Bi-Reforming of Methane and Natural Gas Under High Pressure

Bi-Reforming of Methane and Natural Gas Under High Pressure

Alain Goeppert, Miklos Czaun, Robert B. May, G. K. Surya Prakash, George A. Olah, Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA

Introduction

By choosing the right proportions between water, CO₂ and CH₄, the combination of steam and dry reforming of methane can generate syn-gas with a H₂/CO ratio of 2 ideal for the synthesis of methanol.^[1,2] This combination of steam and dry reforming has been named bi-reforming.

Bi-reforming could be advantageous in the use of natural gas sources containing substantial amounts of CO₂. This CO₂ would, otherwise, have to be separated to allow further processing of the natural gas. Some natural gas sources contain CO₂ concentration from 5% up to 70%. In most cases, once separated, the CO₂ is then released into the atmosphere. Only in few locations is CO₂ sequestered. The natural gas at the Sleipner platform in Norway containing 9% CO₂ is for example currently separated and sequestered beneath the North Sea in a deep saline aquifer.

Experimental

To mimic conditions closer to commercial operations, the bi-reforming reaction was conducted at pressures up to 35 bars in a tubular reactor system specially built for this purpose and able to withstand both high pressure and high temperature in a gas mixture with a high carbon activity. The catalysts used were based on Ni deposited on various supports including alumina, alkali earth oxides and combinations thereof. Reaction temperatures ranging from 700°C to 870°C were investigated. A gas feed composition of CH₄/CO₂/H₂O with a molar ratio of 3/1.2/2.4 was typically used. The reaction was followed by an online GC equipped with a TCD.

Results

In general the catalysts were tested for at least 50 hours to determine their stability as a function of time. The conversion of methane as well as carbon dioxide was stable over the length of the experiments (Figure 1). The obtained H₂/CO ratio of the reaction gases was close to the desired value of 2. Increasing the amount of water and CO₂ compared to methane increased the methane conversion but did not significantly change the H₂/CO ratio.

As expected from a thermodynamic point of view the methane conversion decreased with increasing pressure. To some extent this effect could be compensated by a higher reaction temperature and/or higher water and CO₂ content in the feed gas.

Figure 1. Bi-reforming at 7 bars. Conversion of methane and carbon dioxide.

Acknowledgements

Support of our work by the Loker Hydrocarbon Research Institute and the United States Department of Energy is gratefully acknowledged.

References

[1]        G. A. Olah, G. K. S. Prakash, A. Goeppert, J. Am. Chem. Soc. 2011, 133, 12881.

[2]        G. A. Olah, A. Goeppert, G. K. S. Prakash, Beyond Oil and Gas: The Methanol Economy, 2^nd ed., Wiley VCH, Weinheim, Germany, 2009.