Gas oil cracked

The activity of a cracking catalyst declines with time on stream. A case of gas oil cracking has the rate equation, dC 8.5C ... 

We have characterized HY zeolites dealuminated by different procedures and at different levels and have shown that the proportion of the different types of EFAL can be controlled. Furthermore, all the zeolite modifications clearly influence the product distribution during gas-oil cracking. 

Gas-oil cracking was carried out in a fixed bed tubular reactor at atmospheric pressure and 482 °C. Average yields of the different products -diesel, gasoline, gases (methane, ethane, ethylene, C, C ), and coke- were measured at different levels of conversion jy varying the catalyst to oil ratio in the range 0.025-0.40 g.g, but always at 60 sec on-stream. The operational procedure has been detailed elsewhere (6). 

Figure 7, Selectivities to different products of gas-oil cracking on HYUS catalysts, as a function of the number of A1 per unit cell.

Finally, the variation of the yields of gasoline and diesel versus A1 per unit cell allow us to conclude that highly steam-dealuminated HY zeolites behave, from the point of view of gas-oil cracking, like a well-dispersed active alumina. 

Gas Oil Cracking by the Dual Zeolite Catalyst. After the steam pre-treatment, the gas oil cracking activity of REY was about 100 times greater than the activity of the pure matrix catalyst. 

Figure 1. Paraffin yield as a function of carbon number for three catalysts during gas oil cracking.

Gas chromatographs of products from gas oil cracking with three catalysts 100% matrix catalyst (above), 1 Wt.% ZSM-5 in the matrix (middle) and 10 Wt.% REY in the matrix (below). Peaks marked with indicate heavy (020 ) paraffins. 

A mechanism that postulates prevention of paraffin formation during gas oil cracking with the dual zeolite catalyst can explain the above data. Such a prevention could take place by more than one route. ZSM-5 present in the catalyst could prevent certain secondary reactions that lead to the formation of gasoline range... 

Comparison of the catalytic properties of H-Beta and H-Y zeolites for cracking n-heptane and gasoil shows that zeolite Beta should have more than one type of channel with different dimensions. For gas-oil cracking, zeolite Beta is less active and produces more coke and less gasoline than zeolite HY. 

Product selectivity curves for gas-oil cracking on a Beta zeolite with a nominal Si/Al ratio of 10 and 27 are compared in Figures 8 and 9 with those for HY zeolites with framework Si/Al ratios of 7.7 and 35, respectively. 

Figure 7. Comparison between H-Beta zeolites (open circles and dashed lines) and HY zeolites (continuous lines) for gas-oil cracking (a) First-order activity constant by specific surface area vs, Si/Al ratio (b) and (c) Average total conversion vs. gas-oil ratio for a H-Beta with Si/Al=27 and a HY Si/Al=35, and for a H-Beta with Si/Al=10 and a Hy with Si/Al=7.7 respectively. Solid circles correspond to the H-Beta steamed at 750 C and 1 atmosphere of water pressure.

Figure 8. Comparison of selectivity curves for gas-oil cracking on an H-Beta with Si/Al=10 (open circles) and a HY with Si/Al= 7.7 (continuous line).

H-Beta are more active for n-heptane cracking than HY-zeolites with the same Si/Al ratio, while for gas-oil cracking the opposite occurs. Nevertheless we have not looked here to mesoporosity of the zeolites which may be critical for explaining the activity in gasoil cracking. Steaming causes a smaller decreases in activity of H-Beta than on HY zeolite. H-Beta gives a lower ratio than... 

HY in the cracking of n-heptane, while gives more coke and gas, and less gasoline than H-Y for gas-oil cracking. 

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