HETEROPHASE NITRATION OF o-NITROTOLUENE
rate and isomeric composition of DNT depend on CONCLUSIONS
1877
the agitation intensity (Table 4; run nos. 1 4, 5 8,
etc.). The increase in the 2,4-/2,6-DNT ratio from 1.80
to 2.03 on raising the stirrer rotation rate from 700 to
(1) The heterophase nitration of o-nitrotoluene can
be performed with weak sulfuric nitric acid mixtures
of various compositions and a nitrating activity factor
equal to 70.
5
000 rpm (Table 3) confirms the increasing contribu-
tion of the nitration in the boundary region and is well
consistent with the previously obtained data [1].
(2) Raising the gas content of the reaction mixture
The noticeable increase in the contribution of o-NT
in the boundary layer in the entire range of composi-
tions of acid mixtures studied at an agitation intensity
of 5000 rpm can be further confirmed by the effect of
temperature on the yield and relative contents of
isomers in the forming DNT. It would be expected
that, as the reaction temperature is raised, the solubil-
ity of o-NT in the mineral phase should increase and
the interaction between drops should be enhanced,
with their size increasing and the rate of mass-
exchange within drops becoming slower [8]. Con-
sequently, the contribution of the boundary reaction in
the adsorption layer to the overall kinetic component
of the process will decrease.
by high-intensity agitation (>2000 rpm) results in that
the contribution of the reaction in boundary adsorp-
tion monolayer to the overall process rate increases,
the yield of 2,4-dinitrotoluene grows, and the 2,4-/2,6-
DNT isomer ratio becomes larger.
(3) The rise in the contribution of nitration in the
bulk of the acid phase as a result of a decrease in the
reaction temperature and an increase in the molar con-
centration of nitric acid in the acid mixture is ac-
companied by an increase in the yield of 2,6-dinitro-
toluene.
(4) The deceleration of the mass exchange between
phases, observed as the gas content of the reaction
mass increases, occurs because, at high agitation in-
tensity, the interaction between drops of the dispersed
organic phase is largely suppressed and the drops
behave as solid spheres within which mass exchange
is hindered.
In the range of acid mixtures studied, the content of
2,4-DNT falls as the nitration temperature is raised.
For example, the 2,4-/2,6-DNT isomer ratio in nitra-
tion with an acid mixture containing 15.5 mol %
HNO3 falls from 2.21 to 1.80 as temperature is
elevated from 25 to 75 C (Table 5, run nos. 13 15).
This dependence is observed at 5000 rpm, i.e., under
high gas content conditions (Table 5).
REFERENCES
1
. Modak, S.Y. and Juvekar, V.A., Ind. Eng. Chem. Res.,
At the same time, a slight increase in the total yield
in 60 min of the reaction was observed at nitric acid
contents in the range 22.3 31.1 mol % as temperature
was elevated (e.g., from 61.2 to 67.5% on raising the
temperature by 25 C) (Table 5, run nos. 4 and 6). An
insignificant increase in the reaction rate is observed
when the rate-determining stage of nitration is diffu-
sion of components into the reaction zone at a high
rate of the chemical reaction itself. This behavior can
be understood if the temperature coefficients of the
rates of the chemical reaction and diffusion are com-
pared. For example, raising the temperature by 10 C
leads to a 3 4-fold increase in the rate constant of the
chemical reaction of nitration, whereas the diffusion
rate of aromatic compounds increases by only a factor
of 1.1 1.5 [7]. In nitration with a weaker acid mixture
1995, vol. 34, pp. 4297 4309.
2. Milligan, B., Ind. Eng. Chem. Fundam., 1986, vol. 25,
pp. 783 789.
3
4
5
6
. Kasarekar, R.B., Ramakrishna, M., and Juvekar, V.A.,
Chem. Eng. Technol., 1997, vol. 20, pp. 282 284.
. Edwards, H.G.M. and Fawcett, V., J. Mol. Struct.,
1994, vol. 326, pp. 131 143.
. Kobe, K.A. and Fortman, J.T., Ind. Eng. Chem., 1961,
vol. 53, pp. 269 274.
. Braginskii, L.N., Begachev, V.I., and Barabash, V.M.,
Peremeshivanie v zhidkikh sredakh (Agitation in Liquid
Media), Leningrad: Khimiya, 1984, pp. 212 213.
. Orlova, E.Yu., Khimiya i tekhnologiya vzryvchatykh
veshchestv (Chemistry and Technology of Explosives),
Leningrad: Khimiya, 1973.
. Giles, J., Hanson, C., and Ismail, A.M., Industrial and
Laboratory Nitrations, ACS Symp. Ser. 22, Washington,
DC: Am. Chem. Soc., 1976, pp. 190 209.
. Schieferle, D.F., Hanson, C., and Albright, L.F., In-
dustrial and Laboratory Nitrations, ACS Symp. Ser. 22,
Washington, DC: Am. Chem. Soc., 1976, pp. 176 182.
7
8
9
containing 15.5 mol % HNO , the increase in the
3
product yield with temperature is more pronounced
(Table 5, run nos. 13 15), which indicates that the
contribution of the chemical reaction stage to the
overall process rate increases.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 11 2007