Nitrogen generators use a supply of dry, oil-free air to purify nitrogen via a selectively permeable membrane or carbon molecular sieve material which removes oxygen, carbon monoxide and carbon dioxide. Purified nitrogen is then stored in a buffer tank to ensure constant flow and pressure of nitrogen is supplied to the application.

Purified Air generators also require a supply of dry, oil-free compressed air which is passed through a catalyst chamber, or filtration system to remove methane, CO2 moisture and carbon monoxide. Gas is supplied to application from a buffer tank so that flow and pressure remain constant.

Hydrogen generators electrolyse deionised water to oxygen and hydrogen via a proton exchange membrane (PEM). Hydrogen ions diffuse through the PEM membrane whereas oxygen is retained and is then vented to atmosphere. The hydrogen is then further purified using a desiccant drier or pressure swing adsorption drier before being supplied to the application.

How does this differ from conventional techniques of supplying gas, such as in cylinders?

Gas cylinders have been the traditional way to store and supply gases to applications in the lab and most gas users don’t think of using alternatives despite the potential danger and inconvenience associated with using cylinders.

Cylinders contain large quantities of gas at high pressure and therefore present a potential health and safety problem. Not only must the cylinders, which are fairly heavy, be periodically moved, but an accident can release a large volume of gas into the lab environment.

If the gas released is nitrogen, there is potential for asphyxiation of anybody unlucky enough to be in the lab. If the gas is hydrogen, there is the potential for an explosion to occur. Once the level of hydrogen in atmosphere reaches 4.1% by volume in air it can explode if there is an ignition source present.

Releasing the contents of a large hydrogen cylinder, which contains around 9000 liters of hydrogen at atmospheric pressure, rapidly into a small lab would present a major risk of explosion. Compare this with a hydrogen generator which produces 500cc/min of hydrogen and you can easily see the safety benefits of using a generator.

Cylinders offer a challenge in terms of user convenience since they need to be periodically changed and moved. Changing cylinders can allow air and impurities into the analytical instrument, which means down-time for instruments whilst the air is purged from the system as well as the opportunity for impurities to enter the system. New cylinders must be monitored, ordered and swopped out, which takes up valuable time of lab personnel.

The other potential problem with cylinders is inconsistency in purity from cylinder to cylinder and that impurities collect at the bottom of the cylinder meaning that the last 10% of the gas is not of as good a quality and is not recommended for use. In addition to these factors, there is the transportation of cylinders which are usually transported by road and therefore add to street congestion and pollution.

What are the primary applications of gas generators?

The main applications supported by gas generators are analytical lab applications such as LC/MS, GC/MS, GC, TOC, FTIR as well as a variety of sample preparation techniques such as static or dynamic headspace and automated evaporation systems.

Environmental benefits to generating your own gas supply as and when it is needed rather than storing it in cylinders

Once installed, a generator requires only a supply of electricity, and in the case of hydrogen generators deionised water, to produce a high purity gas suitable to supply highly sensitive analytical instruments. Therefore, generators have a small carbon footprint compared with cylinders which need to be transported to and from the lab repeatedly because of their limited capacity.

A nitrogen generator supplying 32 litres per minute of nitrogen to an LC/MS will produce over 9.5 million litres of nitrogen before needing to be serviced. This volume of gas is equivalent to over 1000 nitrogen cylinders which would need to be transported to and from the cylinder depot, therefore the environmental benefits of using a generator, as well as the time and cost savings are quite clear.

What are the major advantages of using Gas Generators over using cylinders?

The main advantages of gas generators over using cylinders are safety and convenience. Generators provide a constant supply of gas for lab applications without risking the safety for lab users.

Cylinders have the potential to release of thousands of litres of gas into the lab atmosphere in a very short space of time, which could have fatal consequences

The set-up of gas generators is very straight forward and maintenance is required every 6-12 months depending on the system. The majority of gas generators require just an annual service, which can be conducted on site in only a few hours.


Posted by Abdulhakeem Owolabi

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