Published: 2011-11-03
ISBN: 978-91-7393-070-3
ISSN: 1650-3686 (print), 1650-3740 (online)
Bioethanol is an alternative transport fuel produced mainly by the biochemical conversion of biomasses. This can be carried out efficiently and economically by simultaneous saccharification and fermentation (SSF): a process which integrates the enzymatic saccharification of the cellulose to glucose with the fermentative synthesis of ethanol. However; the SSF unit operation still contributes nearly 50% to the cost of ethanol production. For cellulosic ethanol to be cost competitive; there is the need to intensify the production process in smaller; more efficient and more economical bioreactors. In this work; SSF was performed in an intensified form of plug flow reactor; called the Oscillatory Baffled Reactor (OBR). The OBR is a continuous tubular reactor fitted with equally-spaced orifice plate baffles. An oscillatory component; provided by moving bellows in this design; is superimposed on the net flow through the reactor; generating short-lived vortices due to the interaction of the oscillating fluid with the baffles. This results in uniform mixing in each of the inter-baffle regions; with each behaving as a stirred tank reactor (STR); producing a plug flow residence time distribution (RTD) for the reactor as a whole; in which the mixing effects are largely decoupled from the mean flow (unlike conventional PFRs). The process was evaluated using 2.5% SigmaCell cellulose; 40 FPU cellulase loading/g of cellulose and 10% cellobiase. Saccharomyces cerevisiae was employed as the fermenting organism at 38 oC and pH 4.8. In the first part of this work the use of the OBR resulted in a 7% increase in glucose yield compared to a shake flask; after 48 h of saccharification and 8.0 g/L ethanol in the OBR. This represented 89.8 % of the theoretical yield; as compared to 7.7 g/L in the shake flask representing 81.29%; a difference of 9 percentage point. This increased glucose yield is attributable to better mixing in the OBR.
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