A Detailed Look at Hydrogen

    When most people hear the word "hydrogen" they have flashing images of an exploding blimp.  Hydrogen is a fuel that requires energy to retrieve it.  In other words, you have to extract hydrogen from another substance....that's the bad news.  The good news is that many chemicals (including water) contain hydrogen.

Just the Facts

• Energy Content: 1 kg of hydrogen equals 3.5 L of petroleum

• Energy to Volume ratio is 1/4 that of petroleum and 1/3 that of natural gas

• Water consists of 11.2% hydrogen by mass

• Hydrogen burning temperatures can reach 3000 ⁰C in an oxygen atmosphere  

• Explosive region for hydrogen is 13%-59%

• Diffusion coefficient for hydrogen is 0.61 cm³/s (4 times that of methane)

• Hydrogen's lower heating value is 120,000 kJ/kg

• Combustion of pure hydrogen yields water as a by-product

Production Methods (Conventional)
    Currently, the vast majority of hydrogen is produced from fossil fuel sources as a by-product or reforming.

Steam Reforming of Natural Gas
   Steam reforming of natural gas is an endothermic, catalytic process carried out at about 850 ⁰C and around 2.5 MPa according to the following reactions:

CH₄ + H₂O -----> CO + 3H₂

CO + H₂O -----> CO₂ + H₂

The carbon monoxide is removed by absorption or membrane separation.

Partial Oxidation of Hydrocarbons
    Partial oxidation of hydrocarbons is the exothermic reaction with oxygen and steam.  The amounts of oxygen and water vapor are controlled so that the reaction proceeds without the need for external energy.  An example reaction for this process is:

C₈H₁₈ + H₂O + 9/2O₂ -----> 6CO + 2CO₂ + 10H₂

Plasma Arc Process
    Plasma arc processing of natural gas or oil uses electricity to produce pure carbon and hydrogen at temperatures near 1600 ⁰C.  A pilot plant utilizing this technology produced 500 kg/h of carbon and 2000 m³/h of hydrogen from 1000 m³/h of natural gas and 2100 KW of electricity.

Production Methods (Renewables)
    Several production methods are used to make hydrogen that utilize a renewable resource as their main fuel source.  These renewable resources include biomasses and water.

Steam Gasification of Biomass
    Biomass can be used to produce hydrogen via pyrolysis (thermal decomposition) and gasification.  The pyrolysis reaction yields coke, methanol, and other gases.  With the addition of air the gasification reaction then results is a stream of 20% H₂, 20% CO, 10% CO₂, 5% CH₄, and 45% N₂.   This stream can be further processed by reacting it with steam to produce more hydrogen from the carbon monoxide:

CO + H₂O -----> CO₂ + H₂

Biological Hydrogen Production
   Various types of biological hydrogen production methods are in the research stages.  Forms of synthetic photosynthesis and fermentation are receiving special attention.  One system that seems to be leading the way is an algae-bacteria system that should be ready for the market in around 5 years.  A final technology worth noting is the simple electrolysis of water into it's component gases, oxygen and hydrogen