Sept. 10, 1935. W. GROSS 2,013,984 PROCESS FOR THE OXIDATION OF TO Filed June 8, 1931

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NVENTOR Dilalier Gross BY his ATTORNEYS Patented Sept. 10, 1935 2,013,984

UNITED STATES PATENT OFFICE 2,013,984 PROCESS FOR THE OXDATION OF NITRITES TO NTRATES Walter Gross, Neuroessen, Germany, assignor to H. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany Application June 8, 1931, Serial No. 542,914 in Germany June 1, 1930 5 Claims. (C. 23-102) The present invention relates to an improved The present invention offers special advan process for the oxidation of nitrites to nitrates. tages with - solutions containing In the production of nitric by the Oxida such as are obtained, for example, tion of , or , the last traces of by the absorption of oxides of nitrogen with milk oxides of nitrogen in the gases are usually re of lime, because the carbon dioxide set free by 5 Covered by absorption in soda solutions, a liquor the causes no trouble but is removed being obtained which contains from the process together with the waste gases and Soditin initrate. Either the nitrite as Well free from oxides of nitrogen. When employing as the nitrate are separately recovered from this milk of line as the absorption agent, the reac O liquor, or the nitrite is converted into nitrate by tion proceeds smoothly in accordance with the 10 treatment With nitric acid. The nitrogen oxides equation Ca (NO2)2--O2=Ca (NO3)2. thus set free are returned to the absorption plant. The present invention therefore allows of a A certain part of it produces further amounts direct conversion of nitrites to nitrates in a sim Of nitrite and nitrate in the alkaline absorption ple manner. The apparatus of large dimensions 5 liquid. hitherto necessary, especially when working up 5 If the oxides of nitrogen are to be combined liquors containing , for filter in the form of , the last traces ing the liquors and washing and removing the of the oxides of nitrogen are preferably ab sludge are dispensed with. The costs of the SOrbed in milk of lime instead of in alkalies. The evaporation of the Washing water are saved and liquor containing calcium nitrite and calcium the loss of nitrogen compounds by reason of the 20 nitrate thus obtained which also contains calcium residual sludge is avoided. carbonate in suspension, necessitates lengthy and The nature of the invention will be further troublesome operations to convert the nitrite described with reference to the accompanying into nitrate. The calcium carbonate must first drawing which illustrates apparatus suitable for 25 be separated, because otherwise when treated carrying out the invention but the invention is 25 With nitric acid carbon dioxide Would be set free not restricted to the particular apparatus shown. in addition to the oxides of nitrogen. When these The nitrite-nitrate liquor, nitric acid and gases are returned to the absorption plant again, Oxygen or gases containing oxygen are forced calcium carbonate is again formed and thus car through pipes S, T, and O, respectively by pumps 30 bon dioxide becomes enriched in this system. or blowers P1, P2 and P3 into a pressure tight 30 I have now found that the conversion of ni tube A of acid-resistant material below a grate trites into the corresponding nitrates by Oxida B. The Space above the grate B is provided with tion in aqueous Solution by means of nitric acid fillers Falmost to the top. The liquid leaves the and OXygen or gases containing oxygen is car reaction chamber through a valve V1 and the gas ried out in a very advantageous manner indus through a valve V2. The valves are regulated 35 trially by producing an intimate mixture of the So that a certain pressure (indicated on the Solution containing nitrite with the nitric acid manometer M) always prevails in the apparatus, and OXygen. Or gases containing oxygen in the Care being taken by using an observation glass lower part of a vertical tube, the mixture then W that the liquid keeps a constant level in the 40 being allowed to ascend in the tube, the height of Which is so chosen as to effect the complete con Smalltube andas p0SSible. the gas space above the liquid is as 40 version, and the separation of the liquid from The fillers F may be dispensed with and the the gas then being effected at the upper end of gaS dispersed by Sieves arranged. One above an the tube. By working in this manner, advan Other. tageously under elevated pressure, the oxides of The following examples will further illustrate 45 nitrogen formed from the nitrite are completely the nature of the invention as applied to an ap combined as nitrate in a continuous operation. paratus, such as that shown in the accompany The gases leaving the reaction tower consist of ing drawing, but the invention is not restricted excess oxygen which is mixed with nitrogen, to these examples. when air is used as the gas containing oxygen, The oxygen content of the oxidizing gases, the 50 and carbon dioxide When carbonates are present preSSure employed and the dimensions of the tube in the initial material. By this method, how are not restricted to those specified in the ex ever, no gas is obtained which must be supplied amples but depend in each case on the composi again to the absorption stage, and this entails a tion of the liquors and the nature of the gases great Saving in absorption plant. containing oxygen available. Thus, as shown in 55 2 2,013,984 What I claim is: Example 3, the time of reaction may be so in 1. The process for the oxidation of a nitrite creased by lengthening the reaction tube and re to the corresponding nitrate which comprises ducing the throughput that the oxidation of Supplying a Solution of the nitrite, nitric acid and the nitrite proceeds Smoothly even When em a gas comprising elementary oxygen to the lower 5 5 ploying air. end of a column of aqueous liquid and separately Eacample 1 Withdrawing gas and liquid at the upper end of 500 liters of calcium nitrite-calcium nitrate Said column, said column being of Sufficient length sludge containing 3.8 per cent of nitrite nitrogen to effect substantially complete oxidation of the and 3 per cent of calcium carbonate, 250 liters of nitrite and to produce a gas Substantially free 10 O 60 per cent (by volume) nitric acid and 19 cubic from oxides of nitrogen. meters of a mixture of Oxygen and nitrogen COIn 2. The process for the oxidation of calcium taining 87 per cent of oxygen are pumped or nitrite to calcium nitrate which comprises Sup blown per hour into the lower part of a tube 6 plying a Solution of the nitrite, nitric acid and a meters long and 100 millimeters in diameter. gaS comprising elementary oxygen to the lower 15 The gases are released from a preSSure of 7 end of a Column of aqueous liquid and Separately atmospheres to atmospheric pressure at the upper Withdrawing gas and liquid at the upper end of end of the tube. The nitrite in the Solution is Said column, Said column being of Sufficient length converted into nitrate to the extent of 99.4 to effect Substantially complete oxidation of the per cent. nitrite and to produce a gas Substantially free 20 Eacample 2 from Oxides of nitrogen. 100 liters of calcium nitrate-calcium nitrite 3. The process for the oxidation of calcium sludge containing 3.8 per cent of nitrite nitrogen nitrite to calcium nitrate which comprises Sup and 3 per cent of calcium carbonate, 50 liters of plying a Solution of the nitrite containing cal 60 per cent (by volume) nitric acid and 10 cubic cium nitrate and calcium carbonate, nitric acid 25 meters of a mixture of oxygen and nitrogen con and a gaS COInprising elementary oxygen to the taining 50 per cent of oxygen are led per hour lower end of a column of aqueous liquid and through the tube described in Example 1. With Separately withdrawing gas and liquid at the a pressure of 8 atmospheres, 99.9 per cent of the upper end of Said column, Said column being of nitrite is converted into nitrate. sufficient length to effect substantially complete 30 30 oxidation of the nitrite and to produce a gas sub Eacample 3 Stantially free from Oxides of nitrogen. 90 liters of calcium nitrate-calcium nitrite 4. The process for the oxidation of Sodium sludge containing 4 per cent of Initrite nitrogen nitrite to Which comprises supply and 3.5 per cent of calcium carbonate, 100 liters ing a Solution of the nitrite, nitric acid and a 35 35 of 60 per cent (by volune) nitric acid and 25 gaS COmprising elementary OXygen to the lower cubic meters of air are passed hourly into a tube end of a Column of aqueous liquid and separately 10 meters in length and 100 millimeters in di Withdrawing gas and liquid at the upper end of ameter. With a pressure of 3.6 atmospheres, 98 Said column, Said column being of Sufficient length per cent of the nitrite are converted into nitrate. to effect Substantially complete oxidation of the 40 40 Eacample 4 nitrite and to produce a gas Substantially free from Oxides of nitrogen. 100 liters of an aqueous Solution containing 6 5. The process for the oxidation of Sodium per cent of sodium nitrate, 3 per cent of sodium nitrite to Sodium nitrate which comprises Sup nitrite and 2 per cent of sodium carbonate, to plying a Solution of the nitrite containing sodium 45 gether with 20 liters of 60 per cent (by volume) nitrate and SOdium carbonate, nitric acid and of nitric acid and 2 cubic meters of a mixture a gas comprising elementary oxygen to the lower of equal volumes of oxygen and nitrogen are passed per hour through a tube 10 meters long end of a column of aqueous liquid and separately and 100 millimeters in diameter. When a pres withdira Wing gas and liquid at the upper end of sure of 8 atmospheres is maintained, 99.9 per Said column, said column being of Sufficient length 50 cent of the nitrite are converted into nitrate. to effect Substantially complete Oxidation of the The process according to the present invention nitrite and to produce a gas Substantially free is applied in a similar manner to the Oxida from oxides of nitrogen. tion of other nitrites, in particular those of the WALTER GROSS. 55 5 5 alkali metals and alkaline earth metals.