Improvements in Bioethanol Production Process from Straw

Jäger, A. (Speaker), Heike Kahr (Speaker)

Activity: Talk or presentationOral presentation


Motivation: The carbon-containing fossil fuel resources like oil, gas and coal are limited and oil production may cause environmental problems such as the oil catastrophe in the Gulf of Mexico. One effective solution for these problems is the production of sustainable, carbon-neutral, renewable fuels like bioethanol and biogas from straw and other agricultural by-products. The scientific focus of the Bioethanolics group is the improvement of the bioethanol production using straw as an alternative energy source. Straw is an exceptional resource offering the opportunity to reuse agricultural by-products. Until now, no industrial bioethanol plant using straw has been established. Methods: The ethanol production process is already well studied and established on a laboratory scale. The process involves the following steps: the pretreatment of straw with pressure, heat and an abrupt release of the pressure for accessing cellulose in a process called steam explosion. In this process, lignin and some of the hemicellulose are removed and cellulose becomes accessible for enzymatic hydrolysis to obtain hexoses. Subsequently, yeast ferments the obtained glucose to ethanol. Unfortunately, inhibitors such as weak acids, furans and phenolic compounds are generated during the pretreatment and hydrolysis process, thereby reducing the glucose concentration and ethanol yield. Fermentation tests were performed with glucose solutions containing diverse inhibitors. Results and limitations: Pretreatment of straw was performed with the steam explosion process. The hydrolysis of the pretreated straw with commercial enzymes has been well established. Enhancement of the dry substance has achieved a linear increase in glucose and ethanol content. Glucose concentration was raised up to more than 300g/l and ethanol content up to 10% by means of optimization of the process (washing steps and recirculation). Diverse substances inhibit the fermentation and reduce the ethanol content. The relevant inhibitory substances were analyzed in fermentation tests. Several improvements, like washing steps prior to hydrolysis, clearly reduced the inhibitory substances. Treatment with the enzyme laccase after hydrolysis leads to a clear reduction of the total phenol concentration. An alternative approach to reduce the inhibitors with membrane process will be tested. The generation of an inhibitor-tolerant yeast strain through adaptation to the straw hydrolysate was initiated. Conclusion: The ethanol and glucose yield was improved due to optimization of the bioethanol production. The effects of various inhibitors during the fermentation were analyzed. Now an efficient procedure to reduce the inhibitors has to be established to plan a pilot plant. The ethanol content has to be raised to a minimum of 10% ethanol to achieve an economically efficient production process.
Period28 Apr 2011
Event titleFFH 2011 - 5. Forschungsforum der öst. Fachhochschulen: null
Event typeConference
LocationFH Campus Wien, Austria