Investigation of the enzymatic hydrolysis of torrefied biomass samples

Biomass pretreatement is one of the most energy-demanding steps of the lignocellulosic ethanol production, therefore it largely affects the process energy efficiency and economic viability. A promising approach of biomass pretreatment could be mild torrefaction, which is a thermal treatment between 200 and 300°C in an inert atmosphere. Biomass torrefaction can reduce the energy demand of grinding before pretreatment, and by opening the biomass structure, it makes the biomass more accessible for the hydrolytic enzymes. It can also increase the energy density of biomass, which can decrease the logistics and transportation costs of the biomass in a system, where the biomass is pretreated in a decentralised way.

In this study torrefaction of wheat straw, rape straw and black locust wood was performed at different temperatures (225°C, 250°C and 300°C) for 1 hour. These biomass types were selected, since they were potential candidates for bioethanol production in Hungary. The loss of sample mass and the evolution profile of the released products were monitored by thermogravimetry mass spectrometry (TG/MS) during the torrefaction and also during the thermal decomposition of pretreated samples. The enzymatic hydrolysis experiments of the torrefied samples were carried out at constant temperature (50°C) and stirring (150 rpm) for 72 hours in 0.05 M acetate buffer (pH 5). Water-insoluble solid (WIS) concentration was 2 %, and an enzyme loading (CTec2, Novozymes) of 2% of WIS was applied. The sugar concentrations were quantified by high performance liquid chromatography. The torrefaction was also evaluated based on the cellulose conversion in the hydrolysis.