Choice between

Having considered reactor temperature and pressure, we are now in a position to judge whether the reactor phase will be gas, liquid, or multiphase. Given a free choice between gas- and liquid-phase reactions, operation in the liquid phase is usually preferred. Consider the single reaction system from Eq. (2.19) ... 

Another important class of dryer is the fluidized-bed dryers. Some designs combine spray and fluidized-bed dryers. Choice between dryers is usually based on practicalities such as the materials handling characteristics, product decomposition, product physical form (e.g., if a porous granular material is required), etc. Also, dryer efficiency can be used to compare the performance of different dryer designs. This is usually defined as follows -. 

The penalty as a result of the constraint having been identified enables judgment as to whether it is acceptable or too expensive. If it is too expensive, there is a choice between two options ... 

Also, if there are two separators, the order of separation can change. The tradeoffs for these two alternative flowsheets will be different. The choice between different separation sequences can be made using the methods described in Chap. 5. However, we should be on guard to the fact that as the reactor conversion changes, the most appropriate sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

The choice between X-ray fluorescence and the two other methods will be guided by the concentration levels and by the duration of the analytical procedure X-ray fluorescence is usually less sensitive than atomic absorption, but, at least for petroleum products, it requires less preparation after obtaining the calibration curve. Table 2.4 shows the detectable limits and accuracies of the three methods given above for the most commonly analyzed metals in petroleum products. For atomic absorption and plasma, the figures are given for analysis in an organic medium without mineralization. 

In the calculation of vapor phase partial fugacities the use of an equation of state is always justified. In regard to the liquid phase fugacities, there is a choice between two paths ... 

The use of these techniques is an important element of industrial policy since they contribute to the creation of a business friendly regulatory environment allowing the combination of measures taken for internal organisational reasons and obligations of certification without lowering the level of safety to be achieved. Wlienever possible a choice between product control and quality assurance procedures is offered to manufacturers. 

The directive will initially come into force on 29 November 1999. From that date until 28 May 2002 manufacturers have a choice between applying the pressure equipment directive or continuing with the application of the existing national legislation. From 29 May 2002 the pressure equipment directive will be obligatory throughout the European Union. 

Sometimes a choice between two disconnections of this sort can be made by our first criterion (a good mechanism). How would you make TM 47 ... 

Sometimes we must make a choice between two mechanistically reasonable disconnections. How about TM 114 ... 

The measurements are predicted computationally with orbital-based techniques that can compute transition dipole moments (and thus intensities) for transitions between electronic states. VCD is particularly difficult to predict due to the fact that the Born-Oppenheimer approximation is not valid for this property. Thus, there is a choice between using the wave functions computed with the Born-Oppenheimer approximation giving limited accuracy, or very computationally intensive exact computations. Further technical difficulties are encountered due to the gauge dependence of many techniques (dependence on the coordinate system origin). 

Another important consideration is the amount of labor necessary on the part of the user. One major difference between different software packages is the developer s choices between ease of use and efficiency of operation. For example, the Spartan program is extremely easy to use, but the price for this is that the algorithms are not always the most efficient available. Many chemistry users begin with software that is very simple, but when more sophisticated problems need to be solved, it is often easier to learn to use more complicated software than to purchase a supercomputer to solve a problem that could be done by a workstation with different software. 

For large molecules, the choice between semiempirical calculations and empirical calculations should be based on a test case. 

Ah initio calculations with core potentials are usually the method of choice. The researcher must make a difficult choice between minimizing the CPU time requirements and obtaining more accurate results when deciding which core potential to use. Correlation is particularly difficult to include because of the large number of electrons even in just the valence region of these elements. 

Later experiments do not allow a clear choice between these alternatives. The high proportion of o-isomer formed when nitration is effected with acetyl nitrate in acetic anhydride is confirmed by the results of expts. 10-14 (table 5.5). The use of fuming, rather than pure nitric acid, in the preparation of the reagent, which may lead to nitration... 

Either route is feasible and indeed styrene has been prepared from both combinations of reactants Typically there will be two Wittig routes to an alkene and any choice between them is made on the basis of availability of the particular starting materials... 

If there is a choice between components of the same size containing the same number and kind of heteroatoms, choose as the base component that one with the lower numbers for the heteroatoms before fusion. When a fusion position is occupied by a heteroatom, the names of the component rings to be fused are selected to contain the heteroatom. 

Plastic dmms are made with either integral or removable heads, depending on the need of the customer. The chemical industry is more likely to use integral or tight-head dmms, whereas the food industry is prone to use open-head dmms to which separate covers can be fastened. The choice between these two styles often is deterrnined by the requirement for cleaning the dmm interior. 

In order to assure control of the reaction, the vapor-phase inhibitor concentration must be closely controlled in the ppm range. Although several compounds have been claimed to be useful, it is likely that commercial processes use only ethylene dichloride or some of the simpler chlorinated aromatics (102). In general, the choice between inhibitors is not based on their differences in performance, but rather on the designers preference for dealing with the type of control problems each inhibitor system imposes (102). 

The method of allocating overheads can seriously affect the assigned costs of a project and hence the apparent cash flows for that project . Since these cash flows are used to assess profitability by the net-present-value (NPV) and discounted-cash-flow-rate-of-return (DCFRR) methods, unfair allocation of overhead costs can result in a wrong choice between alternative projec ts. 

Transportation is often an important part of produc t cost. Bulk transportation may provide significant savings. When there is a choice between two or more forms of transportation, the competition may result in rate reduc tion. Transportation is subject to considerable regulation, which will be discussed in some detail under specific headings. 

Ultimately, the economic choice between counterflow and cross-flow is determined by the effectiveness of the fill, design conditions, and the costs of tower manufacture. 

Leaching Cycle and Contact Method As is true generally, the choice between continuous and intermittent operation is largely a matter of the size and nature of the process of which the extraction is a part. The choice of a percolation or solids-dispersion technique depends principally on the amenability of the extraction to effective, sufficiently rapid percolation. 

Source of Heat Industrial furnaces are either fuel-fired or electric, and the first decision that a prospective furnace user must make is between these two. Although elecdric furnaces are uniquely suited to a few apphcations in the chemical industiy (manufacture of sihcon carbide, calcium carbide, and graphite, for example), their principal use is in the metallurgical and metal-treatment industries. In most cases the choice between elecdric and fuel-fired is economic or custom-dictated, because most tasks that can be done in one can be done equally well in the other. Except for an occasional passing reference, electric furnaces will not be considered further here. The interested reader will find useful reviews of them in Kirk-Othmer Encyclopedia of Chemical Technology (4th ed., vol. 12, articles by Cotchen, Sommer, and Walton, pp. 228-265, Wiley, New York, 1994) and in Marks Standard Handbook for Mechanical Engineers (9th ed., article by Lewis, pp. 7.59-7.68, McGraw-Hill, New York, 1987). 

The choice between different types of dryers is often guided by the chemicals involved and their physical properties, particularly heat sensitivity. As when selecting other equipment, the designer should first ask if the step is necessary if so, whether this is the correct or safest process step. Does the material being processed have to have all of the liquid removed Can the downstream step or customer use the material in a liquid, slurry or paste form ... 

Arresters or diverters are generally of the following types and the choice between them will depend upon the power frequency system voltage, characteristics of the voltage surges and the grounding system, i.e. 

Series and shunt capacitors both provide the same degree of compensation. But it is the correct reactive support that provides a more stable system less prone to load and voltage lluctuations. Thus i Judicious choice between the shunt and the series capacitors is required. In the following our main thrust is to arrive at the most appropriate type and extent of reactive support to achieve a higher level of utilization of a power transmission or distribution system, on the one hand, and more stability, on the other. 

The power frequency voJiage lest refers to indoor units. The outdoor eapaciior units must be subjected to a wet test as in lEC 60060-1.. 3 The choice between list I and list 2 will depend upon the extent of exposure of the units to the internal and external vollage surges and... 

The statistical measures can be calculated using most scientific calculators, but confusion can arise if the calculator offers the choice between dividing the sum of squares by N or by W — 1 . If the object is to simply calculate the variance of a set of data, divide by N . If, on the other hand, a sample set of data is being used to estimate the properties of a supposed population, division of the sum of squares by W — r gives a better estimate of the population variance. The reason is that the sample mean is unlikely to coincide exactly with the (unknown) true population mean and so the sum of squares about the sample mean will be less than the true sum of squares about the population mean. This is compensated for by using the divisor W — 1 . Obviously, this becomes important with smaller samples. 

These examples illustrate the relationship between kinetic results and the determination of reaction mechanism. Kinetic results can exclude from consideration all mechanisms that require a rate law different from the observed one. It is often true, however, that related mechanisms give rise to identical predicted rate expressions. In this case, the mechanisms are kinetically equivalent, and a choice between them is not possible on the basis of kinetic data. A further limitation on the information that kinetic studies provide should also be recognized. Although the data can give the composition of the activated complex for the rate-determining step and preceding steps, it provides no information about the structure of the intermediate. Sometimes the structure can be inferred from related chemical experience, but it is never established by kinetic data alone. 

Gradual velocity reduction method. This method is a variation of the constant friction approach, where a maximum velocity is used for the main and branch ducts. This procedure provides a reasonable solution and choice between the velocity, diameter, and resistance. The method is not useful to provide the same static pressure at each outlet. 

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