Exergetic study of catalytic steam reforming of bio-ethanol over Pd–Rh/CeO2 with hydrogen purification in a membrane reactor

In this work, we present the application of exergy analysis in the evaluation of the ethanol steam reforming (ESR) process in a catalytic membrane reactor (CMR) containing Pd-Ag membranes sandwiched by PdRh/CeO2 catalyst to produce fuel cell grade pure hydrogen (no sweep gas). ESR experiments were performed at T=873-923 K and P=4-12 bar. The fuel was a mixture of ethanol and distilled water with steam to carbon ratio=1.6, 2, and 3. The exergy evaluation of the system is based on the experimental data, where total yields of 3.5 mol H2 permeated per mol ethanol in feed with maximum hydrogen recuperation of 90% were measured at 923 K and 12 bar. The exergy efficiency of the system was evaluated considering both the insulated reactor (without heat loss), and non-insulated reactor (with heat loss). Exergy efficiency up to around 50% was reached in the case of the insulated reactor at 12 bar and 923 K. It was concluded that the highest amount of exergy was destructed by heat losses. The study showed that the exergy content of the retentate gas can provide the reactor with a notable fraction of its required heat at steady state conditions which can remarkably increase the overall exergy efficiency of the system. In this case, thermal efficiency of the insulated reactor was between 70-90%, which decreased to 40-60% when the heat loss was considered.