Pillared rectorite

At this point, the most promising types of pillared clays for use as cracking catalysts are the pillared rectorite developed by Jie et al. (3) and the large pore Ce/Al-pillared smectites developed by McCauley W. Further studies will have to be performed in order to determine the feasibility of these to types of materials for this application. 

Figure 5. A comparison of catalytic activities using a light cycle oil over deactivated catalysts based on pillared montmorillonite, pillared rectorite, NaY and an amorphous silica-alumina FCC.

Pillared rectorites are expanded clay minerals with a surface area in the 150-220 mVg range, and thermal and hydrothermal stability similar to that of zeolites with the faujasite structure (1-4). After steaming at 760°C/5h (100% steam, 1 atm), these materials retain their pillared structure, and at microactivity test conditions (MAT) they are as active as commercial fluid cracking catalysts (FCC) for gas oil conversion... 

The high-resolution characterization of the various rectorite samples was performed at 200 and 400 Kv in a Jeol-2000 electron microscope. The analytical microscopy was performed in a Jeol-lOOCX machine fitted with a Tracor Northern 5500 x-ray detector. Samples were embedded in resin (6, 7) and microtomed in the direction perpendicular to the basal planes (8). The parent rectorite was intercalated with tetrapropylammonium bromide solutions (TPA-Br) to improve the clay stability in the microscope column. The pillared rectorite was instead dispersed in isopropyl alcohol the clay particles were then separated by ultrasonification and deposited onto copper grids. 

Rectorite type clays pillared with AliOj-clusters are initially stable under the electron beam of the microscope however, after exposure for several minutes, the clay crystallinity is lost. At the intermediate magnification power of about 100 kx, pillared rectorite crystals show a sharp edge detail. It is possible to observe a series of rectorite... 

FIGURE 6-9. High-resolution image of pillared rectorite showing nonswelling (ns) and swelling (s) type interlayer spaces. 

FIGURES 6-11 AND 12. ED patterns from faulty crystals of pillared rectorite. Most of the internal reflections are unsymmetrical and some spikes are apparent. 

Other stacking defects observed in the pillared rectorites under study are ... 

A schematic representation of the most common stacking defects observed in pillared rectorites is shown in Hgure 6-19. 

FIGURE 6-20. Electron diffraction pattern from a pillared rectorite crystal. The difruse scattering appears mainly in the central disc and in the mmetrical spots outside the first ring. 

FIGURES 6-24 AND 25. Optical transforms from computer models shown in Figures 6-22 and 6-23, respectively. Notice the diffuse scattering spots, which are similar to ED patterns arising from pillared rectorite crystals (i.e.. Figure 6-20). 

Although there is a fairly good agreement between the Si content in the parent clay measured by AA and by EDS, the pillared rectorite EDS gives lower Si values than AA, as in Table 6-1. The presence of bulky Alu-clusters changes the composition on the clay silicate layers and could prevent the accurate detection of all of the Si present on the clay crystal surfaces. The pillaring reaction removes most of the Na-ions from the crystal surfaces however, residual Mg-ions are still present. Table 6-1. The increased Al Oj content in the expanded rectorite represents that portion of the Alu-cations retained as pillars in the clay interlayer space, see Table 6-1. 

FIGURE 6-7. Lattice resolution image of pillared rectorite. The crystals are 6 to 16 layers thick. The typical edge-on orientation is observed in the upper right-hand comer. 

THERMAL STABILITY, ACIDITY AND CRACKING PROPERTIES OF PILLARED RECTORITE CATALYSTS... 

X-ray diffraction (XRD), pyridine chemisorption, and microactivity test (MAT) results have been used to characterize a sample of natural rectorite pillared with alumina clusters. After reaction with chlorhydrol, a pillared product was obtained that after drying at 100°C/10h had d(OOl) spacing of 28.7 A. The pillared rectorite retained its structure even after calcining in air at 800 C/5h or after steam aging at 760°C/5h with steam at 1 atm. Thus, pillared rectorites have thermal and hydrothermal stability comparable to that of zeolites with the Faujasite structure. 

Steam-aged pillared rectorites, at MAT conditions, have cracking activity similar to that of a commercial fluidized cracking catalyst (FCC) and can be regenerated with ease. However, their coke and light gas (h, CH.) selectivity will have to be drastically improved before these clays can compete with zeolites in cracking catalyst preparation. 

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