Equilibrium yield calculation

The mass-action equations have been written in the same form as those given by Marynowski et al. (6) so that the equilibrium constants can be used directly. (Should more accurate data become available, the equilibrium yields calculated here will require revision.) The fourth equation, which applies to the heterogeneous equilibrium between carbon and nitrogen, is included for completeness but is unnecessary for the general solution. It can be shown that when the total pressure of the system is F, the partial pressure of cyanogen radicals is given by the equation ... 

These multicomponent calculations are now computerized, and complicated systems, such as tire Si-C-H-Cl quaternaty, may be solved by the use of commercially available software, e. g. the IVTAN database. The solution to this multicomponent system which is obtained by this means is somewhat subjective, since, at the time of writing for example, data are available for 72 gaseous species in the quaternary system Si-C-H-Cl. Choosing 19 of the most probable of tlrese, and using tire IVTAN software to solve this multicomponent equilibrium, yields the following results for tire most probable species (see Table 3.2). 

ILLUSTRATION 2.1 CALCULATION OF EQUILIBRIUM YIELD FOR A CHEMICAL REACTION... 

For example, classic thermodynamic methods predict that the maximum equUi-brium yield of ammonia from nitrogen and hydrogen is obtained at low temperatures. Yet, under these optimum thermodynamic conditions, the rate of reaction is so slow that the process is not practical for industrial use. Thus, a smaller equilibrium yield at high temperature must be accepted to obtain a suitable reaction rate. However, although the thermodynamic calculations provide no assurance that an equUibrium yield will be obtained in a finite time, it was as a result of such calculations for the synthesis of ammonia that an intensive search was made for a catalyst that would allow equilibrium to be reached. 

If the value of for a reaction is calculated from the value of AG, we must have values of the 7, to substimte into Equation (16.27) or Equation (16.30) to obtain equilibrium yields in terms of m, or A,. The determination of these quantities from experimental data will be discussed in Chapters 17 and 19. 

Table 6.1 lists the stoichiometric yields of hydrogen and percentage yields by weight from steam reforming of some representative model compounds present in biomass pyrolysis oils, and also several biomass and related materials. The table also shows the equilibrium yield of H2, as a percentage of the stoichiometric yield, predicted by thermodynamic calculations at 750 °C and vdth a steam-to-carbon (S/C) ratio of 5 [32]. 

The coordinates of thermodynamics do not include time, ie, thermodynamics does not predict rates at which processes take place. It is concerned with equilibrium states and with the effects of temperature, pressure, and composition changes on such states. For example, the equilibrium yield of a chemical reaction can be calculated for given T and P, but not the time required to approach the equilibrium state. It is however true that the rate at which a system approaches equilibrium depends direcdy on its displacement from equilibrium. One can therefore imagine a limiting kind of process that occurs at an infinitesimal rate by virtue of never being displaced more than differentially from its equilibrium state. Such a process may be reversed in direction at any time by an infinitesimal change in external conditions, and is therefore said to be reversible. A system undeigoing a reversible process traverses equilibrium states characterized by the thermodynamic coordinates. 

The results of the calculations show that with increasing pressure the equilibrium yield of ammonia is increasing and that the non-ideality of the gas mixtures has in this case a positive effect on the equilibrium conversion. 

Slanina et at. (1989) have considered the thermodynamics of the fullerenes in carbon vapour, and their work demonstrates that the C70/C60 ratio of approximately unity (ratios obtained vary roughly from 0.1 to 10) found in extracts from graphitic soot is incompatible with thermodynamic equilibrium being established between these two species when they were formed. In their work, the sum of the partial pressures of C60 and C70, PM 70, at which the species are present in equal concentrations at equilibrium was calculated, and PrM 70 is never larger than 10-13 bar below 5000 K. The observed C60 and C70 yields cannot be reached with such a small partial pressure of product. If the sum of the C60 and C70 partial pressures is raised, C70 rapidly becomes totally dominant at thermodynamic equilibrium. 

Fundamental thermodynamic and kinetic studies of the decomposition reaction (1) have confirmed that hydrogen sulphide is a stable sulphide and that the dissociation is thermodynamically unfavorable below 1800°K. Nevertheless, some decomposition does, of course, occur below these temperatures and equilibrium hydrogen yields range from less than 1% at 750°K through about 5% at 1000°K to almost 30% at 1400°K. [These values are based on equilibrium product calculations which considered all possible sulphur/hydrogen species which could be present at equilibrium including various sulphur vapor species (S S to S ), and sulphanes (H2Sx) as well as H2S, H and The values which are... 

Columns between Ke and y(H2) may contain intermediate quantities in the calculation of yni First test your program for the conditions of part (a) and verify that it is correct. Then try a variety of values of the input variables and draw conclusions about the conditions (reactor temperature and feed composition) that maximize the equilibrium yield of hydrogen. 

In cases in which the reaction quickly proceeds to equilibrium, the yields are easily estimated as the equilibrium yields. Under these circumstances, the only possibilities for process optimization are to change the temperature, pressure, or feed composition, so as to obtain a different equilibrium mixture. The calculation of reaction equilibrium is easily carried out using commercial process simulation programs. 

Fig. 8.8 The calculated effect of pressure and temperature upon the equilibrium yield of CCI4 from the dismutation of phosgene [ICI8,ICI9].

Equilibrium yields have been calculated for the hypothetical production of methyl isocyanate from the reaction of MCgN and COCI3 [167] ... 

The experimentally determined S-L-V equilibrium data for salicylic acid (2-hydroxy-benzoic acid)-l-propanol-C02 were correlated by using the Stryjek-Vera modification of the Peng Robinson EOS in conjunction with Eq. (35) for the solid state fugacity of the solute (58,62), as described earlier. This procedure also yielded good agreement of the liquid phase compositions of salicylic acid in the temperature and pressure ranges of 273 to 367 K and 1.0 to 12.5 MPa. The P-Ttraces of S-L and L-V equilibria were calculated for a fixed solute concentration on C02-free basis, and subsequently the P-T trace for the S-L-V equilibrium was found from the point of intersection of these two lines. The liquid phase compositions of the solute as a function of pressure at a constant temperature at the condition of S-L-V equilibrium were calculated to assess the effect of pressure or addition of antisolvent on solute crystallization. It was reported that two isobaric points of the CO2 mole fraction could be observed on the curve of the S-L equilibrium temperature vs the CO2 mole fraction at constant temperature as it passes through a mini-... 

The steam reforming of methane to produce syngas includes nine basic reactions. The global equilibrium yield (GEY) and the potential maximal equilibrium yield (PMEY) can be calculated by a new method proposed by this paper. The optimal reaction assemblage (ORA) can be constructed by an optimization method. Where hydrogen is the desired product, the ORA is composed of reactions (1) and (2) in the nine-reaction system. The observed peak yield (OPY) of hydrogen equals 2.410 (mole fraction), its PMEY and GEY equal 3.341 (mole fraction). If carbon monoxide is the desired product, the ORA includes only reaction (1) in the nine-reaction system and the OPY, GEY and PMEY of carbon monoxide equal 0.344, 0.2767 and 0.9789 (mole fraction) respectively. Construction of the ORA is the key and fundamental way to improve the yield of a desired product. In this paper, the method of constructing the ORA is developed. 

The author has recently proposed the new concepts of global equilibrium yield (GEY) and potential maximum equilibrium yield (PMEY) of a complex reaction system (D. The GEY is the equilibrium yield of desired products calculated by conventional methods. The PMEY is the thermodynamic constraint. The OPY is the observed peak yield of desired products. The GEY could be exceeded by the OPY with thermodynamic constraints giving the PMEY. These concepts give information on potential and possible optimal yields and thereby shew hew to improve production. 

The second step gives no UV change and is considered to involve the replacement of the asymmetrically coordinated tbn by free tbn towards thermodynamically equilibrated state. The optical yield at equilibrium is calculated by Equation (5)... 

Figure 4.10 shows the mole fraction of 14 species in gas phase equilibrium calculated from thermodynamic data [180]. The figure shows that the equilibrium yield of ethyne is low below 1373 K, but the yield increases strongly with increasing temperature. The figure also shows that the ethene yield also is low at all temperatures, less than 5% over the entire temperature range [179],... 

Figures 3 and 4 are the predicted profiles of vapor and liquid composition along the column with 43 ml of catalyst and a reflux flow rate of 22 g/tnin. It is important to note that both the liquid and vapor concentration profiles for acetone in the column are relatively high and hence it is favorable for the formation of DAA. The equilibrium constants calculated from the equilibrium conversion data [9,10] are given in Figure 5, which indicates that at 54 °C, the Ac conversion at equilibrium conversion is only 4.3 wt %. In order to carry out the aldol condensation of acetone in the CD column, the temperature at the reaction zone of the CD column will be near the boiling point of Ac in order to maintain liquid vapor equilibrium. Our CD experimental results show that a maximum concentration of 55 wt% of DAA concentration was obtained which clearly exceeds the equilibrium conversion. The aldol condensation of Ac to produce DAA is an excellent example to demonstrate that in situ separation in a CD column results in an increased yield for equilibrium limited reactions.

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