To separate hydrogen gas (H2) from water gas (a mixture of hydrogen gas and carbon monoxide), several methods can be employed. Here are a few common techniques:
Water-Gas Shift Reaction: The water-gas shift (WGS) reaction is commonly used to convert carbon monoxide (CO) and water vapor (H2O) into hydrogen gas (H2) and carbon dioxide (CO2). This reaction occurs at high temperatures in the presence of a catalyst, such as iron or chromium oxide. The WGS reaction can be utilized to selectively produce hydrogen gas from water gas.
Pressure Swing Adsorption (PSA): PSA is a cyclic adsorption process that can be used to separate hydrogen gas from water gas. The water gas is passed through an adsorbent bed, typically containing materials like zeolites or activated carbon, which selectively adsorb carbon monoxide and other impurities. The hydrogen gas passes through and is collected, while the adsorbed impurities are subsequently desorbed by reducing the pressure or changing the gas flow direction.
Membrane Separation: Membrane separation processes utilize selective permeable membranes to separate hydrogen gas from water gas. These membranes can allow the smaller hydrogen molecules to pass through while obstructing larger molecules like carbon monoxide. There are various types of membranes used, including polymeric membranes, ceramic membranes, and palladium membranes, each with its own advantages and limitations.
Cryogenic Separation: Cryogenic separation is another technique to separate hydrogen gas from water gas. The water gas mixture is cooled to very low temperatures, typically below the boiling point of hydrogen (-252.87°C or -423.17°F), causing the hydrogen gas to condense into a liquid. The condensed hydrogen can then be collected separately, while the remaining gases, including carbon monoxide, remain in the gaseous phase.
Selective Absorption: Selective absorption processes involve using specific solvents or absorbents that selectively absorb carbon monoxide from water gas while allowing hydrogen gas to pass through. The absorbed carbon monoxide can be subsequently desorbed, while the purified hydrogen gas is collected.
These methods offer different advantages and can be employed based on the specific requirements, scale, and cost considerations of the hydrogen separation process. The choice of method depends on factors such as purity requirements, efficiency, energy consumption, and the presence of other impurities in the water gas mixture.