Electrochemical membrane processes

Membranes have applications in electrochemical separations in the areas of effluent treatment and recycling. Electrodialysis, ED, is a process in which electrolyte solutions are either concentrated or diluted (or deionised). The process has over the years been the dominant technique for the desalination of brackish water. Electrodialysis has many potential applications for the removal or recovery of ionic species and generally the process can be used to perform a number of functions such as  

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An electrochemical membrane process can, in principle, perform the entire sequence in a single step while enriching the process gas slightly with H2. If the H2S could be electronated at a suitable cathode ... 

McHenry D.J. and Winnick J., Electrochemical membrane process for flue gas desulfurization, AIChE J. 40 143 (1994). 

Salema K, Sandeauxa J, Molenata J, Sandeauxa R, and Gavacha C. Elimination of nitrate from drinking water by electrochemical membrane processes. Desalination 1995 101(Suppl. 2) 123-131. 

A hot-gas electrochemical membrane process is illxistrated schematically in Figure 1. The process gas is passed by the cathode. Here, the most easily reduced component, that is, the strongest Lewis add, will be electronated. With natural gas and coal synthesis gas, it is H S ... 

Electrochemical membrane processes. An electrochemical membrane process for gas separation can utilise the difference in electrochemical potentials set up across an appropriate membrane by the application of a potential gradient [61]. For example the purification of contaminated chlorine gas has been achieved using electrochemical membrane separation. The chlorine gas is cathodically reduced to chloride ion. The chloride ions are then transported across an aqueous HCl electrolyte. 

The electrochemical membrane processes for effluent treatment which are attracting interest are for the removal of SO2 and H2S [61]. These are high temperature processes using eutectic molten salt mixtures immobilised in a ceramic membrane. 

With a strong emphasis on the development of electrochemical membrane processes, e.g., water electrolysis and fuel cells, electrode performance must be well characterized electrochemically. Use of a hydrogen pump concept can provide insight into anode and/or cathode electrode electrochemical characteristics. Furthermore, the method can also be utilized to determine the back diffusion of hydrogen through the membrane [5, 25]. 

Regardless of the source of the hydrogen, the technique can be used for bulk purification of hydrogen as long as the impurities that have to be removed from the hydrogen do not impact the electrochemical membrane process or the ancillary subsystems. 

The catalytic oxidation/electrochemical membrane process consists of an upstream commercial sulfuric acid catalyst to convert SO2 to SO3 followed 1 a molten salt electrochemical cell using a sulfur oxide selective membrane. Removal efficiencies of 95% have been simulated. Projected economics for a 300 MW power plant burning 3.5% sulfur coal are 96/kW capital cost and 3.24 mills/kWh operating cost. Capital cost includes the catalytic converter and oleum plant and assumes cell replacement twice over a 30-year life (McHenry and Winnick, 1991). The process is in a very early stage of development, and no cortunercial or demonstration operations have been reported. 

McHenry, D. J., and Winnick, J., 1991, Electrochemical Membrane Process for Flue Gas Desulfurization, unpublished paper provided by J. Winnick, Univ. of Georgia, August,... 

The first device was a circular-shape microhotplate, which essentially consisted of CMOS-process materials (Sect. 4.1). The fabrication of this microhotplate required a minimum of post-CMOS processing steps. The electrochemical etching process used for the membrane release and the formation of the circular-shape Si island was optimized and can now be routinely apphed on wafer-level. 

Screening strategy Precipitation and coagulation Membrane processes Ion exchange Electrochemical Adsorption... 

The direct electrochemical oxidation (no cell divider membrane) of wastewater has been employed in the textile industry. Typically, this industry produces an organic-contaminated wastewater that also contains sodium chloride sodium chloride is desirable in promoting anodic oxidation. The presence of sodium chloride is fortuitous for textile manufacturers since the hypochlorite byproduct produced in the electrochemical oxidation process is used for textile bleaching operations.24... 

Nomura, M., Fujiwara, S., Ikenoya, K., Kasahara, S., Nakajima, H., Kubo, S., Hwang, G.-J., Choi, H.-S., and Onuki, K., Application of an electrochemical membrane reactor to the thermochemical water splitting IS process for hydrogen production, Journal of Membrane Science, 240, 221-226, 2004. 

Principles and applications of electrochemical remediation of industrial discharges are presented by Pallav Tatapudi and James M. Fenton. Essentials of direct and indirect oxidation and reduction, membrane processes, electrodialysis, and treatment of gas streams, and of soils, are complemented by discussions of electrode materials, catalysts, and elements of reactor design. 

During the last two decades, pressure-driven membrane processes namely reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have found increased applications in water utilities and chemical industries. Unlike RO, NF, and UF, the Donnan membrane process (DMP) or Donnan dialysis is driven by an electrochemical potential gradient across an ion-exchange membrane. Theoretically, the DMP is not susceptible to fouling because particulate matter or large organic molecules do not concentrate on the membrane surface, as commonly observed with pressure-driven membrane processes. DMP has been used in the past in hydrometallurgical operations [19,20], for concentration of ionic contaminants [21,22] and for separation of... 

The DMFC operates, as its name suggests, by direct, complete electrooxidation of methanol to CO2 at the cell anode. The methanol anode is coupled in the DMFC with an air cathode, completing a cell schematically shown in Fig. 50. In the majority of recent development efforts, the DMFC has been based on a protonconducting polymeric membrane. The uniqueness of this type of fuel cell is the direct anodic oxidation of a carbonaceous fuel. Such a direct electrochemical conversion process of liquid fuel and air to electric power at low temperatures can provide a basis for a very simple fuel-cell system. 

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