Reactor with recycle

The reactors with recycle are continuous and may be tanks or tubes. Their main feature is increasing productivity by returning part of unconverted reactants to the entrance of the reactor. For this reason, the reactant conversion increases successively and also the productivity with respect to the desired products. The recycle may also be applied in reactors in series or representing models of nonideal reactors, in which the recycle parameter indicates the deviation from ideal behavior. As limiting cases, we have ideal tank and tubular reactors representing perfect mixture when the recycle is too large, or plug flow reactor(PFR) when there is no recycle. 

To simplify, we assume an irreversible first-order reaction as follows A Products, whose kinetics at constant volume is represented by  

Substituting the rate expression into Equation 15.16 and integrating, we obtain  

Conversion Xai is still unknown and maybe determined by the balance at the intersection 1)by calculating the inlet concentration Cai or conversion Xai - Thus, at the intersection (1), we have  

Substituting Equation (a) into 15.18 and considering a recycle ratio R = we 

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Plug flow reactors with recycle exhibit some of the characteristics of CSTRs, including the possibility of multiple steady states. This topic is explored by Penmutter Stah dity of (%emical Reactors, Prentice-Hall, 1972). 

Figure 11.10(b) can be modeled as a piston flow reactor with recycle. The fluid mechanics of spouting have been examined in detail so that model variables such as pressure drop, gas recycle rate, and solids circulation rate can be estimated. Spouted-bed reactors use relatively large particles. Particles of 1 mm (1000 pm) are typical, compared with 40-100 pm for most fluidizable catalysts. 

The principle of the differential reactor with recycle is illustrated in Fig. 5.4-18. 

Figure 5.4-18. Differential reactor with recycle of the reaction mixture.

For a plug flow reactor with recycle ratio R, relate the concentration change across the reactor to the overall concentration change. 

Fig. 1 Tanks-in-series approximation of a tubular reactor with recycle.

Fig. 2 Startup of the continuous activated sludge reactor with recycle ratio R = 0.3.

M. Berezowski. Effect of delay time on the generation of chaos in continuous systems. One-dimensional model. Two-dimensional model - tubular chemical reactor with recycle. Chaos, Solitons Fractals, 12(l) 83-89, 2001. 

At present we have 90% conversion of a liquid feed (n = 1, C o =10 mol/ liter) to our plug flow reactor with recycle of product (R = 2). If we shut off the recycle stream, by how much will this lower the processing rate of our feed to the same 90% conversion ... 

EXAMPLE 9J ADIABATIC PLUG FLOW REACTOR WITH RECYCLE... 

A gas containing A (2 mol/m ) is fed (1 m /hr) to a plug flow reactor with recycle loop (0.02 m loop volume, 3 kg of catalyst), and the output composition from the reactor system is measured (0.5 mol A/m ). Find the rate equation for the decomposition of A for the following cases. Be sure to give the units of C, and k in your final expression. 

Figure 19.6 Optimum two-stage packed bed reactor with recycle. The conversions shown represent a recycle ratio R = 1 in both stages.

The reforming process model is designed to predict the performance of many reactor configurations. The model can be run in four modes, combining adiabatic or isothermal reactors with recycle or single-pass (no recycle)... 

On the one hand, the differential reactor with recycle permits kinetic measurements of high accuracy. On the other hand, a transfer equipment is required to recycle a fraction of the reaction mixture. This can be difficult when the pressure is high. For this purpose, a jet loop reactor was developed which is equipped with an ejector to recycle the fluid. The design of the jet loop reactor is described in Chapter 4.3.4. 

Single continuous stirred-tank reactor with recycle of A... 

Stirred Tank Reactor with Recycle of Biomass... 

Jacobsen, E. and Berezowski, M. (1998). Chaotic dynamics in homogeneous tubular reactors with recycle. Chem. Eng. Sci., 23, 4023-4029. 

Equipment and Procedure. The fixed bed reactor pilot plant is shown schematically in Figure 1. The reactor was operated as a continuous fixed bed reactor, with recycle of the hydrogen. 

Although the use of membrane reactors for the retention of the enzyme is mostly applied in continuous processes, some authors used a membrane batch reactor in order to reuse the enzyme in consecutive cycles [11, 74]. Flock et al. used a membrane unit coupled to the reactor with recycling of both permeate and retentate streams to the reactor vessel. A valve at the outlet of the membrane maintained pressure within the range fixed by the manufacturer [74]. Pasta et al. operated a reactor with the membrane inside, emptied the reactor content at scheduled times, and thereafter, replenished it with fresh solution of the substrate and the oxidizing system [11]. 

The equations that have been developed for design using these pseudo constants are based on steady-state mass balances of the biomass and the waste components around both the reactor of the system and the device used to separate and recycle microorganisms. Thus, the equations that can be derived will be dependent upon the characteristics of the reactor and the separator. It is impossible here to present equations for all the different types of systems. As an illustration, the equations for a common system (a complete mix - stirred tank reactor with recycle) are presented below. 

Here we have dealt with the control of chemical reactors. We covered some of the fundamentals about kinetics, reactor types, reactor models, and open-loop behavior. In particular we have shown that reactors with recycle or backmixing can exhibit multiple steady states, some of which are unstable. Nonlinearities in reactor systems also frequently give rise to open-loop parametric sensitivity. 

Reactors in which the solid phase is perfectly mixed on a macro scale, such as a stirred tank slurry reactor and the riser reactor with recycle of both phases, are particularly useful for fast catalyst deactivation processes. Notice that the residence time of both phases can be varied independently by introducing an extra recycle flow of... 

Aris (1991a), in addition to the case of M CSTRs in series, has also analyzed two other homotopies the plug flow reactor with recycle ratio R, and a PFR with axial diffusivity and Peclet number P, but only for first-order intrinsic kinetics. The values M = 1(< ), R = >(0), and P = 0( o) yield the CSTR (PFR). The M CSTRs in series were discussed earlier in Section IV,C,1. The solutions are expressed in terms of the Lerch function for the PFR with recycle, and in terms of the Niemand function for the PFR with dispersion. The latter case is the only one that has been attacked for the case of nonlinear intrinsic kinetics, as discussed below in Section IV,C,7,b. Guida et al. (1994a) have recently discussed a different homotopy, which is in some sense a basically different one no work has been done on multicomponent mixture systems in such a homotopy. 

Ercan et al. studied the alkylation of ethylbenzene, EB, with light olefins (ethylene and propylene) over a commercial zeolite Y catalyst in a fixed-bed reactor with recycle [C. Ercan, F. M. Dautzenberg, C. Y. Yeh, and H. E. Earner, Ind. Eng. Chem. Res., 37 (1998) 1724]. The solid-catalyzed liquid-phase reaction was carried out in excess ethylbenzene at 25 bar and 190°C. Assume... 

The overall conversion is reqtrired in apacked-hed reactor with recycle. [2nd Ed. P4-22]... 

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