Rate constants from plug-flow reactor data

Laboratory experiments on the irreversible, homogeneous gas-phase reaction 2A + B = 2C have shown the reaction rate constant to be 1 x 105 (g mol/L)-2 s 1 at 500°C(932°F). Analysis of isothermal data from this reaction has indicated that a rate expression of the form — rA = kCAC2B provides an adequate representation for the data at 500°C and 101.325 kPa (1 atm) total pressure. Calculate the volume of an isothermal, isobaric plug-flow reactor that would be required to process 6 L/s (0.212 ft3/s) of a feed gas containing 25% A, 25% B, and 50% inserts by volume if a fractional conversion of 90% is required for component A. 

Figure E6-3.2 Yield of acetaldehyde as a function of ethanol conversion. Data were obtained at 518 K. Data points (in order of increasing ethanol conversion) were obtained at space velocities of 26,000, 52,000, 104,000, and 208,000 h". The curves were calculated for a first-order series reaction in a plug-flow reactor and show yield of the intermediate species B as a function of the conversion cf reactant for various ratios of rate constants and [Reprinted with permission from/nd. Eng. Chem. Prod Res. Dev. 22, 212 (1983). Copyright 1983American Chemical Society.]...

Figure 11.10. Rate constants for reactions of ozone and OH radicals with solutes, (a, b) Examples of rate constants for direct reactions of ozone with organic and inorganic solutes versus pH (data selected), is related to k by the yield factor, (c) Rate constants for reactions of OH radicals with different solutes. (A03)37 is the required amount of decomposed ozone, which results in the elimination of the quoted substrate to 37% of the initial value (batch-type or plug-flow reactor). This scale is calibrated for eutrophic lakewater (Lac de Bret, DOC = 4 mg liter"[HCOf] = 1.6 mM, pH = 8.3. The latter changes proportionally to the DOC of water). (From Hoignd, 1988.)...

The QSSA is a useful tool in reaction analysis. Material balances for hatch and plug-flow reactors are ordinary differential equations. By applying Equation 5.81 to the components that are QSSA species, their material balances become algebraic equations. These algebraic equations can be used to simplify the reaction expressions and reduce the number of equations that must be solved simultaneously. In addition, appropriate use of the QSSA can eliminate the need to know several difficult-to-measure rate constants. The required information can be reduced to ratios of certain rate constants, which can be more easily estimated from data. In the next section we show how the QSSA is used to develop a rate expression for the production of a component from a statement of the elementary reactions, and illustrate the kinetic model simplification that results from the QSSA model reduction.. 

Deactivation rate constants for the zeolite catalysts were obtained from the time-on-stream activity data (Fig. 1) by using the following expression developed for the case of a first order catalyst deactivation in plug flow fixed bed reactor [20]. 

The Monte Carlo approach was extended to reactors with a plug flow macro-mixing RTD by Rattan and Adler [124]. Here, the coalescing fluid elements are moved through the reactor at a speed corresponding to the constant mean fluid velocity. Rattan and Adler [124] were able to simulate experimental results of Vassilatos and Toor [125]. The coalescence frequency was found from data for extremely rapid reactions, where the observed rate is essentially completely controlled by the micromixing in this situation with a flat velocity profile. Then, these coalescence rates were used to predict the experimental results for rapid and slow reactions taking place in the same equipment. 

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