Production Methods
While hydrogen is the most unburden element on earth it doesn't occur naturally in the environment. Instead it is usually found in compounds that must be decomposed into a usable form. The Hydrogen Fueling Station Team has looked at two potential sources for the hydrogen it requires. The following two methods are the most economical for the size and scale of the current project.
Electrolysis
Electrolysis is the passage of an electric current through an electrolyte with subsequent migration of positively and negatively charged ions to the negative and positive electrodes.
One of the greatest advantages to electrolysis is that it can produce hydrogen from the most abundant natural resource on earth: H2O. This clean and efficient method also has low impact to the environment, because the only by-product to electrolysis is oxygen.
There are currently two types of commercially available electrolyzers: the alkaline electrolyzer, which uses potassium hydroxide (KOH) electrolyte, and the proton exchange membrane (PEM) electrolyzer which uses solid state polymer electrolyte.
Natural Gas Reformation
Steam methane reforming is a process in which natural gas is used to produce hydrogen gas. First, the natural gas is treated with hydrogen to remove sulfur. This sulfur stream is scrubbed and released to the atmosphere. Then the natural gas is mixed with high temperature steam (700-1000°C) at 3-25 bars of pressure over a nickel-alumina catalyst. The reaction produces hydrogen gas and carbon monoxide. A water-gas shift reaction follows. The carbon monoxide and more steam are reacted in two stages. First, a high temperature shift occurs at about 350°C. A low temperature shift follows at about 190-200°C. In this process, the carbon monoxide and steam produce carbon dioxide and more hydrogen. Finally, in the pressure-swing adsorption, CO2 and impurities are removed and discarded appropriately.
There are several advantages associated with natural gas reformation. The reformation process is 56% efficient and could produce hydrogen for $3.00 per kg. Pipelines used for transportation of methane are already in place. The technology used in natural gas reformation is already widely used because 95% of the hydrogen produced in the US is produced using natural gas reformation. Natural gas also has a high H to C ratio, which means that there will be less carbon dioxide emitted per kg of hydrogen produced.
Natural gas reformation does have its drawbacks. For one, natural gas is not renewable. The US is already importing 15% of their natural gas through pipelines from Canada and Mexico, and as Liquid Natural Gas (LNG) from Egypt, Nigeria, Trinidad and some others. Natural gas doesn’t solve the dependence issue, it simply displaces it. Another issue is that natural gas reformation still emits 12 kg of CO2 per kg of H2. Also, natural gas losses to the atmosphere are detrimental. Natural gas has a warming potential of 23. That means it contributes to the greenhouse effect 23 times more than CO2. Natural gas reformation already operates near the theoretical limit with an efficiency of about 56%; therefore there is not much room for improvement.
