Catalyst regeneration cracking process

The most dominant catalytic process in the United States is the fluid catalytic cracking process. In this process, partially vaporized medium-cut petroleum fractions called gas oils are brought in contact with a hot, moving, freshly regenerated catalyst stream for a short period of time at process conditions noted above. Spent catalyst moves continuously into a regenerator where deposited coke on the catalyst is burnt off. The hot, freshly regenerated catalyst moves back to the reactor to contact the hot gas oil (see Catalysts, regeneration). 

Cataljdic reactions performed in fluid beds are not too numerous. Among these are the oxidation of o-xylene to phthalic anhydride, the Deacon process for oxidizing HCl to CI2, producing acrylonitrile from propylene and ammonia in an oxidation, and the ethylene dichloride process. In the petroleum industry, cataljdic cracking and catalyst regeneration is done in fluid beds as well as some hydroforming reactions. 

The catalytic cracking processes, as well as most other refinery catalytic processes, produce coke which collects on the catalyst surface and diminishes its catalytic properties. The catalyst, therefore, needs to be regenerated continuously or periodically essentially by burning the coke off the catalyst at high temperatures. 

Deep catalytic cracking (DCC) is a catalytic cracking process which selectively cracks a wide variety of feedstocks into light olefins. The reactor and the regenerator systems are similar to FCC. However, innovation in the catalyst development, severity, and process variable selection enables DCC to produce more olefins than FCC. In this mode of operation, propylene plus ethylene yields could reach over 25%. In addition, a high yield of amylenes (C5 olefins) is possible. Figure 3-7 shows the DCC process and Table 3-10 compares olefins produced from DCC and FCC processes. ... 

Figure 9.10. Scheme of an FCC Unit. Cracking ofthe heavy hydrocarbon feed occurs in an entrained bed, in which the catalyst spends only a few seconds and becomes largely deactivated by coke deposition. Coke combustion in the regenerator is an exothermic process that generates heat for the regeneration and for the endothermic cracking process. 

Houdriflow A catalytic petroleum cracking process in which the beads of catalyst move continuously through the reactor and the catalyst regenerator. 

R2R A catalytic cracking process using an ultrastable zeolite catalyst with two-stage regeneration. Developed by Institut Frangais du Petrole and used at Idemitsu Kosan s refineries at Aichi and Hokaido. In 1994, 13 existing plants had been converted to this process. 

Olefin cracking has been developed as a process to produce propylene in a highly selective manner from butenes and pentenes. Zeolites used in processes such as UOP s Olefin Cracking Process are often MFI-based in order to avoid coke buildup during the reaction, leading to longer times between catalyst regeneration (Table 12.15). 

During the cracking process, carbon deposits or coke build up on the spent catalyst particles. These deposits can deactivate the catalyst performance and must be removed. This is typically accomplished in two stages. First, the catalyst collected at the bottom of the reactor is steam stripped to remove residual hydrocarbon. The stripped catalyst then passes into the regenerator and is heated with air to temperatures as high as 1,100°F to 1,200°F (539.3°C to 648.9°C). At these temperatures, coke bums off of the catalyst making it ready for reuse within the FCC unit. See FIGURE 2-5. 

Commercial Development of Fixed-Bed Process. From the above process considerations it became obvious that the capacity of a commercial unit, and its economic value, were closely related to its ability to burn coke. Indeed, most of the design problems associated with catalytic cracking have been centered around the question of catalyst regeneration. To obtain the most favorable economic return from a 10,000-barrel-per-day unit, it was designed to burn approximately 6000 pounds per hour of coke. This coke yield represents approximately 5% by weight of the charge. 

---