Petrochemicals - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 53

rock in a process called “fracking.” When the shale is broken up, entrapped
natural gas is released. Drilling techniques have improved to allow turning
the vertical shaft as much as 90 degrees to then allow horizontal drilling. This
enables the mining of a much larger area with a single well. The discovery
of large shale deposits, improvements in fracking technology, and the ability
to drill horizontally have remarkably improved the economics of natural gas.
The technique is not without controversy. There are environmental concerns
about the injection of large volumes of the fracking water and how they may
affect drinking water supplies. There can also be issues with nearby drinking
wells and contamination with methane. Natural gas is purified by a refrigera-
tion and distillation process. This pressurized liquid purified product is mainly
methane and is called liquefied natural gas (LNG). The distinctive smell of
LNG is caused by low levels of an additive, a mixture of mercaptans, which
gives LNG the distinctive rotten-egg smell for safety and leak detection.
LNG is mainly used as a fuel source, much of it in electrical power plants.
The removed higher hydrocarbons such as ethane or propane can also be
used as fuels or can be converted to feedstocks such as ethylene or propylene.
Oil shale rock is another source of oil and energy. This rock can be mined
and then heated to produce oil as well as steam for energy. Oil shale is
sedimentary rock that contains organic matter. The amount of organic matter
varies and is as high as 50% in some high grade deposits, although 5 to 25%
is more common [4]. Compared with fracking, which involves deep wells
and reserves, oil shale is located near the surface.
5.3 ETHYLENE
The world's 140 million metric tons of annual ethylene capacity almost
exclusively employs steam cracking of hydrocarbon feedstocks [5]. The
majority of the feedstocks come from petroleum refining, such as by cracking
of naphtha, but some producers use liquefied natural gas as a feedstock. In
Brazil, where sugar cane is plentiful, Braskem has built a 200,000 metric
ton per year ethylene plant based upon the dehydration of sugar-derived
ethanol [6]. In the United States, natural gas liquids, a mixture of ethane,
propane, butane, and other hydrocarbons, are available from shale deposits.
The ethane is separated and cracked to make ethylene. Depending on the
cost of oil and natural gas, this can be an economic advantage. In 2012, about
70% of United States ethylene production was from ethane [7].
Ethylene is the largest volume organic chemical produced in the world.
Much of it is used captively for conversion into other products. The largest
use is for the polymerization of ethylene to make polyethylene. Polyethylene
has many desirable properties including low cost, and therefore each year