Performance comparison between washcoated and packed-bed monolithic reactors for the low-temperature Fischer-Tropsch synthesis
Washcoating and packing of Co-Re catalyst particles have been employed as structuring methods of parallel channel monoliths used in the low-temperature Fischer-Tropsch synthesis (FTS). These methods were compared with regard to catalyst hold-up, heat transfer properties and pressure drop. Reactors output was assessed in terms of CO conversion, CH4 selectivity and productivity of C5+ hydrocarbons. Washcoating led to much lower pressure drops, but also resulted in considerably lower catalyst inventory. As for the reactors performance (volumetric and per catalyst mass C5+ productivities), the washcoated monoliths were more effective than the packed-bed ones. This has been attributed to their more favorable hydrodynamic behavior that facilitates the drainage of the reaction products (liquids and waxes) through the central hollow of the channels thus reducing the extra-pellet diffusional limitations. For both catalyst configurations, it has been found that the productivity of C5+ per catalyst mass unit increases as the characteristic diffusion length increases within the range of values considered in this study (below 150 µm). This indicates that a moderate level of internal mass transport restrictions is beneficial for the low-temperature FTS, which has been explained in terms of the effects of diffusional limitations on the H2/CO molar ratio, and that of this ratio on the FTS kinetics. The possible influence of thermal effects on these results has been numerically and experimentally discarded. ; Financial support of this work was undertaken by the Basque Government (IT1069-16) and the Spanish Ministerio de Ciencia, Innovación y Universidades and the European Regional Development Fund (ERDF/FEDER) (grants RTI2018-096294-B-C31, RTI2018-096294-B-C32 and CTQ2015-73901-JIN). Open Access funding provided by University of Basque Country. Luis M. Gandía wishes to thank Banco de Santander and Universidad Pública de Navarra for their financial support under the 'Programa de Intensificación de la Investigación 2018' ...