Corky Belobraydich, Parker Hannifin Corporation
Since the gas flow required for the separation step in gas chromatography is frequently lower that that required to optimize
the detection, nitrogen is used as a make-up gas to increase the gas flow for detection. In many facilities, zero grade nitrogen
make-up gas is provided from a cylinder or tank. While this approach works, an in-house "make-up" gas generator can provide
the desired nitrogen with a higher level of purity than bottled nitrogen. In addition, the use of an in-house make-up gas
generator can provide a considerably safer, more convenient, and less expensive approach to supply the required gas.
Design of an In-House Zero-Air Generator
Figure 1
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Zero grade nitrogen for make-up gas can be readily obtained from laboratory compressed air using an in-house generator (Parker
Hannifin FID MakeUpGas Generator) that includes a heated catalytic converter in which a proprietary catalyst blend is combined
with platinum to remove all hydrocarbons by converting them to CO2 and water vapor. The converter is followed by a hollow fiber membrane separator which preferentially allows oxygen and water
vapor to quickly permeate the membrane wall while nitrogen travels through the hollow fiber out the end (Figure 1). The hollow
fiber has a small internal diameter and thousands of fibers are bundled together to provide a large surface area to provide
the desired flow of nitrogen. The makeup gas generator can provide nitrogen with purity of better than 99.9999% with respect
to hydrocarbons (< 1 ppm) and greater than 99% with respect to oxygen.
Performance
Figure 2
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A chromatographic comparison of the nitrogen that was produced by the MakeUpGas generator and gas that was obtained from bottled
fuel air from a commercial supplier is shown in Figure 2. The gas generated by the MakeUpGas generator is much purer than
that from bottled fuel air; and provides an extremely flat baseline with essentially no signal due to hydrocarbons, while
the zero grade bottled air provided an irregular baseline with a significant level of hydrocarbons, which could impact the
analysis.
Conclusions
In addition to the extremely high level of purity provided by the generator, the use of an in-house generator provides benefits
in safety, cost, and convenience. When a MakeUpGas generator is employed, only a small amount of nitrogen is generated at
a given instant and a leak would lead to a negligible change in the composition of the laboratory air. In contrast, a leak
from a full tank could cause problems. When an in-house generator is employed, gas is available on a 24/7 basis and the possibility
of injury or damage during the transportation and installation of a heavy gas tank, which can become a guided missile if the
valve on a full tank is compromised during transport, is eliminated. In addition to the significant safety and convenience
benefits, there is an economic benefit from using a MakeUpGas generator. The running cost of operation maintenance of the
MakeupGas generator is extremely low; as the raw materials to prepare the required gas are air and electricity.
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Parker Hannifin Corporation
Filtration and Separation Division
260 Neck Road, Haverhill MA 01835
tel. (800) 343-4048, (978) 858-0505
Website:
http://www.labgasgenerators.com/
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