Yield reactors

Table 2.2 gives the compositions of the reactor feed and effluent streams. Calculate the conversion, selectivity, and reactor yield with respect to (a) the toluene feed and (b) the hydrogen feed. 

Reactor yield of benzene from toluene = ( luene fed to the reactor)... 

In describing reactor performance, selectivity is usually a more meaningful parameter than reactor yield. Reactor yield is based on the reactant fed to the reactor rather than on that which is consumed. Clearly, part of the reactant fed might be material that has been recycled rather than fresh feed. Because of this, reactor yield takes no account of the ability to separate and recycle unconverted raw materials. Reactor yield is only a meaningful parameter when it is not possible for one reason or another to recycle unconverted raw material to the reactor inlet. By constrast, the yield of the overall process is an extremely important parameter when describing the performance of the overall plant, as will be discussed later. 

Laboratory studies indicate that the reactor yield is a maximum when the concentration of sulfuric acid is maintained at 63 percent. ... 

Batch vs Continuous Reactors. Usually, continuous reactors yield much lower energy use because of increased opportunities for heat interchange. Sometimes the savings are even greater in downstream separation units than in the reaction step itself Especially for batch reactors, any use of refrigeration to remove heat should be critically reviewed. Batch processes often evolve Httle from the laboratory-scale glassware setups where refrigeration is a convenience. 

Similarly a hypothetical spHtter must be defined when a stream is spHt. Furthermore, control units ate identified in calculations flow diagrams when temperatures, pressures, and flows of streams ate controlled on the basis of variables in other parts of flow sheets. Sometimes variables such as product specifications and reactor yields can be represented as hypothetical control units. 

Consider the scale-up of a batch reactor from a pilot plant reactor to a full-scale reactor. Rewriting Equation 13-82 to the full-scale reactor yields ... 

The reactor yield is then determined by performing a component balance. The amount of C5+ in the gasoline boiling range is calculated by subtracting the C4 and lighter components from the total gas plant products. Example 5-4 shows the step-by-step calculation of the component yields. The summary of the results, normalized but unadjusted for the cut points is shown in Table 5-4. 

Determine the maximum batch reactor yield of B for a reversible, first-order reaction ... 

A Grignard reaction between cyclohex-2-enone and diisopropyl magnesium chloride was carried out in a micro reactor yielding a keto and enol product each [168],... 

GP 9] [R 16] By finite-element reactor modeling, it was shown that for conversions as large as 34%, concentration differences within the mini wide fixed-bed reactor of only less than 10% are found [78], Thus, the reactor approximates a continuous-stirred tank reactor (CSTR). This means that the mini wide fixed-bed reactor yields differential kinetics even at large conversions, larger than for reactors used so far (< 10% conversion). 

OS 67] ]R 4a2] ]P 49] Initial micro reactor yields ranged from 58% to almost complete conversion (99%), depending on the voltages applied and the reaction considered [9]. In a later series of experiments, yields from 42 to 99% were reported, depending on the voltages applied and the reaction considered. 

OS 73] [R 4a] [P 54] The micro reactor yield (up to 42%) is comparable to that for batch Stork-enamine reactions using p-toluenesulfonic acid in methanol imder Dean and Stark conditions [11],... 

OS 85] [R 33] ]P 65] Using conducting salt (0.01 M) in a micro reactor yields a current efficiency of 60-65%, whereas operation without any salt has an efficiency of 96-98% [69]. For conventional electrochemical processing of 4-methoxybenzalde-hyde, an efficiency of49-54% is reported (Figure 4.94). 

The first few experiments in the continuous flow reactor yielded inconsistent octene conversions (Figure 28.3). The experiment ran for 218 hours. Initially the conversion was consistent at 3-4% for several hours, then improved significantly to 16% and then rapidly dropped off to less than 2% (Figure 28.3). The selectivity was also very good for this ran, with an average normal to branch isomer ratio of 7 1. 

With industrial reactors it is necessary to distinguish between Reaction yield (chemical yield), which includes only chemical losses to side products and the overall Reactor yield which will include physical losses. 

If the conversion is near 100 per cent it may not be worth separating and recycling the unreacted material the overall reactor yield would then include the loss of unreacted material. If the unreacted material is separated and recycled, the overall yield taken over the reactor and separation step would include any physical losses from the separation... 

Flow of NH3 to oxidiser x reactor yield balance by reaction 2... 

Calculate the conversion, selectivity and reactor yield with respect to the ... 

When dealing with multiple reactions, selectivity or reactor yield is maximized for the chosen conversion. The choice of mixing pattern in the reactor and feed addition policy should be chosen to this end. 

Multiple reactions producing by products. 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 and reactor yield are likely to be more important than reactor volume for a given conversion. 

If there is a significant difference between the effect of pressure on the primary and secondary reactions, the pressure should be chosen to reduce as much as possible the rate of the secondary reactions relative to the primary reaction. Improving the selectivity or reactor yield in this way may require changing the system pressure or perhaps introducing a diluent. 

Multiple reactions in parallel producing by products. After the reactor type is chosen for parallel reaction systems in order to maximize selectivity or reactor yield, conditions can be altered further to improve selectivity. Consider the parallel reaction system from Equation 5.66. To maximize selectivity for this system, the ratio given by Equation 5.67 is minimized ... 

An example of where recycling can be effective in improving selectivity or reactor yield is in the production of benzene from toluene. The series reaction is reversible. Hence, recycling diphenyl to the reactor can be used to suppress its formation at the source. 

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. 

For supported layered catalysts, optimizing the location of the active sites within the catalyst pellets maximizes the effectiveness or the selectivity or reactor yield. 

Prior to conducting the DOE (design of experiments) described in Table 3, it was established that no reaction took place in the absence of a catalyst and that the reactions were conducted in the region where chemical kinetics controlled the reaction rate. The results indicated that operating the reactor at 1000 rpm was sufficient to minimize the external mass-transfer limitations. Pore diffusion limitations were expected to be minimal as the median catalyst particle size is <25 pm. Further, experiments conducted under identical conditions to ensure repeatability and reproducibility in the two reactors yielded results that were within 5%. 

The growth of biomass in the reactor is assumed to follow Monod kinetics with a first-order death rate. A mass balance on the biomass in the reactor yields the following differential equation (assuming that no biomass enters the reactor in the feed) ... 

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