Reaction, consecutive network

The reaction network considered here is the same consecutive network,... 

The simultaneous determination of a great number of constants is a serious disadvantage of this procedure, since it considerably reduces the reliability of the solution. Experimental results can in some, not too complex cases be described well by means of several different sets of equations or of constants. An example would be the study of Wajc et al. (14) who worked up the data of Germain and Blanchard (15) on the isomerization of cyclohexene to methylcyclopentenes under the assumption of a very simple mechanism, or the simulation of the course of the simplest consecutive catalytic reaction A — B —> C, performed by Thomas et al. (16) (Fig. 1). If one studies the kinetics of the coupled system as a whole, one cannot, as a rule, follow and express quantitatively mutually influencing single reactions. Furthermore, a reaction path which at first sight is less probable and has not been therefore considered in the original reaction network can be easily overlooked. 

Interestingly, the ethylene selectivity can increase with increasing methane conversion. This is because of the predominantly consecutive nature of the OCM reaction network ... 

Series reactions involve products formed in consecutive steps. The simplest reaction network for this is given by reaction 5.5-la ... 

Fig. 9.4 Reaction network for the formation of CVD binder carbon during the synthesis of a C3 material from methane. The supporting data were collected from model experiments with carbon-coated ceramic channels and consecutive gas analysis as described [31,32] in the literature. The colored boxes indicate the main reactive intermediates.

The reaction network for isobutane selective oxidation catalyzed by POMs consists of parallel reactions for the formation of methacrolein, methacrylic acid, carbon monoxide, and carbon dioxide. Consecutive reactions occur on methacrolein, which is transformed to acetic acid, methacrylic acid, and carbon oxides. ° Methacrylic acid undergoes consecutive reactions of combustion to carbon oxides and acetic acid, but only under conditions of high isobutane conversion. Isobutene is believed to be an intermediate of isobutane transformation to methacrylic acid, but it can be isolated as a reaction product only for very low alkane conversion. ... 

Even though the governing phenomena of coupled reaction and mass transfer in porous media are principally known since the days of Thiele (1) and Frank-Kamenetskii (2), they are still not frequently used in the modeling of complex organic systems, involving sequences of parallel and consecutive reactions. Simple ad hoc methods, such as evaluation of Thiele modulus and Biot number for first-order reactions are not sufficient for such a network comprising slow and rapid steps with non-linear reaction kinetics. 

Experimental concentration vs time plots for the hydroprocessing of 4-chloronitrobenzene over the sulfided HR 306 and HR 348 catalysts at 200°C and 20 bar Hg are presented in Fig.l and Fig.2, respectively.The curves drawn in Fig.l and Fig.2 are computer-simulated based on the consecutive reaction network shown in Scheme 1. 

Kinetic models which consider demetallation as a complex reaction network of consecutive and parallel reactions taught by model compound studies have been recognized with real feedstocks. Tamm et al. (1981) suggest a sequential mechanism where the metal compounds are activated by H2S. Model compound reaction pathway studies in the absence of H2S, discussed in Section IV,A,1, and experiments in which H2S was present in excess (Pazos et al., 1983) indicate that sequential reactions are inherent to the chemistry of the metal compounds irrespective of the presence of H2S. However, it is possible that both mechanisms contribute to metal removal. 

Derive the porous pellet diffusion reaction equations for a consecutive reaction network... 

The rates of reactions, measured in g(converted)/(g(catalyst) s) for the consecutive-parallel network model are as follows ... 

The network operates through a series of enzyme-catalyzed reactions that constitute the metabolism. Each of the consecutive steps in a metabolic pathway brings about a specific chemical change, usually the removal, transfer, or addition of a particular atom or functional group. The precursor is converted into a product through a series of metabolic intermediates called metabolites. The term intermediary metabolism is often applied to the combined activities of all the metabolic pathways that interconvert precursors, metabolites, and products of low molecular weight. 

Fig. 12.18. Comparison of the optimized reduced amounts that should be dosed and the corresponding internal compositions for a fixed-bed reactor (discrete dosing, top) and a membrane reactor (continuous dosing, bottom). A triangular network of parallel and series reactions was analyzed using an adapted plug-flow reactor model, Eq. 48. One stage (left) and 10 stages connected in series (right) were considered. All reaction orders were assumed to be 1, except for those with respect to the dosed component in the consecutive and parallel reactions (which were assumed to be 2) [66].

Equation (19-22) indicates that, for a nominal 90 percent conversion, an ideal CSTR will need nearly 4 times the residence time (or volume) of a PFR. This result is also worth bearing in mind when batch reactor experiments are converted to a battery of ideal CSTRs in series in the field. The performance of a completely mixed batch reactor and a steady-state PFR having the same residence time is the same [Eqs. (19-5) and (19-19)]. At a given residence time, if a batch reactor provides a nominal 90 percent conversion for a first-order reaction, a single ideal CSTR will only provide a conversion of 70 percent. The above discussion addresses conversion. Product selectivity in complex reaction networks may be profoundly affected by dispersion. This aspect has been addressed from the standpoint of parallel and consecutive reaction networks in Sec. 7. 

Very often a reactant or a set of reactants may simultaneously undergo several parallel reactions, giving different individual products, P which react further in consecutive reactions to give different secondary products, P,y. A commonly encountered situation is the parallel-consecutive reaction network. 

Acrolein is hydrogenated by a network of parallel and consecutive reactions. The main frame of the reaction is ... 

A complex network of reactions is hidden behind the simple stoichiometry of -butane oxidation (Equation 35). Butene, butadiene and furan have been suggested to be intermediates in a cascade of reactions eventually producing the anhydride. Carboxylic acids and carbon oxides are formed in parallel and consecutive oxidations. 

R. Mann and P.N. Sharratt, Diffusion and consecutive reaction in stochastic pore networks, Chem. Eng. Sci, 45 1875 (1988). 

Networks of simultaneous reactions, i.e., consecutive, parallel, complex (combination of consecutive and parallel reactions) ... 

The stoichiometric matrix is the matrix of the stoichiometric coefficients of the reaction network with negative signs for reactants and positive signs for products. For instance, the hydrodechlorination of Freon 12 (CF2Cl2) can proceed with the following consecutive mechanism [Bonarowska et al., Hydrodechlorination of CC12F2 (CFC-12) over Silica-Supported Palladium-Gold Catalysts, Appl. Catal. B Environmental, 30 187-193, 2001] ... 

Effect of Intraparticle Diffusion for Reaction Networks For multiple reactions, intraparticle diffusion resistance can also affect the observed selectivity and yield. For example, for consecutive reactions intraparticle diffusion resistance reduces the yield of the intermediate (often desired) product if both reactions have the same order. For parallel reactions diffusion resistance reduces the selectivity to the higher-order reaction. For more details see, e.g., Carberry, Chemical and Catalytic Reaction Engineering, McGraw-Hill, 1976 and Fevenspiel, Chemical Reaction Engineering, 3d ed., Wiley, 1999. 

Practically any experimental kinetic curve can be reproduced using a model with a few parallel (competitive) or consecutive surface reactions or a more complicated network of chemical reactions (Fig. 4.70) with properly fitted forward and backward rate constants. For example, Hachiya et al. used a model with two parallel reactions when they were unable to reproduce their experimental curves using a model with one reaction. In view of the discussed above results, such models are likely to represent the actual sorption mechanism on time scale of a fraction of one second (with exception of some adsorbates, e.g, Cr that exchange their ligands very slowly). Nevertheless, models based on kinetic equations of chemical reactions were also used to model slow processes. For example, the kinetic model proposed by Araacher et al. [768] for sorption of multivalent cations and anions by soils involves several types of surface sites, which differ in rate constants of forward and backward reaction. These hypothetical reactions are consecutive or concurrent, some reactions are also irreversible. Model parameters were calculated for two and three... 

The kinetic measurements were performed by monitoring the gas phase composition along the length of a fixed bed of catalyst. The reactor was treated as an isothermal plug flow system. The reaction kinetics can be described with a simple triangle network consisting of the main reaction (aldehyde to carboxylic acid), a consecutive reaction (carboxylic acid to byproducts) and a parallel reaction (aldehyde to by-products). 

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