Once-through differential reactors

For evaluation of results from a once-through differential reactor, the rate is calculated from the difference AC( between the entering and exiting concentrations ... 

A differential reactor similar to one previously described is used (2). It is illustrated in Fig. 1. A clock-motor-driven syringe feeds 43 g. of cyclohexane per hour once through the reactor. The standard condition of operation is 430° and atmospheric pressure. A flow of 760 cc./min. of purified hydrogen is provided which enters the reactor between the boiler and preheater. 

The distinction between instantaneous and cumulative yield ratios or selectivities becomes immaterial in gradientless reactors (continuous stirred-tank at steady state or differential once-through reactors) or if the instantaneous values do not vary with conversion. 

For elucidation of mechanisms, rate data at very low conversions may be highly desirable. They can be obtained more easily from a batch reactor than from a CSTR or plug-flow tubular reactor. A standard CSTR would have to be operated at very high flow rates apt to cause fluid-dynamic and control problems. The same is true for a standard tubular reactor unless equipped with a sampling port near its inlet, a mechanical complication apt to perturb the flow pattern. If the problem of confining the reaction to a very small flow reactor can be solved—as is possible, for example, for radiation-induced reactions—a differential reactor operated once-through or with recycle may be the best choice. 

Because of the difficulty of measuring minimal conversions accurately, differential reactors are often operated with recycle instead of once through. A... 

Bench-scale kinetic experiments can be conducted in batch, continuous stirred-tank, tubular plug-flow, or differential reactors. The last of these can be operated with once-through flow or recycle. The advantages and disadvantages of the various types are discussed in Section 3.1. 

Bench-scale kinetic experiments can be conducted in batch, continuous stirred-tank (CSTR), tubular plug-flow, or differential reactors. The last of these can be operated with once-through flow or recycle. Advantages and disadvantages of the various types are discussed. In particular Batch reactors are inexpensive, but require attention to rapid attainment of reaction conditions at start CSTRs are excellent for gas-liquid, but less so for gas-phase reactions tubular reactors are especially suited for reactions of heterogeneous catalysis and differential reactors operated "once through" are best for measurement of initial rates. 

The stoicheiometric number concept has been applied to butane dehydrogenation, the isobutane-isobutene-H2 system, SO2 oxidation and ethanol dehydrogenation. Experimentally it is desirable to operate in a differential mode, using a reactor either of the recirculating or once-through continuous flow type. Since the method is based on the assumption that a steady state exists as regards the concentration of surface intermediates, pulsed flow reactors are not suitable for this type of experiment. 

The above considerations- led to the present design of the MTR fuel assembl ies wi th spacing, of 0.117- in.- between plates. Heat transfer calcu-lations then showed that satisfactory heat transfer could be obtained with a water velocity of approximately. 30 ft/sec through these space s. Once this figure was established, further calculations and experiments (see Appendix 4) established the pressure differentials required and the resultant quantity, of water through the reactor. By this means the necessary.pressure drop across the fuel assemblies was found to be about 40 psi, which, because of parallel flow, is also the pressure drop across the ber yll-ium reflector.- It should be noted that this pressure produces a flow of approximately 20,000 gpm through the. reactor and beryllium, resulting in a water, temperature rise of only about 11 F for 30,000-kw. operation. ... 

Once the effective rate forms at the particle/bubble level are established, and flow patterns as assumed in Figure 6.2 are available, one simply uses these effective rate expressions to write down the corresponding steady-state material balances for the reactor for the assumed flow patterns. Under steady-state conditions, this involves either first-order ordinary differential equations for the phases in which plug flow is assumed or simple difference equations in species concentration in phases in which completely mixed flow is assumed. The treatment in all these cases is very similar to what will be in a single-phase reactor (see, e.g.. Ref [48]), except that one has a separate differential equation balancing for each species concentration and they are coupled through the effective reaction rate term. 

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