2.1.3.6. Production of ammonia during pyrolysis
In the Haber-Bosch process, a fossil hydrogen source (usually methane) is used to fix
atmospheric nitrogen and create ammonia for manufacture of fertiliser. Hydrogen in syngas
streams from pyrolysis (7-8% of slow pyrolysis syngas) can substitute methane and be used,
potentially not only to create ammonia but, if conducted on the same site as the pyrolysis, fix
ammonia to a biochar co-product. This offers the prospect of a crop fertiliser that
simultaneously adds stabilised carbon to soil, possibly with slow release characteristics. This
could offer greater net benefit in terms of CO2 -equivalents than using syngas to, for
example, generate electricity. The process of fixing ammonia from the hydrogen syngas
stream at atmospheric pressure and ambient temperature has been demonstrated (Day et
al., 2005) and is illustrated diagrammatically in Figure 5. However, agronomic evaluation of
the product has not been published and the concept has not yet been commercialised.