RECOVERY OF GLYCOLS FROM USED GLYCOL-CONTAINING TECHNICAL FLUIDS

RECUPERATION DE GLYCOLS CONTENUS DANS DES FLUIDES TECHNIQUES USES

English Abstract

A novel process for recovering glycols from used
glycol-containing technical fluids is disclosed. Used
glycol-containing technical fluids has added to it an
organic solvent which forms with the glycols to be
separated off, an azeotropic mixture which has a lower
boiling point than the glycol itself. This azeotropic
mixture is then distilled off. A typical used glycol-
containing technical fluid as used is antifreeze. The
preferred organic solvent is a xylene or a pseudocumene.
Prior to the addition of solvent which forms the azeotropic
mixture with the glycol, a water portion in the used
glycol-containing technical fluid, if present, can also be
advantageously first removed by distillation.

Claims

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I CLAIM:
1. A process for recovering glycols from used
antifreeze or from used glycol-containing technical fluids
obtained in the manufacture of polyester fibers, which
comprises adding to the said used antifreeze or used
glycol-containing technical fluids alkali metal hydroxides
and an organic solvent which forms, with the glycols to be
separated off, an azeotropic mixture which has a lower
boiling point than the glycol itself and distilling off
this azeotropic mixture.
2. A process as claimed in claim 1 wherein the
organic solvent used is a xylene or a pseudocumene.
3. A process as claimed in claim 1 for recovering
glycols whose main component or the sole component is
ethylene glycol.
4. A process as claimed in claim 1 for recovering
higher glycols.
5. A process as claimed in claim 1 wherein, before
the addition of the solvent which will form an azeotropic
mixture with the glycol, water in the said used antifreeze
or used glycol-containing technical fluids is removed by
distillation.

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6. The use of recovered glycols obtained by the
process as claimed in claims 1 to 5 in the production of
glycol-containing antifreeze or in the production of
glycol-containing technical fluids useful in the
manufacturing of polyester fibres.

Description

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RECOVERY OF GLYCOLS FROM USED GLYCOL-CONTAINING TECHNICAL
FLUIDS
The present invention relates to an improved process
for recovering glycols from used glycol-containing
technical fluids, especially from used antifreeze.
Large amounts of antifreeze are used. After use, it
may contain, in addition to water, up to 50% by weight of
glycols, especially ethylene glycol and propylene glycol,
and specific additives, but also, according to origin and
field of use, specific contaminants. Other glycol-
containing technical fluids may contain, in addition to
water, up to 90% by weight of glycols. For this reason
used antifreeze must not simply be allowed to pass into the
environment, but has to be specially disposed of or else
recycled.
Further, large amounts of liquids containing glycol,
especially ethylene glycol, are obtained in the manufacture
of polyesters, especially polyester fibers; these liquids
also contain, in addition to water, other impurities
stemming from the process.
In the case of recycling, the chief concern is to
recover the glycol components, especially ethylene glycol.
Recovering the additive components as well as specific
contaminants does not make technical sense because of their

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multitude and variety. But it is specifically these
ingredients which, because of their physical and chemical
properties, can appreciably hinder or impair the recovery
of the glycols from the used antifreeze.
A number of methods have been developed for removing
the glycols from the used antifreeze by simple distillation
at atmospheric pressure or reduced pressure, as described
for example in DE-A-40 30 331.
In principle, distillation is the processing method of
choice. However, it is always associated with the
imposition on the material being processed of a certain
thermal stress, which causes the actual problems.
The above mentioned additives are usually organic and
inorganic solids which, on distillation, will gradually
accumulate in the bottom product and settle out. This
gives rise to clumping, encrustation and caking in the
heated parts of the distillation plant. This is the case
even when, instead of a simple batch distillation, a thin-
film or falling-film evaporator is used.
In consequence, the high thermal stress gives rise to
decomposition reactions whose products reappear in the
glycol distillate and have an adverse effect on its
properties even in trace amount.

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For instance, the inorganic nitrites frequently
present an antifreeze as corrosion inhibitors can combine
with organic nitrogen compounds to form nitrosamines. For
this reason the distillation of the used antifreeze should
be preceded by a reduction of the nitrites. Since the
known methods for reducing nitrites almost all operate in
an acid medium, but antifreeze is at best neutral or
usually even alkaline, complete reduction requires the
addition of an acid. The attendant salt formation
additionally worsens the above-described situation of the
distillation.
The intrinsically actually very effective way of
getting rid of the nitrosamines by boiling in a strongly
alkaline medium is not advisable because of the known
safety risks of concentrating glycol bottoms.
The other additives and the contaminants from the use
of the antifreeze, too, interfere with the used antifreeze
processing and glycol recovery. Used antifreeze, for
example from the automotive sector, contains, as a
consequence of its use, contaminants such as solids through
abrasion of metals and sealing materials, and also mineral
oil and lubricant constituents. Lack of care in collecting
the used antifreeze, however, may also mean that, for
example, paint residues, cleaners and used oils are present
as contaminants.

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Altogether, these components have a color- but
especially also an odor-conferring effect on the recovered
glycols - and the higher the processing temperature, the
greater the effect.
Virtually all recycled glycols have a more or less
pronounced, very typical and usually very unpleasant odor.
It is an object of the present invention to provide a
recycling process which is free of the above-described
problems and which yields pure, colorless and odorless
glycol recyclate in as simple a manner as possible.
We have found that this object is achieved by a
process for recovering glycols from used glycol-containing
technical fluids, especially from used antifreeze, which
comprises adding to the used glycol-containing technical
fluids an organic solvent which forms with the glycols to
be separated off an azeotropic mixture which has a lower
boiling point than the glycol itself and distilling off
this azeotropic mixture.
Of particular suitability are those azeotropes which,
on the one hand, have an atmospheric pressure boiling point
which is not too high, i.e. still distinctly below the
boiling point of glycols themselves, and, on the other,
contain high glycol contents and which have miscibility
gaps, in particular at low temperatures.

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Organic solvents which form binary azeotropic mixtures
with glycols, especially with ethylene glycol, include in
particular toluene, o-chlorotoluene, o-bromotoluene,
styrene, o-toluidine, n-octanol, 1,2-dibromo- ethane, 1, 2_
dibromobutane, amyl acetate and dichloromethane.
In principle, the azeotropic mixtures can also be
distilled off at subatmosphere pressure to lower the
boiling points, thus working under milder conditions and
using less energy.
An extremely suitable organic solvent is pseudocumene
(1,2,4-trimethylbenzene), which has a particularly high
proportion of ethylene glycol in the azeotrope.
However, the best results are obtained with xylenes;
it is customary to use the technical grade mixture of
o-, m- and p-xylene. For instance, xylenes and ethylene
glycol form azeotropic mixtures having glycol contents from
15 to 20% by weight and boiling at from 130 to 140C. At
room temperature, the mixtures separate into two phases.
Glycol can therefore be continuously separated off. The
xylenes are recirculated for continuous entrainment, so
that comparatively little entraining agent is needed for
the gentle processing of large quantities of glycol.
It is also possible to use mixtures of the organic
solvents mentioned, for example to form ternary azeotropic

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mixtures.
The glycols to be recovered from the used antifreeze
include ethylene glycol as main component or even as almost
the sole component; in addition propylene glycol,
diethylene glycol, triethylene glycol, dipropylene glycol,
1,3-butylene glycol and hexylene glycol (2-methyl-2,4-
pentandiol) as examples of higher glycols may be found.
The used technical fluids mentioned normally include
10% by weight or more of water, especially 50% by weight or
more of water with antifreeze, the bulk of which should
preferably be removed by distillation prior to glycol
recovery. The distillative removal of water is carried out
either by concentrating under reduced pressure and hence at
temperatures where the thermal stress is only small; or
else by likewise separating off the water by azeotropic
entrainment, advantageously with the same solvent or the
same solvent mixture as also used for entraining the
glycol.
During the azeotropic entrainment of glycols, the
additives and specific contaminants present in the used
technical fluids gradually separate out, but do not clump
or cake; stirring is possible, if necessary. In fact,
these ingredients are obtained as a readily stirrable and
pumpable but also filterable suspension in the particular
entrainer. Nor is there any interference here from

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subsequently added components, for example alkali metal
hydroxides added for avoiding nitrosamine formation in
antifreeze or for hydrolyzing dialkyl terephthalates as an
example.
The glycol phase isolated in this way does already
largely consist of the product of value and additionally
contains at most only traces of the entrainer, which can be
removed by simple means (stripping or distillation). The
entrainer can be freed of the precipitated additives by
filtration or, by addition of water to dissolve the
additives and removal of the aqueous phase, recovered and
re-used.
The process of the present invention yields pure,
colorless and in particular odorless recovered glycols
which are suitable for renewed use in the corresponding
technical process, especially in antifreeze. The present
invention therefore also provides for the use of the
glycols recovered according to the invention in the
corresponding technical process, especially in antifreeze.
The present invention also relates to a process for
recovering glycols from used glycol-containing technical
fluids obtained in the manufacture of polyester fibers.
EXAMPLE
8000 g of a used automotive antifreeze having an ethylene

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glycol content of about 40% by weight were admixed with
from 15 to 20 g of NaOH and substantially freed of the
water content at from 200 to 300 mbar and a maximum
temperature of 150C to give about 3600 g of a concentrated
mixture.
1000 g of this mixture were introduced together with 500 g
of technical grade xylene into a suitable continuous
azeotropic distillation apparatus fitted with a separator
head (condenser, phase separator, return to distillation
flask). The remainder of the concentrate was gradually
added in the course of the distillation.
On completion of the distillation about 3200 g had
been obtained of the separated-off glycol phase with an
ethylene glycol content of 95% by weight. The rest was
made up of propylene glycol and diethylene glycol.
To obtain ethylene glycol of higher purity, a
fractional distillation can be added.