Thermodynamic analysis of aqueous phase reforming of three model compounds in bio-oil for hydrogen production

摘要

Thermodynamic analysis with Gibbs free energy minimization was performed for aqueous phase reforming of methanol, acetic acid, and ethylene glycol as model compounds for hydrogen production from bio-oil. The effects of the temperature (340-660 K) and pressure ratio P_(Sys)/PH_2O (0.1-2.0) on the selectivity of H_2 and CH_4, formation of solid carbon, and conversion of model compounds were analyzed. The influences of CaO and O_2 addition on the formation of H_2, CH_4, and CO_2 in the gas phase and solid phase carbon, CaCO_3, and Ca(OH)_2 were also investigated. With methanation and carbon formation, the conversion of the model compounds was >99.99% with no carbon formation, and methanation was thermodynamically favored over hydrogen production. H_2 selectivity was greatly improved when methanation was suppressed, but most of the inlet model compounds formed solid carbon. After suppressing both methanation and carbon formation, aqueous phase reforming of methanol, acetic acid and ethylene glycol at 500 K and with P_(sys)/PH_2O = 11 gave H_2 selectivity of 74.98%, 66.64% and 71.38%, respectively. These were similar to the maximum stoichiometric hydrogen selectivity of 75.00% (methanol), 66.67% (acetic acid), and 71.43% (ethylene glycol). At 500 K and 2.90 MPa, as the molar ratio of CaO/BMCs increased, the normalized variation in H_2 increased and that for CH_4 decreased. Formation of solid carbon was effectively suppressed by addition of O_2, but this was at the expense of H_2 formation. With the O_2/BMCs molar ratio regulated at 1.0, oxidation and CO_2 capture increased the normalized variation in H_2 to 33.33% (methanol), 50.00% (acetic acid), and 60.00% (ethylene glycol), and the formation of solid carbon decreased to zero.