Hydrocarbons for Hydrogen Generation - Hydrogen Generation, Storage, and Utilization - page 7

2

Hydrocarbons for Hydrogen
Generation

2.1 BASICS ABOUT HYDROCARBONS

Hydrocarbons generally refer to a class of organic compounds that contain
hydrogen and carbon atoms. Saturated hydrocarbons only contain C-H and
C-C single bonds, while unsaturated hydrocarbons contain C=C double or
C≡C triple bonds besides single bonds. Hydrocarbons are very important
for many applications, especially in the petroleum industry. The hydrogen
content in hydrocarbons is often high, when measured in the form of atomic
percentage. Methane (CH 4 ), the major component of natural gas, has a hydro-
gen mass content of 25%, while propane (CH 3 CH 2 CH 3 ) contains about 18%
of hydrogen by mass. The hydrogen content usually decreases with increas-
ing hydrocarbon molecular weight or size.
Under ambient conditions (one atmosphere pressure and room tempera-
ture), hydrocarbons can exist as gas, liquid, or solid, depending on molecular
weight or size. Usually, lighter or smaller molecules are found in gas phase,
while heavier and larger ones are in liquid or solid phase. This is due to
strong intermolecular interaction in large molecules since they are more
polarizable or have larger induced dipole moments.
About 95% of hydrogen produced today comes from carbonaceous
raw materials, primarily fossil in origin. Hydrogen is generated from hydro-
carbons by first breaking the C-H bond. Because this is a relatively strong