Sunday, May 27, 2012

Amine Scrubbing

Fossil fuel-burning power plants, in particular coal-burning power plants, are a major source of a carbon dioxide, a greenhouse gas. When power plants begin capturing their carbon emissions to reduce greenhouse gases it will be an expensive undertaking. Current technologies use about one-third of the energy generated by power plants to capture greenhouse gas emissions, this is referred to as parasitic energy.

Although no commercial power plants currently capture carbon dioxide on a large scale, a few small-scale and pilot plants do. One commonly used process is known as amine scrubbing in which gas emissions are funneled through an amine bath, which absorbs carbon dioxide from the flue gases. Typical amine baths in use are:
  • 32 % by mass aqueous 2-aminoethanol (NH2-CH2-CH2OH) solution
  • 25% by mas aqueous 2,2'-Iminodiethanol (HN(CH2CH2OH)2) solution
  • 40% by mass bis(2-hydroxyethyl)methylamine (CH3N (C2H4OH)2) solution
  • 50% by mass 2-(2-Aminoethoxy)ethanol solution
 The amines are then boiled to release the CO2. Additional energy is required to compress the carbon dioxide so that it can be pumped underground.
The energy needed for this process decreases the amount that can go into making electricity. Calculations show that for a coal-fired power plant, that could amount to approximately 30% of total energy generated.

A group of  scientists from UC Berkeley and EPRI have developed a computer model to calculate energy energy costs of carbon dioxide capture, release and compression, for any material including the amine baths above as well as zeolites (porous materials made of silicon dioxide) and MOFs (metal oxide frameworks).

Li-Chiang Lin, Adam H. Berger, Richard L. Martin, Jihan Kim, Joseph A. Swisher, Kuldeep Jariwala, Chris H. Rycroft, Abhoyjit S. Bhown, Michael W. Deem, Maciej Haranczyk, Berend Smit. In silico screening of carbon-capture materials. Nature Materials, 2012; DOI: 10.1038/nmat3336

Further Reading:
Greenhouse Gases and the Greenhouse Effect
Combustion of Hydrocarbons

Percent By Mass (weight) Concentration 

Suggested Study Questions:
  1.  Give the name and formula of the four main naturally occurring greenhouse gases.
  2. Give the name and formula of four human-induced greenhouse gases.
  3. Write a chemical equation for the complete combustion of coal.
  4. Anthracite is a type of coal that is made up of about 95% carbon. The combustion of 1g of coal releases about 1000 kJ of energy. Calculate the heat of combustion of anthracite in kJ/mol
  5. Write the molecular formula for each of the 4 amines used in amine scrubbing baths.
  6. On the structural formula for each of the amines used in amine scrubbers:
    • circle amino groups in blue
    • circle hydroxyl groups in red
  7. For a 32% by mass aqueous 2-aminoethanol solution, calculate the mass of  2-aminoethanol present in
    • 1 kg of solution
    • 100 g of solution
    • 1 tonne of solution
    • 2500 mg of solution
  8. What is the concentration in mol/L of the1 kg of  a 32% by mass aqueous 2-aminoethanol solution?

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