Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 71 02~ `
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This invention relates to a process of
recovering organic solvents from liquid waste
products comprising such solvents in which polyme~ic
materials are dispersed or dissolved.
The chemical processing industry accu~ulates
each year large tonnages of liquid waste products
which are basically solutions or dispersions of
polymer in organic solvent. We use the word
"solvent" herein in the context in which it is
co~monly understood in the paint, adhesive and allied
industries; that is, a relatively volatile organic
liquid which has the property of dissolving other
less volatile organic compounds, especially film-
forming polymers and resins.
These liquid waste products are not nonmally
useable in their existing form, but their disposal
by dumping or încineration is ecologically unacceptable
and is rapidly becoming an option denied by
legislation. Destructive disposal methods are wasteful
of chemical resources, the solven~ content in
particular being a potentially valuable asset i~ it
can be recovered economi2ally.
Conventional recovery processes, for exam~le,
the recovery of volatiles by direct distillation, are
only a partial answer to the problem. For example 9
~he e~ficiency of release of volatiles from the non-
volatile components may fall well short of theoretical
and a typical end-product in the still is a tarry
residue which has no intrinsic value, but the removal
of which can be a difficult and expensi~e exercise.
We have now found that it is possible to treat
many such wastes in a process which not only gives a
good yield of organic solvent, but also leaves a
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residue which is solid, relatively innocuous and
readily discharged rom ~he processing vessel.
The particular liquid waste products useful in
our process are "heat convertible" materials, by which
we mean that when they are subjected ~o a temperature
of 100C for 60 mins under the test conditions
described hereinunder, they yield a solid residue which
is insoluble at 25C in acetone.
The process involves forming a particulate
dispersion in water of the liquid waste, stripping
water and organic solvent from the dispersion by
distillation and separating the organic solvent from
the water in the distillate. The residue consists of
a free-flowing slurry in water of solid, granular
particles.
We therPfore provide, according to the present
in~ention, a process of recovering organic solvent
from a liquid heat-convertible waste product as
herein defined by the steps of:
(a~ dispersing the liquid waste product in ~ .
particulate form in water in the presence
of a suspending agent for the particles;
(b) heating the dispersion to boiling point
to strip off ste~m and organic solvent
va~ouri
(c) condensing the evolved steam and organic
solvent vapour and separating the water
therefrom; and
(d) recovering the residue as an aqueous free-
flowing slurry of solid granular particles.
Optionally the water can be evaporated from
the slurry to give a residue of dry, solid particles.
The organic solvent can also be further refined by
conventional means, for example by fractional
distillation, when it contains a mixture o solvents.
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~ 17:~2
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Our test for heat convertibility is performed
in the following manner. The liquid waste product
to be tested ls poured or spread on a horizontal test
plate, e.g. a sheet of gl$ss or a flat steel panel,
so that a film of up to 1-2 mm thick is formed thereon.
The test plate is then heated in air to 100C and
held at that te~perature ~or 60 mins It is cooled
to 25C and then moistened with droplets of acetone.
If the required degree of heat convertibility has been
achieved, the residue on the test plate will not
dissolve in the acetone. The effect of the acetone is
sometimes more readily assessed by gently rubbing
the moistened residue with a glass test probe. The
appearance of a satisfactory test area will vary
somewhat depending on the actual composition of the
liquid waste. For example, a satisfactory material
may not be entirely unaEfected by acetone. When
moistf~ned and rubbed with the probe, it may lose
adhesion to the substrate or even break up into
irregular lumps or flakes. In extreme cases it may
even show some wrinkling or swe-lling, but no
dissolution. However, an unsatisfactory test sample
will show definite evidence of d-Lssolution in the
acetone, notably a streaking or smearing on the test
probe or subs~rate and an obvious loss of film
integrity.
We associate the property of heat convertibility
as measured by our acetone solubility test with the
ability of the disperse particles of liquid waste
to form solid, discrete particles during the stPam
stripping stage of our process. This gives rîse to
a slurry of granular particles which is readily
dischaxged ~rom the reaction vessel.
I 1 7~0
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As we understand it, the heat convertibility is
derivQd from cross-linking of polymeric components
o~ the liquid waste. This characteristic may be
inherent in the materials to be treated. For
5 example, paint residues are a form of liquid waste
to which our process is particularly well suited.
One well-known class o~ paints, the "thermosetting"
compositions, have the property of curing from a
liquid to a solid form by a cross-linking chemical
reaction between polymer components thereo. The
cross-linking reaction can be initiated and controlled
by well-known means, for example by the application of
heat, a catalyst or a so-called cross-linking agent.
Many mechanisms of this kind are known and are
discussed in various authoritative texts such as,
for example, "The Chemistry of Organic Film Formers"
Solomon, D.H., Krieger Publishing Co., New York
U.S.A. When the liquid waste comprises such a
the~mosetting composition and the reaction conditions
required to cause cross-linking to take place are
present during the steam stripping cycle of our
process, a satisfactory granular residue is produced.
The cross-linking reaction may require some
acceleration other than by heat alon~. For example,
the above reference discloses other mechanisms, ~.g.
the additiDn to polymers of acid ca~alysts to achieve
heat convertibility. The catalyst addit~o~ is made
to the liquid waste before subjecting it to our
above-described cross-linking test. However, in
carrying out the actual process the catalyst is
~ot necessarily added to the liquid waste; it may
alternati~ely be added to the dispersion of liquid
waste in water, or to the water in which the
disper~ion is to be made provided this is consistent
with the nature of the required cross-linking reaction.
... .
~ 3 71022
Liquid wastes which cross-link in the presence
of an acid catalyst include, for example, wastes
comprising mixtures o hydroxylated acrylic polymers,
e.g. copolymers of methyl metha~rylate and hydroxy-
ethyl methacrylate, and butylated melamine-formaldehyde
resins. The added catalyst might then be, for
example, p-toluene sulphonic acid or phosphoric acid.
We have observed that a surprising number of
liquid waste products, including some which are
normally acid catalysed, will pass our acetone
solubility test for heat convertibility when made
alkaline by the addition of an inorganic base, for
example sodium and potassium hydroxides, before they
are tested. It appears that such mixtures, especially
when usPd in conju~ction with an inorganic suspending
agent, are particularly satisfaotory materials for
use in our process. They typically provide free-
flowing slurries which show little, if any, tendency
to lea~e solid deposits on the walls of the process
equipment.
Alternatively, a liquid waste which is not
inherently able to take part in a cross-linkîng
reaction may be adapted to the requirements of our
process by blending it wi~h hea~-convertible
constituents. For exam~e, thermoplastic lacquer
comprislng polymethyl methacrylate produces a residue
soluble in acetone when subjected to our above-
described cross-linking test. However, the necessary
heat-convertibility can be imparted to it by adding
thereto sufficient carboxylated styrene-maleic
anhydride co~oIymer, difunctional epoxy resin and
tertiary amine catalyst.
3 71022
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A useful practical method of dealing with
waste con~aining essentially thermoplastic polymer,
is to blend that waste with a known heat convertible
waste until a composition is reached which does
satisy our cross-linking test. The proportions to
be blended depend on the compositions o~ the wastes
to be treated and are readily determined by
experiment.
The dispersion of the liquid waste in particulate
form in water can be made, for example, by pouring
the waste into water which is kept agitated by a
mechanical stirrer. The water may be at ambient
room temperature or preferably it may be heated to
boiling before the liquid waste is added to it.
Alterna~ively, if the water is heated by direct
injection o steam, the agitation set up by the
steam sparg~ may be sufficient to break the liquid
waste up into discrete disperse particles.
The suspending agent, which may be present in
either ~he water or in the liqui.d waste may be chosen
~rom the large number of such ag~nts known to
stabilise liquid dispersions in water; our process
will tolerate most types of agent in common use.
However, because the nature bf the waste acceptable
to this process can vary widely in composition and
the di~persion must remain stable during the steam
stripping cycle, some degree of trial may be
necessary to determine the most suitable suspending
agent for use with a particular liquid waste.
We have found that inorganic materials such as
Wyoming bentonite and activated clays of the Hectorite
type can be satisfactory suspending agents. Other
suitable materials are, for example, poly(vinyl
alcohol), gelatine and amphipathic polymeric surface
active agents, eg. triethanolamine oLeate, sorbitol
monostearate, lauryl alcohol ethoxylate and nonyl
~, phenol ethoxylate.
7102
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The requir d coneentration of suspending agent
also varies with bo~h the type o ~uspending age~t
used and the nature of the liquid was~e being
treated. r~i~h orga~ic suspending agents a typical
concentration is 2-5% based on the weight of liquid
waste, while or inorganic suspending agents t~e
corresponding igure is ~ypically 5 10%.
The size of the disperse`particles is not
particularly critical in so far as the recovery
process is concerned. Factors which influence the
disperse particle size distribution in such sy~tems
are well known to the art and include, for example,
the relative viscositle~ of each phase and the
shear force~ generated in the dispersion equipment.
The nature and ~mount of solid material dissolved
.or dispersed in the liquid waste will, in turn,
affect the vi~cosity of the disperse phase. If,
for example, the solid constituents are polymeric
and very viscous, the disperse particles tend
-~ to be coarser than wh~n m~re fluid materials are
us d. Some agglomeration of primary particles ma~
take place, but this is usually a reversible
ac~ion and ~he fi~al slur~y rernains free flowing.
In general, the iner the dispersion the more ~ree-
2S flowing the residue left in the process vessel aterthe steam ~tripping stage.
Typical dispersions we have used successully
in our process have differed quite mar~edly in
average particle diameter, the extremities lying at
30 about a . l ~m and 5 mm.
Ihe dispersion may be raised to boiling point
by e~ternally applied heat or, for example, by steam
injected direc~ly into the proces~ vessel. The
condensed mix~ure of stea~ and organic solvent ~apour
is ~reated by normal phase separation techniques to
recover the organlc ~oLvent, less some losses of
water-soluble fractions which will partition into
.
71~2
_ 9 _
the aqu~ous phase. As menLioned hereinabove, the
organic solv~nt may be further refined, if desired
by, for example, a further fractional distillation
range.
The actual processing cycle is dependent on
~he ~hoice of equipment and limi~ing factors such a~
the tendency of ~he dispersion to fo~m excessively
i~ too-rapid processing is attempted and the
desirability of producing a suitably solid, free-
flowing residue. Typical cycle times are of the order
of 40-90 minu~es.
At the comple~ion of the steam stripping ~ycle~
the solid residue is discharged, preferably by gravity,
from ~he process vessel. It can be readily dewatered
by, for exam~Le, ~iltration. In its dew~tered f~r~,
although still containing an appreciable quantity of
water, l:he granular residue packs do~ to a ~irm
mass and, subj ec~ to ruling environmental protectiorl
laws, is in a suitable form for disposal as solid fill.
I:E desired, it may be completely dried.
The process is broadly applicable to a wide
range of material~ such as, for example, paint
residues, adhesives and dispersions or solu~ions of
polymers u~ed as in~ermediates in the preparation o~
pai~ts and adheRives. Care must be exercised,
however, in using liquid wastes comprising ~aterials
which have a significant reactivity with water~
A par~icularly useful fea~ure of our process is
tha~ if the average particle diameter is held to the
appropria~e dimensions, the residue can be re-cycled
as a iller in products such as, for example, surface
coating~, putties, caulking compounds, fillers and
adhesives. For thls purpose the average particle
diameter is preferably less than about 35 mm.
Dried residue, provided it is suitably
chemicall~ inert, is also poten~ially useful as a
filler in moulded plastic~ ware.
7~2~
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The invention is illustrated by the following
e~amples, in which all parts are expressed in weight.
E ~ ~PLE 1
Recovery of solvent from a liquid thermosetting
acrylic enamel.
The enamel treated by the process comprised a
hydroxylated acrylic polymer and a butylated melamine-
formaldehyde resin. The material was inherently
hea~-convertible when catalysed by an acid.
A sample of the liquid waste, catalysed by
the addition thereto o l~/o by weight of 80% phosphoric
acid, gave a residue insoluble in acetone when -~
subjected to our test for heat convertib~lity.
A mixture of:
water 900 parts -
poly(vinyl alcohol)~ solution 300 "
80% phosphoric acid 3 "
was heated to boiling point in a still fitted wi~h
reflsux condenser and water separator and 500 par~s of
the liquid waste added to it over a period of 30 min~
Organic solvent~was separat d off from condensed
distillate and the water fxa tion, which in the
initial stage of the process, contained approximately
7% solvent in solution, was recycled to the batch.
Steam stripping was continued for a further 90 min.
at which time 95%~by wt.o the~solvent, as determined
by analysis o~ the liquld waste charged to the process9
had been collected. Distillation ~as stopped at that
point.
* A 7.5% solution by weight in water of an 85%
hydrolysed grade of poly(vinyl alcohol).
A satlsfactory product is"Poval"(Trade Mark)
224G.
,i :
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22
The non-volatile residue consisted of hard,
discrete particles with a maximum diameter of about
300 ~m. A slurry o~ these particles in the water
remaining in the still flowed readily when discharged.
EXAMPLE 2
Recovery of solvent from a liquid thermosetting
alkyd enamel.
The enamel treated by the process comprised a
hydroxylated coconut oil-modified alkyd resin and a
butylated melamine-ormaldehyde resin. The
material was inherently heat-convertible when
catalysed by an acid.
A sample of the liquid waste, catalysed by
the addition thereto of 1% by weight of 80%
phosphoric acid, gave a residue insoluble in acetone
when subjec~ed to our test for heat convertibility.
A steam jacketed reaction vessel fitted with a
reflux condenser and water separator was charged
with the following:
water ~ 32 parts
poly(vinyl alcohol) solution 8
(as example 1)
80~/o phosphoric acid 0.13 parts
liquid waste 30
The charge~was stirred mechanically and brought
slowly to ~he boil, then held at reflux for 2.25 hr.
Solvent was stripped off continuously and water from
the reflux condensate re-cycled to the batch. The
yield of solvent against analysed content of the
liquid waste was 95% by wt.
.
~ ~7102~
- 12 -
The residue in the reaction vessel was a free-
flowing aqueous slurry of solid particulates with a
maximum particle diameter o about 200 ~m. The
flash point o the slurry was higher than 61C,
compared with 26 or the original liquid residue.
The Biological Oxygen Demand of a sample of the
slurry was 10 p.p.m. The residue thus presented
significantly less of a disposal problem than the
original liquid waste.
EXAMPLE 3
Use of bentonite as a suspending agent in the
recovery o solvent from a liquid thermosetting
acrylic enamel.
The process o~ example 1 was repeated, but with
the fQllowing substitutions made to the reactants.
The water ~poly(vinyl alcohol) ~phosphoric acid
mixture was replaced by a mixture of 1200 parts
of water and 72 parts of Wyoming bentonite. ThP
phosphoric acid was omitted and its function as
catalyst achieved by dissolving 50 parts of a
styrene-maleic anhydride polymer (acid value
480 mg KOH per~gm and molecular weight 1600) in
the 5~0 parts of liquid was~e. (A suitable polymer
is S.M.A 1000 ex Arco Chemicals Co., U.5.A.~. The
catalysed liquid waste passed our acetone tes~ for
heat convertibility.
The yield of organic solvent was 90% by wt. of
the content estimated by analysis of the original
liquid waste. The disperse particles o rPsidue were
of the order of 5-10 mm.diameter.
2 ç~
- 13 -
EXA~LE 4
___
Use of Hectorite as a suspending agent in the
recovery of solvent from a liquid thermosetting
acrylic enamel.
Example 3 was repeated, but replacing the
Wyoming bentonite of that example with an equal
weight of a swellable synthetic clay (Hectorite~
known by the ~rade name "Laponite".
The same weight of solvent was recovered and
the disperse particles of residue had a mean diameter
of approximately 200 ~m.
EXAMPLE _
The use of amphipathic organic suspending agents
in the recovery of organic solvents from a liquid
thermosetting acrylic enamel.
The enamel used in this e~ample was the same as
that used in example 1 but catalysed by dispersing
therein 1% of p-toluene sulphonie acid. The
catalysed liquid enamel gave a residue insoluble
in acetone when tested by our test for heat convert-
ibility.
A charge o~ 1200 part~ of water was added to a
still fltted with a reflux condenser and water
separator, then heated to boiling point. A mixture of:
liquid thermosetting acryIic
enamel (as e~ample 1) 500 parts
p~toluene sulphonic acid 5 "
sorbitan monopalmitate/
polyoxy ethylene (20 units) 1.5 parts
sorbitan monostearate 1.5 "
`` l ~7102~
was added t~ the boiling water and steam stripping as
generally described in example 1 continued for
90 mins. A yield against analysis of 95% by weight
was recorded. The discrete particles of residue
were somewhat fibrous in nature with an average
length of about S mm.
EXAMPLE 6
Recovery of solvent from a liquid thermoplastic
acrylic lacquer.
The lacquer used in this example was essentially
a pigmented solution in organic solvents of a
poly(methyl methacrylate), which under the conditions
of our test for heat convertibility gave a residue
which was readily solvated by acetone.
To 600 parts of the liquid waste was added
14.4 parts of a styrene-maleic copolymer as used in
example 3, (S.M.A 1000 ex Arco Corp., U.S.A.)
32.4 parts of a liquid epo~y resin("Epikote"828 ex
Shell Chemicals) and 0.5 parts of a tertiary amine
(''Armeen"DMCD ex Armor-Hess CorpO, U.S.A.), dissolved
in 40 parts of a 30:10 (by weight) mixture of
toluene and acetone.
A sample of the liquid waste so modified gave
a residue insoluble in acetone when subjected to
our test for heat convertibility
The 600 parts of modified liquid waste was added
over a period of 30 min. to the following mixture
held at boiling point in a still fitted with reflux
condenser and water separator.
water 900 parts
poly(vinyl alcohol~ solution
as example 1 300 "
sodium carbonate, anhydrous 6
Steam stripping and re-cycling of aqueous condensate
was continued for a further 90 min.to give a yield
0 2 2
- 15 -
of solvent, based on analysis of the liquid waste, of
95%.
The svlid residue was in the form of friable,
gritty aggregates with an average diameter of about
5 ~m.
EXAMPLE 7
Recovery of organic solvent rom a mixed
thermoplastic~thermosetting paint system.
A thermosetting acrylic lacquer as used in
example 1 was added to a thermoplastic acrylic
lacquer as used in example 6 until the blend, when
catalysed by the addition of 1% by weight of 80%
phosphoric acid, gave a residue insoluble in
acetone, when subjected to our test for heat
convertibility.
By the general method of example 1, that blend
as tested was steam stripped to yield about 90% by
weight of the availabLe organic solvent.
The solid residue consisted of coarse, f~iable
crumbs with average diameters o~ the order of 1-10 mm.
~XArrLL 8
Recovery of organic solvent from a thermosetting
acrylic lacquer using steam injection.
The liquid waste used in this example comprised
a copolymer of styrene and hydroxypropyl methacrylate
and a butylated melamine-formaldehyde resin.
When catalysed by the addition there~o o~ 1% by
weight of 80% phosphoric acid and subjected to our
heat convertibility test, the liquid waste yielded
a solid residue insoluble in acetone.
,...
~ 3 ~V22
- 16 -
A mixture of:
water 400 parts
poly(vinyl alcohol) solution
as example 1 180 "
~0% phosphoric acid 3 "
was loaded into a still ~itted with a reflux condenser
and water separator. Steam was injected into the
batch, which reached boiling point in 1 hr. The
steam injection was continued and 540 parts of
liquid waste added ~o the batch at a uniform rate over
a period of 1 hr. Aqueous condensate was re-cycled
continuously to the batch during the steam stripping,
which conti.nued for a further 2~ hr. The recovery
of organic solvent corresponded to 99% by weight of
theoretical. The residue discharæed from the still
was an aqueous slurry of friable aggregates of solid
particles. The aggrPgates had diameters of up to 1 cm.
EXAMPLE 9
Reeovery of organic solvent from an air-drylng0 enamel.
e waste liquid of this example was a solution
in mineral spir~its of an air-dr~ing oil-modified
alkyd resin pigmented with alumirlium powder. The
poLymeric alkyd~resin dld not give a solid residue
2S insoluble in acetone, when subjected to our heat
co~ertibility test. When subjected to the process as
described in example 1, organic solvent was
recoverable from the was~e liquid but a glutinous
mass, dificult to remove from the still, formed before
the theoretical yield of organic solvPnt was realised.
.
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~ 1 7~(~22
- 17 -
The waste liquid was then blended with increments
of the thermosetting acrylic enamel used in example 1
(catalysed with the corresponding amount of 80%
phosphoric acid) until under the conditions of our
test a solid, acetone-insoluble residue was obtained.
The acceptable blend contained approximately equal
par~s by weight of the two liquids.
This blend7 when subjected to the process
described in example l, yielded about 90~/O of
the theoretical content of organic solvent and a slurry
of crum~ly, but somewhat soft, disperse particles,
loosely aggregated into secondary particles of
mean diameter up to 1-2 cm. The slurry discharged
readily fro~ the still.
_
E~AMPLE 10
Recovery of organic solvent from a mixed
thermoplastic/thermosetting pain~ system.
A thermosetting acrylic Lacquer (comprising a
hydroxylated aerylic pol~mer and a butylated melamine-
formaldehyde resin) and a thermoplastic acrylic
lacquer (a pigmented solution of poly(methyl methacryl-
ate? ) were mixed in the weight ratio of 1:1. After
addition of 1% by weight of sodium hydroxide (in the
form of a ~oLution in ethanol, this mixture gave a
residue which w~s essentially insoluble in acetone
when subjected to our test for heat convertibility.
A mixture of
~ia er 1200 parts
sodium bentonite 15 "
sodium hydroxlde 6
l ~71G22
- 18
was heated to boiling in a still fitted with stirrer,
reflux condenser and water separator and 600 parts
of the 1:1 liquid waste mixture previously
described was added thereto over a period of 30 minutes.
Organic solvent was separated off from the condensed
distillate and the water fraction, which in the
initial stage of the process eontained approximately
7% solvent in solution, was recycled to the batch.
Steam stripping was continued for a further 3 hours
at which time 98% by weight of the solvent present
in the waste as determined by analysis had been
collected. Distillation was stopped at that point.
The non-volatile residue ronsisted of hard
discrete particles with a maximum diameter of 6 mm.
A slurry of these particles in the water remaining
in the still flowed readily when discharged.
EXAMæLE 11
Use of verniculite as a suspending agen~ in the
recovery of solvent from a mixed thexmoplastic/
thermosetting paint system.
Example 10 was repeated but replacing the sodium
bentonite of that example with an equal weight o~
vermiculite, the particle size of which was such that
10% was retainPd on a 52 mesh BSS sieve and 70%
maximum on a 100 mesh BSS sieve.
The same weight of solvent was recovered and
the solid particles had a mean diameter of
approximately 5 mm.
. . .
