A Conversion of Units

That is, we use a factor to change the units (mol to g) for one substance (A) or we use a factor to express the ratio of substances (B to A) in terms of the same unit (mol). If we follow the diagrams in the figures in this chapter, do we ever use one factor to make both a conversion for substance and a conversion of units simultaneously ... 

It is often desirable to ronnd a number obtained from a conversion of units in order to retain information on the precision of the value. The following rounding rules may be followed ... 

Strategy Using Equation 14.9, calculate the half-life of a first-order reaction. The rate constant is given in units of s so a conversion of units is needed to express the half-life in minutes. 

Whatever the relationship used, the particular units for each symbol or entity must be consistent with the units for all other entities, which may or may not involve a conversion of units. Therefore, the units of, say, permeability are defined within the context of the rate or flux relationship used and the units of the driving force for example, partial pressure or pressure times mole fraction. 

Solubility data can be found ia a variety of units, and conversion from one set of units to another often is requited before computation of yield can be performed. Guides to such conversions are available. It is often most convenient, however, to express solubiUty and compositions ia mixed streams ia terms of mass ratios, ie, mass of solute per mass of solvent. 

Table 1-7 provides a number of useful conversion factors. To make a conversion of an element in U.S. customary units to SI units, one multiplies the value of the U.S. customary unit, found on the left side in the table, by the equivalent value on the right side. For example, to convert 10 British thermal units to joules, one multiplies 10 by 1054.4 to obtain 10544 joules. 

Since data have been collated from a variety of sources, and tend to be presented in mixed units, and because rapid conversion of units is an advantage in many on-site situations, conversion tables are included in Chapter 18. Finally, since safety with chemicals cannot be addressed exhaustively in a handbook, selected sources of reliable current information on chemical hazards and their control are listed in Chapter 19. 

Sulfur Distribution of the FCC Products as a Fuction of Unit Conversion... 

Figure 2-9. Sulfur distribution of the FCC products as a function of unit conversion.

The quotient 1 L/1000 cm3, which is called a conversion factor, is multiplied by 536 cm3. Because the conversion factor equals 1, this does not change the actual volume. However, it does accomplish the desired conversion of units. The cm3 in the numerator and denominator cancel to give the desired unit liters. 

In a chemical production process at least one of the unit operations (the chemical reactor) is the place in which chemical conversion takes place. However, the chemical upstream reactor is proceeded by a series of unit operations in which the new materials are downstream prepared (the upstream operations). After conversion has taken place, the products are operations subjected to a further series of unit operations (the downstream operations). These downstream operations include product recovery and purification steps. A typical example of a production process is illustrated in Figure 1.1. 

In this example only the main reaction and the two decomposition reactions are considered. For reasons of product quality, a conversion of 99% must be obtained. Also the production rate per unit volume, or space time yield, should be high. This can be expressed as... 

You supplied the result on data line A. You need only nake the proper conversion of units ... 

It is instructive to compare the data emanating from different force measurement techniques. This requires a conversion of the disjoining pressure in energy per unit area. By integration over the thickness of the disjoining pressure, one obtains the corresponding energy per unit area, E h), between two infinite planes ... 

Figure 1. Selectivity for coke and gasoline octane as a function of unit cell. Gasoline octane curve obtained in a fixed fluid bed reactor at 657e conversion, 4 C/0, 30 WHSV, 510°C.

The preferred units for permeability coefficient are mV N"1 (m3ms lPa lm 2) but the terms permeability coefficient or permeability constant are often applied to various transmission rates using a variety of units and care must be taken to avoid confusion. Useful conversion factors are given by Yasuda and Stannett4. When the permeability coefficient is dependent on test piece thickness, it is convenient to use a transmission rate -the amount of permeant transmitted per unit time and area for a given test piece thickness - which may be in units of mV N 1 (m3s lPa lm 2). Transmission rate is almost always used in the case of vapours and often in the units g24h m 2. 

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