Ethanol Production from Biomass- Optimization of Simultaneous Saccharification and Fermentation with Respect to Stirring and Heating

The purpose of this study was to optimize ethanol production in a small glass reactor. The ethanol was produced through simultaneous saccharification and fermentation (SSF) of steam pretreated spruce. Ordinary commercial yeast was used with a concentration of 5 g/L. The method of pretreatment was steam-explosion with SO2 as catalyst. The pretreatment liberates cellulose, giving the enzymes better access to the cellulose. The optimization involved modifying heating and stirring. The reactor was provided with a glass jacket allowing it to be heated with a water bath instead of a hot plate. Different stirring speeds were tried and a new stirrer was designed. The new design was also incorporated as a stirring parameter along with the old one. Different concentrations of pretreated material, 7 % & 10 % water insoluble solids (WIS) were used. The more material used in SSF the more ethanol is potentially produced, but both enzymes and yeast are susceptible to inhibitors present in the pretreated material. Best result was achieved with the jacketed reactor with 7 % WIS and slow stirring with the old stirrer; yielding an ethanol end concentration of 29.9 g/L and a yield of 61.2 %. The yield in question was the amount of ethanol produced from the pretreated material as % of the theoretical possible based on the hexose content in the raw material. The commercial yeast was found unable to cope with the inhibitory effects experienced with 10 % WIS. The enzymes, on the other hand, retained most of their activity. Even with 7 % WIS reproducibility was poor. However, to draw a conclusion with statistical certainty more experiments are needed