Chapter 5
C–C Bond Formation
via the Condensation of Methane
in the Presence or Absence of Oxygen
5.1 Introduction
As discussed in Chapter 1, the formation of C–C bonds to produce higher hydrocarbons (carbon number > 2) via the condensation of methane is difficult to achieve using
direct conversion methods, whether in the presence or absence of oxygen. In contrast,
higher hydrocarbons are produced industrially in the indirect conversion method by
Fischer-Tropsch synthesis, as shown in Fig. 1.2. In this chapter, the condensation of
methane, which is conventionally referred to as the oxidative coupling of methane or
the dehydrogenative coupling of methane, is discussed. Hydrocarbons with carbon
numbers of greater than two are referred to as C 2
+ hydrocarbons in this chapter.
The oxidative coupling of methane, which is shown in reaction (5.1), is more thermodynamically favorable than the dehydrogenative coupling of methane in reaction
(5.2).
(5.1)
(5.2)
The oxidative coupling of methane (OCM) involves the catalytic conversion of
methane and oxygen to ethane (C 2 H 6 ) and H 2 O. The ethane is converted to ethylene
(C 2 H 4 ) in situ; further reactions also produce higher hydrocarbons, such as benzene.
Unfortunately, the presence of oxygen leads irreversibly to oxidation, resulting in
the thermodynamically stable end-product, CO 2 together with CO.
Although the dehydrogenative coupling of methane presents a thermodynamic
disadvantage because of the large positive change in free energy, over-oxidation
does not occur, and CO and CO 2 are not formed. The dehydrogenative coupling of
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_5
103
C–C Bond Formation
via the Condensation of Methane
in the Presence or Absence of Oxygen
5.1 Introduction
As discussed in Chapter 1, the formation of C–C bonds to produce higher hydrocarbons (carbon number > 2) via the condensation of methane is difficult to achieve using
direct conversion methods, whether in the presence or absence of oxygen. In contrast,
higher hydrocarbons are produced industrially in the indirect conversion method by
Fischer-Tropsch synthesis, as shown in Fig. 1.2. In this chapter, the condensation of
methane, which is conventionally referred to as the oxidative coupling of methane or
the dehydrogenative coupling of methane, is discussed. Hydrocarbons with carbon
numbers of greater than two are referred to as C 2
+ hydrocarbons in this chapter.
The oxidative coupling of methane, which is shown in reaction (5.1), is more thermodynamically favorable than the dehydrogenative coupling of methane in reaction
(5.2).
(5.1)
(5.2)
The oxidative coupling of methane (OCM) involves the catalytic conversion of
methane and oxygen to ethane (C 2 H 6 ) and H 2 O. The ethane is converted to ethylene
(C 2 H 4 ) in situ; further reactions also produce higher hydrocarbons, such as benzene.
Unfortunately, the presence of oxygen leads irreversibly to oxidation, resulting in
the thermodynamically stable end-product, CO 2 together with CO.
Although the dehydrogenative coupling of methane presents a thermodynamic
disadvantage because of the large positive change in free energy, over-oxidation
does not occur, and CO and CO 2 are not formed. The dehydrogenative coupling of
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_5
103