Catalytic fast pyrolysis of glucose with HZSM-5: The combined homogeneous and heterogeneous reactions

The production of aromatics from glucose by catalytic fast pyrolysis occurs in two steps. First, glucose is thermally decomposed to smaller oxygenates through retro-aldol fragmentation, Grob fragmentation and dehydration reactions. At low temperatures (<300 °C), retro-aldol and Grob fragmentation reactions are favored with d-glyceraldehyde, hydroxyacetone and hydroxyacetaldehyde being the primary products. At higher temperatures (>300 °C), dehydration is favored with levoglucosan as the major product. The addition of ZSM-5 catalyst to the pyrolysis reactor lowers the temperature at which the fragmentation and dehydration reactions occur at 206 °C and 312 °C, and at 282 °C and 369 °C, respectively. In the second step of catalytic fast pyrolysis, the dehydrated products enter into the catalyst where they are converted into aromatics, CO, CO2 and water. The catalytic conversion step is significantly slower than the initial pyrolysis reaction. The aromatic product selectivity is a function of catalyst to glucose weight ratio, heating rate and reaction temperature. At 600 °C, a maximum carbon yield of 32% aromatics is realized after 240 s with catalysts to feed ratio of 19. The major competing reaction to aromatic production is the formation of coke. Coke is most likely formed by polymerization of the furans on the external catalyst surface.