Monday, April 30, 2007

Temperature and time optimization in LHW pretreatment of wheat straw for ethanol production

Jose Ant. Perez Sr., Mercedes Ballesteros, Ignacio Ballesteros, and Paloma Manzanares. Renewable Energies, CIEMAT, Avda. Complutense 22, Madrid, Spain

Fuel-ethanol production in Spain is currently based on cereal grains. However, the possibility of using the crop by-product as alternative feedstock is becoming a realistic option due to its high availability and the progress made during the last years in lignocellulosic biomass to ethanol technologies. Nevertheless, there are still challenges that need to be faced to increase whole process efficiency thus resulting in a cost competitive fuel.

 In this work, data about Liquid Hot Water (LHW) pretreatment of wheat straw for bioconversion to ethanol are presented.  Experiments aimed to find optima temperature and time conditions were performed in a 500 ml laboratory-scale stirred autoclave. A central composite design in the range of 170 to 220ºC temperature and 1 to 40 min reaction was used.

 Optimization was based on hemisugars recovery yield in prehydrolyzate and enzymatic cellulose digestibility of washed pretreated solids. Acetyl content in pretreated substrates was also analyzed to assess its effect on cellulose digestibility of pretreated straw. First approach showed that the conditions leading to maxima values of both hemisugars recovery and EH yield were 190ºC y 40 minutes residence time. It was also concluded that the optimization of process variables for both responses would need to consider different intervals of time and temperature, since the conditions which led to maximum values of EH yields result in hemisugars degradation in prehydrolyzate. According to these results, separate central composed experimental designs were devised in order to optimize both response variables.  Detail results of this research will be presented.