Haber-Bosch Process

16.10.2024

Haber-Bosch Process

Why in the news?                                                                                                                                                                                                                                     

A hundred million tonnes of nitrogen are now removed from the atmosphere and converted into fertilizer via the Haber-Bosch process, adding 165 million tonnes of reactive nitrogen to the soil.

What is the nitrogen molecule?

• Nearly eight metric tonnes of nitrogen lie on every square metre of the earth’s surface, yet it can’t feed a single blade of grass. Nitrogen in the air is mostly in the form of N2. When two nitrogen atoms join together, they share three pairs of electrons to form a triple bond, rendering the molecule nearly unbreakable.
• The energy required to break the nitrogen triple bond is so high that molecular nitrogen is nearly inert. But if the bond is broken, atomic nitrogen can form ionic nitrides such as ammonia (NH3), ammonium (NH4+), or nitrates (NO3–). Plants need these types of nitrogen, called reactive nitrogen, to synthesize enzymes, proteins, and amino acids.

How is nitrogen availed in nature?

• Among natural things, only lightning has enough energy to destroy the N2 triple bond. In a lightning bolt, nitrogen in the air combines with oxygen to generate nitrogen oxides such as NO and NO2. They can then combine with water vapour to create nitric and nitrous acids (HNO3 and HNO2, respectively). Reactive nitrogen-rich droplets fertilize soil when it rains.
• Apart from lightning, a gentle metabolic process carried out by Azotobacter bacteria can also create reactive nitrogen. Some microorganisms such as Rhizobia have developed symbiotic relationships with legume plants (clover, peas, beans, alfalfa, and acacia) to provide reactive nitrogen in exchange for nutrition.

What is the nitrogen cycle?

• Plants usually get their reactive nitrogen from the soil, where they absorb minerals dissolved in water such as ammonium (NH4+) and nitrate (NO3-).
• Humans and animals need nine pre-made nitrogen-rich amino acids from plants. The nitrogen ingested by plants and animals returns to the soil through excreta and the decomposition of dead bodies. But the cycle is incomplete: some nitrogen is released back into the environment in molecular form.
• Although legumes can produce nitrogen independently, important food crops draw nitrogen from the soil. As the human population multiplies, nitrogen in agricultural soil depletes faster, needing fertilizers to compensate.

How is ammonia made?

• Ammonia (NH3) is made of nitrogen and hydrogen, both of which exist naturally as two-atom molecules. Under extreme heat, the molecules separate and form a compound, but it is short-lived because of the heat. The reversible reaction N2 + 3H2 = 2NH3 (the ‘=’ sign has been used here as a stand-in for bidirectional arrows) must be maintained in specific conditions to harvest considerable amounts of ammonia.
• The German chemist Fritz Haber heated the N2-H2 combination to various temperatures and calculated the amount of ammonia created. At 1,000 degrees Celsius, Haber found that harvestable ammonia made up just one-hundredth of 1% of the mixture.
• Then Haber wondered if pressure could be the answer. He calculated that hydrogen and nitrogen would only remain united in extreme conditions: temperatures of 200 degrees Celsius and pressures of 200 atm (that is, 200-times the average air pressure at sea level). But the ammonia production rate was still too slow, so Haber wanted a catalyst. He also realized that if he could cool the ammonia to a liquid state, he could collect most of it.

What is the Haber-Bosch process?

• Robert Le Rossignol joined Haber’s lab, solving the engineering challenge of maintaining high pressure in the reaction chamber, while mechanic Friedrich Kirchenbauer built the necessary equipment. Haber acknowledged both in his Nobel Prize speech, sharing patents and prize money with them.
• The heated hydrogen and nitrogen combination would circulate in a steel chamber at a pressure of 200 atm. The chamber had a valve that could withstand the high pressure while allowing the N2-H2 mixture to pass through. Haber also built a contraption to ensure the hot gasses departing from the reaction chamber passed their heat to the cooler incoming gasses. Thus the departing combination would rapidly cool while the ingested gas would be heated, achieving two objectives at once.
• Haber soon began testing catalysts. One was osmium, a rare and dense metal found in trace levels on the earth. When Haber inserted an osmium sheet into the chamber, filled it with a N2-H2 mixture, and heated them, the nitrogen triple bond cracked away, leaving reactive nitrogen to fuse with hydrogen and produce a large amount of ammonia.
• Haber tested uranium which worked well, too. However both osmium and uranium were very expensive. When Badische Anilin- und Soda-Fabrik (BASF), a German company, decided to upscale Haber’s experiment to a factory-scale operation, it st out to find a readily available catalyst and found that certain iron oxides were good catalysts. Finally, some brilliant engineering by BASF’s Carl Bosch turned Haber’s tabletop setup into an industrial process to produce fertilizer.

                                                                 Source: The Hindu

What is the primary product of the Haber-Bosch process?

A.Sulphuric Acid

B.Ammonia

C.Methane

D.Hydrogen peroxide

Answer B