Reactor conversion definition

Also, from the definition of reactor conversion, for the special case of a constant density reaction mixture ... 

By definition, the laminar-flow reactor is segregated. Each radial element of fluid is assumed to slide past its adjacent elements with no mixing. Thus, eqn. (34) may be used to predict reactor conversion. The case of a first-order reaction has been analysed by Cleland and Wilhelm [43]. As we have seen previously... 

Here the rate constant for HDS becomes time dependent, the degree of deactivation X(t, I) also being dependent on the location in the reactor/conversion. X can sometimes be directly correlated to the amount of metals or coke deposited on the catalyst in other cases a definition has to be based on the total history of the catalyst (according to Equations 6 and 7), instead of simply its state. 

GL 18] ]R 6a]]P 17/Using the same experimental conditions and catalysts with the same geometric surface area, the performance of micro-channel processing was compared with that of a fixed-bed reactor composed of short wires [17]. The conversion was 89% in the case of the fixed bed the micro channels gave a 58% yield. One possible explanation for this is phase separation, i.e. that some micro channels were filled with liquids only, and some with gas. This is unlikely to occur in a fixed bed. Another explanation is the difference in residence time between the two types of reactors, as the fixed bed had voids three times larger than the micro channel volume. It could not definitively be decided which of these explanations is correct. 

For semibatch operation, the term fraction conversion is somewhat ambiguous for many of the cases of interest. If reactant is present initially in the reactor and is added or removed in feed and effluent streams, the question arises as to the proper basis for the definition of /. In such cases it is best to work either in terms of the weight fraction of a particular component present in the fluid of interest or in terms of concentrations when constant density systems are under consideration. In terms of the symbols shown in Figure 8.20 the fundamental material balance relation becomes ... 

The fraction conversion in the effluent from the first reactor can be determined from equation C and the definition of the fraction conversion. 

Note. If the second reactor had been operated in parallel with the original unit then the treatment rate could only be doubled. Thus, there is a definite advantage in operating these two units in series. This advantage becomes more pronounced at higher conversions. 

This suggests immediately the definition of autocatalysis. A reactive intermediate or heat can act as catalysts to promote the reaction. However, in contrast to conventional catalysis, we do not add the catalyst from outside the system, but the catalyst is generated by the reaction (autocatalysis). We may add promoters or heat to initiate the process, which then accelerates by autocatalysis. Conversely, we may add inhibitors or cool the reactor to prevent both types of autocatalysis. 

In ebullating bed reactor, such as the H-coal process, Ni-Mo or Co-Mo alumina catalysts have been used (96). The catalyst definitely improves the oil yields by accentuating aromatic hydrocracking, achieving conversions around 95% at catalyst make-up rates of 1 3%. 

The simplest case of a reactor is a cuvette, such as that in a photometer. From the Michaelis-Menten equation and the equation for the batch reactor [Eqs. (5.11) and (5.12)], respectively, as well as the definition for the degree of conversion % for the simple reaction S —> P, x = 1 - [S]/[S0] = [P]/[S0], the integrated equation (5.15) for an enzyme reaction following a Michaelis-Menten law in a batch reactor is obtained. 

According to this definition, the relative activities of two catalysts can be obtained without knowing function /, but they may be readily compared by fixing the temperature and varying the Weight Hourly Space Velocity (WHSV), to obtain a chosen degree of conversion [54]. This can be done with the MFBR system [34, 49], where space velocity can be varied individually for each reactor across the 48 library members. 

The fundamental rule for safe operation of an adiabatic exothermic reactor is that it must not be operated with too much conversion. The definition of "too much" is provided by the development described herein. It takes one of two nearly equivalent forms ... 

Equation 5.52 has a clear meaning the difference in the inlet and outlet reaction rates must be small. To apply this criterion the inlet concentration C and temperature T should be known. If they are not measured, as in most recycle reactors, they can be estimated through the measured outlet parameters and the measured net conversion in the reactor, as follows. From the definition of the conversion per cycle (Equation 5.46),... 

For the simple network 5.26 and a reaction with no fluid-density variation, the magnitude of the effect is easily calculated The cumulative selectivity of conversion to P (moles of A converted to P per mole of A consumed, see definition 1.11) in batch and continuous stirred-tank reactors as a function of fractional conversion,/A, is... 

The above criterion, which has been proposed by Gierman (2) is based on the argument that the temperature required for a given conversion in the test reactor should not exceed the theoretical one by more than 1 °C, which can be considered to be within the accuracy of temperature definition in practice. A similar, but more conservative criterion has been proposed earlier by Mears (5) based on a maximum increase of 5% in bed length or catalyst volume to effect the same conversion as in an ideal reactor. In the criterion of Mears, the coefficient 8 in Equation 1 should be replaced by 20. 

Activity. The differences found in activity of the catalyst are caused by two effects the definition of the catalyst-to-oil (CTO) ratio and the feed partial pressure in both reactors. The CTO is time averaged over the reaction time and is not clearly defined in the MST. The contact between the catalyst and oil is not constant throughout the experiment. At the beginning of the MST experiment fresh feed encounters fresh catalyst. However, after some time fresh feed meets a partially deactivated catalyst with coke already deposited on it. At the end of the experiment the situation is the opposite of the contact between catalyst and oil in an industrial unit. This makes the definition of the CTO not unambiguous in the case of the MST and can lead to over- or underestimation of the CTO. However, the most important effect is the difference in partial pressure of the feed in both sets of equipment the nitrogen carrier gas lowers the partial pressure in the MR. A lower partial pressure results in a lower conversion. With these two effects a higher activity for the MST can be expected. 

The polymerization time in continuous processes depends on the time the reactants spend in the reactor. The contents of a batch reactor will all have the same residence time, since they are introduced and removed from the vessel at the same times. The continuous flow tubular reactor has the next narrowest residence time distribution, if flow in the reactor is truly plug-like (i.e., not laminar). These two reactors are best adapted for achieving high conversions, while a CSTR cannot provide high conversion, by definition of its operation. The residence time distribution of the CSTR contents is broader than those of the former types. A cascade of CSTR s will approach the behavior of a plug flow continuous reactor. 

Two definitions of reactant conversion are used in the analysis of chemical reactors with product separation and recycle of unconsumed reactants ... 

Many times reactors are connected in series so that the exit stream of one reactor is the feed stream for another reactor. When this anangement is used it is often possible to speed calculations by defining conversion in terms of location at a point downstream rather than with respect to any single reactor. That is, the conversion X is the total number of moles of A that have reacted up to that point per mole of A fed to the first reactor. However, this definition can only be used provided that there are no side streams withdrawn and the feed stream enters o y the first reactor in the series. 

We have shown that in order to calculate the time necessary to achieve a given conversion X in a batch system, or to calculate the reactor volume needed to achieve a conversion X in a flow system, we need to know the reaction rate as a function of conversion. In tins chapter we show how this functional dependence is obtained. First there is a brief discussion of chemical kinetics, emphasizing definitions, which illustrates how the reaction rate depends on the concentrations of the reacting species. This discussion is followed by instructions on how to convert the reaction rate law from the concentration dependence to a dependence on conversion. Once this dependence is achieved, we can design a number of isothermal reaction systems. 

As a consequence of the different definitions for selectivity and yield, when reading literature dealing with multiple reactions, check careftilJy to ascertain the definition intended by the autoor. Prom an economic standpoint it is the overall selectivities, S, and yields, Y, that are important in determining profits. However, the rate-based selectivities give insists in choosing reactors and reaction schemes that will help maximize the profit. However, many times there is a conflict between selectivity and conversion (yield) because you want to make a lot of your desired product (D) and at the same lime minimize the undesired product (U). However, in many instances the greater conversion you achieve, not only do you make more D, you also form more U. 

---