Bioethanol production from rapeseed straw at high solids loading with different process configurations

• Rapeseed straw is attracting great interest as raw material for fuel production.
• Three strategies are compared for the first time in rapeseed straw.
• Operation at high solids loading (20%) allows feedstock full use.
• Ethanol concentrations as high as 5% are obtained.

Rapeseed is an important source of oil for biodiesel production. Nevertheless, the residues of the cultivation are lacking of practical applications. As a lignocellulosic material, their conversion into ethanol can be of interest. In this work, different process configurations, separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and prehydrolysis and simultaneous saccharification and fermentation (PSSF), were compared at high solids loading (7.5%, 15% and 20% w/v) to produce ethanol from rapeseed straw pretreated by sulfuric acid.Results show that the highest ethanol concentration (39.9 g/L) was obtained from SHF configuration at the highest substrate loading (20% w/v). This product concentration is high enough for distillation purposes from an economic point of view. The final ethanol concentrations and yields did not differ significantly between SSF and PSSF regardless of the solids loading and, for 7.5% and 15% (w/v) solids loading were slightly higher than those attained in the SHF. However, at the highest solids loading the separate process appears to be more favorable.