U.S. patent application number 11/569056 was filed with the patent office on 2007-09-13 for lyocell method and device involving the control of the metal ion content.
This patent application is currently assigned to ZIMMER AKTIENGESELLSCHAFT. Invention is credited to Lutz Glaser, Michael Longin, Werner Schumann, Stefan Zikeli.
Application Number | 20070210481 11/569056 |
Document ID | / |
Family ID | 34962732 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070210481 |
Kind Code |
A1 |
Zikeli; Stefan ; et
al. |
September 13, 2007 |
Lyocell Method and Device Involving the Control of the Metal Ion
Content
Abstract
The invention relates to a method and a device for producing
Lyocell fibers, which are extruded from a spinning mass containing
water, cellulose and tertiary amine oxide. The spinning mass is
obtained from cellulose in a number of process steps, wherein a
treatment medium is added to the cellulose, cellulose suspension
and/or cellulose solution. In order to be able to implement a
stable and environmentally compatible spinning method irrespective
of the type of cellulose used, according to the invention,
provision is made that the content of at least one type of metal
ion destabilising the cellulose suspension and/or cellulose
solution is monitored in the cellulose, cellulose suspension and/or
cellulose solution and adjusted below a stability limit. With the
device according to the invention, the metal ion content is
measured via sensors (23, 23') and the metal ion content is
adjusted using a control device (17).
Inventors: |
Zikeli; Stefan; (Regau,
AT) ; Schumann; Werner; (Bad Blankenburg, DE)
; Glaser; Lutz; (Rudolstadt, DE) ; Longin;
Michael; (Vocklabruck, AT) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH, LLP
100 E WISCONSIN AVENUE
Suite 3300
MILWAUKEE
WI
53202
US
|
Assignee: |
ZIMMER AKTIENGESELLSCHAFT
Borsigallee 1
Frankfurt am Main
DE
60388
|
Family ID: |
34962732 |
Appl. No.: |
11/569056 |
Filed: |
March 1, 2005 |
PCT Filed: |
March 1, 2005 |
PCT NO: |
PCT/EP05/02138 |
371 Date: |
January 23, 2007 |
Current U.S.
Class: |
264/176.1 ;
264/165; 264/187; 264/203; 264/40.1; 425/66 |
Current CPC
Class: |
D01D 1/02 20130101; D01F
2/00 20130101; D01D 13/02 20130101 |
Class at
Publication: |
264/176.1 ;
264/040.1; 264/187; 264/203; 264/165; 425/066 |
International
Class: |
D01D 5/06 20060101
D01D005/06; D01F 2/02 20060101 D01F002/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2004 |
DE |
10 2004 024 029.9 |
Claims
1. A method for producing a Lyocell fiber from a spinning mass
containing water, cellulose and tertiary amine oxide, comprising
producing the spinning mass by adding a treatment medium to a
cellulose, to a cellulose suspension, cellulose solution or
combination thereof, wherein the content of at least one type of
destabilizing metal ions in the cellulose, cellulose suspension,
cellulose solution or combination thereof is monitored and adjusted
below a stability limit.
2. The method according to claim 1, wherein the quantity of the
added treatment medium is adjusted in dependence of the content of
the at least one type of destabilizing metal ion.
3. The method according to claim 1, wherein the added treatment
medium is recovered in a following process step.
4. The method according to claim 3, wherein the content of the at
least one type of metal ion is reduced in the treatment medium
during the recovery.
5. The method according to claim 1, wherein a part of the treatment
medium is discharged from the production process and that the
quantity of the discharged treatment medium depends on the content
of at least one type of destabilizing metal ion in the cellulose,
cellulose suspension, cellulose solution or combination
thereof.
6. The method according to claim 1, wherein a fresh treatment
medium is added simultaneously with the recovered treatment
medium.
7. The method according to claim 6, wherein the proportions of
recovered and fresh treatment medium are adjusted in dependence of
the content of the at least one type of metal ion.
8. The method according to claim 1, wherein the treatment medium is
dosed automatically.
9. The method according to claim 1, wherein the treatment medium is
essentially water.
10. The method according to claim 9, wherein the recovered water is
obtained by expressing the cellulose suspension.
11. The method according to claim 9, wherein the recovered water is
obtained from a spinning bath for the extruded spinning mass.
12. The method according to claim 1, wherein the treatment medium
is a tertiary amine oxide.
13. The method according to claim 12, wherein the tertiary amine
oxide is obtained from a spinning bath for the extruded spinning
mass.
14. The method according to claim 1, wherein the at least one type
of destabilizing metal ion comprises iron ions.
15. The method according to claim 1, wherein the at least one type
of destabilizing metal ion comprises copper ions.
16. The method according to claim 1, wherein the content of the at
least one type of destabilizing metal ion is adjusted to below 10
mg/kg.
17. The method according to claim 1, wherein the content of the at
least one type of destabilizing metal ion is adjusted to below 0.5
mg/kg.
18. The method according to claim 1, wherein the stability limit
depends on the at least one type of destabilizing metal ion.
19. The method according to claim 1, wherein the treatment medium
is fed in a section of a shear zone.
20. A device for production of Lyocell fibers, with comprising a
mixing device, in which a cellulose, cellulose suspension,
cellulose solution or combination thereof can be charged with a
treatment medium, at least one sensor, by which the content of at
least one type of metal ion in the cellulose, cellulose suspension,
cellulose solution or combination thereof can be acquired and a
control signal representing the content of the at least one type of
metal ion can be output, and a control device, by which the content
of the at least one type of metal ion in the cellulose, cellulose
suspension, cellulose solution or combination thereof can be
adjusted below a stability limit in dependence of the control
signal.
Description
[0001] The invention relates to a method for producing a Lyocell
fibre from a spinning mass which is produced by adding a treatment
medium to a cellulose, to a cellulose suspension and/or a cellulose
solution.
[0002] The invention also relates to a device for the production of
Lyocell fibers with a mixing device in which a cellulose, a
cellulose suspension and/or a cellulose solution can be charged
with a treatment medium.
[0003] Methods and devices of this kind are known from the Lyocell
technology. With the Lyocell technology threads, fibers, films and
membranes are extruded as endless molded bodies from the spinning
mass containing cellulose, water and tertiary amine oxide. On
account of its environmental friendliness, the Lyocell technology
is increasingly replacing the conventional viscose methods. The
environmental friendliness of the Lyocell method stems from the
solution of the cellulose without derivatisation in an organic,
aqueous solvent. From this cellulose solution endless molded
bodies, for example fibers and film, are then extruded. Through the
extrusion of the molded bodies and the orientation and regeneration
of the cellulose occurring in the course of the extrusion, molded
bodies of high strength are obtained with numerous possible uses in
the textile and non-textile sectors. The name Lyocell was issued by
the BISFA (International Bureau for the Standardisation of Man-made
Fibers). In the state of the art the Lyocell method is now well
documented.
[0004] Consequently, tertiary amine oxides are known as solvents
for cellulose from U.S. Pat. No. 2,179,181 which solvents can
dissolve cellulose without derivatisation. From these solutions,
the cellulose molded bodies solvents can be obtained by
precipitation.
[0005] The processing of the cellulose, dissolved in an aqueous
amine oxide, particularly N-methylmorpholine-N-oxide (NMMNO), is
however problematical with regard to safety, because the degree of
polymerisation of the cellulose decreases when dissolving the
cellulose in NMMNO. In addition, amine oxides generally exhibit
only limited thermal stability, particularly in the system
NMMNO/cellulose/water, and have a tendency to spontaneous
exothermic reaction. To overcome these problems and to be able to
manufacture Lyocell fibers economically, there is a series of
approaches for a solution in the state of the art.
[0006] In U.S. Pat. No. 4,144,080, it is stated that at high
temperatures the cellulose dissolves more quickly in a tertiary
amine-N-oxide and forms a more homogeneous solution if the
cellulose is milled together with the preferred ingredients of
tertiary amine-N-oxide and water. In WO-94/28219, a method for the
production of a cellulose solution is described in which milled
cellulose and an amine oxide solution are added in a horizontal,
cylinder shaped mixing chamber. The mixing chamber exhibits around
its longitudinal axis rotating, axially spaced stirring elements.
Apart from NMMNO, N-methylpiperidine-N-oxide, N-methylpyrrolidone
oxide, dimethylcyclohexylamine oxide and others can be used as the
amine oxide. Mixing in the mixing chamber occurs between 65.degree.
C. and 85.degree. C. According to WO-A-98/005702, the cellulose is
mixed with the aqueous solution of the tertiary amine oxide in a
device, whereby the mixing device exhibits a mixing tool and a
container which rotates during mixing.
[0007] In WO-A-98/005702, the mixing tool is improved such that it
is formed as a paddle, rail or helix and during mixing preferably
prevents the formation of deposits on the inner surface of the
container. In WO-A-96/33934, a buffer device is described, which
comprises a mixing vessel and a conveyor worm as a discharging
device. In this way, a continuous production of the cellulose
solution is facilitated despite the cellulose being fed in
batches.
[0008] The method of WO-A-96/33934 has now been further advanced by
the method of WO-96/33221, in which a homogeneous cellulose
suspension is produced from milled cellulose and an aqueous amine
oxide solution in one single step. For this purpose, the pulverised
cellulose is brought into contact with the liquid, aqueous tertiary
amine oxide and a first mixture is formed. The first mixture is
spread in layers on a surface and transported under intensive
mixing over this surface. This process can be carried out
continuously. Other methods in which the cellulose solution is
treated in the form of a thin layer are also known from
EP-A-0356419, DE-A-2011493 and WO-A-94/06530.
[0009] Also the milling of the cellulose itself is an object of the
patent publications. For example, U.S. Pat. No. 4,416,698 mentions
it as an advantage if the cellulose is milled to a particle size of
less than 0.5 mm. In WO-A-95/11261, preliminarily disintegrated
cellulose is introduced into an aqueous solution of a tertiary
amine oxide to produce a first suspension. This first suspension is
milled subsequently and then converted into a formable cellulose
solution with the application of heat and a reduced pressure. In
order to feed back the dust, arising from milling or pulverising
the cellulose, into the process, filters are used in WO-A-94/28215
through which the cellulose dust is separated from the air. In
WO-A-96/38625, a system is described which can disintegrate both
cellulose bales as well as cellulose in leaf form. An ejection
chute is provided which opens into a device for predisintegrating
the cellulose.
[0010] In EP-B-0818469 it is suggested that cellulose is dispersed
in aqueous amine oxide solutions and the dispersion thus obtained
treated with xylanases.
[0011] Apart from these efforts to economically produce a
homogeneous cellulose solution capable of being spun, there are
also attempts to overcome the problem of the decomposition
phenomena of the cellulose solution which occurs spontaneously
under an exothermic reaction. In Buijtenhuis et al., The
Degradation and Stabilisation of Cellulose Dissolved in NMMNO, in:
Papier 40 (1986) 12, 615-618 test results are described, according
to which metals appear to reduce the decomposition temperatures of
the NMMNO in the cellulose solution. Primarily, iron and copper
appear to speed up the decomposition of NMMNO. Other metals, such
as for example nickel or chrome, also exert a negative influence on
the decomposition properties of the cellulose solution in
appropriate deposits and appropriate concentration, if they are
present in appropriate concentrations. However, in WO-A-94/28210,
stainless steel is still used as the material for a spinning head
in order to withstand the high pressures during the extrusion of
the cellulose solution.
[0012] In DE-T-699 13 117, a different route is followed to obtain
stable cellulose solutions during the production of Lyocell fibers.
The method In this publication does not intervene in the cellulose
processing according to the Lyocell method, but rather during the
production of celluloses for the Lyocell method. According to the
method of this publication, the content of metal ions is reduced to
obtain celluloses with a low portion of transition metals, in
particular with low portions of iron and copper. Certainly, such
celluloses are particularly suitable for cellulose solutions
serving as the basis for the Lyocell method, because they reduce
the risk of decomposition of the NMMNO in the spinning mass during
cellulose processing and spinning in the Lyocell method. However,
with the method according to DE-T-699 13 117 it is still
problematical that celluloses other than those described in the
said publication nevertheless lead to a destabilisation of the
cellulose solution and/or cellulose suspension during fibre
production and a safe Lyocell method without the destabilisation of
the cellulose solution, therefore, can only be ensured with the
exclusive use of the celluloses of DE-T-699 13 117.
[0013] In addition, during the cellulose processing, the system
NMMNO/cellulose/water in the highly concentrated NMMNO region has
the property of releasing metal ions from the process apparatus,
such as lines, filters, and pumps, which reduces the system
stability. In WO-A-96/27035, a method for the production of
cellulose molded bodies is described in which at least some of the
materials in contact with the cellulose solution contain at least
90% of an element from the group of titanium, zirconium, chrome and
nickel down to a depth of at least 0.5 .mu.m. The important aspect
with regard to WO-A-96/27035 is that the rest of the composition of
the apparatus and piping, where it comes into contact with the
cellulose solution, does not contain any copper, molybdenum,
tungsten or cobalt. According to WO-A-96/27035, this measure should
prevent exothermic decomposition reactions.
[0014] Finally, in DE-C-198 37 210, which is taken as the closest
state of the art, a homogeneous cellulose solution is produced
irrespective of the water content of the cellulose used. In
contrast to the current method, here, the cellulose is first
transported in the absence of NMMNO under homogenisation in a
pulper through an initial shear zone and is only then added to a
low water-content NMMNO.
[0015] Another way of producing the cellulose solution is followed
in DE-A-44 39 149 which forms the closest state of the art.
According to the method of DE-A-44 39 149, the cellulose is
pretreated enzymatically. To increase the effectiveness of the
enzymatic pretreatment, the cellulose can be disintegrated under
shearing in water before the pretreatment. Then the pretreated
cellulose is separated from the liquor and the separated cellulose
is introduced into a melt of NMMNO and water. Here practicably, the
separated liquor can be fed back to the pretreatment after
supplementing the water and enzyme losses. However, in practice,
this type of process management has proven to be impracticable,
because the cellulose solution obtained in this way is
unstable.
[0016] Despite these various approaches to obtaining a homogeneous
and stable cellulose solution and to convey it with the avoidance
of exothermic decomposition reactions through to the extrusion
openings, the environmentally friendly and economical production of
a homogeneous cellulose solution and its stability remain
problematical.
[0017] The object of the invention is therefore to improve the
known methods and devices of the Lyocell technology such that, with
the highest level of environmental compatibility, the method can be
carried out independent of the type of cellulose used in a stable
manner and with consistent quality.
[0018] This object is solved for the aforementioned method in that
the content of at least one type of destabilising metal ions in the
cellulose, in the cellulose suspension and/or in the cellulose
solution is monitored and adjusted below a stability limit.
[0019] For the aforementioned device this object is solved
according to the invention in that a sensor, by which the content
of at least one type of destabilising metal ion can be acquired in
the cellulose, cellulose suspension and/or cellulose solution and a
control signal representing the content of at least one type of
destabilising metal ion can be output, and a control device are
provided through which the metal ion content of the cellulose,
cellulose suspension and/or cellulose solution can be adjusted to
below a stability limit in dependence of the control signal.
[0020] The solution according to the invention is simple and
enables any type of cellulose to be used for the spinning mass
during the cellulose processing used in the production of Lyocell
fibers, irrespective of its content of metal ions destabilising the
cellulose suspension and/or cellulose solution, so that it is no
longer necessary to carefully select the cellulose according to its
content of destabilising metal ions, in particular iron (Fe.sup.3+)
and copper (Cu.sup.2+) ions before its processing, or to mix
several types of cellulose. The production of Lyocell fibers
according to the invention eliminates the problem of the cellulose
processing in that only certain cellulose compositions can be used,
which are specially suitable for the Lyocell process and
correspondingly expensive, such as, for example, the celluloses
produced according to the method of DE-T-699 13 117. Moreover, any
celluloses can be used in the course of the Lyocell method, in
particular also celluloses with a high to very high content of
destabilising metal ions, which until now could not or could only
with expensive additional measures be processed, because they have
led to an instable cellulose suspension and/or cellulose solution
with the risk of an exothermic reaction. The main source of the
metal ions which destabilize the cellulose suspension and/or the
cellulose solution appears to be the cellulose itself.
[0021] The method according to the invention and the device
according to the invention can both be used with the Lyocell
method, in which the cellulose is directly pulped in an aqueous
solution of a tertiary amine oxide or in a tertiary amine oxide and
cellulose solution is produced from it, and also with methods in
which initially a cellulose suspension is produced containing
essentially water and cellulose and only then a tertiary amine
oxide or an aqueous solution therefrom is added to form a cellulose
solution.
[0022] The stability limit for the metal ion content is determined
in dependence of the composition of the cellulose suspension and/or
cellulose solution, their temperature and their residence time in
the plant from the pulper through to the extrusion of the Lyocell
fibers. Each type of metal ion can exhibit different high stability
limits. The less a certain type of metal ion destabilizes the
cellulose suspension and/or cellulose solution, the higher the
stability limit can be. Thus, the stability limit, for example, for
copper ions may lie below the stability limit for iron ions due to
their stronger destabilising effect. The stability limit can be
found experimentally in that for samples of cellulose solutions
with different metal ion contents, different temperatures and
different times of exposure, the percentage of samples producing
exothermic reactions is found. This percentage figure is then used
as the probability value for the occurrence of an exothermic
reaction. The stability limit can be defined based on a probability
value of an exothermic reaction which is realistic for the plant
operation. For example, such a probability value may be below 0.01%
or below 1.times.10.sup.-6% so that with the set stability limit an
exothermic reaction is only to be expected with a probability of
0.01% or 1.times.10.sup.-6%.
[0023] The method according to the invention and the device
according to the invention can be further improved in a series of
advantageous embodiments which can be combined with one another as
required.
[0024] Thus, in an especially advantageous embodiment, the quantity
of the treatment medium added to the cellulose, cellulose
suspension and/or cellulose solution is adjusted in dependence of
the content of the at least one type of metal ion. In this way, the
content of the at least one type of metal ion introduced by the
cellulose in the cellulose suspension and/or cellulose solution is
suppressed below the stability limit. A particularly high level of
environmental compatibility and economy of the method can be
achieved in that, in a further development, the added treatment
medium is recovered in a following processing step in the Lyocell
method.
[0025] For example, the water added to a cellulose suspension in
the course of the pretreatment of the cellulose can be returned as
press water from the expressing stage of the cellulose suspension
and be reused when pulping the cellulose. In further embodiments,
this press water can be purified before it is added to the
cellulose and in particular it can be freed at least partially of
metal ions.
[0026] With the direct pulping of the cellulose in amine oxide or
with the addition of amine oxide to the expressed cellulose
suspension, recovered amine oxide can be used, which for example
can be regenerated from a spinning bath through which the freshly
extruded spinning threads are passed and in which the cellulose
precipitates. Also, the recirculated tertiary amine oxide can be
purified and in particular be freed at least partially of the metal
ions it contains before it is added to the cellulose, cellulose
suspension and/or cellulose solution. A commercially available ion
exchanger can be used to remove the metal ions.
[0027] A reduction in the content of destabilising metal ions below
the stability limit, which is particularly simple to implement,
arises when, in the step in which the recycled treatment medium is
added, a fresh, non-recycled treatment medium of the same kind is
added to the cellulose, cellulose suspension and/or cellulose
solution. For example, fresh water, in particular fully desalinated
or partially desalinated fresh water can be fed into the
recirculated press water and/or fresh tertiary amine oxide can be
fed into the recycled tertiary amine oxide. Since fewer
destabilising metal ions are dissolved in the fresh treatment
medium due to the mixing in the cellulose, cellulose suspension
and/or cellulose solution, the content of destabilising metal ions
does not rise too strongly and in particular not above the
stability limit despite the return of the treatment medium. In
addition, through this method, losses of treatment medium, which
are primarily due to the treatment medium remaining in the spinning
threads, can be prevented.
[0028] If, according to a further embodiment, part of the treatment
medium is discharged from the production process and is therefore
no longer available for return within the process, then,
destabilising metal ions are also removed from the process with the
drained off treatment medium. Thus, the content of the
destabilising metal ions in the cellulose suspension and/or
cellulose solution can also be controlled via the quantity of the
discharge of treatment medium which can no longer be returned to
the process. The discharged treatment medium is preferably replaced
by fresh treatment medium. The quantity of discharged treatment
medium depends preferably on the content of destabilising metal
ions in the cellulose, cellulose suspension and/or cellulose
solution so that as much of the treatment medium as possible can be
recycled.
[0029] The metal ion content can be particularly effectively
controlled if the respective proportions of recycled and fresh
treatment medium are adjusted in dependence of the content of the
at least one type of metal ion. If, for example, the content of the
metal ions increases, then the proportion of the recycled and
returned treatment medium and thus the introduction of metal ions
into the cellulose suspension and/or cellulose solution is reduced.
If the metal ion content decreases, then the proportion of the
recycled treatment medium can be increased with respect to the
proportion of the fresh treatment medium.
[0030] The metal ions can be determined by inline sensors, i.e.
sensors, which are arranged in the plant volume through which the
cellulose suspension and/or cellulose solution flows during the
Lyocell production, and/or in an automatic laboratory analysis
device after a manual sampling. In the first case, the signal from
the sensors can be used by a control device for the automatic
dosing of the relative proportion of the recovered treatment medium
and the fresh treatment medium. This type of automatic dosing can,
for example, be implemented by valves operated by actuators. With
manual sampling, the metal ion content can either be passed to a
control device automatically by the automatic laboratory analysis
device or the content of the metal ions can be entered manually
using an input device.
[0031] For the acquisition of metal ions, mass spectrometers,
devices for the measurement of atomic absorption, sensors based on
Raman scattering and devices with graphite tube technology can be
employed.
[0032] Due to the method according to the invention and the device
according to the invention and their various embodiments, which are
independent of one another, it is now possible to process any type
of cellulose irrespective of its content. The metal ion content is
in each case adjusted below the stability limit. The stability
limit is preferably below 10 mg/kg for iron ions and below 0.5
mg/kg for copper ions.
[0033] In the following, an embodiment of the invention is
described as an example with reference to the drawings. The
features of individual advantageous versions of the invention
according to the above embodiments can be combined with one another
as required and also left out. Furthermore, the invention is
documented based on experimental examples.
[0034] In the following,
[0035] FIG. 1 shows an embodiment of a device according to the
invention for the production of a cellulose solution in a schematic
representation, whereby the method according to the invention can
be implemented by the embodiment;
[0036] FIG. 2 shows a schematic representation of the processing
steps for the production of the cellulose suspension;
[0037] FIG. 3 shows a schematic representation of the variation of
the amount of the removed iron ions against time;
[0038] FIG. 4 shows a schematic representation of the chemical
oxygen demand in the press water against time;
[0039] FIG. 5 shows a schematic representation of a first method
for controlling the metal ion content.
[0040] FIG. 1 shows a plant 1 for the production of endless molded
bodies 2, for example strands, out of a spinnable cellulose
solution containing water, cellulose and tertiary amine oxide.
[0041] First, cellulose in the form of leaves or plates 3 and/or
rolls 4 is fed in batches to a pulper 5. In the pulper 5, the
cellulose 3, 4 is disintegrated with water as treatment medium,
symbolically represented by the arrow 6, and a cellulose suspension
is formed, preferably still without solvent or amine oxide. Enzymes
or enzyme solutions can be added for the homogenisation and
Stabilisation of the cellulose suspension.
[0042] The quantity of the added water 6 is determined in
dependence of the water content of the cellulose. Typically the
water content of the cellulose used is between 5 and 15 percent by
mass. This span of variation is compensated by changing the
addition of water appropriately, so that the water content of the
cellulose suspension or the slurry ratio of solids/liquid remains
approximately constant or attains a freely selected value.
[0043] From the pulper 5, the cellulose suspension is passed
through a thick matter pump 7 via a pipe system 8 to a press device
9, whereby the cellulose suspension of water and cellulose is
preferably maintained in a temperature range from 60 to 100.degree.
C.
[0044] In the press device, the cellulose suspension produced by
the pulper 5 is expressed, for example, by rotating rolls 10. The
expressed water or press water 11 is collected by a collecting
device 11' and passed back at least in part as water 6 serving as
treatment medium to the pulper 5 by a conveying means 12, through
an optional filter device 13 and through a mixing device 14. The
press device 9 can also be provided with a suction device (not
shown) for sucking off excess water from the cellulose suspension.
The drawn-off water is, with this embodiment, passed back, as the
press water, at least in part to the pulper 5. For the purposes of
this invention, sucked-off water or water removed from the
cellulose suspension by other means is also press water which can
be reused for the disintegration of the cellulose.
[0045] The filter 13 can comprise one or more surface filters,
deep-bed filters, membrane filters, plate filters, edge filters,
separators, centrifuges, hydrocyclones, belt filters and vacuum
belt filters, tube filters, filter presses, rotating filters,
reversible-flow filters and multilayer filters. In addition, the
press water 11 can be osmotically treated in the filter 13;
alternatively or additionally, metal ions and particles can be
filtered out of the press water 11 or metal-binding additives can
be fed to the press water 11.
[0046] The respective proportions of the returned treatment medium
11 and of fresh treatment medium 15 fed from another fresh source,
for example fresh water, in the water passed to the pulper are set
by the mixing device 14. In addition, the proportion of the
treatment medium 11, which is passed out of the plant 1 through a
waste water pipe 16, is set by the mixing device 14.
[0047] The mixing device 14 can for example comprise a selector
valve or a number of valves. The mixing device 14 is controlled by
a control device 17 such that the proportions of the press water 11
and the fresh water 15 in the water 6 fed to the pulper 5 can be
set to variably specifiable values by an output signal from the
control device via at least one control line 18.
[0048] After expressing, the cellulose suspension is transported
further through the pipe system 8 to a stirring and conveying means
19 in which a shear stress acting on the cellulose suspension is
generated by a stirring or conveying tool 20, such as a screw,
paddle or blade. For the stirring and conveying means 19, no
annular layer mixers can be employed, such as originating from
DRAIS Misch- and Reaktionssysteme and sold under the designation
CoriMix.RTM.. The annular layer mixers are only used for moistening
or impregnating dry cellulose materials which are not used in the
method described here.
[0049] In the region of the shear stresses of the stirring and
conveying means 19, in the so-called shear zone, a treatment medium
such as tertiary amine oxide, in particular
N-methylmorpholine-N-oxide, is passed in aqueous form via a pipe 21
to the cellulose suspension with a molar ratio NMMNO/H.sub.2O of
between 1:1 and 1:2.5 as solvent for the cellulose. In addition, in
the shear zone, additives such as stabilizers and enzymes, organic
additives, delustering substances, alkalis, solid or liquid
alkaline earth, zeolites, finely pulverised metals such as zinc,
silver, gold, platinum for the production of anti-microbial and/or
electrically or thermally conducting fibers during and after the
spinning process and/or dyes can be added to the cellulose
suspension. The concentration of the additives can be controlled in
the range from 100 to 100,000 ppm referred to the fibre
product.
[0050] The concentration of the fed NMMNO depends on the water
content of the celluloses 3, 4 currently in the cellulose
suspension. The stirring and conveying means 19 acts as a mixer in
that the tertiary amine oxide is mixed with the cellulose
suspension and the cellulose solution is produced. Then, the
cellulose solution to which NMMNO has been added is transported via
the pipe system 8 to a second stirring and conveying means 22. The
stirring and conveying means 22, can comprise a vaporization stage.
From the stirring and conveying means 22 the pipe system can be
heated. In contrast to the unheated pipe system 8, the heated pipe
system in FIG. 1 is given the reference symbol 8'. In particular a
pipe system can be used, as described in WO 01/88232 A1, WO
01/88419 A1 and WO 03/69200 A1.
[0051] After the addition of the tertiary amine oxide, the metal
ion content of the cellulose solution, in particular copper and
iron ions, in the pipe 8' and/or in at least one of the shear zones
19, 22, or before and/or after one of the shear zones is measured
using the sensors 23, 23' and a signal representing the metal
content or the content of individual destabilising metal ions, such
as iron, chrome, copper and/or molybdenum is output to the control
device 17. Alternatively or in addition to an automatic inline
sampling, the metal ion content can, in a further embodiment, be
determined using wet-chemical methods after manual sampling in an
automatic laboratory analysis device and passed on from there to
the control device 17 automatically or manually. However, with a
manual sample extraction compared to the automatic inline sample
extraction directly from the pipe systems 8, 8', there is the
disadvantage that the feedback to the controller for the metal ion
content contains a manual process stage and cannot therefore be
automated.
[0052] The control device 17 compares the metal ion content
measured by the sensors 23, 23' with predetermined limits and
outputs a signal depending on this metal ion content to the mixing
device 14. Due to the control signal to the mixing device 14, the
composition of the water 6 passed as treatment medium to the pulper
5 is set in dependence of the content of the destabilising metal
ions in the cellulose solution and the metal content or the content
of individual metal ions in the cellulose solution to which
tertiary amine oxide has been added is regulated under closed-loop
control to a predetermined value. Since the concentration of
reactions in the cellulose solution increases after the
vaporization stage, preferably a sensor is provided which monitors
the metal content of the cellulose solution after the addition of
all ingredients and after all the vaporization stages.
[0053] If, for example, the content of destabilising metal ions in
the cellulose solution, as acquired by the sensors 23, 23' or by
using wet-chemical methods, is too high, then the proportion of
fresh water in the water 6 fed to the pulper 5 is increased.
Thereby, the metal content is adjusted by the control device 17
such that it remains below a stability limit of 10 mg/kg. The metal
content can also be determined before the formation of the
cellulose solution, i.e. still in the cellulose suspension, whereby
this measurement is more appropriate than the measurement of the
metal content directly in the cellulose solution.
[0054] As sensors 23, 23', devices for atomic absorption
measurement, mass spectrometers, optical detectors for the
acquisition of fluorescence spectra, emission spectra or Raman
scattering can be used. These types of sensors are known and are
produced by various manufacturers, e.g. Perkin Elmer.
[0055] During the control of the composition of the water 6, the
control device 17 takes into account the previously determined
metal content of the cellulose 3, 4 passed to the pulper 5. In this
respect, the analyzed metal content of individual metal ions or the
complete content of metal in the cellulose 3, 4 just used can be
entered into the control device 17 via an input device 24. This
preadjustment is taken into account in the determination of the
proportions of the press water and fresh water in the water fed to
the pulper 5. For example, with cellulose containing a high metal
content, a higher proportion of fresh water 15 is passed to the
pulper 5 at the start or certain metal-binding additives are mixed
into the cellulose suspension.
[0056] If the metal content decreases, as it is acquired by the
sensors 23, 23' in the cellulose solution to which tertiary amine
oxide has been added, below a certain limit which is taken as
sufficient for protection against exothermic reactions, for example
10 mg/kg, then the proportion of press water in the water passed to
the pulper 5 is increased. Consequently, with sufficient protection
against exothermic reactions, less fresh water is consumed and less
press water is discharged to the environment.
[0057] After the stirring or conveying means 22, the now extrudable
cellulose solution is passed to an extrusion head 25 which is
provided with a large number of extrusion openings (not shown). The
highly viscous cellulose solution is extruded into an air gap 26
through each of these extrusion openings to give in each case an
endless molded body 2. An orientation of the cellulose molecules
occurs due to a drawing of the cellulose solution which is still
viscous after the extrusion. To achieve this, the extruded
cellulose solution is drawn away from the extrusion openings by a
drawing device 27 with a speed which is greater than the extrusion
speed.
[0058] After the air gap 26, the endless molded bodies 2 pass
through a precipitation bath 28 containing a liquid such as water
which is a non-solvent, whereby the cellulose in the endless molded
bodies 2 is precipitated. In the air gap 26, the endless moulded
bodies 2 are cooled by a cooling gas flow 29. Here, in contrast to
the theory given in WO 93/19230 A1 and EP 584 318 B1, it has been
found substantially more advantageous if the cooling gas flow does
not emerge directly after the exit of the endless molded bodies 2
from the nozzle, but rather first at a distance from the nozzle
onto the endless molded bodies 2. In order to achieve the best
fibre properties, the cooling gas flow should be turbulent and
exhibit a velocity component in the extrusion direction, as
described in WO 03/57951 A1 and in WO 03/57952 A1.
[0059] The precipitation bath 28 becomes increasingly enriched with
tertiary amine oxide so that it must be continually regenerated by
means of a recovery device 30. In this respect, the liquid from the
precipitation bath is fed during operation to the recovery device
30 via a pipe 31, which for example is connected to an overflow of
the precipitation bath. The recovery device 30 extracts the
tertiary amine oxide from the liquid and returns pure water via a
pipe 32. Non-reusable waste substances are discarded from the
device 1 via a pipe 33 for disposal.
[0060] In the recovery device 30, the amine oxide is separated from
the water and fed via a pipe 34 to a further mixing device 35 to
which fresh amine oxide is also fed by a pipe 36. The regenerated
amine oxide from the pipe 34 is mixed with the fresh amine oxide 36
and fed to the shear zone 19 via the pipe 21.
[0061] Metal ions can be removed from the regenerated amine oxide
via an ion exchanger, for example from Rohm and Haas, Amberlite GT
73, or via a filter 37.
[0062] The mixing device 35 and the purification device 37 can be
controlled by the control device 17 in dependence of the metal ion
content measured by the sensors 23, 23'.
[0063] Then, the endless moulded bodies are treated further, for
example washed, brightened, chemically treated in a device 38 to
influence the cross-linking properties, and/or dried and pressed
out further in a device 39. The endless moulded bodies can also be
processed by a cutting device, which is not shown, to form staple
fibers and passed out of the device 1 in fleece form.
[0064] The overall conveyance of the cellulose solution in the pipe
system 8' occurs continuously, whereby buffer containers 40 can be
provided in the pipe system 8' to compensate variations in the
conveyed amount and/or of the conveying pressure and to facilitate
continuous processing without dead water regions arising. The pipe
system 8' is equipped with a heating system (not shown) to maintain
the cellulose solution during conveyance at a temperature at which
the viscosity is sufficiently low for an economical transport
without decomposition of the tertiary amine oxide. The temperature
of the cellulose solution in the pipe section 8' is here between 75
and 110.degree. C.
[0065] At the same time, the homogenisation and uniform mixing,
which can be increased by static or rotating mixers, is promoted by
the high temperature.
[0066] The residence time of the cellulose suspension or solution
in the pipe system 8, 8' from the thick matter pump 7 to the
extrusion head 25 is between 5 minutes and 2 hours, preferably
about 30 to 60 minutes.
[0067] The implementation of the method according to the invention
is now described based on experimental examples.
[0068] In the following, values are used for the quantity which
have been scaled to the amount of introduced cellulose.
[0069] A first series of experiments deals with the cellulose
pretreatment for the production of the cellulose suspension and the
examination of the press water. In the following, reference is made
to the schematic representation of the pretreatment in FIG. 2, and
furthermore the reference symbols of FIG. 1 are used.
EXPERIMENTAL EXAMPLE 1
[0070] In a process step A, cellulose 3, 4 (cf. FIG. 1) of the type
MoDo Dissolving Wood Pulp, pine sulphite wood pulp, was placed in a
pulper 5 from the company Grubbens with a net filling volume of 2
m.sup.3 with water 6 in a mixing ratio of 1:17 (solids density
5.5%). The cellulose exhibited a Cuoxam DP 650 and an
.alpha.-cellulose content greater or less than 95%. Commercially
available celluloses based on hardwood or softwood can be used.
Hemicellulose contents in the cellulose in the range from 2 to 20%
can also be treated in the process. Other possible celluloses are
Sappi Eucalyptus, Bacell Eucalyptus, Tembec Temfilm HW, Alicell VLV
and Weyerhauser .alpha.-cellulose of less than 95%. The fed water 6
consisted of 30 parts of fully desalinated fresh water 15 and 70
parts of press water.
[0071] Under vigorous stirring, technically pure formic acid 50 in
the ratio of 1:140 and a liquid enzyme preparation 51 in the ratio
1:200, referred in each case to the cellulose content, were added.
An enzymatic pretreatment was then carried out for a duration of
about 35 minutes until a homogeneous cellulose suspension was
obtained. A cellulase enzyme complex, such as for example
Cellupract.RTM. AL 70 from Biopract GmbH or Cellusoft from Novo
Nordisk, can be used as the enzyme preparation 52.
[0072] Then, the pretreatment was terminated in a process step B by
the addition of sodium hydroxide solution 52 in the ratio of 1:500
referred to the cellulose content of the cellulose suspension in
the pulper 5.
[0073] The cellulose suspension was then dewatered in a process
step C in a vacuum belt filter acting as press means 9 with
following expressing system from the company Pannevis to about 50%,
so that the expressed cellulose exhibited a dry content of about
50%. From step C, the expressed cellulose was then passed on via
the pipe 8 for production of a cellulose solution containing NMMNO,
water and cellulose. These steps are not shown in FIG. 2 for the
sake of clarity.
[0074] The press water was collected in the press means 9 and let
off via the pipe 11 (cf. FIG. 1). Approximately 75% of the press
water was fed back to the pulper 5 and about 25% of the press water
was passed via the pipe 16 to a waste water purifier.
[0075] The degree of polymerisation of the cellulose was always
selected such that a DP (degree of polymerisation) of about 450 to
about 550 was obtained in the spinning solution. The cellulose
concentration was set to about 12% in the spinning solution.
[0076] The press water remaining in the system 1 was again mixed in
a mixing device 14 (cf. FIG. 1) in a process step D with the fully
desalinated water, as described above.
EXPERIMENTAL EXAMPLE 2
[0077] In another experiment all the steps of Experimental Example
1 were repeated, except that in process step A the quantity of the
added enzyme preparation was reduced to 1:125 referred to the
cellulose content of the cellulose suspension.
EXPERIMENTAL EXAMPLE 3
[0078] In another experiment the steps of Experimental Examples 1
and 2 were repeated, except that in process step A no enzyme
preparation was added.
RESULTS OF THE EXPERIMENTAL EXAMPLES 1 TO 3
[0079] To verify the effectiveness of the method according to the
invention, the press water collected during the expressing stage
was analyzed for the copper and iron ion content and additionally
the chemical oxygen demand was determined.
[0080] As a result of this experiment it can be recorded that, due
to the circulation of a part of the press water, the acquired
values of the ingredients increase in the first pulp cycles.
However, since a part of the press water with the dissolved
ingredients is permanently transferred out, a steady state is
reached after some time in which the amount of substances
contained, in particular the metal ions, remains constant.
[0081] In total about 10% of the iron ions introduced by the
cellulose 3, 4 and about 40% of the copper ions introduced by the
cellulose was removed by the press water feedback. In continuous
plant operation, with the return of the press water, the percentage
proportion of the iron extracted from the system 1 should be
between 22% and 35% referred to the quantity of iron introduced by
the cellulose.
[0082] FIG. 3 gives a schematic temporal progression of the iron
ion extraction.
[0083] The stable final state of the system 1 is achieved, as
Experimental Examples 1 to 3 show, independent of the amount of
enzyme introduced for the pretreatment of the cellulose.
[0084] This is also confirmed by the temporal progression of the
chemical oxygen demand (COD), as illustrated in FIG. 4. The
chemical oxygen demand was determined in the press water according
to DIN 38409 and approximates to a constant value with increasing
duration of the press water feedback.
[0085] Furthermore, in the cellulose solutions obtained according
to Experimental Examples 1 to 3, the degree of polymerisation and
therefrom the DP reduction as well as the onset temperature of the
spinning solution were determined as indicators of stability. The
results of the experimental examples are shown in Table 1.
TABLE-US-00001 TABLE 1 Experimental DP reduction T.sub.onset
Example [%] .degree. C. 1 27.5 165 2 27 165 3 9 160
[0086] As shown in Table 1, the cellulose solution obtained through
press water feedback is stable and exhibits an onset temperature of
at least 160.degree. C. According to experiments, with this method
an onset temperature of at the most 147.degree. C. is actually
obtained. The onset temperature according to Table 1 using the
method according to the invention with press water feedback also
lies above the onset temperature as obtained with the method of WO
95/08010 and which in practice is about 150.degree. C.
[0087] Based on these investigations it can be seen that despite
the press water feedback, the onset temperatures still lie above
the onset temperatures for the dry processing of cellulose and can
be increased by an enzymatic pretreatment of the cellulose. This
means that the press water feedback is suitable for industrial
use.
[0088] In another series of experiments, the effect of the
substances contained in the press water on the stability of the
cellulose solution was investigated. To achieve this, a concentrate
of 5 l of press water in the ratio 1:270 was added to the cellulose
solution in each of the Experimental Examples 1 and 3 and feedback
of the press water was omitted.
[0089] In both cases, once according to the method of Experimental
Example 1 without enzymatic pretreatment and once according to the
method of Experimental Example 3 with enzymatic pretreatment, a
reduction of the onset temperature to about 141.degree. C. occurred
in each case due to the press water concentrate. Thus, it is
demonstrated that the press water fundamentally reduces the
stability of the cellulose solution.
[0090] This destabilisation of the cellulose solution can however
be prevented by discharging the treatment medium with destabilising
ions. The proportion of the treatment medium fed back depends on
the type of cellulose used, as shown in the following table.
[0091] The iron and copper content as well as the overall metal ion
content of the cellulose varied noticeably with the various types
of cellulose, as can be seen from Table 2. The metal content of the
various types of cellulose was determined by incineration in the
platinum crucible according to DIN EN ISO 11885 (E22) and with
flame AAS. TABLE-US-00002 TABLE 2 Used cellulose Substances
contained Cellulose Cellulose Cellulose Cellulose Cellulose
Cellulose Cellulose Cellulose in cellulose 1 mg/kg 2 mg/kg 3 mg/kg
4 mg/kg 5 mg/kg 6 mg/kg 7 mg/kg 8 mg/kg Fe 1.3 2.0 1.6 5.8 2.2 2.6
14 13 Mn <0.3 <0.1 0.2 0.33 n.d. <0.3 0.4 <0.3 Mg 2 2
226 32 138 2 21 7.8 Co 0.3 <0.3 <0.3 <0.3 <0.3 <0.3
<0.3 <0.3 Ca 54 4 37 64 30 6 130 27 Cr <0.3 <0.3 1.4
<0.3 <0.3 0.4 <0.3 <0.3 Mo <0.3 <0.1 <0.1
<0.1 <0.3 <0.3 <0.3 <0.3 Ni <0.3 <0.3 <0.3
<0.3 <0.3 <0.3 <0.3 <0.3 Cu 0.3 <0.2 0.2 <0.3
<0.3 <0.3 0.3 0.3 Na 396 48 93 92 263 176 335 8.2
[0092] In a final series of experiments, the schematic experimental
set-up of FIG. 5 was carried out. In FIG. 5, the reference symbols
of FIGS. 1 and 2 are used for elements with similar or the same
function.
[0093] With the set-up in FIG. 5, the amount of press water
returned to the pulper 5 was adjusted to the iron and copper
content of the expressed cellulose.
[0094] With the arrangement of FIG. 5, the iron ion and copper ion
content was measured as representative values for the metal ion
content by the sensors 23, 23' (cf. FIG. 1).
[0095] Due to the control of the proportion of the press water in
the water 6 fed to the pulper 5, the iron concentration was
maintained as closely as possible below 10 mg/kg absolutely dry and
the copper concentration just below 0.5 mg/kg absolutely dry. These
values were possible for an adequate stability of the cellulose
solution in the pipe 8 with simultaneous maximum retention of the
press water within the system 1 and consequently with minimum
outward transfer of the press water 16 from the system 1.
[0096] The control of the metal ion content occurred in such a way
that if one of these two limits was exceeded, the amount of press
water outwardly transferred from the system 1 and passed on for
waste water purification was increased by opening a valve 58. At
the same time, closure of the valve 59 reduced the proportion of
press water fed back in the pretreatment stage.
[0097] If a direct pulping of the cellulose 3, 4 occurs in amine
oxide, then the setting of the metal ion content according to the
invention can also be achieved via the tertiary amine oxide
recovered from the spinning bath 28. In this respect, the degree of
purification at the metal ion filter 37 and/or the proportion of
the tertiary amine oxide 36 freshly added to the regenerated
tertiary amine oxide 34 can be set in dependence of the metal ion
content as measured by the sensors 23 and 23', as well as in
dependence of the metal ion content previously found in the
cellulose 3, 4. The control functions similarly as with the press
water feedback.
[0098] In a modification of the method described in FIG. 1, water
from the spinning bath 28 recovered in the recovery device 30 can
be returned to the pulper 5 instead of or together with the press
water.
[0099] The metal ion filter 37, as it is used for the recovery of
the tertiary amine oxide from the spinning bath 28, can of course
also be used for the purification of the returned press water.
* * * * *