Silica-alumina catalyst for

Andreu et ah (11) explained the increased activity (with increasing alumina content of amorphous silica-alumina catalysts) for cracking of sec-butylbenzene by the greater density of acid sites in the high-alumina-content catalysts. Adams et ah (12) proposed that the interaction of several active sites with reactant molecules in mordenite catalysts was partly responsible for the rapid rate of activity loss. 

Nicolaides, C. P., Scurrell, M. S. and Semano, P. M. Nickel silica-alumina catalysts for ethene oligomerization - control of the selectivity to 1-alkene products. Appl. Catal., A, 2003, 245, 43-53. 

The poor selectivity of the thermal decomposition of polyolefins has promoted the development of catalytic cracking. Catalytic cracking lowers the pyrolysis process temperature and lowers the boiling temperature range of the resultant liquid products. The use of molecular sieves and amorphous silica-alumina catalysts for the cracking of waste polymers into a range of hydrocarbons has been widely studied (see Chapters 3-5, 7, 8). 

Commercial production of synthetic silica-alumina catalysts for use in fluid cracking was initiated in 1942. The synthetic catalysts were first manufactured in ground form, but means were later developed for production in MS (micro-spheroidal) form. First shipments of the MS catalyst were made in 1946. The synthetic catalysts contain 10 to 25% alumina. Synthetic silica-magnesia catalyst has also been used commercially in fluid-catalyst units (19,100). Magnesia content is 25 to 35% as MgO (276). 

Morihara K, Kurihara S, Suzuki J (1988) Footprint catalysis LA new method for designing tailor-made catalysts with substrate-specificity-silica (alumina) catalysts for butanolysis of benzoic anhydride. Bull Chem Soc Jpn 61 3991... 

FIGURE 84 Response to shear stress, shown here as the polymer HLMI/MI ratio, as a function of chromium loading on Cr/silica-alumina catalyst for three series of polymers made at constant Ml in the solution process. 

In 1970 Amenomiya and Cvetanovic (7 ) were able to use the reactant chemisorption method in the dimerization and hydrogenation of ethylene over silica-alumina catalysts for et Y ch iso ption they found site densities of the order of 10 to cm for the catalysts. 

Another correlation is shown in Fig. 11 where activity of a number of silica-alumina catalysts for cracking isopropyl benzene is plotted against acidity by titration by anhydrous n-butylamine in nonaqueous medium (Tamele, 9b). Cracking was conducted at 500° at various space velocities. Since the conversion is not a linear function of activity, and the reaction constants could not be calculated from conversions without knowledge of the kinetics of the reaction, values of fc were calculated... 

Cammidge, A.N. Baines, N.J. Bellingham, R.K. Synthesis of heterogeneous palladium catalyst assemblies by molecular imprinting. Chem. Commun. 2001, 2588-2589. Morihara, K. Kurihara, S. Suzuki, J. Footprint catalysis. I. A new method for designing tailor-made catalysts with substrate specificity silica (alumina) catalysts for butanolysis of benzoic anhydride. Bull. Chem. Soc. Jpn. 1988, 61, 3991-3998. Morihara, K. Nishihata, E. Kojima, M. Miyake, S. Footprint catalysis. II. molecular recognition of footprint catalytic sites. Bull. Chem. Soc. Jpn. 1988, 61, 3999-4003. Shimada, T. Makanishi, K. Morihara, K. Footprint catalysis. IV. structural effects of templates on catalytic behavior of imprinted footprint cavities. Bull. Chem. Soc. Jpn. 1992, 65, 954-958. 

Upgrading of the aromatic feedstock (pyrolysis gasoline) over bifunctional Pt catalysts on MFI, BEA, and faujasite (FAU) zeolites, and an amorphous silica-alumina [61] at 5 MPa and 350-450°C was performed in different directions the Pt/MFI catalyst was optimal for a steam cracker feedstock production, the Pt/BEA catalyst—for isoalkane-rich gasoline pool manufacture and the Pt/silica-alumina catalyst for severe aromatic reduction while controlling the extent of ring scission. 

The analysis is thus relatively exact for heterogeneous surfaces and is especially valuable for analyzing changes in an adsorbent following one or another treatment. An example is shown in Fig. XVII-24 [160]. This type of application has also been made to carbon blacks and silica-alumina catalysts [106a]. House and Jaycock [161] compared the Ross-Olivier [55] and Adamson-Ling... 

Zeolites as cracking catalysts are characterized hy higher activity and better selectivity toward middle distillates than amorphous silica-alumina catalysts. This is attrihuted to a greater acid sites density and a higher adsorption power for the reactants on the catalyst surface. 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

As an example of the selective removal of products, Foley et al. [36] anticipated a selective formation of dimethylamine over a catalyst coated with a carbon molecular sieve layer. Nishiyama et al. [37] demonstrated the concept of the selective removal of products. A silica-alumina catalyst coated with a silicalite membrane was used for disproportionation and alkylation of toluene to produce p-xylene. The product fraction of p-xylene in xylene isomers (para-selectivity) for the silicalite-coated catalyst largely exceeded the equilibrium value of about 22%. 

As described in the previous section, the silica-alumina catalyst covered with the silicalite membrane showed exceUent p-xylene selectivity in disproportionation of toluene [37] at the expense of activity, because the thickness of the sihcahte-1 membrane was large (40 pm), limiting the diffusion of the products. In addition, the catalytic activity of silica-alumina was not so high. To solve these problems, Miyamoto et al. [41 -43] have developed a novel composite zeohte catalyst consisting of a zeolite crystal with an inactive thin layer. In Miyamoto s study [41], a sihcahte-1 layer was grown on proton-exchanged ZSM-5 crystals (silicalite/H-ZSM-5) [42]. The silicalite/H-ZSM-5 catalysts showed excellent para-selectivity of >99.9%, compared to the 63.1% for the uncoated sample, and independent of the toluene conversion. 

This work is a contribution to the understanding of the effect of spillover hydrogen in a type of catalyst of considerable industrial importance, namely that composed of transition metal sulfides and amorphous acidic solids. This is typically the case of sulfided CoMo supported on silica-alumina used for mild hydrocracking. 

ILLUSTRATION 12.3 DETERMINATION OF CATALYST EFFECTIVENESS FACTOR FOR THE CUMENE CRACKING REACTION USING THE EFFECTIVE DIFFUSIVITY APPROACH Use the effective diffusivity approach to evaluate the effectiveness factor for the silica-alumina catalyst pellets considered in Illustration 12.2. 

Recently, Muha (83) has found that the concentration of cation radicals is a rather complex function of the half-wave potential the concentration goes through a maximum at a half-wave potential of about 0.7 V. The results were obtained for an amorphous silica-alumina catalyst where the steric problem would not be significant. To explain the observed dependence, the presence of dipositive ions and carbonium ions along with a distribution in the oxidizing strengths of the surface electrophilic sites must be taken into account. The interaction between the different species present is explained by assuming that a chemical equilibrium exists on the surface. 

Kureha A process for making di-isopropyl naphthalene mixtures from naphthalene and propylene by transalkylation. It operates at 200°C, using a silica/alumina catalyst. Operated in 1988 at the Rutgerswerke plant in Duisberg-Meiderich, Germany. The name has also been used for a process for making acetylene from petroleum. 

Leonard A process for making mixed methylamines by reacting ammonia with methanol over a silica-alumina catalyst at elevated temperature and pressure. Developed and licensed by the Leonard Process Company. In 1993, the installed worldwide capacity of this process was 270,000 tonnes/y. 

Xylenes-plus A catalytic process for isomerizing toluene to a mixture of benzene and xylenes. A silica/alumina catalyst is used in a moving bed. It is unlike the related Tatoray process, in that no hydrogen is required. Developed by Sinclair Research in 1964 and then licensed by Atlantic Richfield. 

Let us consider the data taken by Laible (LI) on the dehydration of normal hexyl alcohol at 450°F over a silica alumina catalyst. The single- and dualsite surface reaction controlled models applying to alcohol dehydration were discussed in Section V,A,2. We now consider, however, the functional forms given, for example, by Eq. (84), as probably being capable of describing the data, but do not restrict the Ct and C2 plots to a linear pressure dependence as before. Rather, we obtain an empirical pressure dependence from the... 

Fig. 9. A comparison of the results computed from Eq. (12) for transitional burning (indicated by O) with the observed burning rate behavior for silica-alumina catalyst (solid curve).

Fig. 10. Mass balance y versus z graph for kiln operating with conventional green silica-alumina catalyst.

Fig. 11. Simulation of y versus x for the Beaumont T-2 kiln operating with conventional green silica-alumina catalyst. Computed results are given by the solid curve. The observed values, obtained fix>m a vertical traverse, are given by the points. The operating conditions were as follows flow of air up—23,500 scfm (665 semm) flow of air down—13,600 scfm (385 semm) air temperature at inlet—120°F (4 >°C) O2 in air to kiln—21% catalyst circulation rate—348 tons/hr (3.16 x KF kg/hr) catalyst inlet temperature (1-ft level)—900°F (482°C) coke on catalyst (1-ft level)—1.5%.

We carried out the reaction in a flow system under conditions such that the conversion level was high but well below equilibrium conversion. We used C.P. 1-butene from Matheson and passed it over 100-200 mesh Mobil silica-alumina catalyst [10% AljOj surface area, 393m g (BET)] the batch was heated 1 hr at 450°C in an air stream and kept in a closed container. Gas chromatographic analysis was used neither reactant impurity nor a thermal rate was found to be a complicating factor. The reaction was carried out at 120, 135, 150, and 165°C at several partial pressures, using N2 as diluent, up to 0.95 atm. The reactant flow rate was always 1.56 x 10" mole min A steady state was achieved in about 20 min, and the activity for a run was taken to be the average of three determinations made between 35 and 50 min. 

Also other Type B and C series from Table II are consistent with the above elimination mechanisms. The dehydration rate of the alcohols ROH on an acid clay (series 16) increased with the calculated inductive effect of the group R. For the dehydrochlorination of polychloroethanes on basic catalysts (series 20), the rate could be correlated with a quantum-chemical reactivity index, namely the delocalizability of the hydrogen atoms by a nucleophilic attack similar indices for a radical or electrophilic attack on the chlorine atoms did not fit the data. The rates of alkylbenzene cracking on silica-alumina catalysts have been correlated with the enthalpies of formation of the corresponding alkylcarbonium ions (series 24). Similar correlations have been obtained for the dehydrosulfidation of alkanethiols and dialkyl sulfides on silica-alumina (series 36 and 37) in these cases, correlation by the Taft equation is also possible. The rate of cracking of 1,1-diarylethanes increased with the increasing basicity of the reactants (series 33). 

As another variation, the production of alkanes can be accomplished by modifying the support with a mineral acid (such as HCl) that is co-fed with the aqueous sorbitol reactant. In general, the selectivities to heavier alkanes increase as more acid sites are added to a non-acidic Pt/alumina catalyst by making physical mixtures of Pt/alumina and silica-alumina. The alkane selectivities are similar for an acidic Pt/silica-alumina catalyst and a physical mixture of Pt/alumina and silica-alumina components, both having the same ratio of Pt to acid sites, indicating that the acid and metal sites need not be mixed at the atomic level. The alkane distribution also shifts to heavier alkanes for the non-addic Pt/alumina catalyst when the pH of the aqueous sorbitol feed is lowered by addition of HCl. The advantages of using a solid acid are... 

Silica-alumina catalysts are acidic and presumably can furnish protons for the formation of carbonium ions (Kazanskii and Rozen-gart, 21). 

The rate of reaction of propylene over the MeReOs/HMDS/silica-alumina catalyst (1.4 wt% Re) is shown in Figure 2b. The profile is similar to that of the Sn-promoted perrhenate catalyst, with kobs = (1-78 + 0.09) x 10" s, and the activity responds similarly to subsequent additions of propylene. In fact, the pseudo-first-order rate constant for the organometallic catalyst lies on the same line as the rate constants for the Sn-promoted perrhenate catalyst. Figure 3. Therefore we infer that the same active site is generated in both organometallic and promoted inorganic catalyst systems. 

There has been an enormous technological interest in tertfa/j-butanol (tBA) dehydration during the past thirty years, first as a primary route to methyl te/f-butyl ether (MTBE) (1) and more recently for the production of isooctane and polyisobutylene (2). A number of commercializable processes have been developed for isobutylene manufacture (eq 1) in both the USA and Japan (3,4). These processes typically involve either vapor-phase tBA dehydration over a silica-alumina catalyst at 260-370°C, or liquid-phase processing utilizing either homogenous (sulfonic acid), or solid acid catalysis (e.g. acidic cationic resins). More recently, tBA dehydration has been examined using silica-supported heteropoly acids (5), montmorillonite clays (6), titanosilicates (7), as well as the use of compressed liquid water (8). 

---