Alumina-montmorillonite complexes

Table VIII. Catalytic cracking over alumina-montmorillonite complexes...

The importance of diffusion enhancement to heavy oil cracking is further illustrated by the alumina-montmorillonite complexes which crack heavier feeds, i.e. Wilmington fraction No. 6, more effectively than REY. When used as matrices for REY, the alumina-montmorillonites results in considerably more active catalysts, at the same zeolite content, compared with a catalyst having a kaolin-binder matrix, while the selectivity properties differs very little between the two types of catalysts (Sterte, 3. Otterstedt, 3-E. Submitted to Appl.Catal.). 

The preparation of hydrothermally treated ACH-solutions used in the preparation of alumina montmorillonite complexes (AMC) is described in references (9,10). The ACH-solution (C i = 0.176 M, AI2O3/CI = 0.93) was hydrothermally treated in an autoclave for 2 hr. at temperatures in the range 120-160OC. After deionization and reacidification (to pH 3.9) the colloidal suspensions formed were used at a concentration corresponding to 6.0 g AI2O3 per 1, for the preparation of AMCs. 

Table II. Catalytic Cracking over Alumina-Montmorillonite Complexes alone...

The microporosity of a new tubular silicatelayered silicate nanocomposite formed by the intercalation of imogolite in Na -montmorillonite has been characterized by nitrogen and m-xylene adsorption. The nitrogen adsorption data yielded liquid micropore volume of -0.20 cm g as determined by both the t-plot and the Dubinin-Radusikevich methods. The t-plot provided evidence for a bimodal pore structure which we attributed to intratube and intertube adsorption environments. The m-xylene adsorption data indicated a much smaller liquid pore volume (-0.11 cm g ), most likely due to incomplete filling of intratubular pores by the planar adsorbate. The FTIR spectrum of pyridine adsorbed on the TSLS complex established the presence of both Bronsted and Lewis acid sites. The TSLS complex was shown to be active for the acid-catalyzed dealkylation of cumene at 350 C, but the complex was less reactive than a conventional alumina pillared montmorillonite. 

Figure 8. Catalytic dealkylation of cumene at 350 C over the imogolite-montmorillonite TSLS complex and alumina pillared montmorillonite (APM).

Highly acidic natural clays, montmorillonite are complex layers of S1O4 and AIO4 tetrahedra. They also contain small amounts of MgO and Fe20j. These impurities are leached with sulfuric aid, which also adds protons to increase maximum pK values from -3.0 to -8.2. These clays were the first cracking catalysts used with fixed and moving beds. However, they were quickly replaced by the superior synthetic silica-aluminas that were ideal for fluidized beds. Today, they are used as the matrix in zeolite-based cracking catalyst. 

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

Denecke MA, Reich T, Pompe S, Bubner M, Heise KH, Nitsche H, Allen PG Bucher JJ, Edelstein NM, Shuh DK, Czerwinski KR (1998b) EXAFS investigations of the interaction of humic acids and model compounds with uranyl cations in sohd complexes. Radiochim Acta 82 103-108 Dent AJ, Ramsay JDF, Swanton SW (1992) An EXAFS study of uranyl ions in solutions and sorbed onto sihca and montmorillonite clay colloids. J Colloid Interface Sci 150 45-60 d Espinose de la Caillerie J-B, Kermarec M, Clause (1995a) Impregnation of y-alumina with ( ) and ( ) ions at neutral pH Hydrotalcite-type coprecipitate formation and characterization J Am Chem Soc 117 11471-11481... 

Transalkylation occurs when oxovanadium(iv) octaethylporphyrin is heated with alumina, illite, or montmorillonite, which is an important result in terms of the natural synthesis of porphyrins and their homologues. Spectroscopic studies have been made of the monomer-dimer equilibrium in aqueous media for the 1 1 oxovanadium(iv)-tetrasulphophthalacyanine complex. The dimeric species may contain a V—O—bridge, or the packing of two molecules with a staggered arrangement of the phthalocyanine rings may allow the overlap between their 7t-electron systems to provide the adhesion. ... 

Sylvester, E.R., E.A. Hudson, and P.G Allen. 2000. The structure of uranium(VI) sorption complexes on silica, alumina, and montmorillonite. Geochim. Cosmochim. Acta 64 2431-2438. 

Surface areas determined by N2-BET methods most likely overestimate the amount of sorption sites on layered silicates such as montmorillonite and zeolitic minerals such as clinoptilolite. For example, it is believed that surface complex formation of U(VI) on montmorillonite occurs on the hydroxylated edge sites of the mineral (Zachara McKinley, 1993 Turner et al., 1996). Wanner et al. (1994) estimated that only 10% of the N2-BET specific surface area is accounted for by the crystallite edges of montmorillonite. Assuming that the effective surface area ( e.,) for montmorillonite and clinoptilolite is equivalent to about 10% of the measured 5a, sorption data for montmorillonite and clinoptilolite can be recast in terms of A., , where K. > is normalized to the mineral s 5., (i.e., K = A, /. ). For nonlayered and nonporous minerals such as quartz and a-alumina, A = A, . Figure 10 7 plots... 

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