27
.
0
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol.
IO,
No. 4
of wood of small diameter are practically valueless for preliminary steaming for removal of turpentine a n d pulping purposes as they give no appreciable yield of rosin. FORESTPRODUCTS LABORATORY pulp but consume cooking chemicals. The extraction MADISON,WISCONSIN plant handles 400 tons of chips per day, of which 300 tons are burned under the boilers for fuel purposes. THE PRODUCTION OF'NITRIC ACID FROM NITROGEN This would make possible the rejection of 7 5 per cent OXIDES' of t h e wood for fuel purposes, while in our experiments By GUY B. TAYLOR, JULIAN H. CAPPSAND A. S. COOLIDQE 36.3 per cent of the original wood represented the maxiReceived February 14, 1918 mum amount of screenings rejected. The cost of screenPractically all processes for the fixation of atmosing is small and this matter should receive further study. There is no question t h a t if we had screened pheric nitrogen wherein t h e ultimate product desired out 7 5 per cent of t h e fines and only pulped the com- is nitric acid involve recovery of nitrogen oxides. The arc and ammonia oxidation processes produce these paratively coarse chips better and higher yields of pulp would have been obtained. Further, the ex- gases largely diluted with air or nitrogen. Converting tracted chips were apparently burnt by the steaming t h e nitrogen oxides into concentrated nitric acid refor removal of the oils a n d rosin, as could readily be quires a n extensive equipment and is a considerable seen by the clean fracture obtained in many cases on item in t h e cost of manufacture. The usual industrial procedure is t o pass t h e gases breaking the chip. Rather surprising yields of oils were obtained by containing nitrogen peroxide (NOz) with a n excess condensing the relief gases from the digester. The of oxygen through a series of large packed towers yield of oil on the extracted chips averaged about 2.3 and absorb the nitrogen oxides in water. The strength gallons per ton of bone-dry chips. For cooks 254 t o of the circulating acid varies in each tower, the first 256, made on the fresh wood, a n average of about 6.7 producing acid of 3 0 t o 50 per cent concentration, degallons of oil were obtained per ton of bone-dry chips. pending on the concentration of NO2 in the gas, while The wood during transit and in storage a t t h e Labora- the last is almost entirely water. The diluter acids tory had probably lost some turpentine and other are moved up from tower t o tower as their concentravolatile oils, which will probably explain the discrep- tion increases so t h a t t h e whole of t h e product is conancy between these results and those obtained a t the centrated as far as practicable. This acid is further concentrated, when required, by means of distillation extraction plant. Cooks 247 t o 254 were made on the extracted chips from sulfuric acid. While t h e use of water as a n absorbent produces varying t h e conditions of pulping as can be seen from a study of Table 11. No special difficulties were ex- nitric acid direct, i t has certain disadvantages. T h e perienced in pulping the extracted chips and t h e rather tower space required is very large and storage tanks, low yield of pulp we believe can be remedied t o a large pumping lines and auxiliary equipment for handling extent by the selection of only the larger chips through the dilute acids must be made of special material t o resist attack. The acid produced must nearly always better screening. The strength of t h e paper was low when compared be concentrated further. Also i t is practically imwith t h a t which has been made a t the laboratory from possible t o absorb all the nitrogen oxides by any syslongleaf pine round wood. This weakness, we believe, tem of towers of reasonable size and number. I n was partly due t o the small size of the chips in which some plants a tower circulating caustic soda or sodium the smaller slivers will readily overcook and t o t h e carbonate solution is installed a t the end of the sysapparent burning of the chips b y the steaming treat- tem t o recover the last traces of acid. There have been a large number of patent claims ment. Cook 2 5 3 was run with t h e object of preparing a for processes involving the working up of nitrogen pulp suitable for t h e manufacture of a container board. oxides. Alkaline solutions are mentioned frequently Cooks 254, 2 5 5 and 256 were run on the fresh wood. both for the production of nitrates and nitrites. It I n these cooks apparently insufficient alkali was used has also been proposed t o recover the nitrogen oxides to saponify all the rosin and a t the same time success- in concentrated form from alkaline solutions with fully pulp the wood. Cook 2 5 5 represents a raw cook, regeneration of the alkali. Proposals2 for freezing while cook 256 was so raw t h a t it was not passed over out X204 do not seem commercially practicable. the paper machine. Cooks 2 5 4 t o 256 are of very Patents* are held on a process for concentrating nitric limited interest, as they represent pulping tests made acid by means of liquid nitrogen peroxide. An elecon chips of so high an 'oil and rosin content t h a t com- trolytic process for concentrating dilute acid is proposed in a patent4 held by the Salpetersaure Industrie mercially they would be extracted before pulping. While the above experiments indicate t h a t a com- Gesellschaft wherein N O evolved a t t h e cathode is mercial grade of kraft pulp might be made from long- led into the anode space for re-oxidation. Classens 1 Published with the permission of the Director of the U. S. Bureau of leaf yellow pine extracted chips, i t is evident t h a t the best results will be obtained if the chips are carefully Mines. 2 W. Ramsay, British Patent 26,981 (1907); P. A. Gupe, U. S. Patent selected b y means of a proper screening syptem, b y 1,057,052 (1910). 8 M. Moest, U. S. Patent 1,180,061 (1907); I,. Friedrich, British Patusing the largest chip for extraction compatible with and 403 (1911). maximum recovery of the oils and rosin, and by avoid- ents 4319 British Patent 18,603 (1906). ing as far as possible the burning of the chips in t h e 6 British Patent 18,065 (1915).
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Apr., r g I 8
suggests the use of catalyzers, nickel or cobalt oxides and nitrates, for promoting the oxidation of N O t o NOZ. Among the more prominent methods proposed for the recovery of nitrogen oxides is t h a t of absorption in rather concentrated (go per cent) sulfuric acid with subsequent removal of the oxides of nitrogen by heat or denitrifying agents. The concentrated gas thus obtained is reabsorbed in the presence of air in wal,er t o form nitric acid. I n some experiments in this laboratory on absorbing nitrogen peroxide in sulfuric acid containing chromic acid, it was found t h a t nitric acid was produced directly and if the absorbing liquid is maintained a t 1 5 0 O C., t h e acid issues from the system as a mist which, when precipitated, is 95-100 per cent “ 0 3 . Such a process has two drawbacks: the necessity for absorbing in a hot solution and the electrolytic recovery of chromic and sulfuric acids from chromium sulfate. A number of experiments were made in a n attempt t o produce a strong mixed acid by electrolysis of solutions of NOz in concentrated sulfuric acid. If the nitric oxide from the oxidizer in the presence of excess of air is cooled and allowed sufficient time t o react wholly t o NOz, then its reaction with concentrated sulfuric acid may be written: 2NOz HzS04 = HNOs HNOSOi Theoretically upon electrolysis this reaction may t a k e place: “OS04 ZHZO= HN03 H2S04 Hz 2 faradays This reaction is a n ideal one since i t also removes water by reaction and concentrates the acid. The power required is not great. I n attempting t o realize the reaction experimentally platinum electrodes were used and alundum thimbles as diaphragms. It was found t h a t a t low concentrations of nitrososulfuric acid, equivalent t o I O per cent ” 0 3 in a mixed acid, a current efficiency of 5 0 per cent could be obtained for a short time. However, as the concentration of nitric acid in the solution increased, the efficiency dropped t o a small value. Even when using 95 per cent sulfuric acid in the cathode chamber, nitric acid or nitrososulfuric acid diffused through the diaphragm and was reduced to N O and some free nitrogen. The nitrogen sepresents a loss of acid which might be prevented with efficient diaphragms. However, electrolysis of solutions containing the equivalent of nitric acid ordinarily used in nitrating acids did not work a t all.
+
+
+
+
+
+
ABSORPTION B Y WATER
The chemical reactions involved in the conversion of nitric oxide, which is produced by both the arc and ammonia oxidation processes, t o nitric acid are essentially as follows: 2 NO 0 2 2NOz (1) 2 NO2 HzO HNO, HNOz (2) 3 HNOz ”01 2 NO HzO (3) The N O arising from Equation 3 reacts with oxygen and the cycle is repeated. A full discussion of these reactions is given b y F. Foerster and M. Koch.’
+ +
1
+
Z angew. Chem., 21 (1908), 2161.
+
+
27 1
The reaction expressed by Equation I begins t o proceed in the direction from left t o right when the gases are cooled below 600°, but will not go nearly t o completion even in a large excess of oxygen until 200’ is reached as shown by calculation from the equilibrium formula. However, i t has been shown by Foerster and Blichl t h a t this reaction has a negative temperature coefficient so t h a t the gases must be cooled as far as practicable before entering the absorption system. I t has also been shown t h a t this reaction occurs in distinctly measurable time.2 Hence, i t has been found necessary t o allow the gases t o pass into a large empty chamber or oxidation tower in order t h a t the nitric oxide may react completely t o nitrogen peroxide before the gases enter the absorption system.8 An absorption system proposed by Moscicki4 [British patent 17,355 ( I ~ I I ) ] in which the gases are passed horizontally and a t right angles t o the acid flow inserts a n empty oxidation space between successive units. EXPERIMENTAL
The experiments described in this report were made with a small experimental plant used in experiments t o determine the efficiency of metallic gauzes as catalyzers for ammonia oxidation. I t may be stated a t the outset t h a t i t was fully appreciated t h a t the results obtained could not be strictly carried over t o a n industrial operation on a thousandfold larger scale, especially as t o the ratio between tower space and capacity, but i t was thought t h a t the relative importance of acid concentration in the several towers, temperature, speed of passage of the gases and circulation of the absorption liquid, oxygen excess required, etc., could be obtained, and t h a t many details might be worked out t h a t would be of value in operating a larger system. Such details are generally regarded as legitimate in4ustrial secrets and are almost never published. There is practically no information of a detailed nature available in this country dealing with gases as rich as those produced in ammonia oxidation on any sort of an efficient absorption system. The apparatus consisted essentially of an ammonia saturator for securing a mixture of air and ammonia, a n oxidizer utilizing a platinum gauze, 3 X 6 in., for producing nitric oxide and a n absorption system consisting of a cooler and five stoneware towers. The absorption system is shown diagrammatically in t h e accompanying sketch. The gases from the oxidizer passed through an iron pipe into the Pyrex glass tubes of t h e cooler. These 8/4-in. tubes were arranged in two sets of three U-tubes each, in parallel. The cooling water was continuously passed through the housing box which was 30 X 24 X 2 4 in. Each U-tube was provided with a drain for condensate and liquid sealed with a test-tube. From the condenser the gases passed t o Oxidation Tower o and then in t u r n t o 12.angew. Chem., 23 (1910), 2017. 2 W.Holwech, “Uber die Reaktion zwischen Stickoxyd und Sauerstoff,” Ibid., 21 (1908), 2131. 8 E. K. Scott, “Production of Nitrates from Air, with Special Reference to a New Electric Furnace,” J . SOC.Chsm. I n d . , 34 (1915). 113. An experimental absorption system with oxidation tower is described. 4 E. K . Scott, “Manufacture of Synthetic Nitrates by Electric Power,” Ibid.. 36 (1917). 774.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Air
Vol.
IO,
No. 4
- NH,
$.
uuuuu
the bottom of the coke-packed Towers I , 2 , 3 and 4. These towers are of t h e following dimensions:
.................... ............
Height.. 6 ft. Diameter inside.. 10 in. Capacity.. . . . . . . . . . . . . . . . . . . 3.27 cu. ft. = 1.50 cu. ft. Tower packed with coke 5 1 / 2 ft. at 50 per cent free space. Reaction space above coke and in connecting pipe . . . . . . . . . = 0.40 cu. ft. Reaction space provided by the Oxidation Tower 0, and pipe connecting to Tower 1 . . ......................... = 3.40 CU. ft. Reaction space in each coke tower.. ..................... = 1.90 cu. ft. Total reaction space in the system (not counting space above coke in Tower 4 ) . .................................... = 10.60 cu. f t . The coke was irregular in size, most pieces 1 to 2 in. No accurate estimate could be made of the absorbing surface.
...
The desirability of having such an oxidizing tower as o for the oxidation of N O was demonstrated in small scale laboratory experiments. Nitric oxide from a small oxidizer containipg'an excess of oxygen was cooled t o room temperature by means of a Liebig condenser. By means of suitable stopcocks the cooled gas could be passed through a 7-liter glass vessel into a small glass coke-filled tower or by-passed around the vessel. Forty per cent nitric acid was circulated rapidly through the tower and the efficiency of absorption determined by samples, as will be described later. I n the following table, samples of the gas were taken with the reaction space in circuit and then immediately thereafter with the space ,cut out so t h a t all other conditions were the same. Liters Re action per Space Minute In ............. 0 . 7 out............ 0 . 7 In . . . . . . . . . . . . . 0 . 7 O u t . . . . . . . . . . . . 0.7 I n ............. 1.0 Out. ........... 1 . 0 In 1.8 Out 1.8 In 1.8 1.8 out
............. ............ ............. ............
Total Acid Removed before Tower Per cent 20 13
Total Acid Absorbed in Tower Per cent 49
18
56 46
7
46 54
12
52 43
13 20 5
10 6
51
53
39
Efficiency of Tower Per cent 61 65 56
59
58
58 59
46
58
41
These results show clearly t h a t a t the higher velocity the reaction space increased the efficiency of the tower. The wet walls of the reaction space absorb acid and hence the gases enter the tower less concentrated t h a n in cases where i t was not used, but this fact does not affect the general conclusion t h a t the oxidation space is useful. The rest of the system needs little explanation. The acid was circulated b y sucking u p through glass lines into the feed bottles with a filter pump. Each bottle was provided with a n automatic glass valve which closed under suction. The distributor a t the top was a type manufactured b y M. A. Knight in which acid overflows through 8 small holes arranged in circle. M E T H O D OF O P E R A T I O N
Air was metered and passed through the ammonia saturator so as t o make a mixture containing 8 t o 11 per cent ammonia. Auxiliary air, also metered, was added a t the point A just below the oxidizer. By controlling the relative volume of air and the composition of t h e ammonia-air mixture, any desired oxygen excess could be obtained in the absorption system. The performance of each tower was determined by taking gas samples from the sample holes C. At B a sample was taken, where the gas was still hot and before any condensation could have taken place, which represented the total acid entering the system. The samples were taken into evacuated glass bottles of I or 2 liters capacity. Each bottle was provided with a ground glass stopper carrying a capillary stopcock. After taking the sample, a measured volume of water containing hydrogen peroxide was introduced into each bottle t o absorb the acid a n d sufficient t o bring the resulting nitrogen-oxygen mix-
Apr., 1918
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
ture t o atmospheric pressure. The volume of the bottle, minus t h a t of t h e introduced reagent, gave the volume of gas, which, together with its analysis, furnished t h e necessary data ,required t o calculate the volume of nitrogen present. The acid was titrated with N / 7 NaOH. Since nitrogen does not react and is constant throughout the system, i t is evident t h a t i t may be used as the reference point and the efficiencies calculated from a knowledge of grams of acid per liter of nitrogen. It was not found practicable t o base any conclusions on measurements and analyses of t h e acids produced in each tower since the packing held up an indefinite quantity, and the runs were not long enough t o reduce this source of error. The plant was operated 6 or 7 hrs. per day. Acid was run t o make acid for future experiments. Samples were added t o first tower and the rest allowed t o build up. taken t o determine relative effects of velocity of gas and oxygen concentration. Cooler-water cooled. Acid circulated through towers continuously 6 t o 15 liters per hour. 5 , begun 2:OO P.M.,closed 4 9 0 P.M. R U N 2-Dec. Dec. 6, begun 9:45 A.M., closed 4:15 P.M. Cooler-air cooled. R a t e acid circulation-towers flooded every 30 min. with 4 liters. Strength of acid condensed in cooler--5 per cent HNOa. Strength of acid condensed in Tower 0-30 per cent “ 0 3 . 7, begun 1O:SO A.M.,closed 4:lO P.M. R U N :$-Dee. Dec. 8, begun 9:30 A.M., closed 4:OO P . M . Dec. 10, begun 9:40 A.M., closed 4:lO P.M. Dec. 11, begun 9:30 A.M., closed 4:OO P.M. Cooler-air cooled. Rate acid circulation-tower flooded every 30 min. with 4 liters. Strength acid condensed in cooler-7 per cent “0s. Strength acid condensed in Tower 0- 32.5 per cent ”01. RUN 4-Dec. 14, begun 10 A.M., closed 32-5 P.M. Cooler-water cooled. Rate acid circulation-8 liters per hour continuous. Strength acid condensed in cooler-5 per cent “ 0 s . R U N 5-Dec. 12, begun 10 A.M., closed 2:15 P.M. Cooler-10 t o 1:15 P.M., air cooled; 1:15 t o 2:15, water-cooled. Rate acid circulation-towers flooded every 30 min. with 4 liters. R U N 6-Dec. 13, begun 10:30 A.M., closed 4:OO P.M. Cooler-air cooled. R a t e acid circulation-tower flooded every 30 min. with 4 liters. R U N 7-Dec. 17, begun 10 A.M., closed 3 P.M. Cooler-air cooled. Rate circulation-tower flooded every 30 min. with 4 liters. 7 per cent NaOH solution in Tower 4. R U N 8-Dec. 19, begun 9:45 A.M., closed 1:45 P.M. Same as Run 7 , except 30 per cent NaOH solution in Tower 4. 80 t o 90 per cent of acid absorbed by alkali is in form of nitrite.
RUN ?-Preliminary
The following tables contain the full data of all experiments. The date, time, and cubic feet per hour, and percentage of the total acid absorbed are given a t the moment of taking the samples. I n general, six samples were taken a t once giving the total acid per liter of nitrogen entering t h e system, entering each tower, and leaving the last tower. The temperature of the gas entering each tower and t h e specific gravity of the acid in circulation a t the time were recorded. T h e specific gravity was taken roughly with a hydrometer a t the temperature of the acid running from the tower. I n general, the acid from the first tower was 8 or 10’ lower t h a n the entering gas, in t h e other towers z or 3’ lower. DISCUSSIOPI’ O F RESULTS
Run 3 having demonstrated t h a t the strength of t h e acid could be built up in Tower I t o about 5 0
273
per cent without materially increasing the acid loss from the system, i t was considered sufficient in other cases t o take samples with t h e acid concentrations in the several towers approximating what they would be toward the end of a run or the time when the acids would be moved up t o the next tower. The circulation of the acids through the towers was carried out in such a way as t o be sure t h a t the coke packing was always thoroughly wet. This was done in most cases by periodical flooding, i. e., running in 4 liters of acid a t the top in I O min. a t 30min. intervals. After flooding in this manner i t was found t h a t the absorption capacity of the first tower did not change for a n hour or more. I n general, about I O liters were placed in the jar for each tower a t the beginning of a run. The volume of the circulating liquid increased as absorption took place in Towers I and 2. Tower I received part of the acid indicated as having been removed by Tower o by the gas analytical results, due t o condensation in t h e connecting pipe. The volume of acid in circulation in 3 and 4 decreased, which will be explained later. TEMPERAruRE-Unfortunately, all our experiments were made under winter conditions a n d not much information was secured on the effect of temperature, which is probably the most important factor in determining the size of a n absorption equipment necessary t o handle a given quantity of gas. The small size of the plant did not permit of building up temperatures on short runs. All experience, however, goes t o show t h a t the absorption should be carried out a t as low temperatures as practicable. .The effect of running the cooler air- and water-cooled is interesting. When water-cooled most of t h e water carried by the gas is condensed out with but little acid. The gases enter Tower o a t room tempera- * ture, about 2 5 O , where they warm u p by the reaction going on between nitric oxide and oxygen. .Practically no acid was obtained from Tower o under these conditions. When the cooler was air-cooled, most of the water carried by the gas was condensed in Tower o together with considerable acid. Artificial cooling of the gas in the reaction space (Tower 0) would be advantageous. O X Y G E N EXCESS-when the oxygen in the system was near the theoretical requirement, there was no marked increase in the acid loss. However, i t is probably best not t o let the concentration of oxygen in the exit gas fall below 5 per cent. P R O D U C T I O P ; A N D EFFICIENCY-The first three towers (0, I and 2 ) absorb about 8; per cent of the acid input, the last two only about T O per cent. At a gas velocity of about 2 . 5 cu. f t . per min. doubling the number of towers would probably not recover the other j per cent. On a basis of I O per cent ammonia in the air mixture fed t o the oxidizer and g o per cent efficiency of oxidation, z ; per cent auxiliary air must be added after oxidation t o secure a n oxygen concentration in the exit gas of j per cent. This excess may be secured in industrial operations from the operation of the acid lifts, but it would probably be advantageous t o add
.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
274
TOWER 0
TOWER 1
TOWER 3
TOWER 2
a
2:30 4:OO
P.M. A.M. A.M. P.M. P.M. P.M.
176 145 340 137 107 172
0.2435 9.0 0.2210 65.8 0.2125 7.5 0.1965 55.8 0.2540 6.0 0.2385 42.0 0.3160 7.0 0.2940 37.9 0.2845 10.4 0.2550 37.4 0.2295 7.0 0.2140 21.0
35 32 35 38 36 36 40 41 42 43
RUN No. 2 1.24 0.0765 17.0 24 0.1089 18.6 26 1.26 1.275 0.1022 23.7 30 0.1314 33.7 38 1.285 RUN No. 3 0.0576 17.5 24 1.24 1.245 0.0597 18.9 23 0.0891 21.7 25 1.26 0.0751 24.4 22 1.27 0.0803 25.1 25 1.27 1.285 0.1098 35.0 27 1.295 0.1004 32.4 23 1.30 0.1030 33.9 25 1.31 25 25 1.31 1.31 , 25 1.31 25 25 1.31 ,. 25 1.31 1.32 0..1'485 42.3 24 R U N No. 4 0.1012 22.6 25 1.27 1.29 0.1272 33.6 26
149 146
0.2808 0.2637
5.8 6.5
Dec. 12 Dec. 12 Dec. 12
11 A.M. 265 12:45 P.M. 265 2 : l O p . ~ . 265
Dec. 13 Dec. 13 Dec. 13
11:45 A.M. 2:OO P.M. 3:40 P.M.
Dec. Dec. Dec. Dec.
1 0 : 4 0 ~ . ~ .144 1 1 5 5 A.M. 142 2:io P.M. 116 ~ : ~ O P . M . I34
0.2763 0.2510 0.3590 0.3140
.... .... ..... ...
10:20 11:45 1:35
0.2592 0.2443 0.2313
36 1.315 .... ..... ... ... ...... ... 38 1.315 42 1.315 ..... ... , ...
Dec. 19 Dec. 19 Dec. 19
A.M. A.M. P.M.
140 136 264
0.1638 0.1575 0.2115 0 1638 0.1661 0.1782 0.1737 0.1642
48.2 50.6 46.5 44.1 41.4 31.6 34.2 29.9
35 36 39 35 39 43 39 38 37 , 37 37 , 40 49 40 17.8 41
... . ... .,.... ... .. ... ... ... ... ... ... .. ... .. ... ... .. ... ... . ... . ... ,
o.'idis
0.2646 58.1 30 0.2456 45.0 32
.. . ..... . ..
Cubic feet gas per minute.. Efficiency of absorption-per cent., HNOa recovered in 24 hours-lbs..
... ..... ... ... .....
. ... .... . ... .. .... .... .. ... ... ..... ... 40 38 1.31 1.31
1.25 98 23
2.5 95 44.5
.. ... ... 1.18 ... ..... .. ... ... ..... ... 24 zi i:i4 1.195 RUN No. 8 21 1.21 .... ... ,.... ... 26 1.22 ..... . ... 27 1.24
t h e retower. capaciliter of 4.0 91
68
The last two towers were very inefficient. This was due largely t o the great dilution of the nitrogen oxide when they reached this part of the system. P a r t of the loss is due t o the formation of a n acid mist which, of course, is unabsorbable. The decrease in volume of the circulating liquid in the last two towers cannot be accounted for by evaporation and is caused by this formation of mist. WITH
A
.. ... .. ,.. ... ... .. ....
RUN No. 5 0.1084 25.5 21 0.1399 36.5 22 0.1309 35.4 23 R U N No. 6 0.0587 17.8 19 0.1975 53.6 24 1.30 0.2080 45.8 26 1.30 0.0842 22.3 22 0.2367 44.6 30 1.305 0.1040 24.4 22 R U N No. 7 36 1.295 25
enters most of the air required before the gas action space preceding the first absorption Under the conditions of the tests our plant had ties a s follows, based on 0.285 g. HNO, per nitrogen:
EXPERIMENTS
2.9 4.7 0 13.3 4.2 6.1 5.0 5.7
0.0117 0.0117 0.0186 0.0147 0.0152 0.0204 0.0161 0.0163
1.6 2.3 2.7 3.6 2.6 3.9 3.1 3.1
17 17 19 18 20 21 20 20 18 18 18
1.005 1.01 1.01 1.01 1.015 1.02 1.02 1.02 1.02 1.02 1.02 1.02 1.02 1.02 1.02
0.0081 9.5 0.0072 10.4 0.0115 6.4 0.0075 7.3 0.0097 9.0 0.0119 8.0 0.0095 8.8 0.0099 8.5 00171 2.0 p.0095 3.5 0.0096 5.8 0.0166 1.8 0.0177 2.0 0.0201 1.8 0.0140 6.3
0.0126 0.0239 0.0315
11:15 2:lO
17
0.0137 0.0398 0.0164 0.0156
1.195 1.20 1.20
Dec. 14 Dec. 14
17
1.01 1.015 1.015 1.02
0.2582 23.7 0.2700 23.0 0.2970 20.4
20.6
17 17
22 23 21 22
0.0477 8.2 17 1.075 0.0562 10.3 18 1.075 0.0522 10.2 17 1.085
0.2205 0.1935 0.2628 0.2007 0.2070 0.2173 0.2151 0.2050 0.3213 0.2646 0.3006 0.3294 0.3222 0.3222 0.2412
25.7 18.6 19.6 18.4 19.8 18.0 19.2 19.9
10:20 A.M. 10:35 A.M. 2:05 P.M. 2:20 P.M. 2:40 P.M. 3 5 0 P.M.
134 125 142 160 138 152 150 128 131 140 151 114 121 124 152
67 71 62
1.3 1.3 2.5 3.3
1.195 1.21 1.225
1 1 :So A.M. 1:50 P.M. 3:45 P . M . 10:40 A.M. 12 M 3 :40 P.M. 11 :20 A.M. 3:05 P.M.
A.M. P.M.
0.0174 3.5 23 1.05 0.0437 3.1 25 1.06 6.2 24 1.065 0.0231 0.0246 5.3 24 1.07
0.2403 20.2 p.1917 34.5 40 1.285 0.2286 15.5 0.1935 23.3 48 1.280 0.2232 10.5 0.1998 30.7 36 1.295
7 7 7 8 8 8 10
Dec. Dec. Dec. Dec.
6.0 8.5 7.0 1.6 4.0 6.0
0.0378 0.0393
Dee.
10:10 A.M.
O.'did3 0.0205 0.0306 0.0144 0.0177
1.165 1.17
21.5 0.2270 52.0 22.3 0.2322 41.4 18.0 0.2196 43.5 16.8 0.2286 35.2
Dec.
1.02 1.02 1.025 1.025
0.0189 0.0230 0.0320 0.0263 0.0283 0.0335 0.0306 0.0333
0.2890 0.2997 0.2664 0.2745
10 11 11 11 11 11 11 11
i:di
1.13 1.14 1.145 1.15 1.16 1.175 1.185 1.205 1.21 1.21 1.21 1.23 1.23 1.23 1.24
137 147 143 145
Dec. Dec. Dec. Dec. Dec. Dec. Dec. Dec. Dec.
20 19 21 25
0.0275 0.0531 0.0396 0.0394
3:40 P.M. 11:OO A.M. 1:15 P.M. 3 5 0 P.M.
COTTRELL
PRECIPITATOR-
About a year ago, in making small scale experiments in the laboratory on the catalysis of ammonia oxidation, in which the acid make was determined by absorption in gas washing bottles, the occurrence of a mist throughout these bottles was noted, which caused certain losses from the absorption train even when alkali was used in t h e last bottles. A t t h a t time a fume precipitation apparatus was secured a n d a few successful experiments made. Press of
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other work caused these experiments t o be discontinued. This equipment was installed in our experimental plant after making the experiments described above, b y removing the connecting pipe between Towers 3 and 4 and substituting the 8/4-in. glass t u b e shown in the figure. The high-tension current required was obtained from a transformer such as is used in wireless telegraphy, capable of giving a maximum of 15,000 volts. The current was rectified with a kenotron furnished by the General Electric Company. A platinum wire was placed in the center of the glass t u b e and connected t o the anode of the kenotron. A coil of copper wire was wrapped around the tube and connected with the inside wall with platinum wire. T h i s coil and one terminal of the transformer were grounded. The voltage was regulated b y a variable resistance in circuit with the primary of t h e transformer. This arrangement worked perfectly and stopped all mist even a t considerable velocities of flow through t h e tube. It was found t h a t when all the mist issuing ffom Tower 3 was stopped no further mist was formed i n Tower 4. Under conditions of operation obtaining in Run 3 where the total acid loss was about 5 per cent, it was found t h a t during the first hour of opera-
Apr., 1918
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
tion, circulation acids a t concentrations near end of a run, the acid obtained from the precipitator was about 2 per cent of the total acid input. The quantity of mist decreased steadily t o about 0.5 per cent, where i t remained constant. The quantity of mist varied widely under different conditions, all of which have not been determined. It has been observed in a full-sized plant t h a t sometimes ’there was considerable mist issuing from the absorption system and at other times none a t all. No correlation was established with different conditions of operation. We found in our experimental plant t h a t the mist was increased by increase of the gas velocity, reduction of the oxygen excess, and increase of the acid strength in Tower 3. For example, a t a velocity of 1 5 0 cu. f t . per hour with a slight oxygen deficiency samples were taken of the exit gas with the precipitator turned on and ten minutes after turning i t off. I n the second case the acid in the exit increased from 0.0174 t o 0.0248 g. per liter corresponding t o a n increase in the end loss of from 6 . 5 t o 9.3 per cent. The acid recovered from the precipitator contained very little nitrous acid, being almost wholly nitric of 1 5 t o 2 5 per cent strength. No evidence was secured of any increased absorption capacity of Tower 4 by the high potential discharge. Of the three chemical reactions involved in absorbing nitrogen peroxide in water t o form nitric acid, t h a t represented by Equation I above requires appreciable time, and hence is the controlling one. I n order t o give this reaction sufficient time all the reaction space practicable should be provided. Atomized sprays are used in some cases for absorbing gases b y liquids, and have been suggested as of possible application here. Removal of all packing material would increase the reaction space for the oxidation of NO, and efficient liquid absorption surface would be provided b y the sprays. The Cottrell precipitat o r satisfactorily solves the problem of recovering any mist t h a t would not settle out. Experiments along t h i s line are projected. ACKNOWLEDGMENT
The experiments described are part of the investigation being carried out by the Bureau‘of Mines on t h e oxidation of ammonia under the direction of the chief chemist, Dr. Charles L. Parsons. RUREAU OB MINES WASHINOTON, D. C.
INFLUENCE OF TIME OF HARVEST, DRYING AND FREEZING OF SPEARMINT UPON THE YIELD AND ODOROUS CONSTITUENTS OF THE OIL1 By FRANKRABAK Received October 11, 1917
The cultivation of spearmint is conducted extensively for the production of the volatile oil, which is used largely for the flavoring of chewing gum. The efficacy of the oil for this purpose depends much upon its composition as regards t h e odorous constit1
Published by permission of the Secretary of Agriculture.
275
uents, the exact nature of which is not clearly understood. The constituents which serve at least in part t o produce the peculiar, yet much liked flavor of t h e oil and of t h e products flavored with the oil, are perhaps ester-like or alcoholic in character. It is stated b y Schimmel & C O . , ~t h a t Russian spearmint oil is strikingly different from American, German and Hungarian oils in that, in addition t o carvone, which perhaps constitutes the major portion of these oils, a n alcohol which has been identified as linalool has been found t o be present in considerable quantities. in a n examination of German spearmint oil, states t h a t the carrier of the odorous principle of the oil is the acetic acid ester of dihydrocuminic alcohol. More recently, Nelson,s working with a n American spearmint oil, though unable t o confirm the presence of dihydrocuminic acetate, reported the presence of the acetate of the alcohol dihydrocarveol. This ester is stated t o possess the characteristic odor of spearmint. Investigations of spearmint oil therefore, with a view t o the identification of the constituents t o which the characteristic odor is attributable, indicate t h a t esters or alcoholic compounds play a n important part as carriers of the aroma and flavor. Granting t h a t the odor-bearing constituents are ester-like or alcoholic in character, a study of the plant was undertaken a t Arlington Farm, Va., t o obtain information regarding the effect of time of harvest, drying of t h e plant, and frost action upon the constituents as well as upon the yield and physical properties of the oils. Experiments were conducted through a period of years in which the plants were harvested and distilled a t three distinct stages of growth, viz., budding, flowering and fruiting stages. The plants were distilled in both fresh and dried conditions and t h e oils subjected t o examination and compared both as regards yield of oil and physical and chemical composition. At the same time, the leaves and flowering tops were separated from the fresh material at t h e different stages of growth and distilled in order t o obtain information regarding t h e distribution of the oil in the plant and composition of the oil from the plant parts as compared with the whole fresh herb. An experiment was also conducted t o determine the effect of frost action upon the yield and quality of the oil. A comparison of the yields of oil from fresh and dry herb a t different stages of growth during the seasons of 1908, 1909, 1910 and 1911, together with the dates of harvest and distillation are given in Table I. No definite relationship exists in the yields of oil from the fresh herb a t any stage of growth during the several seasons. The yields apparently vary with the season. Yields of oil during the seasons of 1908 1 Schimmel & Co.,Spearmint Oil. Co., pp. 45-46, April 1898.
Semi-annual Report of Schimmel &
*
“Ueber Rrauseminzol,” Chem.-Zlg., 33 (1910). 1175. 8 “A Chemical Investigation of American Spearmint Oil;’ U. S . Department of Agriculture, Bureau of Chemistry, Circular 92, 1912. 2
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