Hydrogen production by catalytic gasification of cellulose in supercritical water

Cellulose, one of the important components of biomass, was gasified in supercritical water to produce hydrogen-rich gas in an autoclave which was operated batch-wise under high-pressure. K₂CO₃ and Ca(OH)₂ were selected as the catalysts (or promoters). The temperature was kept between 450°C and 500°C while pressure was maintained at 24-26 MPa. The reaction time was 20 min. Experimental results showed that the two catalysts had good catalytic effect and optimum amounts were observed for each catalyst. When 0.2 g K₂ CO₃ was added, the hydrogen yield could reach 9.456 mol·kg^-1 which was two times of the H₂ amount produced without catalyst. When 1.6 g Ca(OH)₂ was added, the H₂ yield was 8.265 mol·kg^-1 which is lower than that obtained using K₂CO₃ as catalyst but is still 1.7 times that achieved without catalyst. Comparing with the results obtained using K₂CO₃ or Ca(OH)₂ alone, the use of a combination of K₂ CO₃ and Ca(OH)₂ could increase the H₂ yield by up to 2.5 times that without catalyst and 25% and 45% more than that obtained using K₂CO₃ and Ca(OH)₂ alone, respectively. It was found that methane was the dominant product at relatively low temperature. When the temperature was increased, the methane reacts with water and is converted to hydrogen and carbon dioxide.