Pyrolysis is a process in which an organic material is heated to a high temperature in the absence of oxygen. Depending on the source materials used, the products from the reaction consist of organic materials and solid carbon in the form of char/charcoal/carbon black. In the case of methane pyrolysis, the products are hydrogen and elemental carbon, according to the following equation.
CH4 ⇌ C + 2H2
High temperature (1065°C) is needed to drive the reaction to the right hand side of the equation. (The use of catalysts allow this temperature to be reduced.) A description of the different types of methane pyrolysis process is provided by Schneider at al. (Schneider, 2020).
The process is endothermic, i.e., it requires an energy input. However, the heat of combustion of the hydrogen produced is much higher than the heat required for the pyrolysis reaction. Therefore heat for the reaction can be obtained by using about a third of the hydrogen just produced.
The hydrogen produced in this process can be used as a fuel for fuel cell electric vehicles, as described in Chapter 15. The produced carbon can be used in the manufacture of a wide range of products such as carbon fibers. If the carbon is simply buried then the overall process becomes a form of direct air carbon capture and storage (DACCS), as described in Chapter 11.