Correlation between structure and performanceof vacuum gas oil hydrocracking catalysts in a batch reactor
Résumé
In order to satisfy the future demand in light and intermediate oil products, refining industry is facing new challenges because of the rarefaction of light and easily exploitable petroleum resources. It needs to upgrade heavier oils through high selectivity conversion processes, such as hydrocracking, while respecting ever more stringent regulations. Thus, the behavior of hydrocracking catalysts needs to be better understood and in order to improve their performance. Relationships between the composition, the structure of the catalysts and their performance are to be investigated. A new approach for studying and modeling complex reaction kinetics with a batch reactor test has been developed. A batch reactor apparatus was therefore developed. Triphasic reactions then took place in a laboratory-scale reactor equipped with a Robinson-Mahoney stationary basket, a hydrogen injection system and liquid/vapor sampling system. Feedstock was a hydrotreated vacuum gas oil, and reaction conditions were 400°C and 120 bars. Different bifunctional catalysts sulfide nickel-molybdenum on a zeolite-containing alumina support were characterized and tested over 3 hour and 6 hour-reactions. Gas and liquid samples were then analyzed by one and two-dimensional gas chromatography, in order to obtain precise composition of each phase during the reaction. The repeatability of conversion and middle distillate selectivity under the test conditions described above was under 1.5 and 1.6%, respectively. The lack of mass transfer limitations at vapor-liquid interface and at liquid-solid interface was confirmed by modifying the stirring speed and the size of the catalyst pellets. This method therefore allows accessing to intrinsic kinetic properties of the catalysts. Afterwards, an experimental design was set up, with the purpose to test catalysts containing different amounts of molybdenum and zeolite. The effects of the bifunctional structure of the catalyst on its reactivity and its selectivity have been observed and discussed.