ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 9, pp. 1524!1527. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + A.A. Gaile, G.D. Zalishchevskii, A.S. Erzhenkov, L.L. Koldobskaya, 2008, published in Zhurnal Prikladnoi Khimii, 2008,
Vol. 81, No. 9, pp. 1449!1452.
OF SYSTEMS AND PROCESSES
Extractive Rectification of the Benzene Fraction
of Reformer Naphtha
Using N-Methylpyrrolidone!N-Formylmorpholine Mixtures
A. A. Gaile, G. D. Zalishchevskii, A. S. Erzhenkov, and L. L. Koldobskaya
St. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia
Kirishinefteorgsintez Production Association, Limited Liability Company, Kirishi, Leningrad oblast, Russia
Received December 28, 2007
Abstract-Extractive rectification of the benzene fraction of reformer naphtha was studied, and the relative
fugacity coefficients of the heptane3benzene system in the presence of N-methylpyrrolidone3N-formyl-
morpholine mixtures of various compositions were determined. A synergistic effect was revealed for a mixed
selective solvent containing 29330wt % N-formylmorpholine, 683 69% N-methylpyrrolidone, and 233wt%
Previously we suggested to use a mixed selective
solvent N-methylpyrrolidne (N-MP)3sulfolane, ex-
hibiting a synergistic effect, for separation of ben-
zene from the benzene fraction of reformer naphtha
. As highly selective solvent added to N-MP
instead of sulfolane, one can use N-formylmorpho-
line (N-FM) which is widely applied to separation of
arenes by selective rectification (Morpholane proc-
ess) or extraction (Morphylex process) . Advant-
ages of N-FM compared to sulfolane are lower
values of the boiling point, viscosity, and enthalpy of
vaporization and higher solvency toward hydrocar-
bons . However, the solubility of saturated
hydrocarbons in N-FM, especially if it contains
several percents of water to decrease the tempera-
ture in the lower sections of the extractive rectifica-
tion and stripping towers, is limited. For example,
at 80oC the solubility of hexane and heptane in
N-FM is about 5.2 and 3.7 mol %, respectively .
The critical points of solution of methylcyclopentane
and methylcyclohexane in N-FM are 130.14 and
131.61oC, respectively .
Thus, on the upper trays of an extractive rectifi-
cation tower at pressures close to 1 atm the N-FM3
hydrocarbons system can undergo phase separation,
which will lead to a decrease in the fugacity coeffi-
cients of saturated hydrocarbons relative to arenes.
Addition of N-MP to N-formylmorpholine is char-
acterized by the following positive effects: homogeni-
zation of the system due to considerably higher
solvency of N-MP; decrease in the process temper-
ature due to lower boiling point of N-MP, which
favors stabilization of p complexes of arenes with
solvents; decrease in the viscosity of the system,
which leads to an increase in the efficiency of trays
of an extractive rectification tower.
With the aim to determine the required content of
water in a mixed solvent, we found the normal boil-
ing points of a 50 : 50 (wt %) N-FM3N-MP mixture
in relation to the water content of the ternary mix-
ture (Fig. 1).
At this composition of a mixed solvent and steam
pressure of 10 atm in the stripping tower, the water
content of the solvent should be about 3 wt %.
The results of benzene recovery from the benzene
fraction of reformer naphtha by extractive rectifica-
tion with N-FM and its mixtures with N-MP are
given in Table 1.
The procedure of extractive rectification experi-
ments was described previously . In all the experi-
ments we detected no toluene in the distillate, i.e.,
the degree of separation of toluene by extractive dis-
tillation with N-FM and its mixtures with N-MP is
virtually 100%. The degree of separation of benzene
with N-FM containing 3 wt % water is low: Even
at a solvent to feed weight ratio of 3 : 1, the benzene
concentration in the distillate exceeds 5 wt %. N-MP