Steam Reforming of Methane

Fig. 1: A schematic representation of Steam Methane Reforming [10].

In recent years, hydrogen (H₂) has gained much research emphasis as an energy carrier due to its environmental friendliness and wide range of energy applications. [1] Approximately 95% of the hydrogen in the United States is generated via methane steam reforming, being utilized predominantly for petroleum refining and the production of industrial commodities such as ammonia. [2] In addition to the maturity of the technology, natural gas reforming is also the most economical among all hydrogen production pathways. [3]

Methane steam reforming is a well-established process as shown in Fig. 1. Steam and hydrocarbon enter the reactor as feedstock, and hydrogen and carbon dioxide are generated at the end of the process. The process is governed by the reactions

The steam forming step, where methane reacts with water to produce carbon monoxide and hydrogen, is an endothermic process. Thus, the process is usually maintained at approximately 850°C to obtain desirable conversion. [4] The second step is known as the water-gas shift reaction where syngas reacts to recover hydrogen. Conventionally, the process is performed in multitubular fixed-bed reactors in the presence of a metal catalyst. [5] However, the overall reaction is limited as both the steam reforming and the water-gas shift reactions are subjected to thermodynamic equilibrium. In the recent years, research has been devoted to the use catalytic membrane reactors in overcoming the equilibrium limitation. [6]

The use of steam reforming unit mitigates the problems of storage and distribution of hydrogen tanks for hydrogen vehicle. In addition, methane steam reforming operates at the highest efficiency compared to other current commercially available hydrogen production methods, such as partial oxidation of heavy oil and coal as well as coal gasification. [7] Unfortunately, the production of hydrogen using steam reforming of natural gas does not eliminate greenhouse gas emissions. However, the carbon dioxide release is in fact lower for fuel cell vehicles powered by natural gas when comparing to those powered by gasoline. [8]

The U.S has an annual hydrogen production of 9 million tons approximately. [9] In order for hydrogen to become competitive in the energy market, the cost of production has to be lower than the other available alternatives. On top of the development of carbon dioxide capture and sequestration technology, another major challenge for methane steam reforming is to improve process efficiency and reduce production cost, in keeping the price affordable in times of natural gas price fluctuations.

© I-Tso Chen. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for non commercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] P. Hoffmann, Tomorrow's Energy: Hydrogen, Fuel Cells, and the Prospects for a Cleaner Planet (MIT Press, 2002).

[2] G. Collodi and F. Wheeler, "Hydrogen Production via Steam Reforming with CO2 Capture," Chemical Engineering Transactions 19, 37 (2010).

[3] G. W. Crabtree, M. S. Dresselhaus and M. V. Buchanan, "The Hydrogen Economy," Physics Today 57 (12), 39 (2004).

[4] F. Gallucci et al., "Steam Reforming of Methane in a Membrane Reactor: An Industrial Case Study," Ind. Eng. Chem. Res. 45, 2294 (2006).

[5] F. Gallucci et al., "Experimental Study of the Methane Steam Reforming Reaction in a Dense Pd/Ag Membrane Reactor," Ind. Eng. Chem. Res. 43, 928 (2004).

[6] T. Tsuru et al., "Methane Steam Reforming by Microporous Catalytic Membrane Reactors," AlChE Journal 50, 2794 (2004).

[7] A. T-Raissi and D. Block, "Hydrogen: Automotive Fuel of the Future," Power and Energy Magazine, IEEE 2, 40 (2004).

[8] B. Gaudernack and S. Lynum, "Hydrogen From Natural Gas Without Release of CO₂ to the Atmosphere," Intl J. Hydrogen Energy 23, 1087 (1998).

[9] J. A. Turner, "Sustainable Hydrogen Production," Science 305, 972 (2004).

[10] J. Molburg and R. Doctor, "Hydrogen from Steam-Methane Reforming with CO₂, Argonne National Laboratory, 30 Jun03.