Dr.Sc Ed Connor
10th dezembro 2019
How does a Hydrogen generator work?
A Hydrogen generator uses a proton exchange membrane (PEM) to produce high purity hydrogen gas from water. The PEM cell was originally developed by NASA and is extensively used in industrial and laboratory applications.
Hydrogen gas production
Hydrogen is the most abundant element in the Universe, although in its gaseous state it does not naturally occur on Earth and must be manufactured. In industry, H2(g) is produced on a large scale by a process called steam reforming, to separate carbon and hydrogen atoms from hydrocarbon fuels. Hydrogen is used in the laboratory for a variety of lab applications such as Gas Chromatography (GC) as fuel or carrier gas and ICP-MS as a collision gas, in the chemical industry to synthesise ammonia, cyclohexane and methanol and in the food industry for hydrogenation of oils to form fats.
Significant research and development has afforded safer, greener, more efficient and cost-effective means of generating on-demand hydrogen gas for laboratory, manufacturing and industrial applications. Safety has improved so much that Hydrogen gas is now being used in some transport vehicles as a clean ‘pollution-free’ fuel with the gas being generated from water with the by-product of its combustion being water.
This article provides answers to several OHS and FAQs collated from worldwide health, environmental, industrial, testing, medical and research laboratories regarding the safe use of hydrogen generators in the workplace.
How does a hydrogen generator work?
Electrolysis of water is the best method of producing high purity hydrogen gas on demand. The most important element of the generator is the electrolyser cell where the electrolysis reaction takes place. The cell consists of two electrodes (an anode and a cathode), which are separated by the ion exchange membrane. To produce the highest purity of hydrogen up to up to 99.9995% purity, a platinum catalyst is used at the electrodes.
When a continuous voltage is applied to the electrodes on the electrolyser cell, the following reactions take place: -
Illustration of electrolysis in a PEM cell
At the anode (the positively charged electrode), the water molecules lose two electrons, forming an oxygen molecule and four hydrogen ions.
Anode 2H2O - 4e = O2 + 4 H+
The oxygen that is produced in this half of the reaction is safely vented to atmosphere from the back of the generator. The four hydrogen ions that have been produced then pass through the ion exchange membrane (attracted by the negatively charged cathode) and collect four electrons reducing them to two hydrogen molecules.
Cathode 4H+ + 4e = 2H2
The hydrogen gas produced is separated from the oxygen by the ion exchange membrane, which is impervious to molecular oxygen.
Why use a Hydrogen gas generator?
Hydrogen gas generators are a safe, convenient and typically the more cost-effective alternative to using high pressure cylinders of H2. A hydrogen generator will provide hydrogen of a consistent purity, eliminating the risk of variation in gas quality, which can impact on analytical results.
A generator also produces gas on-demand around the clock, meaning that you don’t need to worry about running out of gas at an inopportune moment. A hydrogen generator will free up more of your time since you will not need to spend time ordering and changing out replacement cylinders.
A hydrogen generator is an environmentally friendly alternative to cylinders, since once it is installed, the generator will not need to leave the laboratory, providing gas for laboratory applications with all maintenance carried out in the laboratory. The generator also reduces your laboratory’s carbon footprint, since there is no need for trucks to deliver replacement cylinders and remove empty cylinders.
Hydrogen Carrier Gas
Many labs are now switching to hydrogen as a carrier gas as an alternative to helium, which is increasing in price year on year. Using hydrogen carrier gas can decrease average analysis time, increasing sample throughput, because hydrogen has a viscosity that is about half that of helium. Many labs can expect to halve their analysis time if they switch to hydrogen carrier gas.
Use of consumables, such as columns, can also be reduced when using hydrogen gas because of the lower elution temperature of products meaning that lower oven temperatures can be used, and in GC-MS, the frequency of ion source cleaning can be vastly reduced when using hydrogen carrier gas because hydrogen continually cleans the components of the ion source, meaning less downtime.
Many applications can use hydrogen as an alternative to helium carrier gas, such as FAMEs Analysis in foods, Detailed Hydrocarbon Analysis (DHA) and SIMDIST in Oil and gas, and methods such as EPA 8270 in Environmental analysis. Details of the key steps to changing carrier gas are outlined in here.
How can I change from cylinders to a generator with limited downtime?
The changeover is typically seamless. If you are switching from hydrogen gas cylinders to a generator, existing tubing can be disconnected from the cylinder and connected to the generator, using SwageLok fittings. If you are changing from helium to hydrogen, new tubing should be always used.
Is a hydrogen generator safe?
A Peak hydrogen generator stores less than 300cc gas, compared with cylinders, that store up to 9000 L at extremely high pressure (~2000-3000 psi). The Peak Hydrogen Gas Generator range produces gas on demand, meaning only the amount needed by the gas chromatograph (GC) is produced at regulated flow (0.5 L max) and pressure (120 psi max).
How safe is the generator?
A Peak Precision H2 gas generator is equipped with continuous internal and external leak checks in addition to an auto- shut down feature.
- Full diagnostic checks on start-up.
- Continuous pressure based leak check during operation.
- Automatic shutdown by isolation of the H2 generation cell
- Audio and visual alarms
- Forced ventilation throughout the generator
- Low Hydrogen gas throughout the system (< 0.3 L max.)
Should there be an internal leak, the generator will cease gas production and alert laboratory personnel via the HMI touchscreen, which will give a warning as well as an audible alarm. If there is a leak external to the generator, or its capacity is exceeded for 20 minutes, the generator will shut down to prevent build-up of hydrogen gas in the lab environment, or instrument supplied. The system will also shut down if the internal pressure exceeds 120psi.
Hydrogen gas generators eliminate the safety hazards involved with handling high pressure cylinders. Enjoy hassle-free GC analysis with no tanks to change and no downtime.
Our safety officers are concerned about H2 gas build-up and explosion in the lab, is this possible with a H2 gas generator?
Hydrogen is flammable between 4.1% and 78% in air. As an example, a Laboratory measuring 5 m x 4 m x 2.5 m has a volume of 50,000 L. For the lower explosive level (LEL) of 4.1 % Hydrogen gas to be reached, we would need 2050 L of hydrogen gas released into this laboratory space in 1 instant.
An average “G” sized H2 gas cylinder contains 9000 L of gas. Should a cylinder leak, it would need only to release 25 % of its total volume to reach the LEL in this laboratory.
A Peak Precision Hydrogen Trace 500cc generator produces 0.5 L per minute. To reach the LEL with this gas generator, it would need to be in a completely sealed space, not be connected to the GC/application or suffer a severe leak & have complete failure of all safety features. Even in this highly unlikely scenario, the generator would need to operate for 67 hours (~3 days) to reach the LEL.
Has any testing been conducted to evaluate the safety of Hydrogen generators?
Peak hydrogen generators carry the CE and CSA mark and have been externally tested to IEC standards for laboratory use and safety requirements for the residual risk for an explosion hazard. The evaluation was conducted under a worst-case scenario by dilution tests and an unoperated fan. The testing showed that the hazard risk for explosion does not exist, because the LEL of 4.1 % hydrogen was not reached under worst case conditions internally or externally to the generator.
Where should I install my generator?
The generator can reside safely in the laboratory on the bench, floor or under the GC auto-sampler. The stackable design of the Peak Precision range allows placement of the generators close to GCs or other applications. The generator should be located on a flat, level surface for operation.
Precision series gas generator stack to scale
Can I put the generator in a cupboard?
Adequate airflow must be maintained around the generator to allow the ventilation system to perform efficiently. If the generator is stored in an enclosed space the environment must be controlled via an air conditioner or extraction fan. The provision must be made to allow the volume of air in the room to be changed 5 times per hour.
The rear of the generator will become warm to the touch during operation - a minimum clearance of 15 cm (6”) from other bodies is recommended.
The vents should not be obstructed or connected to any application. Safe, forced removal of waste gases has been engineered into the generator to prevent any internal gas or pressure build-up.
Can I place the generator outside the laboratory?
This is possible as long as the recommended environmental conditions required for normal operation are met. Reducing the length of pipework will reduce costs if not already installed and the risk of any potential leaks in the pipework going undetected, improving the safety of the installation. If possible, the generator should be placed near or close (< 10 m) to the GC/application.
Do my GCs need to be ventilated?
If a customer wishes to use a fume extractor, or to connect tubing between the exhaust of the generator and a fume-hood, this is possible, but any hydrogen exhausted from the GC will quickly diffuse in the air and presents no danger to laboratory personnel or the environment. If tubing is attached to the exhaust ports of the generator, it is essential that this is monitored frequently, since any kinks could cause a build-up of gas and cause additional health and safety issues. The lower explosive limit (LEL) of hydrogen is 4.1 % and shown not to be reached by a Peak hydrogen gas generator.The majority of laboratory environment will not be completely sealed, with air conditioning in place, allowing air movement. If you have any concerns, Peak offers complimentary site evaluations, installation surveys and demonstrations.
Will I need hydrogen sensors in the lab or GC oven?
In the laboratory, the amount of hydrogen generated / exhausted into the laboratory is not enough to accumulate and reach the LEL of hydrogen. The risk of a significant build-up of gas in the GC oven is also extremely low, with both the external leak safety shutdown feature of the hydrogen generator and the GC inlet safety shutdown feature in place.
Should your laboratory, state government or business policy require regulation, sensors or monitoring- Peak can offer both external room and in GC oven monitoring sensors for complete peace of mind.
Sounds technical: How difficult are hydrogen gas generators to maintain?
Maintenance is very simple, cost-effective and does not require an engineer for regular maintenance. Simply re-fill the deionized water reservoir weekly. Preventive maintenance (PM) is required biannually - requiring deioniser cartridge swap over.
Peak also offer user training, Skype tutorials, PowerPoints, detailed user manuals, 24/7 phone technical support and field support. Click here to get in touch.
How many GCs can a single hydrogen generator supply?
As a typical rule of thumb, 100 cc will supply two FID detectors. Of course, the required generator will depend on flow rate, carrier gas type, column, other detectors and unique methods.
Your gas requirement calculator can be found here.
Or contact us for a consultative solution.
ROI - will it really be more cost effective?
Calculating the gas, delivery charges, cylinder rental charge, staff downtime time, administration, OHS measures and training, ROI is typically within 9 to 15 months.
What are the benefits of hydrogen generators over cylinders?
- Lower pressure = safer (1-100 psi at outlet)
- Controlled flow maintains safe hydrogen levels (up to 500 cc at outlet)
- Built-in leak sensors and automatic shut-down feature.
- On-demand production = minimal storage.
- Once installed – no need to move
- All maintenance carried out in the lab
- 24/7 operation – no need to monitor supply
- Reduce costs and admin – no repeat orders of gas
- Lower carbon footprint – greener option for your lab
Is it difficult to install a hydrogen generator?
Not at all. Simply remove packaging, connect an external UV protected deionized water bottle (at same height or below the generator), connect to an electrical supply (10 Amp) and allow to reach room temperature. Connect to your GC using 1/8” pre-cleaned (gas purged) refrigerant grade copper or stainless steel pipe.
What piping do I need?
Supply of hydrogen gas should be provided through stainless steel or analytical grade copper tubing using Swagelok compression fittings. It is important to change the tubing that was previously used to supply helium to the GC, since over time, deposits can build up on the inside of the tubing which hydrogen will carry to the application, causing higher background signal for a longer period of time.
For any connections, Swagelok compression fittings are the recommended solution to connect copper or stainless steel tubing. No chemical bonding (such as Loctite), welding or glues should ever be used, since this can introduce volatile organic compounds (VOCs) into the gas supply, which can impact on results.
When running lines >3m it may be necessary to use 1/4" piping reduced to 1/8" to supply each GC. This increases the volume considerably and can make installation more difficult.
For lines >10m between the generator and GC – please consult with Peak or your fitting specialists.
What water can I use for my hydrogen generator?
Peak recommend deionized water (DI) of > 1 megohm resistivity / < 1 µS conductivity purity or better. If MilliQTM water is available at your facility, this is preferred. Peak do not recommend connecting the generator to a constant deionized water supply.
For further local technical, service or advice:
Contact your local technical helpdesk
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