Processes for Producing Hydrogen

Producing Hydrogen with Electrolysis

Electrolysis is the process by which an electric current is passed through water and breaks the chemical bonds between hydrogen and oxygen. An electrolyte, a fluid chemical substance that can carry a current, aids in the bond-breaking procedure. Once the bonds are broken, the atomic components (hydrogen and oxygen) become either positive or negative ions (charged particles). Two terminals (anode and cathode) also have positive and negative charges, drawing the resulting ions toward them. Generally, the positive hydrogen ions gather at the anode (which is negative), while the negative oxygen ions reside at the cathode (which is positive). Gas is then formed at either terminal.

Producing Hydrogen with Steam

It is possible to perform electrolysis at high temperatures. High temperature electrolysis (HTE), also known as steam electrolysis, operates much the same way as conventional electrolysis. The variation occurs in that, rather than using a standard amount of electric current, heat is applied instead. This reduces the total amount of electric energy required to produce hydrogen gas. Steam reforming

Steam reforming, sometimes called reforming or steam methane reforming, is another well-known method for making hydrogen. Natural gas is the most common fuel used in steam reforming. To make hydrogen using steam reforming, natural gas is reacted with steam at a very high temperature in a combustion chamber. The temperature can be from 1472–3982F (800–1700C).

A catalyst (a substance that increases the rate of a reaction without being consumed in the process) is present in some steam reformers. The catalyst is usually made of metal. The catalyst helps break up the natural gas into methane. When the methane and water react, hydrogen is produced. Carbon oxides such as carbon monoxide and carbon dioxide are made as by-products. In some processes, the carbon monoxide is reacted again to form more hydrogen and carbon dioxide.

The steam reforming process has some positive points. Of all the fossil fuels, natural gas is the cleanest burning. In other words, it gives off fewer by-products that can contribute to pollution. The use of natural gas to make hydrogen might help in the creation of an infrastructure for the distribution of hydrogen. Since there are stations that already distribute natural gas, the natural gas could be transported there and converted to hydrogen via steam reforming on site and on a small scale. This means of production could provide hydrogen for cars that run on either hydrogen fuel cells or hydrogen-powered internal combustion engines.

Benefits and drawbacks of existing hydrogen production methods

Each hydrogen-producing method has its own benefits and drawbacks. Electrolysis is considered to be the most environmentally friendly procedure, because it produces no by-products that are harmful to the environment. In addition, it has a potentially positive by-product: oxygen. This oxygen could be captured and used elsewhere. However, large-scale production of hydrogen by electrolysis is very expensive because electricity is used to create the electric currents. If renewable energy sources such as solar energy, hydropower, hydroelectric power, or even nuclear power were used to produce the current, the process would become much more affordable.

The steam reforming process is the most common method used to make hydrogen industrially. One benefit is that it is cheaper than producing hydrogen by electrolysis. A big drawback is the amount of carbon dioxide produced during the process. The issue of what to do with the carbon dioxide produced needs to be addressed— potential solutions exist, and all are costly. The carbon dioxide could be stored in empty gas wells or oil wells where the reservoirs of gas or oil have been depleted. Saline aquifers, which are underground pockets of saltwater, are another storage possibility.

Also, there is some danger to storing the carbon dioxide. If it mixes with a freshwater aquifer (underground stream) or gets to the surface, it could change the chemistry of the soil. Even worse, if the carbon dioxide should escape, the gas, which is heavier than air, could start to collect. If enough carbon dioxide collects, it could suffocate animals or people. This tragedy has happened in the past. In 1986 in Cameroon, 1,800 people died after 87 million cubic yards (80 million cubic meters) of carbon dioxide erupted from a volcanic crater.

Another potential problem with steam reforming is that the natural gas needed for the process is available in only a limited supply, like all fossil fuels. Steam reforming produces hydrogen on a large scale, but a method needs to be developed to do steam reforming on a smaller scale so this reaction can take place either on the vehicle or at a filling station that supplies hydrogen.

 Processes for Producing Hydrogen copyright 2011