Series reactions operating conditions

Consider the possibility of carrying out the reaction used as the basis for Illustrations 10.1 and 10.2 under adiabatic operating conditions. How much B will it be possible to produce from 2.1 million lb/yr of species A using a pair of 1000-gal CSTR s operating in series Assume that you will be able to operate 7000 hr/yr. Use the data from Illustration 10.2. 

Figure 15.10. Figure 15.10(a) represents the total volume as one PFR, with reaction taking place leading to a particular fractional conversion at the outlet. Figure 15.10(b) represents the same total volume divided into three parts, not necessarily equal, in series. Since the mere division of V into three parts does not alter the operating conditions from point to point, the two configurations are equivalent, and lead to the same final conversion. That is, from equation 15.2-2,... 

In this chapter, we develop some guidelines regarding choice of reactor and operating conditions for reaction networks of the types introduced in Chapter 5. These involve features of reversible, parallel, and series reactions. We first consider these features separately in turn, and then in some combinations. The necessary aspects of reaction kinetics for these systems are developed in Chapter 5, together with stoichiometric analysis and variables, such as yield and fractional yield or selectivity, describing product distribution. We continue to consider only ideal reactor models and homogeneous or pseudohomogeneous systems. 

Therefore, complex processes are frequently simplified to assume (1) a single reaction in which the major reactant is converted into the major product or for a more accurate estimate (2) simple series or parallel processes in which there is a major desired and a single major undesired product. The fust approximation sets the approximate size of the reactor, while the second begins to examine different reactor types, operating conditions, feed composition, conversion, separation systems required, etc. 

Mole balance expressions were developed for a general series reaction by Agarwalla and Lund [16], and the same procedures were used here to develop the species balance equations shown in Table I. Boundary conditions and parameter definitions are presented in Tables II and III. Note that the boundary conditions are given only for co-current flow of reactants and inert, which is the only configuration studied. Previous work [16], has shown that counter-current operation is less effective than co-current operation. 

The normalized reaction rate expressions are first linearized about the steady-state operating conditions (ss) using a first-order Taylor series,... 

Most reactors used in industrial operations run isother-mally. For adiabatic operation, principles of thermodynamics are combined with reactor design equations to predict conversion with changing temperature. Rates of reaction normally increase with temperature, but chemical equilibrium must be checked to determine ultimate levels of conversion. The search for an optimum isothermal temperature is common for series or parallel reactions, since the rate constants change differently for each reaction. Special operating conditions must be considered for any highly endothermic or exothermic reaction. 

Discrimination against undesirable reaction product ions is important. The quadrupole cell can be used in a bandpass mode to remove the product ions of intermediate reactions and thus intercept the series of sequential reactions that might otherwise introduce new spectral interferences. The selection of the appropriate reaction gas and cell operating conditions must be assessed, depending on the analyte ion of interest and the spectral overlap ions to be removed. 

Conventional technology, which has been employed for over 25 years, uses three or four fixed bed reactors in series, these operating under adiabatic conditions. They are preceeded by heating furnaces that compensate for the overall endothermicity of the reaction. Catalyst performance was investigated separately in a pilot plant under isothermal conditions, employing ca. 300-400 g of catalyst. 

The study of the deterioration of the hydroxil groups of the catalyst and the nature of the coke that is being deposited have been studied in situ in a catalytic chamber (Spectra Tech) connected in series with a Nicolet 740 FTIR spectrophotometer. The reaction has also been carried out in an automated isothermal fixed bed integral reactor [6], in cycles of reaction-regeneration, with the aim of obtaining partially deactivated catalyst samples under contrasted operation conditions (time on stream, temperature, contact time and number of regenerations of the catalyst). 

The applicability of the intimacy criterion has been demonstrated 19) in a series of tests on n-heptane isomerization under conventional operating conditions, i.e., at elevated hydrogen partial pressure where catalyst deactivation is minimized. The reaction was examined over mechanically distinct but mixed particles of X (Pt-bearing particles) and Y (silica-alumina) of varying particle size R (equal for both types of particles) in 50-50 volume proportion as well as over single type catalyst in the reaction zone. The reaction conditions provided a partial pressure of n-heptane of 2.5 atm., of hydrogen of 20 atm., and a residence time of 17 sec. 

The mass-transfer coefficient depends on the geometry of the solid surface, on the hydrodynamic conditions in the vicinity of the catalyst (which are a function, e.g., of the reactor type, geometry, operating conditions, flow regime), and it also depends on the dif-fusivity of the gas species. Correlations for the mass-transfer coefficient are a large topic and outside the scope of this section. For more details see Bird, Stewart, and Lightfoot, Transport Phenomena, 2d ed., John Wiley Sons, New York, 2002, and relevant sections in this handbook. For non-first-order kinetics a closed-form relationship such as the series of resistances cannot always be derived, but the steady-state assumption of the consecutive mass and reaction steps still applies. 

The systems 1% R11/AI2O3, 1% Pd/Al203 and 1% (Pd+Ru)/Al203 were also tested as catalysts for the NO reduction with H2, CO and propene as reductants, but different operating conditions were adopted. The reaction was conducted in a microreactor, at atmospheric pressure, temperatures from 75°C to 350°C and space velocity of 100 ml/min gcat- In a first series of tests, a large excess of reductant was used, the gas feed composition... 

After addition of HF to the chlorinated olefinic reagent, the reaction can proceed through successive Cl/F halogen exchanges or by formation of olefinic intermediate by elimination of HCI and successive hydrofluorination studies carried out with use of DF have allowed to discover that the first pathway is prevalent [6]. The outline of reaction (1) is very simplified a series of isomerization and disproportionation reactions are known [7] but these can be limited using appropriate operating conditions and adapted catalysts. 

It is noteworthy that the surface chemistry of zirconia sensors under practical operating conditions is much more complicated than expected from the oxygen partial pressures in a simple Equation (3.3). This equation imphes that only oxygen is involved in the potential forming electrode reaction, whereas in reality, a series of electrode reactions occurs together with Equation (3.1) on the SE [8] ... 

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