Effects of RTD On the Performance of NREL High-Solid Continuous Pretreatment Reactor
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Dilute-acid pretreatment is one of the most advanced and widely accepted pretreatment technologies. In this study, improvement in the process was sought specifically in the area of reactor technology. NREL has developed an efficient continuous pretreatment reactor that can be operated with high-solid charge and with short residence time. The reactor is screw-driven and operates under high temperature and pressure conditions. Although the reactor is designed to behave as a PFR, the residence time distribution (RTD) data obtained from tracer tests have shown that the flow pattern in the reactor deviates significantly from PFR. In this study, we have investigated the kinetics of the reactions in the dilute-acid pretreatment of corn stover, covering the reaction conditions employed in the operations of the NREL pretreatment reactor. The primary reaction of this pretreatment is acid-catalyzed hydrolysis of the hemicellulose fraction in the corn stover. The kinetic pattern was modeled as: two different fragments of hemicellulose to oligomers, to xylose, and to decomposition products. Batch experiments were performed and the data were used to determine the kinetic parameters. The kinetic information was then put into the reactor performance model incorporating the RTD information. The results were further analyzed to assess the effects of dispersion (RTD) on the performance of the NREL-continuous reactor. The kinetic data, the model procedure, and the output of reactor performance (yield of xylose and oligomers) as it relates to the degree of dispersion are presented, and the strategy to improve the reactor performance is discussed.