Plug hydrocracking

Table IV presents some data on liquid residence time distributions measured under conditions of hydrocracking in trickle flow. It can be seen that bed dilution with fine inert particles results in a considerable improvement in the plug-flow character of the reactor, which supports the idea that the dispersion is largely determined by the packing of fine particles. Since in the range of Re numbers of interest the Bodenstein number is approximately a constant (see Figure 4), the Peclet numbers for beds of equal length should be inversely proportional to the particle diameter. Dilution of the 1.5 mm particles with 0.2 mm particles should raise Pe by a factor of about 7, which is approximately in line with the data in Table IV.

Residuum hydroconversion is a special case of hydrocracking. Compared to distillate hydrocracking, a significantly different catalyst is used, frequently low metal loading with Mo, with a special pore size distribution less subject to pore plugging by coke. More... 

A Ci6 hydrocracking model with 465 species and 1503 reactions was built automatically in only 14 CPU seconds on a Pentium Pro 200 PC. The corresponding plug flow reactor (PFR) model with molar expansion was then... 

Hydroprocessing - especially hydrocracking - is exothermic. Effective control of produced heat is the primary concern of designers, owners and operators of hydrocracking units. In modem units, a high flux of recycle gas provides a sink for process heat. It also promotes plug flow and the transport of heat through the reactors. Most licensors recommend that the ratio of recycle gas to makeup gas should exceed 4 1. 

When a hydrocracker is operated with recycle of the unconverted feed, PNA with more than seven benzene rings are created. These are called HPNA (heavy polynuclear aromatics). The consequences of PNA formation are shown in Figure 13. The HPNA produced on the catalyst may exit the reactor and cause downstream fouling or they may deposit on the catalyst and form coke, which deactivates the catalyst. Their presence results in plugging... 

Galiasso, R., Caprioli, L. 2005. Catalyst pore plugging effects on hydrocracking reactions in an ebullated bed reactor operation. Catal. Today 109 185-194. 

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