Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor

Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were used to gasify biomass constituents in supercritical water. The first reactor configuration was a micro diameter stainless steel or Hastelloy tube (508 um - 762 um) imbedded into a reactor block. The reactor provided high rates of heat transfer to the reacting fluid to sustain an isothermal reaction temperature and was used to elucidate interactions between phenol, a lignin model compound, and xylose, a hemicellulose model compound, during co-gasification. In addition, a reaction mechanism and kinetics for phenol and xylose gasification by supercritical were estimated. The second microreactor configuration studied was a parallel channel Hastelloy microreactor. The reactor consisted of 14 parallel rectangular microchannels (1000 um by 127 um) integrated into a single contiguous reactor block by diffusion bonding a series of shims between two header plates. Fabrication of the reactor from Hastelloy C-276, a high nickel content alloy, substantially intensified biomass gasification reactions and promoted the water gas shift and methanation reactions due to its high catalytic activity and the large surface area to volume ratio in the microchannel. The dispersion and channel flow distribution in the microchannel reactor was characterized experimentally and modeled using computational fluid dynamics by a tracer pulse study. Furthermore, computational fluid dynamics were used to investigate the effect of endothermic biomass reforming reactions and the average fluid Reynolds number on the reaction temperature. Lastly, xylose was completely gasified to hydrogen and carbon dioxide in the parallel channel microreactor at 650°C and 250 bar within a 1.4 second residence time.