Catalysts mixed

Mixed catalysts have the titanium in the oxidation states four and three together with an organic aluminum compound. The molar ratio of Ti[V to Tini is preferably 2.6 1 (4). Such a catalyst, preactivated with triethylaluminum exhibits a low tendency to form deposits. Other catalyst systems are based on organic zirconium or hafnium compounds. 

One of the most economical routes to most commercial grades of olefin polymers is the loop slurry process with a paraffin diluent. This process was introduced by Chevron Phillips in 1960 (7). There, a mixture of catalyst particles, growing polymer particles, comonomers, and diluent is pumped in a loop. The polymer particles are harvested by guiding a side stream of the slurry to settling chambers, where the polymer particles settle toward the bottom. 

The polymerization process can be carried out at a temperature low enough that the resulting polymer is largely insoluble in the diluent. The pressures in the loop slurry process are in the range of 2.5-4 MPa. 

Alkyl compounds of Group IVB metals can readily eliminate a hydrogen through a mechanism referred to as /1-hydride elimination (8), as shown in Eq. 3.1. 

Properties of polymers obtained with supported zirconium tetra-kis(trimethylsilylmethyl) catalyst systems are shown in Table 3.1. 

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Mixed alginate salts Mixed catalysts Mixed cellulose ethers... 

Molecular Weight Distribution. In industry, the MWD of PE resins is often represented by the value of the melt flow ratio (MER) as defined in Table 2. The MER value of PE is primarilly a function of catalyst type. Phillips catalysts produce PE resins with a broad MWD and their MER usually exceeds 100 Ziegler catalysts provide resins with a MWD of a medium width (MFR = 25-50) and metallocene catalysts produce PE resins with a narrow MWD (MFR = 15-25). IfPE resins with especially broad molecular weight distributions are needed, they can be produced either by using special mixed catalysts or in a series of coimected polymerization reactors operating under different reaction conditions. 

Processes for HDPE with Broad MWD. Synthesis of HDPE with a relatively high molecular weight and a very broad MWD (broader than that of HDPE prepared with chromium oxide catalysts) can be achieved by two separate approaches. The first is to use mixed catalysts containing two types of active centers with widely different properties (50—55) the second is to employ two or more polymerization reactors in a series. In the second approach, polymerization conditions in each reactor are set drastically differendy in order to produce, within each polymer particle, an essential mixture of macromolecules with vasdy different molecular weights. Special plants, both slurry and gas-phase, can produce such resins (74,91—94). 

Monosaccharides such as glucose and fmctose are the most suitable as starting materials. When starch is used, it is first hydrolyzed with oxahc acid or sulfuric acid into a monosaccharide, mainly glucose. It is then oxidized with nitric acid in an approximately 50% sulfuric acid solution at 63—85°C in the presence of a mixed catalyst of vanadium pentoxide and iron(III) sulfate. 

B. A. Kottes Andrews and R. M. Reinhardt, "How Mixed Catalysts Differ," paper presented at the Fourth Mnnual Natural Fibers Textile Conference, New Orleans, La., Sept. 14—16, 1981. 

Static mixing catalysts Operation Monolithic reactors Microreactors Heat exchange reactors Supersonic gas/liquid reactor Jet-impingement reactor Rotating packed-bed reactor... 

Fig. 2. XRD of Cu-Mixed catalyst before and after reaction (A AIF3 B CaF2 C CuO D CaAfF,).

It was eoncluded that the enhanced selectivity and yield for TFE over Cu-Mixed catalyst may be attributed to the surface modifications by the attack of HF produced during the pyrolysis of R22. The results suggest that R23 is formed by the secondary reaction between intermediate CF2 and HF. 

The Ni based anode catalysts were prepared by a physical mixing method. NiO (99.99%, Sigma-Aldrich Co.), YSZ (TZ-8Y, TOSOH Co.), MgO (98%, Nakarai Chemical Co.) and Ce02 (99.9%, Sigma-Aldrich Co.) were used as raw materials. The physically mixed catalyst... 

Rytter et al. reported polymerizations with the dual precatalyst system 14/15 in presence of MAO [30]. Under ethylene-hexene copolymerization conditions, 14/MAO produced a polymer with 0.7 mol% hexene, while the 15/MAO gave a copolymer with ca. 5 mol% hexene. In the mixed catalyst system, the activity and comonomer incorporation were approximate averages of what would be expected for the two catalysts. Using crystallization analysis fractionation (CRYSTAF) and differential scanning calorimetry (DSC) analysis, it was concluded in a later paper by Rytter that the material was a blend containing no block copolymer [31],... 

The GPC trace is dramatically different when a CSA is added in the mixed catalyst system in that a simple composite GPC is not obtained (Fig. 13). Inclusion of either TEA or DEZ in the polymerization produces a single peak in the GPC,... 

Gaseous alkanes such as methane, ethane, and propane were also carboxylated to give acetic, propionic, and butyric acids, respectively, as shown in Table 3 102,103,103a Ethane and propane were best carboxylated by the mixed catalyst of Pd(OAc)2 and Cu(OAc)2, while methane was not effectively carboxylated by the same catalytic system. In the case of methane, Cu(OAc)2 gave the best result among the catalysts employed. However, the yield of acetic acid based on methane is low (Equation (78)). 

Figure 3. Influence of the composition of PVP-Cu,Mn mixed catalyst on activity...

Air or dioxygen can be used as an oxidant with non-chiral DABCO to give a low cost catalyst for dihydroxylation of alkenes into racemic mixtures dihydroquinidine modified catalysts with the air variant give lower e.e. s than the AD-mix catalysts [26],... 

The analysis of the EXAFS of alloy catalyst particles is inherently more complicated than that of single metals. In the case of PtRu catalysts there is an added complication that the backscattering from Pt and Ru neighbors at similar distances interfere with one another, giving rise to beats in the EXAFS data. This phenomenon was first described by McBreen and Mukerjee ° for a poorly alloyed 1 1 atomic ratio PtRu/C catalyst. The presence of beats in the EXAFS data is more apparent in the EXAFS obtained at the Pt L3 edge for a well mixed 1 1 PtRu/C catalyst than in that of a poorly mixed catalyst of the same composition, as shown in Figure 27 compare panels a and c. Pandya et al. showed that the beats occur because the difference in the backscattering phase shifts from Pt and Ru is... 

Reactant Mixing Catalyst Reaction Zone-Zone (cooled) Single Winding Channel (Heated)... 

Jackson, R., Optimal use of mixed catalysts for two successive chemical reactions, Journal of Optimization Theory and Applications 2(1), 27 (1968). 

Generally, variations of the chemical nature of the catalyst have not, so far, yielded as much information as have the systematic variations of the compositions of multicomponent catalysts. Most mixed catalysts in industry are heterogeneous mixtures. It would go beyond the scope of the present article to review them. But it is noticeable that, in general, two kinds of promoter action can be distinguished (1) Structural promotion in which the activation energy of the active constituent... 

A characteristic of catalysis processes is that a variety of compounds may catalyse a particular reaction, but only one or two of these catalysts show enough selectivity, activity and stability to warrant use in an industrial process. Selectivity is the ability of a catalyst to increase the relative rate of formation of a desired product when two or more competing reactions may occur. For modification of the direction of a reaction, mixed catalysts consisting of two compounds both with moderate to good catalytic activity have been developed. For example, the vapour phase oxidation of alcohols to aldehydes and ketones involves a mixed a- Fe203/ M0O3 catalyst rather than a single oxide. 

Aliphatic azo compounds Lewis acids with or without co-initiators Lewis bases Mixed catalysts (Ziegler-Natta catalysts)... 

Besides ethylene, higher olefins (propylene, 1-butylene), dienes, and a number of other monomers can be polymerized with organometallic mixed catalysts the polymerization frequently proceeds stereospecifically, leading to tactic polymers (see Examples 3-30 to 3-32). 

These requirements have met using a mixed catalystic system consisting of an iron catalyst complex that can oligomerize ethylene and a zirconium transition metal complex that can copolymerize ethylene and the nonconjugated monomer 5-ethylidene-2-norbomene. Using this catalytic pair nonbrancy poly(ethylene-co5-ethylidene-2-norbomene) and poly (ethylene-col,4-hexadiene) were prepared. 

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