Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR TEIE HYD~OLYSIS OF PLASTICS, PARTICULARLY
POLYURETlE~ANES
Field of the Invention
The present invention relates to a process for the hydrolysis of plastics,
particularly of polyurethanes.
l~ack~round of the Invention
5 Various processes are known for the recycling of plastics7 particularly poly-
urethanes. Pyrolysis, glycolysis and hydrolysis processes, in particular, have been
described for the recovery of the polyurethane raw products and/or working pro-
ducts.
Simple hydrolysis with water has not been possible as a universal process to date
10 because, unless there is a high content of hydrophilic components, the polymers
are not soluble or sufficiently swellable in water under normal conditions. As aresult, this is the reason, in the processes known in the (patent) liLel~ule7 high
pressure in conjunction with superheated steam was necessary, as described, for
example, in French Patent Specification 1,364,855; German Patent Specifications
2,362,921, 2,442,387; European Patent Specification 0,011,662; U.S. Patent Nos.
4,328,368, 4,281,197 and 3,978,128; German Patent specifications 861,926,
2,207,379; and Japanese Patent Specification J 50110-495, J 51 114 496 and 05
031 000. To implement the processes claimed in the above-mentioned speci-
fications, autoclaves or specific pressure reactors such as twin-screw reactors or
20 special countercurrent reactors are necessary, which cause a relatively largeamount of outlay in terms of apparatus. Another possibility described in the
literature, which avoids pressure reactors, consists of the use of (organic) solvents
for the reaction. The (organic) solvents' main purpose is to dissolve the poly-
urethanes or at least swell them to a considerable extent so that the actual
25 hydrolysis reaction can take place in a homogeneous phase as far as possible.Preferred solvents are usually those with Zerevitinoff active groups, such as
amines (Japanese Patent Specification 73-05280) or alcohols, such as dipropyleneglycol, ethanediol, diethylene glycol and glycerol (e.g., U.S. Patent Nos.
4,316,992, 4,317,939, European Patent Specification 059 594; and J. Gerlock in
Ind. Eng. Chem. Proc. Des. Dev. 1984, p. 545 ff). High-boiling hydrocarbons (J.
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Gerlock in Ind. Eng. Chem. Proc. Des. Dev. 32 (1984) p. 552) or dialkyl ethers
(Japanese patent specification 54 117 580) have, however, also been described as,
for example, auxiliary solvents.
Processes which proceed both under pressure and with solvents are also known
5 (U.S. Patent 4,316,992, German Patent Specification 2,207,379). The feature com-
mon to all these processes is that the solvents, which are used, must first be re-
moved before the recovered PUR raw materials are re-used. If these solvents haveZerevitinoff active groups, they also react with the polyurethane to be broken
down, and new additional fragments arise, which are difficult to separate, if re-
10 quired. In addition, higher-boiling alcohols which are used as auxiliary solvents
are often difficult to separate from the hydrolysis products so that polyol mixtures,
for example, are obtained with a relatively high hydroxyl group content and often
cannot be re-used for the original application.
In the presence of fairly large quantities of strong acids (Japanese Patent
Specification 72-51238) or strong bases (U.S. Patent Specification 5,208,379 forexample), the PUR hydrolysis is apparently possible without further additives, but
a fairly large amount of salt, which has to be disposed of, occurs.
A process has now been found by which it is possible to break polyurethanes,
polyurethane ureas and other hydrolyzable plastics down into their raw materialswith little outlay on energy, apparatus and raw materials and without any increase
in the product quantity.
Summar~v of the Invention
The present invention provides a process for the hydrolysis of plastics which
contain hydrolytically decomposable chemical bonds (groupings) in the polymer
chain, comprising the step of treating the plastics with water in the presence of a
hydrolysate of the same or of a similarly composed plastic, at temperatures from20 to 240~C, optionally, under pressure, until the plastic to be hydrolyzed is
completely dissolved in the hydrolysis mi~ture.
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Detailed Des~ ,lion of the Invention
According to the process of the present invention, all plastics can be used which
contain chemical bonds and/or groupings in the polymer chain which can be
decomposed hydrolytically (and which, hence, make up the polymer chain). For
5 example, (Thio)ester, carbonate, amide, urethane, urea, acetal, aminal and ortho-
ester groups may be regarded as hydrolytically decomposable bonds and/or
groupings. Polyurethanes and polyurethane ureas are preferably used in the pro-
cess according to the present invention Those polyurethanes and/or polyurethane
ureas are preferred which are composed of non-hydrolyzable polyols, such as poly-
10 ethers, e.g., C2-C4 polyethers, as well as polybutanediols. The polyol products
may be di- and higher-functional, but also have mono-functional contents.
Furthermore, the polyurethanes and/or polyurethane ureas to be hydrolyzed may becomposed of natural products such as castor oil and/or linseed oil, sugars and their
derivatives. The polyurethanes and/or polyurethane ureas may contain the non-
15 hydrolyzable polyols individually or in a mixture with each other.
The plastics to be hydrolyzed may, of course, also contain further conventionalauxiliary substances such as inorganic and/or organic fillers, wherein these may
also be hydrolytically decomposable.
Furthermore, according to the process of the present invention, it is possible to use
20 the plastics to be hydrolyzed individually or in a mixture with each other. Poly-
urethane flexible foams of different compositions, for example, may be jointly
hydrolyzed.
According to the process of the present invention, it is appropriate to use the
plastics to be hydrolyzed in a crushed form, as this correspondingly increases the
25 dissolution rate of the plastics in the reaction mixture. In this manner, the process
of the present invention is particularly advantageous for the use of polymer foams.
The process according to the present invention is preferably implemented at
temperatures from 80 to 230~C, particularly preferably - to ensure the speedy pro-
gress of the process - at temperatures from 180 to 230~C. To accelerate this pro-
30 cess, it may also be advantageous to carry out the process under pressure.Pressure ranges of up to 50 bars, preferably up to 30 bars, have proven to be
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particularly advantageous. If the process according to the present invention is
carried out under pressure, it is, of course, possible to choose a higher pressure
range than the aforementioned range. This may further increase the reaction rateof the process.
5 It is essential to the process according to the present invention that the hydrolysis
of the plastics, which are being used, be implemented in the presence o~ hydro-
lysate of the same or a similarly composed plastic and simultaneously, in the pre-
sence of water.
The particular purpose of the hydrolysate of the same or of a similarly composed10 plastic~ which is to be used according to the present invention, is to dissolve the
plastics to be hydrolyzed. The dissolution of the plastic to be hydrolyzed in the
~! hydrolysate takes place in a versatile manner, including by a chemical reaction of
the hydrolysate used of the polymer to be hydrolyzed, wherein a chain breakdown
mostly takes place. Therefore, the new chemical groupings, which are thereby
formed, are usually hydrolyzed again at a later stage through the action of water,
so that after the reaction has ended, the cleavage product mixture (hydrolysate),
which is used, is generally present in a virtually unchanged form from the polymer
to be hydrolyzed and can be used again for the hydrolysis.
For the process according to the present invention, it is advantageous to use a
hydrolysate (cleavage product mixture), which has arisen by hydrolysis of the
same or a very similarly composed plastic, since it contains the same raw
materials and/or synthesis products as the plastics to be hydrolyzed and as a result,
only the desired cleavage products are present in the hydrolysate. Glyco-
hydrolysates can also be used as the hydrolysate in many instances. In special
cases, such as polycaprolactam, for example, the hydrolysate may be a single
chemical compound such as aminocaproic acid.
According to the process of the present invention, the quantity of hydrolysate to
be used is 1 to 300 wt.% with respect to the total quantity of plastic used, prefer-
ably 10 to 150 wt.% The quantity of water that should be present in the
hydrolysis mixture is conventionally, 0.1 to 200 equivalent %, with respect to the
groups to be hydrolyzed. With respect to the reaction rate of the hydrolysis
according to the present invention, it is advantageous to select the amount of water
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to be used for the hydrolysis in such a way, that the temperature of the reaction
mixture does not fall below a certain temperature range (approx. 180 to 190~C).
Such a temperature range is m~int~ined by the corresponding subsequent metering
of water.
5 The process according to the present invention may be implemented in the pre-
sence or absence of catalysts. All known catalysts, which are described for suchhydrolysis reactions, may be considered as suitable catalysts. For example, strong
bases, such as alkali and alkaline earth hydroxides, such as sodium or calcium
hydroxide; or amines, such as triethylene diamine; and strong acids, such as
10 mineral acids, e.g., sulfuric acid, are particularly suitable.
The most favorable quantity of catalysts to be used may easily be determined by
the corresponding prelimin~ry trials. Conventionally, the quantity of catalysts re-
quired is between 0.01 to 5 wt.% with respect to the plastic to be hydrolyzed
According to the process of the present invention, the plastics (to be hydrolyzed),
15 which are to be used, are treated with water and the hydrolysate until the plastic to
be hydrolyzed is completely dissolved in the hydrolysis mixture. The viscosity of
the mixture may be individually selected. The hydrolysis reaction may optionally,
be interrupted before it has ended.
If the hydrolyzed plastic is to be burned, for example, and serve as fuel, it is ad-
20 vantageous to carry on the hydrolysis of the plastic until a "pumpable viscosity" of
the hydrolysis mixture has been achieved (e.g., a viscosity of the hydrolysis mix-
ture in the range from l to 5,000 mPas, measured at 100~C). It is, of course,
possible to carry out the hydrolysis of the plastics used completely, i.e., until the
plastic used is entirely broken down into its constituent components. In this case,
25 the hydrolysis should be regarded as complete when no further temperature rise of
the hydrolysis mixture cont~ining water is observed over a fairly long period oftime of 15 to 120 minlltcs7 for example, with constant pressure.
A suitable embodiment of the process according to the present invention
comprises introducing the hydrolysate at a suitable temperature, 200~C for ex-
30 ample, and adding the plastic to be hydrolyzed portion-wise in such a way that it
dissolves approximately at the feed rate. Water may be added in parallel or after
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the plastic has dissolved, in small portions (drop-wise) in such a way that the
temperature in the reacting melt does not fall below, or falls only a little below,
200OC.
An example of the way in which the process according to the present invention
5 can be implemented is to mix the plastic to be hydrolyzed completely with the
corresponding hydrolysate and meter in the corresponding amount of water during
the hydrolysis reaction. It is, of course, also possible to add the hydrolysate to-
gether with the water to the plastic to be hydrolyzed and to carry out the
hydrolysis with the amount of water calculated.
10 All or part of the hydrolysate obtained in the hydrolysis according to the present
invention may be returned to the reaction or, as mentioned, be used as fuel or be
used to produce new polymers optionally, after previous processing into the
individual components.
In comparison with the known recycling processes for plastics, the process
15 according to the present invention has the particular advantage that it can be
carried out in simple heatable reactors without pressure and that virtually, only the
raw materials and/or working components, which are originally used to make the
plastics, occur and can be recovered in a comparatively simple separation process,
for the manufacture of, for example, new plastics.
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EXAMPLES
Example 1
390 parts by weight of a hydrolysate from a hot molding foam, which was
substantially produced from a propylene oxide (82.5%)-ethylene oxide (17.5%)
5 polyether started on trimethylolpropane with a hydroxyl value of 35 (mg KOH/g),
water and a toluylene diisocyanate/ isomer mixture with an 80% 2,4-diisocyanate
content, are heated to 220~C in a reflux apparatus under agitation. The hydrolysate
has a 2.7% amino group content, a water content of 0.25% and an acid value of
0.6 (mg KOH/g). When the desired temperature is reached, 400 parts by weight
10 of the same PUR foam are added portion-wise corresponding to the progress of
dissolution. 10 parts by weight of water are added in four portions in such a way
that the product temperature in the reaction vessel does not fall below 200~C.
When, after the addition of water, the initially dropped reaction temperature in the
apparatus, which is maintained under standard pressure, does not appreciably rise
15 again, despite adequate heating, the reaction is ended. The reaction product is
allowed to cool. At room temperature, it has a viscosity of 2400 mPa-s, an aminogroup content of 2.8%, an acid value of 0.5 (mg KOH/g) and a water content of
1.2%.
It may be used to operate (industrial) heating systems in a similar way such as
20 heating oil or be processed as described in Example 3.
Examl~le 2
2030 parts by weight of the foam used to produce the hydrolysate introduced and
35 parts by weight of water are added portion-wise to 470 parts by weight of a
hydrolysate of a PUR block foam composed of an ethylene oxide/propylene oxide
25 mixed polyether started from glycerol and propanediol with an OH value of 46,water and a mixture comprising 20% toluylene-2,6-diisocyanate and 80% tolu-
ylene-2,4-diisocyanate in the course of six hours at 210 to 220~C in a stirred,
pressureless reflux apparatus in such a way that the product temperature is main-
tained under heating. A further five parts by weight of water are then added and30 agitation continues for four hours at the same temperature. The product is pressed
through a 70 11 screen at 170~C and treated in vacuo for one hour at 120~C.
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The product has an amino group content of 3.1%7 an acid value of 0.5 and a watercontent of 0.3%. According to E~'LC the hydrolysate contains 9% of free tolu-
ylene diamine.
Examl~le 3
5 (Hydrolysis of the mixture of different PI~R flexible foams)
A mixture comprising the waste of seven different PUR flexible foams: block
foams, molding foams7 flame-retardant and polyester/PUR foams based on tolu-
ylene- and diphenylmethane diisocyanate and its higher homologues7 which con-
tains7 as raw materials7 various branched propylene oxide and propylene
10 oxide/ethylene oxide mixed polyethers of different reactivity7 polyesters such as
branched diethylene glycol polyadipate7 polyhydrazodicarbonamide, inorganic
flame-retardants and melamine resin, is broken down in a hydrolysate of the samefoam mixture.
400 parts by weight of hydrolysate are introduced in the apparatus described in
Example 1 at 220~C. 400 parts by weight of the foam mixture are added portion-
wise in the course of four hours. Four parts by weight of 50% soda Iye are then
added, and then 14 parts by weight of water in portions in such a way that the re-
action temperature does not fall below 200~C~. Agitation continues for three hours
at 200 to 220~C and the reaction melt is pressed through a 70 ,u screen at 170~C.
A solid residue of 14 parts by weight (moist) remains.
100 parts by weight of the hydrolysate obtained as described in Example 3 are
intimately mixed with 400 parts by weight of cyclohexane and 100 parts by
weight of ln hydrochloric acid at room temperature. The mixture is then left to
settle and the water phase is separated off from the upper organic phase after
approx. 30 minutes. The water phase is extracted twice with 100 parts by weight
of cyclohexane each time. The combined organic phases are washed once with 50
parts by weight of 5% sulfuric acid and twice with water. Treatment with one
part by weight of fuller's earth and drying with sodium sulphate then follow andevaporation takes place at 15 mbars and temperatures up to 80~C. An almost
colorless, virtually clear product with an OH value of 49 mg KOH/g, an acid
value of 0.3 rng KOH/g and an amine group content of 0.02% is obtained.
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80 parts by weight of this purified hydrolysate are homogeneously mixed with 20
parts by weight of a propylene/ethylene (10%) oxide mixed polyether (OH value
46 mg KOH/g) started on a mixture of glycerol and propylene glycol, 3 parts by
weight of water, 1.2 parts of a conventional commercial polyether polysiloxane, 1
5 part by weight of a 50% solution of sorbitol in water, 0.15 parts by weight of a
mixture of conventional commercial amine catalysts, 0.12 parts by weight of
tin(II) octoate and 43.5 parts by weight of a mixture comprising 80% toluylene-
2,4-diisocyanate and 20% toluylene-2,6-diisocyanate at room temperature and
poured into an open box lined with paper. An optically flawless open-cell flexible
10 foam is obtained.
Although the invention has been described in detail in the foregoing for the
purpose of illustration, it is to be understood that such detail is solely for that
purpose and that variations can be made therein by those skilled in the art without
departing from the spirit and scope of the invention except as it may be limited by
15 the claims.
