Aniline production

MDI [4,4 -methylenebis (phenylisocyanate)] has been the driving force behind the recovery of the aniline business since 1982 when the industry had a capacity utilization rate of less than 50%. By 1996, capacity utilization had approached 95% in some regions138. 

Aniline s global production capacity in 1999 was 2.9 million tonnes, and demand in 2000 was estimated to be 2.68 million tonnes per year. The capacity in 1999 was found in these regions Western Europe - 47%, North America -30% and Asia / Pacific -19%140,256. In 2000 China had over 20 aniline producers with a total capacity that exceeded 200,000 tonnes per year. Aniline production in 1999 in China was 142,700 for a utilization rate of around 70%. Historical production in the United States is summarized in Table 20.2255. 

Demand equals production plus imports minus exports. 

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Figm 20.2. Ardlme production process emmonolysis of phenol 

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Baltrop and Bunce (Ref 20) employed a variety of radiation wavelengths, nitrocompds and solvents. For wavelengths less than 2900A, aniline was the main product, while above 2900A, bimolecular species such as azobenzene predominated. Since oxygen had little effect on aniline production, expts were performed in the presence of oxygen. For nitrobenzene in isopropyl alcohol, no azoxybenzene was produced as with Hurley and Testa (See above Ref 17). They concluded that the excited state abstracts H-atoms, and suggest that the nitrobenzene triplet is in tt, ti, and that nitrosobenzene is an unobserved intermediate... 

The product is free from secondary aniline product on the basis of infrared and n.m.r. proton analysis. If equimolar amounts of aniline and phosphate are employed, the product is obtained in a higher yield (12.3 g., 65%), but it contains a trace of w-trifluoromethyl-N-methylaniline as detected by infrared analysis. This secondary aniline is readily removed by heating the product to reflux with 1 ml. of acetic anhydride followed by... 

The hydrogenation of nitrobenzene progressed to aniline without any significant by-product formation, only trace amounts of azobenzene were formed (< 1 %) as the reaction went to completion. NMR analysis showed no detectable phenyl hydroxylamine in solution. The hydrogen uptake displayed a smooth curve and the rate of hydrogen consumption coincided with the rate of aniline production. The rate of hydrogenation of nitrobenzene to aniline was 15.5 mmol.mm. g. ... 

In the hydrogenation of azobenzene, the rate of hydrogen consumption followed a smooth curve. The reaction profile showed a direct transformation to aniline with no by-product formation or intermediates detected. The rate of aniline production (8.3 mmol.min. g ) was half the rate of nitrobenzene to aniline. 

At pH >11, aniline production occurs via the anionic carbinolamine only and the overall reaction is first-order in hydroxide ion. At pH 8-10, the path via the carbinolanine gives a constant rate of hydrolysis and at pH 5.5-7 aniline arises solely through the neutral carbinolanine, present in its largest amounts. Eventually, acid catalysis leads to an increase in the rates of hydroly-... 

The reaction of ammonia and phenol is also being used for aniline production. 

Fluorobenzene with ammonia leads only to the formation of aniline+. However, the TOF mass spectra also exhibit signals due to protonated and unprotonated ammonia clusters which must be produced by dissociative electron transfer (dET). In this case, direct evidence for a 1-2 precursor for the aniline+ product with three competing channels is provided ... 

Nitrobenzene Nitrobenzene is made by the direct nitration of benzene with nitric/sulfuric acid mixtures primarily for aniline production. And aniline is a raw material for the manufacture of methylene diphenyl diisocyanate (MDI) that is used to make rigid foams. 

The primary aniline production process in the world is the hydrogenation of nitrobenzene. BASF, DuPont, ChemFirst (purchased by DuPont in 2002) and Rubicon use this process in the United States. This technology is also used by all Western European aniline producers and all but one Japanese aniline producer. 

Figure 20.1. Aniline production process hydrogenation of nitrobenzene...

In 2000, the aniline production in the United States was about 1.9 billion lb. Almost 98 percent of nitrobenzene is used for the production of aniline. Consequently many nitrobenzene plants are integrated with facilities for aniline production. The hydrogenation of nitrobenzene can be done in either the vapor over a copper-silica catalyst or in liquid phase over platinum-palladium catalyst. One of the smaller uses for nitrobenzene is the production of the pain reliever, acetaminophen. 

Aniline can also be made by two other methods. In the first, nitrobenzene is reduced by reaction with scrap iron in the presence of a hydrochloric acid catalyst. The iron is oxidized to the ferrous state, and the coproduct aniline is separated. This route accounts for less than 5 percent of the current aniline production. The other process avoids nitrobenzene entirely and involves the vapor-phase ammonolysis of phenol, using an alumina catalyst. Aniline is formed with dipheny-lamine as a by-product. About 20 percent of the aniline is produced by this route. 

Other aniline uses and the percent of worldwide aniline production that goes into these uses are rubber-processing chemicals (9%), dyes and pigments (2%), agricultural chemicals (3%), specialty fibers (1%), and miscellaneous, such as explosives, epoxy curing agents, and pharmaceuticals (1%).138,255... 

Stream 10 Overheads Containing Aniline Product Stream 11 Bottoms Containing Tar... 

The reaction conditions are optimized to achieve essentially quantitative yields and the reactor effluent is MNB-free. The reactor product is sent to a dehydration column to remove the water of reaction followed by a purification column to produce high-quality aniline product. 

Intermolecular Nucleophilic Substitution with Heteroatom Nucleophiles. A patent issued in 1965 claims substitution for fluoride on fluorobenzene-Cr(CO)3 in dimethyl sulfoxide (DMSO) by a long list of nucleophiles including alkoxides (from simple alcohols, cholesterol, ethylene glycol, pinacol, and dihydroxyacetone), carboxylates, amines, and carbanions (from triphenyhnethane, indene, cyclohexanone, acetone, cyclopentadiene, phenylacetylene, acetic acid, and propiolic acid). In the reaction of methoxide with halobenzene-Cr(CO)3, the fluorobenzene complex is ca. 2000 times more reactive than the chlorobenzene complex. The difference is taken as evidence for a rate-limiting attack on the arene ligand followed by fast loss of halide the concentration of the cyclohexadienyl anion complex does not build up. In the reaction of fluorobenzene-Cr(CO)3 with amine nucleophiles, the coordinated aniline product appears rapidly at 25 °C, and a carefiil mechanistic study suggests that the loss of halide is now rate limiting. 

Zeolite Base Conversion of aniline (%) Product selectivity (mol %) ... 

C. An Example in Reaction-Based Hazard Identification Aniline Production. . . 217... 

Spandex stretch fiber, based on polyurethanes, was developed by DuPont and appeared in 1962. From this time, polyurethanes would account for the greater part of demand for anilines. Aniline production alone had more than doubled, to over 100 million lbs. per year, between 1939 and 1957, in part to satisfy demand in products other than dyes. Half the US output was consumed in the production of rubber additives, mainly diphenylamine and cyclohexylamine, the latter used as a chain stopper in manufacture of polyurethanes (also as a boiler water additive and, in the US until banned in 1970, in the manufacture of cyclamate sweeteners). Other polymers, such as epoxy resins, relied on the bulk availability of various aromatic amines (Chapter 14). 

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