ISSN 1070-4272, Russian Journal of Applied Chemistry, 2017, Vol. 90, No. 3, pp. 415−422. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © I.A. Konoplev, R.A. Kozlovskii, V.F. Shvets, A.E. Kuznetsov, A.V. Beloded, G.G. Kagramanov, V.A. Safronov, A.I. Yartym,
in Zhurnal Prikladnoi Khimii, 2017, Vol. 90, No. 3, pp. 355−362.
AND POLYMERIC MATERIALS
Preparation of L-Lactide of Polymerization Purity
with Removal of Impurities by Fractional Melting
I. A. Konoplev*, R. A. Kozlovskii, V. F. Shvets, A. E. Kuznetsov,
A. V. Beloded, G. G. Kagramanov, V. A. Safronov, and A. I. Yartym
Dmitry Mendeleev University of Chemical Technology of Russia, ul. Miusskaya 9, Moscow, 125047 Russia
Received October 4, 2016
Abstract—Isolation and puriﬁ cation of L-lactide to reach the polymerization purity level with removal of impuri-
ties by fractional melting was studied. The process implementation was suggested, and the inﬂ uence of various
parameters on the rate and degree of impurity removal was examined. The optimum conditions for removal of
the main impurities from L-lactide were found. The method allows preparation of L-lactide of polymerization
purity in approximately 50% yield.
Owing to the convenience, chemical inertness,
and low cost, by the end of the XX century synthetic
polymers as packaging materials largely replaced glass,
paper, and cardboard. However, whereas glass vessels
are, as a rule, reused and paper packaging materials are
biodegradable, synthetic polymer packaging materials,
whose content in home waste reaches approximately
40%, are virtually “eternal,” as they do not degrade
[1, 2]. Speciﬁ cally such chemical inertness of synthetic
polymer materials and their universal use as packaging
materials became today a global environmental problem.
One of the ways to solve this problem is replacement
of traditional polymer materials by biodegradable ma-
terials that can be produced using renewable nontoxic
carbohydrate raw materials (sugar, glucose, etc.) [2, 3].
Production of polymers from renewable raw
materials is also a topical problem from the viewpoint
of diversiﬁ cation of raw materials, as fossil resources
are exhaustible .
Macromolecular compounds derived from hydroxy
carboxylic acids are of much interest among biopoly-
mers. Polylactic acid (polylactide) seems to be the most
promising. It is prepared by ring-opening polymeriza-
tion of lactide (cyclic dimer of lactic acid) [5–7].
The existing technologies of lactide preparation
use lactic acid are a raw material. However, the
lactide prepared by the existing processes is very
expensive because of large number of process steps,
their complexity, and large amount of production
waste. Furthermore, such production processes involve
power- and resource-consuming technologies of lactide
puriﬁ cation to remove water and microimpurities of
lactic acid, as their content in the lactide is strictly limited
(admissible content of lactic acid and water should not
and 100 ppm, respectively) [6, 8].
The formation of a large amount of waste is
determined by the existing industrial procedures for
preparation and recovery of lactic acid, which can be
described by the transformation schemes (Scheme 1).
The common and major drawback of these two routes
is that they involve treatment of lactic acid salts with
strong mineral acids (as a rule, sulfuric acid). Therefore,
virtually equimolar (relative to the produced lactic acid)
amounts of production waste, calcium sulfate (gypsum)
or ammonium sulfate (more than 1 t per ton of lactic
acid) are formed. These by-products are of low purity,
which prevents their efﬁ cient use. Therefore, the cost
of recovery and puriﬁ cation of lactic acid and of waste