BIOMAN 2011 WORKSHOP
MiraCosta College
Instructor: Elmar Schmid, Ph.D.
“Biofuels Production & Analysis”
Session #1 – Biohydrogen
Bio Hydrogen
 Biohydrogen is hydrogen gas (H2) produced with the help of
biological life forms from renewable biomass materials.
 Hydrogen is the single most abundant chemical element in the
universe; it is abundantly present on earth in form of water and
stored in biomass.
 H2 is - with a molecular weight of 2 g/mol - the lightest known gas.
 H2 has a very low solubility in water.
- only 1.93 ml of hydrogen gas dissolves in 100 ml of water at STP
 With 143 MJ/kg, H2 has the highest gravimetric energy density
(or heating value) of any known fuel.
 H2 can be converted into usable heat and electricity with high
conversion efficiency and without carbon emissions, e.g. CO2 or
soot, using fuel cell (FC) technology.
Comparative standard enthalpies and heat values of fuels
Type of Fuel
Origin
Molecular
Standard
Heating
Formula
Enthalpy ΔHo
Value
(kJ/mol)
(MJ/kg)
Crude Oil
fossil
mixture
n.a.
-44.3
Gasoline
fossil
C5-12H12-26
-6,130
-47.3
Kerosene
fossil
mixture
n.a.
-46.2
Coal*
fossil
C135H96O9NS
-55,210
-30.5
fossil & bio
CH4
-890.4
-55.6
Ethanol
bio
C2H5OH
-1,368
-29.7
Methanol
bio
CH3OH
-727.5
-22.7
fossil
C15-18H32-38
n.a.
-44.8
Biodiesel
bio
C9H20
-5,520
-43
Hydrogen
bio
H2
-286
-143
Glucose
bio
C6H12O6
-2,803
-15.57
Wood**
bio
mixture
n.a.
-12.1
Methane/NG
Petroleum Diesel
Industrial Production of Hydrogen
2 H+ + 4 e-
Fossil
Fuels
→
H2
Natural Gas
Coal
Crude Oil
H2
Production of Biohydrogen
 from renewable biomass
Cellulosics
Hemicellulosics
Starch
PreProcessor
+
Enzymes
Fermenter
(Bacteria)
Glucose/
Sucrose
H2
Sun
CO2
H2O
Figure©E.Schmid-2010
PhotoBioreactor
(Algae)
Gas producing microbes
Trapped gas
(H2 + CO2)
Gas-producing
Bacterium
Non-gas-producing
Bacterium
(Glucose broth)
(Glucose broth)
Comparison of important biological hydrogen production processes
Process
Type of
microorganism
Advantages
Disadvantages
Direct biophotolysis
Green algae
H2 directly from cheap water
and free sunlight.
High solar conversion
efficiency
Requires high light intensities.
Low H2 production rate (HPR).
Indirect photolysis
Cyanobacteria
H2 from cheap water with the
help of nitrogenase enzyme.
Ability to generate
ammonium at same time.
Degradation of H2 via uptake
hydrogenases lowers HPR and
H2 yield.
About 30% O2 in gas mixture
has inhibitory effect on
nitrogenase.
Photofermentation
Photosynthetic
bacteria
Utilization of wide spectrum
of light.
H2 production from different
waste materials, e.g. distillery
effluents.
Light conversion efficiency is
with about 1-5% very low.
O2 is strong inhibitor of
hydrogenase.
Dark fermentation
Fermentative
bacteria
(Enterobacter,
Clostridia,
Thermotoga,
Klebsiella)
Continuous H2 production in
the absence of light.
High HPR from diverse
biomass-derived carbon
feedstock.
Simultaneous production of
other value products, such as
butyric acid, lactic acid,
ethanol, etc.
Relatively low H2 yields with
expensive carbon feedstock, e.g.
glucose.
Product gas mixture contains
CO2 and may contain other
noxious gases, i.e. H2S which
have to be separated.
The toxic gas H2S is also
“poisoning” fuel cells.
Fermentation Principle
• Organic substrates are metabolized without the involvement of an exogenous
(external) oxidizing molecule, e.g. O2.
• Fermentation is typically (but not necessarily) anaerobic.
e.g. Glucose
Xylose
2e- + 2 H+
Substrate
Oxidized
product(s)
Bacterium
NAD+
Reduced
products
e.g. H2, CO2
Acetate
Lactate
2,3 Butanediol
NADH +H+
2e- + 2 H+
Internal
intermediates
e.g. Pyr
Bacterial Biohydrogen Production
1. Clostridia bacteria
- Strictly anaerobic bacteria
PFOR
Pyruvate + HS-CoA + 2 Fd
→
Acetyl-CoA + 2 FdH + CO2
Hyd
2 FdH
→
2 Fd + H2
2. Enterobacteriaceae-type - Facultative anaerobic bacteria
PFL
Pyruvate + HS-CoA
→
Acetyl-CoA + Formate (HCOOH)
FHL
HCOOH + X
→
Ni, Se
CO2 + XH2
Hyd
XH2
→
Mg
X + H2
Bacterial Hydrogenases
 Key enzymes used by different hydrogen producing microbes
which produce molecular hydrogen (H2)
 Most hydrogenases are nickel-iron-selenium [NiFeSe]- of nickeliron [NiFe]-containing enzymes
 [NiFe]-dependent uptake hydrogenases catalyze the reversible
heterolytic cleavage of molecular hydrogen (H2 ↔ 2 H+ + 2 e-)
 Hydrogenases are extremely oxygen-sensitive enzymes and become
rapidly inactivated in the presence of molecular oxygen (O2)
- anaerobic conditions are required in biohydrogen fermenters
Visible H2 production by a hydrogen producing microbe
Hydrogen conversion into usable energy
 In the presence of oxygen, H2 can be converted into usable heat
and electricity with the help of combustion or via electrochemical
processes, i.e. fuel cells.
 Hydrogen conversion happens without carbon-based emissions,
i.e. the green house gas CO2 or soot.
 Conversion of hydrogen gas in a fuel cell generates DC electricity
and only water and some heat are released as waste products.
2 H2 (g) + O2 (g)
2 H2O (l)
- 286 kJ/mol
Fuel Cell Working Principle
1 FC stack
H2 Source
Pt or Pd Nafion
Membrane
O2
H2
+
2 H+
H2O
4e-
4eCathode
+
-
Vm
Anode
5-stack PEM Hydrogen Fuel Cell
Power per cell: 200 mW
Power (5 cells): 1 W
(http://www.fuelcellstore.com)
H2
H2O
Anode
O2
+
Cathode
Lab Set-Up
Silicone tubing
Cartridge
(filled with soda lime)
Valve 4
2 ml shaped
Plastic
pipette
Inverted
graduated
cylinder (500 ml)
Valve 3
Spinner
flask
Valve 1
Valve 2
Water
bath
37oC
Bacterial
Culture
Glass
beaker
(500 ml)
Solid
bed
1W
Fuel cell
20% NaOH
N2
Fan
Heater/Stirrer
plate
Graphic©E.Schmid-2010
Voltmeter
Lab Objectives
In this lab session you will measure the amount of hydrogen gas
produced by a batch culture of a hydrogen-producing bacterium
and perform following calculations:
1. Hydrogen production rate
- Amount of hydrogen gas generated per time per volume
- Unit usually given in: ml H2 / h / l or mmol H2 / h / l (mM / h)
2. Hydrogen yield
- Amount of hydrogen gas generated per amount of feedstock
- Units given in: mol H2 per mol glucose
For glucose (C6H12O6) the theoretical (achievable) microbial
hydrogen yield is 4 mol H2 / mol glucose