Biohydrogen Generation and Other Methods - Hydrogen Generation, Storage, and Utilization - page 61

TABLE 4.6 Comparison of Hydrogen Yields Are Obtained by Use of Three
Different Processes

Hydrogen Energy Contents/
Biomass Energy Content Processes Hydrogen Yield (wt%)

Pyrolysis + catalytic reforming 12.6 91

11.5 83

Gasification + shift reaction

Biomass + steam + except
heat (theoretical maximum)

17.1 124

Source : Reproduced with permission from Wang et al. [61].

50
45
40
35
30
25
20
15
10
600

Supercritical fluid
extraction
Conventional pyrolysis

Steam gasification

700 800 900 1000 1100 1200

Temperature, K

FIGURE 4.3 Plots for yield of hydrogen from supercritical fluid extraction, pyrolysis, and steam gas-
ification [(W/S) = 2] of beech wood at different temperatures. Source : Reproduced with permission from
Demirbas [45].

basis) were obtained from the pyrolysis (46%) and steam gasification (55%)
of wheat straw, while the lowest yields were from olive waste. He also inves-
tigated the yield of hydrogen from SFE, pyrolysis and steam gasification of
beech wood at different temperatures. Distilled water was used in the SFE
(the critical temperature of pure water is 647.7 K). Results of this study are
shown in Figure 4.3. From Figure 4.3, the yield of hydrogen from SFE was
considerably high (49%) at lower temperatures. The pyrolysis was carried
out at the moderate temperatures and steam gasification at the highest
temperatures.

4.4 BIOLOGICAL PROCESS FOR HYDROGEN PRODUCTION

Hydrogen produced from water, renewable organic wastes or biomass, either
biologically (biophotolysis and fermentation) or photobiologically (photode-