Irreversible reactions exothermic

These stability considerations are not limited to first-order irreversible reactions. Figure 10.4 depicts the Qg and Qr curves for a reversible exothermic reaction. The intersections of the Qg curve and lines 3 and 4 represent stable... 

Liquid hydrazine (N2H4) decomposes exothermically in a monopropellant rocket operating at 100 atm chamber pressure. The products formed in the chamber are N2, H2, and ammonia (NH3) according to the irreversible reaction... 

There are several control problems in chemical reactors. One of the most commonly studied is the temperature stabilization in exothermic monomolec-ular irreversible reaction A B in a cooled continuous-stirred tank reactor, CSTR. Main theoretical questions in control of chemical reactors address the design of control functions such that, for instance (i) feedback compensates the nonlinear nature of the chemical process to induce linear stable behavior (ii) stabilization is attained in spite of constrains in input control (e.g., bounded control or anti-reset windup) (iii) temperature is regulated in spite of uncertain kinetic model (parametric or kinetics type) or (iv) stabilization is achieved in presence of recycle streams. In addition, reactor stabilization should be achieved for set of physically realizable initial conditions, (i.e., global... 

In the present chapter, steady state, self-oscillating and chaotic behavior of an exothermic CSTR without control and with PI control is considered. The mathematical models have been explained in part one, so it is possible to use a simplified model and a more complex model taking into account the presence of inert. When the reactor works without any control system, and with a simple first order irreversible reaction, it will be shown that there are intervals of the inlet flow temperature and concentration from which a small region or lobe can appears. This lobe is not a basin of attraction or a strange attractor. It represents a zone in the parameters-plane inlet stream flow temperature-concentration where the reactor has self-oscillating behavior, without any periodic external disturbance. 

From the study presented in this chapter, it has been demonstrated that a CSTR in which an exothermic first order irreversible reaction takes place, can work with steady-state, self-oscillating or chaotic dynamic. By using dimensionless variables, and taking into account an external periodic disturbance in the inlet stream temperature and coolant flow rate, it has been shown that chaotic dynamic may appear. This behavior has been analyzed from the Lyapunov exponents and the power spectrum. 

With an irreversible reaction, virtually complete conversion can be achieved in principle, although a very long time may be required if the reaction is slow. With a reversible reaction, it is never possible to exceed the conversion corresponding to thermodynamic equilibrium under the prevailing conditions. Equilibrium calculations have been reviewed briefly in Chap. 1 and it will be recalled that, with an exothermic reversible reaction, the conversion falls as the temperature is raised. The reaction rate increases with temperature for any fixed value of VjF and there is therefore an optimum temperature for isothermal operation of the reactor. At this temperature, the rate of reaction is great enough for the equilibrium state to be approached reasonably closely and the conversion achieved in the reactor is greater than at any other temperature. 

Figure 9.14 Three types of solutions to the energy and material balances for exothermic irreversible reactions.

While not as exothermic as reaction with HO2 or H2CO, HCl should be present in much higher concentrations, such that (Eq. 44) may be the primary route to CH3SnCl20H formation. This compound decomposes via two nonelementary (and irreversible) reactions proposed by Giunta et al ... 

Overview The message in these examples is that reactors in this exothermic irreversible reaction system should not necessarily be designed for the maximum temperature. Operability issues should be considered. Designing for a lower temperature gives a larger reactor with more heat transfer area that is more controllable. 

The reaction considered is an exothermic, irreversible reaction, which is first-order in both reactants. There are two reactants and only one product, so there is a change in the number of moles entering and leaving the reactor. Mass is conserved, but moles are not ... 

These steady-state design results indicate that dynamic controllability of a multiple-CSTR process could be poor if the reactions are irreversible and exothermic. 

Reactors designed for low conversions can present severe control problems with exothermic irreversible reactions. 

There are five fundamental differences between CSTRs and tubular reactors. The first is the variation in properties with axial position down the length of the reactor. For example, in an adiabatic reactor with an exothermic irreversible reaction, the maximum temperature occurs at the exit of the reactor under steady-state conditions. However, in a cooled tubular reactor, the peak temperature usually occurs at an intermediate axial position in the reactor. To control this peak temperature, we must be able to measure a number of temperatures along the reactor length. 

As a numerical example, we consider a gas-phase exothermic irreversible reaction with two reactants and one product that occurs in a PFR packed with a solid catalyst ... 

In many tubular reactors cooling or heating occurs as the process fluid flows through the reactor. This produces a major difference between an adiabatic and a nonadiabatic tubular reactor. In an adiabatic reactor, with an exothermic irreversible reaction, the maximum steady-state temperature occurs at the end of the reactor. In a cooled reactor, the maximum steady-state temperature usually occurs at some axial position part way down the reactor. Thus the temperature does not change monotonically with length. 

Consider an exothermic irreversible reaction with first order kinetics in an adiabatic continuous flow stirred tank reactor. It is possible to determine the stable operating temperatures and conversions by combining both the mass and energy balance equations. For the mass balance equation at constant density and steady state condition,... 

Figure 16 shows an effectiveness factor diagram for a first order, irreversible reaction which has been calculated from eq 95 for various values of the modified Prater number / . From this figure, it can be seen that for exothermal reactions (/ > 0) effectiveness factors above unity may be observed when the catalyst operates at a temperature substantially above the bulk fluid phase temperature. This is caused by the limited heat transfer between the pellet and the surrounding fluid. The crucial parameters controlling occurrence and size of this effect are again the modified Prater number and the Arrhenius number. 

The minus sign applies to positive reaction orders and endothermal reactions, the plus sign to negative reaction orders and exothermal reactions. For an isothermal, nth-order irreversible reaction this gives... 

We conclude that most reaction systems in the chemical industries are exothermic. This has some immediate consequences in terms of unit operation control. For instance, the control system must ensure that the reaction heat is removed from the reactor to maintain a steady state. Failure to remove the heat of reaction would lead to an.accumulation of heat within the system and raise the temperature. Forreversible reactions this would cause a lack of conversion of the reactants into products and would be uneconomical. For irreversible reactions the consequences are more drastic. Due to the rapid escalation in reaction rate with temperature we will have reaction runaway leading to excessive by-product formation, catalyst deactivation, or in the worst case a complete failure of the reactor possibly leading to an environmental release, fire, or explosion. 

There are two main reactions, both of which are irreversible and exothermic ... 

Two additional irreversible and exothermic side reactions produce by-... 

CF-tx is preferable for <1 and CP-7T is superior for <1. When maldistribution is absent, the effects of flow direction become evident, and for highly exothermic, irreversible Reaction, CPRF is preferred. Based on this argument, CP-lt would be the best flow configuration since it gives the best profile and also enjoys the advantageous effects of flow direction for highly exothermic reactions. In any case, the effects of all the factors at a certain reaction condition can be determined from the analysis presented here. 

The rearrangement of tertiary peroxides to secondary allylic peroxides is irreversible and exothermic, whereas the reactions of secondary to secondary or secondary to primary peroxides give mixtures of allylic peroxides. 

The opposing reactant contactor mode applies to both equilibrium and irreversible reactions, if the reaction is sufficiently fast compared to transport resistance (diffusion rate of reactants in the membrane). This concept has been demonstrated experimentally for reactions requiring strict stoichiometric feeds, such as the Claus reaction, or for kinetically fast, strongly exothermic heterogeneous reactions, such as partial oxidations. Triphasic (gas/liquid/solid) reactions, which are limited by the diffusion of the volatile reactant (e.g., olefin hydrogenation), can also be improved by using this concept. 

The increase in rate as an exothermic reaction progresses is hindered by the limit on the conversion The limit for an irreversible reaction is 100%. As the limit is approached, the concentration of reactants and the rate both approach zero, regardless of the temperature level. Hence the curve of reaction rate vs conversion for an exothermic reaction in an adiabatic reactor has a maximum, as shown in Fig. 5- b. At low conversions the relative change in reactants concentration with conversion is small, and the rate increases exponentially because of the dominant temperature effect. At high conversions the reactants concentration approaches zero, and so does the rate. 

The Claisen rearrangement can be formally considered as an intramolecular SN2 addition of a carbonyl enol to an allylic alcohol. In contrast to the Cope rearrangement (see Section D.l. 6.3.1.2.), it is an irreversible, highly exothermic reaction with the exception of some special substrates, such as cyclopropane derivatives43,44 or some bicyclic compounds45-47. 

Equations (4.8a), (4.9a), and (4.10b) in Example 4.10 describe the dynamic behavior of a continuous stirred tank reactor with a simple, exothermic and irreversible reaction, A - B. Develop a numerical procedure that solves these equations and can be implemented on a digital computer. Also, describe a numerical procedure for solving the algebraic steady-state equations of the reactor above. (Note For this problem you need to be familiar with numerical techniques for the solution of differential and algebraic equations on a computer.)... 

This method allows an easier calculation of the reaction energy since it only considers irreversible reactions and leaves out all sensible heat exchanges. The reference temperature for the reactions is 273.16 K. The formation heat is shown in Table 31.29. The total heat of formation is the difference between endothermic and exothermic reactions heat, which is 418.5 kcal/kg cli. 

It is now established that product radical stability is a consideration in determining the outcome of radical addition reactions only where a substituent provides substantial delocalization of the free spin into a n-systeni. Even then, because these reactions are generally irreversible and exothermic (and consequently have early transition states), resonance stabilization of the incipient radical center may play only a minor role in determining reaction rate and specificity." " Thermodynamic factors will be the dominant influence only when polar and steric effects are more or less evenly balanced. " ... 

Numerical exploration of the equations (8.73-74) shows that the curves Qc-T have a S-shape for irreversible reactions, and a maximum for reversible reactions (non-represented). The shape is more complex in the case of multiple reactions, because simultaneously exothermic or endothermic reactions in the individual steps. 

An upper bound on this derivative may be established by recalling that for an exothermic, irreversible reaction the following inequalities are always observed. 

---