8-75: Conversion of lignocellulosic materials to bioethanol at high dry-matter contents for increased ethanol concentration

Production of bioethanol from lignocellulosic material, such as agricultural or forest residues, or dedicated energy crops has been proposed as one potential route for replacement of some of the fossil fuels used today. Today, most bioethanol is produced from sugar- or starch-based raw materials, such as sugar cane, wheat or corn. The sugar- or starch-containing liquids to be fermented have a high sugar concentration, which results in high ethanol concentrations after fermentation, above 8% in most cases. This has a positive effect on the overall energy balance, since distillation is one of the most energy-intensive operations in an ethanol plant.

However, to be able to meet the demand for bioethanol in the near future, other raw materials must be utilized. When lignocellulosic materials are used to produce a sugar-rich substrate, some difficulties appear. Since much of the material consists of lignin (about 50% after pretreatment in many cases) high dry-matter contents must be used during hydrolysis or simultaneous saccharification and fermentation (SSF) to reach reasonable ethanol concentrations (above 4%).

It is a challenge to reach such high concentrations since mixing problems can be severe and inhibitor concentrations are higher. At the start of the hydrolysis the material may appear almost solid, while in later stages the slurry is much less viscous. Preliminary studies using steam-pretreated spruce resulted in ethanol concentrations 65- 70 g/l. The study is on-going and results will be presented.