Why is Hydrogen Difficult to Compress?

Hydrogen is increasingly seen as a promising fuel for the future, offering a clean energy alternative to fossil fuels. However, one of the major challenges in using hydrogen is compressing it for storage and transport. Compressing hydrogen is much more complex than compressing other gases like air or natural gas. Here’s why hydrogen is so difficult to compress:

Hydrogen’s Atomic Size

Hydrogen is the smallest and lightest molecule in the universe, consisting of just one proton and one electron. This small size is what gives hydrogen its high energy density, but it also makes it very difficult to contain and compress.

• Small Molecular Structure: The molecules in hydrogen are much smaller than the components of air, such as nitrogen (N2) and oxygen (O2), or even compressed natural gas (CNG). This makes hydrogen more prone to escaping through traditional seals and valves used in standard gas compressors.
• Leakage and Permeation: Because of its tiny size, hydrogen can easily leak through even the smallest gaps or weaknesses in the materials that make up compressor systems. Standard compressors are not designed to contain such a small molecule, leading to high rates of leakage and inefficiency.

High Pressure Requirements

In most hydrogen applications, the gas needs to be compressed to extremely high pressures, sometimes exceeding 700 bar (10,000 psi). This is far higher than the pressure required for standard gases like air, which adds another layer of difficulty.

• Exacerbated Permeation: The higher the pressure, the more likely hydrogen is to permeate through seals, valves, and other containment components. This increased pressure exacerbates the problem of leakage, which is already a significant challenge due to the small size of hydrogen molecules.

Oil-Free Compression

In many hydrogen applications, especially in fuel cells and chemical processes, the gas must remain oil-free. Standard compressors often use lubricants to seal gaps and reduce friction. However, in hydrogen systems, oil contamination is unacceptable.

• No Lubrication: Without lubricants, maintaining an airtight seal becomes much more difficult. Special attention must be given to the design of seals and components to ensure that hydrogen remains contained without the use of oil, which adds another layer of complexity.

Hydrogen’s small atomic size, its tendency to leak at high pressures, and the need for oil-free operation make it particularly challenging to compress. Specialized technologies and designs, such as hydrogen compressors are needed to effectively and safely compress hydrogen for storage and transport, making it a much more complex task than compressing other gases like air or natural gas.

Come back in a couple weeks for part 2 in our Hydrogen series: How Are Hydrogen Compressors Different from Standard Air Compressors?

 If you have any questions, please contact and expert today.