Maleic anhydride

Maleic anhydride is an organic compound with the formula C₂H₂(CO)₂O. It is the acid anhydride of maleic acid. It is a colorless or white solid with an acrid odor. It is produced industrially on a large scale for applications in coatings and polymers.^[5]

Production

Maleic anhydride is produced by vapor-phase oxidation of n-butane. The overall process converts the methyl groups to carboxylate and dehydrogenates the backbone. The selectivity of the process reflects the robustness of maleic anhydride, with its conjugated double-bond system. Traditionally maleic anhydride was produced by the oxidation of benzene or other aromatic compounds. As of 2006, only a few smaller plants continue to use benzene.

In both cases, benzene and butane are fed into a stream of hot air, and the mixture is passed through a catalyst bed at high temperature. The ratio of air to hydrocarbon is controlled to prevent the mixture from igniting. Vanadium pentoxide and molybdenum trioxide are the catalysts used for the benzene route, whereas vanadium phosphate is used for the butane route:^[5]

C₄H₁₀ + 3.5 O₂ → C₂H₂C₂O₃ + 4 H₂O ∆H = -1236 kJ/mol

The main competing process entails full combustion of the butane, a conversion that is twice as exothermic as the partial oxidation.

Industrial production of maleic anhydride is achieved by integration of following unit processes: catalyst packed bed reactor, adsorption tower, maleic acid reactor, distillation column. The reactant stream of n-butane and air mixture enters the packed bed reactor at a temperature of 120-150 °C and a pressure of 2-3 atm. The product stream is then sent to a packed bed adsorption column, where the condensable maleic anhydride reacts with the water stream to give maleic acid and the non-condensable are sent for fuel gases treatment. The condensable stream from adsorption tower is sent to a maleic acid reactor, where maleic acid is again converted back to the anhydride. This product stream from reactor is sent to distillation column to obtain pure maleic anhydride as product.

The traditional method using benzene became uneconomical due to the high and still rising benzene prices and by complying the regulations of benzene emissions. In addition, in the production of maleic anhydride (4 C-atoms) a third of the original carbon atoms is lost as carbon dioxide when using benzene (6 carbon atoms). The modern catalytic processes start from a 4-carbon molecule and only attaches oxygen and removes water; the 4-C-base body of the molecule remains intact. Overall, the newer method is therefore more material efficient.^[6]

Parallels exist with the production of phthalic anhydride: While older methods use naphthalene, modern methods use o-xylene as feedstock.

Reactions

The chemistry of maleic anhydride is very rich, reflecting its ready availability and bifunctional reactivity. It hydrolyzes, producing maleic acid, cis-HOOC–CH=CH–COOH. With alcohols, the half-ester is generated, e.g., cis-HOOC–CH=CH–COOCH₃.

Maleic anhydride is a classic substrate for Diels-Alder reactions.^[7] It was used for work in 1928, on the reaction between maleic anhydride and 1,3-butadiene, for which Otto Paul Hermann Diels and Kurt Alder were awarded the Nobel Prize in 1950. It is through this reaction that maleic anhydride converted to many pesticides and pharmaceuticals.

In 1979 a patent was granted to Lever Brothers for the Michael reaction of maleic anhydride with active methylene or methine compounds such as malonate or acetoacetate esters in the presence of sodium acetate catalyst. These intermediates were subsequently used for the generation of the Krebs cycle intermediates aconitic and isocitric acids.^[8]

Maleic anhydride dimerizes in a photochemical reaction to form cyclobutane tetracarboxylic dianhydride (CBTA). This compound is used in the production of polyimides and as an alignment film for liquid crystal displays.^[9]

It is also a ligand for low-valent metal complexes, examples being Pt(PPh₃)₂(MA) and Fe(CO)₄(MA).

Uses

Around 50% of world maleic anhydride output is used in the manufacture of unsaturated polyester resins (UPR). Chopped glass fibers are added to UPR to produce fibreglass reinforced plastics which are used in a wide range of applications such as pleasure boats, bathroom fixtures, automobiles, tanks and pipes. However, the UPR market reflects general economic conditions as it is tied to the construction, automobile and marine industries.

The production of 1,4-butanediol (BDO) is also having an impact on the maleic anhydride market. BDO is one of the world’s fastest growing chemicals used in the production of thermoplastic polyurethanes, elastane/Spandex fibers, polybutylene terephthalate (PBT) resins and many other products. However, BDO is made from a crude maleic anhydride which is not traded and only used for this application.

Another market for maleic anhydride is lubricating oil additives, which are used in gasoline and diesel engine crankcase oils as dispersants and corrosion inhibitors. Changes in lubricant specifications and more efficient engines have had a negative effect on the demand for lubricating oil additives, giving flat growth prospects for maleic anhydride in this application.

There are a number of smaller applications for maleic anhydride. The food industry uses maleic anhydride in artificial sweeteners and flavour enhancements. Personal care products consuming maleic anhydride include hair sprays, adhesives and floor polishes. Maleic anhydride is also used in water treatment chemicals, detergents, insecticides and fungicides, pharmaceuticals and copolymers.

Major producers

Company	Location	Capacity (KMT/Year)
Bartek Ingredients Inc.	Canada	28
Sasol-Huntsman	Germany	105
DSM NV	The Netherlands	00
Flint Hills Resources LP	USA	50
Huntsman Corporation	USA	155
Huntsman Performance Products	USA	00
Lanxess Corporation	USA	75
Lonza Group AG	Switzerland	00
Marathon Petroleum Company LLC	USA	55
Mitsubishi Chemical Corporation	Japan	32
Mitsui Chemicals, Inc	Japan	33
Mitsui Chemicals Polyurethanes, Inc.	Japan	00
Nippon Shokubai Co., Ltd	Japan	35
NOF Corporation	Japan	12
Polynt SpA	Italy	96
Suzhou Synthetic Chemical Co, Ltd.	China	15

Source: Kirk & Othmer

Solid State Chemicals, Ltd. started production of solid maleic anhydride pastilles in the USA in 2014.

World Maleic Anhydride Capacity By Region
Data in: kilotonnes per annum

Region	2002	2012	2015 (KMT/Year)
North America	235	311	370
South & Central America	44	41	46
Western Europe	168	456	307
Central & Eastern Europe	64	58	60
Asia	315	483	1864
Africa	10	10	14
Total	836	1359	2771

Source: Kirk & Othmer

Packing and transport

Liquid maleic anhydride is available in road tankers and/or tank-containers which are made of stainless steel, which are insulated and provided with heating systems to maintain the temperature of 65-75 °C. Tank cars must be approved for the transport of molten maleic anhydride.

Liquid/molten maleic anhydride is a dangerous material in accordance with RID/ADR.

Solid maleic anhydride pastilles are transported by transport trucks. Packaging is generally in 25 kg polyethylene bags.

Storage

Requirements for storage buildings
- Local exhaust systems to take vapours away from the places of emission, and general ventilation in rooms.
- Protection against static charges.
- Impervious floor which makes it possible to collect the spilled material and which prevents its entry to the sewage system.
- Storage rooms should be cool and dry.
Storage conditions
- Keep ignition sources away - do not smoke. Product dust may form explosive air-dust mixtures.
- Keep humidity away from storage rooms.
- Keep containers tightly closed. Store them in cool, dry and well ventilated places.
- Tanks / containers must be properly marked.
- Hand-operated / portable fire-fighting equipment should be available in storage rooms.
- Neutral gas blanketing is required inside storage tanks.

Effects on human health and the environment

This compound poses relatively low-risk environmental hazards, an important feature for some applications. In humans, exposure to maleic anhydride may cause irritation to the respiratory tract, eyes, exposed mucosa, and skin. Maleic anhydride is also a skin and respiratory sensitizer.^[10]

Maleic anhydride is a low hazard profile chemical. Maleic anhydride rapidly hydrolyzes to form maleic acid in the presence of water and hence environmental exposures to maleic anhydride itself are unlikely. Maleic acid is biodegradable under aerobic conditions in sewage sludge as well as in soil and water.

Food starch for use in night markets sold from a supplier in Tainan city, Taiwan, were found to contain maleic anhydride in December 2013. The supplier was investigated regarding the 300 tons of tainted starch; an earlier inspection in November had found 32 tons.^[11]

References

↑ Merck Index, 11th Edition, 5586.
1 2 Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 835. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
1 2 3 4 5 6 7 "NIOSH Pocket Guide to Chemical Hazards #0376". National Institute for Occupational Safety and Health (NIOSH).
↑ "Maleic anhydride". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
1 2 Kurt Lohbeck; Herbert Haferkorn; Werner Fuhrmann; Norbert Fedtke (2005), "Maleic and Fumaric Acids", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a16_053
↑ Bertram Philipp, Peter Stevens: Grundzüge der Industriellen Chemie, VCH Verlagsgesellschaft mbH, 1987, S. 179, ISBN 3-527-25991-0.
↑ Samuel Danishefsky; Takeshi Kitahara & Paul F. Schuda (1983). "Preparation and Diels-Alder Reaction of a Highly Nucleophilic Diene: trans-1-Methoxyl-3-Trimethylsiloxy-1,3-Butadiene and 5β-Methoxycyclohexan-1-one-3β,4β-Dicarboxylic acid Andhydride". Org. Synth. 61: 147.
↑ US 4146543 E.Gutierrez
↑ Horie, T.; Sumino, M.; Tanaka, T.; Matsushita, Y.; Ichimura, T.; Yoshida, J. I. (2010). "Photodimerization of Maleic Anhydride in a Microreactor Without Clogging". Organic Process Research & Development. 14 (2): 100128104701019. doi:10.1021/op900306z.
↑ "Substance Evaluation Report: Maleic anhydride" (PDF). Environment Agency Austria.
↑ "Tainted starch found in Tainan yet again". Want China Times. 2013-12-19.

External links

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