Ethanol Steam Reforming: Feasibility of a Two-Steps process

Ethanol is a "clean" energy tank that can be produced from renewable sources and has a reasonably high hydrogen content [1]. Hydrogen generation by ethanol steam reforming (SR) is a potential means to give one way hydrogen supply for fuel cell applications. According to the recent literature [2,3], ethanol steam reforming follows a consecutive three-step mechanism: (i) ethanol adsorption, (ii) ethanol dehydrogenation to acetaldehyde, and (iii) acetaldehyde decomposition to CO and methane. On the other hand, side reactions such as ethanol dehydration can give ethylene that can undergo polymerization with coke formation. In this way, our attentions were focused on a two steps process for hydrogen generation consisting of low-temperature (about 573 K) dehydrogenation of ethanol over copper chromite, followed by steam reforming over Ni/MgO at higher temperature (923 K). In particular, two series of experiments were carried out: first, catalytic single bed tests of ethanol SR on CuCr2O4 have been carried out in a temperature range of 423-623 K and atmospheric pressure in order to verify the compatibility of the low-temperature bed with the presence of water, not needed for the preliminary dehydrogenation, but necessary for the second step. Successively, catalytic ethanol SR tests were carried out using a dual-layer fixed-bed reactor (fig.1). In particular, catalytic performances obtained using two catalytic beds coupled in series resulted better than to that observed with a single bed both in terms of ethanol conversion and hydrogen yield. Moreover, steam reforming of ethanol in a two-step process allows formation of hydrogen with minimal coke formation. However, the two-step process is limited by the need to use a quantity of catalyst for the low-temperature step more than three times in excess of that for the high-temperature catalyst (i.e. Ni/MgO) in order to ensure adequate conversion of ethanol in the first step.