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Synthetic Ammonia

Feeding the World

Content

• the role played by nitrogen in the growth of plants

• the search for a synthetic source of nitrogen to meet global population explosion

• Haber’s discovery of ammonia synthesis • scale up by Bosch from the laboratory bench

into full production • modern production of ammonia and its use • the good, the bad and the ugly

Nitrogen Fixing

1. Nitrogen-fixing bacteria turn nitrogen in the soil into nitrate

2. Nitrogen-fixing bacteria on some plant root nodules turn

nitrogen into nitrate. (legumes)

3. Compounds containing ammonia occur in animal excretion

and in dead animals. The ammonia turns into nitrite and there

are nitrifying bacteria in the soil that turn nitrite (NO2) into

nitrate (NO3).

4. Lightning can cause chemical reactions in the atmosphere

that make nitrogen react with oxygen producing nitrous

oxides.

GUANO

New sources of nutrients

Three alternative sources of nitrogen became available:   •the recovery of by-product ammonia from the coking of coal

•the high temperature synthesis of cyanamide (CaCN2) from calcium carbide and nitrogen

•the fixation of atmospheric nitrogen by electrical discharge, through the availability of cheap electricity (hydro sources)  

Fritz Haber

Fritz Haber was a German chemist of Jewish origin who received the Nobel Prize in Chemistry in 1918 for his development of the Haber process.

Born: December 9, 1868, Wrocław, Poland Died: January 29, 1934, Basel, Switzerland

Ammonia Reaction

Le Châtelier's Principle : When a system at equilibrium is subjected to change, in concentration, temperature, volume, or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established.

This principle is used to manipulate the outcomes of reversible reactions, often to increase the yield of reactions.

From the law of equilibrium it follows that the higher the pressure, the more the equilibrium must shift to the ammonia side.

Earlier experiments had also shown the pointlessness of exceeding dark red heat, i.e. about 600° C.

It was found that a temperature of about 500° C had to be used at the highest possible pressure, which in practice meant at about 150-200 atmospheres.

Haber’s apparatus

Carl BoschCarl Bosch (27 August 1874 – 26 April 1940) was a German chemist and engineer and Nobel laureate in chemistry. He was a pioneer in the field of high-pressure industrial chemistry and founder of IG Farben, at one point the world's largest chemical company.

Bosch’s Three Tasks

Supply of raw materials, i.e. of the gases hydrogen and nitrogen, at a purity and lower price than hitherto possible

Manufacture of effective and stable catalysts

Construction of the production plant that has to operate at high pressures and temperatures

Scale-up – Hydrogen

water gas produced by the reaction of glowing coke with water vapour. C + H2O ⇔ H2 + CO

Then further Hydrogen by reacting CO with steam over catalyst to give CO2 and H2

Scale-up – Catalyst

The original Haber–Bosch reaction chambers used osmium as the catalyst. Haber noted uranium was superior but harder to obtain.

Under Bosch's direction in 1909, the BASF researcher Alwin Mittasch discovered and prepared much less expensive iron-based catalyst; this is still used today.

Subsequent tests showed that the activity of the catalyst may be increased by oxides or certain salts of alkalis and alkaline earth metals, (K2O, CaO, SiO2, and Al2O3.) which in turn can reduce substantially the pressure in the chamber.

Scale-up – Production Process

Limiting corrosion

Achieving yield and energy efficiency

Operating under high pressure

Controlling the process

Challenges

Scale-up – Production Plant Corrosive hydrogen

At high pressure and quite high temperature, carbon steel is invariably corroded by hydrogen. The long sought solution consisted in fitting a pressure bearing steel jacket internally with a quite thin lining of soft steel in such a way that as the hydrogen, which of course only diffuses, passes through the thin lining it is able to escape without building up pressure before it can attack the outer steel jacket at the high temperature.

Scale-up – Production Plant

Achieving yield and energy efficiency

Multiple pass; each pass yields about 15%; circulation and further processing of unreacted gases gives accumulated yield of 97%

With large scale plant, together with good heat exchange, heat losses offset by heat of reaction

Scale-up – Production Plant High Pressures

Scale-up – Production Plant Instruments for control

Gas density recorder

One of the key requirements of the ammonia synthesis plant was to run it continuously, as every stoppage at a single point affects the entire plant. Also, the need to continuously monitor process conditions

Detection of traces of oxygen

A historical (1921) high-pressure steel reactor for production of ammonia via the Haber process is displayed at the Karlsruhe Institute of Technology, Germany

Oppau site after explosion 1921

The Leuna site near Merseburg around 1920

Modern ammonia production plant

New source of Gas feed Centrifugal compressors

Ammonia Synthesis Centrifugal Compressor

Modern Ammonia Process – Flow Diagram

Ammonia – Historical Production Trends

Good!

Feeding the World

“Without ammonia based fertilisers, it would not have been possible to support the unprecedented numbers of people with diets whose adequacy is unmatched in history.”

The development of high pressure technologies, plant and equipment, which later enabled amongst others the first production of polyethylene by ICI, and the Fischer- Tropsch process for the manufacture of petrol by the gasification of coal

The design and development of many instruments for the control of gas and gas/liquid processes

The first design and operation of a continuous, as distinct from, a batch process operation.

Improving process technology

Good!

Bad

The production of synthetic ammonia by Germany enabled it to sustain its war machine and to prolong the First World War.

Ammonia nitrate use in armaments

Fertilizers as a source of ground and river pollution

Bad

BadEnergy demands

Ammonia plants and their associated fertiliser plants are located near cheap sources of energy.

Hydrogen gas by electrolysis of water

Bio energy from organic wastes (such as biomass or food-industry waste), using catalytic (thermal) reforming

Need for renewable sources:

The Ugly

Haber’s role in gas warfare

The Ugly

The Victims

Clara Immerwahr (June 21, 1870 – May 2, 1915) was a German chemist. She was the first woman to be awarded a doctorate in chemistry in Germany. She was also an active women's rights activist.[

Haber’s Nobel Prize Certificate

Carl Bosch Receiving Nobel Prize in 1931