Fossil fuel reforming

Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to make hydrogen. There is also interest in the development of much smaller units based on similar technology to produce hydrogen as a feedstock for fuel cells. Small-scale steam reforming units to supply fuel cells are currently the subject of research and development, typically involving the reforming of methanol or natural gas but other fuels are also being considered such as propane, gasoline, autogas, diesel fuel, and ethanol.

History

• 1923 - The first synthetic methanol was produced by BASF in Leuna making use of hydrogen derived from lignite.

Industrial reforming

Main article: Methane reformer

Steam reforming of natural gas or syngas sometimes referred to as steam methane reforming (SMR) is the most common method of producing commercial bulk hydrogen as well as the hydrogen used in the industrial synthesis of ammonia. It is also the least expensive method. At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen. These two reactions are reversible in nature.

CH₄ + H₂O → CO + 3 H₂

Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarized by:

CO + H₂O → CO₂ + H₂

The first reaction is strongly endothermic (consumes heat), the second reaction is mildly exothermic (produces heat).

The United States produces nine million tons of hydrogen per year, mostly with steam reforming of natural gas. The worldwide ammonia production, using hydrogen derived from steam reforming, was 109 million metric tonnes in 2004.

This SMR process is quite different from and not to be confused with catalytic reforming of naphtha, an oil refinery process that also produces significant amounts of hydrogen along with high octane gasoline.

The efficiency of the process is approximately 65% to 75%.

Reforming for fuel cells

Advantages of reforming for supplying fuel cells

Steam reforming of gaseous hydrocarbons is seen as a potential way to provide fuel for fuel cells. The basic idea for vehicle on-board reforming is that for example a methanol tank and a steam reforming unit would replace the bulky pressurized hydrogen tanks that would otherwise be necessary. This might mitigate the distribution problems associated with hydrogen vehicles, however the major market players discarded the approach of on-board reforming as impractical.

Disadvantages of reforming for supplying fuel cells

The reformer–fuel-cell system is still being researched but in the near term, systems would continue to run on existing fuels, such as natural gas or gasoline or diesel. However, there is an active debate about whether using these fuels to make hydrogen is beneficial while global warming is an issue. Fossil fuel reforming does not eliminate carbon dioxide release into the atmosphere but reduces the carbon dioxide emissions as compared to the burning of conventional fuels due to increased efficiency. However, by turning the release of carbon dioxide into a point source rather than distributed release, carbon capture and storage becomes a possibility, which would prevent the carbon dioxide's release to the atmosphere, while adding to the cost of the process.

The cost of hydrogen production by reforming fossil fuels depends on the scale at which it is done, the capital cost of the reformer and the efficiency of the unit, so that whilst it may cost only a few dollars per kilogram of hydrogen at industrial scale, it could be more expensive at the smaller scale needed for fuel cells. Recently, a Polish company Bioleux Polska has been advertising renewable hydrogen (RH2) plasma reformers, producing RH2 at under $2 per kilogram^{[citation needed]}, and available for lightweight mobile applications using vegetable oil or glycerol as feedstock.

Current challenges with reformers supplying fuel cells

However, there are several challenges associated with this technology:

• The reforming reaction takes place at high temperatures, making it slow to start up and requiring costly high temperature materials.
• Sulfur compounds in the fuel will poison certain catalysts, making it difficult to run this type of system from ordinary gasoline. Some new technologies have overcome this challenge with sulfur-tolerant catalysts.
• Low temperature polymer fuel cell membranes can be poisoned by the carbon monoxide (CO) produced by the reactor, making it necessary to include complex CO-removal systems. Solid oxide fuel cells (SOFC) and Molten carbonate fuel cells (MCFC) do not have this problem, but operate at higher temperatures, slowing start-up time, and requiring costly materials and bulky insulation.
• The thermodynamic efficiency of the process is between 70% and 85% (LHV basis) depending on the purity of the hydrogen product.
• The catalyst in low temperature fuel cells is based on platinum, and is very expensive. A typical automotive fuel cell stack prototype (100 kW) contains 20-30g of platinum metal in the form of nano-particles supported on carbon black.

External links

• "New catalyst boosts hydrogen as transport fuel". By Alok Jha. August 21, 2008. The Guardian.
• "Hydrogen Production - Steam Methane Reforming (SMR)"

See also

• Biogas
• Cracking (chemistry)
• Hydrogen pinch
• Hydrogen technologies
• Lane hydrogen producer
• PROX
• Reformer sponge iron cycle
• Timeline of hydrogen technologies

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