Electrically heated microreactors for methanol steam reforming

Hydrogen generation for automotive fuel cell application faces the demands of fast load alternations. These may be met in an excellent manner by microstructured reactors for methanol steam reforming. Calculations reveal fast heating when using heat transfer oil and negligible temperature gradients in the catalyst layers. By solving the differential equation for heat transport with boundary conditions adjusted for the microchannel system, the temperature gradients in microstructured foil stacks may be estimated. The results were verified experimentally by gradient measurements in electrically heated lab-scale reformers (demonstrators, i.e. pre-prototype stage). Effects on temperature gradients and conversion by changing the material of both reformer body and foils were examined, as well as effects due to constrained temperature gradients. These studies were performed with PdZn-catalyst systems based on nanoparticle washcoats both in the steady state and during dynamic operation. The hydrogen output of the demonstrators corresponded to 200W(el) taking into account a system efficiency of the propulsion system of about 40%. After load changes, the hydrogen output reached its new value within 10 s to a degree of 90%. After temperature changes of 80K in the range 230-310degreesC, the hydrogen output reached its new value after 240 s to a degree of 90%. The secondary reaction to dimethyl ether was extremely dependent on the reactor material during load changes.