Reactive Stage

As a numerical example we consider a column with 39 reactive stages each of lm3 holdup. The pure propylene feed of llOkmol/h split into two equal parts enters the column on plates 20 and 35. This operation takes better advantage of the propylene concentration and offers better temperature control. Benzene is fed on the top stage in excess of 60% above the stoichiometry. This excess is necessary mainly to limit the temperature in bottom, but helps the selectivity to IPB too. Taking into account the reflux around the column, an overall benzene/propylene ratio larger than five may be realized. The following kinetic data are used in simulation [14, 15] ... 

A pressure of 14 bar gives a good compromise between the above aspects. The RD column is simulated as reboiled stripper with reactive stages. Although the highly exothermic reaction should make unnecessary the use of a heat source, we consider just a small reboiler to prevent residual propylene entrained in the bottom. For this reason, few reactive stages below the low feed of propylene are useful. 

Figure 8.7 Concentration and temperature profiles for the esterification of lauric acid with 2-ethylhexanol with an equilibrium-based model. Top Pressure 0.3bar. Seven reactive stages, acid feed on 3 and 5 with 0.5 split, alcohol feed on 7.

The sensitivity to feed quality and the scope for the real implementation of designs involving extreme feed qualities is investigated in this section with case B. The details for this case are 26 stages, 14 reactive stages (5-18), total reactive holdup equal to 1.1 kmole, two feeds (stages 9 and 20) with feed qualities of -2 and 2, respectively. 

In Fig. 5.3, a fully RD column is depicted in which the chemical reaction Aj A2 takes place. The educt Aj is fed at the point of its highest concentration within the column, that is the reboiler. In general, the Damkohler numbers of the reboiler, DUfeb. of the condenser, nd of the reactive stages, Da, can be chosen independently. Their corresponding mass balances are given by... 

Fig. 7.7 a) Acetic acid conversion and purities of MeOAc and A/ater in leaving product streams as a function of reboil ratio. The volumetric liquid hold-up on each reactive stage is set at 3 m. b) Acetic acid conversion as a function of the reboil ratio for various liquid hold-ups on each reactive stage... 

The munber of theoretical and reactive stages is determined from the distillation line and from the intersection of the distillation line and chemical equilibrium manifold (GEM) and represents the boimdary of the forward and backward reactions) (Giessler et al., 1999). Since there are multiple pairs of X and product composition that satisfy the mass balance, the method sets one of the product composition as reference point and solves for the other two (for a 3-component system) by using material balance expressions. Thus, two of the components compositions and X lie on the same line of mass balance (LMB) in the diagram and allow the estimation of the ratio D/B at a certain reboil ratio only by exploring the ratio of the line segments (figure 3.1f>). 

Limitations (i) the Damkohler number is assumed to be invariant on all the reactive stages (ii) the effect of structural aspects of the unit (e.g. feed ratio t e, location of multiple feeds, reflux and reboil ratios) are not considered and (m) the energy balances are left out from the design methodology. 

This approach is tested in the gas-phase disproportionation of toluene and in the de-hydratation of methanol into water and dimethyl ether. In the first case study the most competitive configuration is reported to be the reaction zone in the stripping and feed sections. The effect of the reaction equilibrium constant is analyzed in the second example, resulting in feasible configurations with a single reactive stage. 

Reactivation stage when the soil or rock mass slides along one or several preexisting shear surfaces. This reactivation can be occasional or continuous with seasonal variations of the rate of movement. 

Electrical surface modification of biopolymers requires surface activation. In the presence of radicals, the two reactive groups —OH and —NH easily lose their protons into the surrounding environment (Fig. 10.4). The resulting radicals, for example, —O and —NH, are able to anchor to ECMs, after which propagation of the ECMs ensues. The intermediate complex of the radical ECMs-biopolymer is called a radical reactivation stage. 

Upon heating water becomes less viscous (section 15.2). This makes the transport of reactants faster. If the diffusive step is fast compared with the reactive stage taking place within the boundaries of the reaction encounter volume, the overall rate of bimolecular reactions is limited by the chemical transformation, and k k. Following the transition state theory (TST) the bimolecular reaction eqn (15.9) can be considered as a two-step process, in which the transition state complex AB, formed in a reversible step, decays into products in an irreversible step. 

The spent electroless bath has to be in an active state for this method to work efficiently. Adding sodium hydroxide (NaOH) and/or formaldehyde (HCHO) to the bath will shift the equilibrium in the bath to this reactive stage. When this stage is reached, a small addition of sodium borohydride will catalyze the reaction, and reduced copper will precipitate out as metallic fines. 

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