Internal reflux generation

Heavy cycle oil, heavy naphtha, and other circulating side pumparound reflux streams are used to remove heat from the fractionator. They supply reboil heat to the gas plant and generate steam. The amount of heat removed at any pumparound point is set to distribute vapor and liquid loads evenly throughout the column and to provide the necessary internal reflux. 

In the present estimation, a continuous dehydrogenation reactor in which decalin is supplied to the catalyst at various feed rates without internal refluxing is assumed. Here all the condensable products and unconverted decalin were removed from the reactor to the condensation part (see Figure 13.22). Now, the stationary rates of hydrogen generation (VH), naphthalene formation (VN), and evaporation of unconverted decalin (VD) are defined as the magnitudes per area of the catalyst layer (mol/m2h). All these rates are expressed from mass balance as follows . 

The side-product liquid streams shown in Figs. 1, 2 and 4 may be generated at each zone by liquid pumparounds, which also provide internal reflux for rectification. Of course, it would be possible to condense only at the top of the column, but the heat recovery would be greatly damaged because of the poor thermodynamic reversibility. Also, the hydraulic load in the upper column would be a problem. 

Methoxy-l-naphthyl sulfoxide 39b is stable in THF at room temperature however, it undergoes a gradual internal redox reaction in THF at reflux, generating the corresponding phosphine oxide, presumably due to the stereoelectronic effect of the 2-methoxy-l-naphthyl substituent (Scheme 19). 

Apparatus A 10-mL. a 50-mL. and a 100-mL round-bottom flask, separatory funnel, ice-water bath. 13-mm x 120-mm test tube, apparatus for heating under reflux, simple distillation, magnetic stirring, steam distillation with internal steam generation. vacuum filtration, and flameless heating. 

The flow rate ratio Kin/Kin) called the internal reflux ratio, as opposed to external reflux ratio of definition (8.1.137) since no formal reflux stream is generated in Figure 9.1.1(b). This flow rate ratio provides an estimate of the heavy fraction flow rate downward in the cascade below stage n in the enriching section. We are interested in its variation with the stage number n. 

The second iteration starts with initial estimates for almost all streams. An exception is stream L4, for which no estimate is needed. Initial estimates of streams V3 and Lr are used in an adiabatic flash calculation for stage 4 to determine an initial estimate for stream L4. Subsequently, flash calculations are performed in order for stages 3, 2, and 1, and then back up the column for stages 2, 3, and 4 followed by the total condenser and reflux divider. At the conclusion of the second iteration, generally all internal vapor and liquid flow rates are increased over values generated during the first iteration. 

The variations of intramolecular—intermolecular and intramolecular-intramolecular DTHDA sequences of this cross-conjugated thiatriene system have been reported (Scheme 2.4) [10], The thiatrienes 6 generated from the corresponding ketones by thionation with Lawesson s reagent in refluxing benzene were trapped in situ by the internal dienophile to give the initial HDA monoadducts 7. The second DA reaction of each separated stereoisomer 7... 

---