Industrial concepts

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  • Publicado : 24 de febrero de 2012
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Industrial Electrochemistry (Electrolysis: )G is positive, calculated E is negative) Why electrochemistry? • clean and green (not always true!) • often no or few byproducts • electrons the cheapestredox “reagents” Industrial electrochemical processes • Primary metal production (electrowinning): Al, Mg, Na, and recently developed methods for Cu, Ni • • Metal refining: Cu, Ni – also electroplatingInorganic chemicals: Cl2/NaOH; H2O2 and other peroxy compounds; O3; chromic acid; KMnO4 Organic compounds: adiponitrile Waste water purification and recycling

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In North America: • Alproduction = 10% of total electrical energy production • Cl2 production = 3% of total electrical energy production

Differences between laboratory set-up and industrial processes • importance of masstransfer S stirred/unstirred solutions S batch vs continuous S planar vs 3-D electrodes mass transport occurs by: S diffusion = migration due to concentration gradient S migration of charged species dueto potential gradient S convection (mechanical stirring or agitation) Other issues • undivided vs divided cells • distance between electrodes • potentiostatic vs amperostatic control • importance ofcurrent efficiency • what is the reaction at the other electrode? Under laboratory conditions of electrochemical synthesis of a few grams of material, these issues are of minor importance. They are ofimmense importance industrially because of their impact on process costs, when thousands of kg – or even tonnes – of material are to be produced.

Mass transport and overpotential The Tafel equationlinks (over)potential (a thermodynamic concept) with current (a kinetic concept) For an anodic process: log i = log i0 + "AnF0/(2.303RT) "A = anode transfer coefficient 0 = overpotential i0 =equilibrium exchange current density i.e. log iexp " 0 Eventually, the current (rate) levels off because of mass transport limitation (example: limiting currents in voltammetry) —> no benefit from further...
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