30.4 Value Added Products from Lignocellulose and Starchy Residues

465

Pressure cooking

Acid/alkali

Physiochemical

Filtration

Steam explosion

Liquid hot water, etc.

Butanol

recovery by

distillation

Size

reduction

Cutting

Pre-treatment

Enzyme

Fermentable sugar

hexose/pentose

Milling

Grinding, etc.

Cellulose

Hemicellulose

Lignin

ABE fermentation (3 : 6 : 1)

(C. acetobutylicum)

HO

HO

HO

OH

OH

O

Figure 30.3

Biobutanol process descriptions.

mole of glucose is converted into either 1 mol of butyric acid or 2 mol of acetic acid

via acidogenesis. In the stationary phase products of acidogenesis are shifted into

solventogenic phase. In this phase, bacteria form spore and acid are transformed

into solvents. The acetic acid is converted into acetone and ethanol, while butyric

acid is converted into butanol. At the end of fermentation the ABE solvents like

acetone, butanol, and ethanol are formed in the proportion of 3 : 6 : 1. The solvent

from fermentation broth can be recovered by gas stripping, pervaporation, adsorp-

tion, extraction through reverse osmosis, etc.

30.4.3

Economics of Biobutanol Production

The economic production of biobutanol depends on the mode of processing,

separation technique and quality of the feed stock. The fixed capital investment is

determined by the first two factors and the total production cost is controlled by

the third factor. There are many studies on economic analysis of ABE fermentation

of corn, molasses, wheat straw, and whey permeate [39]. Utilization of these

food crops for butanol production is not feasible. Though there are many reports

on butanol production from various feedstocks, industries still experience many

challenges which needs to be resolved for economical production. There are several

bottlenecks restricting the commercial use of feedstock, such as continuous supply

of feedstock, selection of non-food crop, low cost processing, and high carbohydrate

content.