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.