BIOMAN 2011 WORKSHOP MiraCosta College Instructor: Elmar Schmid, Ph.D. “Biofuels Production & Analysis” Session #1 – Biohydrogen.

BIOMAN 2011 WORKSHOP

MiraCosta CollegeInstructor: Elmar Schmid, Ph.D.

“Biofuels Production & Analysis”

Session #1 – Biohydrogen

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.

Bio

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

Methane/NG fossil & bio CH4 -890.4 -55.6

Ethanol bio C2H5OH -1,368 -29.7

Methanol bio CH3OH -727.5 -22.7

Petroleum Diesel 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

Comparative standard enthalpies and heat values of fuels

2 H+  +  4 e- →  H2

H2

Industrial Production of Hydrogen

Natural Gas

Coal

Crude Oil

FossilFuels

Production of Biohydrogen from renewable biomass

Pre-Processor

+Enzymes Fermenter

(Bacteria)

H2

Cellulosics

Hemicellulosics

Starch

Glucose/Sucrose

SunPhoto-

Bioreactor(Algae)

CO2

H2OFigure©E.Schmid-2010

Trapped gas(H2 + CO2)

Gas-producing Bacterium

(Glucose broth)

Non-gas-producing Bacterium

(Glucose broth)

Gas producing microbes

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.

Comparison of important biological hydrogen production processes

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.

SubstrateOxidized

product(s)

Reducedproducts

NAD+NAD+ NADH +HNADH +H++

Internalintermediates

e.g. Pyr2e- + 2 H+

2e- + 2 H+

e.g. H2, CO2

Acetate Lactate 2,3 Butanediol

Bacterium

e.g. Glucose Xylose

Pyruvate  +  HS-CoA  +  2 Fd → Acetyl-CoA  +  2 FdH  +  CO2

1. Clostridia bacteria

2 FdH → 2 Fd  + H2

PFOR

Hyd

Bacterial Biohydrogen Production

- Strictly anaerobic bacteria

Pyruvate  +  HS-CoA → Acetyl-CoA  +  Formate (HCOOH)PFL

HCOOH  + X → CO2  +  XH2

XH2 → X  +

FHL

Ni, Se

Mg

HydH2

2. Enterobacteriaceae-type - Facultative anaerobic bacteria

Key enzymes used by different hydrogen producing microbes which produce molecular hydrogen (H2)

Most hydrogenases are nickel-iron-selenium [NiFeSe]- of nickel- iron [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

Bacterial Hydrogenases

Visible H2 production by a hydrogen producing microbe

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.

Hydrogen conversion into usable energy

2 H2 (g) + O2 (g) 2 H2O (l)

- 286 kJ/mol

H2

4e-

2 H+

O2

H2O

+

4e-

1 FC stack

H2 Source

Vm

+Cathode - Anode

Pt or Pd NafionMembrane

Fuel Cell Working Principle

5-stack PEM Hydrogen Fuel Cell

Power per cell: 200 mW Power (5 cells): 1 W (http://www.fuelcellstore.com)

H2

H2O O2

-

+Cathode

Anode

37oC

N2

Heater/Stirrer plate

Solidbed

BacterialCulture(500 ml)

Spinnerflask

Valve 4

Cartridge(filled with soda lime)

Glassbeaker

20% NaOH

Invertedgraduated

cylinder (500 ml)

Silicone tubing

1 WFuel cell

Voltmeter

Lab Set-Up

Graphic©E.Schmid-2010

2 ml shapedPlastic pipette

Water bath

Valve 1

Valve 2

Valve 3

Fan

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

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:

For glucose (C6H12O6) the theoretical (achievable) microbialhydrogen yield is 4 mol H2 / mol glucose