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A one-step process for the selective production of methane from low-value aqueous carbohydrate streams is proposed. Sorbitol, used herein as a model compound, is fully converted to methane, CO2, and a minor amount of H2 by using a physical mixture of Pt and Ru (1:5 in mass basis) at 220 °C and 35 bar. This conversion is the result of hydrogenolysis of part of the sorbitol over Ru and the in situ production of H2 through the aqueous-phase reforming of the remaining carbohydrate over Pt. A synergistic effect of the combination of these two catalysts results in the rapid and highly selective conversion of the carbohydrate to methane. This process offers the possibility of upgrading a low-value carbohydrate stream into a valuable fuel with no addition of H2. Exergy analysis reveals that nearly 80 % of the exergy of the reactant is recovered as methane. [ABSTRACT FROM AUTHOR]

Glucose oxidation using platinum promoted by bismuth was studied as a three-phase model reaction. Using catalyst nanoparticles and measuring the oxygen concentration in the bulk liquid, the kinetic parameters and mass transfer characteristics were determined at a temperature of 333 K. The overall reaction rate was studied experimentally using three different support types: slurry catalysts, pellets, and a solid foam stirrer. The glucose conversion rate and the deactivation rate of the catalyst depend strongly on the ratio between mass transfer and reaction rate. At low catalyst concentrations, the glucose oxidation process is liquid–solid mass-transfer-limited. The block stirrer shows a superior performance over the slurry catalysts due to the high liquid–solid volumetric mass transfer coefficient. The bimodal pore size distribution of the catalyst layer further increases the conversion rate. Using slurry catalysts, a loading of 1 wt % in combination with pure oxygen feed is required to achieve acceptable conversion rates. Under these conditions, the gas–liquid mass transfer and partially the liquid–solid mass transfer are the rate-limiting steps. The foam block stirrer shows good gas–liquid mass transfer rates and high liquid–solid mass transfer rates, which still increase at high power input. Working under external mass transfer control and using this stirrer type, the catalyst loading can be strongly reduced to loadings less than 0.4 wt %, while the conversion rate remains comparable to slurry particles with loadings of 1 wt %. As the catalyst is fixed, attrition and agglomeration in high viscosity liquids are circumvented. There is further no need for filtration, and the catalyst can simply be reused. [ABSTRACT FROM AUTHOR]