What Acrylic Acid Is
Acrylic acid, CAS 79-10-7, is the simplest unsaturated carboxylic acid, with the molecular formula C3H4O2 and a molecular weight of 72.06 g/mol. It is a clear, colourless liquid with a sharp, acrid odour. The molecule carries both a carboxyl group and a carbon-carbon double bond, so it behaves as a carboxylic acid and can also polymerise through the vinyl group. That dual reactivity is why the product is a high-volume chemical building block rather than a speciality reagent.
| Property | Value |
|---|---|
| Molecular formula | C3H4O2 |
| Molecular weight | 72.06 g/mol |
| Melting point | About 14 °C |
| Boiling point | About 141 °C at atmospheric pressure |
| Density at 20 °C | About 1.05 g/cm3 |
| Vapour pressure at 20 °C | About 4 hPa |
| Flash point | About 50 °C in a closed cup |
| Solubility | Miscible with water, alcohols, ether and chloroform |
| Appearance | Clear colourless liquid with a pungent, acrid odour |
Acrylic acid solidifies just below room temperature, so logistics in cool climates rely on heated or insulated tanks, trace-heated lines and drum warming before transfer. Because the monomer polymerises readily, commercial material is supplied stabilised, typically with about 200 ppm of monomethyl ether hydroquinone (MEHQ). MEHQ inhibition depends on dissolved oxygen, so tanks are normally aerated rather than inerted.
How Acrylic Acid Is Produced
The dominant industrial route is the two-stage catalytic gas-phase oxidation of propylene. Propylene is first oxidised to acrolein over a mixed-oxide catalyst, and the acrolein is then oxidised to acrylic acid over a molybdenum-vanadium oxide catalyst. The crude acid is absorbed, distilled and fractionated into glacial and technical grades. An older route hydrolyses acrylonitrile under acid or alkaline conditions and generates a large by-product salt stream; it now accounts for only a small share of capacity.
Almost all commercial tonnage comes from propylene oxidation because of its yield, selectivity and economics, and because the process integrates with acrylate ester plants on the same site.
Main Uses of Acrylic Acid
Acrylate esters: the largest outlet, covering methyl, ethyl, butyl and 2-ethylhexyl acrylate for paints, coatings, pressure-sensitive adhesives, sealants and textile binders.
Superabsorbent polymers: partially neutralised sodium polyacrylate for hygiene products, plus agricultural water-retention and cable applications.
Water treatment and dispersants: polyacrylic acid and its salts as scale inhibitors, flocculants and pigment dispersants.
Thickeners: alkali-swellable emulsions and hydrophobically modified associative types, which also improve adhesion and film hardness in emulsion polymerisation systems.
Speciality finishing: leather and textile treatment agents, chelating agents and paper-making additives.
Safety, Handling and Storage
Acrylic acid is corrosive, causing severe skin burns and serious eye damage, and it is harmful if swallowed or inhaled. Its flammability, with a flash point of about 50 °C in a closed cup, and its ability to polymerise violently when heat is applied or inhibitor is lost make it one of the more demanding bulk monomers to store and move.
Wear chemical-resistant gloves, chemical splash goggles or a face shield, and protective clothing; work under local exhaust ventilation.
Hold tanks within a controlled window, commonly 15-25 °C, and never store near heat, ignition sources or polymerisation initiators.
Verify inhibitor level and dissolved oxygen at defined intervals, and keep aeration in service on stored inventory.
Use 316L stainless steel, higher-alloy or lined vessels; avoid carbon steel and copper alloys.
Contain spills with inert absorbent, and treat overheated stock or polymer deposits as hazardous under the site emergency procedure.
Quality Specifications and Supply
Buyers normally specify acrylic acid by assay, water content, inhibitor level and colour, referencing a recognised material specification such as ASTM D4416. Commercial assays are usually 99.0 % and 99.5 % minimum, with water held to low tenths of a percent and MEHQ set at around 200 ppm to suit the customer process. Deliveries arrive in 200 L drums, 1000 L intermediate bulk containers, ISO tank containers and insulated road tankers, each lot accompanied by a certificate of analysis.
Frequently Asked Questions
Q: What is acrylic acid?
Acrylic acid is the simplest unsaturated carboxylic acid, with the formula C3H4O2, the CAS number 79-10-7 and a molecular weight of 72.06 g/mol.
Q: How is acrylic acid produced industrially?
The main route is two-stage catalytic gas-phase oxidation of propylene through acrolein; an older route hydrolyses acrylonitrile.
Q: What is acrylic acid mainly used for?
It makes acrylate esters and polymers for paints, coatings, adhesives, sealants, textiles, leather treatment, water treatment and superabsorbent products.
Q: Is acrylic acid dangerous?
Yes, it is corrosive and can burn skin and eyes, it is harmful if inhaled or swallowed, and it is flammable with a flash point near 50 °C.
Q: Why is acrylic acid supplied with an inhibitor?
Uninhibited material can polymerise spontaneously, so about 200 ppm MEHQ is added and dissolved oxygen is maintained to keep the inhibitor active.