Pyrolysis of methane (main component of natural gas) is one of the alternatives under study to achieve the sustainable production of hydrogen. No CO₂ or other green house effect (GHE) gases are produced in this route as carbon is obtained as a solid co-product at the end of the reaction (CH₄ <==> C + 2H₂). This process can be thermally or catalytically conducted. In the first case, high temperatures (> 1300 K) have to be reached, whereas it can be lowered down to 800 – 1100 K if appropriate catalysts are used. Currently, these materials are based on transition metals with hydrogenation / dehydrogenation properties (Ni, Pt or Pd).
All these alternatives have been studied in the present work from an environmental point of view, using life cycle analysis (LCA) tools. Their different characteristics (higher temperature, use of metal compounds as catalysts, generation of carbon without further use, generation of wastes…) were evaluated. They were compared to steam reforming of methane, the most usual hydrogen obtaining process. As well, different energy sources were included in the study.
The selected functional unit was 1 Nm³ of hydrogen. The transport, use and end of life stages of the life cycle were considered the same for all the scenarios. Therefore, the LCA was focused on material and raw materials acquisition and manufacturing stages. All the pyrolysis alternatives demonstrated to be more environmental-friendly than steam reforming and the autocatalytic route was the most promising.