No description available.

A sampler has been fabricated to facilitate the in-situ speciation of Cr. Teflon® was selected as the material for the samplers because of its inert chemical nature. The design of the sampler is based on the Supported Liquid Membrane (SLM) extraction technique, which utilizes charged organic carrier molecules loaded onto a polymeric (Teflon®) support membrane and the principles of electrostatics to selectively transport Cr ions through an ion-pairing mechanism. Cr ions in the feed solution that have an opposite charge from the carrier molecule form an ion-pair with the carrier and are transported through the membrane and deposited into a second aqueous phase referred to as the acceptor phase. A counter-ion from the acceptor phase is exchanged for the Cr ion to complete the extraction process. Since the acceptor phase is contained in a Teflon® bottle, the SLM sampler is capable of speciation and storage of Cr ions, which is a major advantage over current speciation techniques. A food coloring test was used to check the samplers for leaks. A plastic barrier was used in place of the polymeric membrane and the acceptor phase bottle was filled with DI water. The sampler was submerged in a beaker containing food coloring and DI water. The bottle contents were checked for the presence of food coloring using UV-vis spectroscopy. The sampler was determined to be leak-free if the bottle did not contain food coloring. All systems prepared were validated upon the initial test and required no further manipulation to ensure structural soundness. The SLM extraction technique involves two liquid-liquid extractions (LLEs). Before the samplers could be evaluated for their performance and stability in Cr speciation applications, liquid-liquid extraction studies were conducted on both systems (Cr (III) and Cr (VI)) to determine the optimal operating parameters (carrier concentration, decanol concentration, and acceptor phase concentration) of the SLM system. The selectivity of each system was also evaluated to validate proper SLM function. The performance of the samplers was evaluated in a series of tank studies that focused on the uptake of Cr into the acceptor phase as well as the depletion of Cr ion from this phase. The goal of the performance studies was to determine the mechanical and chemical stability of the SLM samplers. As part of the validation process, selectivity studies and studies without the carrier molecule were conducted to ensure that the systems were functioning according to SLM theory. Tank studies that simulated natural sampling condition were also conducted. The results of the tests conducted in the laboratory indicate that the SLM samplers are a stable, reliable, and viable method for Cr speciation. Future directions of this project will include the incorporation of the SLM sampler into the existing Multi-layer Sampler (MLS) technology as well as the analysis of the stability and performance of the incorporated systems in the ""in-situ speciation application. / Ph. D.

No description available.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2011 / Treatment of waste material from mining and mineral processing is gaining increasing importance as a result of the increasing demand for high purity products and environmental concerns. Supported liquid membranes (SLMs) have been proposed as a new technology for the selective removal of metal ions from a solution. This technology can be described as the simultaneous extraction and stripping operation, combined in a continuous single process unit. Theoretically, the rate of mass transfer through SLM systems could be controlled by three resistances, namely: · Resistance through the feed-side · Resistance through the strip-side laminar layers; and · Diffusion through the membrane. It has been reported that transport resistance in the feed-side laminar layer is controlling. (Srisurichan et al, 2005:186). The objective of this research was to extract copper ions in a TSLM system, evaluate the effect of the feed characteristics on the feed-side laminar layer and determine a relationship between the applicable dimensionless numbers, i.e. Sherwood, Schmidt and Reynolds numbers. A Counter-current, double pipe Perspex bench-scale reactor, consisting of a single hydrophobic PVDF tubular membrane mounted vertically within, was used for the test work. The membrane was impregnated with LIX 984N-C and became the support for this organic transport medium. Dilute Copper solution passed through the centre pipe and sulphuric acid, as a strippant, passed through the shell side. In this test work, Copper was successfully transported from the feed-side to the strip-side and through repetitive results; a relationship between dimensionless numbers was achieved.

This report details the development and validation of a model for the simulation of supported liquid membrane processes, as applied to the extraction of lanthanides. Supported liquid membranes are systems where two phases, usually aqueous, are separated by a third phase, typically organic, which acts as a membrane, in order to separate solutes from one phase to the other. The model employs an analytical solution to the diffusion equation for the organic phase and linear approximations of the resistances to mass transfer in the aqueous phase boundary layers. The goal of this model is to underline the importance of taking these boundary layer resistances into account. / Detta arbete introducerar, deriverar och evaluerar en matematisk modell för simulering av vätskemembranprocesser, tillämpat på vätskeextraktion av lantanider. Immobiliserade vätskemembran betecknar system där två faser oftast vatten, separeras av en tredje organisk fas som agerar membran för att separera och transportera lösta komponenter från den ena vattenfasen till den andra. Modellen utnyttjar sig av en analytisk lösning till diffusionsekvationen för den organiska fasen och linjära approximationer för motstånden mot masstransport i de båda vattenfasernas gränsskikt. Målet med modellen är att understryka vikten av att inkludera dessa gränsskikt i beräkningarna.

Este trabajo tiene como objetivo el desarrollo de la metodología de diseño óptimo de procesos de separación con membranas líquidas selectivas en su aplicación a la separación de mezclas multicomponentes con recuperación selectiva del componente de interés. Para ello se ha investigado la separación selectiva y concentración de cromo(VI) presente inicialmente en un acuífero subterráneo contaminado por acción de la actividad industrial desarrollada a nivel superficial y donde a su vez, coexisten otras especies aniónicas competitivas (sulfato y cloruro mayoritariamente) presentes por las propias características del acuífero y por su localización en una zona litoral. Tras la selección de Alamine 336 (amina terciaria) y NaOH como agentes de extracción y reextracción respectivamente, se caracterizaron experimentalmente las reacciones químicas responsables de la etapa de extracción, así como la cinética del proceso de separación-concentración cuando se emplea la tecnología de pertracción en emulsión (EPT) en contactores de fibra hueca. Finalmente, se desarrolló un modelo matemático multicomponente y se determinaron los parámetros característicos del mismo con el fin de llevar a cabo el diseño óptimo del proceso mediante técnicas de optimización matemática. / This work aims at the development of the methodology for the optimal design of selective liquid membrane processes as efficient alternatives for the separation and selective recovery of raw materials and valuable compounds from multicomponent systems. For this purpose, the proposed methodology has been applied to the remediation of polluted groundwater containing hexavalent chromium as a consequence of effluent leaking from surface deposition of industrial wastes. Furthermore, other competitive anionic species (mainly sulphate and chloride anions) were also present in the groundwaters due to the specific location being close to the shore.After selecting Alamine 336 (tertiary amine) and NaOH as the best extraction and back-extraction agents respectively, a careful experimental design was performed in order to analyse the chemical equilibria involved in the extraction step. Once the emulsion pertraction technology (EPT) was selected as the most suitable separation-concentration process configuration, the experimental kinetic analysis and mathematical modeling of EPT were carried calculating the values of the design parameters. Finally, the proposed multicomponent model was employed to carry out the optimal process design by means of mathematical optimization techniques.

El presente trabajo de Tesis tiene como finalidad analizar el potencial de los líquidos iónicos como medios de reacción y separación en reacciones de transesterificación enzimáticas. Los ILs inmiscibles con agua han resultado medios muy adecuados para llevar a cabo la síntesis de ésteres catalizada por la lipasa B de Candida antarctica (CALB), incrementando la actividad y selectividad enzimática con respecto a los valores obtenidos en disolventes orgánicos convencionales como n-hexano. El uso de líquidos iónicos miscibles con agua ha dado lugar a menores valores de actividad enzimática que n-hexano, aunque la selectividad en estos medios es mucho mayor. Los ILs se han revelado también como prometedores disolventes en su empleo en procesos de separación, más concretamente como fase líquida en membranas líquidas soportadas (SLMs). Se han desarrollado SLMs basadas en ILs altamente estables que permiten llevar a cabo la separación selectiva de sustratos y productos de reacciones de transesterificación. / The main objective of this thesis is to analyze the potential use of ionic liquids as reaction and separation media in lipase-catalysed transesterification reactions. The use of ionic liquids in biocatalytic processes has been shown to be an environmentally attractive alternative to classical organic solvents. Water-immiscible ionic liquids appeared as suitable media for the transesterification reactions catalysed by Candida antarctica lipase B (CALB), increasing the activity and selectivity with respect to the values obtained with a classical organic solvent, n-hexane. The use of water-miscible ionic liquids led to lower activities than obtained in n-hexane, although the selectivity values were much higher in these media. Ionic liquids have also been shown to be promising solvents for the use in separation processes, more specifically as liquid phase in supported liquid membranes (SLMs). Highly stable SLMs based on ionic liquids have been succesfully used for the selective separation of different organic compounds which are substrates and products of transesterification reactions.

El control d'herbicides i altres anàlits orgànics presents en el medi ambient constitueix una pràctica habitual en els laboratoris des de l'establiment de legislacions que limiten la seva concentració. Per aquesta raó, cal el desenvolupament de noves metodologies analítiques per al seguiment de compostos orgànics en el medi. Molt sovint aquests anàlits es troben a nivells traça en aigües i sòls, conjuntament amb un alt contingut de substàncies húmiques i fúlviques. Així, un dels reptes existents és el tractament de la mostra (extracció, concentració i "clean-up" d'aquests anàlits per a una bona quantificació). Aquests processos han de venir complementats per tècniques cromatogràfiques que permetin la mesura final dels anàlits.La investigació que es presenta en aquesta tesi es centra en el desenvolupament d'un mètode per a la determinació de 2,4-D i MCPA i els seus metabòlits fenòlics i d'un altre per a la determinació de cafeïna. El primer dels procediments desenvolupats s'ha aplicat al seguiment dels herbicides i els metabòlits fenòlics en sòls d'un camp de golf, mentre que el segon s'ha emprat per a la determinació de cafeïna en aigües naturals i, posteriorment, en aigües residuals. / The control of herbicides and other organic pollutants present in the environment has become a routine practise in many laboratories since the establishment of legislations that indicates the maximum allowed levels for these compounds. For this reason, it is necessary to develop new analytical methodologies for the monitoring of organic compounds in the environment. These analytes are often found at trace levels in waters and soils, with a high humic and fulvic organic matter content associated. One of the most important challenges in this field is the sample treatment (i.e. extraction, concentration and clean-up of the compounds to obtain a correct quantification). These procedures have to be coupled to chromatographic techniques to allow the determination of the compounds. This study is devoted to the development of a method for the determination of 2,4-D, MCPA and their phenolic metabolites and another method for the determination of caffeine. The first method has been applied for the monitoring of the herbicides and their metabolites in soils from a golf course; the second has been applied to the determination of caffeine in natural and urban wastewaters.

Separation of dissolved metals from aqueous solutions using liquid membrane technology is highly advantageous owing to the degree of separation achieved, efficiency and application potential. In the present investigation four types of liquid membranes - bulk liquid membrane (BLM), emulsion liquid membrane (ELM), electrostatic pseudo liquid membrane (ESPLIM) and unified liquid membrane (ULM) have been extensively studied, for their application in extraction and concentration of dissolved metals from effluents. Experiments were conducted with various metal systems to optimize both system and process conditions and to find out the effect of various parameters on the performance of the process. Different mass transport models were proposed for each type, taking diffusional and kinetic resistances into account. Models were extended for simultaneous extraction systems and were verified by different metal-carrier experiments. Good agreement was found between the concentration profiles obtained from the models and the experimental data, thereby establishing the validity of models for all the four types of liquid membranes. The stirred cell employed in BLM process eliminates emulsification and demulsification processes. It also provides simultaneous contact of the organic liquid membrane phase with aqueous feed and strip phases. Overall rate expressions for extraction and stripping in BLM are based on an assumed kinetic mechanism to explain the process qualitatively. It was found that the magnitude^ of diffusional and kinetic resistances determines the overall mass transfer coefficient. The relative magnitude of mass transfer coefficient, reaction rate constants and equilibrium constants enables to visualize the controlling regime of the process. The problem of low flux rate due to high diffusion resistances, inefficient operation and exorbitant costs encountered in bulk and supported liquid membranes (SLM) are overcome in an ELM. In the ELM process, an emulsion of organic membrane phase and aqueous inner phase, is dispersed in the continuous aqueous feed phase. This gives a highly selective and ultra thin liquid film generating a large mass transfer area for separation. Experimental results on membrane instability and emulsion swelling indicate that volumetric leakage rate depends linearly on the stirring speed and that the nature of surfactant does not have any appreciable effect on emulsion swelling. A general permeation model was developed taking into account the external mass transfer around the emulsion drop, diffusion in the drop, reaction at the aqueous-organic interface, leakage of the internal phase to the external phase due to membrane breakup and emulsion swelling due to osmotic pressure difference. Model equations with appropriate boundary conditions were numerically solved by orthogonal collocation technique for a set of model parameters obtained either from known correlations or from independent experiments. Comparison of the model predictions with experimental data from the batch permeation of chromium and other metals using carrier Alamine 336 or LIX 64N, shows that the model predictions are in very good agreement with the experimental findings. Further this model can be used to simulate the effects of various experimental conditions such as metal and hydrogen ion concentrations, carrier concentration, drop diameters, etc., for similar systems. Studies on ESPLIM were conducted with the aim of demonstrating the effectiveness of this new separation process and to develop a simple transport model for metal permeation. In the ESPLIM process, a high electrical field (3-5 kV A.C.) is used for phase dispersion. This system consists of a rectangular reactor filled with membrane solution divided into extraction and stripping cells by a centrally placed integrated type baffle which also acts as an electrode. Two more electrodes were placed in the extraction and stripping cells, where feed and strip phases are introduced from the top of the reactor. When high electrical field is applied across the electrodes, fine droplets of feed and strip are formed and are dispersed in extraction and stripping cells where simultaneous extraction and stripping occurs. The process can be viewed as simultaneous counter current extraction and stripping. The aqueous drops coalesce in the settlers at the bottom of the reactor and are removed continuously. Steady state mass transport model proposed for ESPLIM system accounts for the vertical counter-current extraction and stripping processes taking place in the extraction and stripping cells, together with the lateral transport process of the metal-complex and carrier across the two cells through the integrated baffle zone. The model equations were solved analytically to obtain concentration profiles as a function of the height of the reactor. The required parameters such as mass transfer coefficients, diffusion coefficients etc. were estimated using different correlations. Model predictions agreed remarkably well with the experimental data under various process conditions. From this investigation, it was found that ESPLIM is a simple, efficient and economical process and can be applied in a variety of situations. Based on a suitable combination of solvent extraction, dispersion and liquid membrane technique, a new type of separation system called " Unified Liquid Membrane " was developed. The ULM unit was designed and fabricated, and experiments were conducted to evaluate its performance. The ULM is basically derived from ESPLIM by changing the reactor, baffle design and dispersion technique. Aqueous feed and strip phases were atomized using compressed air through a fine nozzle and are dispersed on either side of an integrated baffle plate that divides the reactor into extraction and stripping cells. Tapering bottom of the reactor reduces the dead volume of the liquid in the settlers and the baffle plate remarkably reduces the leakage problem as well as the resistance through the baffle. Experiments were conducted using LIX 64N and Alamine 336 as carriers for copper and chromium and / or zinc. Mass transport model proposed considers both chemical and phase equilibria in extraction and stripping cells, vertical and lateral transport of carrier and complex across the extraction and stripping cells through the baffle zone. The model equations were solved using initial conditions at the top of the reactor, and equilibrium data for extraction and stripping cells. Effect of various experimental conditions and process parameters was simulated using this model and the model predictions are found to be in excellent agreement with the experimental data. The ULM system developed in this investigation overcomes the major limitations encountered with the other types of liquid membranes while retaining all the advantages of this technology. The problem of high mass transfer resistance from bulk phase to metal permeation as in the case of BLM was eliminated by good phase dispersion. Additional resistance to mass transport from solid membrane as in the case of SLM was removed by using an integrated baffle which also avoids problems of membrane instability, pore clogging and selectivity. The complex problems of emulsification and demulsification were completely eliminated making the system much simpler and efficient. Very good phase dispersion was obtained by atomization without the need for either stirring the whole system or application of high electrical field in the reactor. The membrane liquid within the integrated baffle elements allows easy transport of different species between extraction and stripping cells while completely preventing the mixing of the two aqueous phases. The problems of leakage, swelling and occlusion were avoided due to very short residence time of the aqueous drops in the reactor. It was found that the new ULM configuration is simple, elegant, highly efficient and superior to the other types of liquid membrane systems.