Nitric acid denitration

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Further work by Baum and co-workers showed that the nitration of l,l-diamino-2,2-dinitroethylenes with trifluoroacetic anhydride and nitric acid in methylene chloride yields 1,1,1-trinitromethyl derivatives via addition of nitronium ion to the double bond of the enamine such treatment also resulting in the A-nitration of the products. In this way, trini-tromethyl derivatives like (185) and (188) are obtained. Further treatment of these trinitromethyl derivatives with aqueous potassium iodide results in reductive denitration and the formation... 

The original plant had the facility to fractionate the vapors from this evaporator to recover nitric acid present in the magnesium nitrate stream, but the high degree of denitration obtainable in the extractive distillation column made this recovery operation unnecessary and it is no longer used. 

According to British reports from World War I [33], during nitroglycerine manufacture the nitrogen content of the nitric acid (including that recovered by denitration) was consumed as follows ... 

A range of nitrocotton samples containing from 11.3 to 13.1% N, and nitro-ramie of 10% N prepared by denitrating nitroramie of 13% N by acting with nitric acid 80%, have been fractionated by G. G. Jones and Miles [HO] by a method of successive extraction with aqueous acetone every subsequent solvent was richer in acetone than the preceding one. They demonstrated that particular fractions differed in nitrogen content and viscosity. 

In concentrated nitric acid, sp. gr. 1.52, it dissolves on warming (80 to 90°C). As the result of the prolonged action of more dilute nitric add, specific gravity 1.41, a partial denitration and formation of oxycellulose occurs. 

Clement and Riviere [59] also reported that cellulose acetate or a mixed ester — a nitrate-acetate — can be obtained by reacting cellulose nitrate with acetic anhydride, acetic acid, and sulphuric acid. According to more recent contributions, e.g. Wolfrom, Bower and Maker [60], the reaction should be performed as follows Cellulose nitrate is dissolved in the cold in a little sulphuric add and acetic anhydride, the surplus of acetic anhydride is then hydrolysed also in the cold, and cellulose acetate is extracted with a suitable solvent, such as chloroform. Other methods of acetylating nitrocellulose consist in reduction, for instance with zinc and hydrogen chloride, which entails denitration of the ester, followed by acetylation with acetic anhydride. All these reactions are carried out in the same vessel. Further, it is possible to synthesize mixed esters, cellulose nitrate-acetates, by subjecting cellulose to the action of a mixture that includes nitric acid, acetic add and acetic anhydride in the presence of sulphuric acid (Kruger [61]). The use of a large amount of nitric acid favours the formation of nitrocellulose only. Mixed esters are formed... 

The authors also denitrated nitrocellulose with nitric acid, obtaining rather non-uniform products. 

After the cotton has been removed from the nitration tank (Fig. 135) the composition of the acid in the tank is adjusted so that in quantity and strength of it remains unchanged throughout. The waste acid from the centrifuge is low in nitric acid. The regeneration of this spent acid by addition of oleum and fresh nitric acid is uneconomic. Spent acid is denitrated. 

Sugar nitric acid esters are also subject to reductive denitration (see p. 9) and to the chemical reactions typical of sugar nitrates. 

Denitration Removal of nitric acid, nitrates or nitrogen oxides from acids and other substances. 

Detection oj nitrocellulose. A little of the residue obtained on evaporation of the solvent (see above) is treated in a thoroughly dry disli with concentrated sulphuric acid containing in solution a little diphenylamine in presence of nitrocellulose the intense blue coloration due to nitric acid and nitro-derivatives is observed. Sometimes, however, the nitrocelluloses are partially denitrated, so that the reaction with diphenylamine is feeble in such cases test 4, b should be carried out. 

As described in Figure 3.7, TRU separation is performed by implementing the DIDPA process on pretreated PUREX raffinates. A front-end denitration step by formic acid is thus required to reduce the nitric acid concentration of the feed down to 0.5 M to allow the TRU elements to be extracted by the cation exchanger di-fvo-dccyl-phosphoric acid (DIDPA). This preliminary step, however, induces the precipitation of Mo and Zr (and thus the potential carrying of Pu), which requires filtration steps. The TRU and Ln(III) elements are coextracted by a solvent composed of the dimerized DIDPA and TBP, dissolved at 0.5 and 0.1 M, respectively, in n-dodecane. The An(III) + Ln(III) fraction is back-extracted into a concentrated 4 M nitric acid solution, whereas Np and Pu are selectively stripped by oxalic acid. 

In the reverse TALSPEAK process, the An(III) + Ln(III) fraction is first coextracted from a feed, the acidity of which has to be reduced to 0.1 M by denitration or nitric acid extraction. An(III) are then selectively stripped using DTPA in citric acid (1 M) at pH 3 (hence the name reverse TALSPEAK process), and the Ln(III) are finally stripped by 6 M HN03. Attempts to apply this TALSPEAK variant to the treatment of actual UREX + raffinates are reported in the literature, but they involve several steps. The problematic Zr and Mo elements are first removed by direct extraction with HDEHP (0.8 M in di-iso-propylbenzene) from the high-acidity raffinate stream arising from the UREX + co-decontamination process (238). The remaining fission products and actinides can then be concentrated by acid evaporation and denitration processes. This concentrate is further diluted to a lower acidity (e.g., [HN03] = 0.03 M) to allow the coextraction of An(III) and Ln(III) by the TALSPEAK solvent. 

Di-iso-decylphosphoric Acid The DIDPA Process An(III) and Ln(III) can be partitioned using the DIDPA solvent (DIDPA and TBP, respectively dissolved at 0.5 and 0.1 M in n-dodecane) in a two-step process approach. First coextracted and costripped in a 4 M nitric acid solution in a first DIDPA cycle (see Section 3.3.1.1.4), the An(III) + Ln(III) fraction is partitioned in a second cycle after denitration of the An(III) + Ln(III) product by formic acid to reduce the nitric acid concentration to at least 0.5 M. In this second DIDPA cycle, An(III) and Ln(III) are first coextracted by the DIDPA solvent, and the An(III) are selectively stripped by DTPA (0.05-0.1 M) in a solution buffered at pH 3 with lactic acid (1 M). The triva-lent lanthanides are further stripped with a 4 M nitric acid solution (134). 

Tetraphenylborate (TPB) was used at Savannah River to recover cesium from alkaline solutions, but attempts to treat HLW tanks with TPB resulted in the production of benzene (a TPB decomposition product) at levels that did not permit the safe operation of the process.8 Crown ethers and dicarbollides were proposed as extractants to remove cesium from acidic HAW, but these compounds are not selective enough to allow cesium to be removed from solutions containing large amounts of nitric acid or sodium nitrate.9 Dicarbollides were used in Russia at industrial scale to recover cesium from HAW, but the removal of cesium was only possible after partial denitration of the liquid waste.10... 

Later the detoluation operation was combined with partial nitration of MNT to DNT, by adding to the spent acid a certain quantity of nitric acid from the recovery operation (denitration). 

The nitrating mixture is prepared from fresh concentrated nitric acid, 55% regenerated nitric acid (from the denitration of spent acid), and 96% sulphuric acid recovered by distillation. The mixture of acids is fed into the nitrator from a metering tank through a vacuum started siphon. Toluene is conveyed to the nitrator from another metering tank by means of compressed nitrogen. Air is considered as too dangerous to use, because the explosibility of mixtures of toluene vapour with air. 

To handle the volume of solution (about 30,000 L) necessary in the plant operation, a semi-batch denitration was necessary. Slow evaporation during product accumulation reduced the volume to <12,000 L, but increased the nitric acid concentration to about 11M. Experiments indicated that for a semi-batch denitration mode, a projected nitric acid concentration of 2M was an excellent stopping point, because no residual formic acid remains through the reflux and evaporation steps. Additional high nitric acid solution can then be added to the evaporated-denitrated solution without auto-initiation of a formic acid-nitric acid reaction. After all the Am-bearing solution had been transferred to the denitration evaporator and denitrated to <2M, the solution could be evaporated to 2500 L and denitrated to a residual free-acid concentration of 0.5 to 0.8M. In actual practice, the final 2500 L of solution was denitrated to 0.25M HNO3. 

Three simulated tests were run using only nitric and formic acids. In each case, the reaction began promptly and proceeded smoothly. After the second test, the denitrated material was evaporated and additional nitric acid added to simulate the tandem semi-batch operation to be used with actual process solution. At the end of formic acid feed for Test 3, the material was refluxed for 2 hours and evaporated to 2500 L to simulate the final canyon product batch. A final formic acid denitration reduced the acidity of the simulated concentrate to <1M HNO3. 

As a result of the high concentration of nitrate (from sodium and aluminum nitrate) the reaction rate was controlled by the formic acid addition rate until the free acid concentration was reduced to about 0.5M. For semi-batch denitrations it appears that a nitric acid concentration of 1 to 2M at the end of each individual denitration is an excellent stopping point. Using 1 to 2M HNO3 as a projected stopping point assured that there will be no residual formic acid at the end of the reflux and evaporation... 

Recently, Baum and coworkers154 reported the nitration of 1,1-diamino-2,2-dini-troethylene. On treatment with nitric acid and trifluoroacetic anhydride in methylene chloride at 0 °C, 1,1-enediamines 42 are converted to 3-nitro-2-(trinitromethyl)-l,3-diazacyclic compounds 192 in good yields (equation 79). Compounds 192 have also been prepared from the nitration of 7, although the yields are lower (16-22%). Denitration of 192 to 193 includes a reductive denitration of 192 with potassium iodide and acidification of initially formed salts of 193. Nitration of 193 regenerates 192 (equation 79). 

We have seen how smoother nitrations are obtained in the laboratory by using a 10 per cent excess of nitric acid. In plant processes, a much smaller excess is used and even this is recovered completely by separating the waste acid into its components, sulfuric and nitric acids. This is done with steam in denitrating towers. 

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