Page 130 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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The titration is carried out consecutively with two indicators, &st with
phenolphthalein, and second with methylorange.
The reactions in titration with the first indicator are as follows:

H 2O (28)

Na 2CO 3 + HCl=NaHCO 3 + NaCl (29)

Na 2CO 3 + HCl=NaHCO 3 + NaCl (30)

To increase the accuracy of the analyses it was offered [69] instead of
phenolphthalein to use a mixed indicator consisting of cresol red and thymol
blue [70]. The advantage of this indicator is that it changes colour in very small
interval of pH, 8.2-8.4, which correspond very well to the pH of the reaction
(30).
In titration with the second indicator the following reaction takes place:

NaHCO 3+HCl=NaCl +COa +H 2O. (31)

3
The concentration C L of the absorbed COj in kmol/m can be calculated
by the equation:

C L= V Ha2N HC/V s. (32)

Where VHCU is the volume of the titrating salt acid between first and second
equivalence point in ml;
3
Nffcr normality of the salt acid in g mol/liter = mol/m ;
V s- difference in ml between the volume of the sample and the volume of the
added NaOH solution.
It is easy to calculate that at concentration of COj in the air, usually
about 0.03%, and at the given experimental gas and liquid superficial velocities,
the equilibrium concentration in the liquid phase is to be neglected. Under this
condition the mass transfer equation of the desorption process can be written as
follows: