Reactant conversion

The conversion is defined as the fraction of a reactant that has been consumed. For batch reactors, the conversion of reactant A at time t, is defined by 

For flow reactors operating at steady state, the conversion of reactant A in the 

Rate reactant A is fed to the system Three points concerning the conversion should be noted  

The eonversion is defined only for reactants, and, by definition, its value is between 0 and 1. 

The eonversion is related to the composition (or flow rate) of a reactant, and it is not defined on the basis of any specific chemical reaction. When multiple chemieal reactions take place, a reactant may be consumed in several chemical reactions. However, if reactant A is produced by any independent chemical reaction, its conversion is not defined. 

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Table 14-2 illustrates the observed variations in values for different packing types and sizes for the COg-NaOH system at a 25 percent reactant-conversion level for two different liquid flow rates. The lower rate of 2.7 kg/(s-m ) or 2000 lb/(h-ft ) is equivalent to 4 (U.S. gal/min)/ft and is typical of the liquid rates employed in fume scrubbers. The higher rate of 13.6 kg/(s-m ) or 10,000 lb/(h-fU) is equivalent to 20 (U.S. gal/min)/ft and is more typical of absorption towers such as are used in CO9 removal systems. For example. We note also that two different gas velocities are represented in the table, corresponding to superficial velocities of 0.59 and 1.05 m/s (1.94 and 3.44 ft/s). 

III. Complete reactant conversion. Reactant conversion should be kept preferably below 10%. Remedy Increase the flowrate. 

Note that the rates of product formation and reactant conversion indeed have the dimensions of mol per unit of time, and that these rates are proportional to the number of sites, or, in fact, the amount of catalyst present in the reactor. Also, in the case of a second order reaction, e.g. betv een adsorbed species A and B, we write the rate in the form r = Nk0j 0 by applying the mean-field approximation. Here the rate is proportional to both the total number of sites on the surface and the probability of finding a species A adjacent to a species B on the surface, the latter being proportional to the coverages of A and B. In the mean-field approximation A and B are distributed randomly over the N available sites this only tends to be valid when the adsorbents repel each other. Thus the rate is not r= k(N0/ )(N02,) since the reactants need to be on adjacent sites. Another important consideration is that we want the rate to be linearly proportional to the amount of catalyst in the reactor, in accordance with r = Nk0A0B for a second order surface reaction. 

In the mechanistic discussion which follows, it should be assumed unless otherwise specified, that the reaction mixture contained a large excess of hydrogen and that the reaction was carried out at atmospheric pressure or below. Furthermore, distributions of reaction products to which we shall refer correspond to low reactant conversion (< 10%), so the influence of secondary reactions arising from the readsorption of initial reaction products is, in most cases, negligible. 

The developed model allows the simultaneous prediction of both the reactants conversion and n-paraffins and a-olefins selectivity from C, to C49 as a function of process conditions. 

The detailed kinetic description of a chemical process is a primary feature for both the industrial practice and the comprehension of the reaction mechanism. The development of a kinetic model able to predict at the same time the reactants conversion and the products distribution (i.e., a detailed kinetic model) is a prerequisite for the design, optimization, and simulation of the industrial process. Also, the detailed description of process kinetics allows the ex post evaluation of the goodness of the mechanistic scheme on the basis of which the model itself is developed, making possible the collection of further insight in the chemistry of the process. 

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

A mathematical model is described [138] in which the self-heating of material layers under industrial conditions is simulated. The model takes into account oxygen (or gas) diffusion and consumption, reactant conversion, heat conduction in, and heat transfer to and from the layer. Scale-up experiments were performed which showed the model can be successfully applied to predict the self-heating phenomenon in the layers. 

Fig. 11. CO formation rates determined from reactant conversions and product selectivities in a fixed-bed flow reactor for C02 reforming of CH4. The catalysts were nickel supported on La203, y-Al203, or CaO. Each catalyst contained 17 wt% Ni. Before reaction, the catalyst was reduced in flowing H2 at 773 K for at least 5 h and then at 1023 K for 2 h. Reaction conditions pressure, 1.0 atm temperature, 1023 K feed gas molar ratio, CH4/C02/He = 2/2/6 GHSV, 1,800,000 mL (g catalyst)-1 h-1 (227).

Another study was performed on a catalytic hydrogenation of 1,3,5-trimethyl-benzene to 1,3,4-trimethylcyclohexane, which is a typical first-order reversible reaction [168]. By optimizing various operating conditions it was possible to achieve a product purity of 96% and a reactant conversion of 0.83 compared to a thermodynamic equilibrium conversion of only 0.4. The results were successfully described with a mathematical model derived by the same authors [169]. Comparison to a real countercurrent moving bed chromatographic reactor yielded very similar results for both types [170]. 

The pyrolysis temperature and the rate of addition are chosen such that about 50% of the acid chloride is recovered as 2-toluic acid after hydrolysis. Under these conditions only a small amount of benzyl chloride and polymeric material is formed in addition to benzocyclobutenone. The percentage of reactant conversion depends not only on the pyrolysis temperature, but also on the pressure in the reactor and on the rate of reactant addition. It is advisable, therefore, to optimize the pyrolysis temperature in trial runs keeping the other variables constant. 

PNP production was monitored at 402 nm and quantitated using extinction coefficients determined experimentally for each reaction medium. The fraction of reactant conversion to product was given by the ratio (Aj. - Aq)/(A - A ) where the subscripts t, o, and <<> refer, respectively, to absorbance values taken at time t, initially, and at long reaction times when PNP liberation clearly stopped. 

Madnia, C.K., S.H. Frankel, and P. Givi. 1992. Reactant conversion in homogeneous turbulence Mathematical modeling, computational validations and practical applications. Theoretical Computational Fluid Dynamics 4 79-93. 

Reactant conversion into its mirror image, NARCISSISTIC REACTION REACTING BOND RULES REACTING ENZYME CENTRIFUGATION REACTION COORDINATE DIAGRAM POTENTIAL ENERGY DIAGRAM SADDLE POINT... 

Hofmann [34] has performed more extensive calculations, setting the bounds on possible reactant conversion for various numbers of CSTRs in series. For the particular case of a second-order reaction with = 10,... 

The reactor start-up was performed by feeding a water-free mixture of methane and air with an O2/CH4 molar ratio of 1.36 and by inducing for few seconds the voltaic arc between the spark plugs. When the mixture is ignited, the temperature on the SiC foam suddenly (1 min) reaches around 1000 °C. Furthermore, due to the heat transfer, the temperature in the catalytic zone reaches in about 2 min the light-off value with full reactants conversion. The whole start-up phase is no longer than 3 min. 

The small-scale test (see A2.4)i which measures dT/dt, and hence q, for the.runaway reaction must be performed in a way which simulates the same external heating rate as for the full-scale reactor. This is to ensure that a safe value of q is obtained. If the small-scale test was not also externally heated, the relief pressure would be reached at a higher reactant conversion and consequent lower reaction rate, than in the full scale vessel with external heat input. It should also be noted that, as there is no mass loss in the small-scale test, the whole initial mass of reactants, mR, rather than mR/2 can be used in the calculation of the rate of temperature rise due to external... 

The catalyst decay during nitrobenzene reduction was studied in long-time experiments. The gradual poisoning of the catalyst was observed (Table 5) which led in 4-5 hrs to the significant diminishing of reactant conversion. 

Figure 14-15 illustrates the influence of system composition and degree of reactant conversion upon the numerical values of KGa for the absorption of C02 into sodium hydroxide at constant conditions of temperature, pressure, and type of packing. An excellent experimental study of the influence of operating variables upon overall K a values is that of Field et al. (Pilot-Plant Studies of the Hot Carbonate... 

If after the cooling failure unconverted reactants are still present in the reaction mixture, they will react in an uncontrolled way and lead to an adiabatic temperature increase. The remaining unconverted reactants are referred to as accumulated reactants. The available energy is proportional to the accumulated fraction. Thus, the answer to this question necessitates the study of the reactant conversion as a function of time, in order to determine the degree of accumulation of unconverted reactants (Xac). The concept of Maximal Temperature of the Synthesis Reaction (MTSR) was developed for this purpose ... 

First, let us define some key terms. One method for quantifying a reaction s efficiency is by examining the reactant conversion, the product selectivity, and the product yield over time. The reactant conversion is the fraction of reactant molecules that have transformed to product molecules (regardless of which product it is). The selectivity to product P is the fraction (or percentage) of the converted reactant that has turned into this specific product P. The yield of P is simply conversion x selectivity. High conversions in short time spans mean smaller and safer reactors. Similarly, high selectivity means less waste, and simpler and cheaper separation units. Thus, conversion, selectivity, and yield are all measures of the reaction efficiency. 

Clearly the losses and gains of a particular species present in the product gasoline as compared to the parent feed gasoline can represent the balance of complex reactions. However, under the reaction conditions employed, it is not likely that there will be appreciable generation of C6+ hydrocarbons other than as intermediates, so that an examination of reactant losses in this region provides a reasonable comparison of reactant conversion over the two zeolites. 

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