Process Configurations and Catalysts

As practiced today, FCC is a fluidized-bed process with continuous catalyst regeneration which reUes on short contact in a riser reactor between the feed and catalyst, fluidized with an inert gas, followed by disengagement and catalyst regeneration to burn off coke deposits and return the catalyst to near-fresh activity. 

The Changing Role of the FCC Transportation Fuei Production or Petrochemicai Feed Production 

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As the process configuration and catalysts are to some extent different for steam reforming and partial oxidation, they are treated separately here. 

As is evident from the discussion in section 6.2, HC catalysts are exposed to very different environments, depending on process configuration, and therefore vary... 

Default factors. It is possible to have several different sets of tuning factors or calibrations corresponding to a variety of process, feedstock and catalyst configurations. However, we recommend that each file should not have more than one set of calibration or tuning factors in addition to the Default calibration factors. 

Technology licensors recently made significant advances in process design and they now offer many variations and improvements of these basic scheme, however the discussion below only examines these four basic designs because their reaction environments encompass all conditions that impact the elementary catalytic steps and their implications on catalyst and materials requirements. From a catalytic perspective these four configurations may be grouped into two sets which differ significantly in the reaction environments the catalysts operate in as discussed in the section below. 

Processes 4, 5 and 6 are all essentially one step oxidations of SO2 to SO3 and hence sulphuric acid. The first pair are modified versions of the traditional Contact and Chamber processes for sulphuric acid manufacture, with the principal change being in their ability to accept dilute SO2 gas streams as the feedstock. The use of Activated Carbon as an air oxidation catalyst has clearly received international attention, with success or failure depending to a large extent on subtle modifications in catalyst preparation and catalyst presentation to the reactant gases. Virtually every type of catalyst bed configuration has been explored. 

Whatever the configuration and the nature of the process, all of the catalysts examined show high activities and selectivities of up to 90%, but low enantioselectivity (in the best case 64% ee data reported in Table 3). Heterogenised catalysts (entries 2 and 4, Table 3) are slightly better in terms of both... 

In seeking new and improved ways for achieving the ultralow levels of sulfur in the fuels of the future, it is important to understand the nature of the sulfur compounds that are to be converted (especially PASCs), as described in Section III. It is equally important to understand how these transformations occur through interactions with catalytic surface species, the pathways involved during these transformations, and the associated kinetic and thermodynamic limitations. These considerations dictate the process conditions and reactor process configurations that must be used to promote such transformations. In this section, we describe the reactor configurations and process conditions being used today what is known about the catalyst compositions, structure, and chemistry and what is known about the chemistry and reaction pathways for conversion of PASCs in conventional HDS processes. 

Thus, industry has a major challenge to develop new catalysts and processes for future clean-fuel production. In the following discussion, we review the state of knowledge of present-day catalyst compositions and surface chemistry and of mechanistic reaction pathways to aid in identifying where improvements can be made in catalyst composition and process configurations. 

Having established reliable values for all of the important rate constants as a function of alkyl substitution on dibenzothiophenes, it is now possible to examine critically how these rate constants (and associated changes in product selectivity) are affected by other components of commercial gas oils and by the H2S that is produced during the HDS process. It is also possible to evaluate how these various rate constants are affected by changes in catalyst composition and by process conditions. Knowledge of the details of these effects can lead to novel catalyst modifications and process configurations that may be able to reach the new stricter standards of 0.05% S. These topics are discussed in later sections. However, for perspective, we will first summarize what is known about present-day catalyst compositions and catalytic mechanisms that bring about the transformations observed in HDS processes. 

Nevertheless, we have not yet developed a liquefaction process that can supply fuel at a price competitive with the present price of oil. Researchers in several countries are searching for further improvements. New catalyst and process configurations are the keys to solving the following problems. 

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