FCC

Comparing the overall concentrations of these different carbons designated generally as structural patterns , measured before and after a process such as FCC or hydrocracking (see Chapter 10), enables the conversion to be monitored the simple knowledge of the percentage of condensed aromatic carbon of a feedstock gives an indication of its tendency to form coke. 

Figure 3.12 shows the spectrum of carbon 13 obtained from a distillation residue and Table 3.10 gives average parameters for two FCC feedstocks as measured by NMR. 

Process Atmospheric distillation Atmospheric distillation FCC Hydro- cracking Vis- breaking Coking Hydrocracking... 

One can react methanol with the tertiary olefins having five c irbon atoms (isoamylenes). This process increases the octane number of FCC olefinic C5 fractions, in order to reduce the concentration of olefins and to increase gasoline production. 

Table 10.10 is an evaluation of the improvement resulting from the addition of alkylate and ethers to an FCC gasoline. 

Feedstocks Propylene fraction from FCC Fuel gas from FCC... 

Vacuum flashing of an effluent from thermal conyersion allows recovery of a distillate that is sent to the FCC and replaced as diluent by a product of lesser quality coming from the FCC, (HCO or LCO). 

Table 10.15 provides some general data concerning FCC feedstocks and products. 

Figure 10.6 shows the position of an FCC and its related units in a refining flowsheet. 

Figure 10.7 presents the case of an FCC feedstock comprising a mixture of vacuum distillate and light atmospheric residue, and the case of an FCC feedstock composed of vacuum distillate and DAO, as well as the constraints of such configurations. 

Figure 10.7 FCC unit using feedstock either as a VD-DAO. light mixture of VD-AR or a mixture of...

Figure 10.8 presents a variant of the FCC process, the RCC (Residue Catalytic Cracking) capable of processing heavier feedstocks (atmospheric residue or a mixture of atmospheric residue and vacuum distillate) provided that certain restrictions be taken into account (Heinrich et al., 1993). 

Figure 10.9 shows advantages of a hydrodesulfurization unit upstream of an FCC or RCC unit. 

Residue to lube oil plant, steam cracking plant, FCC... 

Fractions treated by this process are light products from the primary distillation LPG to Kerosene, or light products from thermal and catalytic cracking (visbreaking, coking, FCC). 

The treated water containing sodium chloride, cyanides, phenols and traces of H2S and NH3 is recycled to the crude desalting unit and used as wash water for the hydrotreaters and FCC units. 

Heinrich, G., R. Bonnifay, J.-L. Mauleon, M. Demar and M.A. Silverman (1993), Advances in FCC design. Parts 1 and 11 . Refining process services Seminar, Amsterdam. 

Only even values of Wi -t- m2 -t- m3 are used for the FCC lattice. The numerical values of these lattice sums are dependent on the exponents used for U(r), and Eq. VII-11 may be written... 

A related approach carries out lattice sums using a suitable interatomic potential, much as has been done for rare gas crystals [82]. One may also obtain the dispersion component to E by estimating the Hamaker constant A by means of the Lifshitz theory (Eq. VI-30), but again using lattice sums [83]. Thus for a FCC crystal the dispersion contributions are... 

Fig. VIII-8. Surface structures (a) (1 x 1) structure on the (100) surface of a FCC crystal (from Ref. 76) (b) C(2 x 1) surface structure on the (100) surface of a FCC ciystal (from Ref. 76). In both cases the unit cell is indicated with heavy lines, and the atoms in the second layer with pluses. In (b) the shaded circles mark shifted atoms. (See also Ref. 77.)...

The FCC structure is illustrated in figure Al.3.2. Metallic elements such as calcium, nickel, and copper fonu in the FCC structure, as well as some of the inert gases. The conventional unit cell of the FCC structure is cubic with the lengdi of the edge given by the lattice parameter, a. There are four atoms in the conventional cell. In the primitive unit cell, there is only one atom. This atom coincides with the lattice pomts. The lattice vectors for the primitive cell are given by... 

The rocksalt stmcture is illustrated in figure Al.3.5. This stmcture represents one of the simplest compound stmctures. Numerous ionic crystals fonn in the rocksalt stmcture, such as sodium chloride (NaCl). The conventional unit cell of the rocksalt stmcture is cubic. There are eight atoms in the conventional cell. For the primitive unit cell, the lattice vectors are the same as FCC. The basis consists of two atoms one at the origin and one displaced by one-half the body diagonal of the conventional cell. 

In fignre A1.3.9 the Brillouin zone for a FCC and a BCC crystal are illustrated. It is a connnon practice to label high-synnnetry point and directions by letters or symbols. For example, the k = 0 point is called the F point. For cubic crystals, there exist 48 symmetry operations and this synnnetry is maintained in the energy bands e.g., E k, k, k is mvariant under sign pennutations of (x,y, z). As such, one need only have knowledge of (k) in Tof the zone to detennine the energy band tlnoughout the zone. The part of the zone which caimot be reduced by synnnetry is called the irreducible Brillouin zone. 

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