Reactor pressure multiple reactions

Design and operation of gas-phase plug-flow reactors with multiple reactions where the pressure drop along the reactor is not negligible... 

The selection of reactor pressure for vapor-phase reversible reactions depends on whether there is a decrease or increase in the number of moles and whether there is a system of single or multiple reactions. 

Multiple reactions producing byproducts. The arguments presented for the effect of pressure on single vapor-phase reactions can be used for the primary reaction when dealing with multiple reactions. Again, selectivity is likely to be more important than reactor volume for a given conversion. 

It should be emphasized that these recommendations for the initial settings of the reactor conversion will almost certainly change at a later stage, since reactor conversion is an extremely important optimization variable. When dealing with multiple reactions, selectivity is maximized for the chosen conversion. Thus a reactor type, temperature, pressure, and catalyst are chosen to this end. Figure 2.10 summarizes the basic decisions which must be made to maximize selectivity. ... 

The selection of reactor pressure for vapor-phase reversible reactions depends on whether there is a decrease or an increase in the number of moles. The value of AN in Equation 6.25 dictates whether the equilibrium conversion will increase or decrease with increasing pressure. If AN is negative, the equilibrium conversion will increase with increasing pressure. If AN is positive, it will decrease. The choice of pressure must also take account of whether the system involves multiple reactions. 

For reaction systems involving multiple reactions producing by products, selectivity and reactor yield can also be enhanced by appropriate changes to the reactor temperature, pressure and concentration. The appropriate choice of catalyst can also influence selectivity and reactor yield. The arguments are summarized in Figure 6.912. 

In a variable-density reactor the residence time depends on the conversion (and on the selectivity in a multiple-reaction system). Also, in ary reactor involving gases, the density is also a function of reactor pressure and temperature, even if there is no change in number of moles in the reaction. Therefore, we frequently base reactor performance on the number of moles or mass of reactants processed per unit time, based on the molar or mass flow rates of the feed into the reactor. These feed variables can be kept constant as reactor parameters such as conversion, T, and P are varied. 

Equation (4-28) will be the one we use when multiple reactions are occurring or when there is pressure drop in a membrane reactor. However, for single reactions in packed-bed reactors it is more convenient to express the Ergun equation in terms of the conversion X. RecaUing Equation (3-42) for Fj-,... 

In materials and catalyst research, combinatorial methods and associated instrumentation are increasingly being used also for optimizing process conditions. The availability of analytical tools that can handle multiple reactors in real time and in parallel make possible the efficient studies of multiple reactions conducted under different process conditions of temperature, pressure, and other variables simultaneously. The new tools have extended that capability dramatically affording a much higher degree of flexibility in the number of reactors and the parameters that can be independently varied. ... 

The tubular reactor with static mixers was chosen for the documented capability of static mixers to accomphsh the following important functions for fast multiple reactions in turbulent flow (1) homogeneity down to the molecular level can be achieved in a few tube diameters (2) very short mixing time and narrow residence time distributions are required and (3) high rates of energy dissipation are achievable (average energy dissipation rates can be calculated from pressure drop and local rates can be estimated). 

We will use Equation (5-28) when multiple reactions are occurring or when there is pressure drop in a membrane reactor. However, for single reac-... 

Aspen is capable of modeling chemical reactions. It can handle single and multiple reactions. Material balance can be done in the stoichiometric reactor, Rsto/c from Reactors in the model library. Click on Material Streams, and connect the inlet and product streams. Click on Components and choose the components involved. Peng-Robinson EOS is selected as the thermodynamic fluid package. Doubleclick on the conversion reaction block. Click on the Specification tab enter pressure as 1 atm and temperature as 25°C. Then click on the Reactions tab, click on New and enter the components involved in the reaction, stoichiometric coefficient, and fractional conversion as shown in Figure 3.13. Close the stoichiometric windows and then double click on the inlet stream, specify temperature, pressure, flow rate, and composition. Click Run and then generate the stream table as shown in Figure 3.14. 

PRO/II is capable of handling multiple reactions. The same procedure of Example 3.2 is used here. First, perform the process flow sheet of the conversion reactor and specify the feed stream with the given total flow rate and compositions, Temperature is 350°C and pressure is 30 atm. Under the Reactions input menu, select Reaction Data and enter the two reactions as shown in Figure 3.29. Select reaction set R1 from the Reaction set Name of the pull-down menu. Click on Extent of Reaction and specify 100% conversion (fractional conversion is 1) for... 

An innovative way effacing this challenge is sequencing of multiple reactions in the same reactor without release of pressure, so that the energy cost is distributed. Several examples are presented in the review by Hans and Poliakoff [55]. An example suggested is the dehydration of cyclohexanol to cyclo-... 

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