The scale of operation

The dimensions of the apparatus to be used for the distillation must obviously be suited to the amount of the charge. It would, of course, be possible in an emergency to distil large quantities in a small apparatus with a great expenditure of time, but on the other hand too large an apparatus would lead to excessive losses and erroneous results. 

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Another way to narrow the choice of methods is to consider the scale on which the analysis must be conducted. Three limitations of particular importance are the amount of sample available for the analysis, the concentration of analyte in the sample, and the absolute amount of analyte needed to obtain a measurable signal. The first and second limitations define the scale of operations shown in Figure 3.6 the last limitation positions a method within the scale of operations. ... 

Scale of Operation The scale of operation for precipitation gravimetry is governed by the sensitivity of the balance and the availability of sample. To achieve an accuracy of 0.1% using an analytical balance with a sensitivity of 0.1 mg, the precipitate must weigh at least 100 mg. As a consequence, precipitation gravimetry is usually limited to major or minor analytes, and macro or meso samples (see Figure 3.6 in Chapter 3). The analysis of trace level analytes or micro samples usually requires a microanalytical balance. 

The scale of operations, accuracy, precision, sensitivity, time, and cost of methods involving redox titrations are similar to those described earlier in the chapter for acid-base and complexometric titrimetric methods. As with acid-base titrations, redox titrations can be extended to the analysis of mixtures if there is a significant difference in the ease with which the analytes can be oxidized or reduced. Figure 9.40 shows an example of the titration curve for a mixture of Fe + and Sn +, using Ce + as the titrant. The titration of a mixture of analytes whose standard-state potentials or formal potentials differ by at least 200 mV will result in a separate equivalence point for each analyte. 

Where in the scale of operations do the microtitration techniques discussed in Section 9B.8 belong ... 

Scale of Operation Molecular UV/Vis absorption is routinely used for the analysis of trace analytes in macro and meso samples. Major and minor analytes can be determined by diluting samples before analysis, and concentrating a sample may allow for the analysis of ultratrace analytes. The scale of operations for infrared absorption is generally poorer than that for UV/Vis absorption. 

Scale of Operation The scale of operations for atomic emission is ideal for the direct analysis of trace and ultratrace analytes in macro and meso samples. With appropriate dilutions, atomic emission also can be applied to major and minor analytes. 

The second factor influencing detection limits is the instrumental method used to monitor the reaction s progress. Most reactions are monitored spectrophotometrically or electro-chemically. The scale of operation for these methods was discussed in Chapters 10 and 11 and, therefore, is not discussed here. 

The majority of FI A applications are modifications of conventional titrimetric, spectrophotometric, and electrochemical methods of analysis. For this reason it is appropriate to evaluate FIA in relation to these conventional methods. The scale of operations for FIA allows for the routine analysis of minor and trace analytes and for macro-, meso-, and microsamples. The ability to work with microliter injection volumes is useful when the sample is scarce. Conventional methods of analysis, however, may allow the determination of smaller concentrations of analyte. 

Control technology requirements vary according to the scale of operation and type of emission problem. For instance, electrostatic precipitator design requirements for fly-ash control from 1000-MW coal-fired power boilers differ from those for a chemical process operation. In the discussion that follows, priority is given to control technology for the CPI as opposed to the somewhat special needs of other industries. 

The recycle requirements of products in different apphcations can vaiy substantially depending upon the scale of operation, the ease of diying, and the finished-product specification. The location of reintroduction of undried material back into the diying medium has a significant impact upon the dryer performance and final-product characteristics. 

The reaction is frequently carried out in the presence of scrap iron (with low P and S content) to produce ferrosilicon alloys these are used in the metallurgical industry to deoxidize steel, to manufacture high-Si corrosion-resistant Fe, and Si/steel laminations for electric motors. The scale of operations can be gauged from the 1980 world production figures which were in excess of 5 megatonnes. Consumption of high purity (semiconductor grade) Si leapt from less than 10 tonnes in 1955 to 2800 tonnes in 1980. 

The following general observations apply to both kinds of problems. The scale of operations is fixed by the necessity of comparing adjacent sections of tissue only microns in width, which makes it advisable to use the photographic plate as detector, in order that the necessary measurements of x-ray intensity can be made on greatly enlarged areas. Inas-... 

The product synthesis steps also dictate the type and number of downstream equipment necessary. Depending on the scale of operation this workup may... 

During the preparation of mono- or di-bromogermane, either the scale of operation or the rate of addition of bromine must be closely controlled to prevent explosive reaction occurring. 

The distinction between preparative and production chromatography is sometimes drawn in terms of the scale of operation though it is really a matter of purpose. The... 

The process has been used in the USA for 25 years, but a large extrapolation of experience was necessary to reach the scale of operation needed for the Canadian nuclear industry. A typical Canadian enriching unit has a nominal capacity of 50 kg D20/h. However, with an overall extraction of about 20% of the deuterium in the feedwater, the total feed rate is about 0.5 metric tons per second. Three large towers are used in parallel. (Table II)... 

Process economics of the GMODS are dependent on the scale of operation (D14276H, p. 5). Based on theoretical considerations (the limited number of process steps), GMODS has the potential to be a relatively low-cost process for treatment of radioactive wastes (D14276H, p. 37). In some cases, specialized equipment may be used to minimize waste volume prior to treatment, in an effort to minimize costs (D14276H, p. A-3). 

As described in the sidebar on pages 50-52, the principles of quantum mechanics are involved in the STM s operation. Considering the scale of operation, this is unavoidable. Although quantum mechanics consists of some imfamiliar concepts, the equations provide an accurate and reliable way of understanding behavior on the atomic level. 

Variable costs become relatively more important, constituting an increasingly large proportion of the total costs, as the scale of operation increases and especially as the manufacturing process is simplified, thereby decreasing the requirement for expensive... 

Furthermore, unit operations may function in a rate-limiting manner as the scale of operation increases. When Astarita (4) decried the fact, in the mid-1980s, that there is no scale-up algorithm which permits us to rigorously predict the behavior of a large scale process based upon the behavior of a small scale process, it was presumably as a consequence of all of these problematic aspects of scale-up. 

A simple example is the heating of a liquid. If the amount of the fluid is rather small (e.g., 1 kl day ), then batch heating is more economical and practical, with the use of a tank that can hold the entire liquid volume and is equipped with a built-in heater. However, when the amount of the liquid is fairly large (e.g., 1000 kl day ), then continuous heating is more practical, using a heater in which the liquid Hows at a constant rate and is heated to a required constant temperature. Most unit operations can be carried out either batchwise or continuously, depending on the scale of operation. 

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