Molar flow rates membrane reactors

In the same suidy [Itoh et al., 1985], the molar flow rate of cyclohexane at the reactor outlet is calculated as a function of the membrane thickness which has the most effect on the permeation rate of gases. For a given constant inlet molar flow rate, the reaction does not proceed beyond the equilibrium conversion for a conventional reactor. With membrane permeation, however, the overall conversion (i.e., the combined conversions of cyclohexane on the tube and shell sides) reaches a maximum for a certain membrane... 

As we shall see later in the book, there ate some instances in which it is timch more convenient to work in teims of the number of moles (Aa.Ab) or molar flow rates (F, Fg, etc.) rather than conveision. Membrane reactors and gas-phase multiple reactions are two such cases where molar flow rates rather than conversion are preferred. Consequently, the concentrations in the rate laws need to be expressed in terms of (he molar flow rates. We start by recalling and combining Equations (3-40) and (3-41) ... 

Detailed modeling of the transport and reaction steps in membrane reactors is beyond the scope of this text but can be found in Membrane Reactor Technology. The salient features, however, can be illustrated by the following example. When analyzing membrane reactors, it is much more convenient to use molar flow rates rather than conversion. 

Rework Example 4-10. Plot the molar flow rates of A, B, and C as a function of reactor length (i.e., volume) for different values of between kf = 0.0 (a conventional PFR) and kj = 7.0min , What parameters would you expect to affect your results the most Vary the parameters k,k, Kc,Ffji to study how the reaction might be optimized. Ask such questions as What is the effect of the ratio of It to or of k, t to What generalizations can you make How would your an.swer change if the reactor temperature were raised significantly What if somEone claimed that membrane reactora were not as safe as. semibatch reactors What would you tell them ... 

A reference case for the C02-selective WGS membrane reactor was chosen with the C02/H2 selectivity of 40, the C02 permeability of 4000 Barrer, the inlet sweep-to-feed molar flow rate ratio of 1, the membrane thickness of 5jum, 52,500 hollow libers (a length of 61 cm, an inner diameter of 0.1 cm, and a porous support with a porosity of 50% and a thickness of 30jLon), both inlet feed and sweep temperatures of 140 °C, and the feed and sweep pressures of 3 and latm, respectively. With respect to this case, the effects of C02/H2 selectivity, C02 permeability, sweep-to-feed ratio, inlet feed temperature, inlet sweep temperature, and catalyst activity on the reactor behavior were then investigated. 

We see tliiu conversion is not used in this sum. The molar flow rates, Fj, are found by solving the mole balance etjuations. Equation (.1-42) will be u.seci for measures other than ctmversion when we discuss nienibrane reactors (Chapter 4 Part 2) and multiple reactions (Chapter 6). We will use this form of the concentration equation for multiple gas-phase reactions and for membrane reactors. 

We divide the chapter into two parts Part 1 Mote Balances in Terms of Conversion, and Part 2 Mole Balances in Terms of Concentration, C,. and Molar Flow Rates, F,." In Pan 1, we will concentrate on batch reactors, CSTRs, and PFRs where conversion is the preferred measure of a reaction s progress for single reactions. In Part 2. we will analyze membrane reactors, the startup of a CSTR. and semibatch reactors, which are most easily analyzed using concentration and molar How rates as the variables rather than conversion. We will again use mole balances in terms of these variables (Q. f,) for multiple reactors in Chapter 6. 

Example 4-6 Calculating X in a Reactor with Pressure Drop Example 4 7 Gas-Phase Reaction in Microreactor—Molar Flow Rate Example 4-8 Membrane Reaeior Example CDR4.1 Spherical Reactor Example 4.3.1 Aerosol Reactor Example 4-9 Isothermal Semibatch Reactor Profe.ssional Reference Shelf R4.1. Spherical Packed-Bed Reactor. ... 

PFR, Now assume the reaction. take place in the gas phase. U.se the [ ceding data to plot the molar flow rates as a function of PFR volume. pressure drop parameter is 0.001 dm , the total concentj ation ettlei the reactor is 0.2 moiAJm and iiy = 100 dm Vniin. What are 5d/E nnd Sc Membrane Reactor. Repeal (i) when species C diffuses out of me brane reactor and the transport coefficient, kc- is 10 min". Compare y results with part (i). 

Chemical Reaction Engineering. There is a greater emphasis on the use of mole balances in terms of concentrations and molar flow rates rather than conversion. It is introduced early in the text so that these forms of the balance equations can be easily applied to membrane reactors and multiple reactions, as well as PFRs. PBRs. and CSTRs. 

Figure 4. Effect of Sweep-To-Feed Molar Flow Rate Ratio on Hydrogen Recovery for the Countercurrent Membrane Reactor With the 18.63% CO Syngas From Steam Reforming...

Example 6-1 Gas-Phase Reaction in Microreactor—Molar Flow Rate Example 6-2 Membrane Reactor Example 6-3 Isothermal Semibatch Reactor Proressional Reference Shelf R6,1 UnsH udy CSTRs and Semihaich Reactors R6.1A Start-up of a CSTR... 

It is proposed to replace the conventional PBR with a membrane reactor in order to improve the selectivity. As a rule of thumb, a 1% increa.se in the selectivity to ethylene oxide translates to an increase in profit of about 2 mil-lion/yr. The feed consists of (2% (mole) oxygen. 6% ethylene, and the remainder nitrogen at a temperature of 250 C and a pressure of 2 atm. The total molar flow rate is 0.0093 mol/s to a reactor containing 2 kg of catalyst. 

What conversion and selectivity. 5, are expected in a conventional PBR Whai would be the conversion and selectivity if the total molar flow rate were divided and the 12% oxygen stream (no ethylene) were uniformly fed through the sides of the membrane reactor, and 6% ethylene (no oxygen) were fed at the entrance ... 

Equation (12-5) is coupled with llte mole balances on each species [Equation (11 -33)]. Next, we express as a function of either the concentrations for liquid systems or molar flow rates for gas systems, as desenbed in Chapter 4. We will use the molar flow rate form of the energy balance for membrane reactors and also extend this form to multiple reactions. 

Fig. 5. Methane conversion and oxygen flux during partial oxidation of methane in a ceramic membrane reactor. Reaction conditions pressure, 1 atm temperature, 1173 K, feed gas molar ratio, CH Ar = 80/20 feed flow rate, 20 mL min-1 (NTP) catalyst mass, 1.5 g membrane surface area, 8.4 cm2 (57).

Figure 13.9 MSR reaction. CH4 equilibrium conversion for both traditional and membrane reactors. I is the ratio ofthe sweep flow rate to the CH4 feed flow rate. H20/CH4 feed molar ratio = 3, permeate pressure = 100 kPa.

For a rapid conversion of lab-scale results into an economically viable reaction-pervaporation system, an optimum value can be determined for each parameter. Based on experimental results as well as a model describing the kinetics of the system, it has been found that the temperature has the strongest influence on the performance of the system as it affects both the kinetics of esterification and of pervaporation. The rate of reaction increases with temperature according to an Arrhenius law, whereas the pervaporation is accelerated by an increased temperature also. Consequently, the water content fluctuates much faster at a higher temperature. The second important parameter is the initial molar ratio. It has to be noted, however, that a deviation in the initial molar ratio from the stoichiometric value requires a rather expensive separation step to recover the unreacted component afterwards. The third factor is the ratio of membrane area to reaction volume, at least in the case of a batch reactor. For continuous operation, the flow rate should be considered as the determining factor for the contact time of the mixture with the membrane and subsequently the permeation... 

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