From: Alan \"Uncle Al\" Schwartz <uncleal0@ix.netcom.com>
Newsgroups: sci.chem
Subject: Re: Need advice re:Halocarbons or like materials
Date: 13 Apr 1996 14:12:30 GMT

greendm@tiac.net (Don Green) wrote:
>inovex@magnet.at (INOVEX GmbH) wrote:
>
>>.. Have you ever thought on supercritical CO2 ? It is non toxic (?) , the
>>technology is very well known
>> and  it is cheap. --- 
>>It is depending on your application ! an extraction or solvation proces is
>>easily done with SC- CO2..
>>It is possible to "immitate" all  solvent polaryties with C02 ! 
>
>WHAT is Supercritical CO2?
>How does one obtain Supercritical CO2?  

You take CO2, introduce a sufficient quantity into a stout sealed vessel, 
and warm above its 304.14 K critical temp.

The first part of the fun is that above the critical temperature a 
meniscus does not exist.  You have a fluid whose density (primary solvent 
and physical properties) depends only upon the pressure (critical 
pressure of 7.7.375 MPA).  Thus you can dial in properties by controlling 
pressure and co-solvents (like methanol or fluorinated surfactants).  the 
patter goes that CO2 is something your planet needs anyway, unless you 
get research grants about the Greenhouse Effect, and at the end you just 
open the valve and there is your stuff waiting for you.  Supercritical 
N20, and water are also popular.

The second part of the fun is that above the critical temperature, a 
Joule-Thompson expansion won't give you anything but gas phase.  Thus a 
ruptured CO2 tank is pretty exciting, but most of what you get after the 
initital pop is solid Dry Ice.  A ruptured supercritical reactor is 100% 
gas phase - blast wave plus shrapnel.  Whatever economies of solvent 
removal are hallucinated, one still must compress the CO2.  This is an 
expensive sponge for non-recoverable energy.  Your reaction vessels must 
be heavily overdesigned or in armored blast enclosures.  You will also 
need overpressure vents (and woe unto you if the diaphragm ruptures for 
good or ill and you emit a visible plume - starts with a $10,000 fine).

This is called "Environmentalism."

-- 
Alan "Uncle Al" Schwartz
UncleAl0@ix.netcom.com  ("zero" before "@")
http://www.netprophet.co.nz/uncleal/          (naughty beyond measure;
"Quis custudiet ipsos custodes?"  The Net!     funny beyond endurance)

Newsgroups: sci.chem
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Supercritical Extraction - was Re: Help Needed - Pine Oil Extraction
Date: Fri, 5 Jul 1996 07:35:44 LOCAL

In article <1090838429.39572424@magnet.at>
 inovex@magnet.at (INOVEX GmbH) writes:

>Probably with the method : SUPER  CRITICAL FLUID EXTRACTION, you 
>could safely (= enviromentaly) extract any charged compound from a matrix. 
>... You would need : CO2 an SFE Apparatus, ( ask Applied Separations PA) 

Absolute nonsense!. Given the low value of pine oil, and the high
moisture content of wood, supercritical CO2 would be a totally
uneconomic process. CO2 SFE is appropriate for products that
are almost anhydrous, and are of relatively high value. The cost 
of the plant precludes substitution for many "common" applications, 
unless a high value is placed on being solvent residue-free. There
are few applications where products that cost $/kg can be
competitively extracted by supercritical fluids. We have 4 SFE
plants, the largest with a 75 litre capacity, and probably design
and produce some of the lowest-cost, large capacity, SFE plants
in the world.  Incidently, supercritical CO2 behaves more like 
hexane - it extracts non-polar material - not charged species,
entrainers have to be added to extract polar species economically.
There are many good applications for SFE, but replacing cheap
processes making cheap products isn't one.

Pine oil is obtained from pinus palustris and other species by 
several methods, such as solvent extraction followed by steam 
distillation, or just steam distillation alone, or destructive  
distillation of the wood. Any chemical process text should give 
you the details.

               Bruce Hamilton