(i) Shown below is an impedance circuit representation of a polyamide thin-film-
ID: 2293801 • Letter: #
Question
(i) Shown below is an impedance circuit representation of a polyamide thin-film-composite reverse osmosis membrane system featuring the feed solution (Zjeed) in series with the polyamide active layer (Zactive layer), substrate and support structures for the active layer Zstruture) and the filtrate (Z filtrate) (not shown) Describe in a few sentences with the aid of features of the bipolar structure of the active feed and filtrate solutions that manifest a citance of Cbarrier to the movement of active layer sketches, if required, the physicochemical bipolar Gbarrier! !... layer and the electrochemical exchanges with -feed ier of conductance Gbarrier and bipolar barrier ! ions through the membrane as well as associated regions of conductance totalling Gvipolar and capacitance totalling Cb c bipolar. () Over what frequency ranges can measurements of the total impedance of the membrane system yield the best estimates of Gbarrier and Cbarrier, assuming that the conductances of the regions comprising the system are ordered so; filtrate ? struture » e ? Gbipolar > Gbarrl and the frequency constants for those regions are ordered so; > ?struture > ?bipolar > WbarrierExplanation / Answer
A polymer bipolar ion-exchange membrane consists of a layered structure involving one cation and one anion ion-exchange layer joined together in series. In this study, the ionic selectivity and water dissociation rate of six commercial bipolar membranes was evaluated from the measurements of the membrane potential in a concentration cell and the current–voltage curve in a four-point measuring cell. Bipolar membrane technology requires polymer membranes presenting high ion selectivities and water dissociation rates. A polymer bipolar ion-exchange membrane (BM) is composed of one cation and one anion ion-exchange layer joined together in series. This particular arrangement shows high ionic selectivity and its most noticeable characteristic is the electric field enhanced (EFE) water dissociation that occurs at the bipolar junction of the membrane when a high
dc electric current is forced through this junction [. The capability of the system to dissociate water makes it suitable
for a large variety of applications, such as generation and recovery of acids and bases and the chemical processing of effluents resulting from organic chemistry and biochemistry processes.
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