Coke selectivity

Catalyst A higher level of rare earth or an increase in the matrix content. Switch to a more coke-selective catalyst. 

Install high efficiency Feed Nozzles Lower Preheat Temperature Inject Naphtha Quench to Riser Increase Stripping and Dispersion Steam Switch to a Coke Selective Catalyst... 

As a consequence of the lower coke selectivity of the Cs-exchanged catalyst, the selectivity to the desired benzene product was largely increased by about 35% and remained more stable with TOS with respect to the untreated catalyst (Fig. 5). As expected from their high coke formation, the steamed catalysts displayed the lowest benzene selectivity. 

Coke selectivities as Wt.% of feed (A) were measured on a MAT unit, 3 C/0, 16 WHSV, 510°C, WTGO feed. 

The other advantage of dealumination is improved coke selectivity. Vlhile coke selectivity correlates with unit cell size, the correlation is different than the one for octane, and there is no correlation between coke selectivity and sodium content 5). 

The differences in the way octane and coke selectivity relate to the unit cell are illustrated in Figure 1. 

The surface area of the catalyst as well as the pore size distribution can easily be measured, and the zeolite and matrix surface areas of the catalyst can be determined by the t-plot method. The different FCC yields can then be plotted as a function of the ZSA/MSA ratio, zeolite surface area or matrix surface area, and valuable information can be obtained [9], The original recommendation was that a residue catalyst should have a large active matrix surface area and a moderate zeolite surface area [10,11]. This recommendation should be compared with the corresponding recommendation for a VGO catalyst a VGO catalyst should have a low-matrix surface area in order to improve the coke selectivity and allow efficient stripping of the carbons from the catalyst [12], Besides precracking the large molecules in the feed, the matrix also must maintain the metal resistance of the catalyst. 

Generally speaking, resid FCC (RFCC) catalysts should be very effective in bottoms cracking, be metals tolerant, and coke and dry gas selective. Based on many years of fundamental research and industrial experiences, a series of RFCC catalysts, such as Orbit, DVR, and MLC, have been developed by the SINOPEC Research Institute of Petroleum Processing (RIPP) and successfully commercialized [1]. These catalysts are very effective in paraffinic residue cracking. However, in recent years more and more intermediate-based residue has been introduced into FCC units, and the performances of conventional RFCC catalysts are now unsatisfactory. Therefore, novel zeolites and matrices have been developed to formulate a new generation of RFCC catalysts with improved bottoms cracking activity and coke selectivity. 

In China, most of the traditional RFCC catalysts (such as Orbit, DVR, and MFC mentioned above) are based on alnmina matrix, and the most widely used materials for alumina matrix preparation are alumina sol and modified active alumina [4]. Alumina matrix combines the virtnes of alumina-sol (better attrition resistance and coke selectivity) and active alnmina (higher cracking activity), thus improving the cracking activity and selectivity of the catalysts. However, the coke selectivity of the alumina matrix is nnsatisfactory when processing resid feed due to the insufficient amount of meso/macropores and higher concentration of acid sites. 

To improve bottoms cracking activity and coke selectivity of RFCC catalysts, novel zeolites and matrices have been developed recently. Commercial results showed that both VRCC-1 catalyst containing SOY zeolite and RSC-2006 based on silica modified alumina matrix have demonstrated excellent bottoms cracking capability and... 

Put heavy recycle downstream of the feed nozzles to improve dry gas and coke selectivities... 

The initial molar propane/propene-ratio (at 10 % of catalyst life time) is a measure of catalyst activity. It grossly correlates with the catalyst Si/Al-ratio. Fig. 7 concerns further proofs of catalyst life time. No correlation is observed between the amount of coke deposited and the total amount of methanol which is converted during the catalyst life time. However, a correlation appears to exist between (1) coke selectivity and catalyst life time and (2) methane selectivity and coke selectivity. 

Cumene Cracking Activity. Portions of each of the first five separated fractions were regenerated and subjected to cumene cracking investigations in order to determine relative acidity and coke selectivity trends. The catalyst within the... 

A. Net Coke Content and Coke Selectivity at Constant Conversion... 

Catalyst Fraction Corrected1 Wt% Coke (wt%) "Coke Selectivity" (conv/coke)... 

In this paper, we will first illustrate the mathematical models used to describe the coke-conversion selectivity for FFB, MAT and riser reactors. The models also include matrix and zeolite contributions. Intrinsic activity parameters estimated from a small isothermal riser will then be used to predict the FFB and MAT data. The inverse problem of predicting riser performance from FFB and MAT data is straightforward based on the proposed theory. A parametric study is performed to show the sensitivity to changes in coke selectivity and heat of reaction which are affected by catalyst type. We will highlight the quantitative differences in observed conversion and coke-conversion selectivity of various reactors. 

In Figure 2, we compare the coke-conversion selectivity behavior as a function of activity for MAT, FFB and riser reactors. The kc is relatively flat for the FFB test, with correspondingly higher negative slopes for MAT and steady state risers. The riser results show the steepest slope indicating that even though the kg observed in the FFB test is relatively independent of activity, the coke selectivity improves with activity in a riser. 

Figure 6. Coke selectivity of catalysts. Conversion was varied by varying the duration of hydrothermal pretreatment.

An improvement in coke selectivity can have a large impact on... 

It is also clear that in the case of FCC with heat removal, the frontier of resid processability can at a certain moment be determined by the coke selectivity of the catalyst, while on the other hand the conversion of resid in a unit without heat removal may also be limited by the metal resistance of a catalyst. 

Figure 6 shows an example of the coke selectivity in the MST unit with a normal VGO feedstock. 

Reduce the catalytic coke formation of the catalyst in order to allow some room for the additional coke formed by these poisons. In this approach we accept that the extra coke formed is unavoidable, and that we need to compensate by improving the coke selectivity of the catalyst. 

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