U.S. patent application number 11/569061 was filed with the patent office on 2008-02-28 for lyocell method comprising an adjustment of the processing duration based on the degree of polymerization.
This patent application is currently assigned to ZIMMER AKTIENGESELLSCHAFT. Invention is credited to Michael Longin, Stefan Zikeli.
Application Number | 20080048358 11/569061 |
Document ID | / |
Family ID | 34960921 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080048358 |
Kind Code |
A1 |
Zikeli; Stefan ; et
al. |
February 28, 2008 |
Lyocell Method Comprising an Adjustment of the Processing Duration
Based on the Degree of Polymerization
Abstract
The invention relates to a method and a device for producing
Lyocell fibres which are extruded from a cellulose solution of
water, cellulose and tertiary amine oxide in a spinning head (25).
The cellulose solution is obtained in a number of process steps
directly from the cellulose (3, 4) or with the formation of a
cellulose suspension. Since the degree of polymerisation decreases
in the course of processing the cellulose through to its extrusion
in the cellulose solution, with the processing of celluloses with a
low degree of polymerisation there is the risk that the endless
moulded bodies (2) extruded in the spinning head (25) exhibit
defective quality. In order to also be able to process celluloses
(3, 4) with a low degree of polymerisation without having to accept
reduced quality, according to the invention, the residence time of
the cellulose from its introduction into the device (1) through to
the extrusion of the cellulose (3, 4) in the cellulose solution is
set in dependence of the degree of polymerisation of the cellulose,
of the cellulose suspension and/or of the cellulose solution.
Inventors: |
Zikeli; Stefan; (Regau,
AT) ; Longin; Michael; (Vocklabruck, AT) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Assignee: |
ZIMMER AKTIENGESELLSCHAFT
Frankfurt am Main
DE
|
Family ID: |
34960921 |
Appl. No.: |
11/569061 |
Filed: |
February 28, 2005 |
PCT Filed: |
February 28, 2005 |
PCT NO: |
PCT/EP05/02088 |
371 Date: |
January 23, 2007 |
Current U.S.
Class: |
264/211.24 ;
425/113; 425/200 |
Current CPC
Class: |
B29C 48/92 20190201;
D01D 1/02 20130101; C08B 1/003 20130101; B29C 2948/92904 20190201;
D01D 5/06 20130101; B29B 7/905 20130101; B29C 2948/92314 20190201;
B29C 48/919 20190201; B29C 48/05 20190201; B29C 2948/92409
20190201; D01F 2/00 20130101; B29C 2948/92809 20190201 |
Class at
Publication: |
264/211.24 ;
425/113; 425/200 |
International
Class: |
D01F 2/24 20060101
D01F002/24 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2004 |
DE |
10 2004 024 030.2 |
Claims
1. A method for producing Lyocell fibers comprising a cellulose
with a predetermined degree of polymerization is introduced
producing a cellulose solution, or initially a cellulose suspension
and from this then the cellulose solution, from the cellulose with
the addition of a treatment medium; extruding the cellulose
solution to form endless molded bodies; monitoring the degree of
polymerization of the cellulose, the cellulose suspension, the
cellulose solution or combination thereof; and setting the
residence time of the cellulose from its introduction through to
its extrusion dependence of the measured degree of
polymerization.
2. The method according to claim 1, wherein the cellulose
suspension is subjected to an enzymatic pretreatment.
3. The method according to claim 2, wherein the duration of the
enzymatic pretreatment is adjusted in dependence of the degree of
polymerization of the introduced cellulose.
4. The method according to claim 3, wherein the enzymatic
pretreatment for a cellulose with a lower degree of polymerization
is carried out over a shorter time than for a cellulose with a
higher degree of polymerization.
5. The method according to claim 2, wherein the enzymatic
pretreatment is set between 20 minutes and 80 minutes.
6. The method according to claim 2, wherein for the enzymatic
pretreatment at least one cellulase enzyme complex is added to the
cellulose suspension.
7. The method according to claim 1, wherein the cellulose solution
is conveyed through a heated pipe system for extrusion and that the
conveying speed of the cellulose solution in the pipe system is set
in dependence of the degree of polymerization.
8. The method according to claim 7, wherein during the processing
of a cellulose with a lower degree of polymerization in the
cellulose solution the conveying speed of the cellulose solution is
set higher than the conveying speed during the processing of a
cellulose in the cellulose solution with a higher degree of
polymerization.
9. The method according to claim 1, wherein the residence duration
of the cellulose from its introduction through to its extrusion in
the cellulose solution is at most two hours.
10. The method according to claim 1, wherein the residence time of
the cellulose from its introduction through to its extrusion in the
cellulose solution is at least five minutes.
11. The method according to claim 1, wherein the conveying speed of
the pump arrangement conveying the cellulose suspension, the
cellulose solution or combination thereof is set in dependence of
the degree of polymerization in the cellulose, the cellulose
suspension, the cellulose solution or combination thereof.
12. The method according to claim 1, wherein the degree of
polymerization of the cellulose solution shortly before the
extrusion is set to a DP value of at least 450 DP to 550 DP.
13. The method according to claim 1, wherein the duration of an
enzymatic pretreatment of the cellulose is set such that its DP
value is at least 500 immediately after termination of the
enzymatic pretreatment.
14. The method according to claim 1, wherein the power of an
agitating machine is monitored as a representative quantity for the
degree of polymerization of the cellulose suspension.
15. A device for the production of Lyocell fibers, comprising a
mixing device, to which a cellulose can be fed and in which a
cellulose solution directly or with the formation of a cellulose
suspension can be processed with the addition of a treatment
medium, a spinning head through which the cellulose solution can be
extruded to form endless molded bodies, a conveying device through
which the cellulose suspension cellulose solution or combination
thereof can be conveyed from the mixing device to the spinning
head, a monitoring device, through which a degree of polymerization
of the cellulose, of the cellulose suspension, of the cellulose
solution or combination thereof can be monitored during the
operation of the device, and a control device, through which the
processing duration from the introduction of the cellulose through
to the extrusion in the spinning head can be set in dependence of
the measured degree of polymerization.
16. The device according to claim 15, wherein the conveying
capacity of the conveying device is designed to be controlled by
the control unit in dependence of the degree of polymerization.
17. The device according to claim 15, wherein a sensor is provided
through which the power of an agitating machine can be monitored.
Description
[0001] The invention relates to a method of producing Lyocell
fibres, in which a cellulose is introduced with a predetermined
degree of polymerisation, and from the cellulose, with the addition
of a treatment medium, a cellulose solution or initially a
cellulose suspension and from this then the cellulose solution is
produced, and in which the cellulose solution is extruded to form
endless moulded bodies.
[0002] The invention also relates to a device for the production of
Lyocell fibres with a mixing device to which a cellulose can be fed
and in which a cellulose solution, with the addition of a treatment
medium, directly or with the formation of a cellulose suspension
can be processed, with a spinning head, through which the cellulose
solution can be extruded to form endless moulded bodies, and with a
conveying device, through which the cellulose suspension and/or the
cellulose solution can be conveyed from the mixing device to the
spinning head.
[0003] These types of methods and devices are known from the
Lyocell technology. With the Lyocell technology threads, fibres,
films and membranes are extruded as endless moulded bodies from the
spinning mass containing cellulose, water and tertiary amine oxide.
Due to its environmental compatibility, the Lyocell technology is
increasingly replacing the conventional viscose methods. The
environmental compatibility of the Lyocell method is based on the
solution of the cellulose without derivatisation in an organic,
aqueous solvent. From this cellulose solution endless moulded
bodies are extruded, for example fibres and films. Through the
extrusion of the moulded bodies and the orientation and
regeneration of the cellulose in the course of the extrusion
moulded bodies of high strength are obtained with versatile
possible uses in the textile and non-textile sector. The name
Lyocell was issued by the BISFA (International Bureau for the
Standardisation of Man-made Fibres). In the state of the art, the
Lyocell method is now well documented.
[0004] Tertiary amine oxides are known as solvents for cellulose
from U.S. Pat. No. 2,179,181 which can dissolve cellulose without
derivatisation. From these solutions, the cellulose moulded bodies
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 on dissolving the cellulose in
NMMNO decreases. 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 fibres economically, there is a series of
methods for 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 together with the preferred ingredients of tertiary
amine-N-oxide and water is milled. 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 placed in a horizontal,
cylindrical mixing chamber. The mixing chamber exhibits axially
spaced stirring elements that are rotating around its longitudinal
axis. Apart from NMMNO, N-methylpiperidine-N-oxide,
N-methylpyrolidone 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 in a device with the aqueous
solution of the tertiary amine oxide, 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 conveying screw 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 been further developed by
the method of WO-96/33221, in which a homogeneous cellulose
suspension is produced from pulverised 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 in this
way. 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 pulverisation of the cellulose itself is an object
of 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, prepulverised
cellulose is introduced into an aqueous solution of a tertiary
amine oxide to produce a first suspension. This first suspension is
then milled and 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 pulverise both cellulose bales as
well as cellulose in leaf form. For this purpose, an ejection
hopper is provided which opens into a device for prepulverising 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 occur 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, investigation 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
occurrence 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 addition, 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 moulded 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.
[0013] 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 current methods, here the cellulose is first
transported through an initial shear zone in the absence of NMMNO
under homogenisation in a pulper and is only then added to a low
water-content NMMNO.
[0014] 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 before
the pretreatment under shearing in water. Then, the pretreated
cellulose is separated from the liquor and the separated cellulose
is introduced into a melt of NMMNO and water. Hereby, the separated
liquor can practicably 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.
[0015] Despite these various approaches to obtaining a homogeneous
and stable cellulose solution and to convey it through to the
extrusion openings, while avoiding exothermic decomposition
reactions, the environmentally friendly and economical production
of a homogeneous cellulose solution and its stability remain
problematical. Furthermore, it is problematical that the cellulose
solution ages, which is expressed in an increasing reduction in the
degree of polymerisation with time. With some celluloses which are
supplied with already a low degree of polymerisation and are
processed to form a spinning mass, ageing may lead to unacceptable
reductions in quality.
[0016] The object of the invention is therefore to improve the
known methods and devices of the Lyocell technology such that, with
the highest environmental compatibility, the method can be
implemented independent of the type of cellulose used in a stable
manner and with consistently constant quality.
[0017] This object is solved for the aforementioned method in that
the degree of polymerisation of the cellulose, the cellulose
suspension and/or the cellulose solution is monitored and that, in
dependence of the determined degree of polymerisation, the
residence period of the cellulose from its introduction to its
extrusion is set.
[0018] For the aforementioned device, this object is solved
according to the invention by a monitoring device, through which a
degree of polymerisation of the cellulose, the cellulose suspension
and/or the cellulose solution can be monitored during the operation
of the device, and by a control device, through which the
processing duration from the introduction of the cellulose to its
extrusion in the spinning head can be set in dependence of the
measured degree of polymerisation.
[0019] The solution according to the invention is simple and
enables any type of cellulose to be used in the production of
Lyocell fibres irrespective of its degree of polymerisation. Due to
the control, according to the invention, of the processing or
residence duration of the cellulose from its pulping through to its
extrusion to give endless moulded bodies, a uniform quality of the
Lyocell fibres is obtained irrespective of the degree of
polymerisation of the processed cellulose. Since additionally, the
degree of polymerisation is monitored according to the invention
during the processing of the cellulose, it is no longer necessary
to only process carefully selected celluloses. According to the
invention, any cellulose can now be processed, because a change of
the degree of polymerisation in the cellulose, the cellulose
suspension and/or the cellulose solution during the processing can
be acquired and the processing duration adapted accordingly.
[0020] 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 first
a cellulose suspension is produced containing essentially water and
cellulose and only then is a tertiary amine oxide or an aqueous
solution of it added to form a cellulose solution.
[0021] In an advantageous embodiment of the method according to the
invention, the cellulose or the cellulose suspension is subjected
to an enzymatic pretreatment. In the course of the enzymatic
pretreatment a liquid enzyme preparation can, for example, be added
in the ratio of 200:1 referred to the cellulose content. As the
liquid enzymatic preparation, a cellulase enzyme complex, for
example Cellupract AL70 from the company Biopract GmbH, or
Cellusoft from the company Novo Nordisk, can be used. To prevent a
too strong reduction in the degree of polymerisation, in particular
when celluloses with low initial degrees of polymerisation are
processed to form Lyocell fibres, in an advantageous embodiment the
duration of the enzymatic pretreatment can be set in dependence of
the degree of polymerisation of the introduced cellulose. In
addition, the degree of polymerisation can also be monitored during
the enzymatic pretreatment and the duration of the enzymatic
pretreatment can be shortened if the degree of polymerisation is
strongly reduced. The enzymatic pretreatment can be carried out in
a pulper.
[0022] In order to monitor the polymerisation decomposition in an
agitating machine, in particular during the production of the
cellulose suspension and/or during the enzymatic pretreatment, the
known parameters (Newton's number, Reynold's number, Froude's
number) in the agitating technology can first be determined.
Furthermore, the concentrations, temperatures, mixing times and the
mixing quality can be accurately observed and determined in order
to obtain information about the decomposition behaviour during the
formation of the emulsion or suspension. The temperature control
can be carried out via temperature measurement devices, e.g. of
type Pt100. The exact concentration can be set using continuous
flow measurement devices for the emulsion or suspension agent. The
cellulose can be accurately measured using a differential dosage
weighing system and similarly continuously charged.
[0023] The suspension criteria, such as filling level, agitation
duration and concentration of the emulsion/suspension particles
over the container height can be determined by the insertion of a
measurement sampling lance into the suspension vessel or pulper or
into the agitating machine and by the sampling of suspended
material. It has been found to be particularly advantageous if the
form of the bottom of the suspension vessel is realised as a dished
or spherical bottom.
[0024] An impeller agitator is preferably used as the stirring
element. However, propellers, inclined blade mixers, disc mixers,
toothed stirrers, anchor stirrers as well as spiral stirrers or
coaxial agitating machines can also be used. The shaft of the
stirring machine which is connected to a drive motor is controlled
and monitored for speed. Similarly, the monitoring of the drive
power, the input energy and the torque takes place during the
emulsion and suspension processes for the control of the enzymatic
breakdown of the cellulose and thus for the control of the degree
of polymerisation using at least one sensor.
[0025] Surprisingly, it was found that during the addition of the
enzyme, decomposition of the polymer chains took place and the rate
of decomposition could be derived via the input emulsifying and
suspension power or from power input by an agitating machine.
[0026] The degree of polymerisation of the cellulose, the cellulose
suspension and/or the cellulose solution can be determined by
inline sensors such as torque sensors with associated software and
control with computation of the relative reduction in viscosity.
These types of systems are, for example, offered by the company
PORPOISE. Alternatively, the degree of polymerisation can be
determined by manual sample extraction followed by analytical
determination of the degree of polymerisation, which however
reduces the degree of automation for the method.
[0027] As inline sensors, for example strain gauges, fitted between
the drive motor and agitating machine or eddy current sensors, can
be used for the measurement of power and torque. The eddy current
measurement is based on the principle that the permeability for
magnetic field lines is modified by mechanical stresses. The
magnetic field generated by a stationary sensor head penetrates the
agitator drive shaft and induces electrical voltages in the
secondary coils of the sensor head in relation to the mechanical
stress which are proportional to the torque. The measurement takes
place without contact and free of any reactive forces.
[0028] A prerequisite for the use of this method in the suspension
production system is that a free, accessible piece of the shaft is
available on the drive side of the agitating machine to which the
sensor can be aligned.
[0029] After a manual extraction of the sample, the degree of
polymerisation can be determined via the viscosity according to the
cuoxam method. The measurements and the measurement signals from
the inline sensors are calibrated with the analytical results,
correlated and are used for the process control and are to be
preferred over a manual sample extraction, because they facilitate
the automation of the control of the residence duration.
[0030] During the processing of celluloses with a low degree of
polymerisation, for example with a DP value of at the most 550, the
enzymatic pretreatment is realised over a shorter time period than
for a cellulose with a higher degree of polymerisation, for example
of at least DP 700.
[0031] The enzymatic pretreatment can last between 20 minutes and
80 minutes, whereby the degree of polymerisation after the
termination of the enzymatic pretreatment does not drop below a DP
value of 520. If the DP value falls below 520, the enzymatic
pretreatment is terminated. Then follows the production of the
cellulose solution through the vaporisation of water from the
enzymatically broken down cellulose and the aqueous tertiary amine
oxide. Also in this process step further DP breakdown can be
monitored via inline sensors such as for example an inline
viscosity device, e.g. from Porpoise, and can be controlled in
conjunction with the enzymatic DP breakdown behaviour. In this
respect the rheometer is mounted in a branch of the pipe carrying
the mass. Thus, a very fast online measurement with high precision
is obtained. Through the measurement of the viscosity, the viscous
flow, structural viscosity, polymer swelling properties, elasticity
and normal stresses can be derived, which in turn can be used for
the control of the enzymatic breakdown.
[0032] In a further advantageous embodiment, the cellulose solution
can be transported to the spinning head by a heated pipe system.
Since a reduction in the degree of polymerisation also occurs in
the course of this transport, the transport speed of the cellulose
solution in the pipe system can be set in relation to the degree of
polymerisation of the cellulose solution, of the preceding
cellulose suspension and/or the introduced cellulose which is
dissolved in the cellulose solution. The lower the degree of
polymerisation of the cellulose solution, the faster the cellulose
solution is transported to the spinning head according to the
invention in order to prevent the extrusion of endless moulded
bodies with a degree of polymerisation which is too low. The
duration of processing the cellulose solution until its extrusion
can be set in a particularly easy way in an advantageous embodiment
in that the transport speed of a pump arrangement transporting the
cellulose suspension and/or cellulose solution is set in relation
to the degree of polymerisation.
[0033] The processing duration of the cellulose from its
introduction through to its extrusion to form endless moulded
bodies is preferably set such that it is at the most 80 minutes
and/or at least 20 minutes. In this time frame, a good solution of
the cellulose in the tertiary amine oxide can be achieved and at
the same time the degree of polymerisation cannot fall below values
which lead to an impaired quality of the Lyocell fibres.
[0034] In the following, an embodiment of the invention is
described as an example, with reference to the drawings. Here,
features, as related to versions of the above individual
advantageous embodiments of the invention, can be arbitrarily
combined with one another as required or also omitted. In addition,
the invention is documented based on experimental examples.
[0035] It is shown in:
[0036] FIG. 1 an embodiment of a device according to the invention
for the production of a cellulose solution in a schematic
illustration, whereby the method according to the invention can be
implemented;
[0037] FIG. 2 a schematic illustration of the steps of the method
for the production of the cellulose suspension;
[0038] FIG. 3 a schematic illustration of the change of the
quantity of iron ions borne out over time;
[0039] FIG. 4 a schematic illustration of the chemical oxygen
demand in the press water over time;
[0040] FIG. 5 a schematic illustration of a first method for the
control of the metal ion content;
[0041] FIG. 6 a schematic illustration of the power transfer of an
agitating machine for a cellulose suspension over the residence
time;
[0042] FIG. 7 a schematic illustration of the reduction in the
degree of polymerisation over the residence time for the cellulose
suspension.
[0043] FIG. 1 shows a plant 1 for the production of endless moulded
bodies 2, for example spinning filaments, from a spinnable
cellulose solution containing water, cellulose and tertiary amine
oxide.
[0044] First, cellulose in the form of leaves or plates 3 and/or
rolls 4 is passed to a pulper 5 in batches. In the pulper 5, the
cellulose 3, 4 is treated with water as a 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.
[0045] The quantity of the added water 6 is determined in relation
to the water content of the cellulose. Typically the water content
of the cellulose used is between 5 and 15 percent by mass. This
variation is compensated by changing the addition of water
appropriately, so that the water content of the cellulose
suspension or the bath ratio of solids/liquid remains approximately
constant or attains a freely selected value.
[0046] 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.
[0047] In the press device, the cellulose suspension produced by
the pulper 5 is for example expressed by rotating rolls 10. The
expressed water or press water 11 is collected by a collecting
device 11' and passed back to the pulper 5 by a conveying means 12,
through an optional filter device 13 and through a mixing device 14
at least in part as water 6. The press device 9 can also be fitted
with a suction device (not shown) for drawing off excess water from
the cellulose suspension. In this embodiment, the drawn-off water
is passed back, as the press water, at least in part to the pulper
5. For the purposes of this invention, drawn-off water or water
removed from the cellulose suspension by other means is also press
water which can be recycled for the treatment or disintegration of
the cellulose.
[0048] 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, multilayer filters and also flotation
methods. 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.
[0049] The respective proportions of the returned treatment medium
11 and of fresh treatment medium 15, for example fresh water, fed
from another fresh source are adjusted by a mixing device 14 in the
water passed to the pulper 5. In addition, the proportion of the
treatment medium 11, which is passed or discharged out of the plant
1 through a waste water pipe 16, is set by the mixing device
14.
[0050] 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 of the fresh water 15 in the water 6 fed to the pulper 5 can be
set to variably specifiable values in response to an output signal
from the control device via at least one control line 18.
[0051] 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 screws,
paddles or blades. For the stirring and conveying means 19, no
annular layer mixers can be employed, such as originating from
DRAIS Misch- und 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.
[0052] 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 supplied to the cellulose suspension
in aqueous form with a molar ratio NMMNO/H.sub.2O of between 1:1
and 1:2.5 as solvent for the cellulose via a pipe 21. In addition,
additives such as stabilisers and enzymes, organic additives,
delustering substances, alkalis, solid or liquid earthy bases,
zeolites, finely pulverised metals such as zinc, silver, gold and
platinum for the production of anti-microbial and/or electrically
or thermally conducting fibres during and after the spinning
process and/or dyes can be added to the cellulose suspension in the
shear zone. The concentration of the additives can be controlled in
the range from 100 to 100,000 ppm referred to the fibre
product.
[0053] The concentration of the supplied 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 vaporisation stage.
From the stirring and conveying means 22 on, 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. Conveying devices 7' in the form of
pumps can be arranged both in the pipe system 8 as well as in the
pipe system 8' to transport the cellulose suspension and/or the
cellulose solution.
[0054] 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, 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
sample extraction, the metal ion content can in a further
embodiment be determined after a manual sample extraction using
wet-chemical methods 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.
[0055] The control device 17 compares the metal ion content
measured by the sensors 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 as treatment medium passed to the pulper 5 is set in
dependence of the content of the destabilising metal ions of 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 vaporisation stage,
preferably a sensor is provided which monitors the metal content of
the cellulose solution after the addition of all constituents and
after all the vaporisation stages.
[0056] If, for example, the metal content of destabilising metal
ions in the cellulose solution, as acquired by the sensors 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. The
metal content is then 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.
[0057] As sensors 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 sensor are known and are produced by various
manufacturers, for example by Perkin Elmer.
[0058] Furthermore, the degree of polymerisation of the cellulose
suspension and/or the cellulose solution can be determined via
inline sensors 23', for example from the company PORPOISE, the
number of which is as required, for example via a viscosity
measurement. Instead of the inline sensors 23', a sample can be
taken manually at the corresponding point and its degree of
polymerisation be found in the normal way, for example according to
the cuoxam method. Furthermore, as the sensors 23', sensors can be
used which monitor the power transferred by agitating machines,
such as torque sensors, eddy current sensors or strain-gauge
sensors.
[0059] As shown in FIG. 1, the sensors 23' for the degree of
polymerisation are arranged in the pulper 5 and in the pipe system
8, 8'. The measured degree of polymerisation is passed in signal
form to the control device 17. The inline sensors are rheometers
from the company PORPOISE.
[0060] 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. For
this, the analysed 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 and/or its degree of
polymerisation via an input device 24. The preadjustment or present
default value of the metal content 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
having 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.
[0061] If the metal content decreases, as it is acquired by the
sensors 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.
[0062] The control device 17 also controls the residence or
processing period of the cellulose 3, 4 in the plant 1 in
dependence of the degree of polymerisation as entered manually into
the input device 24 or, during operation, determined by the sensors
23' or by means of manually extracted samples analysed in the
laboratory. The sensors 23' and/or the laboratory analysis devices
for the samples extracted manually act as monitoring devices for
the degree of polymerisation. The processing duration of the
cellulose from its introduction into the pulper 5 through to its
extrusion in an extrusion head 25 is set such that close to the
extrusion head 25, shortly before the extrusion of the cellulose
solution, the degree of polymerisation does not fall below 450 DP,
preferably not below 550 DP. If a cellulose 3, 4 is processed,
which already has a low degree of polymerisation, then the
transport speed of the cellulose suspension and the cellulose
solution in the pipe system 8, 8' is increased, whereby the
residence period of the cellulose in plant 1 is reduced.
[0063] The control device 17 controls in particular the conveying
device 7 which empties the pulper 5. With celluloses having a low
degree of polymerisation, the pretreatment and prepulping are
shortened by operating the pump 7 at an earlier time.
Simultaneously, the conveying capacity of the further pumps 7' in
the pipe systems 8, 8' is increased. The duration of the
pretreatment in the plant 1 takes, for example with celluloses 3, 4
having a high degree of polymerisation of at least 600 DP, about 40
minutes, and, with celluloses 3, 4 having a relatively low degree
of polymerisation of 400 DP and less, at the most 25-30
minutes.
[0064] After the agitation and conveying means 22, the now
extrudable cellulose solution is passed to the extrusion head 25,
which is fitted with a large number of extrusion openings (not
shown). The highly viscous cellulose solution is extruded through
each of these extrusion openings to form an endless moulded body 2
into an air gap 26. 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 off the extrusion openings by a
take-off mechanism 27 with a speed which is greater than the
extrusion speed.
[0065] After the air gap 26 the endless moulded bodies 2 cross a
precipitation bath 28 containing a non-solvent such as water,
whereby the cellulose in the endless moulded 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 teachings
of WO 93/19230 A1 and EP 584 318 B1, it has been found
substantially more advantageous if the cooling gas flow does not
impinge on the endless moulded bodies 2 immediately after the exit
of the endless moulded bodies 2 from the die, but rather at a
distance from the die. 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.
[0066] The precipitation bath 28 becomes increasingly enriched with
tertiary amine oxide, so that it must be continuously regenerated
using a recovery device 30. For this, in operation, the liquid from
the precipitation bath is fed to the recovery device 30 via a pipe
31, which for example is connected to an overflow on the
precipitation bath. The recovery device 30 removes the tertiary
amine oxide from the liquid and returns purified water via a pipe
32. Waste substances that cannot be recycled are ejected from the
device 1 via a pipe 33 and taken for disposal.
[0067] In the recovery device 30, the amine oxide is separated from
the water and passed via a pipe 34 to a further mixing device 35,
to which fresh amine oxide is fed via a pipe 36. The regenerated
amine oxide from the pipe 34 is mixed with the fresh amine oxide 36
and passed via the pipe 21 to the shear zone 19.
[0068] Metal ions can be removed from the regenerated amine oxide
by an ion exchanger, for example from the company Rohm und Haas,
Amberlite GT 73 or filters 37.
[0069] The mixing device 35 and the purification device 37 can be
controlled by the control device 17 in dependence of the metal ion
content as measured by the sensors 23.
[0070] 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
fibres and passed in non-woven form from the device 1.
[0071] All of the 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 take up variations in the
conveyed amount and/or of the conveying pressure and to facilitate
continuous processing without the occurrence of dead water regions.
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 economical transport
without decomposition of the tertiary amine oxide. The temperature
of the cellulose solution in the pipe section 8' is between 75 and
110.degree. C.
[0072] At the same time, the high temperature promotes the
homogenisation and uniform mixing, which can be increased by static
or rotating mixers.
[0073] The residence time of the cellulose suspension or solution
in the pipe system 8, 8' from the thick matter pump 7 through to
the extrusion head 25 can be, depending on the degree of
polymerisation of the processed cellulose and with the use of
special additives for the cellulose suspension and cellulose
solution, between 5 minutes and 2 hours, preferably about 30 to 60
minutes. The implementation of the method according to the
invention is now described based on experimental examples.
[0074] In order that the required enzymatic breakdown or
decomposition of the cellulose can be reliably set also in larger
plants, the production of the suspension was examined more closely
in laboratory experiments, because the mixing and stirring stages
occur in a very complex manner and turbulence mechanisms can also
affect the rheology of the treated product. Therefore, before
transferring to large scale, it was necessary to specifically
investigate the enzymatically controlled breakdown behaviour
(reduction of DP).
[0075] In the laboratory model experiments, the parameters
(Newton's number, Reynold's number, Froude's number) known in
agitation technology were determined. The concentrations,
temperatures, mixing times and mixing quality were exactly observed
and determined in order to obtain information about the breakdown
or decomposition behaviour during the formation of the emulsion or
suspension. The exact adjustment of the concentration occurred
through continuous flow measurement devices for emulsion or
suspension agents, and the addition of the cellulose also occurred
continuously, exactly measured via a differential dosage weighing
system. The suspension criteria, such as filling level, stirring
duration and concentration of the emulsion/suspension particles
over the container height were determined by inserting a
measurement sampling lance and the extraction of suspended
material. An impeller stirrer was used as the stirring element.
However, propellers, inclined blade mixers, disc mixers, toothed
stirrers, anchor stirrers as well as spiral stirrers or coaxial
agitating machines can also be used. The shaft of the stirring
machine which is connected to a drive motor is controlled and
monitored for speed. Similarly, the monitoring of the drive power,
the input energy and the torque occurs during the emulsion and
suspension stages for the control of the enzymatic breakdown of the
cellulose and thus for the control of the degree of
polymerisation.
[0076] A first series of experiments involved 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 illustration of the pretreatment in FIG. 2 and
also the reference symbols of FIG. 1 are used.
EXPERIMENTAL EXAMPLE 1
[0077] In a process step A cellulose 3, 4 (cf. FIG. 1) of type MoDo
Dissolving Wood Pulp, pine sulphite wood pulp, was placed in a
pulper 5 from the company Grubbens having a net filling volume of 2
m.sup.3 with water 6 in a mixing ratio of 1:17 (solid density
5.5%). The cellulose exhibited a cuoxam DP of 650 and an
.alpha.-cellulose content greater or smaller 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 processed in the method. 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.
[0078] Under vigorous stirring, technically pure formic acid 50 in
the ratio of 1:140 and a liquid enzyme preparation 51 in the ratio
of 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.
[0079] Then, the pretreatment was interrupted in a process step B
by the addition of sodium hydroxide solution (soda lye) 52 in the
ratio of 1:500 referred to the cellulose content of the cellulose
suspension in the pulper 5.
[0080] The cellulose suspension was then dehydratised to about 50%
in a process step C in a vacuum belt filter acting as press means 9
followed by an expressing system from the company Pannevis, 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 the cellulose solution containing NMMNO, water
and cellulose. These steps are not shown in FIG. 2 for the sake of
clarity.
[0081] The press water was collected in the press means 9 and led
away 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.
[0082] 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.
[0083] 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
[0084] 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
[0085] 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
[0086] To check the effectiveness of the method according to the
invention, the press water collected during the expressing stage
was analysed for copper and iron ion content and additionally the
chemical oxygen demand was determined.
[0087] As a result of this experiment, it can be summarized that,
in the first pulp cycles, the measured values of the ingredients
increase due to the circulation of a part of the press water.
Since, however, a part of the press water is permanently
transferred out together with the ingredients dissolved therein, a
steady state sets in after some time in which the amount of
ingredients or content substances, in particular the metal ions,
remains constant.
[0088] 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 a continuous
plant operation with a return of the press water, the percentage
proportion of the iron extracted from the system 1 may be between
22% and 35% referred to the quantity of iron introduced by the
cellulose.
[0089] FIG. 3 gives a schematic temporal trace of the iron ion
extraction.
[0090] The stable final state of the system 1 is achieved, as
Experimental Examples 1 to 3 show, independent of the amount of
introduced enzymes for the pretreatment of the cellulose.
[0091] This is also confirmed by the temporal change 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 with increasing duration of the press
water feedback to a constant value.
[0092] Furthermore, the degree of polymerisation and the DP
reduction as well as the onset temperature of the spinning solution
were determined as indicators of stability in the cellulose
solutions obtained according to Experimental Examples 1 to 3. 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
[0093] 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. The onset temperature shown in Table 1
according to the method with press water return according to the
invention is also above the onset temperature as it is obtained by
the method of WO 95/08010, and in practice is about 150.degree.
C.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] This destabilisation of the cellulose solution can however
be prevented by the outward transfer of the treatment medium with
the destabilising metal ions. The proportion of the returned
treatment medium depends on the type of cellulose used, as shown in
the following table.
[0098] The iron and copper content as well as the metal ion content
of the cellulose overall 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 Contained substances
Cellulose 1 Cellulose 2 Cellulose 3 Cellulose 4 Cellulose 5
Cellulose 6 Cellulose 7 Cellulose 8 in cellulose mg/kg mg/kg mg/kg
mg/kg mg/kg mg/kg mg/kg 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
[0099] In a final series of experiments the schematic experimental
set-up of FIG. 5 was used. In FIG. 5 the reference symbols of FIGS.
1 and 2 are used for elements with similar or the same
function.
[0100] 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.
[0101] 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).
[0102] 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.
[0103] 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.
[0104] 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 on 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.
[0105] In a modification of the method described in FIG. 1, in the
recovery device 30 recovered water from the spinning bath 28 can be
returned instead of or together with the press water to the pulper
5.
[0106] The metal ion filter 37, as it is used in 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.
EXPERIMENTAL EXAMPLE 4
[0107] In this experimental example, the method was carried out
according to Experimental Example 1 and the DP value in the
cellulose was measured at various points in the enzymatic
treatment, in the cellulose suspension and in the cellulose
solution. Table 3 shows the figures obtained. From this table it
can be seen that through to the extrusion of the endless moulded
body the degree of polymerisation is reduced by 20% from originally
628 in the cellulose 3, 4 to 504. A substantial proportion of the
reduction in the degree of polymerisation is provided by the
enzymatic pretreatment, which in addition offers the advantage that
its duration correlates well with the polymerisation breakdown. The
reduction in the degree of polymerisation can be prevented in a
simple manner if the duration of the enzymatic treatment is set
such that for example a degree of polymerisation of at least 590 DP
to 600 DP is present at the end of the enzymatic treatment.
Furthermore, the transport of the cellulose suspension and/or the
cellulose solution can be speeded up such that a degree of
polymerisation of at least 550 DP is obtained before the extrusion
of the cellulose solution.
TABLE-US-00003 TABLE 3 DP value Overall reduction Cellulose 628 0%
Enzymatic treatment 30 minutes 603 4.14% Enzymatic treatment 45
minutes 592 5.73% Enzymatic treatment 60 minutes 582 7.32%
Cellulose suspension 582 7.32% Cellulose solution 538 14.33%
Endless moulded bodies 504 19.75%
EXPERIMENTAL EXAMPLE 5
[0108] In this experiment the method was implemented similar to
Experimental Example 4, but only the activation step was observed
and the DP value in the cellulose suspension, in the spinning
solution and in the endless moulded body was not measured.
[0109] The starting cellulose was selected with a DP of 780 and the
enzyme concentration was increased by the factor 0.5. Furthermore,
the power consumption of the agitating machine was also recorded
during the activation step and scaled to the container volume and
the solids concentration. Table 4 shows the figures measured when
carrying out the experiment.
TABLE-US-00004 TABLE 4 Power consumption Treatment [kW/m.sup.3 of
input Cellulose Power transferred [kW/kg DP of Step in the method
time [s] liquid] content [%] of cell.] cell. Input liquid 300 0.4 0
-- Cellulose feed 1 360 0.49 1.0% 0.0049 780 Cellulose feed 2 420
0.52 2.0% 0.0104 780 Cellulose feed 3 480 0.8 3.0% 0.0240 780
Cellulose feed 4 540 1.81 4.0% 0.0724 780 Cellulose feed 5 600 2.55
5.0% 0.1275 780 Homogenisation 660 2.53 5.0% 0.1265 780
Homogenisation 720 2.4 5.0% 0.1200 780 Homogenisation 780 2.5 5.0%
0.1250 780 Enzyme addition 780 2.51 5.0% 0.1255 780 Homogenisation
840 2.53 5.0% 0.1265 780 Homogenisation 900 2.5 5.0% 0.1250 773
Homogenisation 960 2.41 5.0% 0.1205 765 Homogenisation 1020 2.3
5.0% 0.1150 751 Homogenisation 1080 2.17 5.0% 0.1085 747
Homogenisation 1380 1.88 5.0% 0.0940 701 Homogenisation 1680 1.65
5.0% 0.0825 657 Homogenisation 1980 1.52 5.0% 0.0760 613
Homogenisation 2280 1.5 5.0% 0.0750 569 Homogenisation 2580 1.45
5.0% 0.0725 522
[0110] FIG. 6 illustrates the trace of the power in kilowatts per
kilogram of cellulose applied by the agitating machine over the
treatment period of the cellulose suspension in the agitating
machine, FIG. 7 shows the change of the degree of polymerisation in
the agitating machine.
[0111] As can be seen from Table 4 and FIGS. 6 and 7, the degree of
polymerisation reduces with increasing treatment time for the
cellulose suspension.
[0112] The reduction in the degree of polymerisation can be seen
from the clearly reduced power applied by the agitating machine.
With a reduced degree of polymerisation the power applied in the
agitating machine also reduces.
[0113] Consequently, during the production of the cellulose
suspension, in particular during the enzymatic pretreatment, in the
agitating machine the power of the agitating machine can be used as
a representative quantity for the degree of polymerisation in the
control of the degree of polymerisation. The same method for
monitoring the degree of polymerisation is also possible with the
following agitating machines. If, for example, the power of the
agitating machine falls under a certain predetermined value, e.g. a
limit determined by experiments, this is a sign that the degree of
polymerisation is falling or has fallen below a figure specified
for this processing stage. As a consequence, the remaining
residence time of the cellulose suspension and/or the cellulose
solution in the process step is shortened.
* * * * *