In equilibrium catalyst

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

The metal content in the catalyst increased linearly during 24 h operation. The catalyst obtained at the end of the run (samples 24CD and 48CD) contained Ni and V concentrations very close to the target values of 700 and 2900 ppmw. A V/Ni ratio of 4 is typically found in equilibrium catalysts in Mexico. The metal content produced on the catalyst by the VGO itself was less than 50 ppmw. 

The microactivity test (MAT) based on the ASTM-D-3907 [11] standard was used to determine activity and product selectivity of catalysts. MAT runs were performed in a X)Uel automated equipment with 4.0 g of catalyst using the same VGO as in the pilot plant runs. Unless otherwise specified catalyst samples were previously calcined at 853 K for three hours. Operating conditions were 793 K, CTO ratio of 4, 75 s injection time and WHSV of 15.7 h. Product analysis and conversion and selectivity calculations were done as in the pilot plant. The relative error of data was 5%. We analyzed coke bum products in-situ by IR analysis using an HORIBA VIA-510 analyzer. Product distribution was expressed in terms of produet yield/ activity ratio as defined in Table 2 as currently used for interpreting MAT numbers in equilibrium catalysts. 

Finally, the V concentrations on particle surfaces of sample CPS were only slightly higher than those determined by AA while no Ni was detected. Thus, we conclude that metals in the particles of sample CPS are distributed throughout the particles and more homogeneously than in CD samples. These results are roughly in line with what has been reported [5] regarding metal distribution in equilibrium catalysts and catalysts prepared by cyclic deactivation and impregnation. 

Differences in MAT numbers between oxidized and reduced catalysts are proposed to be related to the extent of metal aging. Metals were comparatively more active in the metallated samples than in the equilibrium catalysts. Although this was less evident for the catalyst deactivated by CD, it was observed that the metal aging procedure failed to reproduce completely the state of metals found in equilibrium catalysts. Therefore the aging process of deposited metals still remains a key factor for simulating more closely the properties of FCC equilibrium catalysts. 

Enolization (Sections 18.4 through 18.6) Aldehydes and ketones having at least one a hydrogen exist in equilibrium with their enol forms. The rate at which equilibrium is achieved is increased by acidic or basic catalysts. The enol content of simple aldehydes and ketones is quite small p-diketones, however, are extensively enolized. 

The circulating catalyst in the FCC unit is called equilibrium catalyst, or simply E-cat. Periodically, quantities of equilibrium catalyst are withdrawn and stored in the E-cat hopper for future disposal. A refinery that processes residue feedstocks can use good-quality F-cat from a refinery that processes light sweet feed. Residue feedstocks contain large quantities of impurities, such as metals and requires high rates of fresh catalyst. The use of a good-quality E-cat in conjunction with fresh catalyst can be cost-effective in maintaining low catahst costs. 

Another problem associated with sodium appears in the form of sodium chloride. Chlorides tend to reactivate aged metals by redistributing the metals on the equilibrium catalyst and allowing them to cause more damage. 

A freshly manufactured zeolite has a relatively high UCS in the range of 24.50°A to 24.75°A. The thermal and hydrothermal environment of the regenerator extracts alumina from the zeolite structure and, therefore, reduces its UCS. The final UCS level depends on the rare earth and sodium level of the zeolite. The lower the sodium and rare earth content of the fresh zeolite, the lower UCS of the equilibrium catalyst (E-cat). 

Bulk density can be used to troubleshoot catalyst flow problems. A too-high ABD can restrict fluidization, and a too-low ABD can result in excessive catalyst loss. Normally, the ABD of the equilibrium catalyst is higher than the fresh catalyst ABD due to thermal and hydrothermal changes in pore structure that occur in the unit. 

A decrease in the 0 to 40 microns fraction of the equilibrium catalyst or an increase in average particle size... 

Plot the physical properties of the equilibrium catalyst. The plotted properties will include particle size distribution and apparent bulk density. The graph confirms any changes in catalyst properties. 

Plot properties of the fresh and equilibrium catalysts ensure that the catalyst vendor is meeting the agreed quality control specifications. Verify that the catalyst vendor has the latest data on feed properties, unit condition, and target products. Verify the fresh makeup rate. Check for recent temperature excursions in the regenerator or afterburning problems. 

This refers to the total gas flow through a plane of catalyst where Nx is the mole fraction of X in the gas passing through the plane, NWeq is the mole fraction of X at equilibrium under conditions at this point in the catalyst bed, and dv is the incremental catalyst volume. 

Optimal conditions for ATRP depend strongly on the particular monomer(s) to be polymerized. This is mainly due to the strong dependence of the activation-deactivation equilibrium constant (A ), and hence the rate of initiation, on the type of propagating radical (Section 9.4.1.3). When using monomers of different types, polymer isolation and changes in the catalyst are frequently necessary before making the second block... 

P the total pressure, aHj the mole fraction of hydrogen in the gas phase, and vHj the stoichiometric coefficient of hydrogen. It is assumed that the hydrogen concentration at the catalyst surface is in equilibrium with the hydrogen concentration in the liquid and is related to this through a Freundlich isotherm with the exponent a. The quantity Hj is related to co by stoichiometry, and Eg and Ag are related to - co because the reaction is accompanied by reduction of the gas-phase volume. The corresponding relationships are introduced into Eqs. (7)-(9), and these equations are solved by analog computation. 

Cationic oxazaborinane 59 (Figure 3.10) is a chiral super-Lewis-acidic catalyst recently described by Corey and coworkers [61]. The catalyst is in equilibrium with 59a and the oxazaborinane system 59 59a is unstable and undergoes... 

The Langmuir adsorption isotherm is easy to derive. Again we assume that the catalyst contains equivalent adsorption sites, and that the adsorbed molecules do not interact. If the adsorbed molecules are in equilibrium with the gas phase, we may write the reaction equation as... 

If the catalyst contains sufficient platinum to allow the hydrogenation-dehydrogenation steps to be in equilibrium, the isomerization can be taken as the rate-limiting step, and the rate becomes ... 

In ICC 1 there were only a few references to diffusional limitations, but they may have been present in a number of papers. Despite improved attention, problems may still exist particularly in systems involving transport from the gas to the liquid phase. Absent a demonstration that the rate of a hydrogenation was proportional to the amount of catalyst one may suspect that C(H2)(liq.) was not in equilibrium with P(H2)(gas). 

The optically active Schiff bases containing intramolecular hydrogen bonds are of major interest because of their use as ligands for complexes employed as catalysts in enantioselective reactions or model compounds in studies of enzymatic reactions. In the studies of intramolecularly hydrogen bonded Schiff bases, the NMR spectroscopy is widely used and allows detection of the presence of proton transfer equilibrium and determination of the mole fraction of tautomers [21]. Literature gives a few names of tautomers in equilibrium. The OH-tautomer has been also known as OH-, enol- or imine-form, while NH tautomer as NH-, keto-, enamine-, or proton-transferred form. More detail information concerning the application of NMR spectroscopy for investigation of proton transfer equilibrium in Schiff bases is presented in reviews.42-44... 

The reaction of crotyl bromide with ethyl diazoacetate once again reveals distinct differences between rhodium and copper catalysis. Whereas with copper catalysts, the products 125 and 126, expected from a [2,3] and a [1,2] rearrangement of an intermediary halonium ylide, are obtained by analogy with the crotyl chloride reaction 152a), the latter product is absent in the rhodium-catalyzed reaction at or below room temperature. Only when the temperature is raised to ca. 40 °C, 126 is found as well, together with a substantial amount of bromoacetate 128. It was assured that only a minor part of 126 arose from [2,3] rearrangement of an ylide derived from 3-bromo-l-butene which is in equilibrium with the isomeric crotyl bromide at 40 °C. 

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