Acrylic acid

Description

Acrylic acid, scientifically known as prop-2-enoic acid (CH2=CHCO2H), is the fundamental unsaturated carboxylic acid featuring a vinyl group directly attached to a carboxylic acid group. This colorless liquid, recognized by its pungent, tart odor, is highly soluble in water, alcohols, ethers, and chloroform. With an annual production exceeding one billion kilograms, acrylic acid's high reactivity allows it to polymerize into polyacrylic acid, utilized in absorbent hygiene products. Additionally, it can esterify with alcohols to form acrylates, which are integral in numerous polymer formulations. Despite the common misconception, polymers known as acrylics, such as Plexiglas and textiles, often derive from sources other than acrylic acid, even though they contain acrylate monomers.

Chemical properties

Acrylic acid is a colorless, flammable, and corrosive liquid or solid (below 13 C) with an irritating, rancid, odor. Sinks and mixes with water; irritating vapor is produced.

The Uses of Acrylic acid

Acrylic acid undergoes the typical reactions of a carboxylic acid and, when reacted with an alcohol, it will form the corresponding ester. The esters and salts of acrylic acid are collectively known as acrylates (or propenoates). The most common alkyl esters of acrylic acid are methyl-, butyl-, ethyl-, and 2-ethylhexyl-acrylate.
Acrylic acid and its esters readily combine with themselves (to form polyacrylic acid) or other monomers (e.g. acrylamides, acrylonitrile, vinyl, styrene, and butadiene) by reacting at their double bond, forming homopolymers or copolymers which are used in the manufacture of various plastics, coatings, adhesives, elastomers, as well as floor polishes, and paints.

What are the applications of Application

Acrylic acid is synthesised by oxidation of acrolein or hydrolysis of acrylonitrile and can be used:
(1) The production of various plastics;
(2) As a component of paints, polishes and adhesives to enhance their adhesive and protective properties;
(3) As a coating for leather to improve its durability and appearance;
(4) Used as an antimicrobial agent；
(5) used as an intermediate in the synthesis of acrylates, which are essential for the manufacture of various polymers.

Definition

An unsaturated liquid carboxylic acid with a pungent odor. The acid and its esters are used to make ACRYLIC RESINS.

Production Methods

Acrylic acid is produced from propene which is a by product of ethylene and gasoline production. CH₂=CHCH₃ + 1.5 O₂→ CH₂=CHCO₂H + H₂O Because acrylic acid and its esters have long been valued commercially, many other methods have been developed but most have been abandoned for economic or environmental reasons. An early method was the hydrocarboxylation of acetylene ("Reppe chemistry") : HCCH + CO + H₂O → CH₂=CHCO₂H This method requires nickel carbonyl and high pressures of carbon monoxide. It was once manufactured by the hydrolysis of acrylonitrile which is derived from propene by ammoxidation, but was abandoned because the method cogenerates ammonium derivatives. Other now abandoned precursors to acrylic acid include ethenone and ethylene cyanohydrin.

Preparation

There are three routes to acrylic acid which have commercial significance; they are based on propylene, acetylene and ethylene respectively. At the present time, most acrylic acid is produced via the propylene route.
(i) Propylene route. This route involves the two-stage oxidation of propylene:

A mixture of propylene, air and steam is fed into a reactor containing a catalyst at about 320??C to give acrolein. This intermediate is not isolated but is passed directly to a second reactor, also containing a catalyst, at about 280??C. The effluent is cooled by contact with cold aqueous acrylic acid.
Acrylic acid is extracted from the solution with a solvent and then separated by distillation. Because of the ready availability of low cost propylene, this route has become the preferred route for the production of acrylic acid. (ii) Acetylene route. This route involves the reaction of acetylene, carbon monoxide and water:

In one process, the reaction is conducted in solution in tetrahydrofuran at about 200??C and 6-20 MPa (60--200 atmospheres). Nickel bromide is used as catalyst. The solution of acrylic acid in tetrahydrofuran, after separation of the unconverted acetylene and carbon monoxide in a degassing column, passes to a distillation tower where tetrahydrofuran is taken overhead and acrylic acid is the bottom product. The reaction between acetylene, carbon monoxide and water may also be carried out by using nickel carbonyl as the source of carbon monoxide. In this case, milder reaction conditions are possible. Owing to the high cost of acetylene, this route is now of little commercial importance.
(iii) Ethylene route. This route consists of the following sequence:

The addition of hydrogen cyanide to ethylene oxide takes place at 55-60??C in the presence of a basic catalyst such as diethylamine. The reaction is exothermic and is carried out in solution to facilitate control; the solvent is conveniently ethylene cyanohydrin. The reaction mixture is neutralized and ethylene cyanohydrin is separated by distillation. The second stage of the synthesis involves the dehydration and hydrolysis of ethylene cyanohydrin; these reactions are carried out in one step by heating the cyanohydrin with aqueous sulphuric acid at about 175??C. (It is possible, of course, that the intermediate in this conversion may be acrylonitrile, as shown, or P-hydroxypropionic acid or both.) At one time this was the standard route for the preparation of acrylic acid but it has been largely displaced by the more economical propylene route.

General Description

Acrylic acid is a colorless liquid with a distinctive acrid odor. Flash point 130°F. Boiling point 286°F. Freezing point 53°F. Corrosive to metals and tissue. Prolonged exposure to fire or heat can cause polymerization. If polymerization takes place in a closed container, violent rupture may occur. The inhibitor (usually hydroquinone) greatly reduces the tendency to polymerize.

Air & Water Reactions

Flammable. Soluble in water. The presence of water, due to different solubilities of the acid and inhibitor (partitioning one from the other), may initiate polymerization.

Reactivity Profile

ACRYLIC ACID may polymerize violently especially when the frozen acid is partially thawed (freezing point 12°C or 53°F). Frozen acid should be melted at room temperature and the process should be well stirred. Do not use heat during the melting process [Kirk-Othmer, 3rd ed., Vol. 1, 1978, p. 330]. Corrodes iron and steel and polymerization may occur on contact with iron salts. The uninhibited acid polymerizes exothermically at ambient temperature and explodes if confined. The inhibitor (usually hydroquinone) greatly reduces the tendency to polymerize. Explosive polymerization can also occur with strong bases, amines, ammonia, oleum, chlorosulfonic acid, and peroxides. Mixing with 2-aminoethanol, 28% ammonium hydroxide, ethylenediamine or ethyleneimine in a closed container causes an increase in temperature and pressure. Can react violently with oxidizing reagents and strong bases [Bretherick, 5th ed., 1995, p. 419].

Health Hazard

May burn skin or eyes upon short contact. INHALATION: eye and nasal irritation and lacrimation. INGESTION: may cause severe damage to the gastrointestinal tract.

Health Hazard

Acrylic acid is a corrosive liquid that cancause skin burns. Spill into the eyes candamage vision. The vapors are an irritantto the eyes. The inhalation hazard is oflow order. An exposure to 4000 ppm for4 hours was lethal to rats. The oral LD50values reported in the literature show widevariation. The dermal LD50 value in rabbitsis 280 mg/kg.

Fire Hazard

Combustible liquid; flash point (closed cup) 54°C (130°F), (open cup) 68°C (155°F); vapor pressure 31 torr at 25°C (77°F); vapor density 2.5 (air=1); autoignition temperature 360°C (680°F). Vapors of acrylic acid form explosive mixtures with air within the range 2.9–8.0% by volume in air. Fireextinguishing agent: water spray, “alcohol” foam, dry chemical, or CO2; use a water spray to flush and dilute the spill and to disperse the vapors.
Acrylic acid may readily polymerize at ambient temperature. Polymerization may be inhibited with 200 ppm of hydroquinone monomethyl ether (Aldrich 2006). In the presence of a catalyst or at an elevated temperature, the polymerization rate may accelerate, causing an explosion. The reactions of acrylic acid with amines, imines, and oleum are exothermic but not violent. Acrylic acid should be stored below its melting point with a trace quantity of polymerization inhibitor. Its reactions with strong oxidizing substances can be violent.

Flammability and Explosibility

Flammable

Contact allergens

Acrylates are esters from acrylic acid. Occupational contact allergies from acrylates have frequently been reported and mainly concern workers exposed to the glues based on acrylic acid, as well as dental workers and beauticians.

Safety Profile

Poison by ingestion, skin contact, and intraperitoneal routes. An experimental teratogen. Other experimental reproductive effects. A severe skin and eye irritant. Questionable carcinogen with experimental carcinogenic and tumorigenic data. Corrosive. Flammable liquid. May undergo exothermic polymerization at room temperature. May become explosive if confined. A fire hazard when exposed to heat or flame.

Safety

Acrylic acid is severely irritating and corrosive to the skin and the respiratory tract. Eye contact can result in severe and irreversible injury. Low exposure will cause minimal or no health effects, while high exposure could result in pulmonary edema. The LD₅₀ is 340 mg/kg (rat, oral).

Potential Exposure

Acrylic acid is chiefly used in manufacture of plastics, acrylates, polyacrylic acids, polymer, and resins; as a monomer in the manufacture of acrylic resins and plastic products, leather treatment, and paper coatings. Also, it is used as a tackifier and flocculant.

Environmental Fate

Acrylic acid is corrosive, and its toxicity occurs at the site of contact.

Shipping

UN2218 Acrylic acid, stabilized, Hazard class: 8; Labels: 8-Corrosive material, 3-Flammable liquid

Purification Methods

It can be purified by steam distillation, or vacuum distillation through a column packed with copper gauze to inhibit polymerisation. (This treatment also removes inhibitors such as methylene blue that may be present.) Azeotropic distillation of the water with *benzene converts aqueous acrylic acid to the anhydrous material. [Beilstein 2 H 397, 2 I 186, 2 II 383, 2 III 1215, 2 IV 1455.]

Substituents

As a substituent acrylic acid can be found as an acyl group or a carboxyalkyl group depending on the removal of the group from the molecule. More specifically these are :
The acryloyl group, with the removal of the -OH from carbon-1.
The 2-carboxy ethenyl group, with the removal of a -H from carbon-3. This substituent group is found in chlorophyll..

Toxicity evaluation

Acrylic acid’s large-scale use and production results in its release into the environment. The most likely route of exposure is inhalation because acrylic acid has a low vapor pressure. The miscibility of acrylic acid in water combined with its low vapor pressure prevent it from accumulating in the soil. Acrylic acid that is emitted into the atmosphere is degraded photochemically by reaction with hydroxyl radicals. There is no potential for long-range atmospheric transport of acrylic acid because it has an atmospheric lifetime of 1 month.

Incompatibilities

May form explosive mixture with air. Light, heat, and peroxides can cause polymerization. Use MEHQ (monomethyl ether of hydroquinone) as an inhibitor. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Incompatible with sulfuric acid, caustics, ammonia, amines, isocyanates, alkylene oxides; epichlorohydrin, toluene diamine, oleum, pyridine, methyl pyridine, n-methyl pyrrolidone, 2-methyl-6-ethyl aniline, aniline, ethylene diamine, ethyleneimine, and 2aminoethanol. Severely corrodes carbon steel and iron; attacks other metals. May accumulate static electrical charges and may cause ignition of its vapors.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. Incineration. 100 500 ppm potassium permanganate will degrade acrylic acid to a hydroxy acid which can be disposed of at a sewage treatment.