Acrylic Acid
HAZARDOUS MATERIAL
CHEMICAL DATA NOTEBOOK SERIES #35
ACRYLIC ACID is a corrosive, combustible, polymerizable, reactive, toxic, irritating, colorless liquid with a sharp, rancid odor that some describe as sweet but unpleasant. It is an organic acid, and it has different corrosive properties than the inorganic or mineral acids. It is used in the manufacture of paints, photographic chemicals, plastics, rubber, and in the production of paper coatings. Glacial acrylic acid has a purity of from 97% to 99.5%.
PROPERTIES
Acrylic acid has a flash point of 118°F, an ignition temperature of 774°F (one reference has ignition temperature at 374°F, a probable typographical error), and a flammable range of 2.0% to 8.0% in air. It has a specific gravity of 1.05, a molecular weight of 72, and a vapor density of 2.48. It boils at 285.8°F, freezes at 55.8°F, and is soluble in water. Its chemical formula is C2H3COOH, and its structural formula is:
HAZARDS
Acrylic acid is soluble in and not reactive with water, alcohol, and ether. It is corrosive to metals such as steel, copper alloys, and lead. Acrylic acid is an organic acid, and therefore it is not as corrosive as most inorganic acids (such as sulfuric, nitric, and hydrochloric). However, its corrosivity is still a major hazard and may cause death to exposed humans. It may react with a very wide variety of chemicals such as caustics and other acids, organic compounds such as amines, ammonia, azo and diazo compounds, cresois, hydrazines, phenols, peroxides (possibly inorganic peroxides also), and explosives. It may also react with inorganic compounds such as cyanides, iron salts, nitrides, and sulfides.
Acrylic acid is a monomer for some acrylic plastics, and this is an added hazard. As the structural formula shows, acrylic acid contains a carbon-to-carbon double bond in a relatively small molecule. Any time this double bond occurs between carbon atoms, it is a “weak” or reactive point in the molecule. Since acrylic acid is a small molecule, it possesses a chemical property reserved for chemicals of its type, that of being able to react with itself to form a giant molecule called a polymer. The chemical reaction in which this occurs is called polymerization, and is conducted within large reactor vessels under strictly controlled conditions. However, since the very nature of a monomer is that it can polymerize, this reaction could happen outside the reactor, in storage or during transportation. For this reason, all monomers are considered unstable materials, even though some are more stable than others.
If the polymerization reaction occurs outside the reactor in some other container (acrylic acid is shipped in rail tankers, tank wagons, and drums), the results could be disastrous. The polymerization reaction is closely controlled by the company making the polymer for several reasons—one of them is safety. If the polymerization reaction does get out of control (no matter where in the container it happens), the tremendous amount of energy (heat) released could cause a catastrophic failure of the container. The resulting explosion could be devastating, depending, of course, on the j amount of acrylic acid present and the design strength of the container.
To protect against this reaction, which is called runaway or uncontrolled polymerization, the manufacturer of the monomer will add a chemical called an inhibitor or a stabilizer to it during manufacture. In acrylic acid’s case, this inhibitor may be monomethylether of hydroquinone, and it will be added in very small amounts, usually less than 0.5%. As long as the inhibitor stays mixed with the monomer, polymerization should not take place. If during transportation or storage the monomer is allowed to freeze (remember that acrylic acid freezes at the relatively high temperature of 55.8°F) and rethaw, the inhibitor may not be well-mixed and the acrylic acid will become unstable and subject to runaway polymerization. Also, if extreme heat is allowed to contact the container, the inhibitor may be driven out by evaporation or simply overcome by the input of energy, and the uncontrolled polymerization may commence. It’s also important to keep the monomer from being contaminated by any chemicals with which it is reactive, since this will also overcome the inhibitor and cause runaway polymerization.
Once the monomer has been delivered to the polymerizer and is added to the reactor, a chemical called an initiator is added to overcome the stabilizing power of the inhibitor. The polymerization reaction begins, this time under controlled conditions.
Acrylic acid’s flash point of 118°F indicates that it is a combustible liquid. This, of course, means that if its temperature reaches 118°F (and it can be just a small portion of the liquid that reaches this temperature), sufficient vapors will be liberated that will ignite if an ignition source produces a temperature of 774°F. All common ignition sources will produce this temperature, and the resulting ignition may produce a powerful explosion if enough vapors have been generated.
Acrylic acid is toxic by all routes of entry and has a TLV-TWA (threshold limit value-time weighted average) of 2 ppm (parts of vapor per million parts of air) and 6 mg/m3 (milligrams of substance per cubic meter of air). The vapors of acrylic acid are very irritating to the eyes, respiratory tract, and skin. Ingestion of the product may cause severe burns to the mouth, esophagus, stomach, and gastrointestinal tract. If damage is severe enough, death or irreversible damage may occur. Contact with the skin will cause severe burns, and rashes may develop. Absorption of the acid through the skin is possible and may cause nausea and vomiting.
SYNONYMS
acroleic acid
acrylic acid, glacial
acrylic acid, inhibited
ethylene carboxylic acid
GAA
glacial acrylic acid
propene acid
propenoic acid
2-propenoic acid
vinylformic acid
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Service)
79-10-7
RTECS
(Registry of Toxic Effects of Chemical Substances)
AS4375000
STCC
(Standard Transportation Commodity Code)
4931405
UN/NA
(United Nations/North America)
2218
CHRIS
(Chemical Hazard Response Information System)
ACR
RCRA Waste Number
(Resource Conservation and Recovery Act)
U008
NFPA Rating
3-2-0
DOT
(U.S. Department of Transportation)
Corrosive
IMO
(International Maritime Organization)
Corrosive, 8
NONFIRE RELEASE
If glacial acrylic acid is spilled or is otherwise released from its original container, containment is the first concern. This may be accomplished by building a containment pond by using diking materials such as soil, sand, clay, or other absorbent materials. Trenches or ditches may also be dug that lead to a pit dug for containment purposes. Be advised that any containment of the material in soil will cause contamination as the liquid percolates into the earth. If the air temperature is below 55.8°F (assuming the ground is also at that temperature or below), that material will freeze, making containment easier and extensive contamination unlikely. In any case, if containment ponds are built or pits are dug, be certain that all tools that may come into contact with the material will resist acrylic acid’s corrosivity. The proper environmental authorities must be notified immediately.
If the material is frozen or is a liquid at ambient temperature, generation of vapors will not be a serious problem due to its low vapor pressure. At higher ambient temperatures (80°F or higher), generation of vapors will naturally be higher and could be irritating or corrosive if concentrated.
The liquid may be suctioned into secure containers (always by compatible equipment) by the manufacturer, shipper, salvage firm, or any other enterprise that is educated, trained, and equipped to handle such activities. Remaining liquid may be absorbed by soil, sand, clay, or any other absorbent material and disposed of in accordance with federal, state, and local regulations. Any such salvage, cleanup, or disposal should always be performed under the guidance of the proper environmental authorities, who will make decisions on how far the contamination has spread and how much earth has to be removed with the product. Salvage and/or cleanup by emergency responders is tricky at best, and at worst could cause injury and/or death, or other damage that could incur liability. These activities by fire department personnel should be discouraged.
Entry into sewers or waterways must be prevented by the use of dikes or dams of absorbent material. If acrylic acid does enter a sewer, the sewage treatment facility must be notified immediately, giving them as much information as to quantity and concentration as possible. If it reaches a waterway, the acid will dissolve in the water fairly quickly, certainly too quickly for recovery activities. If the waterway cannot be dammed or diverted to isolate the contaminated water, all downstream users must be notified immediately. As a matter of safety, they should be notified even if the water can be dammed or diverted, just in case some is accidently released or the dam gives way. Any intake of the contaminated water downstream that will be used for cooling hot manufacturing processes will probably heat the water to temperatures above 118°F This will cause the liberation of the acid vapors in sufficient quantities to be explosive in contact with an ignition source.
In situations where there is no fire threat and the acrylic acid is self-contained or frozen, no direct action by emergency responders may be required. In other words, if there is no imminent danger, alert the proper authorities and don’t involve yourselves or your personnel in any activity that will bring you or them into contact with the material.
FIRE SCENARIO
When a container of acrylic acid is exposed to the radiated heat of a fire or the heat from direct flame contact, catastrophic failure of the container is possible if internal pressure rises above the design strength of the tank. This will release a combustible liquid to the environment with fire present, which will exacerbate the problem. The failure of the tank can be explosive, with a resulting deadly fireball. It will be necessary to cool the container with water delivered from as far away as possible. preferably with unmanned monitors. If the accident has occurred where there is no threat to life, the environment, vital systems, or property, the fire need not be attacked at all. Alert the proper authorities and stand back. A minimum of 2,000 feet is recommended as a radius of evacuation from a container of acrylic acid threatened by heat.
GLOSSARY
Glacial—A term used to describe acids that in their pure state have a freezing point slightly below room temperature.
Inhibitor—A chemical added to a monomer to prevent polymerization during storage or transportation. May also be called a stabilizer.
Initiator—A chemical added to a monomer that will overcome the stabilizer to allow the polymerization reaction to begin.
Monomer—A “tiny” molecule that has the unique chemical property of being able to react with itself to form a polymer.
Polymer—A “giant” molecule made up of thousands of monomer molecules that have reacted with themselves.
Polymerization—The chemical reaction in which monomers react with themselves to form polymers.
If vapors are evolving from the heated container, they will cool and hang near the ground because of acrylic acid’s vapor density of 2.48. Evacuation downwind must always be considered since thc vapors will move along low spots in the ground (if undisturbed by strong breezes) and gather in low areas or confined spaces. These accumulations of acid vapors are toxic traps for the exposed person and potential explosive situations for anyone nearby. Vapors liberated from a heated container may be dissolved from the air by use of highpressure sprays or fogs in a sweeping motion near the point of release. Care must be exercised to contain the runoff in order to minimize contamination.
If released liquid has ignited, the fire may be extinguished by the use of water spray or fog, alcohol type foam, dry chemical, or carbon dioxide, depending on the size of the spill and wind conditions. Ignition may be prevented by the use of alcohol foam on the released material or contained spill to prevent the generation of vapors.
If the containment area is large enough, directly adding water to the liquid may extinguish the fire by diluting the acrylic acid, thereby cooling it and, more importantly, raising its flash point. Dilution of the liquid before ignition may also be a technique that’s effective in preventing ignition.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing and equipment must be selected to prevent contact of the liquid or vapor with the eyes, skin, or respiratory system. Required equipment should include splash-proof safety goggles, face shields, and positive-pressure self-contained breathing apparatus. SCBAs are required whenever the concentration of vapors in air is unknown and in every firefighting situation. Required clothing should include rubber gloves and boots, and other impervious clothing. Any personnel entering the “hot zone” should be equipped with total encapsulating suits that will resist acrylic acid. Claims of resistance are made by manufacturers of suits constructed of butyl rubber (moderate resistance), chlorinated polyethylene (CPE), and certain fluoropolymer composites such as Teflon-coated Nomex. There may be more materials that give good protection, and manufacturers of the suits should be consulted.
Remember, protection is relative. Even though a material may be resistant to a particular chemical, there are other considerations for your safety. These include thickness of the material, flexibility of the fabric, lack of breaks in the material, integrity of the closures and seams, concentration of the chemical contacted, length of contact, and temperature of the exposed surface of the suit.
FIRST AID
For inhalation, the victim must be removed to fresh air. If the victim has stopped breathing or breathing has become difficult, artificial respiration must be administered. (Mouth-to-mouth resuscitation may expose the provider of first aid to the material in the victim’s mouth or vomit.) Medical attention for the victim must be provided immediately.
For skin contact, all contaminated clothing should be removed and all affected body areas washed with large amounts of water. Medical attention is necessary if irritation of the skin persists after washing.
For eye contact, the eyes should be flushed immediately with large amounts of water for 15 minutes, occasionally lifting the eyelids. Medical attention should be provided immediately.
For ingestion, do not make the victim vomit. If the victim is conscious, administer large amounts of water or milk. Keep the victim warm and get immediate medical attention
