Stirrer speed adaption is beneficial for liquefaction of cellulose

Enzymatic hydrolysis of cellulose is a key step in the valorisation of lignocellulosic material subsequent to pretreatment. The optimization of hydrolytic enzymes is in the focus of intensive research of different institutes and companies whereby not much attention is being paid to the process engineering parameters such as the stirrer velocity. We therefore focused on a stirrer speed adaption strategy during enzymatic cellulose hydrolysis in larger lab-scale. Mixing time measurements were performed with carboxymethyl cellulose solutions in a 10 L-tank reactor equipped with a segmented helical stirrer to determine agitator speed levels adapted to the cellulose suspensions' viscosities at the certain hydrolysis time. Comparing the optimized hydrolysis with adaptation of stirrer speed to the hydrolysis performed at a constant stirrer velocity, a 30% higher glucose yield and 25% lower energy input was observed. Overall, the enzymatic hydrolysis of cellulose applying a step-wise adaption of the stirrer velocity thus resulted in a faster liquefaction, while at the same time the overall power requirement was reduced.