Steady-state flow reactor

Figure 4.1 Broad classification of reactor types, a) The batch reactor, b) The steady-state flow reactor, (c), d), and (e) Various forms of the semibatch reactor.

Where the composition within the reactor is uniform (independent of position), the accounting may be made over the whole reactor. Where the composition is not uniform, it must be made over a differential element of volume and then integrated across the whole reactor for the appropriate flow and concentration conditions. For the various reactor types this equation simplifies one way or another, and the resultant expression when integrated gives the basic performance equation for that type of unit. Thus, in the batch reactor the first two terms are zero in the steady-state flow reactor the fourth term disappears for the semibatch reactor all four terms may have to be considered. 

The other ideal steady-state flow reactor is called the mixed reactor, the backmix reactor, the ideal stirred tank reactor, the C " (meaning C-star), CSTR, or the CFSTR (constant flow stirred tank reactor), and, as its names suggest, it is a reactor in which the contents are well stirred and uniform throughout. Thus, the exit stream from this reactor has the same composition as the fluid within the reactor. We refer to this type of flow as mixed flow, and the corresponding reactor the mixed flow reactor, or MFR. 

The reactive transport of contaminants in FePRBs has been modeled using several approaches [179,184,186,205-208]. The simplest approach treats the FePRB as an ideal plug-flow reactor (PFR), which is a steady-state flow reactor in which mixing (i.e., dispersion) and sorption are negligible. Removal rates (and therefore required wall widths, W) can be estimated based on first-order contaminant degradation and residence times calculated from the average linear groundwater velocity [Eq. (27)]. The usefulness of... 

Figure 7.1c and d show two types of the steady-state flow reactors with a continuous supply of reactants and continuous removal of product(s). Figure 7.1c shows the continuous stirred-tank reactor (CSTR) in which the reactor contents are perfectly mixed and uniform throughout the reactor. Thus, the composition of the outlet flow is constant, and the same as that in the reactor. Figure 7.Id shows the plug flow reactor (PFR). Plug flow is the idealized flow, with a uniform fluid velocity across the entire flow channel, and with no mixing in the axial and radial...

Confined Enzymes in Steady-State Flow Reactors... 

Fig. 10. Amounts of (A) H20, (B) CH , and (C) C02 produced from consecutive pulses of CO over a Rh/Ti02 catalyst in a H2 flow following reduction at (a) 473 K and (b) 773 K. For comparison, the amounts produced in a steady-state flow reactor are included. (After Ref. 94.)...

Now we can really see why the CSTR operated at steady state is so different from the transient batch reactor. If the inlet feed flow rates and concentrations are fixed and set to be equal in sum to the outlet flow rate, then, because the volume of the reactor is constant, the concentrations at the exit are completely defined for fixed kinetic parameters. Or, in other words, if we need to evaluate kab and kd, we simply need to vary the flow rates and to collect the corresponding concentrations in order to fit the data to these equations to obtain their magnitudes. We do not need to do any integration in order to obtain the result. Significantly, we do not need to have fast analysis of the exit concentrations, even if the kinetics are very fast. We set up the reactor flows, let the system come to steady state, and then take as many measurements as we need of the steady-state concentration. Then we set up a new set of flows and repeat the process. We do this for as many points as necessary in order to obtain a statistically valid set of rate parameters. This is why the steady-state flow reactor is considered to be the best experimental reactor type to be used for gathering chemical kinetics. 

Problem 14.22 A reversible reaction is conducted in a steady-state flow reactor. To improve conversion, a junior member of the design team suggests that you recycle a fraction of the reactor outlet back into the reactor. What is your opinion about this suggestion Hint Use the reaction A(g) = BCg) as an example and show that the recycle stream has no effect whatsoever. 

Steady-state flow reactors, with a constant supply of reactants and continuous removal of products, can be operated as both a continuous stirred-tank bioreactor (CSTB) and as a plug flow bioreactor (PFB). It is possible to have different configurations of the membrane bioreactor where the biocatalyst is immobilized in the fractionated membrane support (Katoh and Yoshida, 2010). In Fig. 1.6 the scheme of a CSMB in which the biocatalyst is immobilized on the surface of the membrane beads is presented. The biocatalyst immobilized in the porous structure of a fractioned membrane can also be operated in CSMB. For example, two configurations are shown in Fig. 1.7 (a) for flat-sheet and (b) for spherical porous structures, respectively. Such structures could also be adopted for PFB, where a bed of membrane support with the immobilized biocatalyst could be utilized, in either a fixed or fluid configuration. 

An experimentally measured RTD of a steady state flow reactor reflects the spatial characteristics of the macro-flow and -mixing in the reactor, including eventual effects of micro-flow and -mixing phenomena on the macro-flow and -mixing. Hence, inspection of experimental RTD can be used to infer certain properties of the flow pattern. Local information on the macro- or micro-flow and mixing behavior inside the reactor can, however, not be revealed, due to the length scale over which RTD are defined (see (12.6.1-2)) and measurements are... 

First, set up a stoichiometric table (Table 4-11). Rather than working with moles perse, as in the case of batch reactors, stoichiometric tables for steady-state flow reactors should be constmcted in terms of molar flow rates. For a CSTR, the second column contains the inlet molar flow rates and the third column contains the molar flow rates in the reactor effluent. 

Equations (1.1) to (1.3) are diflerent ways of expressing the overall mass balance for a flow system with variable inventory. In steady-state flow, the derivatives vanish, the total mass in the system is constant, and the overall mass balance simply states that input equals output. In batch systems, the flow terms are zero, the time derivative is zero, and the total mass in the system remains constant. We will return to the general form of Equation (1.3) when unsteady reactors are treated in Chapter 14. Until then, the overall mass balance merely serves as a consistency check on more detailed component balances that apply to individual substances. 

Appropriate setting of two on-off valves (Fig. 1) allows the system to be operated either as a batch recycle reactor or as a continuous-flow steady-state recycle reactor. 

A chemical reaction is being studied in a laboratory scale steady-state flow system. The reactor is a well-stirred 1000 cm3 flask containing an aqueous solution. The reactor contents (1000 cm3 of solution) are uniform throughout. The stoichiometric equation and data are given below. What is the expression for the rate of this reaction Determine the reaction order and the activation energy. 

We have recently described another spectroscopic rnethod for observing IM reactions at atmospheric pressure that utilizes the photodetachment-modulated electron capture detector (PDM-ECD) as a means of monitoring the negative ions either consumed or produced in an IM reaction. The reaction of interest is made to occiu in a steady-state flow-through reactor in which ionization of the buffer gas is continuously caused by a Ni-on-Pt foil beta emitter. A chopped light beam of... 

Equipment in which homogeneous reactions are effected can be one of three general types the batch, the steady-state flow, and the unsteady-state flow or semibatch reactor. The last classification includes all reactors that do not fall into the first two categories. These types are shown in Fig. 4.1. 

In a series of steady-state flow experiments (Cao = 100, Crq = C o 0) in a laboratory mixed flow reactor the following results are obtained ... 

Each term in the preceding equations has units of energy/time. Note the signs on each term indicating that heat is removed or added to the reactor. We preserve the minus sign on A Hji because we are more interested in exothermic reactions for which A Hr < 0. The student can recognize each term on the right side from the steady-state enthalpy balance we derived in the previous section from the thermodynamics of a steady-state flow system. 

Idealized Reactor with Progressive Mixing. A reactor system of the first type under steady state flow conditions may be described by an expression, as follows, where the number of moles of constituent I converted in an infinitesimal volume, dV, would be given by... 

Careful analysis of the reaction products in the HDN of the 2,6-lutidine (2,6-dimethylpyridine) and the 2,6-lupetidine (2,6-dimethylpiperidine) allowed Ledoux et al.37 to conclude that under these low pressure conditions (1 atm H2, 5-10 Torr amine, in a steady state flow system, at 300°C on Mo03/A1203 in a fixed-bed reactor) the hydrogenated product is not the intermediate for the HDN of the aromatic compound because the distributions of the products obtained by the reaction of the two amines are fundamentally different. 2,6-Lutidine gives at initial conversion 60% toluene, 21% C3 + C4 and 8% olefinic n-C7, while 2,6-lupetidine gives only 18% toluene, 4% C3 + C4 but 69% of olefinic n-C7. Under the same experimental conditions (but at 380°C), analysis of the pyridine and piperidine HDN products38 shows that... 

There is no accumulation in the reactor of any species i. This implies the reactor is at steady-state flow conditions. 

Consider a constant pressure, steady-state flow process with an inflow of reactant in section (1) and the outflow of the product in section (2) leaving the system boundary (i.e., a chemical reactor). 

Only the case of a batch reactor will be considered here. The transposition of equations to deal with steady-state continuous reactors is done by replacing mole numbers (mole) by molar flows (moles-1). 

The fundamental objection to the above relations is that they are derived assuming steady-state flow. In practice, the intensity of turbulence in agitated slurry reactors is time dependent. Also, an accurate estimate of the relative velocity between the liquid and solid is often difficult.45,12S The relative velocity has been related to various system parameters by Kuboi et al.67,68... 

First, a steady-state flow of monomer is established, and the system pressure Pi is read. Then, at time zero, the valve that connects the reactor to the pumping system is closed and the increase in pressure dpjdt, which is given by an initial straight line of the pressure versus time plot, is read. The flow rate F is given by... 

In Table I the high-vacuum (HV) range means a pressure of 10 to 10 Torr entries designated by Torr mean pressures between 0.1 and 10 Torr flow refers to an unspecified steady-state flow pattern. It is apparent from Table I that there is a great diversity in the different oscillation conditions and catalytic systems. The pressures under which oscillations have been observed vary from 10 Torr for the CO/NO reaction on Pt(lOO) 141, 142) to atmospheric pressure for a large number of systems. The reactors used in these studies include ultrahigh-vacuum (UHV) systems, continuous stirred tank reactors (CSTRs), flow reactors, and reactors designed as infrared (IR) cells, calorimeters, and ellipsometric systems. 

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