Nitrophosphate process

The nitrophosphate process , also known as the Odda process , is used for the industrial production of various nitrogen and phosphorus fertilizers from phosphate rocks, nitric acid and ammonia.

history

The nitrophosphate process was invented in 1927 by Erling Johnson , employed at Odda Smelting Works ( Odda Smelteverk ) in Odda, Norway. In 1929 and 1930 the process was registered for a patent, which was granted in 1932. However, the smelters never used the process themselves and licensed it to Norsk Hydro , BASF , Hoechst AG and DSM Dutch States Mines . They developed it further and in turn granted further licenses. At the moment the process is still used by BASF, Yara International (emerged from Norsk Hydro), Borealis AG and GNFC Gujarat Narmada Valley Fertilizers.

Procedure

Larger occurrences of the plant nutrient phosphate are found in nature almost exclusively as poorly water-soluble calcium minerals (apatites), which first have to be converted into a water-soluble form for use as fertilizer . This is usually achieved by acid digestion and treatment of the resulting phosphoric acid with ammonia or ammonium salts. Inevitably, a calcium compound has to be separated off as a by-product.

As a first step, a mixture of ground phosphate rock and calcium phosphates from the process is dissolved in nitric acid .

${\displaystyle \mathrm {Ca_{3}(PO_{4})_{2}+6\ HNO_{3}\ \longrightarrow \ 2\ H_{3}PO_{4}\ +3\ Ca(NO_{3})_{2}} }$

The reaction is complete when all of the rock has dissolved or no gas evolution from vaporizing nitric acid or nitrous gases can be detected . Depending on the original phosphate content, the undissolved rock is mixed with fresh apatites and further digested or removed from the process as waste.

By adding sodium or potassium salts, dissolved fluorosilicates can be precipitated and separated off as the corresponding alkali metal hexafluoridosilicate.

${\displaystyle \mathrm {H_{2}SiF_{6}+2\ NaCl\rightarrow Na_{2}SiF_{6}+2\ HCl} }$

This is particularly necessary when producing calcium phosphates for use as fodder.

By cooling the solution to below 0 ° C., part of the calcium nitrate formed crystallizes out as tetrahydrate and is separated off. Up to 95% of the calcium can be removed from the process in the form of a nitrogen fertilizer. This is a great advantage of the process, as it reduces the amount of calcium phosphates that are precipitated again in the further course and that have to be digested again with nitric acid.

The calcium nitrate obtained can be used directly as fertilizer. Because of its deliquescent crystals and the resulting problems during processing, transport and storage, it is usually converted into manageable fertilizers, for this purpose it is dissolved in water and ammonia and carbon dioxide are introduced.

${\displaystyle \mathrm {Ca(NO_{3})_{2}+2\ NH_{3}+CO_{2}+H_{2}O\ \longrightarrow \ 2\ NH_{4}NO_{3}+CaCO_{3}} }$

If the calcium carbonate formed is separated off before the solution is evaporated , pure ammonium nitrate is obtained , otherwise calcium ammonium nitrate .

In addition to phosphoric acid, the mother liquor of the digestion also contains various proportions of nitric acid and calcium nitrate. The amount of ammonia introduced can be used to control whether the calcium precipitates as calcium phosphate Ca ₃ (PO ₃ ) ₂ or calcium hydrogen phosphate CaHPO ₄ ; ammonium phosphate and ammonium nitrate are also formed.

${\displaystyle \mathrm {3\ Ca(NO_{3})_{2}+6\ H_{3}PO_{4}+14\ NH_{3}\ \longrightarrow \ 4\ (NH_{4})_{2}HPO_{4}+6\ NH_{4}NO_{3}+Ca_{3}(PO_{4})_{2}\downarrow } }$

${\displaystyle \mathrm {3\ Ca(NO_{3})_{2}+6\ H_{3}PO_{4}+12\ NH_{3}\ \longrightarrow \ 3\ (NH_{4})_{2}HPO_{4}+6\ NH_{4}NO_{3}+3\ CaH(PO_{4})\downarrow } }$

If you add potassium salts and evaporate, you get a homogeneous complete fertilizer . The strong heat generated by neutralization can be used for evaporation. Both calcium phosphate and calcium hydrogen phosphate can be filtered off and fed to the first process step. The filter residue also contains insoluble iron and aluminum compounds and, if fluoride has not been removed, calcium fluoride .

Separated calcium hydrogen phosphate can be treated one more time with ammonia before a further acid digestion in order to obtain nitrate-free ammonium phosphate.

${\displaystyle \mathrm {3\ CaH(PO_{4})+2\ NH_{3}\ \longrightarrow \ (NH_{4})_{2}HPO_{4}+Ca_{3}(PO_{4})_{2}\downarrow } }$

The precipitated calcium phosphate is separated off and returned to the digestion. The diammonium hydrogen phosphate is obtained by evaporating the solution .

As an alternative to ammonia, ammonium carbonate can be used, but then the reaction does not proceed completely.

${\displaystyle \mathrm {3\ CaH(PO_{4})+2\ (NH_{3})_{2}CO_{3}\ \longrightarrow \ (NH_{4})_{2}HPO_{4}+2\ CaCO_{3}\downarrow +CaH(PO_{4})\downarrow } }$

Here, too, the residue is returned to the first process step and the ammonium hydrogen phosphate is obtained by evaporating the solution.

If the crystallization of calcium nitrate after digestion is controlled in such a way that the solution contains the same amounts of calcium nitrate and phosphoric acid, ammonium nitrate and ammonium phosphate can be produced separately from each other via precipitation as calcium hydrogen phosphate and its reaction with ammonia or ammonium carbonate.

${\displaystyle \mathrm {6\ Ca(NO_{3})_{2}+6\ H_{3}PO_{4}+12\ NH_{3}\ \longrightarrow \ 12\ NH_{4}NO_{3}+6\ CaH(PO_{4})\downarrow } }$

${\displaystyle \mathrm {6\ CaH(PO_{4})+4\ NH_{3}\ \longrightarrow \ 2\ (NH_{4})_{2}HPO_{4}+2\ Ca_{3}(PO_{4})_{2}\downarrow } }$

In this process variant, the corresponding nitrates can also be obtained by precipitating the calcium nitrate with alkali and alkaline earth carbonates.

It is possible to optimize the process so that all of the calcium phosphate is converted into ammonium phosphate without a by-product. For this purpose, the digestion solution is subjected to a distillation and the nitric acid is separated off, which is used again in the first process step.

${\displaystyle \mathrm {3\ Ca(NO_{3})_{2}+6\ H_{3}PO_{4}\ \longrightarrow \ 3\ Ca(H_{2}PO_{4})_{2}+6\ HNO_{3}\uparrow } }$

The calcium dihydrogen phosphate is treated with ammonia or ammonia and ammonium carbonate to produce calcium phosphate and ammonium phosphate.

${\displaystyle \mathrm {3\ Ca(H_{2}PO_{4})_{2}+8\ NH_{3}\ \longrightarrow \ 2\ (NH_{4})_{2}HPO_{4}+Ca_{3}(PO_{4})_{2}} }$

To increase the reaction rate of the precipitations of calcium phosphates, they should be carried out at elevated temperature and pressure with an excess of ammonia or ammonium carbonate. The excess chemicals are recovered by distillation after the reaction.

What was innovative about this process was that a complete fertilizer could be produced without consuming sulfuric acid or generating gypsum as a by-product. However, due to the low sales price of the by-products compared to the production of diammonium hydrogen phosphate from ammonia, apatites and sulfuric acid, it is not competitive, which was discussed at specialist conferences due to the difficult comparison of the processes.

Further patents based on this

Quoted from patent	Registered	Publication date	Inventor	Applicant	title
US2656266	March 15, 1949	October 20, 1953	Bang Calmeyer Reidar	Norsk Hydro Elektrisk	Method of reducing the acidity of nitric acid-calcium nitrate compounds, which contain phosphate ions
US2683075	5th June 1951	July 6, 1954	Caldwell Paul	Cannac Res and Dev Company	Outcrop of phosphate rock
US2750270	April 27, 1953	June 12, 1956	Barnes Marion D.	Monsanto Chemicals	Production of soluble phosphates
US2753252	March 22, 1952	3rd July 1956	Barnes Marion D.	Monsanto Chemicals	The manufacturing process of fertilizers from citric acid- soluble phosphate- containing materials
US2803531	June 17, 1954	20th August 1957	Swensen Just Riddervo Lindeman and Swensen Gunder Georg U Wasmuth	Norsk Hydro Elektrisk	Process for the production of mono ammonium phosphate and other products from rock phosphate
US2819955	February 16, 1953	January 14, 1958	Slot Willem	Stamicarbon	Treatment of contaminated calcium nitrate
US2849280	17th August 1953	August 26, 1958	Le Baron Ira M. and Mccullough Robert F.	Le Baron Ira M. and Mccullough Robert F.	Treatment of depleted zones / soils with nitric acid
US3132935	March 10, 1958	May 12, 1964	Vorster Fritz, Nees Hugo and Geiersberger Karl	Chemical factory Kalk GmbH	Process for the manufacture of complex fertilizers
US3325246	November 20, 1963	June 13, 1967	Sawhill Duane L.	Olin Mathieson	Process for providing sodium triphosphate hexahydrate
US3431098	March 11, 1966	4th March 1969	Pierre Dumont and Honore Trimbach	Potasse & Engrais Chimiques (PEC)	Process improvements in the manufacture of complex fertilizers
US3472616	July 7, 1966	October 14, 1969	Douglas O Hauge	Bohna & Co BD	Production process for monoammonium and diammonium phosphate
US3628940	2nd January 1969	December 21, 1971	Paul R. Geissler and Ellington M. Magee	Exxon Research Engineering Co.	Production method for nitrophosphate fertilizer
US4399110 also published under DE3021839A1, EP0041758A1, EP0041758B1	June 11, 1981	August 16, 1983	Hans-Friedrich Kurandt	Chemical works Hüls Aktiengesellschaft	Process to reduce the radioactivity of calcium sulphate, which was processed from phosphate rock
US4952379	September 28, 1988	August 28, 1990	Johnny Nikolaisen	Norsk Hydro AS	Method of purifying molten / dissolved calcium nitrate, which is separated from the mixture by a solution of phosphate rock with citric acid
US6562308 also published under CA2428843A1, CA2428843C, WO2002040426A2, WO2002040426A3	November 15, 2000	May 13, 2003	Leslie L. Carstens and Nick P. Wynnyk	Agrium , Inc.	Process for the extraction of phosphate from phosphate rock

literature

• J. Steen; H. Aasum; T. Heggeboe: Chapter 15 The Norsk Hydro Nitrophosphate Processin . In: FT Nielsson (Ed.): Manual of fertilizer processing . CRC Press , 1986 ISBN 0-8247-7522-8 , pp. 393-420.

Individual evidence

1. ↑ Patent US1856187 : Process of producing calcium nitrate and ammonium salts from phosphate rock and like phosphate material. Published on May 3, 1932 , inventor: Erling Johnson ( original patent application with detailed process description and the 15 other patents referring to it , accessed on May 24, 2015). ‌
2. ↑ Patent US 2683075: Digestion of phosphate rock . Published July 6, 1953, inventor: Paul Caldwell.
3. ↑ ^{a b} Patent US 2803531: Process for the production of monoammonium phosphate and other products from raw phosphate . Published August 20, 1957.
4. ^ DW Bixby and GR Burns: Sulphuric or Nitric-Based Phosphates-an Economic and Agronomic Evaluation . In: Proceedings of the 17th annual meeting (Fertilizer Industry Round Table). 1967, pp. 53–57, accessed May 24, 2015.