Steam reforming of volatile fatty acids (VFAs) over supported Pt/Al2O3 catalysts

Abstract

Volatile fatty acids (VFAs), easily produced using acid fermentation of biomass, were used to generate hydrogen via steam reforming. Three short-chain carboxylic acids (C-2-C-4) acetic, propionic and butyric acids were used as model compounds in addition to VFAs produced in a typical anaerobic batch reactor. Catalytic steam reforming of VFAs using alumina-supported platinum catalysts was studied in a fixed-bed quartz reactor at various temperatures between 300 and 600 degrees C. The influence of reaction conditions such as temperature, oxygen to carbon ratio (O/C) and gas hourly space velocity (GHSV) was investigated. VFAs were successfully converted to CO and hydrogen. A hydrogen yield of up to 70% was achieved, based on typical stoichiometry at 600 degrees C and a GHSV of 25,000 h(-1). Temperature-programmed oxidation (TPO), X-ray diffraction (XRD) and pore size distribution (PSD) were used to characterize coke deposition. Graphitic carbon on catalysts was not identified by XRD, which implies that amorphous coke had formed in the small pores. The catalysts could be reactivated by oxidation and reduction. A detrimental effect on hydrogen yield was observed by adding a small amount of O-2 to the VFA feed, due to the high concentration of oxygen in the feed composition. Steam reforming of real VFAs (S/C = 9) in the acid fermentation of food waste was performed with different GHSVs at a reaction temperature of 600 degrees C. Conversion of VFAs decreased significantly with increasing GHSV, but the hydrogen selectivity was still above 60%. The conversion pathways of the VFAs to CO and hydrogen are most likely complex, particularly due to the variety of the chemical compounds present in the real VFAs. The steam reforming of VFAs was investigated over various noble metal (Ruthenium, Palladium, Rodium, Nickel) catalysts supported on alumina, the specific activity based on the active surface area decreased in the order of Ru > Pd Rh > Pt > Ni. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.