Nitrobenzene process

Nitrobenzene is made by three processes direct nitration, dehydrating nitration and adiabatic nitration. The first process involves the direct nitration of benzene using a mixture of nitric acid and sulfuric acid46,258. 

The sulfuric acid promotes the formation of the nitrating agent (the nitronium ion) and prevents the dissociation of nitric acid into an oxidizing NO3 ion by binding water as a hydrate. It also enhances the solubility between the aqueous and organic phases46. 

This process may be carried out by a batch or a continuous process. The continuous process is more effective for large plants. Both processes wash the crude nitrobenzene with water. The crude nitrobenzene is fed to a distillation system to separate the water, benzene and dinitrobenzene. This process requires reactor cooling and a system for sulfuric acid reconcentration. Yields by the continuous process are 95% to 96% of theoretical. Bayer used this process in the United States until it discontinued nitrobenzene production in 1994258.  

The continuous nitration plant consists of a cascade of stirred vessels (usually three nitrating vessels) with a stepwise, slowly increasing temperature (35 to 40°C in the first vessel, 50°C in the second and 55 to 60°C for the final reaction. The largest units are the final settling and washing vessels46. 

DuPont developed a dehydrating nitration process by which water produced in the mixed acid nitration reaction is removed by humidification of the inert gas stream. This eliminates the energy-intensive sulfuric acid process258. 

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Batch microwave reactors, reactions in, 16 554-555 Batch mixers, 16 721 Batch mononitrotoluene process, 17 265 Batch multipurpose plants, for fine chemical manufacture, 11 427 Batch nitrobenzene process, 17 252 Batch-operated settling tanks, 22 59 Batch pilot plants, 19 458 Batch plants, certified, 20 703 Batch polymerization, of vinyl acetate, 25 608... 

Continuous membrane system, 21 638 Continuous microwave reactors (CMR), reactions in, 16 554 Continuous mixers, 16 722 Continuous nitrobenzene process, 17 252-253, 254... 

The organic reduction process also termed the aniline, laux or nitrobenzene process. This method leads to black, yellow or red pigments. 

This process is used principally in Europe. It was first developed in 1854 for the production of aniline. Nitrobenzene was reduced to aniline using metallic iron, hence the process was termed the aniline or nitrobenzene process. Iron oxides were formed as unusable, grey/black products. Around 1925, Laux found that addition of iron chloride modified the process so that iron oxides suitable for use as pigments could be produced. With this additive alone, magnetite with a high tinting strength results, i. e. 

A modification of the nitrobenzene process, which utilizes nitrobenzene and sulfuric acid simultaneously, is in operation at the Sinclair Refining Co. refinery at Wellsville. N. Y. 

In 1861 Laurent and Castelhaz [8] patented the action of nitrobenzene on iron and hydrochloric acid, and this is evidently the first opening of the nitrobenzene process. In the same year the synthesis of rosolic acid was effected by Kolbe and Schmitt [9]. 

A simplified process flow diagram for aniline by the hydrogenation of nitrobenzene process is illustrated in Figure 4. The flow diagram depicts a vapor phase reactor and hydrogen recycle loop, as well as the essential downstream separation equipment [3]. 

Nitrobenzene Process (37c, 45, 46, 127). Nitrobenzene is both highly selective and fairly soluble with lubricating-oil fractions, and consequently is used at relatively low temperatures (50°F.) and in small amounts (50 to 200 per cent of the feed). The presence of precipitated paraffin wax does... 

Figure 10.50 Aniline is obtained from either nitrobenzene (Process 1), phenol (Process 2), or chlorobenzene (Process 3)...

Nitrations are usually carried out at comparatively low temperatures at higher temperatures there may be loss of material because of the oxidising action of the nitric acid. For substances which do not nitrate readily with a mixture of concentrated nitric and sulphuric acids ( mixed acid ), the intensity of the reaction may be increased inler alia by the use of fuming sulphuric acid (containing up to 60 per cent, of sulphur trioxide) or by fuming nitric acid. Thus nitrobenzene is converted by a mixture of fuming nitric acid and concentrated sulphuric acid into about 90 per cent, of wi-dinitrobenzene and small amounts of the o- and p-isomers the latter are eliminated in the process of recrystallisation ... 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

The argument for the S 2 process, when the transition from acetic acid as solvent to nitric acid as solvent is considered, is less direct, for because of the experimental need to use less reactive compounds, zeroth-order nitration has not been observed in nitric acid. It can be estimated, however, that a substance such as nitrobenzene would react about 10 faster in first-order nitration in nitric acid than in a solution of nitric acid (7 mol 1 ) in acetic acid. Such a large increase is understandable in terms of the S z mechanism, but not otherwise. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

The single-step -duoroaruline [31-40-4] process based on duorodeoxygenation of nitrobenzene (via in situ generation of /V-phenylhydroxyl amine) in anhydrous hydrogen duoride (94—96) has not been commercialized primarily due to concurrent formation of aniline, as well as limited catalyst life. The potential attractiveness of this approach is evidenced by numerous patents (97—101). Concurrent interest has been shown in the two-step process based on /V-phenylhydroxylamine (HF-Bamberger reaction) (102—104). 

The demonstration unit was later transported to the CECOS faciHty at Niagara Falls, New York. In tests performed in 1985, approximately 3400 L of a mixed waste containing 2-chlorophenol [95-57-8] nitrobenzene [98-95-3] and 1,1,2-trichloroethane [79-00-5] were processed over 145 operating hours 2-propanol was used as a supplemental fuel the temperature was maintained at 615 to 635°C. Another 95-h test was conducted on a PCB containing transformer waste. Very high destmction efficiencies were achieved for all compounds studied (17). A later bench-scale study, conducted at Smith Kline and French Laboratories in conjunction with Modar (18), showed that simulated chemical and biological wastes, a fermentation broth, and extreme thermophilic bacteria were all completely destroyed within detection limits. 

The reduction of the nitro group to yield aniline is the most commercially important reaction of nitrobenzene. Usually the reaction is carried out by the catalytic hydrogenation of nitrobenzene, either in the gas phase or in solution, or by using iron borings and dilute hydrochloric acid (the Bechamp process). Depending on the conditions, the reduction of nitrobenzene can lead to a variety of products. The series of reduction products is shown in Figure 1 (see Amines byreduction). Nitrosobenzene, /V-pbenylbydroxylamine, and aniline are primary reduction products. Azoxybenzene is formed by the condensation of nitrosobenzene and /V-pbenylbydroxylamine in alkaline solutions, and azoxybenzene can be reduced to form azobenzene and hydrazobenzene. The reduction products of nitrobenzene under various conditions ate given in Table 2. 

In the last few years several modifications to the traditional mixed acid nitration procedure have been reported. An adiabatic nitration process was developed for the production of nitrobenzene (9). This method eliminated the need to remove the heat of reaction by excessive cooling. The excess heat can be used in the sulfuric acid reconcentration step. An additional advantage of this method is the reduction in reaction times to 0.5—7.5 minutes. 

For the process step involving handling of spent sulfuric acid, several patents have been issued in which improvements in this step were a main claim. The azeotropic nitration of benzene essentially eliminates the need to reconcentrate sulfuric acid (10,11). The nitration step is carried out at higher than usual temperatures (120—160°C). Because excess benzene is used, the higher temperature allows water to be removed as a water—benzene azeotrope. The water is separated and the benzene phase, containing approximately 8% nitrobenzene, is recycled back into the reactor. The dry sulfuric acid is then reused continuously. 

Another concentration method involves passing an inert gas such as N2 or CO2 through the reaction medium (12). As the gas passes through, it becomes humidified and carries captured water with it. Most of the energy required for the gas humidification comes from the heat of reaction. An advantage is that expensive drying equipment is not needed. Also, the sulfuric acid mist formed in typical concentrators is minimized. Du Pont uses a similar process in its nitrobenzene production faciUty. 

Environmental aspects, as well as the requirement of efficient mixing in the mixed acid process, have led to the development of single-phase nitrations. These can be divided into Hquid- and vapor-phase nitrations. One Hquid-phase technique involves the use of > 98% by weight nitric acid, with temperatures of 20—60°C and atmospheric pressure (21). The molar ratios of nitric acid benzene are 2 1 to 4 1. After the reaction is complete, excess nitric acid is vacuum distilled and recycled. An analogous process is used to simultaneously produce a nitrobenzene and dinitrotoluene mixture (22). A conversion of 100% is obtained without the formation of nitrophenols or nitrocresols. The nitrobenzene and dinitrotoluene are separated by distillation. 

Economic Aspects. The two main areas affecting the economic aspects for nitrobenzene production are process related costs, including raw ... 

Manufacture and Processing. Mononitrotoluenes are produced by the nitration of toluene in a manner similar to that described for nitrobenzene. The presence of the methyl group on the aromatic ring faciUtates the nitration of toluene, as compared to that of benzene, and increases the ease of oxidation which results in undesirable by-products. Thus the nitration of toluene generally is carried out at lower temperatures than the nitration of benzene to minimize oxidative side reactions. Because toluene nitrates at a faster rate than benzene, the milder conditions also reduce the formation of dinitrotoluenes. Toluene is less soluble than benzene in the acid phase, thus vigorous agitation of the reaction mixture is necessary to maximize the interfacial area of the two phases and the mass transfer of the reactants. The rate of a typical industrial nitration can be modeled in terms of a fast reaction taking place in a zone in the aqueous phase adjacent to the interface where the reaction is diffusion controlled. 

Solvent Treatment. Solvent processes can be divided into two main categories, solvent extraction and solvent dewaxing. The solvent used in the extraction processes include propane and cresyHc acid, 2,2 -dichlorodiethyl ether, phenol (qv), furfural, sulfur dioxide, benzene, and nitrobenzene. In the dewaxing process (28), the principal solvents are benzene, methyl ethyl ketone, methyl isobutyl ketone, propane, petroleum naphtha, ethylene dichloride, methylene chloride, sulfur dioxide, and iV-methylpyrroHdinone. 

The second process to finish phthalocyanine, which is more important for P-copper phthalocyanine, involves grinding the dry or aqueous form in a ball mill or a kneader (64). Agents such as sodium chloride, which have to be removed by boiling with water after the grinding, are used. Solvents like aromatic hydrocarbons, xylene, nitrobenzene or chlorobenzene, alcohols, ketones, or esters can be used (1). In the absence of a solvent, the cmde P-phthalocyanine is converted to the a-form (57,65) and has to be treated with a solvent to regain the P-modification. The aggregate stmcture also has an impact on the dispersion behavior of a- and P-copper phthalocyanine pigments (66). 

The Faux process is a modification of the Bechamp reaction that was discovered in 1854. It has been used for the reduction of nitrobenzene to aniline using metallic iron ... 

Aromatic amines can be produced by reduction of the corresponding nitro compound, the ammonolysis of an aromatic haUde or phenol, and by direct amination of the aromatic ring. At present, the catalytic reduction of nitrobenzene is the predominant process for manufacture of aniline. To a smaller extent aniline is also produced by ammonolysis of phenol. 

In another process variant, only 88% of the nitrobenzene is reduced, and the reaction mixture then consists of two phases the precious metal catalyst (palladium on activated carbon) remains in the unreacted nitrobenzene phase. Therefore, phase separation is sufficient as work-up, and the nitrobenzene phase can be recycled direcdy to the next batch. The aqueous sulfuric acid phase contains 4-aminophenol and by-product aniline. After neutralization, the aniline is stripped, and the aminophenol is obtained by crystallization after the aqueous phase is purified with activated carbon (53). 

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