Dmitri Bessarabov

Review of electro-assisted methods for water purification

Many different methods for improving the hygienic quality of waste, industrial and drinking water are already established. These include pressure-driven membrane-based methods such as reverse osmosis, ultrafiltration and microfiltration, biological treatment, treatment of water by means of various chemicals such as ozone or chlorine, and treatment with UV radiation. This review deals with electro-assisted methods for water purification which stand apart from the well-established technologies. Although electrodialysis is a competitive electro-assisted method for water treatment, electrochemical systems for water treatment have, in general, not yet attracted adequate attention. Electrochemistry, a link between physical chemistry and electronic science, has proved to be a clean, versatile and powerful tool for the development of new advanced methods for water purification. The freedom of choice in adjusting the electrode potential and electrode material, to meet almost any demand, makes electrochemistry extremely selective and flexible. This survey covers both established and recent developments in the field of electrochemical technologies for waste water and drinking water treatment.

Sol-gel film-preparation of novel electrodes for the electrocatalytic oxidation of organic pollutants in water

Abstract The electrochemical oxidation of phenol as a model contaminant, has been studied using different electrode materials (Ebonex, Ebonex PbO 2 , Ti SnO 2 ) in water by means of cyclic voltammetry. Best results have been obtained with doped SnO2-films on titanium foils prepared by a sol-gel dip-coating technique. The cyclovoltam-mograms reveal a high overpotential for oxygen-evolution, resulting in a well separated peak for the oxidation of phenol. Improvements of the conductivities of the films and higher current densities for the oxidation were obtained by doping the film sol-gel solution with 10% Sb. Doping with fluoride increased the conductivity, but decreased the oxidation peaks. The PbO2-coated Ebonex-electrodes were obtained by the galvanostatic deposition in an acidic PbNO3-solution. Upon the addition of phenol to the electrolyte, however, the electrodes did not show a separated oxidation peak. The oxidation peak is partially hidden by oxygen evolution. The electrochemical characteristics of the electrode material Ebonex is not significantly changed by the addition of phenol to the electrolyte.

Use of nonporous polymeric flat-sheet gas-separation membranes in a membrane-liquid contactor: experimental studies

Flat-sheet non-porous asymmetric poly(vinyltrimethylsilane) (PVTMS) membranes and composite membranes comprising a dense layer of polydimethylsiloxane/polyphenylsilsesquioxane (PDMS/PPSQ) block copolymer were evaluated for low-temperature bubble-free deoxygenation of water flowing in a two-channel countercurrent liquid-membrane contactor. A novel large-scale three-channel flowing-liquid-membrane module (selective membrane valve), designed for gas separation, is also described. The system comprised PVTMS or PDMS/PPSQ non-porous membranes which acted as gas-permeable barriers. A membrane system (SMV) in which pure water formed a flowing liquid membrane was evaluated to control hydrogen transfer rates. The liquid flowing along the turbulence-promoter spacers between the membranes reduced liquid-film resistance. The overall mass-transfer coefficients were found to be a function of the liquid flow rate. The liquid-film resistance controlled the rate of gas transfer in such membrane contactors.

Characterisation of membranes for electrochemically aided gas separation:: Morphology of platinum deposition

Abstract A novel membrane technique to effect electroinduced facilitated transport of ethylene in Pt-containing ion exchange membranes was recently demonstrated. It was shown that by applying an electric current to such a membrane, the permeability of ethylene increased six-fold compared with that of an initial Pt-coated membrane without applied current. Experiments have been carried out with platinum-coated Nafion membranes in Cu 2+ ionic form to determine the permeability of ethylene. This paper deals with the characterisation of these membranes by various techniques, such as scanning electron microscopy (SEM), Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) techniques. A relevant literature survey is also presented. An idealised theoretical model describing concentration profiles of copper ions in various valence states in the membrane is formulated.

New opportunities for osmotic membrane distillation

This article discusses a potential large-scale application for osmotic membrane distillation — a relatively new membrane technology. More specifically, commercial opportunities for the technology are discussed using an example of NaCl brine re-concentration in the chlor-alkali industry. Some general considerations concerning the possibility of maintaining a water balance between different technological loops at large chemical plants, by means of osmotic membrane distillation, are also discussed, as is the selection of suitable membranes for an osmotic membrane distillation application in the chlor-alkali industry. In addition, this article covers research activities at Aker Kvaerner Chemetics that aim to commercialize the membrane contactor technology. A relevant patent application cited in the article has been filed recently.

Solid polyelectrolyte (SPE) membranes containing a textured platinum catalyst

Abstract Perfluorinated cation-exchange flat-sheet membranes were treated with cetyltrimethylammonium bromide surfactant (CH 3 (CH 2 ) 15 N(CH 3 ) 3 Br) to investigate the effect of the membranes modification with the surfactant on the morphology of deposition of a Pt catalyst. The electroless chemical deposition of a platinum catalyst onto the membranes treated with the surfactant was achieved by the Takenaka–Torikai method. The effect of the membranes modification on their electrical conductivity was studied. The morphology of the platinum micro-particles deposited onto the membranes modified with the surfactant was investigated by means of atomic force microscopy (AFM).

Membranes help to produce high-concentration ozone: new challenges

Abstract This article briefly looks at current research trends, available technologies, and challenges and possible applications of membrane science for electrocatalytic generation of ozone. It also provides details of research and development work carried out by South African company Dinax Technologies CC, in cooperation with the Chemistry Department at the University of Stellenbosch, and the Water Research Commission of South Africa.

Phenomenological analysis of ethylene transport in a membrane contactor containing solutions of silver nitrate

A phenomenological analysis has been developed of an olefin/paraffin gaseous separation process in a liquid-membrane contacting system comprising polymeric non-porous gas-separation membranes and aqueous silver nitrate flowing within an absorber/stripper cascade. New analytical solutions of the problem, taking into account the reversible chemical reaction of silver ions and olefins, are presented and numerically computed. Calculated dependences of the desorber productivity and selectivity are compared with experimental data. It is shown that the model can be used for a rough estimation of the systems behavior. In particular, it is shown that with an increase in the liquid-membrane flow rate productivity increased rapidly and then stabilized. Selectivity decreased with an increase in the liquid membrane flow rate. It was shown further that concentration profiles in the absorber system could be distinguished between equilibrium and non-equilibrium states.

Morphological diversity of platinum clusters deposited on proton-exchange, perfluorinated membranes

Abstract This article is a summary of a talk that was presented during the fuel-cell session of the ‘12th Annual Meeting of the North American Membrane Society’, which was held on 15–20 May 2001, in Lexington, Kentucky, USA. It describes methods to control the morphology of a platinum catalyst, which is chemically deposited onto proton-exchange, perfluorinated membranes. Potential applications of the membranes are discussed and an extensive list of related references is provided. Some general considerations on heterogeneous membrane electrocatalysis are also given. This topic is one of the research interests of Membrane Technologys editorial board member Dr Dmitri Bessarabov, who has recently joined Kvaerner Chemetics (a division of Kvaerner Canada Inc) as a senior research chemist.

Galvanodynamic study of the electrochemical switching effect in perfluorinated cation-exchange membranes modified by ethylenediamine

Abstract Perfluorinated sulfonyl-fluoride cation-exchange flat-sheet membranes were treated with ethylene diamine to investigate the influence of EDA-surface-treatment on the process of electrochemical “switching” in such membranes. The galvanodynamic method was used to obtain i–V cyclic curves of the membranes. Electroless chemical deposition of Pt particles on modified membranes was achieved using the Takenaka–Torikai method. Galvanodynamic i–V cyclic curves of the plain and platinum-containing aminated membranes were compared. Chemical modification of the membrane surface and membrane structure was investigated by means of electrical conductivity measurements and IR-spectroscopy. Experimental results indicated that the “switching” phenomenon is more likely to occur due to a pH change in the electrolyte resulting in the formation of additional fixed-charged groups in the aminated layers of the membranes rather than due to heterolytic dissociation of water according to the second Wien effect.