PTQ Q4 2025 Issue

80%

70%

200 ppm

HT E HT F HT G HT H

HT F HT G HT H HT D

HT A HT B HT C HT E

HT A HT B HT C HT D

TOS (day)

Figure 3 Left panel: N slip for pretreatment reactors. Right panel: apparent conversion for hydrocracking reactors

of the catalyst set is abbreviated as ‘HT X’. The following hydrocracking reactor is then represented as ‘HC X’; for instance, ‘HT A’ is the pretreatment reactor of ‘HC A’ (HC reactor of ‘A’). The N slip and the conversion of the heavier part of the oil were measured daily (Figure 3). The first five days were used to run all reactors at 650°F to allow them to line out. In a test programme defined by CITGO, the objective of the first condition was to compare the performance of each catalyst to the others at the same temperatures. This made it possible to obtain some preliminary activity information. For the first two conditions, the pretreatment catalysts worked at a target temperature, and not at a target N slip, and the same holds true for the hydrocracking catalysts. It is therefore possible to observe it from TOS 5 to 10, based on the range of measured N slips spanning between 200 and 500 ppm. The temperature in HT A and HT D was increased by 10°F at TOS 16 in order to prevent the pos - sible passivation of the active sides from relatively high N content (HT A-500 ppm and HT D-400 ppm).

At the same TOS, the temperature of the hydrocracking catalysts that were observed to be working at a lower con- version (HC B, HC C, and HC F) was increased by 10°F. Conversely, the temperature of the catalysts that were working at a higher conversion (HC G, HC E, and HC H) was decreased by 10°F. The temperature of the two reac - tors exposed to a higher N slip was not changed to allow them to recover in terms of activity. These two conditions were used not only to gather some preliminary insight into the relative activity of each system in comparison to the others, but also to make more robust adjustments for the last two conditions. The catalysts were ultimately compared to one another at a target constant N slip of 200 ppm and two different conversion levels, which correspond to the two extreme operational limits of the refinery. In this context, the refinery was also limited by design in the maximum temperature at which the catalysts could be operated. The temperatures of catalysts D and A needed to be increased quite significantly just to make them active at the lowest conversion limit.

200 ppm

HT E HT F HT G HT H

HT A HT B HT C HT D

HT E HT F HT G HT H

HT A HT B HT C HT D

10 %

10 ppm

Temperature (˚F)

Figure 4 Activity plot for pretreatment catalysts (left) and hydrocracking catalysts (right)

PTQ Q4 2025