Nitration continuous methods

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

Modern practice tends to continuous methods, but many nitrated materials are still produced by batch processes. Below, we will describe the technology of manuf of TNT and NM, examples of C-nitmtion NG and NC, examples of O-nitration,... 

Factors affecting the rate of nitration of DNT TNT will be discussed in Section VIII Urbanski (Ref 74) lists several processes for die batchwise manufacture of TNT (eg, the French , British , USSR etc). All of them are essentially similar with only minor differences in MA comp ns and methods of separating the crude TNT from its spent acid. These processes hav been largely replaced by continuous nitration techniques. The Biazzi and Bofors continuous processes for the manuf of TNT are described briefly under Continuous Methods of Manufacturing Explosives in Vol 3, CS01-L. 

Crude TNT produced by either batch or continuous methods requires purification. The ultimate objective of TNT purification is to remove all those products which are more reactive than TNT itself (isomers, nitrocresols, nitro-benzoic acids, etc), or which can easily give oily exudation products, such as isomers or lower nitrated substances... 

NG. Batch-wise production of NG is described in Vol 6, G99-102, and continuous methods such as the Schmid t-Meissner and Biazzi processes are discussed in Vol 3, C501 — 505. The Swedish injector process and the Hercules tubular nitrator will be described below, but before doing this we will discuss certain aspects of glycerin nitration that are common to both batch and continuous methods, and then contrast the main features of the batch process vs the continuous process... 

Tetryl. In the manufacture of Tetryl, it is usual not to nitrate dime thy laniline directly, but to dissolve it first in coned sulfuric acid and then to nitrate the dimethylaniline sulfate so obtained. Direct nitration of dimethylaniline proceeds so violently that it can be carried out only under specialized conditions. Many years experience of Tetryl manufacture has shown that the ratio of sulfuric acid to dimethylaniline should not be lower than 3 1, since a smaller amount of sulfuric acid may be detrimental to the nitration process. However, the ratio of sulfuric acid to dimethylaniline must not be too high, otherwise Tetryl yield is decreased. Temp must be maintained between 20-45° to avoid sulfonation of the benzene ring. Care must be exercised not to leave any unreacted dimethylaniline prior to introduction of nitric acid, because of the potential violence of the dimethyl-aniline-nitric acid reaction. Consequently, continuous methods of prepn are to be preferred as they inherently minimize accumulation of unreacted dimethylaniline... 

During and since the Second World War, the three-stage process has been replaced by continuous methods of nitration employing a larger number of stages. In these, the chemical engineering can differ widely, but in principle toluene enters the process at one end and trinitrotoluene is... 

Buhr, S. M., M. P. Buhr, F. C. Fehsenfeld, J. S. Flolloway, U. Karst, R. B. Norton, D. D. Parrish, and R. E. Sievers, Development of a Semi-Continuous Method for the Measurement of Nitric Acid Vapor and Particulate Nitrate and Suflate, Atmos. Environ., 29, 2609-2624 (1995). 

Continuous methods using the same installations as for manuf of NG are used now in Europe. Two of these installations, Schmid-Meissner and Biazzi, are described in Vol 3 of Encyci, pp C502—C504. We also know that continuous method of Schmid-Meissner is installed in Argentina at the Naval Explosives Plant. The same plant employs Bofors Continuous Method for manuf of TNT. Accdg to Ref 24, nearly 100% conversion of Gc to NGc is achieved by mixed acid nitration in liquid sulfur dioxide... 

Nitration (see Bain [59] and Rinkenbach [29]). A continuous method of nitration at 70°C is the safest and most advantageous. The lay-out shown diagrammati-cally in Fig. 8 is typical. 

The following methods of manufg Normal LSt are briefly described by Urbanski (Ref 21, pp 218-20) l) Method used at Wolfrats-hausen, Germany and 2) Continuous Method of J. Meissner. In both methods starting materials are MgO, TNR Pb nitrate. In the 1st part of manuf, a suspension of Mg reacts with TNR in w to form soluble Mg Styphnate, while in the 2nd part MgSt reacts... 

Herz succeeded in preparing RDX by direct nitration of hexamine, but the yields were low and the process was expensive and unattractive for large scale production. Hale, at Picatinny Arsenal in 1925, developed a process for manufacturing RDX which produced yields of 68%. However, no further substantial improvements were made in the manufacture of RDX until 1940 when Meissner developed a continuous method for the manufacture of RDX, and Ross and Schiessler from Canada developed a process which did not require the use of hexamine as a starting material. At the same time, Bachmann developed a manufacturing process for RDX (1.5) from hexamine which gave the greatest yield. 

From experience gained over many years, special equipment and methods of nitration and purification of nitroglycerine have been developed and certain traditions established. Recently, however, changes have occurred in this field. Continuous methods of nitroglycerine manufacture have been introduced. In many cases they have revolutionized traditional techniques and led to new manufacturing processes. 

In the recently introduced continuous methods of nitroglycerine manufacture nitrators made from acid resistant steel are used since the art of welding stainless steel had progressed remarkably by the 1930 s. The design and construction of nitrators for nitrating glycerine are included in the descriptions of individual methods of nitration. 

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 invention of continuous methods of nitration of glycerine stimulated the improvement of the old batch processes by transformation into semi-continuous ones. One such methods was designed by Jarek [52] and is in use in Poland (Fig. 60). 

The nitration of pentaerythritol to produce PETN by a semi-continuous method as used at Kriimmel [46] was carried out as follows (Fig. 74). 

The continuous method of nitration is particularly useful when the rate of nitration is rapid (such as in case of manufg NG, NGc, or PETN) and an overheating and expln might take place with the batch process. Nitration of cellulose, on the other hand, does not proceed very rapidly (unless mixed acid contains phosphoric or glacial... 

Continuous methods for manufg expls usually consist of the following operations nitration, separation of nitrated product from spent acid, and purification of nitrated product. In some Cases only nitration is continuous while separation and purification are batch processes... 

After Schmid s accidental death in 1930, Meissner extented the application of continuous method to nitration of substances like benzene, toluene, etc, The,FirmaMeissner", Koln,... 

Continuous methods have also been developed for manuf of expls other than NG. As examples may be cited nitration plants for benzene (Refs 5 6a) aromatic hydrocarbons other than benz (Refs 7, 13 16) PE (Refs 17, 19, 21, 21b 22) DEG (Refs 21, 22 28) various org compds (Ref 36) cellulose, starch, sugar, etc (Ref 21) methyl nitrate (Ref 23a), etc. A continuous method for manufg propellants is described in Ref 46. A continuous method for manuf of TNT by the method of Bofors was installed in 1955 at the Fabrica Naval de Explosivos, Azul, Argentina (Ref 34a) Description of Some Continuous Methods for Manufacturing Explosives. 

Continuous Methods for Manufacturing Nitrocellulose. Several methods are known, of which the Dietzsch process developed during WWII in Germany is briefly described here under Combustible and Consumable Cartridge Cases. This method combines vapor-phase and liquid-phase nitration processes. The Japanese used during WWII a continuous liquid-phase method of nitration of paper pulp, which was in the form of a sheet... 

Continuous partial pressure nitrator using nitric acid alone) 19)A.A. Swanson, PB Rept 320 (1945) O.W.Strickland et al, PB Rept 925 (1945) (Continuous methods for manuf of P ETN, which were used in Germany during WWII) 20JN.Shreve, ChemMetEngrg 52, 103 05 (Way 1945) (History of continuous process development) 21)E.Berl, USP 2384415... 

Review of literature on nitration, including continuous method .) 29)Kirk Othmer 6 (1951), 29-30 9(1952, 324-27(Continuous methods of Schmid, Schmid Meissner Biazzi) 30)Stettbacher, Polvoras (1952), 81-3 (Continuous method of Biazzi) 31)W. deC. Crater,... 

The mato feature of a contiguous process is that the final expl product does not remain in the app for a prolonged period of rime and the quantity accumulated at any period of time is much smaller than that in the batch process. The large quantity of expl material accumulated in a batch process, especially at the end of exothermic nitration,presents a serious safety hazard which is more or less absent in current continuous processes The continuous method of nitration is particularly useful when the rate of nitration is rapid (such as in case of manufg NG, NGc, or PETN) and an overheating and expln might take place with the batch process. Nitration of cellulose, on the other hand, does not proceed very rapidly (unless mixed acid contains phosphoric or glacial... 

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