Chemical Engineering January 2022 - 21

Technology Profile
Production of Ethylene from Ethane
By Intratec Solutions
E
thylene is used almost exclusively
as a building block - it
is the largest-volume petrochemical
produced worldwide
(Figure 1). Production of ethylene grew
rapidly in the middle of the 20th century,
when oil and chemical companies
began separating it from petroleum refinery
waste gas and producing it from
natural gas and ethane (obtained from
byproduct refinery streams).
Ethylene is mostly used as a raw
material for the production of polymers
and other organic chemicals
in consumable end uses, especially
packaging. Polyethylene (PE) is responsible
for about 60% of global
ethylene demand. The main class
of PE produced in the world is highdensity
polyethylene (HDPE), which
is responsible for the consumption
of one-third of the available ethylene.
This is followed by low-density polyethylene
(LDPE) and linear low-density
(LLDPE) varieties.
Ethylene is stored as a liquid under
high pressure or at low temperatures.
However, most of the time, ethylene
is directly supplied to consumers, via
pipeline grids.
Steam cracking
Steam cracking - high temperature
pyrolysis in the presence of steam -
is the main technology used to make
ethylene. The petroleum-based feedstocks
used in steam cracking are
grouped as gaseous (ethane, propane,
n-butane, natural gas liquids
and any mixture of them) and liquid
(field condensates, natural gasoline,
benzene, toluene, xylenes, raffinate,
naphtha). Different feedstocks and
cracking conditions generate different
product slates. In general, high
yields of ethylene with small amounts
of byproducts are obtained from gaseous
feedstocks, while lower ethylene
yields with larger amounts of byproducts
are obtained from cracking
liquid feedstocks.
Process
Production of polymer-grade (PG) ethylene
from ethane feedstock can be
divided in three main parts: cracking
and quenching; compression and drying;
and separation (Figure 2).
Cracking and quenching. Ethane
and dilute steam are fed to furnaces in
which, under high-severity conditions,
ethane is cracked, forming ethylene
and some byproducts. The furnace
outlet stream is subsequently fed to a
water-based quench, to prevent further
reactions and formation of undesirable
byproducts. From the quench
tower, the cracked gas is directed to
compression and drying.
Compression and drying. The compression
of the cracked gas is performed
across five stages. After the
third stage of compression, carbon
dioxide and sulfur are removed from
cracked gas by caustic soda and water
washes in a caustic scrubber.
Separation. After caustic wash, the
cracked gas is sent to a fourth compression
stage and then fed into a
column for removing C3+ hydrocarbons.
The overheads product from
this column, composed primarily of
ethylene and ethane, is fed to the last
compression stage. The compressed
FIGURE 1. Ethylene is the most produced petrochemical
worldwide, by volume
gas is fed to an acetylene converter
and then to a cold box for hydrogen
and light hydrocarbons removal, ensuring
that ethylene losses are minimal.
At this point, the product from
the chilling train is fed to two further
separation columns. In the first column,
methane is obtained from the
top and further used in the cold box,
while the bottom stream is fractionated
in the C2-splitter. In this column,
high-purity ethylene is drawn from
the column as a side stream. Ethane,
from the C2-splitter bottom, is recycled
to the cracking furnaces.
Economics
Most recently, growing environmental
concerns have increased interest
in alternative routes to conventional
petroleum-based ethylene production,
especially the dehydration of
bio-derived ethanol. With such a diverse
range of derivative products,
ethylene demand is highly sensitive
to economic cycles. In fact, it is often
used as a reference in the performance
evaluation of the petrochemical
industry. The economics of
ethylene production is largely dependent
on the prices for feedstocks and
co-products (mainly propylene). In
general, heavier feeds lead to higher
production costs and capital investment
required.
n
1. Cracking furnace
2. Quench column
3. Caustic scrubber
4. De-ethanizer
5. Acetylene hydrogenation
6. Cold box
7. Demethanizer
8. C2-splitter
9. Cooling tower
CW Cooling water
Source: www.intratec.us
Editor's note: The
content for this column is
developed by Intratec Solutions
LLC (Houston; www.
intratec.us) and edited by
Chemical Engineering.
The analyses and models
presented are based on
publicly available and nonconfidential
information.
The content represents the
opinions of Intratec only.
FIGURE 2. The diagram shows the process for producing ethylene by cracking ethane
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Chemical Engineering January 2022

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