Mixing design for enzymatic hydrolysis of sugarcane bagasse: methodology for selection of impeller configuration

One of the major process bottlenecks for viable industrial production of second generation ethanol is related with technical–economic difficulties in the hydrolysis step. The development of a methodology to choose the best configuration of impellers towards improving mass transfer and hydrolysis yield together with a low power consumption is important to make the process cost-effective. In this work, four dual impeller configurations (DICs) were evaluated during hydrolysis of sugarcane bagasse (SCB) experiments in a stirred tank reactor (3 L). The systems tested were dual Rushton turbine impellers (DIC1), Rushton and elephant ear (down-pumping) turbines (DIC2), Rushton and elephant ear (up-pumping) turbines (DIC3), and down-pumping and up-pumping elephant ear turbines (DIC4). The experiments were conducted during 96 h, using 10 % (m/v) SCB, pH 4.8, 50 °C, 10 FPU/g_biomass, 470 rpm. The mixing time was successfully used as the characteristic parameter to select the best impeller configuration. Rheological parameters were determined using a rotational rheometer, and the power consumptions of the four DICs were on-line measured with a dynamometer. The values obtained for the energetic efficiency (the ratio between the cellulose to glucose conversion and the total energy) showed that the proposed methodology was successful in choosing a suitable configuration of impellers, wherein the DIC4 obtained approximately three times higher energetic efficiency than DIC1. Furthermore a scale-up protocol (factor scale-up 1000) for the enzymatic hydrolysis reactor was proposed.