Sunday, May 3, 2009
3-68

Simplex optimization and mathematical modeling of wheat straw dilute acid hydrolysis

Talita Fernandes, Luís C. Duarte, Florbela Carvalheiro, and Francisco Gírio. Departamento de Biotecnologia, INETI, Estrada do Paço do Lumiar, 22, Lisboa, 1649-038, Portugal

Wheat straw is an interesting biorefinery raw material, due to its abundance, chemical composition, and cost. Among the different pretreatments suitable for its processing, dilute acid hydrolysis still presents some benefits due to its simplicity. Nevertheless, it requires a careful optimization to avoid excessive by-products formation and catalyst spending. An attractive and simple optimization approach is the Sequential Simplex Method, an iterative procedure that enables to rapidly screen a large area of operational conditions and effectively encircle the optimal.

In this work, dilute acid hydrolysis of wheat straw was optimized to selectively hydrolyze the hemicellulose fraction and obtain a pentose-rich fermentable hydrolyzate. The influence of time (up to 180 min), and sulfuric acid concentration (up to 4%, w/w) were studied. The hydrolyzates obtained in the optimized conditions mainly contain free sugars (total content higher than 46 g/L). The main potential microbial inhibitors found were acetic acid, furfural, and HMF, in concentrations lower than 4.8, 1.7 and 0.3 g/L, respectively.

Empirical models describing the influence of the studied variables on sugars and by-products formation were validated for the entire domain. Sulfuric acid concentration was found to be the most influential variable, although both variables are statistically significant for xylose recovery. Interaction effects play a significant (negative) role. Data was also modeled based on the combined severity parameter (CS) and the results of these two approaches are compared and discussed. These hydrolyzates were easily utilized by Debaryomyces hansenii, a natural pentose assimilating yeast.

This work was funded by the project BIOREFINO (PTDC/AGR-AAM/71533/2006F).


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See more of The 31st Symposium on Biotechnology for Fuels and Chemicals (May 3-6, 2009)