Chemical Associates

Monochloroacetic acid

CAS Number 79-11-8
EC Number 607-003-00-1
UN Number 1751

Monochloroacetic Acid

Global production of Monochloroacetic acid (MCAA or chloroacetic acid) exceeds 500,000te/yr. MCAA is of great value in organic chemical synthesis because of the ease of substitution of its chlorine atom and its acidity.

This note briefly describes its uses, its key properties, its environmental impact, discusses its manufacturing technology and lists the world’s main producers.

MCAA manufacturers in Europe, the USA, Japan and at Akzo’s new plant in China use sophisticated modern technology. Producers in Eastern Europe, China and India have smaller plants using more basic technology and supplying a cheaper product. Most purify the product by crystallization which tends to limit the final product purity. The obstacle to their adopting hydrodehalogenation and the latest crystallization technology is the high cost of the catalyst, the availability of hydrogen and the need for expensive materials of construction. Making these large investments would compromise their low prices but would improve the purity of their product and the security of their supply. Thus there is scope for a limited number of companies in India and China making the investment in more modern worldscale technology, as Akzo have done at Taixing. CABB have taken a step in this direction by purchasing a majority stake in Karnavati's MCAA Plant in India

1) USES OF MONOCHLOROACETIC ACID ¹

The major industrial use of monochloroacetic acid (MCAA), accounting for 30-40% of its production, is in the manufacture of Carboxymethyl cellulose (CMC). The sodium salt of CMC is made by reacting starch with MCAA in a strongly alkaline NaOH medium. The MCAA is usually used as an 80% solution. MCAA will react with other hydroxyl containing polysaccharides but these reactions are less important.

MCAA is used to make the important arylhydroxyacetic acid, methyl ß-napthyloxyacetate and benazoline based herbicides, as well as the insecticides dimethoate, 2,4-dichlorophenoxyacetic acid (2,4-D) and dimethoate. MCAA is also used to make glycophosate, the increasingly popular non-selective herbicide.

Glycolic acid (and diglycolic acid) is prepared industrially by heating MCAA with an alkali hydroxide. Glycolic acid is used in textile printing, leather treatments and cleaners. Glycolic acid esters are used to make plasticizers.

Heating MCAA with sodium or potassium hydrogen sulphide gives thioglycolic acid. Thioglycolic acid and its derivatives are used in the production of hair cosmetics. The use of tin alkyl thioglycolates are increasing in importance as they replace more toxic lead based PVC thermal stabilizers.

MCAA is used to make surfactants, particularly mild bentine amphoteric surfactants.

Because of its reactivity, MCAA is widely used in many other organic syntheses. It reacts with alcohols to give alkoacetic acids. With ammonia and amines it gives a-amino acids and phenyl glycine. With alkali cyanides it is used to make cyanoacetic acid and then by saponification, malonic acid. Finally it reacts with phenols to give phenoxyacetic acid.

MCCA is used to make caffeine, barbituric acid, chloroacetyl chloride.

The sodium salt, sodium chloroacetate, is easier to handle and can be used in place of the more hazardous parent acid. It is a made by reacting MCAA with sodium carbonate or hydroxide. It is sold as a solid, often as prills.

2) PROPERTIES ¹

Monochloroacetic acid (MCAA) is a white crystalline hydroscopic solid of density 1.58 (liquid density 1.37) with a pungent odour.

Its formula is CH₂Cl·COOH with a mol wt of 94.5. CAS Number 79-11-8.MCCA melts at 62°C and boils at 189°C. It exists in a number of other less stable crystalline forms which melt at 44-56°C. It is very soluble in water (81g/100g water at 20°C), alcohols, acetone and ether but not in hydrocarbons and chlorinated hydrocarbons.

It is very corrosive and toxic. Thus it requires careful handling in corrosion resistant equipment and containers. It thermally decomposes >250°C. It has a flash point of 126°C and a lower explosion limit in air of 8%.

Commercially it is supplied as a solid or as an 80% solution in water or alcohols. Its sodium salt is supplied as a solid.

3) TOXICITY AND ENVIRONMENTAL ²

MCAA is very hazardous; very toxic (LD50 (oral rats) 75-300mg/kg) and corrosive. It is non carcinogenic.

It will burn the skin and is rapidly absorbed, often with fatal consequences. It will irritate and can permanently damage the eyes. It is toxic by ingestion. Thus personnel contact must be avoided. Personnel handing it should be aware of its dangers and wear the appropriate protective clothing. This would include chemical goggles and full face mask and clothing to prevent skin contact

It is very toxic to animals, plants and aquatic organisms. MCAA must be treated before disposal and should not be added directly to sewage systems, rivers and lakes.

Small quantities of MCAA are found uniformly throughout the natural environment, suggesting it is also produced naturally. Because of its solubility in water it is usually found in aqueous environments such as water courses, damp soil and in rain. It does not absorb onto particles of soil and does not bioaccumulate. It is biodegradable.

4) MANUFACTURE

MCAA is manufactured industrially by two main routes, the most important being direct chlorination of acetic acid.

Chlorination of Acetic Acid:

Chlorine is bubbled through acetic acid at a temperature of ~120°C and a pressure of ~4 bar, in the presence of acetic anhydride as a catalyst. The reaction is exothermic and needs to be cooled.

A typical mass balance is:

MCAA 1000 kg
Acetic Acid 600 kg
Chlorine 750 kg
Acetic anhydride 50 kg

A schematic flow diagram of a modern Industrial Chlorination Plant can be seen in Fig 1.

FIG 1. SCHEMATIC FLOW DIAGRAM OF CONTINUOUS MCAA PRODUCTION PLANT

Chlorination is carried out batch wise or on more modern plants, continuously. HCl and the acetic anhydride are recycled.

Small amounts (~6%) of by-product dichloroacetic acid (DCAA) and HCl are also produced. A number of older patents claim the use of additives to improve the selectivity for MCAA but it not clear whether they are still used commercially ¹.

The product from the chlorinator is a liquid melt containing mainly MCA, and up to 10% DCA with some acetic acid and water. While this is acceptable for technical grades, most applications require a purer product (>99.5% MCAA). There are a number of ways of purifying the crude melt.

Hydrogenation converts most of the DCAA back to MCAA and generates by-product HCl. Hydrogen gas is mixed with the crude MCAA melt or vapour in the presence of a palladium catalyst on carbon at 120-140°C at pressures of 2-4 barg. The vapour phase reaction gives better yields and a higher purity product but requires more energy. The reaction is usually carried out continuously in a column but can be done batch-wise in a stirred tank. Care must be taken not to convert MCAA back to AA. Aldehydes can form which colour the MCAA. Akzo have patented a process to removal aldehydes by oxidation with peroxycarboxylic acids ³.

Distillation is carried out in two stages. One removes volatile acetic acid (Bpt 118°C) and acetic anhydride (Bpt 140°C) which are returned to the chlorinator. Then pure MCAA is evaporated and is sent to product recovery.

Akzo have patented a reactive distillation process ⁴ which they claim gives better control over chlorination, reducing the formation of DCA and is a more effective way of recycling the acetic anhydride/acetyl chloride catalyst.

The MCAA can also be purified by crystallisation from the melt or solution. A number of solution technologies have been patented involving crystallization from water or chlorinated solvents but it is not known whether they are in commercial use ⁵. The difficulty with melt crystallization is the recovery of a handleable solid from the concentrated melt and its separation from the mother liquor. Hoechst (now CABB) have patented the use of stationary cold finger crystallisers coated with polyolefins to prevent corrosion ⁶,⁷. Sulzer offer more sophisticated Fractional Crystallisation Technology which is known to be in use in the USA. It involves an additional “sweating cycle” to further purify the acid ⁸. The MCAA crystals which form on the stationary fingers are removed by melting. Alternatively the melt could be crystallized in a stirred crystalliser and the small crystals removed by centrifugation. The mother liquor (containing ~30% MCAA, ~40% DCAA, water and acetic acid) is recovered and can be used to make DCAA and TCAA.

Most western MCAA producer’s use hydrogenation to dehalogenate the DCAA and then distill the crude melt. This gives a product containing >99.5% MCAA. Some also crystallize the hydrogenated melt to improve its purity still further. Many of the Indian and Chinese producers do not hydrogenate the melt, but purify it by crystallization, which limits its purity to 98-99.5% MCAA. Some manufactures sell by-product mother liquid containing ~30% MCAA, ~40% DCAA to manufacturers of DCAA and TCAA.

MCA is sold as a crystalline or flaked solid. It is also sold as an 80% solution in water (Fpt ~17°C) or in methanol (Fpt -20°C) or ethanol. CMC manufactures tend to use 80% aqueous solutions.

Condensable gases are returned to the chlorinator. Non condensable waste gases (HCl) are treated before venting to the atmosphere. This can involve absorption by alkalis. 32% HCl solution is recovered and used elsewhere.

Akzo recently closed their Hengelo Plant in the Netherlands and moved its production to Delfzijl. The Delfzijl Site manufactures chlorine using the latest membrane technology. Chlorine is delivered directly to the MCAA Plant by pipeline and by-product hydrogen is available from the chlorine plant. This avoids the need for road transport of hazardous chemicals.

Hydrolysis of Trichloroethylene:

Equal amounts of trichloroethylene (TCE) and 75 % sulfuric acid are heated to 130 –140 °C:

A mixture of TCE and H2SO4 is continuously fed into the base of the reactor. The overflow contains approximately 50% MCAA and H₂SO₄. It is vacuum distilled to give pure MCAA and the H2SO4 is recycled. The resultant hydrogen chloride gas is washed with fresh trichloroethylene and then purified by freezing and absorbing in water.

A typical mass balance is:

MCAA 1000 kg
Trichloroethylene 1650 kg
H₂SO₄ 95% 600 kg
HCl by-product 700 kg

The trichloroethylene method produces highly pure MCAA free of DCAA or TCAA. Despite the purity of the MCA, this method is less popular because of the high cost of trichloroethylene and the large amount of by-product HCl. However, it is still believed to be used on an industrial scale in several countries (Former States of USSR, Romania, Macedonia, Japan, etc.).

Sodium Chloroacetate:
Sodium chloroacetate Is made by reacting MCAA with alkali sodium salts. The product can be spray dried or granulated.

5) GLOBAL PRODUCERS

MCAA is manufactured in Europe, the USA, India, China and Japan. Table 1 lists the key manufacturers.

Akzo manufactures MCAA in a number of countries, with plants in Europe (the Netherlands and Sweden), China and in Japan with Danak, a 50/50 JV with Denki. They also have a plant in Alabama, USA, which prepares MCAA solutions, from imported acid. The other major European Manufacturer is CABB (the ex Hoechst and Clariant Plants) in Germany. CABB, the world's largest producer, has recently purchased a majority stake in India's Karnavati and intends to double its output. There are smaller plants in Spain, Poland, Hungary, Romania and Russia but details are sketchy. There is some evidence that new plants are being built in Poland and Russia to replace older more polluting factories. According to reports these are due to come on steam in 2009. In 2005 Arkema closed their 45,000te/yr plant in St Auban, France, helping to balance the previous production surplus in Europe.

The two US manufacturers are Dow and Niacet. Dow only sells MCAA in solution to approved customers for product stewardship reasons, because of the hazardous nature of the acid. Production in the USA is relatively small and they are thought to import ~50% of their requirements, most of which comes from Germany and Holland.

In addition to Danak (Akzo JV), MCAA is made in Japan by Diacel Industries.

There are many manufactures of MCAA in India and China, some of which are very small. In 2004 China consumed 200,000te/yr of MCAA, approximately 70,000te of which was used to make pesticides and 16,000te pharmaceuticals. In 2007 these figures are expected to rise to 300,000te/yr, 100,000te and 24,000te respectively. Imports of MCAA into China are less than 10,000te/yr and thus it is reasonably self sufficient.

Atanor has a MCAA Plant in Rio Tercero, Argentina.

Table 1 lists some of these producers but it is not complete and might contain some inaccuracies.

Historically a number of MCAA producers used the acid to make CMC in-house. However these plants have closed (Hopewell, Virginia, USA and Metsa Serla, Finland) and they now obtain MCAA on the open market. A number of the Chinese and Indian producers use the acid for the in-house production of pharmaceutical intermediates and pesticides, which form their main lines of business.

Manufacturers in Europe, the USA, Japan and Akzo in China use sophisticated modern technology. Producers in Eastern Europe, China and India have smaller plants using more basic technology and supply a cheaper product. Most purify the product by crystallization which tends to limit the final product purity. The obstacle to their adopting hydrodehalogenation and latest crystallization technology is the high cost of the catalyst, the availability of hydrogen and the need for expensive materials of construction. Making these large investments would compromise their low prices but would improve the purity of their product and the security of their supply. Thus there is scope for one or two companies in India and China making the investment in more modern worldscale technology, as Akzo have done at Taixing.

Table 1. MCAA MANUFACTURERS.

If you require further information or have any comments, email us using the enquiry form on our contact page

6) REFERENCES

1. "Chloroacetic Acids", Koenig, G, Lohmar, E and Rupprich, N in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co., 2000.
2. European Risk Assessment Report Monochloroacetic Acid (MCAA), Chemical Substances Bureau, The Netherlands 2005.
3. US Patent Application US 2005/0148794.
4. US Patent Application US 2005/0272953.
5. US Patent US 4 383 121
6. GB Patent GB 1 275 231
7. US Patent US 5 756 840
8. http://www.sulzerchemtech.com