S019_PROC-852.2015

ACHEMA Worldwide News2/2015

or — if chemical production is the target — methanol. A number of production concepts combine hydrogen generation with other steps to achieve a competitive production process; TU Clausthal has developed a scheme that combines water electrolysis with air rectification to provide the resources for the production of ammonia that is then oxidized to nitric acid with the oxygen from the electrolysis. The use of oxygen on site without additional transport is the key to competitive processes. Organic electrochemistry is also experiencing a revival. The development of new electrodes has opened possibilities for many selective reactions; however, these are often not needed on the necessary scale. An interesting process could be the production of adipic acid; the current process generates N2O that has to be catalytically decomposed. What Is to Consider? The following conditions have to be considered when analyzing potential processes: • Oxidation reactions are more simply implemented than reduction reactions. • The product has to be protected against secondary reactions; one way to do this it to design reactors where the product is removed fast from the reaction zone. • In general, protic solvents are more suitable than aprotic solvents because they allow for a much larger electricity density, leading to higher space-timeyields. • There is a need for new, ionic conducting membranes with higher conductivity and longer endurance. Picture: Fotolia - ©Aania, Natis, okinawakasawa With prices of 6 €ct/Mol for one electricity equivalent the electrochemical oxidation is not competitive to catalytic oxidation with oxygen from air. Options for anorganic processes include the switch between oxygen depolarized cathodes — requiring less — and hydrogen electrodes — requiring more energy. The flexibility of aluminum production is limited by a shorter lifetime of the electrodes. But electrolytic processes for the generation of zinc or copper and galvanic processes are candidates as well as certain process steps in metal recycling. Act Big — Think Small (and Modular) A significant electricity surplus will materialize only when the share of renewable energy is large and back-up capacities are no longer in place. The German government predicts 2.3 TWh of “dumped energy” in 2032; this corresponds to 500 million m³ hydrogen or 275,000 tons per year methanol. This volume would have to be produced decentralized — according to the location of the energy generation plants — with the corresponding negative impact on economics. Therefore, new catalytic methods and plant concepts are required to develop efficient, small production plants. In the end, there won’t be just one specific process but a large variety of basically new chemistry-based concepts in order to claim the existing potential. An interdisciplinary approach and, not least, reliable political frameworks are necessary to make the most efficient use of generated energy. n A special edition from PROCESS 19


ACHEMA Worldwide News2/2015
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