphthalene from dodecane using aqueous surfactant membranes. This enhancement is achieved by adding various water-soluble chemical compounds (“additives”) to the water phase. Seven different additives were tried in this study and their efficacy was determined by carrying out mass transfer permeation experiments to determine both the rates of transfer and the selectivity of separation. In line with our previous work (Sharma et al. [5]; Krishna et al. [6]), we have corrected the mass transfer coefficients for emulsion breakage, and found these coefficients, and the selectivity, to correlate well with the work of transfer of the additive-containing surfactant system. The increase in selectivity in the presence of the additive has been shown to be due to the relative increase in the activity coefficient of 1-methylnaphthalene in the aqueous solution with respect to that of dodecane. The presence of the additive increases the selectivity by about one order of magnitude, and the present study should aid in the development of a viable liquid membrane separation process for the selective removal of aromatics from kerosene, a process which is required for the production of aviation turbine fuel from crudes having a high aromatic content in the lighter distillates.

Effect of emulsion breakage on selectivity in the separation of hydrocarbon mixtures using aqueous surfactant membranes

In liquid membrane separation processes emulsion breakage results in non-selective physical mixing of the feed mixture with the receiving solvent phase. In this paper a model is developed for describing the interphase transfer process, which takes emulsion breakage into account. The overall transfer is envisaged as a result of two parallel transfer mechanisms: (i) diffusive transport across the membrane and (ii) non-selective physical mixing of the feed with the receiving phase due to emulsion breakage. For selective removal of aromatics from non-aromatics in a feed mixture the “ideal” selectivity, β, obtained in the absence of non-selective breakage, will he given as the ratio of the products of the distribution coefficients times the diffusivity in the aqueous membrane phase. Experiments were carried out in a batch stirred cell to determine the permeation rates for a benzene-n-heptane mixture. From the experimentally observed selectivities the contribution due to emulsion breakage was estimated. This fractional breakage was in good agreement with values determined independently using a water-insoluble dye tracer technique, lending support to the developed model. Further experiments were carried out with the system 1-methylnaphthalene-dodecane, and breakage-corrected transfer rates were determined. The model developed in this paper, together with the experimental studies, sheds light on the mechanism of liquid membrane permeation and should aid in scaling-up processes for dearomatization of naphtha and kerosine.

Membrane Recovery in Liquid Membrane Separation Processes

Abstract The use of conventional electrostatic coalescers with bare metal electrodes for the separation of rich water-in-oil emulsions often causes the formation of a sponge-like emulsion. This effect was eliminated by the use of insulated electrodes in a coalescer that allow the application of high electric fields at the oil/water interface, resulting in a clean separation of oil from water.