Ind. Eng. Chem. Prod, Res. Dev. 1985, 2 4 , 645-650
645
Compatibility of the Nitrification Inhibitors Dicyandiamide and Thiourea with Anhydrous and Aqueous Ammonia Joe Gautney,' Yong K. Kim, and Patrick M. Gagen Division of Chemical Development, National Fertllizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama 35660
The solubilities and stabilities of the nitrification inhibitors dicyandiamide (DCD) and thiourea (TU) were determined in anhydrous and aqueous ammonia (30% NH,). Corrosion tests also were conducted to determine the corrosiveness of aqueous and anhydrous ammonia-inhibitor mixtures to four typical alloys used in the construction of ammonia pressure vessels. The results showed that both DCD and TU are soluble and stable enough for use with either anhydrous or aqueous ammonia. The DCD and TU solubilities in anhydrous ammonia at 30 "C were 56.6 and 64.4 wt %, respectively. I n aqueous ammonia at 25 "C the solubilities were 11.3 wt % for DCD and 31.3 wt % for TU. I n the corrosion studies, all of the alloys tested corroded at rates less than 0.5 mil/year, which is considered excellent corrosion resistance.
The nitrification inhibitor nitrapyrin [2-chloro-6-(trichloromethy1)pyridinel (Dow Chemical Co. USA) has become popular in recent years, especially in the midwestern United States, for use with aqueous and anhydrous ammonia. Midwestern farmers are using nitrapyrin as a time-management tool. Use of the inhibitor allows application of ammonia in the fall and early spring, thus avoiding the risk of delays imposed by inclement weather near planting time. Delays in fertilizer application often prevent planting of the crop at the optimum time. The inhibitor delays the biological oxidation of NH4+to NOzand NO< forms, thus reducing nitrogen losses that would occur by leaching and denitrification reactions of NO, if no inhibitor were added. It is estimated that about 25% of the total applied fertilizer nitrogen is lost by leaching and denitrification reactions (Huber, 1980). In addition to serving as a time-management tool by conserving nitrogen, nitrification inhibitors provide several other potential benefits, all related tQ improved nitrogen efficiency. Among these potential benefits are higher yields, improved crop quality, reduced plant disease, and reduced groundwater polIution (Page and Hoffman, 1982). Currently, nitrapyrin is the only nitrification inhibitor commercially available in the United States. Another nitrification inhibitor [5-ethoxy-3-(trichloromethyl)-l,2,4thiadiazole or E m , previously manufactured by Olin Corp. under the trade name Dwell] (Emerson, 1982; Evrad et al., 1982) was available commercially for a short time. Two compounds that have recently attracted much attention from the Tennessee Valley Authority (TVA) and others for use as nitrification inhibitors are dicyandiamide (DCD) (Hauck and Behnke, 1981; Slangen and Kerkhoff, 1984) and thiourea (TU) (Malhi and Nyborg, 1979). TVA data on the feasibility of cogranulating these inhibitors with urea (Gautney et al., 1984) and solubilities and stabilities in fluid fertilizers (Gautney et al., 1985) have been previously presented or published. The present paper gives data on the solubilities and stabilities of DCD and TU in both anhydrous and aqueous ammonia (30% NH,). Ashworth and Rodgers (1981) have published limited data on the compatibility of DCD with anhydrous ammonia; Hays and Forbes (1974) have measured the solubility of TU at 22 "C in aqueous ammonia. The solubilities of DCD
and TU in anhydrous ammonia were measured previously by German researchers in the early 1930s (Janecke and Rahlfs, 1930; Janeke and Hoffmann, 1932). In addition to the solubility and stability data, the results of tests to determine the corrosiveness of aqueous and anhydrous ammonia-inhibitor mixtures to typical alloys used in the construction of ammonia pressure vessels also are presented.
Solubility and Stability Data Solubility measurements with anhydrous ammonia were made at -34,0, and 30 "C. Solubility measurements with aqueous ammonia were made only at one temperature, 25 "C. Stability measurements with both anhydrous and aqueous ammonia were made at 25 "C. The DCD, TU, and aqueous ammonia used in the tests were reagent grade. The anhydrous ammonia used was refrigeration grade, which was obtained directly from a process line in the TVA ammonia plant. The ammonia was clear, boiled at -34 "C, and left no residue on evaporation. Proper safety precautions were taken at all times when anhydrous ammonia, was used. The solubility measurements with anhydrous ammonia (NH,) at the boiling point (-34 "C) were made by using the following procedure. Liquid NH, was poured from a Dewar flask into a clear glass vacuum-jacketed beaker. Inhibitor was added until the solution was saturated. More NH3 was added until all the inhibitor had dissolved; the open beaker was left to stir on a magnetic stirrer and the ammonia allowed to evaporate until inhibitor precipitation began. The stirrer was turned off, and a sample of the clear, saturated solution was taken. The inhibitor solubility was calculated from the weight of NH, and inhibitor in the saturated solution. The recovered solid was analyzed for purity by high-performance liquid chromatography (HPLC) methods described in a previous paper (Gautney et al., 1984). The apparatus used for measuring inhibitor solubilities in anhydrous ammonia at 0 and 30 "C is shown in Figure 1. The apparatus was constructed from 1.91-cm (0.d.) heavy-wall glass tubing to withstand the vapor pressure of ammonia, which in the pure ammonia system is equal to 62 and 168 psia at 0 and 30 "C, respectively. A known
This article not subject to U.S. Copyright. Published 1985 by the American Chemical Society
646
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985
Table I. DCD and TU Solubilities in NH3 and NH,OH t e m n "C DCD sn nb TU sa nb Average Solubility in NH3, wt % -34 44.15 0.07 6 34.97 0.18 12 0.23 4 51.29 3.69 5 0 48.36 30 56.56 0.56 6 64.35 0.84 4 Average Solubility in NH40H, w t % 11.32 0.14 4 31.28 1.17
25
a s = standard deviation. calculate average.
6
n = number of observations used to
3 - DATA FROM PRESENT STUW A - DATA OF JANECKE AND RPHLFS , l 9 l c m (OD1 HEAVY-WALL
fl
I I
7001
L J l Figure 1. Apparatus for measuring inhibitor solubilities in NH3 a t 0 and 30 "C.
amount of inhibitor and NH3 was added to section A. The amount of inhibitor added was greater than that required to saturate the solution. The vessel was sealed and placed in a constant-temperature bath with section A horizontal and the sample allowed to equilibrate while shaking. During equilibration no solid or liquid entered section B. The sample initially was allowed to equilibrate at a temperature slightly above the temperature selected for the solubility measurement and then allowed to equilibrate at the selected temperature. After equilibration the vessel was turned in an upright position in the bath and the excess solid inhibitor allowed to settle in the bottom of section A. Saturated solution then was decanted into section B. Section B was filled as full as possible to minimize condensation of NH3 upon cooling. Sections A and B were frozen, separated, and sealed. The weights of inhibitor and NH, in each section were determined. The weight of inhibitor in the saturated solution was determined directly from section B and indirectly from section A by taking the difference between the inhibitor orginally added at the beginning of the experiment and that found in section A at the end of the experiment. Inhibitor solubility was calculated from the weight data. The recovered inhibitors were analyzed for purity by HPLC. The solubility measurements with the inhibitors in aqueous ammonia (NH40H) were made by preparing samples of NH40H with increasing amounts of the inhibitors, allowing the samples to equilibrate on a shaker for one day, and then analyzing a sample of the clear solution phase for inhibitor by HPLC. Saturation was assumed when constant values were obtained for the samples with increased amounts of the inhibitor. After saturation, several repeat analyses were made on each sample. The time interval between these repeat analyses was at least 1 day. The stability tests (anhydrous ammonia) were run by sealing known weights of inhibitor and NH3 in 1.91-cm (0.d.) heavy-wall glass tubes. The individual tubes were stored at room temperature (25 "C) and opened periodically, and the ammonia was allowed to evaporate. The amount of solid recovered after the sample was dried overnight in an oven at 90 "C was compared to the amount added. The recovered solids from the stability tests also
533;
4001
0
-50
Ion
50 TEMPERATURE
I
150
, 'C
Figure 2. Effect of temperature on DCD solubility in NH3.
-
0
:
DATA FROM PRESENT STdDY
A
:
DATA OF JANEKE AND HOFFMANN , 1932
I
/" 20
IC
-9c
A - 59
0 TEMPERATURE ,
50
I00
'C
Figure 3. Effect of temperature on TU solubility in NH3
were analyzed for purity by HPLC. The initial concentrations used were 17.9 and 19.9 wt % for DCD and TU, respectively. The stability measurements with NH40H were made by using initial DCD and TU concentrations of 6.6 and 7.2 wt % , respectively. After inhibitor addition the NH40H samples were shaken for one day, stored at room temperature, and then analyzed periodically for inhibitor by HPLC. The results of the solubility measurements are shown in Table I. The NH3 solubility data in Table I are in good agreement with the literature data of Janecke and Rahlfs (1930) and Janeke and Hoffmann (1932). The NH, data from Table I and the literature values are plotted in Figures 2 and 3 for DCD and TU, respectively. The solubility of TU decreases with decreasing temperature, even at the low temperatures, whereas the solubility of DCD, which also decreases with decreasing temperature, appears to somewhat level off at temperatures below 0 "C. Both DCD
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985 647
detectable decomposition of either DCD or TU in NH3 and NH40H at 25 "C, even after two months or more of storage. High-pressure liquid chromatographic analysis of the recovered solids from the stability tests showed that they were pure inhibitors.
Table 11. Stability of DCD and TU in NH, at 25 "C wt%
inhibitor in recovered time. davs % inhibitor recovered" solidb DCD (17.9 wt %, 15% Total N Basis) 14 99.26 100.53 14 99.85 28 99.60 100.24 28 100.10 42 100.08 100.98 42 99.92 42 100.38 56 100.07 100.23 56 100.26 99.95 av 100.50 av 0.34 sC 0.35 sc 14 14 28 28 42 42 56 57
~
T U (19.9 wt %, 10% Total N Basis) 102.75 99.25 99.79 100.21 99.18 100.47 100.65 99.93 100.69 100.78 100.86 98.93 100.78 av 99.32 av 0.87 sC 0.43 sc
Percent inhibitor recovered by weight after NH3 evaporation. bRecovered solid analyzed for inhibitor by HPLC. c s = standard deviation.
Table 111. Stability of DCD and TU in NHdOH at 25 "C av w t % av w t % time. davs inhibitor" time, davs inhibitor" DCD (6.6 wt %, 16% T U (7.2 w t %, 10% Total N Basis) Total N Basis) 1 6.58 1 7.24 28 6.26 28 7.47 43 6.41 43 7.23 58 6.33 57 7.39 6.40 av 77 7.29 7.32 av 0.14 sb 0.10 S b "wt % values are average of duplicate experiments. standard deviation.
b~
=
and TU are very soluble in anhydrous NH3, even at very low temperatures. Concentrations of 17.9 and 19.9 wt 70 DCD and TU, respectively, can be dissolved easily. These concentrations correspond to 15 and 10% of the total N as DCD-N and TU-N, respectively, and are the maximum concentrations being considered for nitrification inhibition field studies. The solubilities of DCD and TU in NH40H also are relatively high at 25 "C, 11.32 and 31.28 wt %, respectively. These solubilities correspond to 25.6 and 40.4% of the total N as inhibitor N for DCD and TU, respectively. The results of the stability testa are given in Tables I1 and I11 for NH3 and NH40H, respectively. There was no
Corrosion Studies Tests also were conducted to determine the corrosiveness of anhydrous and aqueous ammonia-inhibitor mixtures to typical alloys used in the construction of ammonia pressure vessels. Four alloys were tested. They were American Society for Testing and Materials (ASTM, 1982) numbers A 202-B, A 516-70, A 517-D, and A 612. These are typical alloys used in the construction of bulk storage, transport, nurse, and applicator tanks for use with anhydrous ammonia. The alloys, along with some of their properties and their uses, are listed in Table IV. A total of 24 corrosion tests was conducted. This number included each of the four alloys with DCD and TU and without inhibitor for both the anhydrous and aqueous ammonia. The concentrations of the inhibitors used were approximately 75% of their respective solubilities in the anhydrous and aqueous ammonia at 25 "C. These concentrations were 42.08 and 46.88 wt % for DCD and TU, respectively, in the anhydrous ammonia and 8.49 and 23.46 w t % for DCD and TU, respectively, in the aqueous ammonia. Individual alloy specimens for the tests were cut from pieces of alloy plates by using a cutting machine with a water-cooled, tungsten-carbide blade and then polished by hand. After the alloy specimens were polished, they were stamped with an identification number and their dimensions carefully measured; they were then weighed. The procedures were as follows. In the tests with anhydrous ammonia, the inhibitor and alloy specimen were added to a 1.9-cm (0.d.) thick-walled glass tube. The anhydrous ammonia was added, and the glass tube was sealed. The samples were shaken to dissolve the inhibitor. In the tests with aqueous ammonia, the inhibitor and alloy specimen were added to a 25 mm X 200 mm glass culture tube with a Teflon-lined screw cap. The samples were shaken for 6 h on a mechanical shaker to dissolve the inhibitor and then stored upright at room temperature. Samples were shaken once each workday until the tests were terminated. The total weight of solution (inhibitor plus solvent) was approximately 50 g for the aqueous ammonia tests and 10 g for the anhydrous ammonia tests. Upon completion of the corrosion tests, the alloy specimens were removed from the solutions and examined by energy-dispersive X-ray (EDX) techniques. Prior to EDX examination the alloy specimens were washed as necessary by using water, acetone, or petroleum ether to remove the inhibitor, which precipitated on the alloy surface of the specimens upon solvent evaporation. The samples then were cleaned in a sonic bath, followed by washing for 5 min in 4 wt 7'0 HC1. The cleaned samples were washed in water, rinsed with acetone, dried, and weighed to deter-
Table IV. Typical Alloys Used in Construction of Ammonia Pressure Vessels ASTM typical applications no." alloy tempered use A 202-B C, Cr, Mn, Si no transport vessels welded boilers and other pressure vessels A 516-70 C, Mn, Si no nurse tanks and older tanks welded pressure vessels where improved notch toughness is important A 517-D C, Mn, Si, Cr, Mo, B, Ti yes transport vessels high strength quenched and tempered; for use in fusion welded boilers and pressure vessels A 612 killed C, Mn, Si no bulk storage welded pressure vessels in service at moderate and lower temperatures a
American Society for Testing and Materials.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985
648
Table V. Corrosion Test Data ASTM no."
inhibitor
A 202-B A 516-70 A 517-D A 612 A 202-B A 516-70 A 517-D A 612 A 202-B A 516-70 A 517-D A 612
DCD DCD DCD DCD
A 202-B A 516-70 A 517-D A 612 A 202-B A 516-70 A 517-D A 612 A 202-B A 516-70 A 517-D A 612
DCD DCD DCD DCD
TU TU TU TU none none none none
specimen dimensions, i n b specimen wt, g L W T initial final difference Anhydisous Ammcmia
0.724 1.158 1.092 1.060 0.618 1.004 1.234 1.467 1.395 1.132 1.235 1.030
0.301 0.255 0.253 0.295 0.304 0.282 0.254 0.302 0.296 0.294 0.256 0.281
0.082 0.079 0.120 0.054 0.081 0.074 0.104 0.086 0.082 0.078 0.104 0.111
0.750 1.082 1.176 1.087 0.807 1.115 1.154 1.071 0.712 1.147 1.108 0.097
0.304 0.244 0.255 0.296 0.303 0.256 0.256 0.307 0.300 0.268 0.254 0.297
0.104 0.079 0.103 0.065 0.095 0.083 0.107 0.057 0.100 0.078 0.1150.071
1.9998 2.9295 3.9871 1.7950 1.8650 2.6305 3.6870 4.3359 4.0828 3.1500 3.9014 3.7102
exposure time, days
corrosion rate, mil/year
1.9868 2.9158 3.9867 1.7849 1.8590 2.6205 3.6786 4.3238 4.0800 3.1470 3.8970 3.7082
0.0130 0.0137 0.0004 0.0101 0.0060 0.0100 0.0084 0.0121 0.0028 0.0030 0.0044 0.0020
153 153 153 153 133 133 133 133 133 133 133 133
0.46 0.32 0.01 0.29 0.26 0.29 0.22 0.25 0.06 0.08 0.11 0.05
2.6278 2.6496 3.7499 2.2121 2.9504 2.9928 3.6935 2.4959 2.7087 2.9994 3.92352.5647
0.0001 0.0001 0.0001 0.0002 0.0037 0.0064 0.0065 0.0038 0.0002 0.0000
64 64 64 64 64 64 64 64 64 64 64 64
0.01 0.01 0.01 0.01 0.24 0.36 0.36 0.20 0.01 0.00
AquecIUS Ammcinia
TU TU TU TU none none none none
2.6279 2.6497 3.7500 2.2123 2.9541 2.9992 3.7000 2.4997 2.7089 2.9994 3.9234 2.5647
-0.ooo1 0.0000
-0.01
0.00
"American Society for Testing and Materials. b L = length; W = width; T = thickness.
1 050
-
NOTE NO SIGNIFICANT CORROSION DETECTED FOR ANY OF THE ALLOYS WITH AOUEOUS AMMONIA ALONE OR WITH AOUEOUS AMMONIA CONTAINING DC3
OCD
1
1
: 1
ry1
NO INHIBITOR
Figure 4. Alloy corrosion rates in NH,
Figure 5. Alloy corrosion rates in NH,OH containing TU.
mine the weight loss due to corrosion. The cleaned samples were examined with a scanning electron microscope (SEM). The corrosion test data and calculated corrosion rates are given in Table V and plotted in Figures 4 and 5 for anhydrous and aqueous ammonia, respectively. The corrosion rates were calculated by assuming that the corrosion was uniform (i.e., no localized attack). All of the corrosion rates were less than 2 mil/year, which is considered excellent corrosion resistance (Kirby, 1980). In the anhydrous ammonia solution containing DCD, three of the alloys (A 202-B, A 516-70, and A 612) corroded slowly (corrosion rates ranged from 0.29 to 0.46 mil/year). Alloy A 517-D showed no significant corrosion (0.01 mil/year), even though the same alloy in anhydrous ammonia without inhibitor corroded at the rate of 0.11 mil/year. This indicates that DCD may act as a corrosion inhibitor for alloy A 517-D. In the absence of inhibitor, alloys A 202-B, A 516-70, and A 612 corroded at the rates of 0.06, 0.08, and 0.05 mil/year, respectively. Before the samples with DCD and alloys A 202-B, A 516-70, and A 612 were opened, a light coating of a reddish-brown solid was seen on the glass above the solution level; after the tubes were opened, the recovered DCD from
these samples was light brown instead of white in color. This coating was not observed in the sample containing the A 517-D alloy, and the recovered DCD was white in color. The reddish-brown solid was first observed about 1week after sample preparation. Microscopic examination of the alloy specimens from the anhydrous ammonia solution containing DCD before any cleaning showed that they were coated with DCD and fine grains of an opaque material. Some of the opaque grains were magnetic. Energy-dispersive X-ray examination showed that the surfaces of all four alloys in contact with inhibitor were composed primarily of iron. Scanning electron microscopy examination of the same alloys after cleaning revealed that alloys A 202-B, A 516-70, and A 612 were generally etched and pitted over the entire surface of the samples, with the cutting marks obscured. The pitting, which was observed at magnifications of 500-5000 X, was considered minor. Alloy A 517-D was slightly pitted, but the cutting marks were still evident. Prior to cleaning, the specimen of alloy A 517-D, which was exposed to anhydrous ammonia without inhibitor, was coated with an orange-red, mudlike material with cracks. After the specimen was cleaned with acid, SEM examination revealed that it was pitted, but cutting marks were still evident.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985 649
All four alloys in the anhydrous ammonia containing TU also corroded slowly. Corrosion rates ranged from 0.22 to 0.29 millyear. The samples were coated with a black solid. The solid also was in the liquid and was first observed in the samples within 1 day of sample preparation. Examination of the alloy specimens by EDX showed that the black solid contained Fe and S, indicating that the solid was iron suKde. The SEM examinations showed that the surfaces of the alloy specimens were slightly etched with some distinct pits and holes, but cutting marks were still evident on all the alloys except A 517-D. The pitting was considered minor. There was no significant corrosion of any of the four alloys in either the aqueous ammonia solutions containing DCD or in the aqueous ammonia solutions without inhibitor. However, all four alloys showed slight corrosion when exposed to aqueous ammonia containing TU. Corrosion rates ranged from 0.20 to 0.36 millyear. All of the alloys in the TU solutions were coated with a fine black solid very similar to that observed in the anhydrous system. The fine black solid also was present in the solutions and was observed on the alloys and in the solutions within 1 day after sample preparation. Samples with alloys A 516-70 and A 517-D were darker than those with alloys A 202-B and A 612, which had lower corrosion rates. Examination of the alloy specimens by EDX showed that the black solid contained Fe or Fe and S in combination. Acidification of the black solid with HCl gave a strong odor of H2S, indicating that the black solid was an iron sulfide. Because of the black color, it is suspected that the solid was FeS. Examination of the alloy specimens by SEM showed that the surfaces were slightly pitted, but cutting marks were still visible. Summary and Conclusions The nitrogen loss inhibitors DCD and TU are soluble and stable enough for use with either anhydrous or aqueous ammonia. The corrosion data indicate that there should be no problem with the use of the alloys studied to construct equipment to store, transport, and handle aqueous and anhydrous ammonia containing DCD or TU. Since in practice the concentrations of inhibitors used will be much lower than 75% of their solubilities (the concentrations used in the corrosion tests), corrosion rates probably will be lower than those measured in this study. On the basis of the information given in the literature (Gmelin, 1978) and the experimental observations, it is postulated that the following corrosion reaction occurs in the absence of oxygen in aqueous ammonia-thiourea solutions: S
I1
Fe t NHz-C-NHz
t H20
-
0
II
FeS t NHz-C-NH2
t H2 (1)
Therefore, it is possible that hydrogen may be produced during the alloy corrosion process. It should be emphasized that eq 1 is postulated, and there is no conclusive evidence that hydrogen is a product of the corrosion. The possibility of hydrogen formation is pointed out as a safety precaution. No reactions are postulated for the corrosion of DCD and TU in anhydrous ammonia. A comparison of the relative cost per unit of nitrogen for addition of the inhibitors ET", nitrapyrin, DCD, and TU to anhydrous ammonia is given in Figure 6. The relative costs were calculated by using the purchase prices of the inhibitors and ammonia. These prices were obtained from the manufacturer, distributor, or U.S.Department of Agriculture (USDA). The additional cost per unit of nitrogen as a result of inhibitor addition ranges from 23 to 58%. The relatively low materials cost for production
E T T a (*32,000b/T0N)
158%
0.5 Ib E T T o / A C R E
NITRAPYRIN ( ~ 2 6 , W O b / T O N )
147%
0 5 I b NITRAPYRIN/ACRE
T U (Bl,72Ob/TON--
1420C/TON)
126 %
N FROM T U = 2 % OF T O T A L - N
I 2 3 010
-
5 % OF TOTAL N
N FROM DCD
N H s (1275b/TON)
1
0 o b C
1
1
1
1
loo%
1
1
1
1
1
1
1
1
1
1
1
1
100
I50 RELATIVE COST PER UNIT OF N 50
5-ETHOXY-3-(TRICHLOROMETHYL)
- l,2,4
1
1
200
THIADIAZOLE
PURCHASE PRICE PROVIDED BY MANUFACTURER DISTRIBUTOR, OR USDA. THIS VALUE USED TO CALCULATE RELATIVECOST. COST OF MATERIALS TO PRODUCE I TON OF INHIBITOR. MATERIALS COSTS FROM CHEMICAL MARKETING REPORTER, FEBRUARY, 1982.
Figure 6. Cost of adding inhibitors to NH3.
of the inhibitors DCD and TU compared to the purchase prices (numbers in parentheses in Figure 6) indicates that these inhibitors might be produced at a much lower cost than the purchase price. In summary, the results of the compatibility studies indicate that there should be no problem in the use of DCD and TU with anhydrous or aqueous ammonia. Registry No. A 202-B, 42613-91-2; A 516-70, 12732-03-5; A 5 1 7 - ~ , 57890-89-8; A 612, 63108-63-8; (NH,),c=s, 62-56-6; N H 4 0 H , 1336-21-6; NH,C(NHCN)=CNH, 461-58-5; NH3.NH2C(NHCN)=CNH, 98483-53-5; NH,.(NH,)~c=s, g t ~ a 3 - 5 4 - 6 ; NH40H.NH2C(NHCN)=CNH, 98483-55-7; NH40H.(NH2),C=S, 98483-56-8; NH,, 7664-41-7.
Literature Cited Ashworth, J.; Rodgers, 0. A. Can. J. Soil Sci. 1981, 61, 461-463. ASTM "Annual Book of ASTM Standards"; American Society for Testing and Materials: Philadelphia, 1982. Dow Chemical Co. USA. "N-Serve Nitrogen Stabilizer", Technical Information Bulletin, Ag-Organics Dept., Mldiand, MI. Emerson, S. Agrichem. Age 1982, 26(4), 351-37. Evrad, T. 0.; Parteilo, P. E.; Rockwell, J. C. "Abstracts of Papers", 184th National Meeting of the American Chemical Society, Kansas City, MO, Sept 1982; American Chemical Society: Washington, DC, 1982. Gautney, J.; Kim, Y. K.; Barnard, A. R. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 155-161. Gautney, J.; Kim, Y. K.; Gagen, P. M. Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 483-489. Gmelin, L. "Gmelin Handbuch dsr Anorganischen Chemie"; Springer-Verlag: Berlin, 1978; Vol. 14C. Hawk, R. D.; Behnke. H. presented at the Technical Workshop on Dicyandiamide, Muscle Shoals, AL, Dec 4-5, 1981.
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 650-654
850
Hays, J. T.; Forbes, D. J. J. Agric. Food Chem. 1974, 22, 468-470. Huber, D. M. Solutions 1980, 24(2). 86-92. Janecke, E.; Rahlfs, E. Z . Elekfrochem. Angew. Phys. Chem. 1930, 36. 645-654. Janeke, E.; Hoffmann, A. 2.Nektrochem. Angew. Phys. Chem. 1932, 3 8 ,
Page, J. L.; Hoffman, J. R. "Abstracts of Papers", 184th National Meeting of the American Chemical Society, Kansas City, MO, Sept 1982; American Chemical Society: Washington, DC, 1982. Siangen, J. H. G.; Kerkhoff, P. Fed. Res. 1984, 5(1),1-76.
880-883.
Received for review February 26, Accepted June 14,
Kirby, G. N. Chem. Eng. 1980, Nov 3, 86-131. Maihi, S. S.; Nyborg, M. Plant Soil 1979, 5 7 , 177-186.
1985 1985
Liquid-Phase Oxidation of Cumene Initiated by Ozone in the Presence of Sodium Cyclohexanecarboxylate Josh L. Sotelo,' Fernando J. BeRrBn, JesBs BeArBn-Heredla, and Manuel GonrBlez Departamento de Qdmica Tknica, Facultad de Clenclas, Unlversidad de Extremadura, Eadajoz 0607 1, Spain
Liquid-phase oxidation of cumene initiited by ozone using sodium naphthenate as a catalyst has been investigated. The effects of temperature, catalyst concentration, ozone partial pressure, and initiation time have been studied. Maximum selectivitiesand yields of cumene hydroperoxide of about 65 % and 85 % , respectively, were reached. Likewise, a mechanism and kinetic equation for hydroperoxide formation were deduced. In this mechanism, the bimolecular hydroperoxide decomposition and the catalyst attack on hydroperoxide constitute the initiation step in the autoxidation period. Finally, the kinetic equation reproduces experimental hydroperoxide concentrations within
a 15% deviation.
Introduction Cumene hydroperoxide may be used in organic synthesis processes like epoxidation of cu,P-unsaturated ketones (Yang and Finnegan, 1958), polymerization reactions (Walling and Buckler, 1955),etc., but the most important industrial application is in phenol manufacture. For the formation of cumene hydroperoxide, cumene is commonly oxidized in liquid phase. Because of its great industrial application, this oxidation has been studied by many authors (see Table I). When oxidation is carried out with only oxygen or air, it is called autoxidation; although high hydroperoxide yields are reached, the reaction time is extremely lengthy because the process has a long induction period and the reaction rate is very low at the beginning. The presence of an alkaline ion as a catalyst leads to higher hydroperoxide concentrations, but the reaction time still remains long. The induction period disappears when cumene oxidation is carried out in the presence of initiators or catalysts like transition-metal oxides or their corresponding organic salta. Only low hydroperoxide yields are obtained by the use of these catalysts, while the presence of an initiator like ozone leads to concentrations similar to those obtained from the autoxidation. As can be seen from Table I, all these ways have some advantages as well as disadvantages. Hydroperoxide formation is considerably improved when cumene oxidation is initiated by ozone in the presence of an alkaline ion. In these conditions there is no induction period and the maximum hydroperoxide yield is very high (Wagner, 1965; Sotelo et al., 1983). The alkaline compounds used until now, mainly sodium carbonate and hydroxide, are not soluble in cumene, and hence it is very difficult both to know the exact catalyst concentration and to be sure of the homogeneity of the solution. Therefore, sduble sodium naphthenate was used as a catalyst and ozone as an initiator with the following aims: (a) obtaining higher hydroperoxide yields at relatively low reaction times and (b) studying the reaction kinetics more accurately, deducing an equation for hydroperoxide for0196-4321/85/1224-0650$01.50/0
mation based on a reaction mechanism. Experimental Section Materials. Cumene, reagent grade, was washed in a stirred tank with a 20% aqueous sodium hydroxide solution in the ratio 1:l for 24 h. After decantation, it was dried over CaC1,. Sodium cyclohexanecarboxylate (referred to as sodium naphthenate) was prepared by adding cyclohexanecarboxylic acid (naphthenic acid) to a hot concentrated aqueous sodium hydroxide solution until pH reached 10. Then the organic and aqueous phases were separated and the former was heated, in order to dry it, at about 100 OC for 24 h. The resulting sodium naphthenate was dissolved in cumene. The naphthenate concentration was determined by volumetric analysis (Piffer et al., 1953). Oxygen was taken directly from a commercial cylinder and fed to an ozone generator with a maximum production rate of 6 g/h of ozone. Procedure. Experiments were carried out in a 500-cm3 spherical glass reactor that was submerged in a thermostated bath containing a silicone oil as heating fluid. The tap of the reactor had several inlets for gas feed (oxygen or 02-O3 mixture), stirring, sampling, venting, and temperature measuring. Ozone in the gas stream was analyzed iodometrically (Kolthoff and Belcher, 1957). The 02-03 mixture was bubbled into the liquid during the initiation time. Then the oxidation was continued with oxygen until the maximum hydroperoxide concentration was reached. Nonreacted cumene and the liquid-phase products, cumene hydroperoxide, acetophenone, and dimethylphenylcarbinol, were analyzed by HPLC on a Waters Chromatograph with UV detector at 254 nm using a 10-cm pBondapack-C18 radial compression column and the gradient conditions shown in Table 11. Results and Discussion Four variables were studied: temperature, sodium naphthenate concentration, ozone partial pressure, and initiation time. Their influences on overall conversion of 0 1985 American
Chemical Society
