Biomass Conversion to Hydrogen Using Supercritical Water

Abstract

In this work, SCWG of glucose, cellulose and pinewood was studied at different operating conditions with and without catalyst. Three parameters studied included temperature (400, 470, 500 and 550oC), water to biomass weight ratio (3:1 and 7:1) and catalyst (Ni/MgO, Ni/activated carbon, Ni/Al2O3, Ni/CeO2/Al2O3, dolomite, NaOH, KOH, activated carbon and olivine), which were varied for gasification of glucose, cellulose and pinewood. By comparing the results from model compound (glucose and cellulose) with that from real biomass (pinewood), the mechanism of how the individual compounds are gasified was explored. For catalytic runs with glucose, NaOH had the best activity for improving H2 formation. H2 yield increased by 135% using NaOH compared to that for run without catalyst at 500oC with a water to biomass weight ratio of 3:1. At the same operating conditions, the presence of Ni/activated carbon (Ni/AC) contributed to an 81% increase in H2 yield, followed by 62% with Ni/MgO, 60% with Ni/CeO2/Al2O3 and 52% with Ni/Al2O3. For catalytic runs with cellulose, the H2 yield increased by 194% with KOH compared to that for run without catalyst at 400oC with a water to biomass ratio of 3:1. At the same operating conditions, the presence of Ni/CeO2/Al2O3 contributed to a 31% increase in H2 yield followed by a 28% increase with dolomite. When the water to biomass ratio was increased from 3:1 to 7:1, H2 yield from glucose gasification was increased by 40% and 33% at 400 and 500oC, respectively, and the H2 yield of cellulose gasification was increased by 44%, 11% and 22% at 400, 470 and 550oC, respectively. The higher heating value of the oil products derived from SCWG of both glucose and cellulose incresed in the presence of catalysts. As real biomass, pinewood was gasified in supercritical water at the suitable operation conditions (550oC with water to biomass ratio of 7:1) obtained from previous experiments, using three kinds of catalyst: Ni/CeO2/Al2O3, dolomite and KOH. At the same operating conditions, the gasification of pinewood had smaller yields of H2 (20 to 41%) compared with that from cellulose. The effect of the catalyst on H2 production from SCW in the absence of biomass was studied. The results showed that a trace amount of H2 was formed with Ni based catalyst/dolomite only while some CO2 was formed with Ni/AC. Most of the runs presented in this report were repeated once, some of the runs had been triplicated, and the deviation of all results was in the range of ±5%.