Environmental Engineering Reference
In-Depth Information
Table 11.1
Comparison of various conventional methods of hydrogen production
Method
Advantages
Disadvantages
Reformation of natural gas
CH HO CO
Most common ( 80 % H
2
production)
Well understood process
Widespread infrastructure
Dependent on
non-renewable
natural gas
High CO
2
(GHG)
emissions
+ →+
3
H
4
2
2
2
CO HO CO
+ →+
2
H
2
Gasification of coal
CHO OH
Coal is abundant and
inexpensive
Low yields
High CO
2
(GHG)
emissions
High SOx and CO
emissions
+ →+
2
2
CO HO CO
+ →+
2
H
2
2
Electrolysis of water
HO OH
2
Second most common
method used
Well understood
Widespread infrastructure
Potentially emission free,
depending on source of
electricity generation
Energy intensive
High CO
2
(GHG)
emissions if fos-
sil fuels (coal,
natural gas)
used to generate
electricity
→+
2
2
2
Biomass reformation
CHON HO 4CO+CH
Potentially carbon neutral
Inexpensive
Can use organic waste
streams
Not yet well
understood
+ → + /
CH HO CO
2
3 2
H
672
2
4
2
+ →+
CO HO CO
3
H
4
2
2
+ →+
2
H
2
2
Biohydrogen production
HO light energy OH
2
Carbon neutral
Can use light or organic
waste streams
Low energy input
May have poor
yields
Not yet well
understood
+
→ +
2
2
2
C H O
+ →+
H O
CO
H
6
12
6
2
2
2
+
Organic molecules
the near future in order to meet the demand for refining increasingly heavier, higher
sulfur crude oils and oil sands and to meet more stringent regulations on the levels
of sulfur in gasoline and diesel fuel. Hydrogen use will also increase up to 40 mil-
lion t of hydrogen per year in order to meet the fuel need of transportation sector for
100 million fuel cell-powered cars after full market penetration.
Thermo-chemical and electro-chemical methods are the common hydrogen pro-
duction methods using a diverse array of potential feedstock including fossil fuels,
water, and organic matter (Table
11.1
). Currently, over 80 % of hydrogen produc-
tion occurs via steam reformation of natural gas during which methane, the primary
constituent of natural gas, is combined with high temperature steam (700-1000 °C)
in the presence of a catalyst, breaking it apart into H
2
and CO. The CO produced
further reacts with water at high temperatures to produce H
2
and CO
2
via a process
known as the gas shift reaction. The main drawback of this process is that it is de-
pendent on a limited reserve of natural gas and the carbon dioxide emissions. Simi-
lar to natural gas gasification, hydrogen can be produced via coal gasification, how-
ever this process produces even more CO
2
emissions and is more expensive (H
2
to
CO
2
production ratios: 1:1 for coal gasification and 4:1 for natural gas reformation).
