Catalyst Process Attributes

The activity of an experimental catalyst is an important property of a potential commercial catalyst. Because many commercial polyethylene 

As a general rule, the Cr-based Phillips catalyst used worldwide to manufacture HDPE with a relatively broad MWD, exhibits high catalyst productivity and a steady or increasing rate of polymerization so that polymer morphology is excellent. 

This is not the case for Ti-based catalysts in the presence of high levels of comonomer reqxiired for the manxifactxire of EEDPE. This type of catalyst exhibits a kinetic profile in which the initial rate of polymerization is very high, followed by a rapid decay in kinetics, which may cause operational problems in a commercial reactor. These operational problems are due to the initial rapid rate of polymerization, which affects the manner in which the catalyst particle fragments and the manner in which the polymer particle grows. Other concerns woxild be partial polymer particle melting due to poor removal of the heat of polymerization, which in turn may cause reactor fouling. 

Granular resin bxilk density is an important physical property of finished polyethylene material. Polymer particle morphology determines the amount of polymer that may be contained within the reactor and determines the conveying rates of granular material as the polymer is transferred 

2 Reactivity with Higher 1 -Olefins such as 1 -Butene, 

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Phenol-formaldehyde reactions catalyzed by zinc acetate as opposed to strong acids have been investigated, but this results in lower yields and requires longer reaction times. The reported ortho-ortho content yield was as high as 97%. Several divalent metal species such as Ca, Ba, Sr, Mg, Zn, Co, and Pb combined with an organic acid (such as sulfonic and/or fluoroboric acid) improved the reaction efficiencies.14 The importance of an acid catalyst was attributed to facilitated decomposition of any dibenzyl ether groups formed in the process. It was also found that reaction rates could be accelerated with continuous azeotropic removal of water. 

The narrow molecular weight distributions accomplished by the supported catalysts were attributed to the absence of any organoaluminium co-catalyst dissocia-tion/reassociation processes at the heterogenized active neodymium centers. Furthermore, the order of the grafting sequence seemed to have minor implications for the catalyst performance. Control experiments have been conducted to explain the lower activity [0.9 (47) and 1.1 kg-PBD molNd h (48)] of the supported neodymium catalyst. Accordingly, an increase of the catalyst concentration (48) and use of a nonporous silica support (49) suggested that monomer diffusion and accessibility of the Nd centers are limited by the relatively small mesopores [dp = 2.4 (47) and 2.5 nm (48), after grafting]. 

The economics of the fluid catalyst process represent a considerable improvement over the conventional fixed-bed process. This is attributed to reduced investment and operating costs in addition to the improved yield picture. The investment cost now visualized is very nearly the same as that for the thermal reforming plus catalytic polymerization combination mentioned previously. Consequently, the pay-out times are now shorter than for that process in high or low fuel cost areas. 

These and other observations suggest that a Ru2+ olefin complex is the catalyst precursor. In the absence of a reducing agent, the formation of Ru2+ from Ru3 + salts under the reaction conditions has been shown to occur through a disproportionation process. The increased activity of these recycled Ru2+ and Ru3 + catalysts is attributed to 1) The reduction of the Ru3+ to Ru2 3 (when applicable) and 2) the in situ formation of Ru2+-olefin complexes. 

Gallic acid functions as an effective silicon complexing agent in aqueous ethanolamine solutions. In the absence of it the etch rate is zero. Etch rate increases with water content. The additions of pyrazines, pyridazines, and triazoles show various catalytic effects on the etching process [140]. The catalysts that lead to faster oxidation result in faster etch rates, and the difference among the catalysts is attributed to a steric effect. Oxidative catalysts tend to influence the etching selectivity of the major crystal orientations [94]. 

Figure 1 shows the in-situ XRD patterns of PP-samples recorded at different temperatures. The formation of cerianite form of Ce02 (JCPD-ICDD 43-1002) was observed at around 573 K, and well defined at 973 K. The formation of Cc2(W04)3 phase (JCPD-ICDD 31-0340) was irreversible only at 973 K. The reflections corresponding to this phase were well defined at 1123 K, and the crystallization process was completed at 1173 K (Fig. IB). The same behavior was also observed for the CIT samples (Fig. 2). The formation of this phase seems to occur as a solid-solid reaction between Ce02 and WOx. It is worth to mention that in none of the investigated catalyst, reflections attributable to tungsten oxide species have been detected.

A serious drawback of the process is the catalyst deactivation, which results in low reaction rates and the necessity of a relatively high catalyst/substrate ratio. There are numerous reports in the literature on catalyst deactivation, attributed variously to overoxidation of the catalyst [3-5], irreversible adsorption of by-products [6-8] or dissolution and re-deposition of Pt [5]. It has been suggested that the over-oxidation of active sites can be avoided by working at low and constant level of dissolved oxygen [9]. 

Silica supported chromium catalysts that polymerize ethylene to polyethylene with as many as 12 methyl branches/1000 carbon atoms have been reported. The small amount of branching observed in the ethylene homopolymers prepared by these supported chromocene catalysts was attributed to a chain isomerization process (a) Karol, F. J. Karapinka, G. L. Wu,... 

The high methanol tolerance of PtPd/C alloy catalysts is attributed to the weak competitive reaction of methanol oxidation, which could be induced by composition effects associated with the presence of Pd atoms. The methanol adsorption-dehydrogenation process requires at least three neighboring Pt atoms with appropriate crystallographic arrangement, so, in the case of Pt-Au/C materials, the probability this arrangement in the surface decreases for increasing Au contents. 

A knowledge of these compounds is important because they often have undesirable attributes, e.g., unpleasant odor, the SO2 formed by combustion, catalyst poisoning. There are a number of refining processes to eliminate sulfur compounds. 

Product stereochemistry is a function of the specific catalyst used for hydro-genation. For example, palladium generally gives more of the thermodynamically stable product than other catalysts. This effect has been attributed to an increased rate of equilibration of the steps in the hydrogenation process. Consequently, palladium should not be used to hydrogenate readily isomerizable olefins such as A - and A -steroids. ... 

The biradical catalysts described previously for double-base propints (Ref 80) are also effective for hydrocarbon propints. Table 34 shows how p,p,-biphenylene-bis(diphenylmethyl) compares to n butyl ferrocene as a catalyst in a carboxy-terminated polybutadiene. These catalysts are claimed to overcome all of the processing difficulties, chemical stability and volatility disadvantages attributed to catalysts based on ferrocene and carborane derivatives. Another somewhat similar functioning catalyst, the free radical compd, 2,2-diphenylpicrylhydrazyl,... 

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