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Thread: Semi Permeable Membranes for Carbon Dioxide

  1. #1 Semi Permeable Membranes for Carbon Dioxide 
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    What kind of semipermeable membrane would you use to filter out carbon dioxide from the air?


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  3. #2  
    exchemist
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    Quote Originally Posted by jwscienceman View Post
    What kind of semipermeable membrane would you use to filter out carbon dioxide from the air?
    Here is one starting point: Carbon Dioxide Control: Molecular Sieves


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  4. #3  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by jwscienceman View Post
    What kind of semipermeable membrane would you use to filter out carbon dioxide from the air?
    Here is one starting point: Carbon Dioxide Control: Molecular Sieves
    Good one.

    However, it's a pity that one has to remove water vapour from the air stream before it can be passed through the molecular sieve to absorb CO2.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    So is CO2 being absorbed by another substance here, or is it just being filtered out without the need for absorption?
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    Quote Originally Posted by jwscienceman View Post
    So is CO2 being absorbed by another substance here, or is it just being filtered out without the need for absorption?
    The terms used is adsorption rather than absorption. Adsorption denotes the binding of the molecules to a surface, either by ordinary intermolecular attractions or by becoming bound by chemical bonds i.e. a reaction occurs. Often you can release the bound molecules again by heating or something: you will see the article speaks of regeneration of the molecular sieve, which is the process that does that.
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  7. #6  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by jwscienceman View Post
    So is CO2 being absorbed by another substance here, or is it just being filtered out without the need for absorption?
    The terms used is adsorption rather than absorption. Adsorption denotes the binding of the molecules to a surface, either by ordinary intermolecular attractions or by becoming bound by chemical bonds i.e. a reaction occurs. Often you can release the bound molecules again by heating or something: you will see the article speaks of regeneration of the molecular sieve, which is the process that does that.
    Okay, I think I understand now. Where does the carbon dioxide go after it is filtered out of the air?
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  8. #7  
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    Quote Originally Posted by jwscienceman View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by jwscienceman View Post
    So is CO2 being absorbed by another substance here, or is it just being filtered out without the need for absorption?
    The terms used is adsorption rather than absorption. Adsorption denotes the binding of the molecules to a surface, either by ordinary intermolecular attractions or by becoming bound by chemical bonds i.e. a reaction occurs. Often you can release the bound molecules again by heating or something: you will see the article speaks of regeneration of the molecular sieve, which is the process that does that.
    Okay, I think I understand now. Where does the carbon dioxide go after it is filtered out of the air?
    Stays adsorbed until you "desorb" it. It captures it but does not get rid of it. After it is full of CO2 you have desorb it, do something with it and reuse your filter. You can read all this on the web.
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    I get it now. Thanks.
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  10. #9  
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    Rubber is much more permeable by carbon dioxide than is air. The ratio of permeability of rubber to air in comparison with hydrogen is 0.23. By comparison, the ratio for carbon dioxide to hydrogen is 2.91. There is a lot of discussion of this effect in various places. An original research paper containing the information, that came through with some terrible formatting errors is:

    Full text of "Permeability of rubber to gases"

    As, I recall, the mechanism behind this effect is akin to a solution/dissolution process.

    I found out about this when someone asked why balloons filled with carbon dioxide shrank faster than balloons filled with air. This reference and explanation is perhaps a little easier to read than the previous one.

    http://www.madsci.org/posts/archives...2329.Ch.r.html

    It makes me wonder about those small carbon dioxide cylinders that are used to fill bicycle tyres. I wonder if they tend to go flat faster than normal?
    Last edited by Warron; October 8th, 2014 at 09:57 PM.
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