SCHEDULED MAINTENANCE
Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors†
Abstract
The effectiveness of hydrogen-permselective palladium membrane reactors for non-oxidative methane dehydroaromatization (MDA) over 4 wt% Mo/HZSM-5 catalysts was investigated as a function of weight hourly space velocity (WHSV) at 700 °C and atmospheric pressure. CH4 conversion and aromatic product yield decrease with increasing WHSV from 750 to 9000 cm3 gcat−1 h−1. C6H6 is the main C-containing product at and below 3000 cm3 gcat−1 h−1 whereas C2H4 dominates the C-product distribution at higher WHSVs. Due to selective removal of H2 from the reaction products in catalytic membrane reactors, C6H6 yield is significantly improved over the whole WHSV range compared to those obtained in fixed-bed reactors. H2 recovery is strongly influenced by WHSV as it decreases from 48.3% at 750 cm3 gcat−1 h−1 to 6.8% at 9000 cm3 gcat−1 h−1. There exists a trade-off between catalytic activity and H2 recovery, which results in the maximum enhancement (~360%) in C6H6 yield at 3000 cm3 gcat−1 h−1. At this intermediate space velocity, the largest concentration of H2 is found in the retentate stream and helps alleviate coke accumulation particularly on HZSM-5. Carbon is deposited on the inner surface of the membrane reactor portion in contact with the catalyst bed and transports to the outer surface, thus causing H2 permeability to decrease over the 15 h reaction period.
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