Chemistry: fertilizers – Processes and products – Organic material-containing
Reexamination Certificate
2002-04-08
2004-11-23
Sayala, C. (Department: 1761)
Chemistry: fertilizers
Processes and products
Organic material-containing
C071S034000
Reexamination Certificate
active
06821311
ABSTRACT:
The invention relates to a method for manufacturing a solid product that contains nitrogen and phosphor, especially a solid ammonium phosphate and/or urea ammonium phosphate product from a solution containing urea and phosphoric acid.
The invention is also directed at an ammonium phosphate and/or urea ammonium phosphate product manufactured by the method and its use as a fertilizer either alone or as part of a mixed fertilizer. The invention is also directed at a method for simultaneously manufacturing urea phosphate and a solid ammonium phosphate and/or urea ammonium phosphate containing product.
In the fertilizer process, solutions are formed and used which contain urea and phosphoric acid. As an example, the mother liquid of the urea phosphate process, which contains urea and phosphoric acid, as well as the urea containing scrubber solution of the NPK process to which phosphoric aced has been added, can be mentioned.
In the manufacture of urea phosphate, the impurities originating in the urea and the phosphoric acid used as raw material mainly remain in the mother liquid. We have to accept a low yield percentage of the end product in particular, when we want to manufacture clean, completely water-soluble urea phosphate. In that case, as much as 20 to 40% of the raw material mentioned above can remain in the mother liquid in addition to impurities. Therefore, the productivity of the urea phosphate process is to a great extent affected by how well we can utilize the raw material that remains in the mother liquid.
Various methods have been tested to utilize the mother liquid. For example, we have offered mother liquid as such to fertilizer factories that manufacture field fertilizers. However, mother liquid contains a lot of water, so that the storage and transportation costs of the solution become high, especially if the fertilizer factory is not located in the immediate vicinity of the urea phosphate factory. Furthermore, the hydrologic balance of fertilizer factories is not apt to allow additional water into the process without technical problems that mainly concern granulation, and without economic loss. During storage and transportation, salts can also precipitate from the mother liquid, causing problems in tanks when settling, and blocking tube systems.
As the viscosity of an acidic solution grows when concentrating and the solution becomes very viscous and extremely difficult to treat, concentrating the solution by evaporating water does not solve the problem.
U.S. Pat. No. 4,461,913 describes an improvement on the urea phosphate process, according to which it was possible to decrease the formation of precipitate by adding sulphuric acid, and to slightly increase the performance of the urea phosphate process; however, this improvement did not eliminate the actual problem with the mother liquid. Part of the raw material of the process still remains in the mother liquid.
Mother liquid has also been neutralized by liquefied ammonia and the formed precipitate has been filtered, resulting in a solvent fertilizer and a metalline precipitate (J. Agric. Food Chem., Vol. 29, No. 2,1981). However, liquefied ammonia is toxic and dangerous to handle. Its safe storage, transportation, and use require special containers and treatment equipment that meet the safety criteria, making it difficult to use safely and increasing costs. The solid residual precipitate is still a disadvantage.
Urea phosphate has also been decomposed thermally to form ammonium poly-phosphate (German Patent 2308408) or urea ammonium polyphosphate (U.S. Pat. No. 3,713,802, Fert Res 1994, 39(1), 59-69), which can be used as fertiizers. These products are soluble but polyphosphates as such are not until they are hydrolysed to form orthophosphate, a form useful for plants. This hydrolysing is dependent on external conditions and typically slow. The original material used in these processes was pure urea phosphate and not impure mother liquid.
To avoid the problem with impurities, attempts have been made to in advance purify the phosphoric acid used as raw material (Jap. pat 49-8498). However, removing impurities from phosphoric acid is a separate, expensive process.
Furthermore, attempts have been made to render mother liquid a suspension that could be used as such (CA 112:20428, PL 146113B2, Fert Res 1994, 39 (1), 59-69) by adding clay mineral and other nutrients. However, the suspension thus obtained still continues a lot of water, limiting its use to the immediate vicinity. Moreover, special equipment is required to spread it in the fields.
The present invention is directed at a method for manufacturing a solid product containing nitrogen and phosphor, especially an ammonium phosphate and/or urea ammonium phosphate product from process solutions containing urea and phosphoric acid; for example, from the mother liquid of a urea phosphate process or from the scrubber solution of the NPK process to which phosphoric acid has been added, by heating the said solution in a reactor, so that the urea contained by the mother liquid is decomposed into ammonia and carbon dioxide. The carbon dioxide and the forming water vapour are evenly removed from the reactor by suitable agitation and, at the same time, effervescence/foaming is prevented.
The ammonia generated by the decomposition neutralizes the phosphoric acid in the mother liquid, so that a suspension containing ammonium phosphate and/or urea ammonium phosphate is generated, possibly also containing other salts, phosphates or sulphates, for example, depending on the origin of the initial material used.
The suspension thus obtained is solidified by cooling, dried, crushed, ground, and/or granulated to form a product that contains nitrogen and phosphor, an ammonium phosphate and/or urea ammonium phosphate product in particular.
The invention is also directed at a solid product containing nitrogen and phosphor, manufactured by the method, an ammonium phosphate and/or urea ammonium phosphate product in particular, and its use as a fertilizer either alone or as part of a mixed fertilizer.
We observed that the urea and the phosphoric acid of various process solutions containing urea and/or impure phosphoric acid, as well as the other salts possibly contained by them as impurities, such as sodium salt, potassium salt, calcium salt, magnesium salt, iron salt, manganese salt, could be utilized by the method according to the invention by manufacturing from them a solid product that dissolved well in water and almost completely in an ammonium citrate solution and contained nitrogen and phosphor, an ammonium phosphate and/or urea ammonium phosphate product in particular. The product as such can be used as a fertilizer or it can be used as raw material in manufacturing mixed fertilizers.
In addition to the mother liquid of the urea phosphate process and the phosphoric acid treated scrubber solution of the NPK process, for example, agricultural residual solutions containing urea, phosphoric acid solutions generated by the surface finish of metal, the solids-bearing phosphoric acid suspensions in the sedimentation of phosphoric acid, or their mixtures are suitable to be used as initial solutions in the method according to the invention. Phosphates precipitated by water purification can also be utilized as part of the feed material.
When e.g. the mother liquid of the urea phosphate process is heated, the following actions can be effected at the same time: 1) evaporation of water, 2) decomposition of urea into ammonia and carbon dioxide, and 3) a neutralizing reaction of the generated ammonia with phosphoric acid. Adjusting the temperature and the reaction time can control these three phases of reaction.
The rate of decomposition of urea mainly depends on the temperature and the pH of the solution. Although urea is decomposed at relatively low temperatures, beginning from about 50° C., the reaction time becomes fairly long, when considering practical applications; especially, if the initial solution has high water content. Raising the temperature to about 80° C. guarantees a sufficien
Karonen Janne
Weckman Anders
Birch & Stewart Kolasch & Birch, LLP
Kemira Growhow Oy
Sayala C.
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