9-05: Process development of integrated cellulose- and starch-based ethanol production

The aim of this study is to develop processes for production of ethanol from cellulose-based raw materials, mainly agricultural residues such as wheat straw, barley straw and corn stover (second- generation bioethanol), integrated with starch-based ethanol production (first-generation bioethanol). In this manner higher ethanol yield, lower energy demand and lower production cost can be reached.

 The study comprises both experimental studies and techno-economic evaluation of the results using commercial flow sheeting- and cost-estimation programs. Several process configurations for the integration are possible, from integration already at the front end, i.e., after pretreatment of the raw materials, to integration only of the downstream processes, i.e., distillation and evaporation.

 Integration of the steam-pretreated wheat straw with liquefied and pre-hydrolyzed starch from wheat (5%+0.5-3% WIS (Water Insoluble Solids) respectively) in SSF (Simultaneous Saccharification and Fermentation) configuration has been investigated, using baker’s yeast. Ethanol yields above 80% of the theoretical (from the hexose sugars) and ethanol concentrations around 6 wt-% have been reached. This results in lower total energy demand in comparison with separate production of ethanol in a starch- or in a cellulose-based process.

 The study is now continued using genetically modified yeast to also ferment the pentose sugars and further increase the WIS content of the pretreated wheat straw in the SSF step thereby increasing both the yield and the concentration. Furthermore, integration of the steam-pretreated wheat straw with only liquefied starch in order to reduce the availability of glucose in the SSF step is also under investigation.