MadSci Network: Physics

Re: How do you evaporate water that is bound in materials?

Date: Wed Sep 28 13:15:34 2011
Posted By: James Griepenburg, , Chemical consultant, Chemmet Services
Area of science: Physics
ID: 1315791794.Ph

Boy have I over-answered your question! My approach would be to first remove everything from the house and physically remove as much water as possible. Maximize air circulation through the house. Use the furnace to warm the house, and clean as much as possible since dirt will hold moisture. And be patient. Hand dry all removed items placed on towels etc. to absorb water. Wash dry all clothing rugs. Warming evaporates water but too much heating may cause warpage. A space heater fan combo could help in enclosed areas. The use of dehumidifiers might be best after the house is almost dry and opening windows is impractical. Vapor pressure increases with temperature so it is important to keep the surfaces warm and to keep a high flow of dry warm air through the house.

There are many drying techniques depending on the delicate nature of the matrix and the tenacity of and chemical nature of the bound water. Some of the methods are:

  1. Air drying with or without gentle heating, such as hanging clothes on line, or a clothes dryer
  2. Placing in contact with a drying agent or in a closed container with a drying agent: use of a dessicator
  3. Use of gentle heat: a drying oven or microwave, possibly combined with vacuum and cold traps
  4. Severe heat possibly combined with vacuum: muffle furnace meker burner
  5. Phase separation such as water in oil using a separatory funnel or centrifuge
  6. Fractional distillation for mutually soluble such as methanol and water
  7. Azeotropic distillation such as using benzene to remove water from ethanol
  8. Solvent extraction such as washing a solid with alcohol
  9. Crystalization of water by freezing: removing ice by filtering or evaporation [freeze drying] or recovering dewatered liquid [Applejack]
  10. Physical blotting: ink blotter or bath towel
  11. Chemical reaction: reaction with active metals such as sodium or magnesium or metal hydrides. Karl Fischer reaction.
  12. Reverse osmosis, membrane separation.
  13. Electrolysis.
  14. Zone refining..

These are common methods and the list is not meant to be all inclusive. I have used all of them. Usually a combination of methods is used depending on the material, sample size, particle size, chemical reactivity and what is meant to be recovered.

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