Abstract
The production of ethanol from industrial dry-milled corn starch was studied in a laboratory-scale fluidized-bed bioreactor using immobilized biocatalysts. Saccharification and fermentation were carried out either simultaneously or separately. Simultaneous saccharification and fermentation (SSF) experiments were performed using small, uniform κ-carrageenan beads (1.5–2.5 mm in diameter) of co-immobilized glucoamylase and Zymomonas mobilis. Dextrin feeds obtained by the hydrolysis of 15% drymilled corn starch were pumped through the bioreactor at residence times of 1.5–4h. Single-pass conversion of dextrins ranged from 54–89%, and ethanol concentrations of 23–36 g/L were obtained at volumetric productivities of 9–15 g/L-h. Very low levels of glucose were observed in the reactor, indicating that saccharification was the rate-limiting step. In separate hydrolysis and fermentation (SHF) experiments, dextrin feed solutions of 150–160 g/L were first pumped through an immobilized-glucoamylase packed column. At 55°C and a residence time of 1 h, greater than 95% conversion was obtained, giving product streams of 162–172 g glucose/L. These streams were then pumped through the fluidized-bed bioreactor containing immobilized Z. mobilis. At a residence time of 2 h, 94% conversion and ethanol concentration of 70 g/L were achieved, resulting in an overall process productivity of 23 g/L-h. Atresidence times of 1.5 and 1 h, conversions of 75 and 76%, ethanol concentrations of 49 and 47 g/L, and overall process productivities of 19 and 25 g/L-h, respectively, were achieved.
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The submitted manuscript has been authored by a contractor of the US government under contract DE-AC05-960R22464. Accordingly, the US government retains a non-exclusive, royalty-free license to publish or reproduce the published form of the contribution, or allow others to do so, for US government purposes.
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Krishnan, M.S., Nghiem, N.P. & Davison, B.H. Ethanol production from corn starch in a fluidized-bed bioreactor. Appl Biochem Biotechnol 78, 359–372 (1999). https://doi.org/10.1385/ABAB:78:1-3:359
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DOI: https://doi.org/10.1385/ABAB:78:1-3:359