Catalyst parameters

The semibatch model GASPP is consistent with most of the data published by Wisseroth on gas phase propylene polymerization. The data are too scattered to make quantitative statements about the model discrepancies. There are essentially three catalysts used in his tests. These BASF catalysts are characterized by the parameters listed in Table I. The high solubles for BASF are expected at 80 C and without modifiers in the recipe. The fact that the BASF catalyst parameters are so similar to those evaluated earlier in slurry systems lends credence to the kinetic model. 

BASF CATALYST PARAMETERS AT REFERENCE TEMPERATURE OF 80 C GAS PHASE PROPYLENE POLYMERIZATION... 

Table II summarizes the yields obtained from the CONGAS computer output variable study of the gas phase polymerization of propylene. The reactor is assumed to be a perfect backmix type. The base case for this comparison corresponds to the most active BASF TiC 3 operated at almost the same conditions used by Wisseroth, 80 C and 400 psig. Agitation speed is assumed to have no effect on yield provided there is sufficient mixing. The variable study is divided into two parts for discussion catalyst parameters and reactor conditions. The catalyst is characterized by kg , X, and d7. Percent solubles is not considered because there is presently so little kinetic data to describe this. The reactor conditions chosen for study are those that have some significant effect on the kinetics temperature, pressure, and gas composition.

The conditions that lead to the formation of the first C-C bond during MTO, the mechanism for making ethylene and propylene from methanol, the critical catalyst parameters that are responsible for the wide variation in light alkene selectivities observed among different framework types and between fresh versus aged catalysts are some of the most intriguing questions of the catalysis field today [100-105]. 

We now can begin to see how we choose catalyst parameters in a catalytic reactor if we want the pseudohomogeneous rate to be as high as possible. We write the general expression for a catalytic reaction rate as... 

The pilot unit responds as expected to changes in catalyst parameters and on differences in the feed composition. The ARCO pilot unit shows the correct behavior of all independent gas component yields. The yield of butylenes goes through the same maximum as has been observed in the FCCU at the Mongstad refinery. 

The employed physical and chemically based modeling approach enables a relatively large variation of geometrical catalyst parameters, e.g. catalyst length, diameter, etc., with the global reaction kinetics and therefore the overall... 

Catalyst structure. For supported Ni catalysts the optimal Ni particle size was estimated to be 10-20 nm. But there is no correlation between ee and any catalyst parameter which is valid generally [1, 4, 6]. 

As a rule, synthetic chemists will consider only those new reactions and catalysts for preparative purposes where the enantioselectivity reaches a certain degree (e.g. >80%) and where both the catalyst and the technology are readily available. For heterogeneous catalysts this is not always the case because the relevant catalyst parameters are often unknown. It is therefore of interest that two types of modified Nickel catalysts are now commercially available a Raney nickel/tartrate/NaBr from Degussa [64] and a nickel powder/tartrate/NaBr from Heraeus [65, 66]. It was also demonstrated that commercial Pt catalysts are suitable for the enantioselective hydrogenation of a-ketoesters [30, 31]. With some catalytic experience, both systems are quite easy to handle and give reproducible results. 

Few studies have attempted to relate catalytic activity to catalyst parameters. Ueda and Todo (47, 105) have developed a complex correlation between hydrodesulfurization of thio-/3-naphthol and paramagnetic species present on the catalyst. Their correlation involves Mo3+, Co2+, and a surface complex containing an organic species. 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

In conclusion, reductive dehalogenation with Pd catalysts offers a number of advantages it can treat a wide variety of compounds, including mixtures it generally results in simple alkanes, with few halogenated intermediates, if any and it is extremely rapid, which allows small, in-well reactors. As more studies are conducted, the applicability to a broad range of conditions will be tested and will provide opportunities to better understand the process. This will facilitate optimization of catalyst parameters and column operation for the most effective remediation under a variety of field conditions. 

The use of in analyzing data from pilot units was proposed by Krambeck in the early 1970 s and has been used in Mobil since then. More recently, the same concept has been published in the open literature, and the reciprocal of kg is defined as UOP dynamic activity (14). The dynamic activity is now popularly used in the FCC literature, and is even used to correlate catalyst performance with fundamental catalyst parameters such as unit cell size (15). In this paper, however, we will use the Mobil defined kg parameter. 

REY Catalysts. REY catalysts always give lower FFB conversions than MAT conversions (Figure 1). To simulate the observed conversion differences in the MAT and FFB units for REY catalysts, the intrinsic cracking activity kj is increased at constant coking activity Aj. This choice of parameters is a first order approximation for the activity and coke-conversion selectivity variation of equilibrium catalysts. Parameters summarized in Table V are used as the initial starting point. 

It is the objective of the FFB or the MAT test to determine cracking and coking activities of the catalyst (kj, A ). Therefore, all other parameters should be known from independent experiments or estimated prior to determining these intrinsic catalyst parameters. These other parameter estimates are described below. 

In all of the above there is assumed no product inhibition. Nonlinear regression of the kinetic data revealed the four parameter model, Eq. 1, to be marginally better than the two parameter model of Eq. 2 with both models the maximum error was less than 20%, as shown in Figures 1 and 2. Eq. 2 is quite adequate for the range of variables studied and affords a more direct comparison of deactivation effects, hence it is used in the following. Fresh catalyst parameters are given below. 

In processing VGO it has been argued that the heavy poly-aromatic structures characterised by the Ramsbottom Carbon Residue (RCR, Table 1) can be considered as coke precursors [8]. An increase of the boiling point of those structures via condensation reactions or dehydrogenation reactions is responsible for coke deposition onto the catalyst. In order to increase our level of understanding of these processes we consider first the effects of catalyst parameters on the coke formation. 

Development of fundamental kinetics for improved understanding of complex reaction systems is another frontier. More advanced catalyst characterization tools, including on-line and in-line measurements, need to be developed to provide better understanding of critical catalyst parameters. This should involve application of predictive chemistry capability to design better catalysts which carry out desired conversions in complex reaction systems. 

CSBR). In this case the bioconversion is run under approximately steady-state conditions where the position of reaction equilibrium lies toward the products of the conversion. In this case the concentration of product (proportional to Sj — S0 ) at a given reactor residence time becomes a function of both the flow rate (Q) into the reactor and reactor volume, in addition to the factors discussed above for batch mode reactors (i.e., catalyst parameters and density, inlet substrate concentration S and outlet substrate concentration S0). 

Note that v, when divided by the total concentration of active centers [K]o, gives the very important catalyst parameter of the catalyst activity that is the turnover frequency of the active center, TOP ... 

Ballarini et al. (8) posed the question of whether vanadium phosphate catalysts for n-butane oxidation offer the scope for further improvements. They concluded that as a consequence of the complexity of the dynamic surface species present on the catalyst, optimization of such material will not be forthcoming without further fundamental investigations. Previous investigations have involved probing of a number of catalyst parameters, including the V P ratio, the content of metal ion dopants, and the method of preparation. These and related topics are evaluated in detail below. 

H. Combined Effects of Structural Catalyst Parameters on Fischer-Tropsch Selectivity... 

Dimensional analysis of the coupled kinetic-transport equations shows that a Thiele modulus (4> ) and a Peclet number (Peo) completely characterize diffusion and convection effects, respectively, on reactive processes of a-olefins [Eqs. (8)-(14)]. The Thiele modulus [Eq. (15)] contains a term ( // ) that depends only on the properties of the diffusing molecule and a term ( -) that includes all relevant structural catalyst parameters. The first term introduces carbon number effects on selectivity, whereas the second introduces the effects of pellet size and pore structure and of metal dispersion and site density. The Peclet number accounts for the effects of bed residence time effects on secondary reactions of a-olefins and relates it to the corresponding contribution of pore residence time. 

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