Fluid catalytic cracking , feedstock

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

Deep C t lytic Crocking. This process is a variation of fluid catalytic cracking. It uses heavy petroleum fractions, such as heavy vacuum gas oil, to produce propylene- and butylene-rich gaseous products and an aromatic-rich Hquid product. The Hquid product contains predorninantiy ben2ene, toluene, and xylene (see BTX processing). This process is being developed by SINOPEC in China (42,73). SINOPEC is currentiy converting one of its fluid catalytic units into a demonstration unit with a capacity of 60,000 t/yr of vacuum gas oil feedstock. 

Hydrocarbon feedstocks for fluid catalytic cracking units (FCCU s) contain organo-sulfur compounds. The sulfur content of these feedstocks is about 0.3% to 3.0%, expressed as elemental sulfur. 

In response to recent federal and local environmental concerns (e.g., industrial emission controls and lead phase-out) and to the growing interest of refiners in cracking residual fuels, researchers have generated new families of cracking catalysts. There is now a need to review the merits of these newly developed materials. This volume contains contributions from researchers involved in the preparation and characterization of cracking catalysts. Other important aspects of fluid catalytic cracking, such as feedstocks and process hardware effects in refining, have been intentionally omitted because of time limitations and should be treated separately in future volumes. 

Venugopal, R., Selvavathy, V., Lavanya, M., and Balu, K. Additional Feedstock for Fluid Catalytic Cracking Unit. Petroleum Science and Technology 26 (2008) 436-45. 

Gas oils Utilized as straight-run distillate after desulfurization. Lighter atmospheric and vacuum gas oils are often hydrocracked or catalytically cracked to produce gasoline, jet, and diesel fuel fractions heavy vacuum gas oils can be used to produce lubestocks or as fluid catalytic cracking (FCC) feedstock... 

Table 7 shows the yield distribution of the C4 isomers from different feedstocks with specific processing schemes. The largest yield of butylenes comes from the refineries processing middle distillates and from olefins plants cracking naphtha. The refinery product contains 35 to 65% butanes olefins plants, 3 to 5%. Catalyst type and operating severity determine the selectivity of the C4 isomer distribution (41) in the refinery process stream. Processes that parallel fluid catalytic cracking to produce butylenes and propylene from heavy cmde oil fractions are under development (42). 

Catalytic cracking using a fluidized bed is the most popular form of cracking and is the emphasis of this section. To reaffirm this statement, there are more than 370 fluid catalytic cracking units in use worldwide with the capacity to produce more than 460,000,000 gallons of gasoline from heavier feedstocks (Slade, 1998). 

The ET-II process is a thermal cracking process for the production of distillates and cracked residuum for use as a metallurgical coke and is designed to accommodate feedstocks such as heavy oils, atmospheric residua, and vacuum residua (Kuwahara, 1987). The distillate (referred to in the process as cracked oil) is suitable as a feedstock to hydrocracker and fluid catalytic cracking. The basic technology of the ET-II process is derived from that of the original Eureka process. 

The volatile products from the soaking drum enter the fractionator where the distillates are fractionated into desired product oil streams, including a heavy gas oil fraction. The cracked gas product is compressed and used as refinery fuel gas after sweetening. The cracked oil product after hydrotreating is used as fluid catalytic cracking or hydrocracker feedstock. The residuum is suitable for use as boiler fuel, road asphalt, binder for the coking industry, and as a feedstock for partial oxidation. 

The fluid catalytic cracking process using vacuum gas oil feedstock was introduced into the refineries in the 1930s. In recent years, because of a trend for low-boiling products, most refineries perform the operation by partially blending... 

In the process, a residuum is desulfurized and the nonvolatile fraction from the hydrodesulfurizer is charged to the residuum fluid catalytic cracking unit. The reaction system is an external vertical riser terminating in a closed cyclone system. Dispersion steam in amounts higher than that used for gas oils is used to assist in the vaporization of any volatile constituents of heavy feedstocks. 

The R2R process is a fluid catalytic cracking process for conversion of heavy feedstocks. 

In the S W fluid catalytic cracking process (Figure 8-15), the heavy feedstock is injected into a stabilized, upward flowing catalyst stream whereupon the feedstock-steam-catalyst mixture travels up the riser and is separated by a high efficiency inertial separator. The product vapor goes overhead to the main fractionator (Long, 1987). 

The Demex process is a solvent extraction demetallizing process that separates high metal vacuum residuum into demetallized oil of relatively low metal content and asphaltene of high metal content (Table 8-5) (Houde, 1997). The asphaltene and condensed aromatic contents of the demetallized oil are very low. The demetallized oil is a desirable feedstock for fixed-bed hydrodesulfurization and, in cases where the metals and carbon residues are sufficiently low, is a desirable feedstock for fluid catalytic cracking and hydrocracking units. 

Combined with hydrodesulfurization, the process is fully applicable to the feed preparation for fluid catalytic cracking and hydrocracking. The process is capable of using a variety of feedstocks including atmospheric and vacuum residues derived from various crude oils, oil sand, visbroken tar and so on. 

Hydrotreating processes have two definite roles (1) desulfurization to supply low-sulfur fuel oils and (2) pretreatment of feed residua for residuum fluid catalytic cracking processes. The main goal is to remove sulfur, metal, and asphaltene contents from residua and other heavy feedstocks to a desired level. 

The major goal of hydroconversion is the cracking of residua with desulfurization, metal removal, denitrogenation, and asphaltene conversion. The residuum hydroconversion process offers production of kerosene and gas oil, and production of feedstocks for hydrocracking, fluid catalytic cracking, and petrochemical applications. 

Riser pipe the pipe in a fluid catalytic cracking process (q.v.) where catalyst and feedstock arc lifted into the reactor the pipe in which most of the reaction takes place or is initiated. 

The first feedstock studied under this contract was Paraho shale oil. In a series of recent papers (1-4) and a DOE report (5 ), three basic shale oil processing routes for the production of transportation fuels were studied hydrotreating followed by hydrocracking, hydrotreating followed by fluid catalytic cracking (FCC), and severe coking followed by hydrotreating. 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Fluid catalytic cracking (FCC) of heavy oil fractions is a well-known process in oil refineries. Numerous books (e.g., 1—3) and publications about the different aspects of this subject are available. This chapter is concerned with the modeling of the transfer line or riser reactor of an FCC unit (FCCU) or of a pilot plant. The riser reactor in FCCUs is a vertical pipe about 1 m in diameter and 10-30 m in height. The hot catalyst coming from the regenerator at about 710 ° C first comes in contact with steam and is fluidized. Then, at a height of some meters above, the catalyst is mixed with the preheated feedstock at about 300 ° C. 

The olefins ethylene and propylene are highly important synthetic chemicals in the petrochemical industry. Large quantities of such chemicals are used as feedstock in the production of polyethylene, polypropylene, and so on [31]. The prime source of lower olefins is the olefin-paraffin mixtures from steam cracking or fluid catalytic cracking in the refining process [32]. Such mixtures are intrinsically difficult to... 

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