High nutrient value liquid fertilizer

A liquid fertilizer containing about 6% to 9% nitrogen (N), 24% to 30% phosphoruspentoxide (P.sub.2 O.sub.5), and 5% to 9% potassium oxide (K.sub.2 O). The fertilizer is produced by the reaction of ammonium phosphate solution with phosphoric acid and a potassium-containing compound, such as potassium hydroxide.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION 
This invention relates to liquid fertilizers, and more particularly to a 
liquid fertilizer of high nutrient value containing above about 35% by 
weight of the essential nutrients, and preferably above about 40% by 
weight of such nutrients: nitrogen (N), phosphorus (expressed in terms of 
phosphoruspentoxide-P.sub.2 O.sub.5), and potassium (expressed in terms of 
potassium oxide-K.sub.2 O). 
Heretofore, a completely liquid fertilizer, free of precipitates, of 
relatively high nutrient value and containing all essential nutrients 
(nitrogen, phosphorus, and potassium) has been difficult to produce. U.S. 
Pat. Nos. 2,770,538 and 2,869,996 to Vierling are representative and 
disclose the mixing together of potassium hydroxide and phosphoric acid 
with ammonia, and possibly urea to produce a fertilizer having the claimed 
nutrient value: 10% N, 20% P.sub.2 O.sub.5, and 10% K.sub.2 O. The 
Vierling processes involve use of the essentially unstable ammonia, either 
in gaseous form or aqueous ammonia solution. U.S. Patent to Vierling U.S. 
Pat. No. 2,869,998 is similar, involving the further component nitric 
acid; in this case, a relatively low nutrient value product (8% N, 8% 
P.sub.2 O.sub.5, and 8% K.sub.2 O) is produced. U.S. Pat. No. 3,183,073 to 
Preston discloses a high nutrient value liquid fertilizer produced by use 
of a superacid (highly concentrated phosphoric acid and sucrose), together 
with ammonia and potassium hydroxide. U.S. Pat. No. 3,711,269 to Curless 
discloses a process for manufacturing liquid fertilizer utilizing 
potassium phosphate, phosphoric acid, and ammonia. In this case, the 
separation of precipitated solids and ammonia is required. U.S. Pat. No. 
3,347,656 to Potts et al discloses a liquid fertilizer produced from 
potassium chloride, phosphoric acid, and ammonia, containing all three 
essential nutrients ranging from 10% to 60% by weight of the total 
product. U.S. Pat. No. 3,024,099 to Martinson disclosed a liquid 
fertilizer utilizing a fluosilicate. U.S. Pat. No. 2,950,961 to Striplin 
et al discloses a liquid fertilizer produced from ammonia, superphosphoric 
acid, potash salts. Liquid fertilizers from superphosphoric acids are 
discussed in Tennessee Valley Authority, Division of Chemical Development, 
"Proceedings of the Liquid Fertilizer Conference," 11 June 1959, by M. M. 
Striplin, Jr. The "Encyclopedia of Chemical Technology," third edition, 
volume 10, published by John Wiley & Sons, pages 98 to 105, contains a 
discussion of liquid mixed fertilizers. 
In none of the above references is there disclosed a high nutrient value 
liquid fertilizer containing between about 6% to 9% N, 24% to 30% P.sub.2 
O.sub.5, and 5% to 9% K.sub.2 O, which is produced by the use of 
reasonably stable component materials which are admixed together, as in 
the present invention. The present invention involves the reaction of 
ammonium phosphate solution, preferably containing polyphosphate and 
orthophosphate components, with phosphoric acid and a potassium-containing 
compound, such as potassium hydroxide, to produce such a high nutrient 
value liquid fertilizer which is stable over a wide range of temperatures 
and in which salts in solution do not precipitate out.

The invention will be more completely understood by reference to the 
following detailed description of a presently preferred embodiment. 
DETAILED DESCRIPTION 
Preferably ammonium polyphosphate solution (10-34-0), commercially 
available, is utilized in the production of a liquid fertilizer in 
accordance with the present invention. Such ammonium polyphosphate 
solution contains about 10% N and 34% P.sub.2 O.sub.5 by weight. The 
P.sub.2 O.sub.5 component in turn is composed of from 30% to 45% 
orthophosphate (H.sub.2 PO.sub.4)- and from 55% to 70% polyphosphate 
(H.sub.2 PO.sub.4 -HPO.sub.3n -1). To produce 100 pounds of liquid 
fertilizer in accordance with the present invention, 70 pounds (5.94 
gallons) of the ammonium polyphosphate solution (10-34-0) may be combined 
in a stainless steel reactor with 3.95 pounds (0.47 gallon) of water. 
Preferably the water and ammonium polyphosphate solutions are added to the 
container simultaneously. Following the addition of these materials to the 
container and their mixing therein, 75% technical furnace grade phosphoric 
acid (75% H.sub.3 PO.sub.4) is added to the container, preferably 
introduced into the solution already in the container below the surface of 
that solution. 45% chemical grade aqueous potassium hydroxide (45% KOH) is 
also added to the mixture in the container, preferably below the surface 
thereof. A total of 7.72 pounds (0.59 gallon) of the phosphoric acid and 
18.33 pounds (1.50 gallons) of potassium hydroxide are added, to provide a 
total constituent weight of 100 pounds (8.50 gallons) of produced liquid 
fertilizer solution. In the adding of the phosphoric acid and potassium 
hydroxide, the rate of addition is adjusted to maintain a slightly acidic 
medium (pH maintained between about 6 and 8) throughout the production 
process. This is preferably achieved by first adding an amount of 
phosphoric acid, followed by the addition of potassium hydroxide, followed 
by more phosphoric acid and more potassium hydroxide, in that order, so as 
to maintain slight acidity in the solution. By retaining the solution 
slightly acidic, the production of ammonia gas is minimized. It has been 
found, however, that some ammonia gas is produced, and hence it may be 
advantageous to spray the vent stack from the container with jets of water 
to return the ammonia gas into solution. 
The above process is carried out at room temperature, and the temperature 
of the solution reaches approximately 130% F. After the addition of all 
constituent materials, the solution is cooled to 90% by processing it 
through a heat exchanger, and the production of the liquid fertilizer is 
completed. 
A greenish, transluscent concentrated liquid fertilizer solution is 
produced weighing about 11.76 pounds per gallon and having a pH between 
about 6.5 and 7.5. The salts in the solution remain within solution over a 
wide range of temperatures and do not precipitate out. Thus the product 
exhibits long shelf life, and is extremely stable. An analysis of the 
product produced by the above process shows that it is a true liquid 
fertilizer characterized as 7-28-7, i.e., 7% N, 28% P.sub.2 O.sub.5, and 
7% K.sub.2 O, by weight. This true liquid fertilizer thus has a nutrient 
value of 42% by weight. 
The fertilizer produced in accordance with the present invention has wide 
agricultural and horticultural use in connection of the fertilization of 
corn, beans, and similar plants. Typically, the fertilizer is used as a 
starter fertilizer which is broadcast or banded alongside rather than in a 
trench containing seed. The application rate is probably between 3 to 15 
or 20 gallons per acre as a starter fertilizer. 
The above is a presently preferred liquid fertilizer formulation. While 
constituents for 8.50 gallons of fertilizer have been given, the 
formulation may be used to manufacture a batch with a final volume of 
anywhere from 1 gallon (a practical minimum) to over 5,000 gallons. While 
a fertilizer analyzing at 7-28-7 is produced, variations in constituents 
may provide for a range in the nutrient values of from 6% to 9% N, 25% to 
30% P.sub.2 O.sub.5, and 4% to 9% K.sub.2 O. The nutrients in the liquid 
fertilizer produced are in the form of dihydrogen phosphate ions (H.sub.2 
PO.sub.4 -) and hydrogen phosphate ions (HPO.sub.4 2-), as well as various 
forms of the polyphosphate ions, potassium ions (K+), and ammonium ions 
(NH.sub.4 +). The ions are free to interact individually as ion pairs. In 
the fertilizer solution itself, the nutrients exist in the form of complex 
ion pairs. The chemical equation governing the production of the liquid 
fertilizer in accordance with the present invention is believed to be the 
following: 
##STR1## 
While the invention has been described above in terms of a presently 
preferred embodiment thereof, it will be understood by those skilled in 
the art that modifications may be made. For example, 75% wet processed 
phosphoric acid (green acid) may be substituted for the 75% technical 
furnace grade phosphoric acid noted above in connection with the presently 
preferred embodiment of this invention. By such substitution, the shelf 
life of the resultant liquid fertilizer may be reduced. Other forms of 
phosphoric acid may be employed. Further, 62% white crystalline potassium 
chloride (KCl) may be substituted for the potassium hydroxide. Again, the 
substitution may lessen shelf life of the resultant liquid fertilizer 
product, and the rust characteristic of the fertilizer may be increased 
due to the presence of chloride ions. 
Still further, to change nitrogen content, urea might be added, or the 
ammonium phosphate solution might be varied (e.g., use of 11-33-0 or 
11-37-0). The K.sub.2 O content of the resultant fertilizer could be 
adjusted by suitable variation of phosphoric acid and/or potassium 
hydroxide. The P.sub.2 O.sub.5 content might be changed by suitable 
variation of phosphoric acid. 
As to the mechanism by which the present invention is effective, it is 
possible that the orthophosphate in the ammonium polyphosphate solution is 
neutralizing the potassium hydroxide. Another alternative is that the 
polyphosphate bonds are being hydrolized to some extent and are also 
reacting with the potassium hydroxide to produce the near neutral pH 
solution. 
Accordingly, the invention should be taken to be defined by the following 
claims.