Rolling Your Own Provides Safety, Economy
The prospect of gas cylinder accidents inspires awe and fear in lab workers. However, a safer alternative exists for some of the more common specialty gases: on-site or point-of-use generation that uses membranes, catalysts, or pressure swing absorption to generate pure gases from air or water.
The point of on-site generation is to avoid storage by generating gas as it is needed. Gone are tanks and everything associated with them: rental, delivery, supply, and accidents.
In situ nitrogen generation is a membrane process; hydrogen is generated through electrolysis of deionized water using a palladium membrane catalyst.
“We’ve been in this market since 1989,” notes Phil Allison, global business leader for gas-generation products at Parker Hannifin (Haverhill, MA). “Most of the on-site gas-generating technologies are the same as those available at industrial scale, but in miniaturized form.”
One exception is zero-grade (hydrocarbon- depleted) air, which is produced at the plant by blending very pure oxygen and nitrogen. At the benchtop, the gas generator uses a compressed air feedstock, purifies it, then uses a catalyst to oxidize out the hydrocarbons.
Point-of-use production varies significantly among gases. Because nitrogen is the principal component of air (78% by volume, 75% by weight), on-site generation systems produce the equivalent of about seven cylinders per day. Zero-grade air generation has a capacity of about 140 liters per minute. For hydrogen, generators produce anywhere from 100 milliliters to 20 liters per minute.
A recent study by Loctite, a subsidiary of chemical giant Henkel, found that a typical analytical laboratory using two gas chromatographs could save $20,000 per year by generating its hydrogen gas at the point of use. Hydrogen cylinders are normally trucked in and stored in a utility area or directly behind the GC. When the main tank empties, the analytical operation shuts down unless a backup tank is on-site. The purity of point-of-use hydrogen is 99.99999 percent.
On-site hydrogen generation makes sense even for labs that only occasionally use hydrogen. “Why would you want to spend $5,000 per year on cylinder gas when you can buy a generator for $8K which pays for itself in less than two years?” Mr. Allison asks.
The GC connection
Hydrogen is normally associated with GCs as the gas that fuels the instrument’s flame ionization detector (FID). Increasingly, labs are using hydrogen as the carrier gas.
According to John Speranza, VP of sales at Proton Onsite (Wallingford, CT) the cost of helium has reached $200 per tank— twice that of hydrogen. Labs that are able to, are switching in droves from helium to hydrogen, he says. Stagnant capacity and increased demand are behind the rise in helium prices.
“Not only is hydrogen half the price of helium, but that gas’s lower viscosity makes gas chromatography more efficient,” Mr. Speranza says. “And this is not a temporary situation.”
Chromatographers considering the switch may need to re-validate their methods, but otherwise the switch is seamless.
But isn’t hydrogen much more dangerous than helium? Yes, hydrogen’s suspect safety record only applies to large volumes, or buildup of gas that goes unnoticed. On-demand generation eliminates that problem because the gas is used as quickly as it is generated. Column gas is simply vented into the lab air or through a fume hood, while FID gas is burned.
For lab managers tired of dealing with rusted or de-threaded tank caps and with the hand wheel valves on standard tanks, but who are not yet ready to generate their own gases, Air Liquide Canada (Montreal, PQ) has a new design that is both safer and less frustrating. The Smartop™ and Scandina ™ caps replace the screw cap with a protective surrounding that allows users to open and close the tank through a readilyaccessible lever instead of the more common wheel. The protective Smartop remains on the cylinder during use. “We even include a built-in pressure gauge so the user knows how much gas remains in the tank,” says Gene Strynatka, business development manager at Air Liquide Canada.
Extra level of QA
Gas testing has become a critical service as industry and laboratories demand evermore- complex and higher-purity gases and mixtures. In May, BOC, the U.K. subsidiary of Linde (Pullach, Germany), was awarded “elite” accreditation from the U.K. Accreditation Service as a gas testing laboratory.
Linde has long sold calibration gas mixtures to regulated industries. The accreditation means the company may now offer U.K. and global customers sampling and testing services for aviation- and breathing- related work involving oxygen, liquid nitrogen, and compressed air.
Steve Harrison, head of specialty gases at Linde, explains that where BOC had previously enjoyed status as a calibration lab, now its capabilities extend to testing. “This means we’re not just manufacturing, certifying, and selling product, but providing a test report for samples that we analyze as well,” he says. BOC’s facility will test the gases it produces and sells as well as thirdparty gases.
Mr. Harrison explains that for some applications, in fact most laboratory work, the producer’s quality certification usually suffices for the gas at the time of production. However, between the plant and the end-user, quality may be compromised by transferring gas from one container to another or as it travels through piping from the tank to the application. “There are lots of opportunities for things to go wrong. Think of testing as one extra level of quality assurance.”
Testing consists of identifying and confirming that the major component (say, oxygen) is present in a specified concentration and that contaminants are minimized. Breathing gases are examined for low levels of hydrocarbons, moisture, and carbon monoxide. Gas chromatography and GCMS are common analytical methods, with various detectors used depending on the target analyte.