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produce the full defects. Obviously the relative difference in hardening between core and surrounding material is important; the insulated unhydrated lime particles, embedded in an unaffected material, are the special cause of t h e destruction. These experiments are described t o show the effect of the intermediate processes between burning and preparing the mortar. More careful sieving could have prevented the defects, a t least in part, and no doubt better slaking and larger soaking could have had a similar effect.
3. X-ray analysis showed t h a t the cores contained unhydrated lime (CaO) in spite of previous slaking and soaking. 4. A clinkered covering was formed during the burning process which delayed hydration. 5. The behavior mentioned in conclusion 2 is kinetically connected with that of 3 and 4. 6. The deteriorating effect of unhydrated particles of lime embedded in an unaffected mortar was demonstrated experimentally.
Conclusions
Literature Cited
1. Certain mortar defects are explained by the presence of insulated cores embedded in the mortar. 2 . These defects were the result of the core material being carbonized less than the surrounding material.
(1) Gerlach, W., Z . Physik, 9, 188 (1922). (2) Olshausen, von, 2. Krist, 61, 490 (1925). RECEIVED August 10, 1936.
POTASSIUM NITRATE FROM POTASSIUM CHLORIDE AND DONALD L. REED K. CLARK NITROGEN PEROXIDE Bureau Chemistry a n d Soils,
AND G. of U. S. Department of Agriculture, Washington, D. C.
P
RESENT-DAY chemical technology is making possible the synthesis of compounds formerly considered too costly for general fertilizer use. These possibilities and the trend toward the use of more concentrated fertilizers are arousing interest in new products as a source of valuable plant foods. Potassium nitrate contains nitrogen and potassium, two important plant food elements, and has physical and chemical properties that make its use in fertilizer mixtures advantageous. Whittaker and Lundstrom (18) pointed o u t that, although these properties of potassium nitrate have long been recognized, its cost of production has limited its use for fertilizer purposes. The advent of low-cost ammonia, resulting from the development of the synthetic process, has made possible the consideration of ammonia as a source of nitrogen for the production of potassium nitrate. Numerous articles and patents have recently appeared on such processes (1, 3, I , 10, 11, 19). As early as 1926 the Bureau of Soils considered the problem of potassium nitrate production from potassium chloride and nitric acid or oxides of nitrogen derived from ammonia oxidation. Mehring, Ross, and Merz (6) investigated the conditions suitable for the direct treatment of potassium chloride with nitric acid and obtained good yields of potassium nitrate; but they were unable to prevent loss of nitrogen, a portion of which was volatilized (as nitrosyl chloride and nitrogen oxides) with the hydrochloric acid resulting from the reaction. Whittaker, Lundstrom, and Mera ( I S ) considered the thermodynamics of the reaction: 2NOz(g.)
+ KCl(5.)
+ KNOa(s.)
+ NOCl(g.)
and found that it should proceed as indicated. Their experimental results showed that in the absence of moisture the reaction between pure nitrogen peroxide gas and solid potassium chloride ceased before appreciable quantities of potassium nitrate were produced. With 3 per cent of water present in the potassium chloride, however, good conversions were obtained.
A study has been made of the factors influencing the conversion of potassium chloride to potassium nitrate by the passage of nitrogen peroxide-air-nitrogen mixtures, derived from the oxidation of ammonia with air and ranging in cornposition from 5.2 to 1 1 .O per cent nitrogen dioxide by volume, through beds of moistened potassium chloride. Under comparable conditions of particle size, moisture content of the chloride, diameter and depth of the bed, and rate of flow of the nitrogen peroxide the more concentrated peroxide mixtures reacted more rapidly but less completely in a single pass than the less concentrated mixtures. Stepwise countercurrent nitration, with oxidation chambers between successive beds, indicated complete reaction of an 8 per cent peroxide mixture when half of the nitrogen oxides were converted to potassium nitrate and the other half to nitrosyl chloride. Mirkin ( 7 ) produced potassium nitrate from potassium chloride by passing concentrated mixtures of nitrogen peroxide (9 to 90 per cent by volume) and air through beds of potassium chloride crystals that contained various amounts of moisture. He met with only moderate success, and, partially because of limited facilities, his yields of potassium nitrate were low and recovery of nitrogen poor. He concluded that moisture was an important factor in the reactions, probably because it
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The ammonia content of the dry airammonia mixtures was determined by bubbling gas from the system through an excess of standard acid. The percentage of ammonia present was calculated from the volume of the unabsorbed gas as measured by a compensometer (8),and from the amount of standard acid neutralized as shown by titration of the excess. The moist gas mixtures entering and leaving the chloride tower were sampled by withdrawing the gas into a partially evacuated glass bulb. The volume of the sample taken was calculated from the known volume of the bulb and its initial and final pressures. An excess of standard alkali was added to the bulb, and the total acid equivalent of the gas was determined from the amount of alkali neutralized as shown by the back titration. The acid nitrogen, expressed as per cent of nitrogen dioxide by volume, present in the peroGde FIQURE 1 . DIAQRAM OF APPARATUS mixtures entering the tower was calcuA. Carbon dioxide-ethanol bath G. 80 mesh platinum-gauze catalyst lated from the volume of the sample and B . Heating coil H. Condenser its acid equivalent. C. Air flowmeter I. Oxidizing chamber D . Ammonia flowmeter J . Potassium chloride tower The gases l e a v i n g t h e tower were E. Furnace K. Gas-sampling ports sampled and titrated in a similar manner F. Platinum-platinrhodium thermocouple L. T o constant pressure overflow t o determine their total acid equivalent, and the n e u t r a l i z e d s o l u t i o n s were titrated with standard silver nitrate to determine their acid equivalent due to chlorides. The difference combined with nitrogen peroxide t o produce nitric acid which between these titrations represented the acid nitrogen. The exreacted t o form potassium nitrate. P m e n t a l conditions suggest the possibility of free chlorine, ydrochloric acid, nitrosyl chloride (NOCl), nitryl chloride Experimental Procedure (NOZCl), and nitric oxide being formed as products of the reI n the present work mixtures of nitrogen peroxide air, and action and appearing in the exit gas. The work of Coates and nitrogen that contained from 5.2 t o 11.0 er cent of nitrogen Finney (8) and Trautz and Wachenheim (9) on the rate of redioxide1 by volume were passed upward tgrough beds of solid action and equilibrium between nitric oxide and chlorine showed potassium chloride. These beds of potassium chloride were conthat a t normal temperatures these substances do not exist in the tained in vertical glass tubes or towers (Figure 1, J) 4.45 cm. presence of each other but form nitrosyl chloride. Kiss (6) re(1.75 inches) in diameter. The depth of the salt bed varied, in orted that nitrogen peroxide and chlorine form nitryl chloride gut that nitryl chloride and nitric oxide react t o form nitrosyl accordance with the experiment, from 10.1 om. (4.0 inches) to Chloride and nitro en peroxide. At equilibrium, therefore, no 30.5 cm. (12.0 inches). free chlorine woulcfexist in the mixture when the ratio of acid The nitrogen peroxide mixtures were prepared by passing airammonia mixtures over a heated catalyst in an ammonia burner nitrogen to chlorine (N/C1) was equal to or greater than one. That no free chlorine existed in the gas when this ratio was less similar to that described by Yee and Emmett (14). The ammonia burner together with the auxiliary apparatus used is shown than one was shown by the failure to obtain an increased silver nitrate titration on boiling the neutralized solution with ammonia in Figure 1. The air used for preparing the air-ammonia mixto convert any hypochlorites or chlorates present to chlorides. tures was cooled in the carbon dioxide+thanol bath, A , to remove impurities that would oison the catalyst, and then returned to The volume composition of the gas leaving the tower, therefore, room temperature by feating coil B . The purified air and the was calculated from the volume and the acid nitrogen and chlorine equivalents of the sample on the assumption that the ammonia gas were measured by capillary flowmeters C and D, active constituents were either nitrogen dioxide or hydrochloric thoroughly mixed, and assed over an 80-mesh platinum gauze, acid and nitrosyl chloride. G, maintained a t 850' !C in the vertical tube furnace, E, to convert the ammonia to nitric oxide and water va or. The platinunplatinrhodium thermocouple F , permitted cfetermination of the Preliminary Experiments urnace temperature. The hot colorless gases issuing from the burner were cooled by condenser H (which also separated out most of the moisture) before being led into oxidation chamber I where Dry Of potassium to mm- in Size, were Placed in contact with moist nitrogen oxidation of the nitric oxide to nitrogen peroxide was com leted. peroxide mixtures derived from ammonia oxidation. After a Gas samdes were taken at the entrance to the ammoniafh-ne, and at thg entrance and exit of the potassium chloride tower. few days of contact The rate of flow of the ammonia was maintained constant in all with the gas a liquid but a few preliminary experiments, a t 4.0 grams per hour. The film was observed desired concentration of nitrogen peroxide was obtained by conabout each crystal, trolling the amount of air admitted to the oxidizing unit. Since nitrogen dioxide is very reactive toward rubber, all rubber conand at the end of 3 nections were avoided between the ammonia burner and the weeks of contact potassium chloride tower. Gas that had passed through the petrographic examitower was usually of such composition that very little attack on nation showed that rubber occurred. The ammonia gas used in these experiments was drawn directly a homogeneous shell from a cylinder containing the commercial anhydrous liquid. of p o t a s s i u m niThe potassium chloride was the c. P. grade. trate, estimated t o represent 10 t o 15 Analytical Methods per cent nitration of The chlorine content of the potassium chloride used and of the the chloride, sursalt after treatment with the nitrogen peroxide mixtures was determined by titration of wei hed amounts of the dried materials rounded each parwith standard silver nitrate sofiution. The percentage conversion ticle. The l i q u i d FIGURE 2. COMPOSITION OF THE GAS of the chloride to the nitrate was calculated from the observed LEAVINGA BED O F 8- TO 14-MEBH film a b o u t e a c h change in the chlorine content. POTASSIUM CHLORIDE,MOISTENED crystal apparently WITH 5 PER CENT WATER, WHEN * These mixtures contain both nitrogen tetroxide (NzO4)and nitrogen fostered the reaction TREATED WITH AN 11 PERCENTNIdioxide (NOS) but for convenience their composition is reported on the basis b e t w e e n the perTROGEN PEROXIDE MIXTURE of complete dissociation of the tetroxide to the dioxide.
c
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335
INDUSTRIAL AND ENGINEERING CHEMISTRY
oxide and the chloride by taking both into solution. The reactions under such conditions are probably the same as those taking place during passage of nitrogen peroxide mixtures through either saturated potassiunl chloride solutions or moist beds of potassium chloride. An 11 per cent nitrogen dioxide mixture was passed upward through a bed of 8- to 14-mesh potassium chloride moistened with 5 per cent of its weight of water. The bed of potassium chloride was 4.45 em. in diameter and 10.1 em. deep. The peroxide flow was equivalent to the oxidation of about 24 grams of ammonia per hour. The composition of the moist gas escaping from the top of the bed is shown in Figure 2. At the end of 4 hours approximately 30 per cent of the chloride had been converted to the nitrate. The gas analyses showed, however, that after a short initial period most of the peroxide passed through the tower without reacting, an indication that the contact time allowed, approximately 1 second, was too short for efficient reaction with a bed of this particle size and moisture content. In a series of experiments nitrogen peroxide mixtures of various concentrations equivalent to the oxidation of 4 grams of ammonia per hour were passed upward through beds of through 14-mesh potassium chloride that contained various amounts of moisture. The slight temperature rise accompanying the initial contact of the gas and solid evaporated moisture from the lower portion of the bed, most of which, however, condensed in the upper portions. It was found that as much as 12 per cent of moisture, based on the weight of the dry saIt, could be added to the lower two-thirds of the tower without seriously affecting its mechanical operation, and that after the initial contact period the moisture appeared to be more or lesF: uniformly distributed.
Effect of Nitrogen Peroxide Concentration
L !
I
0
I
1
1
I
I
20 40 60 80 100 PER CENT POTASSIUM CHLORIDE NITRATED
FIGURE 3. NITRATIONO F BEDSO F THROUGH 14-MESH POTASSIUM CHLORIDE,MOISTENEDWITH 12 PER CENT WATER,BY 5.2 TO 10.4 PERCENT NITROGEN PEROXIDE MIXTURES
The effect of various concentrations of nitrogen peroxide on bed, varied only from 3 to 4 seconds while the reaction zone varied from 7 to 13 cm. in depth. In order to obtain the same the conversion of the chloride to the nitrate was studied in a series of experiments in which the concentration of the peroxide degree of nitration a t the base of the tower in all experiments, it is obvious that the more dilute gas mixtures would have to be mixture varied from 5.2 to 10.4 per cent. The ammonia flow to the converter was 4.0 grams per hour, equivalent with a passed through the bed for a considerably longer period and that the depth of the reaction zone would be still greater. converter efficiency of 92-93 per cent to 88 cc. of nitrogen The areas under the curves which represent the relative dioxide per minute a t room temperature. The potassium amount of chloride converted to the nitrate are greater for the chloride bed, which was 4.45 cm. (1.75 inches) in diameter and from 10.4 cm. t o 13.5 cm. (4.1 to 5.3 lower Deroxide concentrations and thus show t'hat a greater portion of the perinches) in depth, contained from 150 to oxide in the dilute gases reacted than in the 190 grams of through 14-mesh potassium 28 more concentrated ones. That the more chloride, the lower two-thirds of which had been moistened with water to the exdilute gases reacted somewhat more com24 tent of 12 per cent of the weight of the pletely may be explained by the greater amount of oxygen present and the intotal dry salt. The duration of each excreased tendency for any nitric oxide periment was 10 hours 17 minutes. 20 formed to become oxidked. At the conclusion of each experiment the contents of the tower were removed s-16 i 'I / , 1I 1I Effect of Particle Size I I I I in five approximately equal horizontal sections and dried for several hours a t The effect of larger particles on the 110' C.prior to analysis. The chlorine depth of the reaction zone was studied by content of each section was determined passing an 8 per cent peroxide mixture and the percentage of the potassium upward through a bed of through 4-mesh chloride nitrated calculated. The degree and 92 per cent on 28-mesh potassium of nitration of the bed for each of the chloride 4.45 cm. (1.75 inches) in diameter peroxide concentrations used is shown in and 30.5 cm. (12 inches) deep. The bed y l 4 Figure 3. 1 1 , contained 400 grams of potassium chloride -_ A comparison of these curves shows moistened with 48 grams of water as in that a higher degree of nitration was atthe preceding experiments. The peroxide tained by the more concentrated mixtures mixture was passed through the bed a t in a shorter reaction zone. The time of the same rate (88 cc. of nitrogen dioxide FIGURE 4. NITRATIONOF A BED OF THROUGH &MESH AND 92 P E R CENT ON contact, however, between the gas and per minute) for 16 hours 35 minutes, or 28-MESH POTASSIUM CHLORIDE, MOIS- until appreciable quantities of the persolid as estimated from the depth of the TENED WITH 12 PERCENTWATER,BY reaction zone a t the end of the experiment oxide appeared to be coming through the AN 8 P E R CENT NITROGEN PEROXIDE on the basis of 50 per cent voids in the tower unreacted. MIXTURE
1 1 I / i
I--__
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A comparison of the nitration curve of this experiment (Figure 4) with those of Figure 3 clearly indicates the effect of increased particle sizes in increasing the depth of the reaction zone and consequently in decreasing the rate of reaction for a given peroxide concentration.
Nitration in Multiple Towers The experiments with various peroxide concentrations showed that the maximum absorption of the peroxide did not occur in a single passage through a bed of potaseium chloride with the particle sizes and rates of flow employed even when the reaction zone was apparently considerably less than the total bed depth. This phenomenon indicated that lower oxides of nitrogen were formed as intermediate products of reaction and that under the conditions of the experiments their slow rate of reoxidation to the peroxide determined the absorption efficiency attained. TABLE I. COMPOSITION OF GASLEAVINQ THE MULTIPLE TOWERSYSTEM -TimesHT. Man.
58 59 62 64
N/Clb
--Camp., Vol.
SOCl
HCl
%-
NO2
5 35 45 0 35 45 45 55 16 15 20 15 10 45 15 41 38 43 48 23 28
1.00 3.6 0.0 0.0 0.95 0.2 3.8 0.0 0.95 3.7 0.2 0.0 1.03 3.9 0.0 0.1 0.98 4.4 0.1 0.0 * 1.02 4.0 0.1 0.0 0.98 69 4.0 0.1 0.0 1.00 3.5 0.0 0.0 0.95 3.7 .. 0.2 0.0 1.00 3.8 78 0.0 0.0 1.00 80 4.0 0.0 0.0 1.03 81 3.7 0.0 0.1 1.03 3.5 83 0.1 0.0 1.05 83 4.1 0.0 0.2 1.05 86 0.2 4.0 0.0 0.97 85 3.0 0.0 0.1 86 1.02 0.0 0.1 4.1 87 0.3 1.07 0.0 4.0 92 3.7 1.03 0.1 0.0 94 1.05 0'2 4.1 0.0 95 1.07 0.3 4.3 0.0 Av. 1.01 a Elapsed time after introduction of a freshly prepared final tower in the system. b Ratio of the acid nitrogen t o chlorine equivalents of the exit gas.
x7" E
The validity of this conclusion was tested by passing peroxide mixtures through three chloride towers in series with oxidation chambers between successive towers. Each of the chloride towers had a bed depth of 3 0.5 cm. and contained 400 grams of through 30-mesh potassium chloride moistened with 12 per cent of water. The oxidation chambers inserted between successive towers allowed an oxidation period of approximately 3 minutes. An 8 per cent peroxide mixture was introduced into the system a t the rate of 88 cc. of nitrogen dioxide per minute. The tower system was operated in a stepwise countercurrent manner t o simulate true countercurrent flow of solids and gases by replacing the first tower by the second, the second by the third, andintroducing a fresh tower for the third as the first tower in the system became nitrated. Figure 5 shows the nitration curves for the three towers in the system a t the end of the experiment and after the first tower had been in the system for 182 hours 24 minutes, the second for 136 hours 36 minutes, and the third for 95 hours 38 minutes. Severe channeling occurred in the first tower and nitration was rather erratic on this account. The second and third towers, however, do not show any effects of channeling but show an increased absorption of nitrogen peroxide following the oxidation period, which indicates that a relatively slow oxidation reaction, such as the oxidation of nitric oxide to nitrogen dioxide is involved. Table I gives the composition of the gases leaving the third tower during the last 37 hours 23 minutes of the experiment.
4
I
9
I
h
I\-4 I
.
I
FIGURE 5. NITRATION O F BEDSO F THROUGH 30-MESH POTASSIUM CHLORIDE, MOISTENED WITH 12 PERCENT WATER,BY AN 8 PERCENTNITROGEN PEROXIDE MIXTURE IN A MULTIPLE-TOWER SYSTEM These gas compositions, which are typical of those obtained throughout the entire experiment, show an average N/C1 ratio of approximately 1.0 in accordance with the equation : 2N02
+ KC1 = KNOa + NOCl
The increased nitration following an oxidation period, however, indicates that nitrogen peroxide does not react directly with the chloride but first forms nitric acid and nitric oxide.
Acknowledgment The experiments described in this paper were initiated and carried on for some time under the direction of J. W. Turrentine.
Literature Cited (1) Atmospheric Nitrogen Corp., French Patent 747,384 (1935). (2) Coates, J. E., and Finney, A,, J . Chem. Soc., 105,2444-62 (1914). (3) Kali-Forschungs-Anstalt G. m. b. H., French Patent 770,459 (1934). (4) Kaselitz, Oscar, U. S. Patent 1,893,945(1933). (5) Kiss, A,. Rec. trau. chim., 43, 68-79 (1924). (6) Mehring, A. L., Ross, W. H., and Merz, A. R., IND. ENQ. CHEM.,21, 379-82 (1929). (7) Mirkin, I. A., J. Chem. Ind. (U. S. S. R.), 8,351-9 (1931). (8) Tour, R. S., Chem. & Met. Eng., 23, 1104-6 (1920). (9) Trautz, Max, and Wachenheim, Lili, Z . anorg. allgem. Chem., 97,241-84 (1916). (10) Uebler, Bruno, U. S. Patent 1,918,941 (1933). (11) Whittaker, C.W., and Lundstrom, F. O., Ibid., 1,920,333(1933). (12) Whittaker, C. W., and Lundstrom, F. O., U. S. Dept. Agr., Mise. Pub. 192 (1934). (13) Whittaker, C. W.; Lundstrom, F. O., and Merz, A. R.. IND. ENQ. CHEM.,23, 1410-13 (1931). (14) Yee, J. Y., and Emmett, P. H., Ibid., 23, 1090-2 (1931). RECEIVEDOctober 8, 1936. Presented before the Division of Fertilizer Chemistry et the 92nd Meeting of the American Chemical Society, P i t t a burgh, Pa.. September 7 t o 11, 1936.
