Chemistry: fertilizers – Processes and products – Inorganic material
Reexamination Certificate
2001-10-04
2004-02-10
Sayala, Chhaya (Department: 1761)
Chemistry: fertilizers
Processes and products
Inorganic material
C071S061000
Reexamination Certificate
active
06689181
ABSTRACT:
BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION
The present invention relates to ammonium sulfate nitrate composites useful as fertilizers having desirable levels of nitrate ions, superior stability against detonation, higher density, greater resistance to moisture, and a method for their manufacture.
2. Description of the Related Art
Ammonium sulfate nitrate (ASN), one of the first synthetic fertilizers, has been in continuous use for nearly 100 years providing the important primary and secondary nutrients, nitrogen and sulfur. Nitrogen is provided in part through the nitrate ion, desirable because it is readily adsorbed by many plants and promotes early growth. As historically used, the term “ammonium sulfate nitrate” has not referred to a specific chemical compound with elements in fixed proportions. Rather, it has been used to describe various mixtures of ammonium nitrate and ammonium sulfate. The Association of American Plant Food Officials (AAPFCO), which has assumed the role of monitoring and defining fertilizers, has attempted to bring order to the nomenclature. APPFCO has defined ASN as a double salt of ammonium sulfate and ammonium nitrate in equal molar proportions having a nitrogen content not less than 26%. An equal molar mixture of ammonium sulfate and ammonium nitrate has a nitrogen content of 26.4%.
Despite the AAPFCO definition, the name, ammonium sulfate nitrate, has been used to designate many combinations of ammonium sulfate and ammonium nitrate. See for instance, R. S. Meline,
J. Agric. Food Chem.
, 16(2), 235-240 (1968), where one product has a 30% nitrogen content. U.S. Pat. No. 2,795,495 describes ammonium sulfate nitrate as having an ammonium sulfate/ammonium nitrate mole ratio of 1:2 not 1:1. Great Britain Patent No. 798,690 states that the proportion of ammonium sulfate is not critical and may be used in any proportion necessary to obtain the desired nitrogen level. The use of such terminology has led to confusion between pure double salts and mixtures. Additionally, the order of the words, sulfate and nitrate, are sometimes interchanged in the literature.
A double salt is a distinct compound. The AAPFCO definition implies the existence of a compound consisting of one mole of ammonium sulfate and one mole of ammonium nitrate. A few workers have reported such a compound, however, no 1:1 double salt has been isolated and definitively proven to exist. Nikonova et al.,
Zhurnal Prikaladnoi Khimii
, 15(6), 437-446(1942) critique and correct the works of earlier authors.
The mere mixing of ammonium sulfate and ammonium nitrate does not result in either a reaction or a reaction to completion. Sufficient conditions, including time, must exist to bring about a complete chemical reaction between the two initial salts. However, even under ideal conditions, the reaction of equal molar proportions of ammonium sulfate and ammonium nitrate does not yield an equal molar compound. Instead, the reaction products are double salts of other proportions mixed with unreacted ammonium sulfate and/or ammonium nitrate.
Double salts consisting of NH
4
SO
4
·2(NH
4
NO
3
) and NH
4
SO
4
·3(NH
4
NO
3
) (hereinafter the 1:2 double salt and the 1:3 double salt respectively) have been isolated and confirmed. The 1:3 product was isolated from aqueous solution and reported as early as 1909 (Reicher et al.,
Chemish Weekblad
., 3 (Jan.), 51-56 (1909)). Scheinemakers et al. reported in 1910 in the same publication (Volume 6, 1910, pages 51-56) the isolation of a 1:2 double salt as well as the 1:3 double salt from aqueous solutions. The existence of 1:2 and 1:3 double salts have been confirmed by Nikonova (loc. cit.); Itoh,
Kogyo Kagaku Zasshi
, 63(11), 1913-1916 (1960); Emons et al.,
Wissenschaftliche. Zeitschrift Techn. Hocksch. Chem. Leuna-Merseburg
, 14(3), 295-299 (1972); and Smith et al.,
J. Agr. Food Chem.,
10, 77-78 (1962), among others.
Reported manufacturing processes for ammonium sulfate nitrate describe preparation of uniform fertilizer granules. Most products are simply mixtures of ammonium sulfate and ammonium nitrate rather than specific crystal structures since the reported chemical compositions do not reflect any specific compound. An exception is U.S. Pat. No. 2,762,699 that claims a process for the manufacture of the 1:2 double salt.
Crystallization, granulation and prilling manufacturing methods have been reported. GB 798,690 describes a method of crystallization from an aqueous solution of ammonium sulfate and ammonium nitrate. Granulation processes generally employ temperatures below the melting point of ammonium nitrate (170° C.), which assures a product that is incompletely reacted. Examples of granulation processes are described in U.S. Pat. No. 3,635,691, GB 893,389, DE1,039,498, GB 1,259,778, and in the previously mentioned journal article by R. S. Meline, et. al. Prilling processes involve temperatures above the melting point of ammonium nitrate (170° C.). Examples are described in Polish Patent No. PL86,766, and in
Przem. Chem.,
55(12), 611-614 (1976). A small amount of water was added to facilitate the melting of the nitrate. Swedish Patent 70,119 describes a process using up to 10% water with a charge consisting of ammonium sulfate and ammonium nitrate in molar ratio of 0.6:1 and prilling immediately after melting.
Few details on the composition of the products from these processes have been reported. Most of these, if not all, are mixtures consisting of double salts, ammonium sulfate, and ammonium nitrate.
It is clear from many literature references that the products of these processes suffered from low crush strength, adsorption of humidity, and caking. For instance, French Patent No. 1,368,035 stated that ammonium sulfate nitrate fertilizer possessed problems with stability in storage. Belgian Patent No. 388,046 listed several methods that utilized additives to reduce these problems. The susceptibility to caking from absorption of humidity was addressed by adding amphoteric metal oxides. U.S. Pat. No. 2,795,495 described a process to improve the stability of ammonium sulfate nitrate by adding iron salts followed by exposure to ammonia. GB 1,259,778 described a composition incorporating aluminum hydroxide or an aluminum salt to obtain improved anti-caking properties. GB 372,388 improved stability by adding urea and magnesium salts.
J. Turlej,
Prz. Chem,
55(12), 611-614 (1976) described efforts that various manufacturers adopted to improve ammonium sulfate nitrate anti-caking stability. BASF, currently the largest producer, reportedly added aluminum, magnesium, and/or calcium compounds. Ruhrchemie added ferrous sulfate.; Victor-Chemische added ferrous sulfate; Uhde Hebernia added ferrous sulfate and phanolite, a mineral. SBA (Belgium) added certain other substances. Turlej's own work, reported in the same journal, showed the addition of dolomite, aluminum, and/or magnesium compounds to increase stability and eliminate caking.
Several references have reported that ammonium sulfate nitrate always has unreacted starting materials. I. G. Farbenindustries reported in DE. 555,581 and DE 555,902 that free ammonium nitrate is always present. Srinivasa, et al. reported in
Technology,
6(1), 21-23 (1969) that the product always contains free ammonium nitrate. Ammonium nitrate is known to be very hygroscopic and it likely contributed to caking problems and particle weakness.
Ammonium nitrate mixed with organic materials such as fuel oil is an important industrial explosive. It has also been linked to terrorist incidents such as the New York World Trade Center and Oklahoma City bombings. It is desirable to render ammonium nitrate less sensitive to detonation. One way to do that is to dilute ammonium nitrate with a relatively inert material. U.S. Pat. No. 3,366,468, 1968, claimed that 5 to 10% of additives such as ammonium phosphates or ammonium sulfate could desensitize and render ammonium nitrate resistant to flame and detonation. However, the pure ammonium sulfate-ammonium nitrate double salts should also be considered as potential explosive ma
Correale Steven Thomas
Highsmith Ronald Earl
Kweeder James Alphonse
Honeywell International , Inc.
Millikin Margaret S.
Sayala Chhaya
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