From Basics to Breakthroughs: Understanding Hydrogen Purification

Hydrogen fuel is a versatile and efficient energy source that is seeing increasing adoption across market segments and use cases. An important part of using hydrogen is ensuring it’s been purified to an acceptable extent, which minimizes risks associated with hydrogen fuel cells.

And, just as there are multiple hydrogen production methods, there are also several approaches to purifying it.

Below, we’ll break down everything you need to know about purification:

• Importance of hydrogen purity
• Common hydrogen purification methods
• The challenges of hydrogen purification
• Hydrogen purification best practices

First, let’s take a deeper look at the purification of hydrogen gas.

Why Hydrogen Purity Matters

Hydrogen purity is crucial for several reasons, particularly in its applications across various industries such as energy, automotive, electronics, and chemical manufacturing.

• Fuel Cell Performance and Lifespan: In the automotive industry, especially for fuel cell electric vehicles (FCEVs), hydrogen purity directly affects the performance and longevity of the fuel cell. Contaminants such as carbon monoxide, sulfur compounds, and even water vapor can poison the fuel cell catalyst, reducing its efficiency and lifespan. High-purity hydrogen ensures fuel cells operate optimally, maximizing power output and vehicle range.
• Safety: Hydrogen, being a highly flammable gas, requires strict purity standards to ensure safety during storage and handling. Impurities can affect the flammability range of hydrogen gas mixtures, potentially leading to unsafe conditions. Ensuring that hydrogen is of a high purity minimizes risks associated with its flammability and reactivity.
• Chemical Processes: In industries where hydrogen is used as a reactant, such as ammonia production or hydrogenation processes, the presence of impurities can affect the reaction rates, yields, and product purity. High-purity hydrogen is essential to achieve the desired outcomes efficiently and to protect catalysts from deactivation caused by contaminants.
• Energy Efficiency: The efficiency of hydrogen production and utilization processes, including electrolysis and combustion, can be significantly impacted by the presence of impurities. High-purity hydrogen allows for more efficient energy conversion, reducing waste and improving overall system performance.
• Cost-Effectiveness: Although producing high-purity hydrogen can be more costly upfront due to the need for purification processes, it ultimately leads to cost savings by prolonging equipment life, reducing maintenance needs, and improving process efficiencies.

Leading Technologies in Hydrogen Purification

To take advantage of the benefits of hydrogen fuel, stakeholders across industrial niches first need to purify hydrogen gas. At present, there are three approaches commonly used to do so.

1. Pressure Swing Adsorption (PSA)

This is the most prevalent method across hydrogen plants. It works by leveraging properties of hydrogen, such as its affinity for select materials, to separate contaminants from it. Under high pressure, gasses become bonded onto solid surfaces. PSA forces other gasses to un-trap the desired output (i.e., H2) by forcing another gas to adsorb into these same solids and displace it.

Per an overview of H2 purification technologies presented by the US Department of Energy’s Advanced Research Projects Agency - Energy (ARPA-E), this method can produce hydrogen at a purity of up to 99.9999%. It’s also widely applicable because it removes impurities at pressures close to ambient pressure, and it’s suitable for nearly any context regardless of size or capacity.

2. Membrane Technologies

In this approach, hydrogen is passed through a metal membrane. It works like a filter, with hydrogen diffusing at the molecular level and passing through membranes made of select materials such as silver and palladium. Per the ARPA-E presentation cited above, these methods can output H2 at low pressure with purity of about 95% to 98%. Membranes are inexpensive, but additional compressors may be required; this method is best for small-scale H2 purification.

3. Cryogenic Separation

Similar to PSA, this approach leverages the innate properties of hydrogen—in this case, its extremely low boiling point (-253 °C). Since a majority of unwanted impurities have higher boiling points, they are shed by the hydrogen as they boil (and it does not). Per one study, cryogenic hydrogen purification can reach recovery rates of 95% and purity of 90% to 98%.

The authors also note that this approach is especially apt for large-scale purification.

Challenges in Hydrogen Purification

Just as challenges in hydrogen production lead to several different colors of hydrogen, there are many pitfalls organizations fall into when attempting to streamline hydrogen purification.

Controlling Contaminants

Hydrogen gas can harbor many different contaminants, and the same methods may not work for all of them at once. For example, common impurities found in hydrogen fuel include:

• Compounds of hydrogen and carbon (hydrocarbons)
• Halogenated compounds (containing F, Cl, Br, I, At, or Ts)
• Sulfur, such as in the form of hydrogen sulfide
• Formaldehyde (CH₂O)

The main challenges revolve around controlling for the specific kinds of contaminants in an organization’s hydrogen stores based on their climate, supply chain, and other factors. The ARPA-E presentation notes that, in many cases, a hybrid solution (PSA + membrane) is ideal.

Scaling Purification Processes

The various hydrogen purification processes noted above have different use cases with respect to resource costs and output capacity. Cryogenic methods, for example, have a lower barrier to entry. However, unlike the other methods, they require additional infrastructure to operate efficiently, making themthey require additional infrastructure to operate efficieydrogen fuel as an energy source, it’s important to consider its full potential for your company in the long run. PSA might make sense sooner rather than later.

Best Practices for Hydrogen Purification

Ultimately, the ways and scale at which your organization plans to utilize H2 fuel will dictate which purification methods work best. Maintaining whatever system you use comes down to the following.

Regular Maintenance and Monitoring

Regardless of which purification method(s) you use, you’ll need to allocate resources to routine performance monitoring maintenance. For PSA and cryogenic systems, these processes are more involved due to the larger scale of equipment. And, although there are fewer (large) moving parts in a membrane system, you’ll need to ensure membranes work over time.

Plus, beyond maintaining the machines and materials used for hydrogen purification, there’s broader energy infrastructure maintenance to account for. Storage facilities, dispensers, and the electric, plumbing, and other infrastructural underpinnings of the system need ongoing care.

Safety and Security Implementation

While many of the public’s fears about the safety of hydrogen fuel are misguided, there are certain precautions that need to be taken in all handling, storage, and use of H2. Hydrogen itself is flammable, and safe H2 use requires minimizing the confluence of ignition, oxidants, and fuel.

But the byproducts of purification are also dangerous—and often a much bigger concern than the purified hydrogen itself. For example, exposure to hydrocarbon compounds can result in dramatic negative effects on individuals, such as narcosis, cardiac arrest, and severe aspiration.

Organizations must practice extreme caution, monitoring and controlling zones where harmful substances may linger. Working with an infrastructural partner can minimize risk.

The Future of Hydrogen Purification

Looking ahead, further innovation into PSA, membrane, cryogenic, and hybrid methods for hydrogen purification will maximize output and impurity while minimizing operational costs and other challenges. This, in turn, will make it easier for more companies and end users to take advantage of carbon-neutral fuel—accelerating our journey to renewable energy resilience.

FASTECH is committed to helping organizations leverage the efficiency of purified hydrogen fuel with our suite of renewable energy engineering, procurement, and construction (EPC) services.

To learn how we can help you purify and leverage hydrogen, get in touch today!