ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 6, pp. 941!944. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + I.L. Glazko, Yu.A. Druzhinina, S.V. Levanova, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 6, pp. 963!966.
AND INDUSTRIAL ORGANIC CHEMISTRY
Performance and Selectivity of Organic Solvents
in Extraction of Caprolactam from Lactam Oil
I. L. Glazko, Yu. A. Druzhinina, and S. V. Levanova
Samara State Technical University, Samara, Russia
Received December 14, 2006; in final form, February, 2007
Abstract-The extraction of lactam from lactam oil with benzene, toluene, cyclohexane, and cyclohexane-
benzene and cyclohexane-cyclohexanol mixtures, followed by its backwashing with water, was studied.
The distribution ratios of caprolactam and main characteristics of the resulting aqueous lactam (permanganate
number, content of volatile bases) were determined.
Caprolactam is one of the most marketable chem-
icals. Approximately 98% of the world production of
caprolactam is consumed for manufacture of a poly-
amide (Nylon-6) .
The characteristics of the polyamide are sensitive
to the purity of the initial caprolactam. The presence
of even minor impurities negatively affects the poly-
merization. Therefore, the quality of caprolactam
must meet stringent requirements [23 4].
The purification of caprolactam to remove impuri-
ties involves extraction, ion-exchange treatment, and
distillation. In extractive purification step, caprolac-
tam is recovered with an organic solvent from lactam
oil prepared by Beckmann rearrangement of cyclohex-
anone oxime . In the second step, caprolactam is
backwashed with water and the resulting aqueous so-
lution is subjected to ion-exchange treatment. The ef-
ficiency of extraction is dependent on the kind of or-
ganic solvent used as extractant and its physicochem-
ical characteristics: solubility in the aqueous phase
and selectivity with respect to caprolactam.
It is known that organic compounds can be recov-
ered from aqueous solutions with organic solvents
of various types: alcohols, ethers, esters, ketones,
phosphorus-, nitrogen-, and sulfur-containing organic
oxides, nitro- and halo-substituted aromatic hydro-
Data on extraction of caprolactam from aqueous
media, available from published papers and patents,
are insufficiently comprehensive. As a rule, these
studies are restricted to determination of the distribu-
tion ratios and do not analyze the selectivity of sol-
vents to caprolactam [7, 8].
In the modern chemical industry, caprolactam is ex-
tracted from lactam oil with trichloroethylene (TCE).
This extractant is characterized by high distribution
ratio of caprolactam, good phase separation, and fire
safety. However, TCE has the following significant
drawbacks: in the course of regeneration, TCE partially
decomposes to give corrosion-active hydrogen chlor-
ide; in oxidation and also in prolonged storage with-
out protection from light, TCE is converted to phos-
gene; and, in combustion of trichloroethylene-contain-
ing waste at 700 oC, environmentally hazardous di-
oxins are formed.
In this study, we tested a series of environmentally
acceptable chlorine-free organic solvents to choose
extractants that would be suitable for effective recov-
ery of caprolactam from aqueous-organic mixtures and
have technical and economic characteristics compa-
rable to, or even exceeding those of TCE. This ex-
tractant must meet the following requirements: high
distribution ratio of caprolactam, high selectivity for
caprolactam (evaluated by the permanganate number
PN), low solubility in water, commercial availability,
and hazard class not worse than 33 4. Furthermore, to
simplify the regeneration, this extractant must be in-
volved into existing industrial cycle of caprolactam
In this study, we examined the extraction of capro-
lactam from lactam oil with benzene, toluene, cyclo-