Analysis of the reduction kinetics of a Fischer-Tropsch Co/TiO2 catalyst using temperature programmed reduction: the implications and applications to industry

摘要

Reduction is a critical step in catalyst preparation in chemical processes.udStability, activity and selectivity of catalysts are affected when certainudparameters, such as temperature and water partial pressures, are notudcontrolled during reduction.udThe main objective of this work is to use information from TemperatureudProgrammed Reduction (TPR) that is both quantitative and qualitative, basedudon the existing literature, experimental data, and the researcher’sudassumptions, to understand the implications of the reduction conditions onudcatalyst in an industrial fixed-bed reactor. This investigation has been carriedudout using simple mass balance calculations; evaluating reduction parameters;uddeveloping and applying methods of kinetic analysis and modeling, for audbetter comparative insight into real operating conditions.udA Co/TiO2 catalyst used in Fischer-Tropsch (FT) synthesis of hydrocarbonsudfrom syngas generated by reforming natural gas and/or coal has been usedudto illustrate this analysis. The catalyst was prepared by incipient wetness.udivudTo obtain accurate results for kinetic analysis, a custom-built TPR wasudmodified and optimized. The parameters used in the analysis to determineudthe position of the maximum rate and shape of H2 consumption peaks wereudalso optimized.udSimple mass balance calculations were made on TPR system to determineudthe rate of reduction and P during the process. This information (andudrelevant literature on the subject) was used to evaluate the implicationsudP on catalyst reducibility in a 12m long tube.udTo evaluate the effect of different parameters on catalyst reducibility, flowudrate, ramping rate, catalyst grain size and drying time prior to reduction wereudstudied. It was found that heating rate and drying time prior to reduction had audsignificant impact on catalyst reducibility.udIt has been established that a lower ramping rate maximizes the extent ofudreduction to active Co metal at low temperatures, while at the same timeudensuring an equilibrium particle size which is stable against sintering.udvudThe study of the effect of water content in the catalyst prior to reduction led toudthe conclusion that it has a significant effect on catalyst reducibility. However,udto arrive at a more conclusive explanation of the effect it was recommendedudthat further FT experiments should be performed on the catalyst with varyingudamounts of water content to investigate the effect, not only on the reducibilityudbut also the activity and selectivity of the catalyst.udIt has been shown that kinetic analysis using TPR can be used to determineudthe optimum reduction temperature among those that occur at differentudstages (in the case of multi-step reduction). These can then be used toudpredict the amount of H2 that will be consumed with increasing temperatures.udFurthermore, this study has established that the mechanism of reductionudobtained from kinetic analysis can help understand the degree of reductionudobserved at various temperatures. It can also contribute to an explanation ofudthe stages of reduction and underlying gas-solid reactions, which in turnudmake it useful as a guide to monitor and control P throughout the reductionudprocess in a 12m long tube.