Table 1. Experiments on p-NEB oxidation with recycle
loaded, g
obtained, g
recycle no.
(starting run)
fresh p-NEB filtrate p-NEB filtrate p-NAP filtrate p-NMPC filtrate p-NEBHP p-NAP p-NBA
0
1
2
77.1
30.6
33.5
27.0
30.3
34.5
2.1
2.0
2.2
36.8
36.0
6.3
5.9
5.0
3.4
0.02
0.02
8
9
34.3
35.3
35.8
5.5
5.1
3.8
3.4
0.01
0.01
33.7
2.1
(filtrate of the 8th recycle)
summary load and yield
340.9
295.9
18.9
Table 2. Quality of the obtained p-NAP
Below we present the calculation of the structural dimen-
sions of the flooded-bubble columns. It is assumed that in
the AP oxidation the maximum permissible O concentration
2
in the outlet flow should not exceed 3 vol%, and for the
p-NEB oxidation it can be increased to 7 vol%. The
calculation of the AP oxidation column is aimed at the
determination of the bubble-layer height that would provide
washing
temperature, °C
reference
sample
quality indexes
80
90
basic material content, mass %
melting temperature, °C
96.1
79-81
96.1
96.4
79-80 79-80
2
for the safe O concentration in the outlet flow at different
column diameters and linear velocities of the oxidant gas.
The results of the calculation would allow choosing the
column on the cost-performance ratio. The analogous
calculation of the bubble-layer height in the p-NEB oxidation
reactor is at the same time verification for the chosen AP
oxidation column. It would be possible to determine whether
the predetermined height would provide for the specified
of recycling no lowering of the reaction rate is observed even
after eight recycles. The results are listed in Table 1.
Altogether there was loaded 340.9 g of p-NEB, and there
was obtained 295.9 g of p-NAP (80% yield) and 18.2 g of
p-NBA (4.8% yield). Other products are in the filtrate of
the last recycle.
The sediment of the raw p-NAP obtained by filtration
contained 5-8% of the mass of p-NEB, 5% of p-NBA, and
traces of p-MNPC. The purification of p-NAP was carried
out according to the following procedure. The obtained
sediment was washed at room temperature by distilled water
2
maximum permissible O concentration in the outlet flow.
Both calculations are based on the link between the O
rate and the rate of its uptake by the liquid phase.
2
feed
In the AP oxidation the viscosity of the liquid phase is
increasing significantly, so that the operating AP conversion
3+
(
150% mass to sediment) to wash out the catalyst. The
washed sediment was stirred in 5% solution of Na CO at
0-90 °C for 10 min to wash out p-NBA. Under these
is about 0.4. Under these conditions the term [Mn ]K[AP]/
1
2
3
[BA]/(1 + K[AP]/[BA]) in eq 3 is virtually constant and it
8
can be transformed to
conditions p-NAP melted and three-phase system: p-NBA
sodium salt solution-p-NEB-p-NAP melt was formed. After
settling layers were segregated while still hot. The p-NAP
melt was poured out into cold water, filtered after crystal-
lisation, and dried until there was a constant mass. The
obtained product was pure enough to be used directly for
the chloramphenicol synthesis (see Table 2).
d[O2]g
-
) k [O ]
(7)
ef
2 1
dτ
where kef is the rate constant of oxygen uptake in the
-1
2 g
chemical reaction, min , l[O ] is the oxygen concentration
in the gas phase, volume fraction, l[O
2 g
] is the liquid-phase
The Designing of AP and p-NEB Explosion-Proof
Oxidation Reactors. The laboratory experiments on AP and
p-NEB oxidation were carried out in a stirred reactor with a
turbine mixer. Such large-scale equipment is complicated,
costly, and unserviceable. In designing large-scale gas-liquid
reactors the flooded-bubble column is the optimal one. This
kind of equipment provides for the high phase contact
surface, has simple design and is quite inexpensive. The flow
structure in this reactor is best described assuming a
continuous stirred tank reactor model for the liquid phase
and the plug flow reactor model for the gas phase.
oxygen concentration, M.
The oxygen mass balance for the adopted flow model on
the element height would be as follows:
6
d(w [O ] )
g
2 g
-
) k [O ] (1 - æ)
(8)
ef
2 1
RT d H
where w
g
is the nominal gas velocity in the reactor, m/s,
and æ is the aeration factor.
(
3) Kuznetsov, M. M.; Obukhova, T. A.; Basaeva, N. N. et al. IzV. VuzoV. Khim.
Khim. Tkhn. 1980, 23, 1220-1224.
Usually air is the more efficient oxidant than pure oxygen.
Thus, its flow should be high enough to provide for the
(4) Kamneva, A. I.; Koroleva, N. V.; Sinitsina, I. M.; Ryuffer, L. I. Neftekhimiya
982, 22, 798-802.
1
(5) Yoshino, Y.; Hayashi, Y.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J. Org.
sufficient O
2
concentration and the high reaction rate along
Chem. 1997, 62, 6810-6813.
the height of the column. At the same time the requirements
(6) Gryaznov, I. A.; Digurov, N. G.; Kafarov, V. V.; Makarov, M. G.
ProektiroVaniye i Raschet ApparatoV OsnoVnogo Organicheskogo i
Neftekhimicheskogo Sinteza [Design and Calculation of the Equipment for
the Basic Organic and Petrochemical Synthesis]; Khimiya: Moscow, 1995.
of the explosion-proof operation limit the O
in the outlet flow by few vol %.
2
concentration
406
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Vol. 3, No. 6, 1999 / Organic Process Research & Development