Industrial Chemistry 1: Ammonia Production

Industrial Chemistry 1: Chapter 4 - Ammonia Production

• Ammonia production is a vital industrial process, used in fertilizers, petroleum, mining, rubber, paper, and leather industries, as well as medicine and cosmetics.

Properties of Ammonia

• Molecular weight: 17 gm/mol
• Boiling point: -33.34 °C
• Freezing point: -77.7 °C
• Standard heat of formation: -46222 KJ/Kmol
• Soluble in chloroform, ether, and ethanol.
• Density: 0.769 Kg/m³ at STP

Uses of Ammonia

• Refrigerant
• Medicine & Cosmetics
• Solvent
• Lab reagent
• Metal treatment
• Preservative
• Transport of H₂

Uses of Ammonia In Industries

• Fertilizer Industry
• Petroleum
• Industry Mining
• Industry Rubber
• Industry Paper
• Industry Leather

Manufacturing Processes

• Synthesis gas for ammonia production is achieved via steam reforming or partial oxidation of hydrocarbon feedstock.
• Commercially used ammonia production processes include:
  • Haber-Bosch Process
  • Braun Purifier Process

1. Haber-Bosch Process

• The industrial implementation of the reaction between nitrogen gas and hydrogen gas.
• Main industrial procedure for ammonia production.
• Reaction: N₂ + 3H₂ → 2NH₃ (ΔH = -92.4 kJ·mol⁻¹)

Flow Scheme of Haber Process

• Nitrogen from the air and hydrogen from natural gas (1:3 volume ratio)
• Reacted at 400-450°C and 200 atm pressure using an iron catalyst.
• Unreacted gases are recycled.
• Gases are cooled to liquefy the ammonia.

Process Flow Diagram

• Details of the process steps, showing various steps including the production of the synthesis mixture, using methane as a feedstock, and the production of ammonia. The diagram outlines the reaction steps, heat exchangers, and other components.

Parameters

• Temperature: 450°C (moderately high); Lower temp increases equilibrium yield but reactions are too slow.
• Pressure: 200-1000 atm; High pressure is beneficial for rate and equilibrium position.
• Catalyst: Iron; catalyst increases reaction rate, allowing for lower temperature.
• The Haber process is exothermic in the forward direction (N₂ + 3H₂ ↔ 2NH₃ + Heat)

Major Engineering

• Reaction kinetics and equilibrium: Lower temperature favors the forward reaction, and higher pressure is favorable for decreasing moles.
• Graph (1) & (2): Equilibrium yield of NH₃ is increased by increasing the pressure and decreasing the temperature.

Catalyst

• Primarily based on FeO.
• Modern catalysts include promoters like oxides of Al, Zr, and K, to enhance porosity and withstand high temperatures.

2. Braun Purifier Process

• Synthetic ammonia (NH₃) is produced from natural gas.
• Natural gas molecules are converted to hydrogen.
• Hydrogen is purified and reacted with nitrogen.

Chemical Processes

• Description of the chemical processes involved in ammonia synthesis from natural gas, including hydrodesulphurization, primary and secondary reforming, high temperature/low temperature shift, CO₂ removal, methanation, and intermediate processes.

Simple Block Diagram

• Shows a schematic of the ammonia production process, outlining the various catalyst types and volumes involved.
• Includes temperatures and pressures at each stage, outlining primary reforming, secondary reforming, High/Low Temperature CO Shifts, CO removal, and methanation stages.

Simplified Process Overview (Pages 15 and 16)

• Purification of impurities (mainly sulfur compounds) from the gas stream.
• Steam reforming in two stages:
  • Primary stage: Endothermic reactions at high temperatures (800°C+) and pressures (~30 bar).
  • Secondary stage: Addition of air to the partially reformed gas and an exothermic reaction.
• Conversion of carbon monoxide to carbon dioxide in the shift reactors, followed by removal.
• Any residual carbon oxides are converted back to methane by methanation before compression.
• Final stage: The reaction of hydrogen and nitrogen to form ammonia at high pressures (100-350 bar). This reaction is highly exothermic.
• Reactor Types (Page 18): Presents different ammonia synthesis reactor types, their cooling methods, and corresponding companies or licensors. Includes pressure and production capacity data.

Reactor for Ammonia Synthesis

• Diagrams of different ammonia reactor designs (Kellogg and Topsoe).