Gasoline yields

A good catalyst is also stable. It must not deactivate at the high temperature levels (1300 to 1400°F) experienced in regenerators. It must also be resistant to contamination. While all catalysts are subject to contamination by certain metals, such as nickel, vanadium, and iron in extremely minute amounts, some are affected much more than others. While metal contaminants deactivate the catalyst slightly, this is not serious. The really important effect of the metals is that they destroy a catalyst s selectivity. The hydrogen and coke yields go up very rapidly, and the gasoline yield goes down. While Zeolite catalysts are not as sensitive to metals as 3A catalysts, they are more sensitive to the carbon level on the catalyst than 3A. Since all commercial catalysts are contaminated to some extent, it has been necessary to set up a measure that will reflect just how badly they are contaminated. 

As severity is increased, C5+ gasoline yields decrease, with a corresponding increase in C, to C4 products. Hydrogen yields increase with severity until the level at which no further aromatics are produced as severity is increased even further, hydrogen yields then decrease. 

The extent to which each of the above reactions occur is strongly influenced by feed quality and the levels selected for the major process variables pressure, temperature, recycle rate, and frequency of regeneration. From a process viewpoint, these variables affect catalyst requirement, gasoline yield, and coke make. 

A large quantity of hydrogen-rich separator gas is normally recycled with the feed stream. Recycle rates may vary from 2,000 to 10,000 MSCF/B. The recycle gas serves to suppress catalyst coke make but normally has relatively little direct effect on gasoline yields or catalyst requirement. However, at lower recycle levels, where an increase in recycle rate may significantly increase reactor hydrogen partial pressure, the effect is similar to a small increase in total... 

The design frequency of regeneration is normally from three to six months for semi-regenerative units, and one reactor every 24 hours in cyclic units. For either case, an increase in regeneration frequency would result in a reduction in average catalyst coke level. Thus, gasoline yields would increase and catalyst requirements decrease. 

There are many factors to be considered in selecting the type of Powerformer to use. It largely depends on the local situation and includes such things as feed stock, octane level, the value of gasoline yield, the use for by-product hydrogen, plant size, etc. While we can not completely generalize, we can mention some of the more important considerations. 

These metals, when deposited on the E-cat catalyst, increase coke and gas-making tendencies of the catalyst. They cause dehydrogenation reactions, which increase hydrogen production and decrease gasoline yields. Vanadium can also destroy the zeolite activity and thus lead to lower conversion. The deleterious effects of these metals also depend on the regenerator temperature the rate of deactivation of a metal-laden catalyst increases as the regenerator temperature increases. 

Hydrogen transfer reactions usually increase gasoline yield and stability. The reactivity of the gasoline is reduced because hydrogen transfer produces fewer olefins. 

In the previous examples, the feed characterizing correlations in Chapter 2 are used to determine composition of the feedstock. The results show that the feedstock is predominantly paraffinic (i.e., 61.6% paraffins. 19.9% naphthenes, and 18.5% aromatics). Paraffinic feedstocks normally yield the most gasoline with the least octane. This confirms the relatively high FCC gasoline yield and low octane observed in the test run. This is the kind of information that should be included in the report. Of course, the effects of other factors, such as catalyst and operating parameters, will also affect the yield structure and will be discussed. 

Increasing the reactor temperature. Increasing the reactor temperature heyond the peak gasoline yield results in overcracking... 

FCC gasoline has always been the most valuable product of a cat cracker unit. FCC gasoline accounts for about 35 vol% of the total U.S. gasoline pool. Historically, the FCC has been run for maximum gasoline yield with the highest octane. 

Feed injection. An improved feed injection system provides optimum atomization and distribution of the feed for rapid mixing and complete vaporization. The benefits of improved feed injection aie reduced coke deposition, reduced dry gas yield, and improved gasoline yield. 

Any mechanical revamp to improve the unit yields should always begin with installing an efficient feed and catalyst distribution system. This is the single most-important component of the FCC unit. An efficient feed and catalyst injection system maximizes gasoline yield and conversion at the expense of lower gas, coke, and decant oil and allows downstream technology to perform at its full potential. 

Lower Conversion High Dry Gas Yield Fig. 8-11B Lower Gasoline Yield Figure 8-11C Lower Gasoline Octane Figure 8-1 ID ... 

The FCC true gasoline yield largely depends on changes in feed quality, catalyst properties, operating variables, and mechanical conditions (Figure 8-11C). 

Paraffinic feedstocks produce the most gasoline yield (but the lowest octane). The common indicators of any increase in feed par-affinicity are ... 

The fresh catalyst properties that increase gasoline yield are ... 

The main mechanical conditions that affect octane are the type and condition of the feed nozzles. Low-efficiency feed nozzles actually increase the gasoline octane due to promotion of thermal reactions in the mix zone. High-efficiency feed nozzles improve feed/catalyst mixing and increase the gasoline yield, but decrease gasoline octane. 

Achieving an ultra-short catalyst-hydrocarbon contact time, designed to maximize olefins and gasoline yields while minimizing the bottoms yields. 

Octane Barrel Yield, as used in the FCC, is defined as (RON -i- MON)/2 times the gasoline yield. 

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