Biofuels in Perspective

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Table 11.3 Overview of oxidoreductases and hydrogenases and encoding gene clusters in some key fermentative hydrogen-producing micro-organisms. Numbers refer to locus tags. Gene clusters are given in brackets. Experimentally confirmed gene products are underlined. Fd = ferredoxin Thermoanaerobacter tengcongensis Thermotoga maritima Pyrococcus furiosus Caldicellulosiruptor saccharolyticus Clostridium thermocellum Escherichia coli K12 Mbx: 1205 → 1217 Mbh: 1423 →1436, Mbx: 1441→1453 Ech: 3020 → 3024 Ech: 1534 → 1539 0123 → 0128 Rnf: 2430 → 2435 Rnf: 0244– −0249 Fd-dependent NiFe membrane-bound hydrogenase complex (Mbh, Mbx) Fd-dependent NiFe membrane-bound hydrogenase complex (EchA-F) NADH: Fd oxidoreductase (Nfo.Rnf) Formate hydrogen lyase complex (HycA → 1) Membrane bound Hyc: 2717 → 2725 1424, 1425, 1426 0890, 0892, 0893, 0894 1860, 1862, 1863, 1864 0338, 0340, 0341, 0342 H-I: 0891→ 0894, H-II: 1329 →1332 NADH-dependent Fe-only hydrogenase (HydA → C/D) NADP-dependent (Sulf)hydrogenase I and II (NiFe) Fd: NADP oxidoreductase (Sulfide dehydrogenase) Cytoplasmic SuDH: 1327,1328
206 Biofuels Clostridium thermocellum and Tt. maritima suggesting that also these thermophiles contain a NADH-dependent hydrogenase (Table 11.3). Alternatively, NADH may transfer its electrons first to ferredoxin by an NADH:ferredoxin reductase, and the reduced ferredoxin is subsequently used for proton reduction. An NADH:ferredoxin reductase (EC 1.18.1.3) was described by Jungermann et al. 43 and Gottschalk et al.; 44 and this activity has since been demonstrated in many anaerobic fermentative bacteria including Tt. maritima 26 and Clostridium cellulolyticum. 45 Cl. butyricum appears to have one bidirectional enzyme, whereas Clostridium acetobutylicum probably has two enzymes (forward and reverse). 46 However, despite the extensive research on these enzymes in the Sixties and Seventies, these enzymes have never been purified and gene sequences are also not known (according to BRENDA database). More recently, NADH:ferredoxin oxidoreductases have been purified from Cl. tetanomorphum, Acidaminococcus fermentans and Fusobacterium nucleatu and they appeared to be membrane-bound enzymes. 36 They either use the energy difference between ferredoxin and NAD to generate a Na + gradient, or they catalyze the reverse reaction and use a Na + gradient to reduce ferredoxin by NADH. Obviously, not all NADH:ferredoxin oxidoreductase interconversions occur at the membrane, because e.g. P. furiosus harbors two cytoplasmic ferredoxin:NADPH oxidoreductases (sulfhydrogenase and sulfide dehydrogenase) 37,47 (Table 11.3). Hydrogen can also be produced in (facultative) anaerobes without ferredoxin or separate hydrogenases. For instance, the facultative anaerobic enterobacteria differ in their hydrogen enzymology by the sequential use of a pyruvate formate lyase and a formate hydrogen lyase. 11.5 Enterobacteria Species of the genus Enterobacteriaceae are facultative anaerobic. In the absence of oxygen and inorganic electron acceptors they perform a mixed acid fermentation, resulting in the formation of hydrogen and other products like formate, acetate, ethanol, lactate, succinate and butane-diol. The ratio at which these products are formed is dependent on the species and the culture conditions. Escherichia coli produces little butane-diol, while this is a main end product of Enterobacter aerogenes (Table 11.4). Interestingly, E. coli forms formate as main product when grown at high pH, while hydrogen is only formed at a low pH. In the aerobic metabolism enterobacteria convert pyruvate to acetyl-CoA and CO2 via an NAD-dependent pyruvate dehydrogenase complex. NADH is oxidized to NAD in the electron transport chain. However, under fermentative conditions a pyruvate formate lyase is involved in pyruvate conversion which results in the formation of acetyl-CoA and formate. Formate is converted to hydrogen and carbon dioxide by means of a formate hydrogen lyase. 49 The role of formate in hydrogen production in E. coli has been discussed by Sawers. 50 Formate is excreted by this bacterium, but at an acid pH it is taken up and split into hydrogen and carbon dioxide. Cleavage of formate results in energy conservation by means of a proton gradient. 51 A proton pumping hydrogenase (Ech) as described by Hedderich and Forzi 41 may be involved. Thermodynamically hydrogen formation from formate (formate − + H2O → H2 + HCO3 − ; �G 0′ =+1.3kJ/mol formate) is intriguing. The �G ◦′ of this conversion is + 1.3 kJ, which implies that this conversion is affected by the P(H2) aswell.
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Biofuels Biofuels. Edited by Wim So
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Biofuels Edited by WIM SOETAERT Ghe
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Contents Series Preface ix Preface
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Contents vii 6.3 Biomass Gasificati
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Series Preface Renewable resources,
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Preface This volume on Biofuels fit
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Editors List of Contributors Wim So
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1 Biofuels in Perspective W. Soetae
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Table 1.1 Approximate average world
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Table 1.3 Energy yields of bio-ener
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Biofuels in Perspective 7 is burnt
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2 Sustainable Production of Cellulo
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Sustainable Production of Cellulosi
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Figure 2.9 2004 US adoption rates o
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3 Bio-Ethanol Development in the US
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Bio-Ethanol Development in the USA
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Biorefineries in Production (115) B
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Cost of Cellulosic Ethanol, $ per g
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4 Bio-Ethanol Development(s) in Bra
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Bio-Ethanol Development(s) in Brazi
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Share of energy consumption 100% 90
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Table 4.2 Main technological improv
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4.7.4 Use of Fertilizers and Pestic
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78 Biofuels Table 5.1 Biodiesel pro
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80 Biofuels CH 2 O CH O COR R1 + 3
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82 Biofuels short reaction times. 9
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84 Biofuels Table 5.4 Overview on h
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86 Biofuels Table 5.5 Critical cond
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88 Biofuels methoxide as catalyst u
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90 Biofuels KOH Methano Oil/Fat Aci
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92 Biofuels 16. J. Graille, P. Loza
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6 Bio-based Fischer-Tropsch Diesel
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6.2.1.2 Catalysts Bio-based Fischer
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Bio-based Fischer-Tropsch Diesel Pr
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7 Plant Oil Biofuel: Rationale, Pro
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Table 7.1 Market milestones for pla
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Water CO 2 Figure 7.1 Closed CO 2 l
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Plant Oil Biofuel: Rationale, Produ
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130 Biofuels Among the attractive f
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132 Biofuels Table 8.1 Enzymatic tr
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134 Biofuels conversion was maintai
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136 Biofuels (diglycerides) decreas
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138 Biofuels ME content (wt.%) Reac
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140 Biofuels Ratio of initial react
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142 Biofuels (a) 34 kDa 31 kDa 34 k
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144 Biofuels preparation of whole-c
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ability to reduce flocculation (% o
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148 Biofuels 5. R. C. Strayer, J. A
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150 Biofuels 46. H. Fukuda, Immobil
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9 Production of Biodiesel from Wast
Page 170 and 171: Production of Biodiesel from Waste
Page 174 and 175: 9.3.2 Processing of Crude and Waste
Page 176 and 177: Heavy layer from alkaline neutralis
Page 182 and 183: CPO I 1 1 Heating 60°C Reaction st
Page 184 and 185: References Production of Biodiesel
Page 186 and 187: 10 Biomass Digestion to Methane in
Page 188 and 189: Cow manure Pig manure Yard manure B
Page 190 and 191: Number of plants 3000 2500 2000 150
Page 192 and 193: Biomass Digestion to Methane in Agr
Page 196 and 197: Table 10.4 Alternative forms of ene
Page 200 and 201: Wet fermentation 3 - 10% TS applica
Page 202 and 203: Rel. Frequency [%] 35 30 25 20 15 1
Page 204 and 205: Steam 2 1 Energy crops (& manure) D
Page 210: Biomass Digestion to Methane in Agr
Page 213 and 214: 198 Biofuels 11.1 Introduction Hydr
Page 215 and 216: 200 Biofuels lactate 6 glucose 1 GA
Page 217 and 218: Table 11.2 Continued Organism Domai
Page 219: 204 Biofuels NADH is that the react
Page 223 and 224: 208 Biofuels in particular in Cl. p
Page 225 and 226: 210 Biofuels ferredoxin-dependent m
Page 227 and 228: 212 Biofuels Concentration (mM) 45
Page 229 and 230: 214 Biofuels genes of the glycolysi
Page 231 and 232: 216 Biofuels 11. S. Tanisho and Y.
Page 233 and 234: 218 Biofuels 49. M. J. Axley, D. A.
Page 235 and 236: 220 Biofuels 83. P. J. Silva, E. C.
Page 238 and 239: 12 Improving Sustainability of the
Page 240 and 241: Table 12.1 Corn ethanol dry mill: e
Page 242 and 243: Table 12.2 Atmospheric CO2 (equival
Page 244 and 245: Table 12.3 Incremental CO2 equivale
Page 246 and 247: Improving Sustainability of the Cor
Page 248 and 249: Improving Sustainability of the Cor
Page 250 and 251: Index italic entries indicate refer
Page 252 and 253: iorefineries 3, 10, 11, 41 and corn
Page 254 and 255: policy (official) 59-61 production
Page 256 and 257: NADH 200-6, 207, 210 natural gas 1
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