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308
TABI,B111-AXMONIARECOVERY
Ammonia Used 400 cc. 5 % ammonium hydroxide.. 200 cc. 2.5% ammonium hydroxide.,
NHaOH Grams 20
............... .............. -5 T O T A L ................. ., 25
Ammonia Recozeved Extract liquor.. Wash liquor., Wood (steam distillate),.......................
............................... ................................
.................
TOTAL
.18.65 5.49 0.78 24.92
DISCUSSION OF EXPERIMENTAL RESULTS The results obtained from the first series of extractions (Table”1) show that under the conditions of these tests ammonia is not an efficient solvent for rosin contained in wood chips of pulp size. Inasmuch as the temperature of extraction cannot be increased and previous studies have shown that increasing concentration is no aid, increase of time is the only variable factor. As shown in Table 11,by doubling the time of digestion the larger chips may be extracted as completely as the smaller size. A comparison in the efficiency of various solvents under the same conditions shows that 70 per cent denatured alcohol is of the same order as the more generally used volatile oils. Inasmuch as this is a product which might well be an endproduct in the use of the extracted chips in hydrolysis or in sulfite pulp, it seems peculiarly advantageous because
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its recovery would utilize the same methods and equipment as are employed in its production. Although no extractions were made by employing other alkaline solutions, such as sodium and potassium hydroxides, the results of commercial practice in the soda process of pulp manufacture from resinous woods show practically complete removal of rosin. Similar results were obtained by Bates,4 showing that the efficiency of rosin extraction with sodium hydroxide in the case of resinous pine is 95 to 97 per cent where the chips are thoroughly washed. Its disadvantage as a purely rosin solvent lies in the difficulty of recovering rosin from the soda liquor. This is obviated by the use of ammonia because of the ease with which the ammonium product is decomposed by heat, and the rosin subsequently recovered. Objections to the use of ammonia as a solvent for rosin have been made on account of the necessary use of gasoline for the separation of humus from the rosin and on account of the retention of ammonia in the chips. The analytical data in this study show that the humus, relatively small in quantity, does not retain any appreciable quantity of a low boiling solvent, and that steam distillation will effectively remove all but traces of ammonia from the wood chips. The absorption and concentration of ammonia involve no problem. 4
THISJOURNAL, 6 (1914), 289.
Analytical Determination of Oxides of Nitrogen in Gas Mi xt u r esl’* By Charles L. Burdick SHEFFIELD EXPERINENT STATION, NITRATE DIVISION OF THE
The following paper describes a simple method of determining oxides of nitrogen in gas mixtures by washing the gas in dilufe alkali. A theorefical consideration of the reactions inaoloed is included.
N connection with an investigation of the equilibrium between aqueous nitric acid, nitrogen peroxide and nitric oxideSand the study of the rate of reaction and catalysis of the oxidation of nitric ~ x i d eit, ~became necessary ho devise a method for the determination of the nitrogen oxide content and the degree of oxidation of a mixture of oxides of nitrogen diluted with nitrogen or air. It was found in the laborat,ory work that washing of a measured volume of the gas in dilute alkali afforded the simplest and most rtccuratc means of determination of the gas compositions. The later work which served to develop the method as a means of technical control analysis was carried out in connection with a study of the performance of nitric acid absorption towers at the.Sheffield Experiment Station at U. S. Nitrate Plant No. 1. The reactions representing the mechanism of the absorption of nitrogen peroxide or mixtures of nitrogen peroxide and nitric oxide in dilute alkali are expressed in Equations I and 11:
I
+
+
+ + +
3N02 2NaOH = 2NaN03 NO HzO NO NO2 2NaOH = 2NaNOz €1~0 2N02 2NaOH = NaN03 NaNOz HsO
+ + +
+
(1) (11) (111)
September 9, 1921. 2 Published by permission of the Chief of Ordnance, War Department. 8 Burdick and Freed, J . Am. Chem. SOC.,48 (1921), 518. 4 Results to be published later. 1 Received
ORDNANCB
DEPARTMBNT, SHEFFIELD, ALA.
Equation I11 represents the direct sum of I and 11, but is not indicative of the mechanism of absorption. Dry mixtures of nitrogen oxides or mixtures containing water vapor not in excess of the saturation value of the corresponding nitric acid a t the temperature of the absorption apparatus react strictly in accordance with the above equations. Thus a gas containing an equimolar or less proportion of NO2 yields pure nitrite on absorption, the excess NO escaping from the solution as such. Mixtures containing an excess of NO2 are completely absorbed in alkali, with the production of a mixture of nitrate and nitrite. The concentration of HNOB vapor in such a gas is in general negligible. It has been determined that ” 0 3 and NO cannot coexist in a gas in appreciable quantities. In the presence of nitric acid mist6 or fog (as distinct from vapor) the absorption takes place as represented above, There is, however, an additional production of nitrate due to the simple absorption and removal of the mist by alkali. The absorption of nitrous gases which contain relatively large quantities of water vapor and which are a t an elevated temperature, such as obtains before a nitric oxide reaction chamber, is a somewhat more involved process than the simple cases above outlined. As long as but one phase is present nitric acid vapor is practically nonexistent in a gas containing NO. However, as the temperature of such a gas falls in its passage to the 6 This mist is not concentrated nitric acid, but is acid of that composition which is in eqn librium with the nitrous gases at the temperature in question. Thus, the mist entrained in a gas containing 0 . 5 per cent NO1 and 0 . 7 per cent NO is a fog or suspension of droplets of 35 per cent nitric acid.8
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absorption bottle, there is a condensation of fog or mist particles and the reaction 3NOg
+ H2O (liq.)
2HN03 (aq.) f NO
takes place. Since this is not an oxidizing or reducing reaction, there is no change in the degree of oxidation of the mixture as a whole, but there is a radical change in its constitution and composition. It has changed from a gaseous mixture containing substantially nothing but NO2, NO, water vapor, and diluent gas t o a two-phase mixture containing aqueous nitric acid in the liquid phase as a mist, and Not, NO, and water vapor in the gaseous phase, the whole being practically a t chemical equilibrium. It is the composition of this latter mixture which determines the absorption behavior in the presence of the alkali. For example, analysis of a gas mixture sampled from a main leading to a reaction chamber showed the composition of the gas reaching the alkali solution to be "01 NO2 NO
mist
Per cent 0.21 0.5 0.7
-
TOTAL 1.4 IExpressed as percentage by volume "03. It would be that volume occupied by the "01 in the mist if it were vaporized without decomposition.
The mean degree of oxidation of this gas mixture in terms of NO2 is 57 per cent. Actually a t the temperature of the gas in the flue (SO') there was no mist existent. The composition of the gas was NOa
AT0
Per cent 0.8 0.6
-
TOTAL 1.4 Degree of oxidation 57.0
The total oxides and degree of Oxidation are the same in both cases. The last analysis represents the composition of the warm gas a t 80' flowing in the pipe, whereas the first represents the composition of the same gas after being cooled to 30". If the equations of absorption were accepted without consideration it would be anticipated that the warm gas in the pipe, since its degree of oxidation was over 50 per cent, would produce a mixture of nitrate and nitrite only and that NO would escape from the absorbing alkali solution. As a result of the condensation of mist on cooling and subsequent progress of the hydrolytic reaction, there was a considerable change in the composition of the gaseous phase of the mixture and, as a matter of fact, very nearly one-third of the NO originally present escaped absorption in the first alkali train in the absorption apparatus. It is evident, then, that an analytical apparatus for the determination of the total oxides of nitrogen and their degree of oxidation which is t o employ the principle of rapid absorption in alkali must consist of two parts, an alkali train for the absorption of all of the NO2 and part of the NO and an aspirating flask or similar device in which the quantity of escaping NO may be determined. DESCRIPTION OF APPARATUS A portable apparatus which has been found convenient for control purposes is shown in the figure. It consists of a frame supporting the absorption bulb B and the aspirating bottle F. The inlet tube A of capillary tubing is protected by the projecting strap iron or wooden guard K which may be raised out of position. The absorber in B is of the special form shown. It has the advantage of being a very efficient absorber, not requiring a large volume of solution, and not requiring a special containing flask. The clamp C is
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used as a support for the absorption apparatus. The absorption apparatus is connected to the evacuated aspirator bottle by a short rubber connection. The volume of the aspirator bottle should be known within 1 per cent. PROCEDURE FOR ANALYSIS A known amount of 0.1 N alkali (carbonate-free) is run into absorption bulb B and diluted with water until the liquid is a t the top of the first bell. According to the concentration of the nitrous gases, from 10 to 50 cc. of carbonatefree alkali will be required. An automatic pipet may be conveniently used. The aspirator bottle must be evacuated and all connections and stoppers should fit firmly, so that absence of leaks is insured. With the strap iron or wooden guard K let down, the apparatus may be safely carried. I n sampling, the tube A is firmly seated in the opening in the flue and the measured quantity of gas aspirated slowly through. The rate of bubbling through the absorber may be a little faster than the bubbles a t the base of the inlet tube can be counted. Cock D is then closed. The opening in the apparatus frame through which tube A projects is purposely made large so that a certain flexibility of setting is obtained. In withdrawing or introducing the sample tube it should he kept well centered in the pipe opening to avoid nitric acid running off the walls into the tube. The solution is removed for analysis by IIIII 1 1 1 lowering the bulb B and rinsing the absorber
c\,
