Isomerization catalyst activity

Disproportionation process those containing Ce or Eu, have an increased catalyst activity and lifetime Isomerization, kinetically controlled in 46... 

Cobalt catalysts such as HCo(CO)4 are widely used for hydroformyla-tion of higher alkenes, despite the higher temperatures and pressures required. The main reason for this is that these catalysts are also efficient alkene isomerization catalysts, allowing a mix of internal and terminal alkenes to be used in the process. Catalyst recovery is more of a problem here, involving production of some waste and adding significantly to the complexity of the process. A common recovery method involves treating the catalyst with aqueous base to make it water soluble, followed by separation and subsequent treatment with acid to recover active catalyst (4.3). 

We compared Pt/silica-alumina, yttria-modified silica-alumina, and fluorided alumina for n-Ci2 isomerization. Not surprisingly, increasing yttria content lowers catalyst activity at a fixed space velocity (Fig. 10). The 9% Y203/Si-Al catalyst compares closely to the 1%F/Al203 catalyst in activity. Of the catalysts evaluated here, the 9%Y203-loaded Si-Al had higher isomerization selectivity at equal conversion (Fig. 11). 

A series of anchored Wilkinson s catalysts were prepared by reacting the homogeneous Wilkinson catalyst with several alumina/heteropoly acid support materials. These catalysts were used to promote the hydrogenation of 1-hexene. The results were compared with those obtained using the homogeneous Wilkinson and a l%Rh/Al203 catalyst with respect to catalyst activity and stabihty as well as the reaction selectivity as measured by the amount of double bond isomerization observed. The effect which the nature of the heteropoly acid exerted on the reaction was also examined. 

Figure 24 shows the cfs-butene isomerization over zinc oxide as a function of time at room temperature (7/). On a per unit area basis the initial rate at room temperature is 4 X 1010 molecules/sec cm2, a rate roughly one third that reported for alumina (69). Since the activation energy for alumina is less than that found for zinc oxide, this means that zinc oxide is comparable (on a per unit area basis) to alumina as an isomerization catalyst at slightly higher temperatures. 

The objective of this work is to determine the influence of the porous structure (size and shape) and acidity (number and strength of the acid sites) on isomerization selectivity during the conversion of ethylbenzene on bifunctional catalysts PLAI2O3/ 10 MR zeolite. The transformation of EB was carried out on intimate mixtures of Pt/Al203 (PtA) and 10 MR zeolites (ZSM-5, ZSM-22, Ferrierite, EU-1) catalysts and compared to Mordenite reference catalyst activity. 

Microwave irradiation of catalysts before their use in chemical reactions has been found to be a new promising tool for catalyst activation. Microwave irradiation has been found to modify not only the size and distribution of metal particles but probably also their shape and, consequently, the nature of their active sites. These phenomena might have a significant effect on the activity and selectivity of catalysts, as found in the isomerization of 2-methylpentene on a Pt catalyst [2],... 

Not all acids are equally active isomerization catalysts. With zeolite H-BEA, nearly identical selectivities are achieved when the feed is 1-butene instead of 2-butene (48). In general, even mildly acidic zeolites are excellent catalysts for double-bond shift isomerization. Sulfuric acid also produces nearly identical... 

Kubica et al45 also investigated the effect of platinum-modified zeolites on the decalin reaction. They found that the addition of Pt enhances the catalyst activity. The initial isomerization was increased 3 times, which can be interpreted in terms of a change in the reaction initiation. In addition to initiation by a PC step over Bronsted acid sites, as proposed for H-form zeolites, a bifunctional initiation path... 

Isomerization processes produce sour water and caustic wastewater. The ether manufacturing process utilizes a water wash to extract methanol or ethanol from the reactor effluent stream. After the alcohol is separated, this water is recycled back to the system and is not released. In those cases where chloride catalyst activation agents are added, a caustic wash is used to neutralize any entrained hydrogen chloride. This process generates a caustic wash water that must be treated before being released. This process also produces a calcium chloride neutralization sludge that must be disposed of off-site. 

The catalytic coke produced by the activity of the catalyst and simultaneous reactions of cracking, isomerization, hydrogen transfer, polymerization, and condensation of complex aromatic structures of high molecular weight. This type of coke is more abundant and constitutes around 35-65% of the total deposited coke on the catalyst surface. This coke determines the shape of temperature programmed oxidation (TPO) spectra. The higher the catalyst activity the higher will be the production of such coke [1],... 

III,C, isomerization often accompanies hydroformylation. It has, however, been found that [(PhCN)2PdCl2] absorbed onto silica gel is 100 times more active for the isomerization of a-olefins, such as 1-heptene, than is the same complex alone (116). This implies some specific role for the silica gel. Attempts to use rhodium(III) chloride absorbed onto silica gel, alumina, activated charcoal, and diatomaceous earth as a-olefin isomerization catalysts showed that all these catalysts were unstable even at room temperature (100). 

The other vapor-phase butane isomerization process, developed cooperatively by the Anglo-Iranian Oil Co. and the Standard Oil Development Co., is somewhat similar to the Isocel process. In the AIOC-Jersey process (18), the reactor is initially filled with bauxite, and aluminum chloride is sublimed into the vaporized feed as necessary to maintain the desired catalyst activity. Upflow of vapor through the reactor is the customary arrangement. Since carry-over of aluminum chloride is not excessive at the usual rates of catalyst addition, about half of the commercial plants employing this process were not equipped with guard chambers. 

Another novel catalyst modification has been suggested in which the active Co-Mo-S catalyst is used in combination with an acidic catalyst such as a zeolite. This combination has the potential of opening another reaction pathway by isomerization of the alkyl groups on molecules such as 4,6-DMDBT to positions that do not sterically interfere with adsorption or oxidative addition. This is illustrated in Fig. 33. Gates and co-workers reported many years ago that the 2,8- and 3,7-dimethyldibenzothiophenes are much more easily desulfurized than 4,6-DMDBT (see Table XII) (26). Therefore, a combination of an isomerization catalyst and a desulfurization catalyst could be synergistic for removing dialkylbenzothiophenes. 

Two studies in 1985 and 1992 focused on the use of superacids in isomerization.20,21 An important advantage of these catalysts is that they may be used at lower temperature because of their greatly increased ability to bring about carbo-cationic process. For example, aluminum chloride, still one of the important isomerization catalysts in industry, can be used at about 80-100°C. In comparison, superacids are active in alkane isomerization at room temperature or below. In addition to avoid side reactions under such conditions, lower reaction temperatures favor thermodynamic equilibria with higher proportion of branched isomers, which is fundamental in increasing the octane number of gasoline. 

Dienes undergo isomerization due to shifts of the double bonds. The reversible isomerization of allenes to acetylenes is catalyzed characteristically by basic reagents (see Section 4.2.2). Nonconjugated alkadienes tend to isomerize to conjugated alkadienes the conversion is usually accompanied by polymerization. Among other catalysts, activated alumina and chromia-alumina may be used to catalyze the formation of conjugated dienes.89,106-108... 

Low temperature isomerization catalysts are of the Friedel Crafts type, such as AICI3 and AlBr3, activated with HX, and dissolved in a suitable solvent such as SbCl3. Application of these extremely acidic and corrosive systems requires special handling and disposal of the catalyst and careful pretreatment of the feed-stock to remove contaminating materials. Low temperature isomerization (< 100° C) is used mainly for isomerization of w-butane, which is generally available in sufficient purity by normal refinery processes. 

In the reaction mechanisms described above the acidity of the catalyst plays an important role. Zeolites can be converted into the H+ form and as such are powerful catalysts for acid-catalyzed reactions. We discuss below some aspects of isomerization catalyst preparation to demonstrate factors which influence the activity of catalysts based on zeolites. In this discussion we are concerned with zeolite Y and mordenite. Data on paraffin isomerization over dual function catalysts besed on other zeolites are scarce, and no data have been published showing that materials like zeolite X, zeolite L, offretite, zeolite omega, or gmelinite can be converted into catalyst bases having an isomerization activity comparable with that of H-zeolite Y or H-mordenite. 

For optimal performance of dual function isomerization catalysts based on zeolite Y or mordenite, extensive removal of sodium is necessary. The finished catalyst must be highly crystalline, and the finely dispersed metallic hydrogenation function should be well distributed throughout the catalyst particles. The proposed mechanism explains the stabilizing influence on conversion and the suppression of cracking reactions by addition of the metallic hydrogenation function to the active acidic catalyst base. 

From the general inaccessibility of both the sodium and TMA ions, we postulate that most of the acidic sites generated by thermal treatment of the derived NH4+/TMA+ zeolite will also be inaccessible to reactant molecules. Likewise, catalytically active metals such as Pt and Pd introduced by ion exchange are expected to be located in or near these same inaccessible sites. This may explain the poor approach to equilibrium observed with the isomerization catalysts, and the poor hydrogenation activity of the hydrocracking catalyst indicated by excessive coking and catalyst decline, even in the presence of a massive 3.1 wt % palladium. 

The commercialized BP and UOP processes employ different dual functional platinum catalysts. The BP process was first commercialized between 1963 and 1966 the UOP process in 1959. The BP catalyst has not been modified since its commercial introduction, but the UOP catalyst system has undergone further development (24). An advantage of the BP process is that the catalyst is activated and regenerated in situ. Considering the hydroscopic nature of all the isomerization catalyst sys-... 

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