Monday, May 5, 2008
9-41

Minimizing Mass Transport Effects in a Continuous Process for Production of Ethanol from Starch

Joubert Trovatti, Roberto Campos Giordano, and Raquel Lima Camargo Giordano. Chemical Engineering Department, Universidade Federal de São Carlos, Washington Luiz, Km 235, Monjolinho, São Carlos, SP, Brazil

In a previous work, a continuous SSF process to produce ethanol from cassava starch was studied, using a set of fixed-bed reactors. The biocatalyst consisted of glucoamylase immobilized in silica particles and co-immobilized with S. cerevisiae in pectin gel. Using 3.77 U/mLreactor and 0.05 g wet yeast/mLreactor at start-up, starch hydrolysis was the rate-limiting step and the maximum ethanol productivity was 5.8 gethanol/L/h, with 94% conversion, and 83% of the ethanol theoretical yield. In this work, the molar mass of the substrate and the biocatalyst particles’ size were reduced, aiming at increasing mass transfer rates. The conditions of the pre-hydrolysis with a-amylase were changed: longer reaction times and higher enzyme concentrations were tested, until obtaining limit dextrin. The diameters of silica and pectin gel particles, in their turn, were reduced: from 100 mm and 3-4 mm, respectively, in the previous work, to 60 mm and 1-1.5 mm. The performance of the packed-bed reactors was then studied, using immobilized glucoamylase concentrations of 2.09, 2.76 and 3,77 U/mLreactor, keeping constant the initial cell concentration as 0,05g wet yeast/mLreactor. Each run was carried on for 11 days at least. In the present work, with a feed concentration of 154 g/L (TRS), and using 3.77 U/mLreactor, fermentation became the rate-limiting step. Productivity reached 11.7 g/L/h, with 97% of conversion and 92% of the ethanol theoretical yield.
Index Entries: ethanol, cassava starch, Saccharomyces cerevisiae, glucoamylase, packed-bed reactor, simultaneous saccharification and fermentation, mass transport effects

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