literature Cited
Barrer, R. &I., Peterson, D. L., Proc. Roy. Soc. ( A ) , 280, 466 (1964). Beecher, R., Voorhies, A., Jr., Eberly, P. E., Jr., Znd. Eng. Chem. Prod. Res. Develop., 7, 203 (1968). Burbidge, B. W., Keen, I. M., Eyles, 11. K., International Conference on Molecular Sieve Zeolites, Worcester, Mass., 1970. Dubinin, M. M., Federova, G. M., Plavnik, G. M., Piguzova, L. I., Prokofeva, E. N., Zzv. Akad. Aauk SSSR, Ser. Khim, 11, 2429 (1968). Eberly, P. E., Jr., J.Phys. Chem., 67,2404 (1963). Eberly, P. E., Jr., Kimberlin, C. N., Jr., Ind. Eng. Chem. Prod. Res. Devehp., 9, 335 (1970).
Eberly, P. E., Jr., Kimberlin, C. N., Jr., Voorhies, A., Jr., paper presented a t Second North American Meeting of the Catalysis Society, Houston, Tex., February 24-26, 1971. Kranich, W.L., Ma, Y. H., Sand, L. B., Weiss, A. H., Zwiebel, I., International Conference on Molecular Sieve Zeolites, Worcester, Mass., 1970. Meier, w, z, Krist., 115, 439 (1961), Weller, S. W., Bauer, J. M., "Studies of the Catalytic and Chemical Properties of Acid-Extracted hIordenite," Preprint, 62 Ann. Meeting A.I.Ch.E., Washington, D.C., 1969. RECEIVED for review March 12, 1971 ACCEPTED July 12, 1971
Ammonium Potassium Polyphosphate Fertilizer Bench-Scale Production Charles A. Hodgel and David R. Boylan Engineering Research Institute, Iowa State University, Ames, Iowa 60010
The technical feasibility of producing an ammonium potassium polyphosphate fertilizer was studied with bench-scale processing equipment. The kinetics of the reaction between potassium chloride and phosphoric acid was experimentally investigated, and the constants in the Arrhenius equation were determined for the forward portion of the reaction. A monopotassium orthophosphate-phosphoric acid melt was ammoniated, and the variables of temperature, pressure, residence time, and ammonia-to-phosphoric acid feed ratio were studied. A specially designed reactor was constructed for the ammoniation reaction. Analysis of the product ranged up to 8-26-17 (NPK) during optimum operating conditions. Experimental results showed that the degree of ammoniation of the final product increased with increasing pressure and residence time; however, the degree of ammoniation decreased with increasing temperature in the range of 177-232OC. The optimum ammoniation conditions for a melt of K:P mole ratio equal to 0.50 were 200-210°C with a pressure in excess of 40 psi and a residence time above 4 min.
I n the past 10 years bhe fertilizer industry has undergone considerable change. The general trend in the industry has been toward large-capacity single-stream processing units for all three of the primary plant food nutrients. Also, the coiicentration of single-plant nutrient fertilizers has increased steadily through the years. I n addition, mixed fertilizers have shown a substantial increase in total plant food analysis. According to published data (TVA, 1969), the average nutrient analysis (N, P205,and K20) of mixed fertilizers containing two or more primary nutrients has risen from 23.1y0 in 1950 to 38.2% in 1968 and is expected t o be slightly above 43% by 1975. Demand has been increasing in the liquid fertilizer industry for phosphates in the polyphosphate form for formuating higher analysis nonprecipitating liquid fertilizers. I n view of this trend, ammonium potassium polyphosphate is of considerable interest, being one of the highest analysis fertilizers known. When transportation, marketing, and agronomics are considered, such a fertilizer could be quite 1 Present address, Division of Chemical Development, Tennessee Valley Authority, Muscle Shoals, Ala. 35660. To whom correspondence should be addressed.
advantageous compared with present three-component fertilizers. Ammonium potassium polyphosphate can be made by reacting potassium chloride with an excess of phosphoric acid and then neutralizing the resulting potassium phosphate and excess phosphoric acid with ammonia. Bench-scale work reported in this paper was undertaken to determine the technical feasibility of such a process. Previous Work
A novel method of producing a complete concentrated fertilizer was tested on a small pilot-plant scale and reported as early as 1925 (Ross, 1925). This fertilizer contained 5,6% N, 24.7% P, and 15.6% K or 5,6% T\;, 56.6% PzOS,and 18.8% K 2 0 . The following main reactions were reported: KCl
+ 2H3P04
+
KHzPOI
+
+ HClt
This process involved two steps. I n the first, potassium chloride was reacted with two or more equivalent amounts of concentrated phosphoric acid a t 25OoC. Three products were obtained : volatilized hydrogen chloride, a liquid solution of Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No.
4, 1971 437
YFAT
STEAM AND UNREACTED AMMONIA TO EXHAUST SYSTEM
t AMMONIATOR GAS-LIOUID SEPARATOR
‘I
AMIXING TEE d i
Y
H3po4 KHzP04
Figure 2.
Figure 1 .
Ammoniation flow diagram
HEAT EXCHANGER FLUID IN’
.
12”
Mixing tee and amrnoniator-reactor
the exothermal reaction was utilized in-dehydrating the product. Description of Process
monopotassium phosphate, and phosphoric acid. The second step of the process consisted of diluting the monopotassium phosphate-phosphoric acid solution with a n equal volume of water, ammoniating to a thick slurry, and drying t o a nonhygroscopic fertilizer. When equivalent amounts of potassium chloride and phosphoric acid are heated to produce potassium metaphosphate, only a small portion of the chloride is replaced by phosphoric acid a t temperatures of 200-3OO0C. HoFever, all the chloride can be replaced and volatilized a t 700-900°C. Ross and Hazen (1923) were able to reduce these severe operating conditions by modifying the potassium metaphosphate process to use an excess of phosphoric acid and then neutralizing the resulting product with ammonia. I n the process developed by Ross and Hazen, increasing the H3POa:KC1 mole feed ratio from 1 to 2 decreased the temperature of reaction and reduced the residence time required for the KC1 to react. However, the resulting product was diluted with water, and ammonia was passed into the solution until a thick slurry was obtained. Direct ammoniation, as now used in the production of ammonium polyphosphate, was not in use at the time of Ross and Hazen’s work. Their process can be improved through the use of a n ammonium polyphosphate reactor for the second portion of the process, thereby eliminating the need for diluting the KH2P04-H3P04 solution and drying the resulting ammoniated product. I n addition to elimination of the dilution and drying steps, in the polyphosphate reactor, a more highly concentrated product is formed because of the highly exothermal reaction. Investigators a t TVA (Potts et al., 1961)’ produced on a laboratory scale liquid fertilizer solutions composed of the same chemical species as found in Ross’s product: concentrated phosphoric acid, ammonia, and potassium without any chlorides or sulfates. The low-chlorine grade liquid fertilizers were made with superphosphoric acid, potassium hydroxide, and ammonia. Neutral high-analysis liquids with little or no chloride content could be formulated from potassium hydroxide instead of the lower analysis acidic liquids made from potassium chloride. Several methods of producing ammonium polyphosphate have been described in the literature. Superphosphoric acid made from furnace acid can be ammoniated (Kelso et al., 1968). Also, superphosphoric acid concentrated from wetprocess acid was ammoniated in the equipment described by Getsinger et al. (1962). -4second process utilizing wet-process acid of lower concentration (23% P) was reported by Getsinger (1968) and Mann (1965) in which the heat from 438 Ind.
Eng. Chem. Prod. Res. Develop., Vol. 10,
No. 4, 1971
The use of a n ammonium polyphosphate-type reactor would have been well suited for the ammoniation step in Ross and Hazen’s ammonium potassium phosphate process. Such a reactor was used in the present work. The main reactions that took place in the production of ammonium potassium polyphosphate can be represented by the following unbalanced equations. KCl
+ (n)
KHZPOa
__ A
KH2P04
+
(n - 1)H,PO4
+ HCl t + H20 t
+ HSPOa + NH3 + mixture of ammonium potassium ortho, pyro, and higher polyphosphates
(
)
Paper chromatography indicated the presence of ortho, pyro, and higher polyphosphates. The first reaction was carried out in a batch reactor under various temperature conditions and H3P04:KC1 feed mole ratios. The reaction solution temperature was varied from 100-160°C. Hydrochloric acid and water vapors evaporated from the solution and were condensed. h i H 3 P 0 4 KCl : mole ratio greater than 1 was used to minimize both the time and temperature required for the KC1 to react. The ammoniation reaction was demonstrated in a continuous bench-scale reactor. A solution of monopotassium orthophosphate and phosphoric acid containing 26.2% P (60.0y0 PzOs) and 16.5% K (19.9% KzO) was fed a t 177°C into a mixing tee. Preheated vaporized ammonia was reacted with this solution in the mixing tee and ammoniator-reactor. The molten product passed into a gas-liquid separator where water vapor and unreacted ammonia were exhausted. Product ammonium potassium polyphosphate melt was collected. Since the study was not concerned with granulation, no attempt to granulate the product was made. Experimental
The reaction kinetics of the KCI-HaPOd reaction was studied, and the constants in the Arrhenius equation were determined for the forward portion of the reaction. Data were obtained by reacting technical grades of KCl and H3PO4 in a batch reactor a t temperatures ranging from 100-160°C with residence times up to 30 min. Two differential methods were used to evaluate the relationship between reactant concentrations and time. For the reaction conditions used, the
Table 1. Ammoniation Operating Conditions 0.50 K : P feed mole ratio 0.25-2.00 N : P feed mole ratio 177-232OC Reactor temperature 25-75 psi Reactor pressure 2.61-6.18 min Calculated residence time 16.5 Melt feed composition, yo K 26.2 Melt feed composition, yo P 3 , 0 - 7 . 1 L/hr Melt feed flow rate
0
050 N:P FEED
Figure 3.
reaction rate order was found with respect to both KCl concentration and H3P04 concentration. The general kinetic rate expression t h a t best represented the kinetic data for the forward portion of the reaction was calculated by using the following reaction and the Arrhenius equation. nH3P04aq)
+ KCl(aq1 >_ KHJ'Oa(aq) HCl(g)
t
+ . . . (n - l)H,POl(aq)
where : CKCI, CHIPO4 = CY,
p
=
e
=
ko
=
E
=
R T
= =
concentration in g mol/l. order of reaction with respect t o the component time, min frequency factor in 1.-min/g mol activation energy of the reaction in cal/g mol ideal gas law constant, 1.987 cal/g mol, OK temp, OK
The ammoniation step was demonstrated by ammoniating a monopotassium orthophosphate-phosphoric acid melt with the objective of determining the effects of K : P mole feed ratio, temperature, pressure, and residence time upon the degree of ammoniation of the final product. A schematic drawing of the ammoniation processing equipment is shown in Figure 1. The actual reaction between ammonia and the KH2P04-H3P04melt occurred in the mixing tee and reactor shown in Figure 2. The reactor and all feed lines were made of Type 316 stainless steel and constructed t o withstand high pressures, high temperatures, and corrosiveness of the reactants and products. A Ucon heat exchanger fluid was used in the heat exchanger surrounding the reactor to heat the reactor initially and to maintain a given reactor temperature during the reaction. This heat exchanger fluid was heated to a maximum of 232OC by means of a 3000-R thermostatically controlled electrical resistance heater system. The pressure in the ammoniator-reactor was measured with a piezoelectric pressure transducer in conjunction with a charge amplifier and a cathode-ray oscilloscope. The ammonia flow rate was measured by passing the ammonia in liquid form through a rotameter. The ammonia was vaporized and heated by means of electrical heating tapes before entering the mixing tee. The melt of monopotassium orthophosphate and phosphoric acid was pumped t o the mixing tee by a Teflon diaphragm pump. The melt flow rate could be varied up to a maximum of 30 lb/hr. Product ammonium potassium polyphosphate passed from the ammoniator-reactor t o the gas-liquid separator made of Type 316 stainless steel. Product steam and uiireacted
100
200
150
MOLE RATIO
Ammoniation efficiency
ammonia were exhausted a t the top of the gas-liquid separator into a steam exhaust system. No attempt was made to recover unreacted ammonia with this experimental equipment. The product ammonium potassium polyphosphate melt flowed by gravity out the base of the gas-liquid separator. With the ammoniation equipment shown in Figures 1 and 2 , the optimum operating conditions for maximizing the N : P mole ratio of the product were determined. The effect of the ?;:P feed ratio upon product composition was evaluated to determine the ammoniation efficiency and the maximum possible degree of product ammoniation. Also, the effects of temperature, pressure, and residence time in the ammoniator-reactor upon product composition were studied. Operating conditions for these studies are shown i n Table I. Results
The experimental reaction rate kinetics of the forward reaction between KCl and H3P04were determined. For the experiment'al conditions used, t'he expression that best represented the data is shown below. ~-dC~al d0
-
(2.72
x
I O I.-niinjg ~ mol)
x
18,088cal/g mol
(e[-
RT
I)
x
(cKCl)(CH,PO,)
+
The degree of ammoniation of molten melt (KH2P04 H,POI) was experimentally determined as a function of X : P feed mole ratio, t'emperature, pressure, and residence time. These results are shown graphically in Figures 3 through 7. Parameter values and product analyses are given in Table 11. Based on the results of varying the 9 : P feed mole ratio, the most practical degree of ammoniation should be attained wit,h a n N : P feed mole ratio of 0.6-0.9 with a 95% or higher ammonia efficiency when using a K : P feed mole ratio of 0.5. X o theoretical maximum degree of ammoniation can be determined since this would vary with t'he proportions of ortho, pyro, and polyphosphates in the product,. The
"2 0 3 z
o
0
050 100 1 5 0 200 N P F E E D MOLE RATIO
Figure 4. Degree of ammoniation of product as function of ammonia input Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No.
4, 1971 439
~
~~~
Table 11. Potassium Orthophosphate-Phosphoric Acid Ammoniation Data N : P mole
N: P mole
ratio
N reacted,
of feed
?6
3 4 5 6 7
0.25 0.50 0.75 1.00 1.25 1.50 2.00
8 9 10 11 12 13
1.oo 1.00 1.00 1.00 1.00 1.00
14 15 16 17 18
1.oo 1.oo 1.00 1.00 1.oo
19 20 21 22 23
1.00 1.oo 1.oo 1.oo
Sample no.
1 2
%
Residence time, min
ratio of product
N
P
K
95 90 79 61 55 48 37
210 210 210 210 210 210 210
40 40 40 40 40 40 40
2.61 2.61 2.61 2.61 2.61 2.61 2.61
0.237 0.450 0.592 0.614 0.686 0,726 0.738
2.79 5.30 7.02 7.14 8.14 8.48 8.67
26.06 26.07 26.24 25.76 26.29 25.85 26.03
16.63 16.51 16.58 15.93 16.55 16.57 16.14
..
177 188 199 210 221 232
40 40 40 40 40 40
2.61 2.61 2.61 2.61 2.61 2.61
0.748 0.702 0.651 0.634 0.595 0.536
8.29 8.05 7.70 7.50 7.19 6.63
24.54 25.37 26.20 26.20 26.77 27.38
15.64 15.83 16.73 16,83 17.04 17.32
210 210 210 210 210
25 40 50 60 75
2.61 2.61 2.61 2.61 2.61
0.562 0.620 0.649 0.678 0,712
6.66 7.46 7.72 8.12 8.39
26.24 26.64 26.33 26.51 26.29
16.35 16.70 16.73 16.87 16.46
210 210 210 210 210
50 40 40 40 40
2.61 3.71 3.71 6.18 6.18
0.631 0.661 0,654 0.682 0.690
7.50 7.86 7.59 8.22 8.31
26.33 26.33 25.81 26.68 26.72
16.39 16.57 16.23 16.67 16.87
..
.. ..
.. ..
.. ..
.. ..
..
.. ..
..
.. ..
1.00
Analysis of product,
O C
Press., psi
Temp,
-
0.70
0.65-
0
i c
5 0.70-
2 0.60P 8
W
d 5
n 055-
8
E 0.60I
35
Figure 5.
I
I
I
65
75
I
45 55 PRESSURE, PSI
4
Effect of pressure on ammoniation 0 50'
I70
low ammoniation efficiency obtained with the experimental equipment was expected since no preneutralization step was utilized as in the TVA ammonium polyphosphate process. Temperature was one of the most important process variables affecting the degree of ammoniation of the product. The degree of ammoniation achieved decreased with increasing temperature. I n the temperature range of 177-200°C, great difficulty was encountered in keeping the product in the fluid state. I n the temperature range of 200232"C, no problem of freezing occurred; however, the degree
0.60' 2
Figure 6.
I
3
I
I
4 5 RESIDENCE TIME,MIN.
I
6
I
7
Effect of residence time on ammoniation
440 Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 4, 1971
Figure 7.
180
,
190
,
200 210 TEMPERATURE;C
1
220
1
230
240
Effect of temperature on ammoniation
of ammoniation of the product decreased significantly in the higher temperature range. The optimum operating temperature range was from 200-210°C when using a 0.5 mole ratio of K : P in the feed melt. Pressure was a significant variable affecting the degree of ammoniation of the product. The product K : P mole ratio increased from 0.562 a t 25 psi to 0.712 a t 75 psi again using a K : P feed mole ratio of 0.5. Seventy-five psi was the pressure limit of the KH2P04-H3P04 feed melt pump. From the experimental results, it appears that pressures above 75 psi would increase the degree of ammoniation possible. Residence time had the least effect of all the process variables upon the degree of ammoniation of the product. This was probably owing t o the intimate mixing of ammonia and KH2P04-H3POamelt achieved for all residence times tested. Kot all the products mere tested for water solubility.
Product sample No. 13, Table 11, was 100% water soluble (AOAC method), Paper chromatography indicated the presence of ortho, pyro, and small amounts of higher polyphosphates in the product sample. Microscopic examination and X-ray diffraction revealed that the bulk of the orthophosphate consisted of the mixed salt (K, NH4)H2P04.All the solid products had low p H values. When the solid products are acidic, part or all of the polyphosphates readily hydrolyze to the ortho form in time. Conclusion
I n the determination of the kinetic rate expression for the reaction between phosphoric acid and potassium chloride, only the forward reaction portion was determined. The constants in the Arrhenius equation were determined experimentally, and the reaction rate was of the first order with respect to both chloride concentration and phosphoric acid concentration. The ammoniation of a KH2P04-H8P04melt can be successfully accomplished with the proper residence time, pressure, and temperature conditions. By use of a K : P mole ratio of 0.5 in the feed melt, the best operating conditions were 200-21OOC with a pressure in excess of 40 psi and a residence time above 4 min. Based on the experimental results, the degree of ammoniation of the final product increased with increased pressure, increased residence time, and decreased temperature. The degree of neutralization ranged from a mole ratio of (NH4 K) : P of 0.74-1.24. Since no preammoniation step was used in this process, this range was lower than t h a t of TVA for ammoniation of superphosphoric
+
acid into ammonium polyphosphate (up to 1.57 moles of N/ mole of P) . As a result of the work with the experimental ammoniatorreactor, the ammoniation portion of the process can be conducted in the same type of processing equipment as that used in the ammonium polyphosphate process. The most significant differences would be the need for higher temperatures and materials of construction that would be resistant to additional corrosiveness of the chloride ion. The results obtained with the experimental ammoniator-reactor could also be of value when considering that the potassium phosphates used in this process can be produced by methods other than the direct reaction of potassium chloride with phosphoric acid. References
Getsinger, J. G., U. S. Patent 3,382,059, May 7, 1968. Getsinger. J. G., Sieael, M. 11..Mann, H. C., J. Agr. Food Chem., 10 (J),341-4’(1962).‘ Hazen, W., Ross, W. H., U. S.Patent 1,456,850, May 29, 1923. Kelso, T. M., Stumpe, J. J., Williamson, P. C., Commer. Fert., 116 (3), 10-6 (1968). Mann, H. C., Chem. Eng. News,43 (39), 63 (September 27, 1965). Potts, J. hl., Elder, H. W., Scott, W. C., J . Agr. Food Chem., 9 (3), 178-80 (1961). Ross, W. H., Trans. Amer. Electrochem. SOC.,48, 299-310 (1925). Ross, W. H., Hazen, W., U. S. (Patent 1,456,831, May 29, 1923. Tennessee Valley Authority, 1968 Fertilizer Summary Data,” p 4, National Fertilizer Development Center, Muscle Shoals, Ala., 1969. RECEIVED for review March 15, 1971 ACCEPTED June 22, 1971 Presented at 160th Meeting, ACS, Chicago, Ill., September 1970. This work was financed by the Chemical Engineering Department and the Engineering Research Institute of Iowa State University.
Dibasic Acids from Ethylene and Dehydroabietic Acid Walter H. Schuller Southern Marketing and Nutrition Research Division, Agricultural Research Service, U S . Department of Agriculture, Olustee, Flu. Sd07.2
Ethylene, reacted with dehydroabietic acid in the presence of palladium(ll) acetate and silver acetate, gives a mixture of dimeric dibasic acids.
T h e reaction of ethylene with benzene in the presence of palladium(I1) acetate gave styrene and stilbene (Fujiwara et al., 1968, 1969). The application of this reaction to dehydroabietic acid was thus considered desirable with the goal of preparing rosin-based dimeric dibasic acids. Experimental
To a solution of 6 grams (0.02 mole) of dehydroabietic acid in 24 ml of glacial acetic acid and 100 ml of n-heptane were added 2.25 grams (0.01 mole) of palladium(I1) acetate and 16.63 grams (0.10 mole) of silver acetate. The mixture
was charged to a 500-ml round-bottomed, four-necked flask equipped with a thermometer, a gas inlet tube extending below the surface of the liquid, a mechanical stirrer, and a reflux condenser terminated with a drying tube filled with Drierite. Ethylene gas was bubbled through the dispersion with vigorous stirring under reflux (89OC) for 8 hr. The dispersion turned black, and the flask was heavily silvered by the end of the reaction. The solution was filtered, water washed, stripped, and the brown friable solid residue dried under reduced pressure over Drierite; yield, 6.86 grams; mp, 154-158OC dec; equiv tvt, 328. A portion was reacted with an excess of ether-diazomethane. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 4, 1971
441
