Sunday, May 4, 2008
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Sequential Process Production of Bioethanol from the Castor Bean Seed Cake (Ricinus communis L.) generated from the Biodiesel Process 

Walber Carvalho Melo1, Luiz Cláudio Souza Carlos1, Lídia Maria Melo Santa Anna2, and Nei Pereira Jr.1. (1) Biochemical Engineering, Federal University of Rio de Janeiro, P. O. Box: 68542 – Zip code: 21.949-900. Rio de Janeiro, RJ, Brazil., Rio de Janeiro, Brazil, (2) Petrobras Research Center (CENPES), Petrobras

The solid residue arisen from the castor bean seed press, named castor bean cake (CBC) is rich in starch and bears a problem linked to the occurrence of a potent toxic protein (ricin). The challenge of this work is the use of this biomass for bioetanol production, optimizing, in a laboratorial scale, the starch hydrolysis process that, concomitantly, assures the detoxification of the CBC.  The chemical hydrolysis was comprised of an acid pretreatment (ratio solid:liquid = 1:6; H2SO4=0.1 mol/L; 120°C; 40 minutes and 150 rpm), which assured the CBC detoxification, since the toxicity in vivo assays (DL50) pointed out a reduction of roughly 240 times in the CBC toxicity. This chemical stage generated a medium with 26 g/L of reducing sugars (hydrolysis efficiency=32%), which, when fermented, produced 11 g/L of ethanol. Another adopted strategy to increase the hydrolysis efficiency as well as the ethanol concentration in the fermented medium was to incorporate the enzymatic hydrolysis after the acid pretreatment, using commercial alpha-amylase (150 microL/g, 90°C, 4 h, pH=6) and glucoamylase (150 microL/g, 60°C, 4 h, pH=5). This resulted in a hydrolysate containing 75.0 g/L of reducing sugars (hydrolysis efficiency=92%), which were further fermented by a strain of Saccharomyces cerevisiae (10 g/L) in an instrumented bioreactor. At the end of fermentation, 34.5 g/L of ethanol were produced leading to a volumetric productivity of 4.25 g/L.h and an ethanol yield on substrate consumed of 0.46 g/g. These values indicate a production of 270 L of ethanol per ton of residual CBC.

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