Investigation of the influence of tar-containing syngas from biomass gasification on dense Pd and Pd–Ru membranes

• Biomass gasification integrated with membrane separation was studied.
• Hydrogen sulfide was not detectable before and after the membrane separation.
• Tar-free syngas caused an appreciable permeation drop through Pd-based membranes.
• Syngas containing tar caused a rapid and significant permeability decline.
• FTIR spectra revealed that the membrane surface organics was PAHs.

The influence of tar-containing synthesis gas (syngas) from a 2 MW biomass gasification plant on dense Pd and Pd–Ru composite membranes was investigated. A slip stream from the product gas was subjected to tar capture, removal and syngas scrubbing before entering a custom-made membrane test unit. The concentration of hydrogen sulfide between the syngas scrubbing and membrane test unit was below the detection limit. Tar sampling analysis showed a total tar concentration of 240 mg/m3, with polycyclic aromatic hydrocarbons contributing more than half. The experimental test showed that there was appreciable influence of tar-free syngas on the permeabilities of both the Pd and Pd–Ru membranes. Inhibition of syngas containing 120 or 240 mg/m3 tar on the membranes resulted in a rapid decline in permeation flux. SEM and EDX analysis showed that surface organics blocked hydrogen adsorption and mass transfer in the membranes. FTIR spectra revealed that aromatic compounds such as naphthalene were most abundant in the surface contamination. Oxidation by air at high temperature partially restored the membrane permeability.

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