Hydrogen is an important fuel with wide applications in fuel cells, liquefaction of coal, and upgrading of heavy oils (e. g., bitumen). Hydrogen can be produced bio­logically by a variety of means, including the steam reformation of bio-oils, dark and photo fermentation of organic materials, and photolysis of water catalyzed by special microalgal species.

The chemical compositions of algae are given in Table 5.10 (Demirbas 2007). Algae are mainly composed of proteins, lipids, and water-soluble carbohydrates.

Two moss samples (Polytrichum commune, Thuidium tamarascinum), one alga sample (Cladophora fracta), and one microalga sample (Chlorella protothecoides) were subjected to pyrolysis and steam gasification for producing hydrogen-rich gas (Demirbas, unpublished work).

The temperature of the reaction vessel was measured with an iron-constantan thermocouple and controlled at ±3 K. The pyrolysis experiments were performed at temperatures of 575, 625, 675, 725, 775, 825, and 925 K. The steam gasification experiments were carried out at temperatures of 825, 875, 925, 975, 1,025, 1,075, 1,125, 1,175, and 1,225K (Demirbas, unpublished work).

Table 5.11 shows the proximate analysis data and higher heating values (HHVs) of samples. The HHV (MJ/kg) of the moss and alga samples as a function of fixed carbon (FC) wt% can be calculated from

HHV = 0.322 (FC) + 10.7123 (5.3)

The HHVs can be calculated using Equation 5.3 and represent high correlation ob­tained by means of regression analysis. The correlation coefficient r is 0.999.

Table 5.10 Chemical compositions of algae on a dry matter basis (%) Species of sample Proteins Carbohydrates Lipids Nucleic acid Scenedesmus obliquus 50-56 10-17 12-14 3-6 Scenedesmus quadricauda 47 — 1.9 — Scenedesmus dimorphus 8-18 21-52 16-40 — Chlamydomonas rheinhardii 48 17 21 — Chlorella vulgaris 51-58 12-17 14-22 4-5 Chlorella pyrenoidosa 57 26 2 — Spirogyra sp. 6-20 33-64 11-21 — Dunaliella bioculata 49 4 8 — Dunaliella salina 57 32 6 — Euglena gracilis 39-61 14-18 14-20 — Prymnesium parvum 28-45 25-33 22-38 1-2 Tetraselmis maculata 52 15 3 — Porphyridium cruentum 28-39 40-57 9-14 — Spirulina platensis 46-63 8-14 4-9 2-5 Spirulina maxima 60-71 13-16 6-7 3-4.5 Synechoccus sp. 63 15 11 5 Anabaena cylindrica 43-56 25-30 4-7 —

Table 5.11 Proximate analysis data and higher heating values (HHVs) of samples (% dry wt basis) Sample Fixed carbon Volatile matter Ash HHV (MJ/kg) Polytrichum commune 19.4 65.8 14.8 17.0 Thuidium tamarascinum 15.4 72.3 12.3 15.5 Cladophora fracta 28.1 65.6 6.3 19.8 Chlorella protothecoides 39.6 54.6 5.8 23.6

The yields of bio-oil from the samples via pyrolysis are presented as a func­tion of temperature (K) in Figure 5.4. The yield of bio-oil from pyrolysis of the samples increased with temperature, as expected. The yields were increased up to 750 K in order to reach the plateau values at 775 K. The maximum yields for Poly­trichum commune, Thuidium tamarascinum, Cladophorafracta, and Chlorella pro — tothecoides were 31.6, 37.3, 45.0, and 50.8% of the sample at 925 K, respectively. The bio-oil yields of pyrolysis from algae were higher than those of mosses. Bio-oil comparable to fossil oil was obtained from microalgae (Miao and Wu 2004). In the pyrolysis process, the yield of charcoal decreases with increasing pyrolysis temper­ature. The yield of the liquid product is highly excessive at temperatures between 625 and 725 K.

The HHVs for bio-oils from mosses 21.5 to 24.8MJ/kg and the HHVs for bio­oils from algae and microalgae 32.5 and 39.7MJ/kg, respectively, were obtained by pyrolysis at temperatures ranging from 775 to 825 K. In general, algae bio-oils are of a higher quality than bio-oils from mosses.

-o-PC TT CF -*-CP Figure 5.4 Yield of bio-oil from moss and alga samples by pyrolysis at different temperatures (K). Polytrichum commune (PC), Thuidium tamarascinum (TT), Cladophorafracta (CF), and Chlorella protothecoides (CP)

Figure 5.5 shows the effect of temperature on yields of gaseous products from the samples by pyrolysis. As can be seen in Figure 5.4, the yields of gaseous products from the samples of Polytrichum commune, Thuidium tamarascinum, Cladophora fracta, and Chlorella protothecoides increased from 5.3 to 40.6%, 6.5 to 42.2%, 8.2 to 39.2%, and 9.5 to 40.6% by volume, respectively, while the final pyrolysis temperature was increased from 575 to 875 K.

Figure 5.6 shows the plots for yields of hydrogen in gaseous products from the samples by pyrolysis. The percent of hydrogen in gaseous products from the sam­ples of Polytrichum commune, Thuidium tamarascinum, Cladophora fracta, and Chlorella protothecoides increased from 21.3 to 38.7%, 23.0 to 41.3%, 25.8 to 44.4%, and 27.6 to 48.7% by volume, respectively, while the final pyrolysis tem­perature was increased from 650 to 875 K.

Figure 5.7 shows the plots for yields of hydrogen in gaseous products from the samples by steam gasification. The percent of hydrogen in gaseous products from the samples of Polytrichum commune, Thuidium tamarascinum, Cladophora fracta, and Chlorella protothecoides increased from 21.8 to 50.0%, 23.5 to 52.0%, 26.3 to 54.7%, and 28.1 to 57.6% by volume, respectively, while the final gasification temperature was increased from 825 to 1,225 K.

Figure 5.8 shows the plots for yields of hydrogen in gaseous products from mi­croalgae and wood samples by pyrolysis. The percent of hydrogen in gaseous prod­ucts from the samples of beech wood and spruce wood increased from 31.5 to 40.5% and 33.3 to 42.3% by volume, respectively, while the final pyrolysis temperature was increased from 650 to 875 K (Demirbas and Arin 2004). Microalgae gaseous prod­ucts are higher quality than gaseous products from wood (Figure 5.8). In general, algal gaseous products are of higher quality than gaseous products from mosses.

-о-PC -»-TT -*-CF — x-CP Temperature, K Figure 5.5 Yields of gaseous products from the samples by pyrolysis: Polytrichum commune (PC), Thuidium tamarascinum (TT), Cladophora fracta (CF), and Chlorella protothecoides (CP)

PC TT CF — x — CP Figure 5.6 Yields of hydrogen in gaseous products from the samples by pyrolysis: Polytrichum commune (PC), Thuidium tamarascinum (TT), Cladophora fracta (CF), and Chlorella protothe — coides (CP)

PC TT — A— CF —X—CP Temperature, K Figure 5.7 Yields of hydrogen in gaseous products from the samples by steam gasification: Poly­trichum commune (PC), Thuidium tamarascinum (TT), Cladophora fracta (CF), and Chlorella protothecoides (CP)

Table 5.12 shows the yields of bio-oil by pyrolysis from moss and algae samples (Demirbas 2006). As can be seen from Table 5.12, the bio-oil yield for Chlorella protothecoides (a microalgae sample) rose from 12.8 to 55.3% as the temperature rose from 575 to 775 K, and then gradually decreased to 51.8% was obtained at 875 K with a heating rate of 10K/s. The bio-oil yield for Polytrichum commune (a moss sample) rose from 10.3 to 39.1% as the temperature rose from 575 to 775 K,

-Ф — CP (Present study) BW (Ref. [16]) — Д — SW (Ref. [16]) Figure 5.8 Yields of hydrogen in gaseous products from microalgae and wood samples by pyrol­ysis: Chlorellaprotothecoides (CP), beech wood (BW), and spruce wood (SW)

Table 5.12 Yields of bio-oil by pyrolysis from moss and algae samples at different tempera­tures (K) Sample 575 625 675 725 775 825 875 Polytrichum commune 10.3 20.0 27.5 35.8 39.1 38.4 36.7 Dicranum scoparium 6.0 15.5 21.8 30.7 34.3 33.8 31.7 Thuidium tamarascinum 5.6 14.2 20.7 29.5 33.6 33.4 31.3 Sphagnum palustre 7.9 17.7 25.3 33.5 37.0 36.3 34.6 Drepanocladus revolvens 6.7 16.4 23.5 31.7 35.4 34.7 32.9 Cladophora fracta 10.5 23.5 33.2 43.4 48.2 46.8 44.6 Chlorella protothecoides 12.8 27.4 38.4 50.2 55.3 53.7 51.6

and then gradually decreased to 36.7% was obtained at 875 K with a heating rate of 10K/s (Demirbas 2006). For algae, maximum bio-oil yields of between 48.2 and 46.8%, and for microalgae 55.3 and 53.7% were obtained at temperatures ranging from 775 to 825 K, whereas for wood, cotton stalk, tobacco stalk, and sunflower bagasse, maximum oil yields between 39.7 and 49.4% were obtained at tempera­tures ranging from 775 to 825 K (Putun 2002; Gercel 2002).

Table 5.13 shows the yields of gaseous product by pyrolysis from moss and algae samples (Demirbas 2006). As shown in Tables 5.12 and 5.13, the yields of gaseous products for Chlorella protothecoides increased from 9.5 to 39.5% as the tempera-

Table 5.13 Yields of gaseous product by pyrolysis from moss and algae samples at different tem­peratures (K) Sample 575 625 675 725 775 825 875 Polytrichum commune 6.5 14.8 22.6 26.4 29.2 36.6 42.2 Dicranum scoparium 5.8 12.5 19.8 25.0 27.6 35.0 40.8 Thuidium tamarascinum 5.3 11.2 17.9 23.5 25.6 33.2 39.3 Sphagnum palustre 5.5 11.9 18.3 24.2 26.5 34.0 39.8 Drepanocladus revolvens 5.6 12.3 18.9 24.7 27.0 34.5 40.4 Cladophora fracta 8.2 19.7 28.2 32.6 35.7 38.0 39.7 Chlorella protothecoides 9.5 21.8 29.5 33.7 36.3 38.1 39.5

ture rose from 575 to 875 K. The char yields of pyrolysis from mosses were higher than those of algae.

With the interaction of water and char from decomposition of biomass occur in­termediate products, which leads to more hydrogen-rich gas yield by steam reform­ing. The pyrolysis is carried out at moderate temperatures and steam gasification at the highest temperatures. In order to clarify the steam gasification mechanism in detail, more kinetic study is necessary. These results suggest that the fundamen­tal information obtained in the gasification of each component could possibly be used to predict the composition of product gas generated in air-steam gasification of biomass.