1-15: Ethanol production from white corn stover

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Cessna L. Moss-Acosta1, Mario Caro-Bermúdez1, Berenice Trujillo-Martínez1, Ricardo Comans-Pérez1, Montserrat Orencio-Trejo2 and Alfredo Martínez -Jímenez1, (1)Ingeniería celular y biocatálisis, Instituto de Biotecnología - UNAM, Cuernavaca, Mexico, (2)Ingeniería Genética, CINVESTAV–Ira, Irapuato, Mexico
White corn stover, from the central region of Mexico, was characterized and the hemicellulosic fraction was hydrolyzed to evaluate its conversion to ethanol with ethanologenic Escherichia coli. White corn stover contain (in percentage): 35.5 glucan, 19.3 xylan, 19.8 lignin, 5.8 ashes, 7.7 extractives, 1.7 acetyl groups, and 5.6 moisture. Thermochemical hydrolysis was performed, at flask scale (5 g dry matter) and pilot-scale (8 kg dry matter), with dilute H2SO4 (2%), a solid:liquid (stover:acid) ratio of 1:6, 130°C with two cycles of 30 and 60 minutes. Hydrolysates with total sugar concentrations of 57 g/L were obtained at both scales. The hydrolysates were overlimed with Ca(OH)2 (pH 10, room temperature), pH adjusted to 7 and  supplemented with ammonium phosphate, citric acid and betain. This broth was fermented with ethanologenic E. coli strain MS04 (MG1655 ΔpflB, ΔadhE, ΔfrdA, ΔldhA, PpflB::pdcZm-adhAZm) in mini-fermentors: 150 rpm, 37°C, pH 7.0, 20% inoculum (v/v) and a working-volume of 200 mL. A total sugar concentration of 50.4 g/L (5.3 g/L arabinose, 7.4 g/L glucose and 37.8 g/L xylose), in the presence of acetate (6.4 g/L), were fermented to ethanol in 72 h with a yield of 94.3% of the maximum theoretical. Experimental conversion of hydrolyzed sugars from glucan (hydrolyzed with cellulases and glucosidases at 50°C and fermented with yeast), xylan and arabinan fractions allow obtaining 285 L of ethanol per metric ton of white corn stover.
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