LYCOS RETRIEVER 
Nitric Acid: Process
built 630 days ago
Nitrites, (compounds containing the NO2- ion), on the other hand, are made from nitrous acid (HNO2), which is a very weak acid compared to its close relative, nitric acid. For example, sodium nitrite, NaNO2 (E250) and potassium nitrite, KNO2 (E249) are used as a preservative in several processed meats, such as bacon, ham, sausage, corned beef, beef jerky, frankfurters, and some fish products. The nitrite ions (NO2-) in these meats inhibit the growth of a bacterium (Clostridium botulinum) which causes the fatal food poisoning known as botulism. They are ... used because they fix the bright-red colour of fresh meat (in the form of a type of diazo-dye), which would otherwise quickly fade to an unpalatable brown. This means that meat on the supermarket shelves, which looks fresh and new, may actually be several days old and just 'dyed' red using the nitrite!
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It is an object of the current invention to provide a method for hydrolyzing polyamide materials in nitric acid solutions while avoiding significant oxidation of the diamine. The polyamides are ... substantially converted to their constituent acid and amine components, capturing most of the monomer value. The recovered monomers may be used to produce polyamides having properties comparable to the original polyamide. It is a further object of the invention to provide a process for the acid hydrolysis of polyamides which avoids the formation of a salt waste stream.
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The main reason for highly corrosive conditions in tail gas preheaters is that droplets of nitric acid are entrained in the tail gas from the absorption tower. When this gas enter into the heater, the droplets will settle on the hot tube wall and start boiling. The temperature of the heating medium, usually hot process gas or steam, can be very high. In this type of condition AISI 304L tends to have short service life.
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The process economics were later improved by feeding nitric acid and strong sulfuric acid separately into the column. In this way, the heat of dilution is available to assist the concentration process. Further improvement in economy is possible by avoiding live steam injection, using instead a reboiler as the source of energy input. This reboiler provides the stripping action required to push nitric acid to the top of the column without dilution of the sulfuric acid. The use of reboilers became the industry standard when tantalum became available as a material of construction.
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The advantages of the nitric acid hydrolysis process are best realized with nylon mixtures containing major amounts of nylon 66. Prior art processes for recovery of e-caprolactam work well for nylon 6, but often destroy any nylon 66 components which may be present. Figure 1 is a schematic representation of an embodiment of the current invention, as applied to the recycling of a mixed feed of nylon 66 and nylon 6. Reclaimed nylon, either as sheared or separated carpet fiber or chopped molded parts, is optionally washed in a pre-wash stage to remove dirt, dyes, etc., then fed to a hydrolyzer, where it is mixed with a solution containing 18-35 wt% nitric acid and heated at reflux. The products of the hydrolysis of N66 are hexamethylene diamine and adipic acid. The product of hydrolysis of nylon 6 is e-aminocaproic acid.
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Recently, the Corrosion Laboratory performed an experiment to establish the amount of hydrogen pickup when pickling titanium strip in a bath with a lower-than-normal concentration of nitric acid. The pickling process involves running the Ti strip through a series of baths for 2 to 2.5 minutes (in each bath). The typical process includes:
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