Transient Operation of a Perovskite Partially Coated Monolith at High Pressure.

This work deals with the experimental study of transient ignition during high-pressure combustion of CH4-enriched syngas. The structured catalyst is a monolith (cordierite 900cpsi, L=50 mm, d=12 mm) where only the external channels are coated with 20wt%LaMnO3/La-?Al2O3. In previous studies, this novel core-shell configuration has shown the opportunity to get complete methane conversion thanks to the occurrence of homogeneous reactions also in the uncoated central channels. Here, homogeneous combustion is stabilized by catalytic combustion occurring in the external channels. In this work, experimental tests were carried out under high pressure conditions (up to 9 bar) at two catalyst coating degrees (80 % and 65 %), and results in terms of performances during the transient phase were compared to those obtained with the fully coated monolith (100 %). The impact of CO2 concentration were investigated by keeping the same heating value at H2/CO ratio equal to 1.56 and total flow rate equal to 60 slph. It has been found that the time required to reach ignition increases as the coating degree decreases. The longer time is related to the time required by homogeneous reaction to be activated and stabilized in the uncoated channels. The CO2 content in the feed mixture retards ignition due to its adsorption over the catalyst surface at temperature lower than 600 °C which negatively affects the catalytic reaction. It has been demonstrated however that CO2 progressively desorbs during the run away phase due to the temperature increase.