Design, Development and Testing of a Monitoring System for the Study of Proton Exchange Fuel Cells and Stacks.

This article is about the design, development and validation of a new monitoring architecture for individual cells and stacks to facilitate the study of proton exchange fuel cells. The system consists of four main elements: input signals, signal processing boards, analogue-to-digital converters (ADCs) and a master terminal unit (MTU). The latter integrates a high-level graphic user interface (GUI) software developed by National Instruments LABVIEW, while the ADCs are based on three digital acquisition units (DAQs). Graphs showing the temperature, currents and voltages in individual cells as well as stacks are integrated for ease of reference. The system validation was carried out both in static and dynamic modes of operation using a Ballard Nexa 1.2 kW fuel cell fed by a hydrogen cylinder, with a Prodigit 32612 electronic load at the output. The system was able to measure the voltage distributions of individual cells, and temperatures at different equidistant points of the stack both with and without an external load, validating its use as an indispensable tool for the study and characterization of these systems.

Sunflower oil transesterification with methanol using immobilized lipase enzymes.

The transesterification of sunflower oil with methanol, using immobilized lipase enzymes as catalysts, was studied. The process was carried out in a semi-continuous mode. Temperature (30-50 °C), methanol flow (0.024-0.04 ml/min), kind of enzyme (Lipozyme 62350, Lipozyme TL-IM, Novozym 435 and Pseudomonas cepacia Sol-Gel-AK) and enzyme concentrations (1.25-10% by weight) were the operating variables. The final product was characterized by the EN 14214 standard. All the parameters, except for cold filter plugging point, were similar to a diesel fuel. For low methanol flows, reaction rate was proportional to methanol concentration. High flows caused catalyst deactivation. Novozyme 435, Lipozyme TL-IM and Lipozyme 62350 showed similar maximum reaction rates, but Novozyme 435 was more resistant to deactivation. Pseudomonas cepacia hardly obtained 1% conversion. The catalyst concentration, up to 2.5%, had a positive effect on the reaction rate and conversion. The optimum temperature was 40 °C. The initial reaction rate was in line with the Arrhenius law, up to 50 °C. By differential and integral methods, the Michaelis-Menten, competitive inhibition and ping-pong bi-bi kinetic parameters were determined. The transesterification of sunflower oil in a semi-continuous regime of alcohol improved the results, compared to the discontinuous regime, and those were similar to the obtained ones in a discontinuous regime with step-by-step methanol addition. The lipase that showed the best yield and higher resistance to deactivation was Novozym 435. The kinetic models that forecast the deactivation of lipases by an inhibitor described the experimental behavior properly.