Fluidised catalytic cracking

Figure 8.11 Refinery flow scheme showing the processes for treatment of the different fractions of crude oil. The main processes that use zeolite catalysts are indicated by shading. (HDS-hydrodesulfurisation, HDT-hydrotreating, FCC-fluidised catalytic cracking) [Adapted from reference 89 with permission. Copyright 1997 Wiley-VCH Verlag GmbH Co. KGaA.]...

Fluidised catalysts are also used in the synthesis of high-grade fuels from mixtures of carbon monoxide and hydrogen, obtained either by coal carbonisation or by partial oxidation of methane. An important application in the chemical industry is the oxidation of naphthalene to phthalic anhydride, as discussed by Riley(131). The kinetics of this reaction are much slower than those of catalytic cracking, and considerable difficulties have been experienced in correctly designing the system. 

A series of experiments varying temperature, micro-sphere size and time on stream have been performed in a fixed fluidised bed microactivity reactor to study the role of intraparticle diffusion in commercial fluid catalytic cracking (FCC) catalysts, particularly on gasoline yield and catalyst deactivation by coke deposition, for the cracking of a vacuum gas oil. Additionally, a mechanistic model that describes interface and intrapartide mass transfer interactions with the cracking reactions, has been used to study the combined influence of pore size and intraparticle mass diffusion on the deactivation of FCC catalysts and the gasoline yield. 

Fluidised bed reactors are rarely suitable for catalytic studies because of their relatively large volume, the large quantity of catalyst to use and the difficulty to control bubble agglomeration and instabilities. However, it is still almost irreplaceable for the testing of fluid-bed cracking catalysts. On a laboratory scale a modification is applied in which an intensive mixing of particles is achieved by means of mechanical vibration. In this case, the gas flow rate can vary over a... 

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