Discovering Fertilisers

By: H L S Tandon
A series of post 1800 inventions of some key processes and materials led to suitable catalysts that revolutionised agriculture and paved the foundations of a fertiliser industry in Germany, Norway, UK and North America.

The Starting Point: The first known mineral fertiliser was sodium nitrate (16 per cent nitrogen ), also known as Chilean nitrate, considered to be the only natural source of nitrogen. Although its deposits were found in several countries, the source of real commercial significance was found in north Chile – hence its name.

Birth of the Phosphates: Crushed bones were one of the first P-rich materials. Justus von Liebig of Germany treated powdered bones with sulphuric acid and found them to be more effective than untreated bones leading to the creation of super phosphate. Historically, there were four main players in the development of phosphate fertilisers—Liebig of Germany, Lawes and Henslow of UK and Murray of Ireland. John Bennet Lawes was perhaps the first person to manufacture single super phosphate (SSP) profitably and won a patent for it in 1842. However, Sir James Murray was the first to produce the fertiliser in 1808, years ahead of Lawes. Murray’s process was based on the acidulation of phosphorite (a rock consisting chiefly of calcium phosphate) with sulphuric acid. Later, Lawes purchased Murray’s patent to get any competition out of the way and amended it. Lawes’s first product consisted of solid and insoluble phosphates derived from coprolites or guano mixed with animal remains. It resembled a product which was best described as soluble bones.

First Organic Compound Synthesised: Urea was the first organic compound to be synthesised from inorganic materials and was separated from urine by Hilaire-Marin Rouelle in 1773. In 1782, Prout separated pure crystalline urea and was synthesised by Friedrich Wohler of Germany in 1828 by heating ammonium cyanate. However, commercial production of urea had to wait until 1922 when large scale synthesis of ammonia was made possible by Fritz Haber and Carl Bosch in 1910. The I G Farbenindustrie in Germany was the first company to synthesise urea commercially from ammonium carbamate in 1920. In 1922, large scale production of urea by the BASF process started. Urea today dominates fertilisers world over. The first urea plant in India was set up in 1959 at Sindri (now Jharkhand).

Anhydrous Ammonia: Synthesised ammonia in anhydrous form (82 per cent nitrogen) became the major intermediate for the production of a variety of solid and liquid fertilisers and emerged as an important nitrogen fertiliser. Anhydrous ammonia was first applied directly in the field on a commercial scale in the United States during 1943-44.

Ammonium Sulphate: It is the first nitrogenous fertiliser to be produced as a byproduct of coal gas in 1815 in England and later from coke-oven battery gas. The fertiliser was first produced in India in 1933 at Jamshedpur (Jharkhand) as a by product of the steel industry and later using sulphuric acid in 1941 at Belagula (Karnataka), using gypsum in 1947 at Ugyogamandal (Kerala) and as a by product of the polymer (caprolactum) industry in 1974 at Vadodara (Gujarat).

Ammonium Nitrate and Calcium Ammonium Nitrate: The production of ammonium nitrate started in Europe after the commercial production of ammonia was made possible. A potential explosive, its first use as a fertiliser was in Europe after World War I when the war surplus material was released for other uses. Later on, to eliminate any possibilities of hazard due to its explosion when in contact with organic materials or other unfavourable conditions, it was diluted with limestone to produce calcium ammonium nitrate (CAN). In India, the production of
CAN started in 1961 at Nangal, Punjab using electrolysis of water to produce hydrogen for ammonia synthesis.

Sulphur and S-based Fertilisers: Marketable elemental sulphur was first produced in 1894 in Sulphur, Louisiana, USA. The most important process for mining of sulphur was the hot water process invented by Herman Frasch. At present, considerable tonnage of sulphur is being recovered from oil and gas deposits. Apart from use as a raw material for the production of sulphuric acid, fertilisers based on elemental sulphur have also been developed and are being marketed in several countries, including India. One such product is sulphur bentonite or bentonite-containing 90 per cent sulphur in elemental form.

Phosphate Rock: Considered a non-renewable natural resource and principal raw material of phosphorus in fertilisers, the first deposits of phosphate rock were discovered in the early 19th century and the first commercial mining started in 1867 in South Carolina, USA. Later, in 1881, the Florida deposits were discovered, followed by Tennessee in 1984. Phosphate rock, a non-renewable natural resource is the principal raw material for the production of phosphatic fertilisers world over. In India, major deposits of phosphate rock were discovered in the 1960s at Jhamarkotra in Rajasthan.

Potassium Fertilisers: Potassium chloride or muriate of potash was the first potash fertiliser to be produced from mined material in Germany. The word muriate is derived from muriatic acid (hydrochloric acid). Potash was mined for the first time in 1856 in Strassfurt, Germany and the country was virtually the only potash producer until 1918. Other potassium fertilisers, such as potassium sulphate, were manufactured later.

Concentrated Fertilisers: The synthesis of phosphoric acid in the USA paved the way for the production of highly concentrated phosphates such as triple superphosphate, diammonium phosphate (DAP) and polyphosphates etc. Wet process phosphoric acid is produced by treating phosphate rock with sulphuric acid. In the process, 5-6 tonnes of by product phospho-gypsum is generated per tonne. Phosphoric acid is used to produce not only triple superphosphate but ammonium phosphates, super phosphoric acid and fluid fertilisers.

Fertilisers with NP and NPK: Superphosphate was first ammoniated with aqua ammonia in the USA in 1926 to produce ammonium phosphate and by 1954 the first large-scale continuous production of DAP based on wet process phosphoric acid began. Modern processes for the production of  monoammonium phosphate and DAP were developed at the Tennessee Valley Authority, USA. These fertilisers are mostly used as intermediates to produce other fertilisers but in India much of the DAP is used for direct application. With production starting in 1967 at Vadodara, Gujarat, DAP today is the dominant source of finished phosphate in India accounting for 63 per cent of total phosphates and also 9.4 per cent of total nitrogen. In India, production of NPK complex started through the nitrophosphate route in 1965. Production of other complexes followed, for example complexes 12-32-16 and 10-26-26 in 1974 at Kandla, Gujarat; 19-19-19, 14-35-14 etc. in 1975 at Zuarinagar, Goa; 17-17-17 in 1976 at Manali, Chennai.

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