Acrylic acid is an unsaturated carboxylic acid, with the formula CH2=CHCO2H. This clear and colourless liquid has a characteristic acrid odour. As it contains a polar carboxylic acid functional group, it is able to dissolve in water and is miscible with relatively polar organic compounds such as alcohols, ethers, and chloroform. Acrylic acid is air and water sensitive as it reacts readily with free radicals and electrophilic or nucleophilic agents. It may polymerise in the presence of acids, alkalis, amines, peroxides, and iron salts. Prolonged exposure to heat or exposure of light can also cause polymerisation. If confined, the polymerisation of acrylic acid can lead to explosion even at room temperature. It is corrosive to metals and tissues.
Acrylic acid can be used in the form of free acids, ammonium and alkali salts in many different applications such as thickeners, dispersing agents, flocculants, wetting agents, coatings, textile finishes protective colloids for stabilizing emulsions and polymer dispersions. It readily undergoes additional reactions with a wide variety of organic and inorganic compounds, which makes it a very useful feedstock for the production of many low molecular compounds. For instance, acrylic acid can be used to produce derivatives of propionic acid with water, alcohols, amines, halogens and chlorinated hydrocarbons. It can also react with other substances to produce unsaturated fatty acids, heterocyclic compounds and Diels-Alder addition products.
As it polymerises with explosive violence, it can only be shipped after being stabilised by an inhibitor such as hydroquinone. The removal of the stabilizer is not usually necessary, since its action can be compensated for by adding an excessive initiator.
The most widely accepted process for making acrylic acid is the vapour phase oxidation of propylene via acrolein, where propylene is a byproduct of ethylene and gasoline production. Typically, Chemical-Grade (CG) propylene is mixed with steam and air to undergo a two-step oxidation where propylene is oxidised to acrolein before further oxidising again to give acrylic acid. These oxidations are done in tubular, fixed-bed reactors where steam is generated by utilising the heat emitted by the exothermic reactions.
Acrylic acid is primarily used as starting material for preparation of chemicals such as methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate. These monomers are polymerised, and are used in hygiene products with superabsorbent resins such as disposable diapers, in water-based paints and coatings, construction adhesives and pressure-sensitive adhesives, coatings for textiles, wood and paper, in leather finishing etc.
They also function mainly as an intermediate for the production of acrylate esters which are used to produce plastic additives, adhesives, coatings, textiles and paints. However, due to environmental concerns, their production was stopped.
Acrylic acid is used in the manufacture of plastics, in latex applications, in floor polish, in polymer solutions for coatings applications, emulsion polymers, paint formulations, leather finishings, and paper coatings.
Acrylics are produced from acrylic acid through a two-step process. They are commonly used in the coatings industry and also used in their sheet forms due to their durability and clarity. In the first step, a reaction between the acrylic acid and an alcohol will produce an alkyl acrylate, which is a monomer of acrylics. After which, the second step is the polymerisation of the monomer to form acrylics. A radical is added to one end of the double bond of the alkyl acrylate to give a radical monomer before polymerising. The properties of the resulting acrylics are dependent on the nature of the alkyl groups on the acrylic acid and alcohol.
Waste Water Treatment
Acrylic acid monomers are copolymerized and are used in waste water treatment. They are used in flocculation of mineral ore fines and waste water, and treatment of sewage.
Usage of acrylic acids has various applications over different industries. They can be found in acrylic nail polish in the cosmetic industry.