Study of Coke Formation and Hydrogen Production under Ethanol Steam Reforming at Low Temperatures

J. VECCHIETTI; A. L. BONIVARDI; D. L. CHIAVASSA; E. L. FORNERO; EDUARDO MIRÓ

Santa Fe

Conferencia; VI San Luis School and Conference on Surfaces, Interfaces and Catalysis; 2018

Nowadays, one of the great challenges is the substitution of fossil fuels by renewable sources of energy to mitigate the impact of green house gases, mainly CO2. For this purpose, the production of hydrogen via steam reforming of ethanol (SRE) is a valid and attractive alternative due to the relatively high content of hydrogen in the alcohol, its ubiquitous availability, non-toxicity and ease to storage and handling. However, there are scientific and technological issues that must be addressed before the practical implementation of SRE, e.g., to minimize the coke production. Calculation of the chemical equilibrium composition is a useful tool to estimate the expected yields under selected thermodynamics conditions and, in particular, those ´regions´ of coke generation. Different authors have already studied the SRE under chemical equilibrium conditions, however graphitic carbon was the carbonaceous species frequently examined, which leads to an incomplete prediction of carbon formation.1-3 In the present work, carbon production was simulated at thermodynamic equilibrium under SRE conditions at low temperatures (200-600 °C), with different H2O/C2H5OH feed ratios (S/E = 1-to-4 mol/mol) and considering the presence of different types of coke (graphitic, amorphous, filamentous, polymeric) and cobalt and nickel carbides.Our thermodynamics calculation results shown that the most stable carbon species are graphite (200-400 °C), amorphous carbon and filamentous carbon nanotubes (450-600 °C). For the full range of explored conditions, it was concluded that, under sub-stoichiometric conditions (S/E = 1-to-2 mol/mol), H2 selectivity is higher when carbonaceous species are included among the reaction products. In other words, under conditions of low water content in the feed, the production of hydrogen would be obtained from the decomposition of ethanol. Currently, mechanistic studies of coke formation under ethanol steam reforming conditions for metal supported catalysts are being carried out in order to compare experimental observations with thermodynamic predictions.