_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Catalysis of reactions of alkenes by transition metal complexes
12.2 Resources
Before 19 50, about 80% of ali organic chemicals were obtained either by
fermentation or from coal. Since then there has been a shift to oii, which now
provides the raw material for about 90% of such products. The primary use for oil
is as a fuel, particularly for transport. Only 5-10% of crude oii is used for chemical
manufacture. The lighter oii fractions provide the main feedstocks. These
comprise light petroleum gases (ethane, propane and butanes) and naphtha
(b.p. 30-190°C) which consists of paraffins, alicyclics (naphthenes) and
aromatics.
The reactions discussed below can be divided into two very broad groups. The
first group is based on alkenes which are produced by steam cracking of
hydrocarbons. The second starts out from synthesis gas, which is essentialiy a
mixture of carbon monoxide and hydrogen. The main methods used to obtain
alkenes and synthesis gas are summarized in Table 12.2.
In the production of fuel oils, heavy petroleum fractions may be converted into
lower molecular weight products by catalytic cracking over a zeolite catalyst.
When this process is carried out under a high pressure of hydrogen (hydrocracking)
saturated hydrocarbons are produced from the intermediate aromatics and
alkenes. On the other hand, motor gasoline of high octane number contains a
high proportion of aromatics. The content of aromatics may be increased by
catalytic reforming over supported platinum catalysts. These processes are
included in Table 12.2, but it is not economic to apply them to naphtha or heavy
petroleum fractions to produce lighter fractions for chemical feedstocks.
12.3 Catalysis of reactions of alkenes by transition metal
complexes
12.3.1 Production of alkenes-steam cracking
Only a limited number of building blocks are required by the large scale chemical
industry. Ofthese ethene occupies a prime position. It is the principal feedstock for
the manufacture of about 30% of ali petrochemicals. In 1985 about 13.8 m
tonnes were produced in the USA alone. Of this 44% was converted into
polyethene, 18% into ethene oxide and 14% into vinyl chloride (for PVC). Ethene
oxide is the precursor to 1, 2-ethane diol (ethylene glycol) which is used as an
antifreeze and as a component for polyester production. These figures emphasize
the dominant position of polymers in the petrochemical industry. Some of the
processes, described below, which employ homogeneous catalysts are carried out
on a much smalier scale and may represent only a smali fraction ofthe total usage
of chemical feedstocks.
Ethene is manufactured by steam cracking. Ethane is the feedstock of choice in
the United States. ( C 2 H 6 ---+ C 2 H 4 + H 2 ). The Fife ethene plant at Mossmorran
which carne into production in 1986 uses ethane piped from the Brent and
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