chemical physics of discharges - Argonne National Laboratory

532
and can be expressed in terms of Equation 8 to give
Therefore
[Bl =I?)
[BH+]lI2
I
!
I
i
(16) ' I
Thus, for a given concentration [BH'] in the aqueous extract, the concentra- ~
tion [B] of base is high for bases of low base strength (Kb).
From Equations 12 and 17, the following generalizations can be
made concerning the selection of an acid and.a base for recovery of nitrogen
i
bases by a regenerative process. To get good extraction, maximize [BH+) by
using an acid with as large a value for Ka as is possible, consistent with
other requirements of the process. To get good regeneration, maximize [B]
(a base with a small Kb value should be involved).
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Accordingly, suitabie systems appear to involve an acid extractant
with a large 1
Ka value and a nitrogen base with a small Kb value. Consistent;
with the above, the ApK was examined as a useful guide in selecting compo.-
1
nents 'for regenerative systems, . ,
where
pK = -log K (19) 1
ApK = (pKb -pKa) , and (20)
ApK is expressed as the absolute value of (PKb - pKa). It is
anticipated that the larger the ApK of a system, the better it w ill function!
in a regenerative recovery process. Therefore it appears that recovery of
nitrogen bases is facilitated by combinations of relatively weak bases and
relatively strong acids or relatively strong bases and weak acids. /
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Systems for Recovery of Ammonia and Pyridine Bases
\
As mentioned above, several processes have previously been
reported for recovery of ammonia and pyridine bases from coke-oven product
streams. The data on ammonia and pyridine are consistent with the discussiol
presented above, Tables I and 11. Experimentally it has been demonstrated I
that, although ammonia can be recovered in a regenerative manner using
'q
monoammonium phosphate, neither phosphoric acid nor sulfuric acid can be
(
used (H2PO4- is suitable for NH3 recovery, whereas H3PO4, HS04-, and H2S04
are not applicable). '.
\
It has also been shown that pyridine can be recovered successfull
with either HjPOl or HSOq-; however, neither H2P04- nor H2S04 can be '6
employed.
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1
k