Beware of CO. As i recall, the CO production is proportional to the
temperature. So keeping the temperature as low as possible, while getting
a good yield is the key. I also found that exciting the CO mixture witha
tesla coil was effective in converting it to CO2.
I never actually measured the fractionation of CO to CO2. But clearly the
C + O2 reaction produced a fractionation when the concentrtion of CO was high.
At 04:57 PM 01/24/2001 +0100, you wrote:
>When converting O2 from a gas mixture, such as the O2-N2 mixture in air, the
>gas mixture has to be circulated over heated graphite-Pt by using a pump.
>This was noted by Kroopnick in his early paper (in Science) on solubility
>fractionation associated with oxygen dissolution. In our experiments (some
>done by the Coastal Science group in Austin, TX), we found that a
>temperature of 700-800 C with a conversion time of about 10 minutes resulted
>in conversion efficiencies of >98% (Aggarwal and Dillon, GCA, 1998).
>Removing the CO2 immediately or at the end of the process did not make a
> Pradeep K. Aggarwal, Ph.D.
> Head, Isotope Hydrology Section
> International Atomic Energy Agency
> P.O. Box 100 (Please use Box 200 for PERSONAL mail)
> Wagramer Strasse 5
> A 1400, Vienna, Austria
> Ph. +43-1-2600-21735
> Fax +43-1-26007
> e-mail: [log in to unmask]
>> From: Kinga M Revesz, Chemist, Reston, VA (Kinga Revesz)
>> Sent: Wednesday, 24 January 2001 15:32
>> To: [log in to unmask]
>> Subject: Re: how to convert O2 into CO2
>> Sergey and others:
>> I agree with Hilary. I remember now, that I had to work with very clean
>> O2. When I froze the O2 on mole sieve, after GC separation, I had to
>> away He (carrier gas) very very well, that meant around 10 minutes pumping
>> after the TC gauge showed no gas. Also, I watched the conversion very
>> closely. I timed the activation, and I stopped the reaction the moment
>> when the TC gauge showed good vacuum. For explanation see Hilary's note.
>> The reaction time of course depended on the amount but usually was very
>> fast even on that temperature. Pt catalyst is a must. We used Pt shield.
>> Some people say that the volume of the converter is critical. Ours was
>> big, but gave good numbers even at 1 micromole O2 conversion.
>> Kinga Revesz
>> Chemist, Stable Isotope Laboratory
>> U.S.Geological Survey
>> MS 431
>> Reston, VA 20192
>> FAX: 703-648-5274
>> Stuart-Williams To:
>> [log in to unmask]
>> <h.stuart-williams@ cc:
>> UEA.AC.UK> Subject: Re: how to
>> convert O2 into CO2
>> Sent by: Stable
>> <[log in to unmask]
>> 01/24/01 03:30 AM
>> Please respond to
>> Stable Isotope
>> With regard to the following :
>> I have used old carbon spectrograph rods soaked in platinum chloride for
>> the O2 - CO2 conversion on a BrF5 line. I found that even with the
>> platinum catalyst that lower temperatures produced a more complete
>> conversion. Some workers prefer to time the reaction, supposedly for
>> reproducibility, but I found it better to stop as soon as the pressure
>> starts to rise again. This is because even tiny amounts of a non-reactive
>> gas, such as nitrogen, slow the process enormously. As the impurities are
>> variable, the time is variable. On that subject, you must have relatively
>> pure O2. Otherwise it appears that the inert gas is swept to the freezing
>> surface in the LN2 and largely blocks freezing down of the CO2. This
>> ultimately leads to substantial CO production.
>> Hliary S_W
>> At 12:54 24/01/01 +1300, you wrote:
>> >Dear Sergey and Kinga,
>> >you could surely use much higher temperature but with a catalyst (Pt
>> >solution), gaining much time. See the literature on O-isotopes in
>> silicates or
>> >anyone who knows that procedure.
>> >Peter B.
>> >c/ IGNS, Lower Hutt, New Zealand
>> Hilary Le Q. Stuart-Williams Ph.D.
>> (Climate, behaviour study and ecology using stable isotopes)
>> Research Officer - Stable Isotope Laboratory
>> School of Environmental Sciences, University of East Anglia
>> Norwich NR4 7TJ, England
>> Telephone 01603 593837 (Work), 01603 507719 (Fax)
>> 01603 503430 (Home)
>> More data at : www.uea.ac.uk/~sil/
Dr. Peter Kroopnick
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