With catalyst deactivation

Although examples of the methodology will utilize entirely reaction rates or reactant concentrations, the procedures are equally valid for other model responses. They have been used, for example, with responses associated with catalyst deactivation and diffusional limitations as well as with copolymer reactivity ratios and average polymer molecular weights. 

Various reports can be found in the literature in connection with catalyst deactivation kinetics (Wojchiechowsky, 1968), some of them also taking into account the effects of diffusion resistance (Beeckman and Froment, 1980). 

Vapor-phase alkylation of benzene by ethene and propene over HY, LaY, and REHY has been studied in a tubular flow reactor. Transient data were obtained. The observed rate of reaction passes through a maximum with time, which results from build-up of product concentration in the zeolite pores coupled with catalyst deactivation. The rate decay is related to aromatic olefin ratio temperature, and olefin type. The observed rate fits a model involving desorption of product from the zeolite crystallites into the gas phase as a rate-limiting step. The activation energy for the desorption term is 16.5 heal/mole, approximately equivalent to the heat of adsorption of ethylbenzene. For low molecular weight alkylates intracrystalline diffusion limitations do not exist. 

Th.Krupp.V.Kohl.H.Schftfer.HJ-lofmann Isomerisation and Disproportionation of 1-Bu-tene.KInetic Analysis of a Complex Reaction System with Catalyst Deactivation AppLCat.78(1991)91... 

Gomm et al. (45) made observations of coke deposition on zeolite catalysts using TEOM with GC analysis of the effluent gases. The mass change observed during conversion of 2-propanol to propene and diisopropyl ether at 273, 323, and 373 K was directly correlated with catalyst deactivation. Other examples involve oligomerization of -butenes on ferrierite catalysts (46) and interaction of isobutylene with various solid acids (47). 

Studies of the behavior of supported ruthenium systems has been stimulated because of the finding that ruthenium appears to be the most active element, based on exposed surface atoms, for carbon monoxide hydrogenation (ref. 65). A number of workers have studied the dissociation of carbon monoxide and subsequent buildup of carbidic carbon on the various crystallographic faces of ruthenium (refs. 66-70). It has been shown that the carbidic carbon is easily hydrogenated and is thought to be a precursor for the hydrocarbon products, while the less reactive graphitic carbon is associated with catalyst deactivation (refs. 34,71-72). 

This paper in many ways presents the author s 35 year encounter with catalyst deactivation in various forms and disguises. It is a combination of personal experience with historical development and scientific progression. Overall developments are surveyed, and in a way how they impacted one worker in the field. Old results are reported in an historical context, but some new ones are also given. There are some lessons ... 

R. Christoph and M. Baems, Modelling of an adiabatic, catalytic fixed bed reactor with catalyst deactivation and pore-diffiisional effects for the methanation of CO, Ber.Bunsnges.Phys. Chem., 90(1986)981. 

The present review provides a summary of the literature dealing with the causes, effects, and correction strategies for deactivation of stationary source air emissions control catalysts. Other authors have dealt with catalyst deactivation in general or with automotive catalyst deactivationl". ... 

This much said, let us now examine the behavior of a PFR in this predicament. The classical example was provided by Froment and Bischolf [G.F. Froment and K.B. Bischoff, Chem. Eng. Set, 10, 189 17, 105 (1962)] for isothermal conditions, with catalyst deactivation by either parallel or series reaction steps (see Chapter 3), and our favorite imaginary reaction A B. Thus we deal with overall sequences such as (XXVI) or (XXVII) of Chapter 3. 

One limitation of this catalyst is degradation via P-C bond cleavage. When (p-FC6H4)3P was used as phosphine, PhF formation was found to be associated with catalyst deactivation. An important step forward was therefore a move to... 

Interestingly these complexes showed high activity without addition of alkyl aluminum compounds in the ionic liquid while they are almost inactive in toluene. These results are interpretable in terms of catalyst stabilization by the imidazolium-based ionic liquid. Reductive elimination of imidazolium is also possible as in toluene as in the ionic liquid but in the ionic liquid, a rapid reoxidation via addition of the solvent imidazolium cation seems possible and may prevent the formation of Ni deposits associated with catalyst deactivation. The carbene complex with R = n-Bu showed the highest activity with a dimer yield of 70.2% (TOF = 7020 h ). The preferred product of the nickel-catalyzed reaction is methylpentene. Additional phosphine ligand had no significant influence on the distribution of the products in this case. 

MarshaU extended the scope of the reaction to the use of allylstannane reagents, which are more reactive nucleophUes. The addition of triflic anhydride as a promoter overcame a problem with catalyst deactivation and allowed the reaction of allylstarmane (6.79) to take place efficiently and with fairly good stereocontrol in the product (6.80). 

Early models did not take into account catalyst deactivation (30,31). By 1973, sufficient studies over a wide range of conditions were performed so that a detailed model could be developed (32). Jenkins and Stephens considered a model consisting of 31 components and 78 reactions in 1980 (33). Other models included diffusional effects (34). A simple model with catalyst deactivation has been published (35). 

Volatile catalyst Non- volatile catalyst Without catalyst deactivating agent With catalyst deactivating agent... 

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