Catalytic reforming of glycerol in supercritical water over bimetallic Pt-Ni catalyst

Catalytic reforming of pure glycerol for the production of hydrogen at low temperature and short residence times in supercritical water was investigated using a bimetallic Pt–Ni catalyst supported on alumina. Initial tests were carried out to study the reforming activity of bimetallic Pt–Ni catalysts by reforming different model compounds having different carbon numbers in supercritical water at 400–450 °C. The influence of different operating parameters such as reaction temperature, initial feed concentration, location of the catalyst bed, and weight hourly space velocity on the carbon to gas conversion and product gas distribution is studied. Continuous experiments were carried out using a fixed bed reactor for a temperature range of 380–500 °C, feed concentrations of up to 20 wt %, at space velocities of up to 45 h–1. The product gas mainly consisted of CO2, H2 and alkanes (CH4 and C2H6) and the liquid effluent after the reaction primarily consisted of unconverted glycerol, 1,2-propanediol, and ethanol, with trace amounts of acetaldehyde, ethanol, and 1,3-propanediol. A comparison of the reforming activity of the catalyst and process with respect to the feedstock characteristics was made by comparing the carbon to gas conversion and product distribution for pure and crude glycerol. The carbon to gas conversion and the product gas distribution of pure and crude glycerol are comparable. Complete conversion of 15 wt % (pure) glycerol in water to gaseous products was achieved at 450–500 °C and the product gas mainly consisted of H2, CO2, and CH4. However, whereas the catalyst deactivated rapidly with crude glycerol, for pure glycerol the catalyst showed stable performance for a long duration run up to 85 h, indicating that catalyst deactivation by for example, coke formation in the gasification reaction system is not a major issue. It is anticipated that with a proper catalyst support material, the gasification of concentrated aqueous glycerol streams can be developed into a viable process