Methanol Purge Gas Applications

Methanol is produced from syngas typically derived from coal or natural gas. Methanol in turn serves as a raw material to a whole host of industrially important products, such as formaldehyde, acetic acid, dimethyl terephthalate, gasoline, etc.

Syngas employed for methanol comprising principally carbon monoxide (CO), carbon dioxide (CO₂) and hydrogen (H₂) is fed to a catalytic reactor. The reactor offgas is cooled to condense product methanol and yield a reactor purge gas stream. This gas stream contains unreacted H₂, CO and CO₂. Also present are methane (CH₄), N2 and depending on the source of the syngas, argon (Ar). Removal and recovery of hydrogen has been shown to increase methanol production between 2-4%, which in large plants is quite significant. Air Liquide Advanced Separations' (ALaS) membranes placed in the reactor purge gas loop downstream of the methanol separator recover 80-90% of the H₂ in the gas stream. H₂ is recycled back to the syngas compressor loop, while the residue gas rich in CO, CH4 is purged by way of the fuel gas header. ALaS offers a range of high performing polyaramide and polyimide membrane products for customers to consider. Utilizing ALaS membranes in a methanol reactor purge gas loop recovers and profitably utilizes H₂; customers are able to realize increased methanol production as almost soon as the membrane unit is started up. 

Hydrogen (H₂) is selectively separated from methane (CH₄), nitrogen (N₂) and argon (Ar) by permeation through a polymeric hollow fiber membrane. The driving force is the partial pressure difference across the membrane for H₂ , CH₄ and other gas components. H₂ is the “fast” gas, whereas inerts are the “slow” gases. The pressurized feed gas enters the bundle from the shell side; the syngas stays under pressure while the H₂ is collected at a lower pressure from the fiber bore.

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Paul Terrien, Director, Hydrogen and Helium Membrane Business Units
Contact by phone +1 781-228-3261