STYRENE PHYSICAL AND CHEMICAL PROPERTIES:
Styrene, also known as vinyl benzene or styrol, is an aromatic
hydrocarbon compound which is clear liquid (colourless to yellowish) with the structural
chemical formula C6H5CH=CH2 and empirical formulae C8H8
USES OF STYRENE
Styrene is copolymerized to manufacture different products
like polystyrene (PS), Butadiene-styrene rubbers or latexes,
Acrylonitrile-Butadiene-styrene rubbers, unsaturated polyester resins, and
paints. All these products are commonly used in electrical, mechanical,
electronic, automotive, packaging and literally everything from food containers
to cars, boats, computers, inhalers, medical equipment, video games, glass or
fibre reinforced laminates, paints and many more products.
STYRENE CHARACTERISTICS
Styrene gets easily co-polymerized due to the presence of a double bond. It is toxic and reactive and is generally stable at ambient
temperature. An exothermic reaction is initiated by heat or contact with peroxides
and the reaction becomes very rapid with the increase in temperature
To prevent co-polymerization under storage conditions p-ter-butyl-catechol
(TBC)(as an Inhibitor) is added in very small quantities (12-15 ppm). Normally,
temperatures above 65°C (149°F) are needed to initiate runaway polymerizations.
·
Styrene can react violently with peroxides, strong acids, and
chlorates.
PROCESSES WHICH CAUSES EXPOSURE TO STYRENE
·
Styrene monomer manufacturing, handling, transportation and
storage.
·
Manufacturing of solid polystyrene (PS) or Expanded
polystyrene foam (EPS).
·
Manufacturing of Styrene-butadiene rubber (SBR) or Styrene
butadiene latex (SBL).
·
Manufacturing of Acrylonitrile-butadiene- styrene rubber
(ABS).
·
Manufacturing of unsaturated polyester Resin where styrene is
used as a diluting and cross-linking agent.
·
Glass or fibre reinforced plastics (GRP) manufacturing.
·
Emulsion paints manufacturing.
HEALTH RISKS ON EXPOSURE
ACUTE:
·
Central nervous depression.
·
Irritation of skin.
·
Irritation of the upper respiratory tract.
·
Asphyxia, muscular weakness and coma/death
CHRONIC:
·
Skin and eye changes
·
Liver dysfunction
·
Neuro behavioural abnormalities
TOXICITY:
STYRENE RECENT ACCIDENTS CASE STUDIES
|
DATE |
PLACE |
INCIDENTS |
REASONS |
|
28/8/2005 |
Cincinnati |
Pressurization of
styrene monomer in rail storage tank resulted in styrene vapours released
into atmosphere |
Self
polymerization of styrene resulting in temperature increase and subsequent
pressurization of the tank leading to styrene vapourization |
|
28/9/2019 |
South Korea |
Explosion and fire
on board of chemical tanker due to styrene polymerization |
Due to over
pressurization the styrene monomer vapour was released, static electricity
and elevated deck temperature created the required ignition source resulting
in explosion |
|
07/05/2020 |
Visakhapatnam |
Pressurization of
styrene monomer in storage tank resulted in styrene vapours released into
atmosphere |
Self
polymerization of styrene resulting in temperature increase and subsequent
pressurization of the tank leading to styrene vapourization |
REASONS
- INITIATION OF SELF
POLYMERIZATION OF STYRENE DURING STORAGE, DUE TO DECREASED CONCENTRATION
OF INHIBITOR OVER PERIOD OF TIME IN STORAGE.
- THIS SELF POLYMERIZATION
RESULTED IN INCREASE IN TEMPERATURE DUE TO EXOTHERMIC REACTION
- THIS INCREASE WILL BE EXPONENTIAL
AFTER 650C, RESULTING IN PRESSURE BUILD-UP INSIDE THE STORAGE
TANK DUE TO HEAT GENERATION
- THE PRESSURE WILL GET RELEASED
AS WHITE FUMES THROUGH SAFETY VENTS AND ESPACE INTO THE ATMOSPHERE,
- RAISE OF TANK PRESSURE DUE TO
CLOGGING OF VENT VALVES(OR) PRESENCE OF ANY IGNITION SOURCES PRESENT AT
SOURCE COMING IN CONTACT WITH VAPOURS WILL IN FIRE AND EXPLOSION.
ROLE OF INHIBITOR
Chemical inhibitor (4-tertiary-butyl-catechol (TBC)) is added to the
tank to maintain the concentration of 12-15 ppm to prevent polymerization. This
inhibitor scavenges impurities and rust present within the tank then can
trigger polymerization. Oxygen (about 10 ppm) is also required to be dissolved
in the styrene monomer for the inhibitor to work. The TBC concentration
decreases with time as it scavenges impurities
CONTROLS
After analyzing all the reasons for accidents during
storage the following controls need to be implemented and monitored while
handling styrene
1) Styrene is easily self
polymerized, hence all the necessary utility equipment and checks that keep
temperature and pressure surrounding styrene under controlled conditions all
the time should be efficiently and effectively maintained, Mechanical integrity
of the system to be ensured.
2) Addition of inhibitor (
requires close monitoring as this prevents undue polymerisation and preserves
stability and polymerization inhibition level should be checked twice weekly if
stored more than 30 days)
3) To develop and establish
(MOC) Management of change procedures to ensure required controls are
established and followed before carrying out any troubleshooting for
rectification (or) implementing alternate methods during the process operations
4) Training of operators to
increase their efficiency both in skill and knowledge in responding to abnormal
situations.
5) Close monitoring of
storage conditions of styrene to observe for any unexplained temperature
increase for which emergency actions to be in place
6) Using of fluoroelastomer
hoses instead of rubber type elastomer to unload styrene is recommended as
rubber may not be resistant to styrene
7) All ignition sources such
as sparks, static electricity and heat source must be prohibited in areas where
styrene is transferred, used or stored.
8) Styrene used in small
quantities as in the fibre or glass-reinforced plastics industry, should not be
stored in a drum, instead, styrene should be stored in safety cans to prevent
high localized concentrations
9) Elevated exposure levels
of styrene are mainly found in reinforced plastic industries ( use of
unsaturated polyester resin) which are carried out in small scale industries
where the working personnel are in close proximity to higher concentrations
resulting in both acute and chronic effects, hence all small scale industries
which are using such styrene-based raw materials should incorporate appropriate
control measures to prevent workers from styrene exposures
10)Elevated exposure levels
of styrene are mainly found in reinforced plastic industries ( use of
unsaturated polyester resin) which are carried out in small scale industries
where the working personnel are in close proximity to higher concentrations
resulting in both acute and chronic effects, hence all small scale industries
which are using such styrene-based raw materials should incorporate appropriate
control measures to prevent workers from styrene exposures
11)Other chemicals like
Butadiene, Ethylene oxide, Furfural and vinyl acetate undergo similarly
polymerization reactions for which proper controls and inhibitor requirements
to be closely followed
Article by PJ Mohan
Sr.Faculty, NIFS
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