Using an In-House Hydrogen Generator to Replace He Carrier Gas for GC

H₂ is commonly used as GC carrier gas as the cost of He is increasing and its availability is decreasing. In addition to the cost/availability issues, H₂ can provide more rapid separations at lower temperatures than He and provides longer column life. H₂ gas is obtained by the electrolysis of water and many laboratories supply it to the GC via an in-house H₂ generator.

Generating Hydrogen via an In-House System

H₂ is generated by the electrolysis of water using two metal electrodes immersed in a strong electrolyte (e.g. 20% NaOH). To provide high purity H₂, a Pd cathode is used; as only H₂ (and its isotopes) can pass through it. Some systems electrolyze water using another metal for the cathode and then remove water with a desiccator. While the initial cost of that approach is lower, the H₂ collected contains significantly more oxygen and moisture than when a palladium cathode is used. The Parker-Balston Model H2PD-300 (Parker Hannifin Corporation, Haverhill, MA), which includes a palladium cathode can generate 99.99999+% pure H₂ with an oxygen content of <0.01% and a moisture content of 0.01 ppm at a maximum flow of 300 mL/min. Alternatively, water can be electrolyzed using a proton exchange membrane such as Nafion via the Parker-Balston H2PEM system, which does not require a strong caustic.

Benefits of Generating H₂ via an In-House System

The benefits of in-house generation include:

• Safety - In-house generators supply the desired volume of gas on demand at low pressure. In contrast, tanks contain a considerable amount of hydrogen gas; if a leak occurred, gas would be released into the laboratory leading to the potential of asphyxiation and/or explosion.

• Convenience - In-house hydrogen provide H₂ on a continuous basis. In contrast, when a tank is employed, the operator must ensure that it contains a sufficient amount of gas for the desired operation (e.g. automated overnight runs). In many facilities, replacement tanks are stored in a remote (outdoor) location for safety reasons and specially qualified personnel may be required to perform tank replacement.

• Elimination of Contamination - When a tank is used, the connection to the GC must be broken to replace it, potentially leading to the introduction of moisture and/or oxygen into the system.

• Cost - The overall cost of operation of an H₂ generator is considerably lower than the use of tanks. An in-house generator requires only electricity and water and the payback period of an in-house generator is approximately a year. When tanks are used, the time/cost of replacing them, demurrage and other costs should be included.

• Environmental Benefits - The energy requirements for an in-house generator is low. When tanks are employed, the gas must be compressed to 2000 psi. Once the tank is filled, it must be transported to the end user's site and the empty tanks must be returned to the supplier.

To download a convenient step by step guide on how to switch from helium to hydrogen as a carrier gas, go to www.parker.com/h2

Parker Hannifin Corp., Filtration and Separation Div.

242 Neck Road, P.O. Box 8223, Haverhill MA 01835-0723

tel. (800) 343-4048, (978) 858-0505, fax (978) 556-7501

Website: www.labgasgenerators.com