Transport reactors catalytic cracking

Catalytic cracking Zeolite in Si02 A1203 matrix plus other ingredients (transport reactor)... 

The feeds to these types of units are usually atmospheric and vacuum residua. The products include feeds for the production of transportation fuels, fuel oils, olefins, etc. However, the operating conditions of the reactor, whether it is a fluid catalytic cracking unit or a fixed-bed unit, is dependent upon the desired product slate and the properties of the feed. 

When deactivation occurs rapidly (in a few seconds during catalytic cracking, for instance), the fresh activity can be found with a transport reactor through which both reactants and fresh catalyst flow without slip and with short contact time. Since catalysts often are sensitive to traces of impurities, the time-deactivation of the catalyst usually can be evaluated only with commercial feedstock, preferably in a pilot plant. 

The large spectrum of reactors is shown in Fig. 2 with the vertical axis showing the progression from the simplest types such as a delayed coker (a semibatch reactor) to the highly complex fluid catalytic cracking (FCC) unit, which has both the reaction phase and the catalyst being transported through the reactor. 

There are processes in which the total amount of catalyst is entrained by the gas. The reactors then belong to the category of transport reactors. Examples are some of the present Fischer-Tropsch reactors for the production of hydrocarbons from synthesis gas and the modern catalytic cracking units. Fig 10.11 shows the Synthol circulating solids reactor. In the dilute side of the circuit, reactant gases carry suspended catalyst upward, and the fluidized bed and stand-pipe on the other side of the circuit provide the driving force for the smooth circulation of the solid catalyst. For the removal of heat, heat exchangers are positioned in the reactor. 

APPLICATIONS OF FLUIDIZATION. Extensive use of fluidization began in the petroleum industry with the development of fluid-bed catalytic cracking. Although the industry now generally uses riser or transport-line reactors for catalytic cracking, rather than fluid beds, the catalyst regeneration is still carried out in fluid-bed reactors, which are as large as 30 ft in diameter. Fluidization is used in... 

A process flow diagram is illustrated in Figure 10. The oxidation reactor is a transport bed or riser reactor similar to the type used for catalytic cracking in a refinery It is essentially a vertical pipe in which the reaction feed gases and solid catalyst enter at the bottom and flow upward in a fluidized state. The product is formed as the butane and catalyst flow upward. The catalyst is separated from the product gases in a cyclone separator, routed... 

At very high velocities, all particles fed to the reactor are carried up with the gas, and this mode of operation is sometimes called fast fluidization. However, since there is no definite bed level, a better term for this system is a transport-line reactor or, as it is called in catalytic cracking, a riser reactor. These are discussed in Chapter 10, on novel types of reactors. 

Catalytic cracking is a process for the conversion of heavy petroleum cuts into gasoline. The catalyst is constituted of microspheres of about 60 /zm diameter contains 10 to 40 % of an acid Y zeolite (REY, USHY...) dispersed in a matrix (clay + binder). This catalyst circulates rapidly in the unit, its contact time with oil in the riser reactor (T 530 0) being of several seconds. The coked catalyst (about 1 wt % coke) is transported to the regenerator where the introduction of air makes possible, in a few minutes the combustion of coke at high temperature (about 700 C). The use of heavier and heavier feeds creates several problems during the regeneration steps ... 

Socony-Vacuum utilized Thermofor kilns to bum off coke deposited on Fuller s earth during the filtration of lube oils (57). They adapted one of these kilns to introduce the first moving bed catalytic cracking process. The first semi-commercial 500 BPD (barrel per day) Thermofor Catalytic Cracking (TCC) unit went on stream in the Paulsboro refinery in 1941. It utilized bucket elevators to transport catalyst from the reactor to the regenerator. In 1943, Socony-Vacuum installed a 10,000 BPD TCC unit (52) at a subsidiary refinery. 

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