36 | Science Reporter | November 2020

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The Incredible Journey of Nitrates and AmmoniaD.K. Srivastava & V.S. Ramamurthy

IT was on the evening of 4 August 2020, that Beirut, the capital city of Lebanon, witnessed one of the largest industrial

accidents amid the COVID-19 pandemic and an economic crisis. A powerful explosion sent a huge orange fireball into the sky, followed by a massive shock wave that overturned cars, damaged buildings, and shook the ground across the city killing at least 220 people, injuring more than 5000 and leaving an estimated 300,000 people homeless.

The explosion was caused by 2750 tons of ammonium nitrate, a chemical compound commonly used as an agricultural fertiliser, which had been stored at the port warehouse for six years. Serious industrial disasters caused by ammonium nitrate were not uncommon in the past. Explosions due to tons of ammonium nitrate on ships and in storage facilities have caused hundreds of fatalities apart from damage to structures, vehicles and even planes flying overhead.

It is therefore not surprising that the news of about 740 tons of ammonium nitrate being stored in a container about 20 kilometres away from the city of Chennai evoked such a panic amongst the public that the authorities had to complete the process of disposal in a very short time and start moving the chemical away from there.

Because of its easy availability, ammonium nitrate has also been used often by terrorists.

Ammonium Nitrate – Grandfather of ExplosivesFor centuries India was the biggest producer and exporter of potassium nitrate or saltpetre or “shora”. With charcoal and Sulphur, it produces an explosive mixture, which we now call gunpowder. Explosives were repeatedly mentioned by Kautilya in his Arthashastra, as “agniyogas” and “agnisamyogas” (https://csboa.com/eBooks/Arthashastra_of_Chanakya_-_English.pdf). Some historians also suggest that Vaishampayan’s Nitiprakashika compiled in 800 BC and Shukraniti attributed to Shukracharya compiled perhaps earlier have mentions of explosives made using saltpetre, coal, and Sulphur.

Aftermath of the Beirut explosion (commons.wikimedia.org)

Saltpetre

Roger Pauly, writing in “Firearms: The Life History of a Technology” suggests that, “While gunpowder was primarily a Chinese innovation, it may have received some Indian inspiration. Just as China embraced Indian Buddhism, the subcontinent’s fascination with fire may have crossed the Himalayas. In 664 AD an Indian visitor to China reportedly demonstrated the peculiar flammability of saltpetre and provided instructions on how to locate it.” Arnold Pacey (Technology in World Civilization: A Thousand-year History) adds, “Later Chinese studies of the chemistry of saltpetre show other evidence of Indian influence which seems to have been the starting point for the Chinese investigations which led to the first recipes for gunpowder.”

The recent devastating explosion in Beirut was caused by 2750 tons of ammonium nitrate, a chemical compound commonly used as an agricultural fertiliser, but also known as

the grandfather of explosives.

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started using it for the subjugation of natives, extraction of gold, capture of territories and slaves, and piracy on the high seas; all of which led to their ascent. Saltpetre was one of the most important chemicals exploited by the Europeans in their initial trading days in India.

The Dutch East India Company is believed to have taken between 3,000,000 to 3,500,000 Dutch lbs. per year for Holland alone, during the first two decades of the eighteenth century (Susil Chaudhuri, Proceedings of the Indian History Congress, 1973, Vol. 34, 1973). In the year before the battle of Waterloo (1815) the East India Company exported 7300 tons of saltpetre to England (Robert Montgomery Martin, Statistics of the Colonies of British Empire). The British victory at Waterloo was facilitated by the use of Indian saltpetre which was far superior to the charcoal-like French product. During the American Civil War (1861-1865), Great Britain provided saltpetre from India to the two warring factions.

Around this time, Hyder Ali and his son Tipu Sultan started making very accurate and powerful rockets. Their main contribution was to fill the gunpowder in iron pipes and tie these pipes to long bamboo sticks, to guide them. During the Second Anglo-Mysore War (1861), Hyder Ali’s rockets had destroyed Colonel William Baillie’s ammunition stores, which contributed to a humiliating British defeat. Tipu Sultan greatly improved his rockets and deployed it extensively and very effectively.

It is generally believed that the Chinese started using gunpowder to make fireworks for display by 700 AD and the Mongols may have learned its use from them. The first confirmed reference to what can be considered gunpowder in China occurred in the 9th century AD, first in a formula contained in the “Taishang Shengzu Jindan Mijue” in 808, and then about 50 years later in a Taoist text known as the “Zhenyuan miaodao yaolüe”.

Rana Hammirdeva of Ranthambore used gunpowder against the army of Alauddin Khiliji in early 1300 AD; there are indications that some Mongol deserters from the latter’s army may have brought this technology with them. There are reports of extensive fireworks in Vijayanagaram in 1443 during the reign of Devaraya II during Mahanavami festival in 1443, which may have used gunpowder. There is strong evidence to suggest that Chutia kings of Assam, used hand cannons (hiloi) as well as canons (bortop) against the invading Ahoms in 1524 AD. Later, Ahoms used it against Turbak Khan, the commander of Gaur in 1532 AD.

One of the guns which the Ahoms procured after defeating the Chutias in 1524 AD (Wikipedia)

Painting of Mysore Rocket Man by Robert Home (Wikipedia)

A painting by Charles H. Hubbell showing the Mysorean army fighting the British forces with Mysorean rockets (Wikipedia, NASA)

Why Bihar produced good quality saltpetre in such vast quantities? Ashutosh K. Jha (Production of Saltpetre in Medieval India) writes that in this region, “… agriculture

The First Battle of Panipat, on 21 April 1526, was fought between the invading forces of Babur and the Lodi dynasty. The battle is known for the use of gunpowder firearms and field artillery. It is generally believed that Babur got this knowledge from Turks, who may have learnt the use of gunpowder from Mongols, who in turn had learnt it from Chinese.

It has been reported by Nathan (Baharistan-I- Ghaybi, M.I. Borah (tr.), Vol. I) that when Raja Pratapaditya of Jessore surrendered to Islam Khan in 1609, he agreed to provide 41 tons of gunpowder in addition to twenty thousand infantry and five hundred war-boats. About 50 years later, when Mir Jumla invaded Assam in 1662-1663 AD, he left with 675 big guns and 190 tons of gunpowder in boxes because they were of much better quality than what he was using.

One of the reasons for the defeat of Nawab Sirajuddaula at Battle of Plassey in 1757 was that his gunpowder became wet due to heavy rain during the battle, while Robert Clive used tarpaulin to cover his gunpowder and “kept it dry”. This victory gave the English East India Company a monopoly over the vast sources of saltpetre in Bihar. It is truly said that “gunpowder and the cannon blew up the medieval world economically and politically”.

Saltpetre from India on the World StageEarlier, European powers, which had made considerable technological development in the use of gunpowder, had

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is the chief occupation and there is consequently a high proportion of domestic animals. Thus, the soil around the villages has an abundant supply of organic nitrogen. The climatic conditions of temperature and humidity are also unusually favourable for the growth of so-called nitrifying bacteria, which convert ammonia by successive stages into nitrous and nitric acid. Wood and cow dung are largely used for fuel, and the immediate vicinity of each village thus forms a perfect laboratory for the formation of Potassium Nitrate. In the long period of continuous surface desiccation which follows a small monsoon rainfall, the compound so formed in the soil is brought to the surface by capillary action and appears as an efflorescence of salt which is collected and purified.”

By mid-nineteenth century nitrate from Atacama Desert of Peru was available and India’s monopoly of saltpetre was challenged. The nitrates also used to be obtained from the walls of caves where the salts were brought to the surface by moisture or from droppings of some seabirds or bats. The development of smokeless explosives like cordite and later TNT reduced the use of saltpetre for making the black gunpowder.

Haber-Bosch ProcessBy the time of the First World War, Fritz Haber along with Carl Bosch had developed a process for industrial production of ammonia, using what is now called Haber-Bosch process, which can easily be converted to nitrates for making fertilizers as well as explosives and thus, the obstruction of the ships bringing nitrates to Germany from Peru had only a limited effect on them.

The Haber-Bosch process revolutionized the availability of fertilizers and increased the production of food grains considerably. It is known that the supply of reactive nitrogen is essential for all life forms. Thus, increases in nitrogen supply have been exploited in agriculture to increase the yield of crops and provide food for the growing global human population. It has been estimated that almost half of the human population at the beginning of the twenty-first century depends on fertilizer nitrogen for their food (J. Erisman, M. Sutton, J. Galloway, et al., How a century of ammonia synthesis changed the world, Nature Geosci. 1, 636–639, 2008). Fritz Haber won the Nobel Prize in Chemistry for this in 1918, though this decision created some controversies as it came soon after the First World War.

The story of Fritz Haber will not be complete unless we recall his role in the production of poisonous gases for use in warfare during the First World War. The chemists of France and Great Britain also lent their support to the production of poisonous gases. It is estimated that up to one million soldiers succumbed to these attacks. When the wife of Fritz Haber, Clara Immerwahr Haber, the first PhD in chemistry from Germany, came to know of the first batch of 6000 soldiers killed by the gases made by her husband in an attack supervised by him, she committed suicide. Haber is also credited with the comment, “During peace, scientist belongs to the world, during the war he belongs to his country”, to justify his role in the production of poison gases.

The world produced more than 170 million tons of ammonia in 2019. Ammonia is used for the production of fertilizers like ammonium sulfate, ammonium phosphate, ammonium nitrate and urea. It is also used for the synthesis of nitric acid, which in turn is used in making explosives such as TNT, nitroglycerine used as a vasodilator (a substance that dilates blood vessels) and PETN (pentaerythritol nitrate), sodium bicarbonate, sodium carbonate, hydrogen cyanide, and hydrazine (used in rocket propulsion systems).

It is also used for making fibres like nylons and plastics, used in large scale refrigeration plants and air-conditioning units, and for making ice. Ammonia is an important input for the pharmaceutical industry, pulp and paper industry, mining, and metallurgy, etc. Ammonium nitrate is also used as an oxidizer in rocket propellants and a nutrient for yeast and antibiotics.

Green Revolution and its AftermathNitrogen has always been the most abundant gas in the atmosphere since life was established on the planet Earth. However, nitrogen atoms form a diatomic bond with each other, and the atoms cannot be taken up by organisms. The rate of conversion of atmospheric nitrogen to organic nitrogen is controlled by the enzyme nitrogenase. This enzyme is present in very few bacteria that live mostly associated with the roots of certain plants of legumes. For centuries, farmers across the world have been rotating crops like wheat with such crops of legumes, to take advantage of this process.

Thus, in the biological nitrogen fixation, the largely un-reactive molecular nitrogen is reduced to ammonium compounds. The fixed nitrogen is subsequently transformed into a wide range of amino acids and oxidized compounds by micro-organisms and finally returned to the atmosphere as molecular nitrogen through microbial denitrification in soils, fresh and marine waters, and sediments.

Ammonium nitrate, when applied to crops as a fertilizer, provides half of its nitrogen in the nitrate form and other half in the ammonium form. The nitrate form moves readily with soil water to the roots, where it is immediately available for plant uptake. The ammonium fraction is taken up by roots or gradually converted to nitrate by soil microorganisms.

However, the excessive use of fertilizers is not without problems. The main problem is that a lot of that fertilizer is wasted — more is applied than plants can absorb — and it washes out of the soil into waterbodies, or evaporates into the atmosphere in the form of nitrous oxide, a potent greenhouse gas as well as a major ozone-depleting agent. Other risks include threats to human health through nitrate pollution in drinking water, to fish and other wildlife through fertilizer run-off causing low oxygen “dead zones” due to algal blooms.

Repeated use of ammonium nitrate can increase the acidity of the soil, even though it causes less increase in acidity as compared to ammonium sulphate, another popular fertilizer. Urea is another fertilizer derived from ammonia. On being used, urea first reacts with water and is converted to ammonium bicarbonate. If the soil has high pH, ammonium bicarbonate can be further converted to ammonia gas, which leads to a significant loss of nitrogen. However, compared

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to ammonium nitrate and ammonium sulfate, urea produces less acidity and typically does not affect soil pH significantly.

The use of fertilizers also requires sufficient irrigation. Farmers across India and elsewhere have met this increasing demand of water by using deep bore-wells, which has greatly lowered the water tables. These require to be recharged, urgently, by rainwater harvesting and construction of check dams. Drip irrigation could help in preserving water but requires a large investment.

Let us also recall that most of the hydrogen (95%) necessary for the production of ammonia is produced from fossil fuels by steam reforming of natural gas, partial oxidation of methane, and gasification of coal. Each of these emits copious amounts of carbon dioxide which further exacerbates the climate change. We get 5 kg to 16 kg of carbon dioxide for every kg of hydrogen, depending on whether we use methane or coal.

Green Hydrogen and Green Ammonia Immediate deployment of renewable and green energy is considered as the only solution to meet the challenge of keeping the rise in global temperature to less than 2 degree Celsius compared to pre-industrial revolution values and to reduce the net emission of carbon dioxide to zero by 2050. However, we also know that renewable energy sources have strong variability due to the day/night and seasonal variations. There are also likely to be phases when the production of power is much more than what we may need.

There have been suggestions of batteries (too expensive and not enough capacity yet) and pumped-up hydroelectric plants (not enough suitable sites with uniform distribution). An entirely different approach which has been suggested involves using electrolysis of water to produce hydrogen and oxygen. This hydrogen can be used in internal combustion engines or fuel cells to run motor vehicles, trains, buses, cars, planes, and ships. The hydrogen can also be transported using pipes or compressed or liquified and taken to wherever it is needed. This, of course, is a green source of energy and the hydrogen thus produced is called “Green Hydrogen”, for obvious reasons.

It has also been suggested that the hydrogen can be converted to ammonia, which is easier to transport, as it is very easy to liquify. If one needs hydrogen at the destination, it can be recovered by cracking. This ammonia will also remain “Green” as no carbon dioxide emission is expected at any stage.

While studying the electrolysis of water in 1809, Humphrey Davy had reported observation of a small amount of ammonia along with the hydrogen gas at the cathode. This was due to presence of the nitrogen dissolved in the water which interacted with the nascent hydrogen to make ammonia. There are efforts to make this more efficient by increasing the amount of nitrogen near the cathode to produce ammonia on a commercial scale. This would be “Green Ammonia” and can be used for production of fertilizers which will also be “Green”.

Figure 1 shows the solar energy potential of top ten states of India, which includes the considerations of availability of

Prof. D.K. Srivastava (srivastava.dinesh.kumar@gmail.com) is presently Homi Bhabha Chair Professor at National Institute of Advanced Studies, Bengaluru. A Fellow of the National Academy of Sciences, India and Indian National Science Academy, he retired as Director and Distinguished Scientist at the Variable Energy Cyclotron Center, Kolkata.

Prof. V.S. Ramamurthy (vsramamurthy@gmail.com) is a well-known Indian nuclear scientist. He has been Director, Institute of Physics, Bhubaneswar and also Secretary, Department of Science & Technology (DST), Government of India. Prof. Ramamurthy was awarded the Padma Bhushan by the Government of India in 2005.

land etc., estimated by National Institute of Solar Energy, Ministry of New and Renewable Energy of the Government of India. This energy can be harvested to provide us either Green Hydrogen or Green Ammonia to meet our needs of clean energy as well as ammonia for production of Green Fertilizers.

To illustrate this potential, we just look at two regions, Rajasthan and Ladakh. Their combined solar energy potential is 250 GWs. Considering eight hours of sunshine, this would mean about 2000 GWh of electricity every day. The electricity needed to produce one kilogram of nitrogen from hydrolysis of water, after taking the efficiency of electrolyzers into account is about 50 kWh. This would then translate to a production of 40,000 tons of hydrogen per day.

If the process of ammonia formation in the electrolyzer cells can be realized, it will translate to 225,000 tons of ammonia per day. This would amount to more than 80 million tons per year of ammonia. This can be compared to the current production of 20 million tons of ammonia per year in the country in a very energy and carbon-intensive Haber-Bosch process. Thus, two vast deserts of the country can provide a vast resource of Green Electricity, or Green Hydrogen, or Green Ammonia and contribute to the prosperity of the country.

Nitrates and ammonia have played a very fascinating role for humankind during wars and peace. We suggest using the abundant sunshine to produce not only Green Electricity, but also abundant supply of Green Hydrogen, Green Ammonia, and Green Fertilizers, without harming our climate or leading to global warming.

Fig. 1: Solar energy potential of top ten states of India

RAJA

STHA

N

LADA

KHM

AHAR

ASTR

AM

ADHY

A PR

ADES

HAN

DHRA

PRA

DESH

GUJAR

ATHI

MAC

HAL P

RADE

SH

ODISH

AKA

RNAT

AKA

UTTA

R PR

ADES

H

4.84

0.02 1.8

2.3

3.6

2.95

0.03

0.4 7.

27

1.09

111.

04

64.3

4

61.6

6

38.4

4

35.7

7

33.8

4

25.7

8

24.7

22.8

3

SOLAR ENERGY POTENTIAL IN GWP OF TOP 10 STATES

Installed Potential

142.

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