Hydrogen Utilization in Chemical Processes - Hydrogen Generation, Storage, and Utilization - page 179

ammonia and recycled. This synthetic loop can eventually achieve a remark-
able conversion efficiency of 97% [10].

10.3.2 Hydrogenation of Unsaturated Hydrocarbons

Hydrogenation has been widely used for converting unsaturated organic
compounds to saturated organic compounds in the presence of transition
metal catalysts [9]. For instance, hydrogenation can convert alkene to alkane,
alkyne to alkene or alkane, aldehyde to primary alcohol, ketone to secondary
alcohol and nitrile to primary amine, and so on, as shown in Equation (10.2),
Equation (10.3), Equation (10.4), and Equation (10.5) Lindlar reduction [12].
Therefore, hydrogenation is one of the most important reactions for organic
synthesis.

H PdCl + H O CaCO + → PdO/CaCO

(10.2)

2 4 2 3 3

PdO/CaCO + HCOOH → Pd/CaCO

(10.3)

3 3

Pb OCOCH ( )

(10.4)

Pd/CaCO → conditioned Pd/CaCO

3 2

3 3

H 2 (1 atm), conditioned Pd/CaCO 3

(10.5)

quinoline, hexane

Moreover, hydrogen has also been used extensively to decrease the degree
of unsaturation in vegetable oils. The reduction of unsaturation in vegetable
oils can increase their melting points and enhance resistance to oxidation
that enables preservation for a longer period of time. The degree of hydro-
genation can be well controlled by varying the amount of hydrogen, reaction
temperature and time, and the catalyst used (Fig. 10.7). For example, vege-
table oil can be converted to margarine via partial hydrogenation. Some trans
fats may be generated in the process of partial hydrogenation [13].

10.4 HYDROGEN UTILIZATION IN METALLURGICAL INDUSTRY

10.4.1 Ore Reduction

Hydrogen is a strong reducing agent that is used for the reduction of metallic
ores to extract metal. Metals rarely exist in pure form. They are usually
bonded to oxygen, sulfur, and occasionally to halogenides. Therefore, metals
can be extracted from those metal ores through reduction process. Carbon,