Hi all,
QUESTION: How many of you use N2 generators (NOT boiloff from an N2
tank) for VT gas, and what systems are hooked up to it? If you use
such a system, how stringent are your users' lineshape requirements?
BACKGROUND:
We have a moderately tricky compressed gas issue. We run a lot of VT
experiments for which we need N2. We need a very low dew point so our
FTS chillers don't develop ice plugs during low-temp experiments, and
we need an inert gas to prevent probe corrosion in our high-temp
experiments.
The trick is we can't use N2 boiloff from a big liquid N2 storage
tank, like I know many of you use. Our house N2 comes from such a
boiloff source, but at a puny 30 psi. Rumor has it that it's wet, too.
Years ago, this facility set itself up with an N2 generator, which
uses selective membranes to remove H2O and O2, leaving enriched N2.
The source is dry enough for us, but the O2 content is still ~1%.
It's known that good shims depend on whether the system is perfused
with N2 or air because the O2 in air is paramagnetic. I've found that
lineshape changes significantly on our 600 when switching between
generated N2 and straight compressed air. I recently noticed that the
O2 content our N2 system delivers varies from 0.8% to 2.2% depending
on how many spectrometers are hooked up to it. Thus, someone who
starts out with a great lineshape on the 600 may end up with a
suboptimal lineshape if in the middle of their run someone on the 400
switches from N2 to air, which changes the load on the N2 generator,
causing the O2 content to change. Our aim is to stabilize the O2
content of our N2.
We're considering whether to expand the capacity of our N2 system to
reduce the variation or get a new generator dedicated to our 600,
which has the most stringent lineshape requirements. Using boiloff
from N2 tanks is always an option, but it's comparatively expensive,
risky, and inconvenient for such routine needs.
I'd appreciate your thoughts on the matter.
Thanks.
- Josh
Josh Kurutz, Ph.D.
Instructor and Senior Scientist for NMR
IMSERC, Chemistry Department
Northwestern University
2145 Sheridan Rd.
Evanston, IL 60208-3113
847-467-1681
fax: 208-978-2599
Facility: www.chem.northwestern.edu/imserc
NMR Blog: www.imserc-nmr.org
Twitter feed: twitter.com/imserc_nmr
Other: www.joshkurutz.com
Received on Wed Mar 31 2010 - 12:37:29 MST