Economic Analysis of Ethanol Conversion Technologies

Several technologies have been developed in order to convert efficiently cellulose to ethanol. The best-known processes that we discuss in the earlier section are: (a) SSF, (b) dilute sulfuric acid hydrolysis and fermentation, and (c) fast pyrolysis and fermentation. We will briefly describe the dilute sulfuric acid hydrolysis process and the fast pyrolysis process, and then compare the cost and the production of ethanol among the three processes.

Figure 3 illustrates the process of ethanol production by dilute sulfuric acid hydrolysis and fermentation. In the hydrolysis step, cellulose is pretreated in 0.05 g/l of sulfuric acid at 180°C. For the purpose of economic comparison, we consider the concentration of sugars yielded to be 103.7 g/l. Following hydrolysis, a strain of fungus is responsible for the continuous fermentation of sugars (pentose and hexose) into ethanol (So and Brown 1999).

Figure 4 shows the Waterloo fast pyrolysis and fermentation process. Its pretreatment step uses 5% hot sulfuric acid. In the fermentation step, fungi degrade cellulose

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Figure 2 Mixed culture hydrolysis and fermentation.

Feed Slack

796 dry lons/day

(wood wilh 50% moisture)

Feed Slack

796 dry lons/day

(wood wilh 50% moisture)

Lignin

HI hnno I Product (95 gal/ton yield)

Figure 3 Dilute sulfuric-acid hydrolysis and fermentation process. From So and Brown (1999).

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HI hnno I Product (95 gal/ton yield)

Figure 3 Dilute sulfuric-acid hydrolysis and fermentation process. From So and Brown (1999).

into sugars while bacteria ferment the different types of sugars (pentose and hexose) to ethanol.

The capital cost analysis given in Table 6 shows that fast hydrolysis, SSF, and acid hydrolysis all have fairly similar total capital costs; the small differences are probably within the error of estimates. Likewise, the operating cost analysis presented in Table 7 also shows similar numbers, albeit the cost of ethanol is the lowest with the SSF process.

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