Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is applicable to the complete material
reprocessing and high finish of all the high polymers made
available by the chemical industry such as plastics, plastic
fibres having passed through one or several utilization processes
and being unsorted in the form of wastes, secondary raw materials
of PVC, polyethylene, polystyrene, polyamides, polyesters,
polyacrylates, etc., polluted or non-polluted and with or without
structure damage due to ageing or due to the action of light and
other environmental influences.
In the past few years the search for possibilities of recycling
high polymer waste products has intenslfied. This includes
particularly waste products such as bottles containers buckets,
piping , sheets, foamed plastics, packages, panels, bullding
materials, chemical fibres, etc., of PVC, polyethylene,
polystyrene, polyamides, polyesters and polyacrylates, etc., but
also intermediate products and monomer products that are required
for their production.
Today some of these high polymer products are collected and
acquired by some means and attempts of recycling them which
principally are more or less incomplete are applied but
nevertheless constitute some kind of saving of raw materials and
energy.
The principal procedure for the re-use particularly of plastic
plastics waste materials lies in remelting down, homogenizing ad
transforming the high polymer waste products.
Thus, for example, a pro~ess for producing moulded parts of
thermoplastic polyester moulding material by means of in;ection
moulding is described in DD-PS 222 544.
A similar process for producing moulded parts from polyurethane
wastes is described in DD-PS 144 885 and a process for the
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preparation of the PU elast mould wastes for said process is
described in DD-PS 262 237.
A process for producing moulded parts from a plastic mixed
material from secondary polyethylene and rubber is described in
DD-PS 137 938.
DD-PS 247 690 relates to the production of a rubber mixture,
capable of being in~ection moulded, from old rubber.
DE-PS 3 603 009 describes a complete process for producing
moulded parts, including the process stages detection,
preclassification, purification and plastification.
Further processes dealing with these problems are described in
DE-PS 3 544 417, DE-PS 3 901 139, DE-PS 3 441 906, DE-PS 3 242
120, EP 0 248 239, WO 85/00 480.
All these processes allow a profitable recycling, that is
sub~ected to substantial limitations and thus has disadvantages:
1. When repeatedly uslng the converted polymer materials there
occurs a substantial loss in stability and quality due to ageing
so that the fields cf application are greatly restricted. An
additional factor is the processing of a large number of
different colours, whereby the optical attractiveness is
substantially reduced. The polymer materlal cannot be passed
through the recycling process several times so that the
hydrocarbon substance of these products eventually gets to the
garbage dumping grounds in any case. A fundamental solutlon of
the raw material problem is thus not attained with this group of
processes. 2. Only thermoplastic high pol~mer waste products
can be processed in the above-mentioned processes. 3. The high
polymer waste products to be processed must be graded and, in
most cases, also purified. This requires the application of
additonal processes (DD235 376, DD 256 048, DD 233 794, DD 207
zo2a~34n
629, DE 3 634 808, DE 3 535 633, DE 3 601 175, DE 2 900 666, DE 2
639 864).
However, a second group of processes allows a better re-use of
the plastics waste products so that by controlled decomposition
re-usable products having a lower degree of quality loss are
formed in that not only ls a physical conversion carried out by a
chemical conversion is also carried out. This group includes a
process according to DD-PS 216 474 in which a rubber that can be
vulcanized again is formed by devulcanization of old rubber wlth
cleavage of the sulphur bridges while protecting the polymer
structure by reducing replastification under the action of
aldehydes.
In a process described in DD-PS 134 773 residues of the ethylene
suspension polymerization are sub~ected to a thermooxidative
degradation at 130C to 250C in the presence of 2 or oxygen-
containing gases and by adding viscosity-reducing substances a
partially oxidized polyethylene wax is formed as produ~t.
A process ln which residues of the ethylene suspenslon
polymerlzatlon are sub~ected to a thermooxldative degradation at
130 to 250C ln the presence f 2 or oxygen-containing gases and
by adding viscosity-reducing substances a partially oxldlzed
polyethylene wax is formed as product, is descrlbed ln DD-PS 134
773.
A process for reprocessing isocyanate-contalning distillation
residues by conversion lnto lsocyanates is described ln DD-PS 238
988. In this process the residues are reacted wlth epoxide
compounds at temperatures below 300C and mixed with dl-or
polyisocyanates.
Furthermore, the reprocessing of special plastics wastes is known
from the following patents: DD 146 826 Production of flexible hot
melt adhesives based on polyester by alcoholysis while
;~0243~
continuously adding diols and polyalkylene oxides at pressures of
up to 2.0 MPA and by subsequent polycondensation. DD 141 525
Recovery of hydrogen-active compounds from polyurethane wastes.
DD 130 256 Process for the production of hot melt adhesives from
polyester wastes. DD 125 979 Process for the utilization of
crosslinked polyester and epoxide resin wastes. DE 3 0~7 829
Conversion of wastes from polyolefins in a careful procedure lnto
higher-valence modified pitches and low-boiling aromatic
substances and olefins at medium pressures and at temperatures
above 300C. DE 2 951 617 Recycling of Polyurethane by
alcoholysis or acidolysis. DE 2 911 203 Process for the recovery
of polystyrene by selectively dissolving them in liquid SO2 in a
first step and by evaporating the SO2 in a second step. EP 0 052
213 Process for the catalytic depolymerization of polytetramethyl
glycol ether in the presence of bleaching clay as catalyst at
~emperatures of 90 to 180C with the aim of producing
tetrahydrofuran. EP 0 048 340 Recovery of caprolactam from
nylonoligomers. EP 0 031 538 Recycling of polyurethane by
alcoholic and acidolysis. EP 0 000 948 Production of polyol-
containing liquids from polyurethane wastes in the presence of
intensily basic compounds at temperatures of 150 to 220C.
All the processes of this group have the following disadvantages:
1. The range of application is highly specifically dlrected to a
specific polymer type with a limited share in the total yleld of
society in most cases. 2. The problem of making the polymers
available in a graded conditlon remalns inasmuch as the starting
product is not a residue that is obtalned directly in the
production of the polymers. 3. The polymer product is converted
into a qualitatively more or less high-grade product that is
useful in a different way; a true recycling for the reproduction
of a new original polymer does not occur.
A further known recycling process is the hydrogenation of carbon-
containing wastes at temperatures of 75C to 600C and at high
pressure of up to 600 ~ars tRheinbraun process DD-PS 249 036).
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Apart from the disadvantages of an additional hydrogen
consumption and of the required high pressures necessitating high
technical expenditure, this process has the disadvantage that
there are formed undefined hydrogen carbon mixtures which cannot
be used without further processing. Recycling directly into the
polymer synthesis is not possible.
FUrthermore, pyrolysis processes operating in the temperature
range of 150C to 500C (DE 3 323 161) and 400C to 650C (DE 3
531 514) are also known. The first process can process only
thermoplastic plastics. The resulting products are of low value
and their further use is difficult. In the second process the
low-grade pyrolysis waste gases are passed to a thermal
afterburning stage without any further utilization. This process
thus is only useful for the destruction of secondary polymers and
varnish sludges.
A process that also is only useful for the removal of plastics
wastes is described in DE-PS 2 409 966. In the process protected
by said patent the photodissocation of plastics wastes by
sunlight is substantially accelerated by applying decomposition
accelerators such as manganese, iron, cobalt, nickel or copper
salts of higher-fatty acid.
Furthermore, process for the plasma pyrolysis and for the plasma
gasification of crude fossil material such as coal, coal-
containing substances, petroleum and natural gas are known. The
pyrolysis of old tires resulting in low-grade and inapplicable
carbon blacks, oils and pyrolysis gases is also known.
It is the aim of the present invention to devise a process which
allows the processing of all the secondary high polymers
obtained, preferably those which originally contain no volatile
matter that can be defined by standardiæed measuring methods,
independently of their chemical composition and physical
consistency, ln a form such that the raw-material substance
~02~4(~
contained therein, i.e., C, H, Cl, can be completely used again
so that by utilizlng the existing sequence chemistry a synthesis
of completely new, unrestrictedly applicable high polymer is
obtained from the old substance, i.e., an almost 100% true
recycling process.
According to the present invention this aim is achieved in that
the hi~h polymer waste products are converted by plasmachemical
means into their chemical basic materials from which they had
originally been synthetized, such as acetylene, ethylene,
hydrogen, HCN, CO, ~Cl and carbon black. The high polymer waste
products are suitably sub~ected to a plasma hydrolysis under
reducing conditions or to a plasma gasiflcation at the
simultaneous presence of reducing and oxidizing plasma
conditions.
For this purpose the high polymer waste products are granulated
or comminuted in some other way, converted into a conveyable
consistency mixed with superheated steam and fed to a hydrogen
plasma ~et having an average mass temperature of at least 1~00C
and a pressure of 0.05 to 0.5 MPa so that the polymer suspension
or granulate and the hydrogen plasma are mixed. The nascent
reactive plasma subsequently enters a plasma reactor. After a
residence time of 10-3 to 30 seconds in the plasma corresponding
to the chemical composition and the physlcal state, for example,
the particle slze, the plasma ~et is quenched to temperatures
below 1000C and thus converted into a pyrolysis gas current.
The solids present in the plasma pyrolysis gas current, such as
carbonized polymer waste products or carbon black, are removed
from the plasma pyrolysis gas, which is completely or partially
separated into its constituents.
For the conversion into a conveyable consistency the comminuted
or granulated polymer waste products suitably are thermally
melted down, preferably in an extruder, dissolved in a solvent or
solvent mixture, suspended in water or hot steam, hydrogen,
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methane, carbon dioxide or fuel gas, etc., are passed in as
entraining gas. The complete or partial separation of the plasma
pyrolysis gas forming in the plasma process into its constituents
is preferably carried out by absorption and low temperatures
distillation. The constituents thus forming can then also be
passed on to corresponding polymer synthesis processes, either
entirely or partially.
The mode of operation of the process according to the present
invention lies in that long-chain molecules, like those
represented by all the high polymers, even those of a textile
nature, have a relatively low bond energy between the carbon
atoms which facilitates easier cleav'age into hydrocarbon
fragments than is the case, for example, in fossile carbon
carriers, e.g., coal.
Under the conditions of a reactive hydro~en plasma all the high
polymers are split into fragments, which split into the
thermodynamically most favourable compounds, such as acetylene
ethylene, hydrogen, CO, HCl, HCN, i.e., highly energetic
compounds which also represent the chemical starting substance
for the todays production of all known polymers. Polyethylene
thus is reacted by the action of a hydrogen plasma ~et according
to the following overall reaction formula:
~ -Plasma
(CH2 ) n ~ -~ ~ a C2H2 + b a2II4 + c ~ + d C
The coefficients a, b, c and d depend on the plasma temperaturs,
i.e., the dlssociation degree and the plasma enthalpy. Polyvinyl
chloride reacts in the hydrogen plasma accordlng to the following
overall reactlon formula:
~02434(:~
~ ~Plasma
(CH2~ICl)n C2H2 ~ b C2H4 t c H2 ~ d C + e HCl
As to the meaning of the coefficients a, b, c, d, and e the same
applies as in the rsaction of polyethylene.
The admixture of superheated steam to the polymer granulate or
suspension prior to mixing them with the plasma ~et prevents the
formation of carbon black in favour of the formation of hydrogen
and of an additional formation of C0, i.e., the superheated steam
participation in the reaction in a controlled manner.
The use of polyacrylates in the plasma ~et results in a
conversion into the products acetylene C2H2, ethylene C2H4,
hydrogen H2, carbon black C and HCN.
In the reaction in a hydrogen plasma ~et polystr~ne yields
acetylene C2H2, ethylene C2H4, hydrogen H2 and carbon black C
and, depending on the application of hot steam, CO in favour of
the formation of carbon black. It is important for the process
according to present invention that the hlgh polymer waste
products usually contain no volatile products deterrable by
conventional test methods, i.e., that these products, as for
example, coal, cannot be measured for this purpose by
standardized methods.
The required reaction time, i.e., the residence time of the high
polymers in the plasma ~et, depends on the manner of introducin~
the high polymer waste products into the plasma jet, i.e.,
granulate suspension or melt, on the particle si2e of the high
polymer waste products and on their chemical structure and is
between 10-3 and 60 seconds.
Finally, from the plasma pyrolysis of high polymer waste products
by means of the process according to the present invention, any
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of the basic chemical materials for today's polymer synthesis,
i.e., acetylene C2H2, ethylene C2~4, hydrogen H2 carbon monoxide
CO, hydrocyanic acid HCN as well as methanol (via H2/CO
mixtures)~ acetaldehyde, acetic acid ( via acetylene), can be
obtained. A basis for a novel synthesis of all known polymer
materials with the known sequence chemistry of the above-
mentioned basic materials is thus provided.
Example 1
A mixture of more than 50% by weight of thermoplastic high
polymer waste products (for example, polyethylene, is granulated
in a granulating mill, then melted down in an extruder at 115C
(thermoplastic component) and subsequently pressed by said
extruder ln to an admixture division of a plasma pyrolysis
reactor that encases a hydrogen plasma ~et having an average mass
temperature of 2500C. In said reactor the surface of the
polymer suspension flow passing through the admixture division is
cleared off and is chemically d~ssociated in the plasma within a
reaction time of 10 seconds and converted into acetylene and
hydrogen.
The reactive plasma is ~quenched~ by the recycle gas quenched at
the outlet of the plasma reactor and the product C2H2, C2H4H2 are
stabilized.
On separating the solids and washing the acetylene solvent the
residual pyrolysis gas mlxture is passed to a gas separator in
order to obtain the pyrolysis gas components in a pure form.
Said components are then again passed to a polymer synthesis.
Example 2
Polyethylene waste products are granulated in a granulating mill
and subsequently melted down in an extruder at 180C and
homogenized. The melt is atomized in a highly fluid state by
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superheated steam havlng a temperature of 250C and a pressure of
0.5 MPa and are passed to a hydrogen plasma ~et having an average
mass temperature of 3000C. The products acetylene, ethylene,
CO, H2 and C formed after reaction time of 0.5 second in the
plasma reactor designed as a fluid~zation reactor, are stabilized
with cold recycle pyrolysis gas at the reactor outlet and, after
separating the carbon black they are passed to a gas separator.
ExamPle 3
Polyvinyl chloride wastes are granulated in a granulating mlll,
whereupon they are mixed with a solvent mixture of
trichloroethylene and tetrachloromethane in an attached agitator
at 80C. At the same time the PVC waste product is partially
dissolved and solubilized and the nascent suspension is fed by
means of pump pressure lnto the admlxture divislon of a plasma
pyrolysis reactor while adding superheated steam. A hydrogen
plasma jet having an average mass temperature of 2000C is
spreading in sald reactor. Solvent and polymer wastes are
~ointly reacted plasma chemically to acetylene, ethylene,
hydrogen, HCl and carbon black within a reaction time of 1
second, quenched with cold pyrolysis recycle gas at the reactor
outlet and subsequently passed to the mechanical separation of
carbon black, then washed with water and passed to gas separator.
In a further variant the polymer/solvent suspenslon is fed by
means of pump pressure to the admixture dlvislon of the plasma
reactor, where it ls in~ected into the hydrogen plasma ~et by
means of hot steam having a temperature of 250C.
Example 4
An undeflnable mixture of various non-thermoplastic polymer
wastes is granulated in a granulating or beater mill, whereupon
it is fluidized with superheated steam of 250C to 300C as
entraining gas in a plasma reactor, which encases an H2 plasma
-- 10 --
~)2434f)
jet having an average mass temperature of 2500C. In the plasma
reactor, designed as fluidized-bed reactor, the granulated
polymer substance is completely reacted into high-grade polymer
products, such as acetylene, ethylene, hydrogen, CO and HCl at an
average residence time of 1 minute.
The pyrolysis gas, which has a resldence time of 10-3 second in
the rector, is quenched in water at the reactor outlet and ls
passed on for the separation of carbon black and subsequent
washing with HCl. The separation into the components of the
polymer starting product is carried out in a subsequent gas
separation analysis.
The quenched pyrolysis gas leaving the reactor has the following
composition:
C2H2 = 5 to 10% by volume
C2H4 = ~ to 3% by volume
H2 = 50 to 70% by volume
CO = 5 to 10% by volume
HCl = 10% by volume
Apart from the complete recycling, further advantages of the
process according to the present invention are:l. it is gentle on
the sources of primary energy carriers. 2. The expenditure for
the extraction and the preparation of fossile raw material can be
dispensed with. 3. Reduction of the energy consumption for the
production of the polymers to 60 tod 70~ as compared with the
procedure via fossile raw materials slnce the high polymer can be
split more readily and more completely. 4. Omission of costly
process stages that are hard on the envlronment (for example, PVC
production: omisslon of the chlorine electrolysis and of the
carbide furnaces for the C2H2 synthesis). 5. Continuous renewal
of the polymer supply in the economy, practically without the use
of raw materials. 6. The composition of the polymer product
mixture influences only the composition of the pyrolysls gas
-- 11 --
~02434~
without having a detrimental effect on the process. 7. The
residues adhering to the high polymer waste products, as for
example household chemicals, are also reacted to useful products,
such as C2H2,C2H4,CO, etc.
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