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Hydrogen Purification

Hydrogen Purification
Hydrogen Purification

In this blog post today, we explore the exciting field of hydrogen purification. In order to achieve exceptionally high purity levels, this vital step requires the rigorous elimination of impurities and pollutants from hydrogen gas. The importance of hydrogen purification cannot be understated because it is essential to making hydrogen appropriate for a wide range of industrial applications, from supplying energy to cutting-edge hydrogen fuel cells to meeting the strict criteria of the chemical sector. Come along as we examine the details of this hydrogen purification procedure and learn why even the slightest amounts of pollutants can have a significant influence on the functionality and security of hydrogen-based systems.

Hydrogen (H2) has garnered significant attention as a promising future energy source due to its high energy density and environmentally friendly attributes. However, the production, utilization, and storage of H2 pose numerous technical challenges that must be overcome to establish a sustainable hydrogen economy. One particularly crucial aspect is the frequent need for high-purity H2, essential for its efficient use as a clean fuel. Achieving this requires energy-efficient and cost-effective purification processes and materials. Moreover, the separation of valuable hydrogen isotopes like deuterium (D) and tritium (T), which share similar physical and chemical properties, is not only a challenging endeavor but also of paramount importance due to their high demand in industrial, medical, and scientific research, despite their limited natural occurrence.

Recently, porous crystalline metal-organic frameworks (MOFs) have emerged as a promising solution for frequent hydrogen purification and isotope separation. Their appeal lies in their designable porosity and functionality, which enable molecular sieving effects as well as kinetic and/or chemical affinity quantum sieving effects. By carefully selecting metal ions and organic ligands during the rational design and synthesis process, MOFs can be tailored to possess specific properties and functionalities. This results in precise control over their structural topology, pore size, shape, and surface polarity. This review aims to provide a comprehensive understanding of the fundamental theories and strategies associated with MOF-based hydrogen purification, including representative examples of hydrogen isotope separation.

Hydrogen purification methods

For many industrial operations, such as the creation of fuel cells, ammonia synthesis, and petrochemical refinement, hydrogen purification is crucial. High-purity hydrogen gas is produced by using purification techniques to remove contaminants. Here are a few popular ways to purify hydrogen:

  1. Pressure Swing Adsorption (PSA): PSA, or pressure swing adsorption, is a popular technique for purifying hydrogen. It is based on the variation in the adsorption of pollutants like hydrogen and carbon dioxide, carbon monoxide, and methane on solid adsorbents under various pressures. While pollutants are desorbed and discharged, hydrogen is selectively adsorbed by cyclically adjusting the pressure.

  2. Membrane Separation: Indeed, membrane separation techniques are pivotal in hydrogen purification. These methods exploit differences in molecular size and permeability, enabling selective passage of hydrogen molecules through semi-permeable membranes while obstructing contaminants. Various types of membranes, including polymer, palladium, and metal alloy variants, find common applications in hydrogen purification processes, ensuring the production of high-purity hydrogen for various industrial applications.

  3. Cryogenic Distillation: In the context of hydrogen purification, cryogenic distillation is a key process. It's employed to liquefy hydrogen by cooling the feed gas to exceptionally low temperatures (below its boiling point of -252.87°C or -423.17°F). This extreme cold causes contaminants to remain in the gaseous phase while the hydrogen condenses into a liquid form. Consequently, hydrogen purification is achieved by physically separating the contaminants from the liquefied hydrogen, yielding a high-purity product.

  4. Chemical Absorption: Chemical absorption techniques are integral to hydrogen purification. To remove pollutants like CO2, H2S, or CO and achieve high-purity hydrogen for various applications, these methods employ absorbent solutions like amines. While hydrogen remains unreactive, the contaminants are chemically absorbed by the absorbent, facilitating hydrogen purification. Later, during a heating or regeneration step, the pollutants are released from the absorbent, leaving behind only pure hydrogen, a crucial step in hydrogen purification processes.

  5. Palladium membrane separation: Thin sheets of palladium or palladium alloy are used in palladium membrane separation, usually at high temperatures. In contrast to other gases like nitrogen and carbon dioxide, which are largely inhibited, hydrogen molecules dissolve into and diffuse through the palladium lattice in a unique way. The special capacity of hydrogen to form a solid solution within palladium, allowing it to flow through the membrane, is the foundation of this selective permeation. This procedure yields hydrogen that is incredibly high in purity, which makes it perfect for fuel cell applications where contaminants can reduce performance. For effective and long-lasting operation, precise temperature regulation and membrane integrity are essential.


How is hydrogen purified for fuel cells?

Hydrogen purification for fuel cells typically involves several steps, including:

  • Removal of impurities like sulfur compounds and moisture through desulfurization and drying processes.

  • Separation from other gases, often using a membrane or pressure swing adsorption (PSA).

  • Final purification through catalytic processes to remove any remaining impurities.

How do you purify hydrogen gas in a laboratory?

In a laboratory, hydrogen gas can be purified by passing it through various purification systems, such as:

  • A palladium membrane, which selectively allows hydrogen to pass while blocking other gases.

  • Pressure swing adsorption (PSA) units that adsorb impurities, allowing pure hydrogen to be released.

  • Chemical methods like scrubbing with chemicals that react with impurities.

How do you purify hydrogen from nitrogen?

To purify hydrogen from nitrogen, you can use a nitrogen-selective membrane or cryogenic distillation. A nitrogen-selective membrane allows hydrogen to pass through while retaining nitrogen. Cryogenic distillation involves cooling the gas mixture to extremely low temperatures to separate hydrogen from nitrogen.

What is the membrane for hydrogen purification?

Membranes used for hydrogen purification are often made of materials like palladium or polymer-based membranes with high hydrogen selectivity. These membranes allow hydrogen to pass through while blocking other gases.

What are 3 methods of generating hydrogen for use in a fuel cell?

Three methods for generating hydrogen for fuel cells include:

  • Steam methane reforming (SMR): It involves reacting natural gas with steam to produce hydrogen and carbon dioxide.

  • Electrolysis: Water electrolysis splits water molecules into hydrogen and oxygen using electricity.

  • Biomass gasification: Organic materials like biomass are converted into hydrogen-rich gas through high-temperature processes.

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