Defining Hydrogen from A to Z: N is for Natural Gas
Continuing in our Defining the Hydrogen Economy series, we return to the letter N and will be discussing the important role of natural gas in hydrogen production.
Natural gas (NG) is a mixture of combustible, light hydrocarbons containing various impurities dependent on the reservoir location. The main component of natural gas is methane (70 – 98 %), with the balance being other light paraffin, nitrogen, helium, carbon dioxide, water, and hydrogen sulfide. In many cases, impurities such as water, carbon dioxide, nitrogen, and hydrogen sulfide are removed before transport to minimize equipment corrosion and remove the possibility of human exposure to toxic gases. Mercaptans, acting as odorizers, are also added to NG for leak checking and safety.
There are two mainstream theories as to the origins of natural gas: inorganic and organic. The inorganic hypothesizes that carbon and hydrogen reacted together under the immense pressures and temperatures below the Earth’s surface to produce NG. Porous rock then allowed these gases to rise closer to the surface until being trapped in impermeable reservoirs. The organic is a more widely accepted theory and states that organic matter (plants, animals) was covered by layers of silt and mud over millions of years. The decaying organisms were then continually compacted under the increasing weight of layers, producing natural gas. This NG was then allowed to travel between and through these layers until being trapped in an impermeable reservoir.
In a historical context, the first recorded use of natural gas was in A. D. 221 – 263 China during the Shu Han dynasty. Here, gas was removed from shallow wells and transported with hollow bamboo for heating. This would not be seen again until the 17th century, when NG was used for lighting and heating in Italy. From an American point of view, NG did not take off until its discovery in Fredonia, New York, in 1821. This sparked the creation of the Fredonia Gas Light Company, the first of many to utilize NG as a source of energy. In the years to come, the amount of NG reservoirs would rise exponentially. By todays estimates there is approximately 200,000 mi3 of recoverable NG worldwide. Given our current rate of consumption this is estimated to last around 250 years. Natural gas is also transported trans-continentally using cryogenic processes to liquefy the NG, producing a denser storage medium.
As mentioned in the “H” is for Hydrogen blog, hydrogen is the most abundant element in the universe but is yet to be found in its free, molecular form. This means that producing hydrogen requires an input of energy to release hydrogen from its partner atom, making it an energy carrier. Because the main constituent in natural gas is methane (CH4), it is considered an ideal source of hydrogen. Not only this, but NG is cheaper than other petroleum products that store hydrogen and is relatively abundant in most regions. Unfortunately, methane is a very stable, nonpolar molecule and as such has a high activation energy. To break these strong C-H bonds, heat, catalyst, oxidizers, or a combination of the three are often used. The most popular method of hydrogen production is steam-methane reforming (SMR), which accounts for 60% of worldwide production. In addition, partial oxidation (POX) and autothermal reforming (ATR) are other conventional methods of producing hydrogen. All three of these processes release large amounts of carbon dioxide (CO2), a harmful greenhouse gas if emitted in large quantities. These traditional means of H2 production fall short if the goal of the hydrogen economy is to offer a cleaner energy medium. GenH2 is currently addressing these issues by developing CO2-free production methods to support the growing hydrogen economy.
Blog written by GenH2 team member: Andrew Earls