Many conventional chemical production processes offer quite some room for improvement in product yield, selectivity, and energy efficiency.. The development of alternative technologies with a more efficient use of resources has become a requirement for a transition towards global sustainability. Electrochemical alternatives are attractive from these perspectives, specially because electrodes bring about chemical change without the use of highly toxic reagents and usually in conditions close to ambient temperature and pressure. Appropiate component, assembly and cell design and reaction conditions can be adapted to maximize the yield and selectivity of the reaction. A wide range of modern cell components and assemblies is now available, from electrocatalysts for highly selective transformations, porous electrode support materials, gas diffusion layers, etc. However, optimized reactor and stack designs are less extended. Conventionally, such designs ...view middle of the document...
An electrochemical synthesis would offer an improvement in the efficiency of the current process, because makes it feasible to control reaction rate and selectivity in an electrochemical cell through electrode potential, catalyst, surface structure and concentrations, while reducing waste heat. The implementation of an alternative electrochemical production process would allow, besides the production of hydroxylamine, cogeneration of electrical power as a co-product through fuel cell operations. For a first proof of concept, a stack suitable for operation with tailor made gas-diffusion-electrodes ought to be designed and validated.
The three dimensional descriptions of the fuel cell were developed with a multidisciplinary modelling approach. The fuel cell geometry which consists of a porous gas diffusion electrode pair separated by an electrolyte compartement, cathodic and anodic gas compartements were modeled through COMSOL Multiphysics 4.3. The secondary current distribution profiles over the electrolyte-electrode interface, velocity and molar fraction profiles of the gas phase through the gas compartements were examined. The influence of different parameters was evaluated; such as electrode geometry, size and positioning of the gas or electrolyte inlets and outles, cell potential, electrochemical kinetics, electrolyte flow rates, gas flow rates. A single-cell reactor and stack were machined and constructed to validate the model. Hydroxylamine was successfully produced in such embodiments. The results obtained through electrochemical and analytical characterizations were found in good agreement with the model. Through the combination of experimental versus modeled results, the conditions for the production of hydroxylamine could be optimized.
In conclusion, electrochemical engineering-based models were successfully developed for the design and optimization of an electrochemistry-based chemical conversion, serving as a platform to further evaluate the feasibility of replacing the conventional chemical process by this proposed alternative. The strategy here used can be extrapolated to any chemical production processes implying exergonic oxidation or reduction reactions.