Enzymatic saccharification of cellulose: a study of mixing and agitation in an oscillatory baffled reactor and a stirred tank reactor

Abstract

Cellulose saccharification has been shown to be a function of agitation. Here, the effect of agitation by oscillatory mixing in an oscillatory baffled reactor (OBR) has been assessed and contrasted with a stirred tank reactor (STR). After 168 h of saccharification at 200 Wm−3, 91% conversion of the cellulose (∼25 g/L glucose) was observed in the OBR, as against 74% conversion (∼21 g/L glucose) in the STR. At 120 Wm−3 in both systems, the conversion in the OBR was 69% (∼19 g/L glucose) within the first 24 h, and 88% conversion (24 g/L glucose) after 168 h. The STR yielded 55% (15.3 g/L glucose) and 67% (∼18.6 g/L glucose) within the same time scale respectively, differences of 14 and 21% respectively. At equivalent power density of 10 Wm−3, the two reactors exhibited the same mean strain rates of 6.65 s−1, but as the power densities increased the mean strain rates in the STR became significantly higher than that in the OBR. This observation could be partly responsible for the seemingly better saccharification observed in the OBR. Although agitation is essential for optimum saccharification, the nature of the agitation is perhaps a more important factor owing to shear stresses on enzymes.