Nitration with mechanical stirring

Nitrating in vessels equipped witli mechanical stirrers is now the most widely used method. It was first introduced by du Pont de Nemours in U.S.A. It was described in 1922 [16]. 

A nitration unit is composed of four nitrators (Figs. 146-149) constructed of acid resistant steel. Each nitrator (Figs. 146) is fitted with two stirrers that rotate 

The process of nitration is as follows The nitrator is charged with 750 kg of mixed acid of the composition shown in Table 97. 

Then 17 kg of cellulosic material are loaded into the nitrator, with the stirrers 

Centrifugation lasts 5 min, followed by unloading, which takes the same time. In order to maintain continuous operation, the four nitrators are used in turn while the first nitrator is being loaded with acid and cotton, in the second nitration is just starting, nitration in the third is nearing completion, and the fourth nitrator is being emptied. 

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According to Nauckhoff and Bergstrom [7] a nitrator with mechanical stirring was used as long ago as the 1870 s in 1872 in the British Dynamite Co. in Ardeer and in 1879 by A. Liedbeck at Isleton in Switzerland, Paulilles in France and Avi-gliana in Italy. 

The process patented by the Thomsons in 1903 (J. M. Thomson and W. T. Thomson [15]) was used only in Great Britain, though during World War I it was used to a lesser extent also in France. It has now been superceded by the use of nitrators with mechanical stirring. 

The nitration is carried out in nitrators with mechanical stirring (or — in earlier days — in pots), the cotton to add ratio being kept within the limits 1 45 to 1 50. In this way nitrocellulose containing 12.1-12.3% of N is obtained. 

Finishing wood cellulose Other sources of cellulose Drying cellulose before nitration Industrial nitration of cellulose Mixed acids Nitration m pots Centrifugal nitration Thomsons method Nitration with mechanical stirring German method Continuous methods of nitration Literature... 

Stirring by means of compressed air has a drawback, in that a certain quantity of nitric add which is volatile is carried out of the nitrator and thus by decreasing the nitric add content in the nitrator, can contribute to a diminished yield of the whole process. Experience has indeed shown that with mechanical stirring the output is usually higher by about 2% as compared with compressed air stirring. 

The continuous method of nitroglycerine manufacture invented by A. Schmid [38] involves not only continuous nitration, but also continuous separation and washing of the product. A novel idea introduced by Schmid was the nitrator made of acid-resistant steel with mechanical stirring (Fig. 38). 

The nitration plant was identical in principle with that described above, with mechanical stirring. In the German method cellulose in the form of crepe paper prepared from 70% birch and 30% spruce was nitrated. Cellulose, tom to pieces in rollers, was dried to reduce its moisture content from 6-7 to 1.2%. Towards the end of the war the drying stage was omitted at Kriimmel, and cellulose containing 6-7% of moisture was nitrated, since the time saved and the economy in steam achieved then was reckoned sufficient compensation for the need to make use of more concentrated acids. 

To a solution of 33 g. (O.S mole) of potassium hydroxide (Note 1) in 1.5 1. of distilled water in a 5-1. flask or other appropriate container fitted with a mechanical stirrer is added 80 g. (0.5 mole) of methyl hydrogen adipate (Note 2). With continuous stirring a solution of 85 g. (0.5 mole) of silver nitrate in 1 1. of distilled water is added rapidly (about IS minutes). The precipitated methyl silver adipate is collected on a Buchner funnel, washed with methanol, and dried in an oven at 50-60°. For the next step the dried silver salt is finely powdered and sieved through a 40-mesh screen. The combined yield from two such runs is, 213 g. (80%). 

Slowly, and with constant stirring, the sodium carbonate solution is added to the thorium nitrate solution. Using a mechanical stirrer to stir the thorium nitrate solution is best, but a glass rod also works. 

In the production of Chardonnet rayon, purified cotton or linters are treated with a mixture of nitric and sulphuric acids at a temperature not exceeding 40°C for a period of between 4 and 6 hours. The excess of acid is then run off and the nitrated cotton is washed with water until free from acid. It is subsequently hydro-extracted and pressed until it contains about 30 per cent of water. This nitrocellulose is dissolved in a mixture composed of equal volumes of alcohol and ether in a closed vessel provided with a stirring mechanism. The solution is filtered under pressure and then stored. 

A relatively early work came from Sarikaya and Akinc [175] who used a mineral oil with Arlacel 83, a non-ionic surfactant (Sorbitan sesquioleate) as the support solvent (continuous phase) and an aqueous solution of aluminum nitrate as the water phase to form the emulsion by mechanical stirring. The most stable emulsions were obtained with W/O ratio of about 0.45-0.55 (with 5% emulsifier). The emulsion thus produced was added dropwise to a hot (240 C) mineral oil to obtain precipitates of an alumina precursor. 

Synthesis ofmullite has been attempted by a range of sol-gel processes, as will be evident from the exanples discussed in this Chapter one of these (Jaymes and Douy, 1995) falls under the procedure of mechanical dispersion of sols. The sol was prepared by addition of TEOS to an aqueous solution of aluminum nitrate. Under vigorous stirring, hydrolysis of TEOS proceeded, and a sol was produced. This sol, diluted with 2-propanol, was spray dried into (i) a basic alcoholic solution or (ii) an aqueous solution of a mixture of ammonium carbamate and hydrogenocarbonate. Fine, colloidal precipitates were obtained. The dried powders (100°C) had specific surface areas in the range of250-300 m /g. Calcination of particles obtained from procedure (i) led to the formation of nearly monophasic mullite (with a small amount of spinel). In case of procedure (ii), a diphasic product, i.e. an alumina-rich spinel phase and orthorhombic mullite was obtained. 

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