BP method

BP Method for Distillation The bubble-point method for distillation, particularly when the components involved cover a relatively narrow range of volatihty, proceeds iteratively by the following steps, where k is the iteration index for the entire distillation column. 

Example 4 Calculation of the BP Method Use the BP method with the SRK eqiiation-of-state for K values and enthalpy departures to compute stage temperatures, interstage vapor and hqiiid flow rates and compositions, and rehoiler and condenser duties for the light-hydrocarhon distdlation-coliimn specifications shown in Fig. 13-51 with feed at 260 psia. The specifications are selected to obtain three products, a vapor distillate rich in Cri and C3, a vapor side-stream rich in n-C4, and a bottoms rich in n-C and n-Cg. 

Another group which is used to mask polar groups in molecules in order to improve GC peak shape is the trimethylsilyl group. Atropine Eye Drops BP are used to dilate the pupil prior to cataract surgery. The 1993 BP method for the analysis of Atropine Eye Drops BP uses derivatisation with a trimethylsilyl group to mask an alchohol group as shown in Figure 11.17. 

The current BP methods for determination of solvent residues in pharmaceuticals remaining from the manufacturing process rely on direct injection of the sample dissolved in a suitable solvent (often water) and are based on packed column GC. Some examples are given in Table 11.4. 

In this method, temperatures for succeeding iterations are found by enthalpy balances rather than by bubblepoint determinations, after new values of the liquid and vapor flow rates have been estimated from solution of the equations for the liquid mol fractions. This procedure is suited to absorption and stripping problems for which the BP method breaks down because of the wide range of relative volatilities involved. The algorithm appears in Figure 13.18. Input data are the same as for the BP method. 

Box 1. Initial temperatures and vapor flow rates are estimated in the same way as in the BP method. 

The BP methods use a form of the equilibrium equation and summation equation to calculate the stage temperatures, The first BP method, by Wang and Henke (24), included the first presentation of the tridiagonal method to calculate the component flow rates or compositions. These are used to calculate the temperatures by solving the bubble-point equation but this temperature calculation can be prone to failure. 

The BP methods generally work best for narrow-boiling, ideal or nearly ideal systems, where composition has a greater effect on temperature than the latent heat of vaporisation,... 

The theta method has found many applications. The FRAKB routines of FLOWTRAN use the theta method, Portions of the theta method, such as the Kb method for temperatures, appear in other rigorous methods. Poor initial temperature and flow rate estimates do not greatly hinder the approach to solution and the calculation is relatively rapid. It has been shown to work well for the systems that the BP methods are meant for, i.e., narrow- and middle-boiling ranges, ideal or nearly ideal mixtures. It has solved columns with as many as 200 stages without great difficulty. 

Simultaneous Convergence Methods One drawback of some tearing methods is their relatively limited range of application. For example, the BP methods are more successful for distillation, and the SR-type methods are considered better for mixtures that exhibit a wide range of (pure-component) boiling points (see, however, our remarks above on modified BP and SR methods). Other possible drawbacks (at least in some cases) include the number of times physical properties must be evaluated (several times per outer loop iteration) if temperature- and composition-dependent physical properties are used. It is the physical properties calculations that generally dominate the computational cost of chemical process simulation problems. Other problems can arise if any of the iteration loops are hard to converge. 

Multicomponent distillation, 393 absorption factor method, 398 azeotropic, 420-426 bubblepoint (BP) method, 406-409 computer program references. 404 concentration profiles, 394 distribution of non-kevs. 395 Edmister method, 398,399 extractive, 412, 417-422 feed tray location, 397 free variables, number of 395 Lewis-Matheson method 404 MESH eauations. 405-407 molecular, 425-427 nomenclature, 405 number of theoretical trays, 397 packed towers, 433-439 petroleum, 411-415 reflux, minimum, 397 reflux, operating, 397 SC (simultaneous correction) method, 408-411... 

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