Page 66 - Introduction to chemical reaction engineering and kinetics

48 Chapter 3: Experimental Methods in Kinetics: Measurement of Rate of Reaction

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Capillary y
tube ---I

Reactor

Figure 3.2 A BR in the form of a dilatometer

a dilatometer, and is illustrated in Figure 3.2. The change in volume is related to
the change in the liquid level in the capillary, which can be followed by a traveling
microscope.
(3) Change of optical rotation in a reacting system involving optically active isomers
(e.g., the inversion of sucrose); the instrument used is a polarimeter to measure
the angle of rotation of polarized light passing through the system.
(4) Change of electrical conductance in a reacting system involving ionic species
(e.g., the hydrolysis of ethyl acetate); the reaction is carried out in a conductivity
cell in an electrical circuit for measuring resistance.
(5) Change of refractive index involving use of a refractometer (for a liquid system)
or an interferometer (for a gas system).
(6) Change of color-use of a cell in a spectrophotometer.
(7) Single-ion electrodes for measurement of concentration of individual species.
(8) Continuous mass measurement for solid reactant, or absorbent for capture of
product(s).

3.3.4 Other Measured Quantities

In addition to chemical composition (concentration of a species) and properties in lieu
of composition, other quantities requiring measurement in kinetics studies, some of
which have been included above, are:
(1) Temperature, T; not only the measurement, but also the control of T is impor-
tant, because of the relatively strong dependence of rate on T;
(2) Pressure, P;
(3) Geometric quantities: length, L, as in the use of a dilatometer described above;
area, A, as in characterizing the extent of surface in a solid catalyst (Chapter 8);
and volume, V , as in describing the size of a vessel;
(4) Time, t; and
(5) Rate of flow of a fluid, q (in a CSTR or PFR).

3.4 EXPERIMENTAL STRATEGIES FOR DETERMINING
RATE PARAMETERS
In this section, we combine discussion of choice of reactor type and of experimental
methods so as to develop the basis for the methodology of experimentation. We focus