USES OF NITRIC ACID

Some of the uses for nitric acid are listed below. 

Nitric acid is used by the steel industry to remove surface oxides (pickling) of stainless steels, to brighten and clean surfaces after salt-bath descaling and to prepare stainless steel surfaces for corrosion resistance (passivation). 

Nitric acid pickling is generally restricted to low-carbon stainless steels of the 200 (nickel-chrome-manganese), 300 (nickel-chrome) and 400 (chrome) series. 

The amount of acid used per ton of stainless steel varies widely, depending on the surface area per unit weight, the temperature of the treated surface, the pretreatment conditions (annealing and rolling temperatures) and the grade of the stainless steel. Industry estimates vary widely, ranging from about 5 to 50 pounds of nitric acid consumed per tome of stainless steel produced. 

Nitric acid may also be used to treat surfaces of nickel and chrome alloys, in metal etching and in treatment of refractory metals such as zirconium. 

The main use of nitric acid is in the preparation of inorganic and organic nitrates. It is also rapidly replacing sulphuric acid in the acid treatment of phosphate. Its uses are shown in Table 3.9. Because of its efficient production from increasingly inexpensive ammonia it has become one of the most economically valuable acids. In combination with ammonia it is readily converted to ammonium nitrate. 

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Ammonia and nitric acid are the two basic ingredients in the manufacture of ammonium nitrate. In addition to consuming ammonia directly, the manufacture of ammonium nitrate consumes ammonia by way of nitric acid production. The largest single use of nitric acid is that of ammonium nitrate production (see Ammonium compounds). Urea (qv) is manufactured by reacting ammonia and carbon dioxide. Urea manufacturing faciHties are often located close to ammonia plants. 

Nitric acid is one of the most used chemicals. The 1994 U.S. production was approximately 17.65 hillion pounds. It is a colorless to a yellow liquid, which is very corrosive. It is a strong oxidizing acid that can attack almost any metal. The most important use of nitric acid is to produce ammonium nitrate fertilizer. 

Uses of Nitric Acid. The primary use of nitric acid is for the production of ammonium nitrate for fertilizers. A second major use of nitric acid is in the field of explosives. It is also a nitrating agent for aromatic and paraffinic compounds, which are useful intermediates in the dye and explosive industries. It is also used in steel refining and in uranium extraction. 

In critical applications, if stainless steel is to be used near its limit (in terms of corrosion), and for cases such as welds, where a good finish cannot be otherwise achieved, additional passivation is required. Nitric acid (10-15 per cent by volume) is the best passivator. It also dissolves iron contamination. In circumstances where the use of nitric acid is not possible for safety or physical reasons (such as the underside of vessel roofs) passivation paste is appropriate. Both materials are used at ambient temperature and require a contact time of approximately 30 minutes. They must be removed by thorough rinsing with low chloride-content water. 

In the field of nuclear energy, titanium has been used for processing of fuel elements, where this demands use of nitric acid or aqua regia ", and for control-rod mechanism, in which the short half-life of irradiated titanium is of advantage. 

Other Uses of Nitric Acid. As mentioned earlier, fuming nitric acid (FNA) when mixed with ale, toluene or acet anhydr will cause an expln. However, there are many other uses for FNA in energetic materials technology. As either red fuming nitric acid (RFNA) or as nitrogen tetrox-ide, it is used extensively as the oxidizer in pro-pint systemsnfor ram-jets, jet motors, space rockets and other missiles (Refs 37, 38 39). See also under Liquid Propellants in Vol 7, L24-Rff... 

The original route from p-xylene was oxidation in the presence of nitric acid. But the use of nitric acid is always problematical. There are corrosion and potential explosion problems, problems of nitrogen contamination of the product, and problems due to the requirement to run the reactions at high temperatures. Just a lot of problems that all led to the development of the liquid air phase oxidation of p-xylene. Ironically the nitrogen contamination problem was the reason that the intermediate DMT route to polyester was developed, since that was easy to purify by distillation. Subsequently, DMT has secured a firm place in the processing scheme. 

Nitric Acid and Nitrates. The use of nitric acid as a major component in liquid oxidizers dates back to at least World War II when it was used in a mixture with oleum (88 wt. % white fuming nitric acid and 12 wt. % oleum) and was denoted as mixed acid. In later years its use as white fuming nitric acid (WFNA) and inhibited white fuming nitric acid (IWFNA) developed because of its higher performance capabilities in these forms. These acids are fairly pure nitric acid WFNA contains a maximum of 2 wt. % H20 and 0.5 wt. % N02 IWFNA addi-... 

Additional uses of nitric acid are for oxidation, nitration, and as a catalyst in numerous reactions. Salts of nitric acid are collectively called nitrates, which are soluble in water. Nitric acid is used in the production of many items such as dyes, pharmaceuticals, and synthetic fabrics. It is also used in a variety of processes including print making. 

Other sulfide-oxidizing processes include the use of nitric acid, a strong oxidant, in place of sulfuric acid ... 

They found that a good yield of ethylenedinitramine may also be obtained from ethylenediamine through diacetylethylenediamine (ethylene-bis-acetamide). The nitration of the latter involves the use of nitric acid (98%) mixed with acetic anhydride ... 

The oxidation can also be effected in the wet way by the use of nitric acid. The crude dioxide prepared in this way can be purified by sublimation.7... 

When one deals with the use of nitric acid in conjunction with a solid acid, one has to keep in mind that the solid may play two fundamentally different roles, which frequently are strongly connected. One of being a CATALYTIC ACID, and the other of being a STOICHIOMETRIC DESSICANT. We tried to separate these two basic functions. 

Pentaerythrite may also be nitrated satisfactorily, and probably in better yield, without the use of sulfuric acid and with the use of nitric acid from which the nitrous acid has been removed. 

Since the early days of organic chemistry, nitration has been considered to be an important reaction and has been widely used. As early as 1825 Faraday discovered benzene and recorded its reaction with nitric acid. Shortly after, the use of nitric acid sulfuric acid mixtures to effect nitration was reported and was soon quoted in a patent. Nitration figured prominently in the development of ideas of theoretical organic chemistry in the early part of the twentieth century and, as the most widely applicable and most widely used example of electrophilic substitution, it played an important role in the consideration of aromatic stability and reactivity. In 1910 the first report of orientation and deactivation in aromatic electrophilic substitution was published (10MI1). 

In another study of the nitration of 5-phenyl- and 3-methyl-5-phenylisox-azole the action of nitric acid sulfuric acid on 5-phenylisoxazoIe produced a 1 1 1 mixture of the ortho, meta, and para 5-(nitrophenyl) products with minor amounts of 4-nitro-5-(3-nitrophenyl)- and 4-nitro-5-(4-nitrophenyl)-dinitro products. The action of nitric acid acetic anhydride produced 4-nitro-5-phenylisoxazole as the major product with some nitrophenyl compounds as minor products. 3-Methyl-5-phenylisoxazole also gave a mixture of the ortho, meta, and para 5-(nitrophenyl) products when mixed acids were used, but no dinitro products were observed. The use of nitric acid acetic anhydride resulted in nitration at the 4-position of the isoxa-zole ring as the largely predominant product, with some phenyl ring substitution (89H1965). 

Phenylthiazoles were also nitrated by earlier workers (47HCA2058 51JPJ869), who showed that the use of nitric acid in sulfuric acid at 0°C produced the 4-nitrophenyl product in each case from 2-, 4-, and 5-phenylthiazole (yields of 80, 90, and 92%, respectively). Yet another study of the nitration of phenylthiazoles has given the results shown in Table V (71BSF4310). 

Studies of the nitration of 4-chloromethyl-2-phenylthiazole have shown that the action of nitric acid (d 1.40) in sulfuric acid at 60°C gives the 4-nitrophenyl product and the use of nitric acid in acetic anhydride at 60°C forms the 5-nitrothiazole product. Chlorination and bromination also result in 5-substitution in the thiazole ring and nitration of these products using mixed acid gives the 4-nitrophenyl products. 2-(4-Bromophenyl)-4-chloromethylthiazole also nitrates at the 5-position of the thiazole ring using nitric acid in acetic anhydride below 60°C (65CB3446). 

Gregory (Ref. G6) is a very comprehensive source specific to the industrial and commercial applications of chemicals. It includes a three page list of the uses of nitric acid. Similar information is presented for many other chemicals in this book. The one fault of this source is that it is 50 years old In that period many process technologies have changed and the applications list, whilst very comprehensive, tends to be dated. 

Uses of nitric acid. Most of the nitric acid produced is used in the manufacture of explosives. This is done either by converting the acid into its salts, the nitrates, or by using the acid in the nitration certain organic compounds. Some of these nitrated organic substances are used as explosives, while others are used in the manufacture of dyes, pharmaceuticals, and so forth. Nitric acid is used also in the production of fertilizers and many other chemicals. 

Lead-chamber process. The essential features of the lead-chamber process are the use of nitric acid to oxidize S02 to S03 and the absorption of S03 by water in large absorber towers. This process has been used for well over 100 years, and the details of equipment and operation are essentially the same today as when the process was first designed. 

The production of trinitrotoluene requires complete nitration of toluene that can be achieved by use of nitric acid. 

The nitrations of a wide range of substituted quinoline N-oxides under various conditions [82HC(382)447] show the usual pattern of substituent effects superimposed upon the pattern resulting from the use of nitric acid/sulfuric acid at low temperature (5,8-positions), weaker mixtures of these acids at high temperature (4-position), or acyl nitrates (3-position). Nitration of acridine N-oxide by nitric acid/sulfuric acid occurs in the 5-position (60JCS3367). 

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