Gasoline selectivity

Rare Earth is a generic name used for the 14 metallic elements of the lanthanide series used in the manufacturing of FCC catalyst to improve stability, activity, and gasoline selectivity of the zeolite. 

A naphthene is used for this illustration as we believe that the relative amounts of naphthene cracking versus hydrogen transfer control product distributions and qualities in octane catalyst systems. Gasoline selective catalysts favor hydrogen transfer reactions with these molecules with consequent formation of coke. 

ALPHA 500 in this Instance actually equilibrated at a slightly lover ao (higher SIO2/AI2O3) than BETA 500. By virtue of this ve may expect somewhat higher gasoline selectivity for ALPHA and the observed product distributions of BETA and Com-USY to be similar. 

Finally, PILC, REY-PILC, and a commercial equilibrium catalyst were evaluated at near constant conversion using a heavier feed, hydrotreated resid. The product yields are shown in Table III. Steam deactivated (D), REY-PILC, produced the same gasoline selectivity, LCO/HCO ratio, and coke yield as calcined PILC. The equilibrium catalyst which represents a more severely deactivated (E) sample had higher gasoline selectivity, lower coke yield, and lower HCO/LCO ratio. The higher coke yield of REY-PILC could be due to occlusion of high molecular weight hydrocarbons in the microstructure of the pillared clay. 

The low H/C-ratio of FCC feed derived from liquefied biomass led to low conversion and poor gasoline selectivity. Addition of alumina to the matrix resulted in a catalyst more active for heavy oil cracking but with a poor selectivity. Alumina-montmorillonite catalysts showed activities for heavy oil cracking comparable to that of a conventional, zeolite based, cracking catalyst. Effects of matrix composition and zeolite type on the heavy oil cracking performance are discussed. 

Cotterman et al. (34) showed that hexadecane-cracking activity of AFS and USY zeolites appeared to be a function of total Al content, independent of method of dealumination, implying that hexadecane cracking occurs over both framework- and extra-framework-acid sites. Hence, extra-framework material in mildly steamed synthetic faujasite, USY, makes a significant contribution to catalyst activity, as previously reported (32). Gasoline selectivity is influenced by both the method of dealumination and steam treatment, and depends on both framework-acid sites and the presence of extra-framework material. 

Figure 1. Effect of zeolite Si02/Al203 ratio on gasoline selectivity in MAT.

In the preceding sections we concentrated mainly on the coke-conversion selectivity aspects of various reactors. In this section we will briefly discuss the selectivities of major FCC products gasoline, LCO, HCO, and light gases in both transient and steady state reactors. Weekman (1-3) has looked at steady state and transient reactors for gasoline selectivity shifts. However, he did not include axial dispersion effects in his analysis which are important for laboratory FFB reactors, and are accounted for here. 

The role of Brpnsted acid sites in the oligomerization of ethylene over HZSM-5 has been studied.[30,31] Amin and Anggoro1311 concluded that dealumination of HZSM-5 led to higher ethylene conversion, but the gasoline selectivity was reduced compared with a nondealuminated HZSM-5 (Si/Al = 15) zeolite sample. 

Table VI indicates that calcined USY and AFS materials show differences in product selectivities and gasoline compositions. AFS samples show lower gasoline selectivities and higher coke yields than USY samples. In addition, products from AFS show slightly decreased olefins and increased aromatics and branched paraffins than those from USY. Calculated octanes are higher for AFS than for USY.

Gasoline selectivity is influenced by both the method of dealumination and steam treatment and, hence, depends on framework acid sites and on presence of extraframework material. Both framework and extraframework sites contribute to the overall zeolite acidity. Framework Al(IV) acid sites are associated with Bronsted acidity whereas extraframework Al(VI) acid sites are associated with Lewis acidity(21). Calcined AFS samples are reported (22) to contain greater Bronsted acidity than USY samples from infrared characterization and to have stronger acidity as measured by ammonia desorption. As a result, the stronger acidity of calcined AFS samples cracks hexadecane to lower molecular weight products than USY. After steaming, the acidities of both AFS and USY are reduced to similar levels and lead to similar gasoline selectivities which are increased relative to the calcined zeolites. 

Gasoline selectivity and octane performance are functions of not only unit cell size but also factors such as extraframework material and spatial distribution of active sites. These factors influence... 

Figure 5. GASOLINE SELECTIVES Consistent Rankings for Most Mathods.

Neste Oy, Engineering Olefins FCCU light gasoline, EC pyrolysis gasoline Selective hydrogenation of C5, C6 and C7 diolefins to olefins 1 1995... 

Gasoline selectivity is poor that is, oil products are a wide distribution of molecular... 

Cracking of heavy petroleum residue Al-S Saponite showed higher activity than y alumina with similar gasoline selectivity and coking characteristic to a steamed FCC. 5o... 

Hatanaka, S., Sadakane, O., and Okazaki, H. Hydrodesulfurization of catalytic cracked gasoline—Selective catalytic cracked gasoline hydrodesulfurization using C0-M0/7-AI2O3 catalyst modified by pyridine. Journal of the Japan Petroleum Institute, 2001, 44, 36. 

As metallation proceeds the product selectivity changes. The coke factor (defined in Table 2) in sample CD increases from 1.5 at 8 hours to 2.1 at 24 hours operation. The gas factor changes from 0.6 to 1.1 for the same period of time. By comparison, factors for ECAT and HTD (1.4 and 1.5) and gas factors (1.3 and 0.6) are almost constant. The gasoline selectivity varies from 67 to 75% for sample CD, 62 to 64% for sample HTD and remains almost constant 69-70% for sample ECAT2. 

Comparison of gasoline yield versus propane/propene ratio shows that inherent gasoline selectivity did not change throughout the aging test (Fig. 10). MTG is somewhat unusual in that the selectivity of the ZSM-5 catalyst for the desired gasoline product actually increases as it ages. 

Fig. 14. Bench and 4 B/D units have same gasoline selectivity...

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