Hydroprocessing Process Conditions

The conditions under which a hydroprocessing unit operates is a strong function of feedstock. Typical processing conditions are shown in Table 5.2-8 for a variety of hydroprocesses [60]. 

Size characterization measurements have provided useful information on the importance of the hydroprocessing catalyst pore size distribution and on the effects of visbreaking and hydroprocessing on the residua molecular size distributions. It is apparent that asphaltenes and maltenes are not unique entities, but instead have considerable overlap in their size distributions. A complete study of the effects of processing conditions would require consideration of all components of a residuum. 

Effect of Process Conditions and Catalyst Properties on Catalyst Deactivation in Residue Hydroprocessing... 

A. L. Hensley, L, M, Quick, Effects of catalyst properties and process conditions In the selectivity of resid hydroprocessing, AIChE 88th National Meeting, (Philadelphia, 6/9-12/80), paper 51B, 1980. 

For fixed-bed hydroprocessing units, the process conditions - pressure, temperature, space velocity, and catalyst - are determined by feed quality and process objectives. Table 12 shows typical process conditions for the hydrotreating of different feeds in fixed-bed hydrotreating units. The values shown are approximate. 

In Section IV, the kinetics and mechanisms of catalytic HDM reactions are presented. Reaction pathways and the interplay of kinetic rate processes and molecular diffusion processes are discussed and compared for demetallation of nickel and vanadium species. Model compound HDM studies are reviewed first to provide fundamental insight into the complex processes occurring with petroleum residua. The effects of feed composition, competitive reactions, and reaction conditions are discussed. Since development of an understanding of the kinetics of metal removal is important from the standpoint of catalyst lifetime, the effect of catalyst properties on reaction kinetics and on the resulting metal deposition profiles in hydroprocessing catalysts are discussed. 

Hydrodemetallation reactions require the diffusion of multiringed aromatic molecules into the pore structure of the catalyst prior to initiation of the sequential conversion mechanism. The observed diffusion rate may be influenced by adsorption interactions with the surface and a contribution from surface diffusion. Experiments with nickel and vanadyl porphyrins at typical hydroprocessing conditions have shown that the reaction rates are independent of particle diameter only for catalysts on the order of 100 /im and smaller (R < 50/im). Thus the kinetic-controlled regime, that is, where the diffusion rate DeU/R2 is larger than the intrinsic reaction rate k, is limited to small particles. This necessitates an understanding of the molecular diffusion process in porous material to interpret the diffusion-disguised kinetics observed with full-size (i -in.) commercial catalysts. 

While the definitions of the various hydroprocesses are (as has been noted above) quite arbitrary, it may be difficult, if not impossible, to limit the process to any one particular reaction in a commercial operation. The prevailing conditions may, to a certain extent, minimize, cracking reactions during a hydrotreating operation. However, with respect to the heavier feedstocks, the ultimate aim of the operation is to produce as much low-sulfur liquid products as possible from the feedstock. Any hydrodesulfurization process that has been designed for application to the heavier oils and residua may require that hydrocracking and hydrodesulfurization occur simultaneously. 

Authentic and synthetic solvent-refined coal filtrates were processed upflow in hydrogen over three different commercially available catalysts. Residual (>850°F bp) solvent-refined coal versions up to 46 wt % were observed under typical hydrotreating conditions on authentic filtrate over a cobalt-molybdenum (Co-Mo) catalyst. A synthetic filtrate comprised of creosote oil containing 52 wt % Tacoma solvent-refined coals was used for evaluating nickel-molybdenum and nickel-tungsten catalysts. Nickel-molybdenum on alumina catalyst converted more 850°F- - solvent-refined coals, consumed less hydrogen, and produced a better product distribution than nickel-tungsten on silica alumina. Net solvent make was observed from both catalysts on synthetic filtrate whereas a solvent loss was observed when authentic filtrate was hydroprocessed. Products were characterized by a number of analytical methods. 

MCM-22 crystallizes in thin sheets or plates. Within these sheets, there is evidence of the existence of a buried T-site (a Si or A1 atom) in the framework structure that is not accessible to a channel wall. This buried T-site appears to be unique to MCM-22 and gives the zeolite structural stability even under severe conditions that would destroy other less-stable zeolites. MCM-22 has been actively studied and over 50 US patents have been issued on its use in varied areas, including hydroprocessing, aromatic/olefin alkylation, paraffin/olefin alkylation and dispro-portionation processes, as well as specialty chemical applications. 

The objective of this book is to serve as a practical reference work on testing for the main hydrocarbon-conversion processes applied in oil refineries catalytic cracking, hydroprocessing, and reforming. These fields were combined because of the clear analogies and congruence between the areas, such as deactivation of active sites by coke, mass-transfer phenomena of hydrocarbons into solid catalysts, hydrocarbon chemistry and reaction kinetics, and downscaling of commercial conditions to realistic small-scale tests. 

The consequences of this reduction in mass transfer may not be too serious, however, in applications such as hydroprocessing of oils. Under the usual trickle-flow conditions at which these processes are now operated, the contribution of gasAiquid mass transfer to the overall mass transfer resistance is generally negligible and considerably smaller... 

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