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Poster Presentation 1-16
Initial Results from a Pilot Scale Pretreatment Reactor Using Very Dilute Sulfuric Acid on a Hardwood Feedstock
Richard T. Elander, Nicholas J. Nagle, Melvin P. Tucker, Raymond O. Ruiz, Byran T. Rohrback and Robert W. Torget
Biotechnology Division for Fuels and Chemicals National Renewable Energy Laboratory 1617 Cole Blvd., Golden, CO 80401
Telephone: (303) 384-6841; Fax: (303) 384-6877; E-mail: richard_elander@nrel.gov
A continuous two stage reactor system to fractionate hardwood at high yields at the pilot scale (200 kg/day) has been installed and operated in an initial campaign of ~100 hours. The reactor design is based upon a horizontal screw plug-flow first stage using steam (170-185ºC) and a vertical countercurrent second stage using very dilute sulfuric acid (<0.1 wt %, 205-225ºC). The vertical countercurrent stage reactor employs an interrupted flight design to mimic the “shrinking bed” effect of a bench-scale spring-loaded percolation reactor system. This bench-scale system has previously been reported to achieve soluble sugar yields from both cellulose and hemicellulose in excess of 90% from hardwood yellow poplar sawdust. Initial results from the pilot scale system included soluble xylose yields approaching 90% (combined oligomers and monomers), but glucose yields from cellulose under 25%. However, at the residence times tested in the vertical stage (5 minutes or less) the glucose yields were only slightly lower than predicted using shrinking-bed reaction kinetics at these residence times. In addition, total soluble sugar concentrations were routinely above 50 g/L and reached a maximum of over 65 g/L, despite the relatively low glucose yields. Several modifications to the reactor system, particularly to the screw flight design of the vertical state reactor, have been proposed to allow for more effective solids movement that could allow for operation at longer residence times. Finally, recently developed fundamental hemicellulose and cellulose hydrolysis reaction concepts are being utilized to guide additional reactor system modifications.
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