Biomass Gasification Syngas Cleanup: Development of a Novel Nickel-Ceramic Filter for Reforming of Tar Model Compound, Naphthalene

Abstract

Biomass gasification has come to the forefront as a promising route for renewable energy to combat climate change and the increasing demand for energy worldwide. To increase the commercial viability of this technology, a novel process intensification approach has been proposed, developed, and evaluated for hot gas filtration of syngas that couples tar reforming and particulate removal operations into one unit. This dissertation investigates the synthesis and performance of a novel nickel-ceramic filter for tar and particulate removal from biomass syngas. A bench scale reactor was designed and fabricated to perform the tar reforming studies using naphthalene as a simulant tar molecule. Catalysts were evaluated at temperatures of 650°C-750°C, steam/carbon molar ratio of 0-7.5, residence time of 0.046 s, and an inlet naphthalene concentration of 8.4 g/m³ to mimic typical fluidized bed gasifier outlet conditions. A traditional incipient impregnation technique was used to produce catalytic ceramic filters with nickel loadings of 0-40 wt%, which were able to achieve 76% and 79% naphthalene conversion at loadings of 15 wt% and 40 wt%, respectively. To further improve the efficiency a urea vacuum impregnation technique was employed. Using this technique, a 15 wt% catalytic filter was able to achieve a naphthalene conversion of up to 82%. A Particle-induced X-ray emission analysis was performed that revealed the increased catalytic activity was most likely due to increased dispersion and greater penetration of nickel into the ceramic filter pores. An estimated activation energy of 126.4 𝑘𝐽/𝑚𝑜𝑙 was determined for this catalytic filter. The urea impregnated filter was able to outperform the traditionally impregnated filter at all conditions tested. This included varying steam/carbon ratio (0-7.5), temperatures (650-750°C), and experimental time duration. In a long-term study the urea impregnated filter achieved a naphthalene conversion of 92%, while maintaining a steady pressure drop. Naphthalene removal efficiencies as high as 97% were achieved when the residence time was increased to 0.092 s for the catalyst synthesized by urea impregnation method, which presents a promising potential for the commercial use of nickel-ceramic filters for syngas cleanup applications and beyond warranting further investigation.