haber process report

The Haber-Bosch Process was developed by Fritz Haber and Karl Bosch in Germany in the early 20th Century. The two chemists discovered the ideal conditions for high yield of ammonia. By 1913 a plant had been built in Germany which utilised this process to produce vast quantities of ammonia.

This process was incredibly useful to the Germans after the outbreak of World War I in 1914. British ships effectively cut off Germany’s supply of mined nitrates. Thanks to the Haber process and the Ostwald process, they could make ammonium nitrate, a powerful explosive, from air, water and coal.

Now the Haber Process is used all over the world to produce ammonia. The technology is owned and the equipment manufactured jointly by Haldor-Topsoe, a Danish catalyst company, and KBR a United States based engineering firm. The production of ammonia now has a 10 – 20% yield and has an energy consumption of 40% less than the early production.

Introduction

Stage 1: Sweetening

The natural gas is processed to remove the sulfur contaminants which can poison the catalysts utilised in later stages. It is removed by reacting the hydrogen sulphide compounds with zinc oxide granules at 285 – 400 ºC with a pressure of 980 – 4900kPa. This process is called “sweetening” as it removes the pungent hydrogen sulphide.

ZnO(s) + H2S(g) ZnS(s) + H2O(g) ∆H=-ve

OptimisationChange in Enthalpy

Favourable Conditions

Pressure Favourable Conditions

Amount of Each Reactant


-ve; therefore the forward reaction is exothermic

Low temperature conditions favour forward reaction.N.B. The temperature is still 285ºC, this means a higher rate of reaction with a small backwards shift in equilibrium as particles in the system collide with the required kinetic energy.

The high pressure does not favour either direction of reaction

The high pressure maintained just ensures a higher number of collisions of the H2S particles with the ZnO particles, resulting in a faster rate of reaction.

The design of the ZnO has a very large surface area.

Increases rate of reaction as there is more surface area for collisions to take place.

Stages of Ammonia Production

Stage 2: Primary Reforming

In the next stage the processed natural gas (Methane) is reacted with steam. This occurs at temperatures around 700 – 800ºC and at a pressure of between 14000kPa and 17000kPa and uses a nickel catalyst. This process is known as Primary Reforming.

CH4(g) + H2O(g) 3H2(g) + CO(g) ∆H= +206kJ mol-1



Pressure Favourable Conditions



+ve; therefore the forward reaction is endothermic

High temperature conditions favour forward reaction. The higher temperature results in equilibrium shifted forwards and a higher rate of reaction, the temperature is limited only by the cost to produce high temperatures

The high pressure does not favour the forward reaction

The high pressure maintained ensures a higher number of collisions of the H2S particles with the ZnO particles, resulting in a faster rate of reaction.

A large amount of steam is added.

According to Le Chatelier’sPrinciple, the system responds to this change by forming more hydrogen and carbon monoxide to remove the steam.


Stage 3: Secondary Reforming

The processed natural gas continues to react with steam, but air is introduced into the system. This allows the methane to be combusted. This reaction removes the oxygen from the air, leaving nitrogen for the Haber process stage and increases the temperature of the system to around 1250 ºC for later stages. This process is known as Secondary Reforming.

CH4(g) + 2O2 (g) 2H2O(l) + CO2 (g) ∆H= -891kJ mol-1


Stage 4: Water Gas Shift

The carbon monoxide still left in the system is converted to carbon dioxide through a Water Gas Shift (WGS) reaction, developed in Italy by Felice Fontana in 1780. The carbon monoxide is reacted with steam in the presence of an Iron and Chromium catalyst to produce carbon dioxide, which is removed from the system through the use of a suitable base, and hydrogen gas, which is used in later stages. This process is traditionally done first at high temperature, then low temperature. However, the low temperature reaction is sometimes omitted for economical reasons.

CO(g) + H2O(g) CO2 (g) + H2 (g) ∆H= -41.1kJ mol-1



Pressure





The initial high temperature gas shift results in a high reaction rate, but with a low yield of CO2 and H2. This quickly removes the bulk of the carbon monoxide. Then the low temperature gas shift favours the forward

The high pressure does not favour either the forward or reverse reactions.

The high pressure just ensures a faster rate of reaction as there is a greater likelihood of collisions occurring.

CO2 is removed from the system.

According to Le Chatelier’sPrinciple, system will try and produce more CO2 in response to this change.


reaction but occurs at a relatively lower rate of reaction. This removes the majority of the remaining CO.

Stage 5: Methanation

Any remaining carbon monoxide is converted to methane in a process known as Methanation, a reversible reaction discovered by Sabatier and Senderens in France in 1902. This maximises the efficiency of the plant by reducing wastage, as the methane is used in stage two and three. This occurs at around 190ºC over a nickel-based catalyst.

CO(g) + 3H2 (g) CH4 (g) + H2O(g) ∆H= -206.4kJ mol-1



Pressure





The temperature is relatively low, therefore favouring the forward reaction. But it is not too low as the particles still require enough kinetic energy for collisions, otherwise the rate of reaction would be too slow.

The reaction is conducted at a similar pressure to the other stages.

The high pressure favours the forward reaction as there are more mols of reactants than products. Also results in a faster rate of reaction as the particles have a greater likelihood of colliding

CH4 is removed from the system.

According to Le Chatelier’sPrinciple, this shifts the equilibrium forwards; as the system will form more CH4 to try and regain equilibrium


Stage 6: The Haber Process

In this stage the nitrogen gas and hydrogen gas in the system are reacted to produce ammonia. It takes place inside a sealed system at pressures between 14000 – 17000 kPa and temperatures of 340 – 450˚C. The mixture passes over the catalyst beds towards the end of the reaction chamber where the temperature drops to almost 10˚C. The ammonia condenses, allowing it to be collected as a liquid and then stored.

The process takes place inside a long enclosed cylinder which looks similar to the LNG tanks at petrol stations except with multiple pipes connecting to it. The parts must be made of a metal such as steel to prevent corrosion. The casing must also be incredibly strong to withstand the pressures created within

the manufacturing chamber.

Production of Ammonia

Reactants from previous stages

Catalyst beds

Liquid Ammonia

Unused nitrogen and hydrogen gas

N2 (g) + 3H2 (g) 2NH3 (g) ΔH = -92.4kJ mol-1

As in other stages, this stage utilises a catalyst to increase the rate of attainment of equilibrium. How it achieves this is by

providing an alternative reaction pathway which lowers the activation energy. The collision theory requires molecules to collide with the correct alignment; the catalyst ensures that more of the molecules in the system are at that correct alignment. This means that the molecule’s energy is more focused and less energy is wasted on poorly aligned molecules. This can be seen in an enthalpy

diagram on the left:

So in the Haber reaction, a catalyst made of predominantly magnetite (iron oxide Fe3O4) with promoters such as aluminium oxide, silicon dioxide, calcium oxide, potassium oxide, makes the reaction proceed at a faster rate. In some more expensive systems a ruthenium catalyst is used, but this is a less economical option.

Ea

Progression of Reaction

En

thalp

y

Catalysed reaction

Uncatalysed reaction


OptimisationChange

in Enthalp

y


Pressure


Amount of Each Reactan

t

Favourable

Conditions


The reaction is conducted at 350-450˚C

The temperature is relatively low, therefore favouring the forward reaction, producing a greater concentration of ammonia. But it is still at a high enough level that the majority of the particles have a high enough kinetic energy to react when they collide. This, according to collision theory, results in a faster rate of reaction.Essentially the manufacturer decides that a small yield of ammonia, but at a fast rate is better than a large yield, at a slow rate. Also raising the temperature increases costs too as the chamber has to be made more heat resistant

Conducted at a pressure of 14000-17000kPa

The high pressure favours the forward reaction, resulting in a greater concentration of NH3. This also results in a faster rate of reaction as, according to collision theory, the particles have a greater likelihood of colliding and thereby reacting. The pressure is not incredibly high as there is a large cost involved with high pressures. The strong chamber in which the reaction takes place would have to be reinforced.

NH3 is removed from the system.

According to Le Chatelier’sPrinciple, system will respond to this change by shifting equilibrium forwards as the system will make more NH3 to regain equilibrium.


and burners have to be put in place.

In agriculture ammonia is used in the formation of ammonium sulfate/nitrate for use in fertilisers. It also is used as a cotton defoliant, an antifungal agent, and a preservative.

Ammonia is used two metal strengthening treatments called Gas Nitriding and Carbonnitriding. When the ammonia gas comes into contact with the strongly heated metal, it dissociates into hydrogen and nitrogen. The nitrogen enters the metal, granting it a stronger surface.

Ammonia is used in the petroleum industry in the form of ammonia solution to neutralise hydrogen sulphide in order to conduct drill stem and wireline tests.

In the mining industry ammonia is used for the extraction of metals such as copper, nickel and molybdenum from ores

It is used in water treatment as a pH modifier and as a simple household cleaning product.

Ammonia was used as a refrigerant mainly in commercial industries as it was deemed unsafe for domestic use, but it is now being used more frequently domestically due to the discovery of the damaging effects of chloroflourocarbons on the ozone layer.

Ammonia is also used in the manufacture of chemicals such as:

Nitric Acid in the first step of the Ostwald Process4NH3 (g) + 5O2 (g) 4NO (g) + 6 H2O (g) ΔH = −905.2 kJ

Alkalies such as soda ash through the Solvay ProcessNaCl(aq) + CO2 (g) + NH3 (aq) + H2O(l) NaHCO3 (s) + NH4Cl(aq)

Pharmaceuticals such as sulphonamides, vitamins and cosmetics

Synthetic textile fibres such as nylon, rayon, and acrylics

Uses of Ammonia

Plastics, phenolics and polyurethanes

Carbon Dioxide EmissionsCarbon dioxide is a by-product of ammonia production. Due to its status as a greenhouse gas, Ammonia Production Facilities are concerned with minimising the amount which they release into the atmosphere. Some is collected and sent to other facilities where carbon dioxide is needed for a reaction. Other facilities use an offset program where either another company reduces its carbon dioxide emissions, known as carbon trading, or they develop a plantation to help reduce CO2 in the atmosphere.

For Example: CSBP Kwinana’s Ammonia Production Plant pumps 70000 tonnes per annum of CO2 to Alcoa World Alumina Australia Kwinana’s residue disposal area. There it is used to make carbonates, preventing the CO2 from being pumped into the atmosphere.

WastewaterWastewater is a major source of environmental contamination from ammonia production plants. Used throughout the processes to clean equipment, the water contains many chemicals which can be harmful to the environment. Water recycling and treatment plants are used to process the water to reduce them to within regulation levels for emission back into the environment. Many of these industries now use recycled water from domestic sewerage to avoid using limited supplies of scheme or ground water.

For Example: CSBP Kwinana’s Ammonia Production Plant gets its water supply from the Kwinana Water Reclamation Plant. They also have a wastewater treating wetland which uses

Environmental Impact

bacteria to remove the nitrogen from the water by converting it to nitrogen gas which is released into the atmosphere.

NoiseThe plants are monitored by sound engineers who produce a report based on their recordings and models which predict noise contamination. They calculate prevailing winds, volume produced by machinery, and distance to nearest residential area and use this information to work out the sound levels that the plant’s neighbours will be affected by. This is then compared with legislation such as Western Australia’s Environmental Protection (Noise) Regulations 1997, to determine if these levels comply with preset standards. If they don’t, a noise management plan is developed, which may involve methods such as sound proofing walls or dirt mounds, to bring the impact to within regulations.

For example: CSBP Kwinana’s Ammonia Production Plant is monitored by Herring Storer Acoustics to ensure their noise pollution remains within acceptable levels.

AmmoniaAmmonia is a potentially harmful chemical and due care must be taken in its storage and use. It is found on the NOHSC List of Designated Hazardous Substances, and is classified as a dangerous chemical in the Australian Code for the Transportation of Dangerous Goods by Road and Rail in the ADGC7.

Ammonia is highly corrosive with metals such as aluminium. It reacts violently with water and is explosive when mixed with oxidizing substances. There is also the risk of an explosion if ammonia is heated in confinement. When stored, ammonia should be stored in a tightly closed, dry container, in a well ventilated area. It should not be allowed to contaminate food

Environmental Impact

and drink, and kept far away from oxidising agents, heat and sources of ignition.

Its effect on the environment is mainly felt by the harm it does to humans and animals. Prolonged or concentrated contact is damaging to the eyes, skin and respiratory system. Ammonia if stored in liquid form can also result in severe cryogenic burns. As a gas it is very toxic to bees and is deadly in the water. Though it dissolves, concentrations as small as 0.068mg L-1 are lethal to marine life.

The stages of production of ammonia in this report are the stages which are utilised at CSBP Kwinana’s Ammonia Production Facility. Understandably the stages vary at different facilities throughout the world as some target rich ammonia production, whilst others a cost-efficient process.

The Catalysts and the conditions of each reaction are those predominantly used. Key figures are those recommended by Haldor-Topsoe and KBR. Any changes in enthalpy given are standard changes in enthalpy at STP and are intended just as a guide to whether the reaction is exothermic or endothermic.

All images and diagrams are my own.

Websites:HTTP://WWW.KBR.COM/

HTTP://WWW.AUSETUTE.COM.AU/HABERPRO.HTML

HTTP://WWW.CSBP.COM.AU/

HTTP://WWW.NAMEDORGANICREACTIONS.CO.UK/HABER.PDF

HTTP://WWW.NATURALGAS.ORG/NATURALGAS/PROCESSING_NG.ASP

HTTP://WWW.OWLNET.RICE.EDU/~CENG403/NH397HEAT1.HTML

References

http://www.owlnet.rice.edu/~ceng403/nh397heat1.html

http://www.naturalgas.org/naturalgas/processing_ng.asp

http://www.namedorganicreactions.co.uk/Haber.pdf

http://www.csbp.com.au/

http://www.ausetute.com.au/haberpro.html

http://www.kbr.com/

HTTP://WWW.PRINCETON.EDU/~HOS/MIKE/TEXTS/READMACH/ZMACZYNSKI.HTM

HTTP://WWW.RMTECH.NET/USES_OF_AMMONIA.HTM

HTTP://WWW.TOPSOE.COM/

http://www.topsoe.com/

http://www.rmtech.net/uses_of_ammonia.htm

http://www.princeton.edu/~hos/mike/texts/readmach/zmaczynski.htm

Reports:MSDS: Ammonia (Anhydrous)CSBP2008

Submission to – Technical Guidelines for the Estimation of Greenhouse Emissions and Energy at the Facility Level, Department of Climate ChangeRefrigerants Australia2008HTTP://WWW.CLIMATECHANGE.GOV.AU/EN/GOVERNMENT/SUBMISSIONS/REPORTING/~/ MEDIA/SUBMISSIONS/REPORTING/NGER/07REFRIGERANTSAUSTRALIA.ASHX

The Australian Dangerous Goods Code 7th EditionDepartment of Infrastructure and Transport2010

Reference Books:Advanced Modeling and Optimization of Manufacturing ProcessesR. Venkata RaoSpringer, 2010

Chemicals from Synthesis GasRoger A. SheldonSpringer 1983

Dictionary of Petroleum Exploration, Drilling and ProductionNorman J. HynePennWell Books, 1991

Encyclopaedia of Occupational Health and Safety 4th EditionJeanne Mager Stellman, International Labour OfficeInternational Labour Organisation, 1998

Excel HSC ChemistryC. M. RoebuckPascal Press, 2003

Gas Usage and ValueDuncan SeddonPennWell Books, 2006

Matheson Gas Data Book (2001)Carl L. Yaws, William BrakerMcGraw-Hill Professional, 2001

The Top Fifty Industrial ChemicalsRaymond Chang, Wayne TikkanenRandom House, 1988

References

http://www.climatechange.gov.au/en/government/submissions/reporting/~/media/submissions/reporting/nger/07refrigerantsaustralia.ashx

http://www.climatechange.gov.au/en/government/submissions/reporting/~/media/submissions/reporting/nger/07refrigerantsaustralia.ashx

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