Continuous countercurrent extraction of hemicellulose from pretreated wood residues |
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Authors: | Kim Kyoung Heon Tucker Melvin P Keller Fred A Aden Andy Nguyen Quang A |
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Institution: | (1) National Renewable Energy Laboratory, 1617 Cole Boulevard, 80401-3393 Golden, CO |
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Abstract: | Two-stage dilute acid pretreatment followed by enzymatic cellulose hydrolysisis an effectivemethod for obtaining high sugar
yields from wood residuessuchassoftwood forest thinnings. In the first-stage hydrolysis step, most of the hemicellulose is
solubilized using relatively mild conditions. The soluble hemicellu losic sugars are recovered from the hydrolysateslurry
by washing with water. The washed solids are then subjected tomoresevere hydrolysis conditions to hydrolyze approx 50% of
the cellulose to glucose. The remaining cellulose can further be hydrolyzed with cellulase enzyme. Our process simulation
indicates that the amount of water used in the hemicellulose recovery step has a significan tim pact on the cost of ethanol
production. It is important to keep water usage as low as possible while mainta ining relatively high recovery of solublesugars.
To achieve this objective, a prototype pilot-scale continuous countercurrent screw extractor was evaluated for the recovery
of hemicellulose from pretreated forest thinnings. Using the 274-cm (9-ft) long extractor, solubles recoveries of 98, 91,
and 77% were obtained with liquid-to-insoluble solids (L/1S) ratios of 5.6, 3.4, and 2.1, respectively. An empirical equation
was developed to predict the performance of the screwextractor. This equation predicts that soluble sugar recovery above 95%
can be obtained with an L/IS ratio as low as 3.0. |
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Keywords: | Extraction hemicellulose softwood pretreatment acid hydrolysis |
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