Reactions with varying volume

Reactions with Varying Volume (for the Example of a Batch Reactor)... 

For a reaction with varying volume, for example, a gas-phase reaction of A to 2B with initial volume Vq, the change of volume is characterized by the fractional change Sy for complete conversion (Xa =1) ... 

Varying KOH ratio in the mixture is a very effective way of controlling porosity development in resultant activated carbons. The trend in the pore volume and BET surface area increase seems to be similar for various precursors (Fig. la). It is interesting to note, however, a sharp widening of pores, resulting in clearly mesoporous texture, when a large excess of KOH is used in reaction with coal semi-coke (Fig. lb). Increase in the reaction temperature within 600-900°C results in a strong development... 

Equations of an Arrhenius type are commonly used for the temperature-dependent rate constants ki = kifiexp(—E i/RT). The kinetics of all participating reactions are still under investigation and are not unambiguously determined [6-8], The published data depend on the specific experimental conditions and the resulting kinetic parameters vary considerably with the assumed kinetic model and the applied data-fitting procedure. Fradet and Marechal [9] pointed out that some data in the literature are erroneous due to the incorrect evaluation of experiments with changing volume. 

Chain-transfer reactions would be expected to increase in rate with increasing pressure since transfer is a bimolecular reaction with a negative volume of activation. The variation of chain-transfer constants with pressure, however, differ depending on the relative effects of pressure on the propagation and transfer rate constants. For the case where only transfer to chain-transfer agent S is important, Cs varies with pressure according to... 

Isopropylidene acetals are cleaved under acidic conditions, with the acid strength and reaction time varying considerably as a function of the substrate. In this case a 1M solution of the acetonide in THF was treated with an equal volume of 6N hydrochloric acid at room temperature Final chromatographic purification was accomplished with an ion exchanger (Dowex 1 x8 200 OH ). 

This expression enhances the fact that the heat release rate is a function of the conversion, but also of the varying volume. The dilution of the reaction mass by the feed will contribute to slow the reaction. Usually with a constant feed rate and as long as the volume varies in the cylindrical part of the reactor, V(t) is a linear function of time. In addition to the pure heat of reaction, the mixing effect of the feed with the reaction mass can be accompanied by thermal effects, for example, dilution enthalpy or mixing enthalpy. 

The great difference with the CSTR (Equation 8.2) is that here the reaction rate varies within the reactor volume instead of being constant. Hence, the reaction rate is in the integral term. If the initial conversion is not zero, the equation becomes... 

Let us now apply the above equation in order to calculate the conversion of a varying number of CSTRs in series with total volume Vtot = 0.6 m3 and volumetric flow rate V = 0.1 m3 h"1 for a first-order reaction with reaction rate constant k = 0.25 h The results are presented in Table 1. 

Figure 3. X-ray diffraction patterns as a function of ethanol content for 2g Na aluminosilicate (Si/Al - 1.33) in 50 mL of 1M NaOH with varying ethanol content. From top 0%, 10%, 25%, 50% and 75% ethanol (volume percent). X-ray patterns taken -8 hours after reaction at 90-95°C. The intensity axis is the same for all the patterns.

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