Note: Descriptions are shown in the official language in which they were submitted.
.CA 022067~9 1997-06-02
RECOVERY OF NYLON FIBRE FROM CARPET
The present invention relates to a method for the
recovery of nylon fibre from carpet, and in particular to
a method of recovery of nylon fibre from either used or
scrap unused carpets, or parts thereof, including both
roll carpets and carpet tiles, especially as part of the
recycling of nylon carpet.
There are a variety of methods for the manufacture
of nylon carpet, depending on the particular style of
carpet, and of nylon carpet tile. In general, nylon
carpet and carpet tile have nylon fibre on one surface
and a carpet backing on the opposite surface. The nylon
fibre is anchored into the carpet, either through use of
the carpet backing or by other techniques. For instance,
in a tufted pile carpet, pile yarn is tufted into a
primary carpet backing in a needle punching operation.
Subsequently, the underside of the tufted primary carpet
backing is coated with a polymeric latex or hot melt
adhesive material to encapsulate the yarns and provide an
adhesive surface on the underside of the carpet. A
variety of polymers may be used in the latex or hot melt
adhesive layer. The primary backing may also be a
variety of sheet or woven materials, the latter including
woven polymer tapes, scrims and jute.
In view of the complex and varied nature of the
construction of carpets and carpet tile, it is difficult
to efficiently and effectively separate the fibre from
the backing and other materials in the carpet or carpet
tile. In addition, most carpet or carpet tile intended
for recycle is used carpet, which would be soiled and
contain dirt, sand and other contaminants.
The difficulties of recycling carpeting having, for
example, nylon tufts, latex adhesive and polypropylene
backing is known, and referred to as difficult to
impossible in WO 97/06004 of R. Akki et al, which
discloses a pile surface structure for the manufacture of
lightweight carpet that is easily recycled. Separating
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components of carpet material for recycling by milling
and use of solutions of different density, adjusted by
addition of a salt, is disclosed in US Patent 5 598 980.
Recyclable carpets that are formed from polyamide tufts,
polyamide backings and polyamide adhesives are disclosed
in EP 625 605. A carpet recycling separation process in
which carpet is shredded and granulated to reduce the
carpet to less than 4 square inches, hammer-milled to
liberate carpet backing and then sifted e.g. using a
shaker conveyer is disclosed in Research Disclosure
388013.
A method has now been found for recovery of nylon
fibre from nylon carpet, including roll carpet and carpet
tile.
Accordingly, an aspect of the present invention
provides a method for the separation and recovery of
nylon fibre from a nylon carpet, said nylon carpet
comprising nylon fibre and backing material, said method
comprising:
a) comminuting said nylon carpet;
b) subjecting the comminuted nylon carpet to at
least one screen to separate at least part of said
backing material from material containing said nylon
fibre;
c) feeding nylon fibre obtained from step b) to a
vessel containing an aqueous solution, agitating material
containing said nylon fibre and effecting further
separation of backing material from said material
containing nylon fibre;
d) subjecting aqueous solution containing nylon
fibre from the vessel in step c) to at least one
centrifugal cleaner for separation of heavy particulate
matter and at least one screen to separate aqueous
solution containing nylon fibre;
e) dewatering the aqueous solution containing
nylon fibre from step d); and
f) recovering nylon fibre.
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In a preferred embodiment of the method of the
present invention, the aqueous solution in step d) is
subjected sequentially to a screen of a first mesh size
and to a screen of a second mesh size, said first mesh
size being larger than said second mesh size.
In another embodiment of the present invention, the
aqueous solution obtained from step d) is subjected to a
dynamic washer to reduce the water content of said
solution prior to dewatering in step e).
In a further embodiment, the comminution of nylon
carpet in step a) includes, in sequence, a step in which
the nylon carpet is shredded and a step in which the
shredded nylon carpet so obtained is subjected to at
least one of grinding, pulverising and hammer milling.
In a still further embodiment, the screen in step b)
is at least one of a shaker screen and a rotary screen.
In yet another embodiment, the nylon carpet that is
comminuted in step a) is one of roll carpet and carpet
tile.
In a still another embodiment, the at least one
centrifugal cleaner and the at least one screen of step
(d) may be in any sequence or combination of sequences.
The present invention is illustrated by the
embodiment shown in the drawings, in which:
Fig. 1 is a schematic representation of the method
of the invention; and
Fig. 2 is a schematic representation of the aqueous
section of an embodiment of the method.
Fig. 1 shows a comminution device, generally
indicated by 1, a screen generally indicated by 2, a
vessel generally indicated by 3, a centrifugal cleaner
generally indicated by 4, a screen generally indicated
by 5 and a de-watering apparatus generally indicated by
6.
The method of the invention is intended to be used
with respect to nylon (polyamide) carpet. Such carpet
may be in a wide variety of forms, including in the form
of scraps or off-cuts of carpet from processes for the
-CA 022067~9 1997-06-02
manufacture or installation of carpet e.g. roll carpet or
carpet tile, including various pieces of such roll carpet
or carpet tile. The roll carpet and carpet tile could be
new (unused) carpet but would more likely be carpet or
carpet tile that had been removed after an extended
period of use e.g. for replacement with new carpet. Such
used carpet, in particular, would be soiled e.g. contain
significant quantities of dirt, sand and other
contaminant matter. The carpet would normally have been
previously separated from other types of carpet, if
necessary, prior to being subjected to the method of the
invention. Techniques for the separation of nylon carpet
from other types of carpet are known, and include
chemical tests and centrifuge tests.
In the method of the invention, the carpet is fed to
a comminution device 1 for comminution of the carpet.
Comminution device 1 would normally be a two-stage
comminution device, with the first stage being for
instance a shredder that is capable of shredding the
carpet to a first coarse particle size e.g. particulate
having diameters in the range of 0.5-0.75 inches,
although a wide range of sizes could be used and the
particle size distribution is likely very broad. The
primary purpose of the shredder is to assist in the
comminution of the carpet into a particulate size
suitable for processing according to the invention, and
it would normally be difficult to obtain a suitable
particulate size in a one-step operation. For instance,
it is believed that there is an optimum range of
particulate size, with particulate that is too fine being
susceptible to difficulties in separation in density
separation processes, in that such processes would not
effect a density separation or would exhibit parachuting
or carry-over of one type of fine particle with a
different type of fine particle. The second stage of
comminution is intended to reduce the particulate size of
the shredded carpet to achieve a suitable particulate
size for screening, and subsequent steps in the process
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as described below e.g. an optimum and relatively uniform
range of particulate size, and would for instance be a
hammer mill, a grinder or a pulveriser. Fibre length of
the comminuted carpet is believed to be important,
especially for separations involving differences in
- density.
The particulate or comminuted carpet passing from
comminution device 1, through transfer pipe 11 to screen
2 would need to be of a particulate size commensurate
with the mesh size of the screen. The mesh size of the
screen is selected so as to effect a primary separation
of particulate matter that is carpet backing from
particulate matter containing nylon fibre. The carpet
backing particulate would be of a greater size than the
carpet fibre particulate. Examples of screen 2 are a
shaker screen or a rotary screen.
The particulate carpet fibre fraction from screen 2
would be passed through screen outlet 12 into vessel 3.
The particulate carpet backing separated in screen 2
would be passed through rejection line 13. It is to be
understood that screen 2 could be a plurality of screens.
Particulate matter passing through screen rejection line
13 could be subjected to further comminution e.g. by
recycling to comminution device 1, or subjected to
further screening e.g. using one or a plurality of
screens in screen rejection line 13, so as to effect a
separation of a higher proportion of the nylon fibre-
containing particulate for feeding to vessel 3.
Vessel 3 contains an aqueous solution. The nylon
fibre-containing particulate fed to vessel 3 is agitated
in the aqueous solution to effect further separation of
nylon fibre from backing material remaining in the
particulate fed to vessel 3. In addition, vessel 3 could
have a pulper or other device to assist in further
comminution or separation of the particulate in vessel 3.
Aqueous solution containing a suspension of the
comminuted carpet material passes from vessel 3 through
vessel outlet 14. Vessel outlet 14 is shown as passing
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in sequence to centrifugal cleaner 4 and screen 5.
However, it is to be understood that vessel outlet 14
could pass to a screen prior to centrifugal cleaner 4
and/or that centrifugal cleaner 4 and screen 5 could be
multiple banks of such cleaners and screens in any
combination and sequence. Centrifugal cleaner 4 and
screen 5 are intended to effect separation of nylon fibre
from carpet backing remaining in the suspension. As noted
above, because the carpet used in the method would
normally be used carpet, it would contain particles of
sand, soil, grit or other material. Such particles would
likely be separated using one or both of centrifugal
cleaner 4 and screen 5.
An example of centrifugal cleaner 4, which is also
known as a hydrocyclone cleaner, is a Posiflow cleaner
which is obtainable from Beloit Jones Division of Beloit
Corporation, Stilton, MASS, U.S.A. Such a cleaner
effects removal of heavy particulate matter as a reject
stream, passing lighter matter through the hydrocyclone
cleaner as an "accept" stream. Thus, if vessel outlet 14
passes to centrifugal cleaner 4, the cleaner is operated
so that centrifugal cleaner outlet 15 contains a higher
proportion of nylon fibre, whereas centrifugal cleaner
reject line 16 contains a higher proportion of other
particulate material, compared to the particulate
material fed to the centrifugal cleaner. It is
understood that centrifugal cleaner reject line 16 could
be fed to other centrifugal cleaners to effect a more
efficient separation of fibre from other material, with
the fibrous material being recycled e.g. to vessel 3 or
centrifugal cleaner 4.
In the embodiment shown in Fig. 1, centrifugal
cleaner outlet 15 passes from centrifugal cleaner 4 to
screen 5. Screen 5 has a mesh size suitable for
separation of nylon fibre from other particulate material
in the feed stream to screen 5. Nylon fibre passes
through screen outlet 17 to de-watering apparatus 6.
Other particulate matter passes from screen 5 to screen
CA 022067~9 1997-06-02
reject line 18. As noted above, a series of screens
could be used, including a series of screens of differing
mesh sizes, generally decreasing in size along the
series.
De-watering apparatus 6 effects a separation of
nylon fibre from aqueous solution. The aqueous solution,
or slurry, being fed to dewatering apparatus 6 should
have a high proportion of nylon fibre, with the solids
content of the slurry preferably being at least 90% nylon
fibre and especially at least 99% nylon fibre. Nylon
fibre passes through de-watering apparatus outlet 19,
whereas aqueous solution separated therefrom would
normally be recycled through water recycle line 20 back
to vessel 3.
Reject streams from any part of the process of the
present invention may be recycled back to the process if
the stream contains sufficient nylon fibre. Otherwise,
it is preferred that the reject streams be fed to
apparatus capable of forming useful products from such
reject streams and/or to recover useful products
therefrom and feed sand and other particu~ate matter to a
waste disposal site.
The aqueous solution in the vessel may contain a
wetting agent to improve the wetting of the fibre and
facilitate movement of the fibre and separation thereof
in the method of the invention. It is understood that
carpets frequently have anti-static, anti-soiling agents
or the like applied thereto, either during the process of
manufacture of the carpet, or subsequent thereto by users
of the carpet in order improve the long term aesthetic
properties of the carpet. Many of such added agents tend
to prevent wetting of the carpet fibres, and addition of
wetting agents to vessel 3 might be necessary in order to
adequately wet the fibre for passage through for example
screens used in the process. In addition, a sanitising
agent may also be added to vessel 3 in order to treat any
bacteria or the like that may be on the fibre.
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.
Screen 5 may be a coarse screen followed by a fine
screen in order to effect separation in a two-stage
manner. The coarse screen would remove larger pieces of
contaminants and/or other material e.g. carpet backing
still in the solution, while allowing nylon fibre to pass
through. As an example, such a screen may be, for
instance, a rotating screen with a mesh size of the order
of 10-12 thousandths of an inch. The fine screen would
be of a finer mesh e.g. a mesh size of 4-6 thousandths of
an inch, and would be used for further cleaning and
separation of contaminant material present with the nylon
fibre. Such a screen may also be a rotating screen.
It is understood that a mixing tank may be placed
between the coarse screen and the fine screen, especially
in that the composition e.g. concentration, also known as
consistency, of the mixture or slurry suitable for
operation of a coarse screen might be different from that
suitable for operation of a fine screen, with the latter
generally requiring a more dilute solution. For
instance, a typical solution fed to a coarse screen may
contain about 1.5-3% w/w of particulate matter, whereas a
typical solution fed to a fine screen may contain about
1% w/w of particulate matter.
The solution passing through screen outlet 17 and
being fed to de-watering apparatus 6 may be fed to an
intervening dynamic washer, which is used to thicken the
slurry i.e. separate water therefrom prior to the
resultant slurry being fed to the de-watering apparatus.
Water separated in such a dynamic washer would normally
be recycled to vessel 3.
In operation of the method illustrated in Fig. 1,
nylon carpet is fed to comminution device 1, normally
being subjected to a shredding operation and then a
grinding operation. In addition to the components of the
nylon carpet, particularly nylon fibre and backing, the
carpet would normally also contain dirt, sand and other
contaminant matter. Comminuted carpet is fed from
comminution device 1 to screen 2 in order to effect a
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primary separation of carpet backing from carpet fibre.
Carpet backing separated by screen 2 could be subjected
to further comminution and recycle to effect separation
of nylon fibre, further screening or other treatment to
separate nylon fibre or fed directly to landfill or
preferably to another process for the manufacture of
useful products. The nylon fibre component passing from
screen 2 is fed to vessel 3, where it is admixed and
possibly comminuted further in aqueous solution. Aqueous
solution with the nylon fibre component in the form of a
slurry passes from vessel 3 and is fed, in the embodiment
illustrated in Fig. 1, to a centrifugal cleaner 4. Heavy
particulate matter is removed in centrifugal cleaner 4,
with the nylon fibre-containing component being fed to
screen 5. As discussed above, centrifugal cleaner 4
could be in the form of a plurality of cleaners in
series. Alternatively, one or more screens 5 could be
inserted prior to centrifugal cleaners 4. In addition,
as discussed above, screen 5 could be in the form of a
coarse screen and a fine screen in series, with matter
e.g. nylon fibre, passing through the fine screen being
fed to the de-watering apparatus. Additional centrifugal
cleaner could be inserted between screen 5 and de-
watering apparatus 6. In addition, dilution tanks could
be inserted in the process before or after centrifugal
cleaner 4 and screen 5 in order to achieve a consistency
of the solution for optimum operation of centrifugal
cleaner 4 and screen 5. The nylon fibre-containing
material passing from screen 5 through screen outlet 17
may be fed to de-water~ing apparatus directly or through a
dynamic washer to effect concentration of the solution
prior to feeding to the de-watering apparatus. De-
watering apparatus 6 would normally be in the form of a
press. Water passing therefrom would normally be
recycled to vessel 3.
Fig. 2 illustrates an embodiment of the part of the
method of the invention involving use of the aqueous
solution. It is understood that carpet would be
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comminuted and screened, as described previously, before
being fed through inlet 30A to vessel 30. In vessel 30,
the comminuted material is contacted and mixed with
water, optionally with wetting or other agents as
described previously. Aqueous solution in the form of a
slurry of comminuted material in water is fed from vessel
30 to centrifugal cleaner 31 in which heavy material is
separated. It is understood the centrifugal cleaner 31
would be operated to pass nylon fibre through the
"accept" outlet, rather than the "reject" outlet. Heavy,
reject, material from centrifugal cleaner 31 is forwarded
to reject outlet 47.
Nylon fibre-containing material is passed from
centrifugal cleaner 31 to coarse screen 32. Material
rejected by coarse screen 32 is passed to reject feed
tank 35, whereas the "accept" of nylon fibre-containing
material is fed to a mixing tank, to adjust the
concentration of the slurry if necessary, before feeding
to fine screen 34. Rejects from fine screen 34 are also
fed to reject feed tank 35. The material in reject feed
tank 35 is fed to reject screen 36. Accepted material
from reject screen 36 is admixed with accepted material
from fine screen 34 and subjected to further processing,
whereas rejected material is fed to reject outlet 47.
The "accept" material from fine screen 34 and reject
screen 36 is fed to dilution tank 37 and then to
centrifugal cleaner 38. Accept material from centrifugal
cleaner 38 is fed to dilution tank 40. Reject material
from centrifugal cleaner 38 is fed through cleaner reject
tank 42 and then to centrifugal cleaner 39. Reject
material from centrifugal cleaner 39 is sent to reject
outlet 47, whereas accept material is fed to dilution
tank 40. Material is fed from dilution tank 40 to
dynamic washer 41. The aqueous solution separated in
dynamic washer 41 is recycled to vessel 30, whereas the
concentrated solution (slurry) passing from dynamic
washer 41 passes to dilution tank 43, for adjustment of
concentration, and then to second dynamic washer 44.
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11
Nylon fibre passing from second dynamic washer 44 passes
to press 45, where it is dried and is sent to nylon fibre
recovery 46. Aqueous solution separated in second
dynamic washer 44 and press 45 is recycled to dilution
tank 40.
The method of Fig. 2 illustrates use of multiple
centrifugal cleaners, screens and dilution tanks, with
recycle of solutions to recover nylon fibre and for reuse
in the system.
In its overall context, the present invention
provides a method of separating nylon fibre from a carpet
without requiring shearing or heating techniques in order
to facilitate such a separation.
