Zeolites surface area

The reported surface area is the combined surface area of zeolite and matrix. In zeolite manufacturing, the measurement of the zeolite surface area is one of the procedures used by catalyst suppliers to control quality. The surface area is commonly determined by the amount of nitrogen adsorbed by the catalyst. 

The surface area correlates fairly well with the fresh catalyst activity. Upon request, catalyst suppliers can also report the zeolite surface area. This data is useful in that it is proportional to the zeolite content of the catalyst. 

The results of this work suggest that the greatest contaminant metals effects are due not only to the most recently deposited metals, but to those recently deposited metals which are present on the most recently added zeolitic particles (i.e., those containing the most zeolite). At constant metals aging then, the contaminant selectivities due to nickel and vanadium are in a large part determined by 1) the presence or absence of zeolite in the particle 2) the non-zeolitic surface area of the particle and 3) the chemical composition of the particle. 

It was obvious that the catalysts had to be optimized for North Sea atmospheric residues. In order to find a more nsefnl catalyst than the reference catalyst, two new catalysts were tested. The first one, Catalyst B, was selected based on resnlts from the previous tests the matrix surface area was reduced to an optimal size. The zeolite surface area was however kept constant. The second new catalyst. Catalyst C, was selected according to the old general recommendation for residne catalysts, and both the zeolite and matrix snrface areas were increased compared to the reference catalyst. The surface areas for the three catalysts are shown in Table 3.10. 

The reference catalyst A and Catalyst B had both a low activity compared with catalyst C as shown in Fignre 3.14. One explanation for this might be the low zeolite surface area for both the reference catalyst and for Catalyst B. Catalyst C had the highest activity of the three catalysts because of its high zeolite surface area and despite its high matrix snrface area. 

The naphtha yield was lower for Catalyst B than for the reference and this illustrates the necessity to have enough zeolite surface area in the catalyst to be able to crack all the components in the feed, both those that can be cracked directly and those that must be precracked on the matrix before they can be cracked by the zeolite. Catalyst C had a slightly higher naphtha maximum than the reference catalyst, despite its high matrix surface area. The high matrix surface area of Catalyst C,... 

The coke yield was highest for the reference catalyst and this might be explained by the fact that the matrix surface area was high but the zeolite surface area was too low to crack all the precracked molecules. These precracked molecules could then... 

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. 

According to the literature, an optimal long residue catalyst should have a pore volume higher than 0.30 cc/g [20]. This limit is however very vague, and we have found catalysts with a pore volume as low as 0.20 cc/g that have performed well in the pilot riser, and opposite is a catalyst with a pore volume of 0.34 cc/g that did not [21]. We have found a slight correlation between the pore volume and the matrix surface area, but not between the pore volume and the zeolite surface area. Due to this lack of correlation, it is not possible to use the pore volume for predicting the performance of a long residue catalyst for our application. 

The total surface area of a FCC catalyst is the sum of the zeolite and matrix surface areas and is therefore not useful for optimizing of the catalysts. However, the ratio between the zeolite and the matrix surface areas (ZSA/MSA) is a valuable parameter, and has been used for optimization of vacuum gas oil catalysts [4] as well as catalysts for North Sea long residue feeds [9,13]. Additional information about the catalyst is also gained by studying the yields as a function of the zeolite surface area and as a function of the matrix surface area [9]. The regression analysis in this paper is performed at a constant conversion of 75 wt%. 

Additional support for our observations was found when catalysts A-1 to A-3 were stndied. Catalyst A-1 was developed according to the old recommendations for a residue catalyst with a moderate zeolite surface area and a large active matrix snrface area. The catalyst did not give as good naphtha selectivity as expected when the North Sea long residue feed was cracked. An attempt to improve this was made with catalyst A-2 where the matrix surface was lowered, while the zeolite surface area was kept the same. The naphtha selectivity was however not improved, and it was concluded that the zeolite surface area was too low. So in catalyst A-3 the zeolite snrface area instead was increased compared with the base catalyst A-1. Now the naphtha selectivity increased, but the gas yields also increased dramatically. This catalyst did indicate that a possible way to go could be to increase the zeolite surface... 

The LPG yield decreased when the ZSA/MSA ratio and the zeolite surface area increased for both types of catalysts, see Figure 4.4a and b. The reason for this might be that the LPG yield nsnally decreases when the naphtha selectivity increases. This might also explain the fact that the LPG yield increased for type A catalysts when the matrix snrface area increased. However, the LPG yield was almost unaffected of any changes in the matrix surface area for Type B catalysts, see Figure 4.4c. 

Pilot unit tests have indicated that there is an upper limit for the zeolite to matrix surface area ratio (ZSA/MSA) for a residue catalyst. This observation was in contrast to the optimization study, which indicated that the ZSA/MSA should be as high as possible for maximum naphtha yield. An increase in the zeolite surface area is, according to the optimization study, expected to increase both the activity of the catalyst and its naphtha yield. But for catalysts with a high ZSA/MSA ratio, close to four or even higher, the observed naphtha yields have been lower than expected in the pilot unit tests, which indicate that there might be an upper limit for the ZSA/ MSA ratio in a residue application. 

As can be seen in Figure 4.8, the activity of the catalysts increased when the zeolite content of the catalyst increased. Since the matrix surface area was kept the same, the ZSA/MSA surface area ratio also increased. When comparing catalyst C-1 and catalyst C-2, the zeolite surface area was increased with 31 m /g, and the ZSA/MSA ratio increased from 2.5 to 3.5. As expected from our optimization studies, the activity for catalyst C-2 was significantly improved compared with catalyst C-1. The increase in activity was however not by far so pronounced for catalyst C-3, where the zeolite surface area was further increased with 21 m /g compared to catalyst C-2, which increased the ZSA/MSA surface area from 3.5 to 3.9. 

The N2 adsorption (with BFT and BJH methods) results listed in Table 5.2 showed that the zeolite surface area and pore volume were apparently increased after CP treatment. For example, compared with DASY(0.0) the specific surface area of SOYO-S3 increased by 53 m /g from 618 to 671 m /g, and the pore volume increased from 0.352 to 0.393 mL/g. In addition, DTA analysis data listed in Table 5.2 showed that the thermal stability of the zeolite was further improved. 

FIGURE 9.1 Correlation between Bronsted acidity and Zeolite surface area for all the trials of CPS and ADV-CPS in the presence of metals. 

When the zeolite surface area is plotted as a function of catalytic coke the correlation improves. The best correlation between the physicochemical properties of the catalyst and catalytic coke is the one involving an amount of aluminums in the framework estimated from the unit cell size by Equation 10.1 [1], as it is evidenced in Figure 10.2. 

By way of example, Figure 3 shews the effect of steaming severity on zeolitic surface area (ZSA) for catalyst A and C. Also identified are typical values for equilibrium catalysts. What is seen is that the conditions needed to deactivate A to typical equilibrium ZSA are different than for C. If C is deactivated using the preferred conditions for A, then activity and surface areas are not in line with commercial experience. If the reverse is true, then A is deactivated too severely. 

Figure 3. STEAMED CATALYST PROPERTIES Zeolite Surface Area Reduction to EQ Level is Catalyst Dependent.

Effect of Sodium on FCC Ecat Matrix and Zeolite Surface Areas As... 

Figure 4. Effect of Sodium on Ecat Zeolite Surface Area...

Figure 2. Effect of oxidative vs. inert atmosphere on vanadium induced loss of zeolite surface area (ZSA).

This treatment causes a decrease of the zeolite surface area as measured by N2 adsorption at 77 K and a decrease in Ga/Si as measured by XPS (Table 1). 

Surface areas of catalysts were determined by N2 adsorption using an ASAP 2000 analyzer from Micromeritics. Matrix and zeolite surface areas were calculated by the t-plot method accordingly to the ASTM-D-4365 standard test [11]. Zeolite unit cell size (UCS) was determined by X-Ray diffraction using a SIEMENS D-500 automated analyzer according to the ASTM-D-3942-80 standard [11]. 

Upon deactivation and metallation veilues of zeolite UCS and matrix surface area (Table 1) are similar to those for ECAT except for the most aged fraction ECAT2F1. It appears that zeolite surface area reduction is essentially due to steaming. Upon metallation it undergoes further reduction similar to that obtained after 10 h steaming. 

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