Impact of product gas impurities from dehydrogenation of perhydro-dibenzyltoluene on the performance of a 10 μm PdAg-membrane

Abstract

The purification of the product gas from dehydrogenation of liquid organic hydrogen carriers (LOHC) by using PdAg-membranes is highly promising, since the low level of impurities in the released hydrogen stream allows low pressure operation and favours the coupling with the dehydrogenation step. Motivated by our recent short-term investigations indicating an influence of these impurities on the membrane performance the behaviour of the membrane by exposure to product gas was investigated in detail over a long period. In total, the membrane was operated for more than 200 days, including approx. 21 days under product gas from the LOHC-dehydrogenation. In the time period the performance has decreased by 88% and could be restored slowly but completely by using pure hydrogen. The degradation is caused by the coverage of active adsorption sites for the dissociation of hydrogen by hydrocarbons other than methane. The activation energy of permeation has almost tripled from 13 kJ mol−1 to 38 kJ mol−1 while desorption of impurities from the surface affect the process and its temperature dependence. SEM-analysis of the still 100%-selective membrane after more than 200 days of operation shows no significant changes in membrane morphology. Under the mild operating conditions, a lifetime of several years seems possible.