5.22    understand  that  nitrogen  from  air,  and  hydrogen  from  natural  gas  or  the  cracking  of hydrocarbons, are used in the manufacture of ammonia

The RAW materials for making ammonia are air and natural gas (or crude oil fractions)

·        Remember that the air is approximately 78% nitrogen by volume (see Section 2.16) and provides the nitrogen needed to manufacture ammonia.

Remember that natural gas is mainly methane (CH4).  This can be heated with steam and passed over a nickel catalyst to produce the hydrogen gas needed.  An alternative source of hydrogen is from cracking heavier fractions of crude oil