Composition calculations

Figure 7-1. Incipient equilibrium vapor-phase compositions calculated with subroutine BUDET.

Adiabatic flame temperatures agree with values measured by optical techniques, when the combustion is essentially complete and when losses are known to be relatively small. Calculated temperatures and gas compositions are thus extremely useful and essential for assessing the combustion process and predicting the effects of variations in process parameters (4). Advances in computational techniques have made flame temperature and equifibrium gas composition calculations, and the prediction of thermodynamic properties, routine for any fuel-oxidizer system for which the enthalpies and heats of formation are available or can be estimated. 

Example 2 Stage and Composition Calculation A 100-kg/h feed stream containing 20 weight percent acetic acid in water is to he extracted with 200 kg/h of recycle MIBK that contains 0.1 percent acetic acid and 0.01 percent water. The aqueous raffinate is to he extracted down to 1 percent acetic acid. How many theoretical stages wiU he required and what will the extract composition he ... 

Continue doivn column using the composition calculated for tray above to substitute in Equation 8-176 to obtain the (xj/xh) for the tray below. 

A zeolite catalyst operated at 1 atm and 325-500 K is so active that the reaction approaches equilibrium. Suppose that stack gas having the equilibrium composition calculated in Example 7.17 is cooled to 500 K. Ignore any reactions involving CO and CO2. Assume the power plant burns methane to produce electric power with an overall efficiency of 70%. How much ammonia is required per kilowatt-hour (kWh) in order to reduce NO , emissions by a factor of 10, and how much will the purchased ammonia add to the cost of electricity. Obtain the cost of tank car quantities of anhydrous ammonia from the Chemical Market Reporter or from the web. 

The quantity occurring in braces is very nearly equal to (1/6) l—V2 — V provided v 2 is small. The fractional error in the composition calculated using this approximation is of the order of v x/b. Substituting this result in Eq. (A-3)... 

The usual procedure is to start the calculation at the top and bottom of the column and proceed toward the feed point. The initial estimates of the component distributions in the products are then revised and the calculations repeated until the compositions calculated from the top and bottom starts mesh, and match the feed at the feed point. 

In laboratory work, the identity of a compound may be established by determining its percent composition experimentally and then comparing the results with the percent composition calculated from its formula. 

As stated, the most commonly used procedure for temperature and composition calculations is the versatile computer program of Gordon and McBride [4], who use the minimization of the Gibbs free energy technique and a descent Newton-Raphson method to solve the equations iteratively. A similar method for solving the equations when equilibrium constants are used is shown in Ref. [7],... 

Multiple solutions to equations occur whenever they have sufficient nonlinearity. A familiar example is equHihrium composition calculations for other than A B. The reaction composition in the reaction A i B yields a cubic polynomial that has three roots, although all but one give nonphysical concentrations because thermodynamic equilihrium (the solution for a reactor with f —> co or T — co) is unique. 

Sample Calculations. For the PSM model, computer-calculations have been done (17). All concentrations are normalized with respect to c - In Figure 3 we show mixed cmc s versus overall surfactant composition calculated for mixed surfactants with c /cj = 3.0, A = 0.0, B = 0.0, cjc — 0.0, and varying values of y j, P- For a given value of a, the calculated cmc for the nonionic/ionic system (y j = 0.6, P = a) is... 

Chemists are often concerned with precisely what percentage of a compound s mass consists of one particular element. Lying awake at night, uttering prayers to Avogadro, they fret over this quantity, called percent composition. Calculating percent composition is trickier than you may think. Consider the following problem, for example. 

Table 1. Forces Acting During the Homogenization of Particulate Filled Composites Calculated for Particles of 20 pm Diameter...

M HC1 and 1 M NaOH for use in buffer preparation. Compositions calculated from Eq. 3-8 will usually yield buffers of pH very close to those expected. 

The permeability of a number of gases through acrylonitrile-vinyl acetate (PAN-PVAc) and acrylonitrile-styrene (PAN-PS) copolymers has been studied over a wide range of composition Calculations on the basis of Eq. (30), or of the (empirical) Higuchi equation 100)... 

Cl" has been diminished by 0.14 from the calculated 0.30 derived from 1.06 p.p.m. given in the analysis to correct initial electrical imbalance between anions and cations. This change is important in the compositions calculated but not in the general pattern of change to be presented. 

Analysis of this material showed it to have the average composition calculated for a tetrasulfide the yield of product, calculated as tetrasulfide, is 83-92%. 

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