Petrochemical
Petrochemicals are chemicals made from petroleum or natural gas. Primary
petrochemicals are divided into three groups, depending on their chemical
structure:
Olefins include ethylene, propylene, and butadiene. Ethylene and propylene
are important sources of industrial chemicals and plastics products.
Butadiene is used in making synthetic rubber. Olefins are produced by
cracking.
Aromatic petrochemicals include benzene, toluene, and xylenes. Benzene
is used in the manufacture of dyes and synthetic detergents. Toluene is used
in making explosives. Manufacturers use xylenes in making plastics and
synthetic fibers. Aromatics are produced by reforming.
Synthesis gas (SynGas) is a mixture of carbon monoxide and hydrogen,
and is used to make the petrochemicals ammonia and methanol. Ammonia
is used in making fertilizers and explosives, where methanol serves as a
source for other chemicals.
Figure 23. Petrochemical tree: feedstock and primary petrochemicals
The primary petrochemicals are not end products, but form building blocks
for a wide range of materials.
Therefore, each primary petrochemical gives
name to a chain of reactions leading to those materials. There are almost
200 petrochemicals that can be described this way. There are more
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processes than end products, as each product may require multiple steps,
so an exhaustive list would not fit within this book. Instead, we will focus on
the main chains, properties and uses of the most important compounds and
a few key processes for this overview.
Many of these processes are based on polymerization, which means that it
is based on processes that first form monomers then let these bind together
to form polymers as long chains or a three dimensional network. Compounds
whose names start with “poly” are generally polymers, but many other trade
names, such as nylon which is a generic name for a family of polyamides,
are polymers.
Petrochemicals are often made in clusters of plants in the same area. These
plants are often operated by separate companies, and this concept is known
as integrated manufacturing. Groups of related materials are often used in
adjacent manufacturing plants, to use common infrastructure and minimize
transport.
WST - Exxon Singapore Petrochemical Complex
7.1 Aromatics
Aromatics, so called because of their distinctive perfumed smell, are a group
of hydrocarbons that include benzene, toluene and the xylenes. These are
basic chemicals used as starting materials for a wide range of consumer
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products.
Almost all aromatics come from crude oil, although small quantities
are made from coal.
7.1.1 Xylene and polyester chain
Figure 24. Aromatics – xylene and polyester chain, derivatives
One of the forms of xylene, paraxylene, is used to make polyesters which
have applications in clothing, packaging and plastic bottles.
The most widely-used polyester is polyethylene terephthalate (PET), used in
lightweight, recyclable soft drink bottles (30% of production), as fibers in
clothing (60% of production), as a filling for anoraks and duvets, in car tire
cords and conveyor belts. It can also be made into a film that is used in
video and audiotapes and X-ray films. Polyester makes up about 18% of
world polymer production and is the third most-produced polymer;
polyethylene (PE) and polypropylene (PP) are first and second, respectively.
Metaxylene is an isomer of mixed xylene. It is used as an intermediate in the
manufacture of polyesters for coatings, inks, reinforced plastics and
packaging applications.
Unsaturated polyester is used over a broad spread of industries, mainly the
construction, boat building, automotive and electrical industries. In most
applications, they are reinforced with small glass fibers. Hence, these
plastics are commonly referred to as glass reinforced plastics (GRP).
Initially a liquid, the resin becomes solid by cross-linking chains. A curative
or hardener creates free radicals at unsaturated bonds, which propagate in a
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chain reaction to adjacent molecules, linking them in the process. Styrene is
often used to lower viscosity and evaporates during hardening, where the
cross linking releases heat.
Orthoxylene is an isomer of mixed xylene. It is primarily used in plasticizers
(primarily in flexible polyvinyl chloride (PVC) material to make it more
flexible), medicines and dyes.
Alkyd resins are a group of sticky synthetic resins used in protective coatings
and paints.
