Comparison of Photocatalytic Hydrogen Production from Glycerol and Crude Glycerol Obtained from Biodiesel Processing

Abstract

Photocatalytic hydrogen generation from aqueous solutions of glycerol and crude glycerol (byproduct of biodiesel manufacturing) were compared using Pt/TiO2 and CuOx/TiO2 catalysts. Glycerol solutions generated more H2 than crude glycerol solutions, with the H2 generation rate approximately 2.5 times higher for Pt/TiO2 and approximately 4 times higher for CuOx/TiO2. Pt/TiO2 produced more H2 than CuOx/TiO2, with a ratio nearly 2.5 times higher for glycerol and nearly 3.5 times higher for crude glycerol. Ion exchange of crude glycerol solutions to replace Na+ with Li+ or K+ had little impact on reactions with CuOx/TiO2 whereas ion exchange with Li+ moderately reduced reaction rates with Pt/TiO2. An anti-foam agent reduced foaming problems associated with higher concentrations of crude glycerol but itself degraded. The addition of 0.4 mM NaH2PO4 reduced the H2 generation rate by nearly 60 % whereas the presence of 0.4 mM NaCl, 0.4 mM NaNO3 or 0.2 mM Na2SO4 reduced the H2 generation rate by only 10–20 % over the course of the reaction.