Hydroprocessing Objectives

The initial focus for the application of hydroprocesses for the conversion of heavy feedstocks was the removal of sulfur. However, many recent processes have concentrated on the objective of achieving high feedstock conversion. The emphasis on sulfur removal, in these process designs, shifts from the primary hydroprocessing step to the secondary hydroprocessing reactor. 

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 plenary papers were mostly reviews covering important topics related to the objectives of the conference. The remaining sections cover various topics of major impact on modern petroleum refining and petrochemical industries. A large number of papers dealt with hydroprocessing of petroleum distillates and residues which reflects the concern over meeting future sulfur-level specifications for diesel and fuel oils. 

For hydroprocessing units, product specifications are set to meet plantwide objectives. For example, the naphtha that goes to catalytic reforming and isomerization units must be (essentially) sulfur free. Before it can be sold as... 

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. 

With hydroprocessing units, most refiners try to maximize feed rate while (a) meeting other process objectives and (b) maintaining a high on-stream factor. Some try to maximize conversion, while others just want to hit a key process target at minimum cost. 

Kinetic and reactor modeling will always be a fundamental step in the design of chemical processes. The main objective of this task is to construct a computational tool for predicting product distribution and reactor behavior at various operating conditions. In this sense, modeling of heavy oil hydroprocessing is of extreme complexity because there are so many parallel physical and chemical processes inside the reactor phase equilibrium, mass transfer of reactants and products between the three phases present in the reactor (gas, liqnid, and solid), intraparticle diffusion, a vast reaction network, and catalyst deactivation, to name a few. Ideally, the contribution of all these events must be accounted for in order to increase prediction capability however, the level of sophistication of the model will generally depend on the pursued objectives. 

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