Stoichiometry batch systems

For continuous processes, checking the steady-state results is very useful. Algebraic equations for this can be added to the program, such that both sides became equal at steady state. For batch systems, all the initial mass must equal all the final mass, not always in mols but in kg. Expressed in mols the stoichiometry must be satisfied. 

Molecules are lost and formed by reaction, and mass conservation requires that amounts of species are related. In a closed (batch) system the change in the numbers of moles of all molecular species Nj are related by reaction stoichiometry. 

Finally, we can comment on the influence of the reactor type on the films that can be deposited. Evidently, the hot-wall reactor tends to deposit very Ta-rich films. Although it may be possible to alter the stoichiometry in this type of reactor, the choices are limited. One must operate under conditions where uniform depositions are achieved both on each wafer and from wafer to wafer, because this is a batch system. In the cold-wall reactor, it was possible to obtain the proper stoichiometry at high deposition rates. Since the higher deposition rates permit development of a single-wafer reactor, there are more choices in the process conditions to be used. 

Paraldehyde decomposition is represented by (CH3CHO)3 ———> 3CH3CHO. The stoichiometry of the reaction is of the form A — ->3B. Assuming that the reaction is first order, then the rate equation for a constant volume batch system is ... 

According to this reaction the stoichiometry of the process can be modeled according to (4.45). To calculate the concentration of every model species in a batch system, the mass balance of the pollutant species (4.46) that of the reagent species (4.47) and the pseudoequilibrium constant (4.48) should also be considered. 

There are two uses for Equation (2.36). The first is to calculate the concentration of components at the end of a batch reaction cycle or at the outlet of a flow reactor. These equations are used for components that do not affect the reaction rate. They are valid for batch and flow systems of arbitrary complexity if the circumflexes in Equation (2.36) are retained. Whether or not there are spatial variations within the reactor makes no difference when d and b are averages over the entire reactor or over the exiting flow stream. All reactors satisfy global stoichiometry. 

One of the last two equations gives the relationship between Cv and CA at any time in a plug flbw or batch reactor. The stoichiometry of the system provides the additional information necessary to describe completely the system composition. 

The reaction system, 2A = B = > C, has been studied in a constant volume, batch reactor with the tabulated results. Assuming the orders conform to the stoichiometry, find the specific rates. 

What the three-step model really points out is that it is theoretically correct to carry out basic combustion calculations for a PBC system based on the mass flow and stoichiometry of the conversion gas from the conversion system and not based on the mass flow of solid fuel entering the conversion system. The two-step model approach applied on a PBC system, which is equivalent to assuming that the conversion efficiency is 100 %, is a functional engineering approach, because the conversion efficiency is in many cases very close to unity. However, there are cases where the two-step model approach results in a physical conflict, for example the mass flows in PBC sysfem of batch type cannot be theoretically analysed with a two-step model. 

The batch conversion of wood fuels with the following conversion concept overfired, updraft, fixed horizontal grate, and batch reactor, has proven to be highly dynamic and stochastic with respect to mass flow and stoichiometry of conversion gas as well as the air factors of the conversion and combustion system. 

The overfired batch conversion process, as well as the combustion process, of wood fuels is shown to be extremely dynamic. The dynamic ranges for the air factor of the conversion system is 10 1 and for the stoichiometric coefficients is CHs.iOiCHoOo during a batch for a constant volume flux of primary air. The dynamics of the stoichiometry indicates the dynamics of the molecular composition of the conversion gas during the course of a run. From the stoichiometry it is possible to conclude that... 

Most combustion processes are chain-branching, but other examples of chain-branching reactions are also found in industrial systems. Chain-branching reaction systems are potentially explosive, and for this reason great care must be taken to avoid safety hazards in dealing with them. The explosion behavior of gaseous fuels as a function of stoichiometry, temperature, and pressure has been an important research area [241]. Experimental data are typically obtained in a batch reactor, a spherical vessel immersed in a liquid bath maintained at a specific temperature. The desire to understand the explosion behavior of various... 

Nonlinear Precipitation of Secondary Minerals from Solution. Most of the studies on dissolution of feldspars, pyroxenes, and amphiboles have employed batch techniques. In these systems the concentration of reaction products increases during an experiment. This can cause formation of secondary aluminosilicate precipitates and affect the stoichiometry of the reaction. A buildup of reaction products alters the ion activity product (IAP) of the solution vis-a-vis the parent material (Holdren and Speyer, 1986). It is not clear how secondary precipitates affect dissolution rates however, they should depress the rate (Aagaard and Helgeson, 1982) and could cause parabolic kinetics. Holdren and Speyer (1986) used a stirred-flow technique to prevent buildup of reaction products. 

Figure 2 presents the effect of the various volumetric ratios of water to rapeseed oil on the yield of fatty acids as prepared with both flow- and batch-type reaction systems at 270°C for 20 min. The volumetric ratios of 1/4 and 4 correspond to the molar ratios of 13 and 217, respectively. For the batch-type system, the hydrolysis rate of triglycerides seemed to be affected more by the amount of water, and a slightly better conversion was seen with the flow-type reaction system. Even though the volumetric ratio of 1/4 is equivalent to the molar ratio of 13 in water, which is theoretically higher than its stoichiometry of 3, the formation of fatty acids in both reaction systems was obviously low. In addition, it was found that at a volumetric ratio less than 2/3, it was difficult to separate hydrolysis products from the water portion that contained glycerol. On the other hand, the presence of water in fatty acids would have a negative effect on the methyl esterification reaction (15). 

Kinetic steps are best identified by measuring the initial products formed from individual species (including postulated intermediates) or from simple mixtures. Isotopically labeled species have proved useful in such experiments. Initial products of homogeneous processes are observable in batch reactors at sufficiently short times or in flow reactors at points sufficiently near the inlet. The most advanced systems for initial product detection are molecular beam reactors (Herschbach 1976 Levine and Bernstein 1987) in which specific collisions are observed. Each of these techniques restricts the number of contributing reactions in a given experiment, so that their stoichiometry and rates can often be inferred. 

After selecting the chromatographic system the operation mode of the batch reactor has to be chosen. High productivities require a high throughput. Therefore, pulsed operation is used (Fig. 8.8). Reactants are supposed to be injected as a rectangle pulse of period tcic le and duration tinj. These parameters are strongly affected by the reaction kinetics, reaction stoichiometry and adsorption isotherm. 

Example 13.1 shows one reason why binary polycondensations are usually performed in batch vessels with batch-weighing systems. Another reason is that some polycondensation reactions involve polyfunctional molecules that will crosslink and plug a continuous flow reactor. An example is phenol, which is trifunctional when condensed with formaldehyde. It can react at two ortho locations and one para location to build an infinite, three-dimensional network. This may occur even when the stoichiometry is less than perfect. See Problem 13.3 for a specific example. In a batch polymerization, any crosslinked polymer is removed after each batch, while it can slowly accumulate and eventually plug a flow reactor. 

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