Chapter 7 "Process Sensitivity to Ni/Alumina Catalysts in the Production of Hydrogen from the Steam-Reforming of Glycerol"

RAÚL A. COMELLI

e-Book "Hydrogen Production: Prospects and Processes". Series “Energy Science, Engineering and Technology”.

Nova Science Publishers Inc.

Lugar: New York; Año: 2011;

The demand of hydrogen, the most simple and abundant element, is growing due to technical advances in the fuel cell industry. Then, it is necessary to find renewable sources of raw materials to produce hydrogen. Glycerol, by-product of biodiesel synthesis and a possible “key compound” in the environment of future biorefinery, could be a bio-renewable substrate to obtain hydrogen. Processes such as steam reforming, partial oxidation, autothermal reforming, aqueous-phase reforming, and supercritical water reforming can produce hydrogen from glycerol, being the steam reforming the most exhaustively studied process. Steam reforming of glycerol was reported on Ni-supported on alumina catalysts, favoring promoters such as Ce, Mg, Zr, and La, the selectivity to hydrogen. Optimal conditions for the glycerol reforming in gas phase varied according to the catalytic system. Moreover, deactivation processes occur, producing a loss of catalytic activity. Ni/Alumina catalysts containing 2.6, 5.8, and 9.9% Ni loadings, prepared by impregnation, were characterized by DRX, FTIR, temperature-programmed reduction, and ammonia temperature-programmed desorption. These materials were evaluated in the steam reforming of glycerol at atmospheric pressure and 600-700ºC, 3.4-10.0 WHSV, 6:1-16:1 water:glycerol molar ratio, 20-60 ml min-1 nitrogen flow, and 300-500ºC reduction temperature. Ni species on the surface of support were difficult to reduce, being the NiO ones in the largest proportion. By increasing the Ni loading, total acidity increased but without changing the profile of acidic strength distribution corresponding to the starting material. Metal oxide species decreased the hydration degree of support surface. By considering the catalytic behavior during the steam reforming of glycerol, conversion was high independent of reaction conditions and operating time; it decreased by decreasing reaction temperature, remained practically constant by changing the other parameters. Hydrogen yield decreased by decreasing temperature, by increasing WHSV, and by diminishing glycerol partial pressure. Considering by-product distributions, carbon monoxide was the main by-product, followed by methane, and then, ethene, ethane, propene, isobutane, propane, and other compounds in small proportion. Catalyst deactivation was strongly influenced by pretreatment and operating conditions; the hydrogen fraction can be increased up to 90 mol% with the corresponding suppression of both carbon monoxide formation and methanation reactions.