[Digestion] New Plastic Membrane

[Duncan Martin]

I suspect the Times of India has simply inverted the mechanism, although the 
shape of the pores* might have an unexpected effect on mols of differing 
size.

In other words, the methane might pass through, while the CO2 is retained. 
Just as effective? (In fact better if other troublesome contaminants, such 
as silanes, are also retained.**)

(*I wonder what they mean by hourglass shaped? On which axis? A "keyhole" 
might have strange - and perhaps useful - selectivity. However, an axis 
perpendicular to the membrane is more likely, in which case you simply have 
a pore the size of the "waist" of the hourglass, with tapered entry and 
exit. Would that be MORE selective than a cylinder the same length of the 
diameter of the waist? A little LESS would seem more likely.)

(**Silanes appear in LFG from cosmetics etc in domestic waste - and end up 
as abrasive silica in generator engines. Not a problem in AD, luckily!)

Duncan J Martin

Centre Councillor
Republic of Ireland Centre
Chartered Institution of Wastes Management

================================
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Duncan J Martin, PhD, CEng, CSci, MIEI, MCIWM, MIChemE
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----- Original Message ----- 
From: "Stephen Etheridge" <spe at pieinternational.com>
To: "Madhu Ranganathan" <madhurangi at yahoo.com>; 
<digestion at listserv.repp.org>
Sent: Sunday, October 14, 2007 4:33 AM
Subject: Re: [Digestion] New Plastic Membrane


> ???? Methane is smaller than Carbon Dioxide in all structural formations!
>
> Dr Stephen Etheridge
> CTO
> AsiaBiogas
>
>
> ----- Original Message ----- 
> From: "Madhu Ranganathan" <madhurangi at yahoo.com>
> To: <digestion at listserv.repp.org>
> Sent: Sunday, October 14, 2007 3:23 AM
> Subject: [Digestion] New Plastic Membrane
>
>
> This new item appeared on the Times Of India
>
> WASHINGTON: A new membrane that mimics pores found in plants and allows
> carbon dioxide to move through while preventing the movement of methane,
> could be used to cut greenhouse gas emissions while purifying water at the
> same time.
>
> The membrane allows small molecules such as those of carbon dioxide to 
> move
> through its pores while preventing the movement of larger molecules such 
> as
> methane.
>
> Separating carbon dioxide from methane is important in natural gas
> processing and gas recovery from landfill.
>
> Dr Anita Hill of CSIRO Materials Science and Engineering, part of the
> research team, said: "This plastic will help solve problems of small
> molecule separation, whether related to clean coal technology, separating
> greenhouse gases, increasing the energy efficiency of water purification, 
> or
> producing and delivering energy from hydrogen".
>
> "The ability of the new plastic to separate small molecules surpasses the
> limits of any conventional plastics. It can separate carbon dioxide from
> natural gas a few hundred times faster than current plastic membranes and
> its performance is four times better in terms of purity of the separated
> gas," she said.
>
> She said the secret lay in the hourglass shape of the pores, which helped
> separate molecules faster and using less energy than other pore shapes.
>
> In plant cell membranes, hourglass-shaped pores known as aquaporins
> selectively conduct water molecules in and out of cells while preventing 
> the
> passage of other molecules such as salt. Dr Hill said the research had 
> shown
> how plastics could be systematically adjusted to block or pass different
> molecules depending on the specific application.
>
> For example, these membranes might provide a low energy method for the
> removal of salt from water, carbon dioxide from natural gas, or hydrogen
> from nitrogen, she said.
>
>
> Would'nt it be just the thing AD needed???????
>
>
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