The Combined Impact of Ni-Based Catalysts and a Binary Carbonate Salts Mixture on the CO2 Gasification Performance of Olive Kernel Biomass Fuel

Abstract

In the present work, the individual or synergistic effect of Ni-based catalysts (Ni/CeO2, Ni/Al2O3) and an eutectic carbonate salt mixture (MS) on the CO2 gasification performance of olive kernels was investigated. It was found that the Ni/CeO2 catalyst presented a relatively superior instant gasification reaction rate (Rco) compared to Ni/Al2O3, in line with the significant redox capability of CeO2. On the other hand, the use of the binary eutectic carbonate salt mixture (MS) lowered the onset and maximum CO2 gasification temperatures, resulting in a notably higher carbon conversion efficiency (81%) compared to the individual Ni-based catalysts and non-catalytic gasification tests (60%). Interestingly, a synergetic catalyst-carbonate salt mixture effect was revealed in the low and intermediate CO2 gasification temperature regimes, boosting the instant gasification reaction rate (Rco). In fact, in the temperature range of 300 to 550 °C, the maximum Rco value for both MS-Ni/Al2O3 and MS-Ni/CeO2 systems were four times higher (4 × 10−3 min−1 at 460 °C) compared to the individual counterparts. The present results demonstrated for the first time the combined effect of two different Ni-based catalysts and an eutectic carbonate salt mixture towards enhancing the CO production rate during CO2 gasification of olive kernel biomass fuel, especially in the devolatilization and tar cracking/reforming zones. On the basis of a systematic characterization study and lab-scale gasification experiments, the beneficial role of catalysts and molten carbonate salts on the gasification process was revealed, which can be ascribed to the catalytic activity as well as the improved mass and heat transport properties offered by the molten carbonate salts.