Sunflower - Bioenergy Crop Plants - page 729

Elsewhere, reports on ethanol production from other lignocellulosics have been reported. Singh
et al . (1984) reported ethanol production from the acid hydrolysate of bagasse using S. cerevisiae
with an efficiency of 82.6% (low because of the presence of 0.3 g/dm 3 of furfural) and a yield factor
Yp/s of 0.422. Tewari et al. (1985) carried out the fermentation of acid and enzymatic hydrolysate
of saw dust by S . cerevisiae var. ellipsoideus . The enzymatically hydrolyzed samples supported
better ethanol production on the basis of reducing sugars than the acid-treated samples. Similar
observations have been observed in our laboratories with sunflower stalks and hulls in which ethanol
yields reduced from 0.444 and 0.454 to 0.439 and 0.419 g/g, respectively (Sharma 2000). Dhillon
et al. (1988) fermented the rice straw hydrolysate containing 7.68% reducing sugars by S. cerevisiae
with ethanol production of 2.89%. Laplace et al. (1991) investigated the combined fermentation of
glucose and xylose to ethanol by separate or co-culture processes using P. stipitis, C. shehatae,
S. cerevisiae, and Z. mobilis .
Roberto et al. (1994) studied the influence of aeration and pH on xylose fermentation to ethanol
by P. stipitis. The best ethanol yields (0.35 g/g) were obtained in flasks agitated at 100 and 150 rpm
for respective VF/VM (volume of flasks/volume of the medium) ratios of 5.0 and 2.5. Furlan et al.
(1994) studied the effect of oxygen on ethanol and xylitol production by xylose fermenting yeasts.
P. stipitis and Candida parapsilosis were the most effective in the production of ethanol and xylitol,
respectively. The optimal oxygen transfer coefficients were 4.8 and 16.3 per hour in the two cases.
The highest ethanol productivity was obtained under microaerobic conditions (Kruse and Schugerl
1996). Kastner et al. (1996) investigated the effect of pH on cell viability and ethanol yields in
D-xylose fermentation by C. shehatae . Ethanol yield increased from 0.25 to 0.37 g/g as the pH was
increased from 2.5 to 6. A pH of 6 also extended the cell viability during anaerobic conditions.
Larsson et al. (1999) studied the effect of acetic acid, formic acid, levulinic acid, furfural,
and 5-hydroxymethyfurfural (5-HMF) (compounds generated during dilute acid hydrolysis of
softwood) on fermentability of dilute acid hydrolysate of softwood by S . cerevisiae. Ethanol yield
and volumetric productivity decreased with increasing concentrations of acetic acid, formic acid,
and levulinic acid. Furfural and 5-HMF decreased the volumetric productivity but did not influence
the final yield of ethanol. Saha and Cotta (2006) reported ethanol production with a yield of 0.23 g/g
from enzymatically saccharified wheat straw.
30.7.2 E thanol r EcovEry
Recovery of ethanol from fermentation broth is at least a three-step process: (1) distillation of
dilute aqueous alcohol to its azeotrope (95.57% ethanol by weight); (2) distillation using a third
component—either an organic solvent or a strong salt solution to break up the azeotrope and remove
the remaining water; and (3) distillation to separate water from the third component so that it can
be recycled. Most of the energy consumption occurs in distilling above 85% ethanol. The ethanol
produced after fermentation in our studies was distilled from the fermentation broth and dehydrated
with calcium chloride (CaCl 2 ) (4-20%), and a maximal dehydration of aqueous ethanol (95.5%, v/v)
was observed with 18% CaCl 2 .
30.8 conclusIons
Sunflower is a known crop for edible oil and biodiesel production. It has been suggested that using
sunflower-based biodiesel in combination with bioethanol can counter the problems of the high sulfur
and flash point of potato-based biodiesel (Ghobadian et al. 2008). Moreover, sunflower processing
also generates significant quantities of lignocellulosics in the form of stalks and seed hulls that can
be used for bioethanol production. Our experiments on utilization of these lignocellulosic substrates
have also revealed their potential for bioethanol production. In this endeavor, the pretreatment of
sunflower stalks and seed hulls was standardized by using them as 40-mesh ground forms that
were treated with 0.5% NaOH followed by steaming in an autoclave at 15 psi for 1.5 h, resulting