U.S. patent application number 11/721229 was filed with the patent office on 2009-02-19 for bentonite for binding impurities during paper production.
Invention is credited to Hubertus Besting, Ulrich Sohling, Genovefa Wendrich.
Application Number | 20090044921 11/721229 |
Document ID | / |
Family ID | 36588237 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090044921 |
Kind Code |
A1 |
Sohling; Ulrich ; et
al. |
February 19, 2009 |
BENTONITE FOR BINDING IMPURITIES DURING PAPER PRODUCTION
Abstract
A method for binding impurities in paper production, comprising
the following steps: a) provision of a bentonite, the proportion of
the monovalent cations, based on the cation exchange capacity (CEC)
of the bentonite, being at least 0.7 and the CEC being more than 85
meq/100 g, preferably more than 90 meq/100 g, in particular more
than 95 meq/100 g; b) addition of the bentonite according to a) to
a paper pulp or fiber suspension; c) binding of the impurities to
the bentonite in the pulp or fiber suspension is described.
Inventors: |
Sohling; Ulrich; (Freising,
DE) ; Besting; Hubertus; (Niederaichbach, DE)
; Wendrich; Genovefa; (Essenbach, DE) |
Correspondence
Address: |
SCOTT R. COX;LYNCH, COX, GILMAN & MAHAN, P.S.C.
500 WEST JEFFERSON STREET, SUITE 2100
LOUISVILLE
KY
40202
US
|
Family ID: |
36588237 |
Appl. No.: |
11/721229 |
Filed: |
November 30, 2005 |
PCT Filed: |
November 30, 2005 |
PCT NO: |
PCT/EP2005/012775 |
371 Date: |
June 8, 2007 |
Current U.S.
Class: |
162/150 ;
162/181.8 |
Current CPC
Class: |
D21H 21/02 20130101;
D21H 17/68 20130101 |
Class at
Publication: |
162/150 ;
162/181.8 |
International
Class: |
D21H 11/00 20060101
D21H011/00; D21H 17/68 20060101 D21H017/68 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2004 |
DE |
10 2004 060 587.4 |
Claims
1. A method for binding impurities in paper production, comprising
the following steps: a) providing bentonite, with a proportion of
monovalent cations of at least about 0.7 based on the cation
exchange capacity (CEC) of the bentonite, wherein the CEC is
greater than 85 meq/100 g; b) adding the bentonite to a paper pulp
or fiber suspension; and c) binding impurities to the bentonite in
the pulp or fiber suspension.
2. The method as claimed in claim 1, characterized in that the
proportion of the monovalent cations, based on the CEC of the
bentonite, is more than 0.8.
3. The method as claimed in claim 1, characterized in that the
proportion of calcium and/or magnesium ions in the bentonite, based
on the CEC of the bentonite, is less than 0.2.
4. The method as claimed in claim 1, characterized in that the
particle size of the bentonite is chosen so that in the wet sieve
residue less than 2% by weight, is 45 .mu.m.
5. The method as claimed in claim 1, characterized in that the
monovalent cations in the bentonite are selected from the group
consisting of sodium, potassium, lithium and mixtures thereof.
6. The method as claimed in claim 1, characterized in that the
bentonite is present in particulate form having a median particle
size (D50, based on volume) of from 0.5 to 10 .mu.m.
7. The method as claimed in claim 1, characterized in that the
addition of the bentonite is effected in the absence of talc.
8. The method as claimed in claim 1, characterized in that the
bentonite has a swellability of at least 25 ml/2 g.
9. The method as claimed in claim 1, characterized in that the
bentonite has a proportion of iron ions, based on the CEC, of less
than about 0.005.
10. The method as claimed in claim 1, characterized in that the
bentonite has a BET surface area of less than 100 m.sup.2/g.
11. The method as claimed in claim 1, characterized in that from
about 0.5 to 10 kg of bentonite are added per tonne of paper pulp
or fiber suspension (dry weight).
12. The method as claimed in claim 1, characterized in that the
paper pulp or fiber suspension contains a groundwood fraction.
13. The method as claimed in claim 12, characterized in that the
groundwood fraction in the paper pulp or the fiber suspension is at
least 10% by weight, based on the total pulp or fiber suspension
(dry weight).
14. The method as claimed in claim 1, characterized in that no
additional talc is added to the paper pulp or fiber suspension.
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. The method as claimed in claim 1, wherein the CEC of the
bentonite is greater than 95 meq/100 g.
20. The method as claimed in claim 1 characterized in that the
proportion of the monovalent cations, based on the CEC of the
bentonite, is more than 0.85.
21. The method as claimed in claim 1 characterized in that the
proportion of calcium and/or magnesium ions in the bentonite, based
on the CEC of the bentonite, is less than 0.15.
22. The method as claimed in claim 1 characterized in that the
particle size of the bentonite is chosen so that the wet sieve
residue less than 2% by weight is 45 .mu.m.
23. The method as claimed in claim 1 characterized in that the
bentonite is present in particulate form having a medium particle
size (D50, based on volume) of from 2 to 6 .mu.m.
24. A method for binding hydrophobic impurities in paper
production, comprising the following steps: a) providing bentonite,
with a proportion of monovalent cations of at least about 0.7 based
on the cation exchange capacity (CEC) of the bentonite, wherein the
CEC is greater than 85 meq/100 g; b) adding the bentonite to a
paper, pulp or fiber suspension; and c) binding hydrophobic
impurities to the bentonite in the pulp and fiber suspension.
Description
[0001] The present invention relates to the use of special
bentonites having a high cation exchange capacity in the binding or
removal of impurities in paper production.
[0002] The removal or binding of impurities in paper production is
becoming increasingly important. The problem is also based on the
fact that the water occurring in paper production is circulated,
impurities gradually becoming more concentrated therein. These
impurities can thus lead to a very wide range of product faults,
such as, for example, to the formation of deposits on the rolls of
the paper machine, to blocking of the wires by adhesion, etc. These
effects lead to interruptions to paper production. In order to
minimize the number of production stops, it is desirable to bind
the impurities occurring in the circulation water by using polymers
or adsorbents in the headbox itself. Most relevant impurities are
negatively charged. These are, for example, humic acids, tree resin
colloids, lignin derivatives, ligninsulfonates, which are
introduced from the fibers into the paper circulation. There are
also anionic impurities, which are introduced into the paper
machine by recycling of broke. This broke is typically re-dispersed
and introduced into the paper machine. As a result, the ingredients
and auxiliaries present therein are completely recycled into the
circulation. For example, carboxymethylcelluloses, polyacrylates,
polyphosphonates and silicates are additionally introduced thereby.
Further anionic charged impurities are the latices which are used
in the paper coat, which are typically hydrophobic but also carry
anionic charges. These have a strong tendency to agglomeration, the
agglomerates being deposited as tacky, white residues on the paper
machine (so-called white pitch).
[0003] The prior art extensively describes the discharge of
stickies by the use of talc. Thus, according to P. Biza, E. Gaksch
and P. Kaiser "Verbesserter Austrag von Stickys durch den Einsatz
von Talkum [Improved discharge of stickies by the use of talc]",
Wochenblatt fur Papierfabrikation 11/12 (2002), page 759 et seq.,
the effect of talc on the reduction of tacky deposits has been
documented since the beginning of the last century at the latest.
Almost all known natural and synthetic tacky substances are
hydrophobic. Talc is very suitable for binding these stickies
because it has a naturally hydrophobic surface which enables it to
be readily adsorbed onto sticky surfaces and to make them less
tacky by coating.
[0004] Furthermore, the use of montmorillonites, such as bentonite,
for controlling impurities in the paper pulp is described, for
example, in U.S. Pat. No. 5,368,692. The alkali treatment of
bentonites is also discussed as a possibility.
[0005] U.S. Pat. No. 4,964,955 likewise describes a process for
reducing the impurities in paper production. There, a particulate
composition containing (a) a water-soluble cationic polymer which
is applied to (b) a substantially water-insoluble particulate
substrate is used for binding impurities. The polymer should be
sufficiently electropositive so that the particulate composition
has a zeta potential of at least about +30 mV. The polymer is
preferably a poly(dialkyldiallylammonium halide). The substrate is,
for example, a phyllosilicate mineral.
[0006] In a similar manner, EP 0 760 406 A2 relates to a
combination of a poly(dadmac/acrylamide) and a bentonite for
binding impurities.
[0007] GB 2 297 334 A in turn discloses the use of a smectic clay
for controlling impurities, the smectic clay being modified as
follows: monovalent exchangeable cations are present in an
equivalent ionic fraction in the range of from 0.20 to 0.60; a
first type of bivalent exchangeable cations is present in an
equivalent ionic fraction in the range of from 0.40 to 0.80; and a
second type of bivalent exchangeable cations is present in an
equivalent ionic fraction in the range of from 0.00 to 0.20, the
first type of bivalent exchangeable cations comprising calcium and
the second type of bivalent exchangeable cations comprising
magnesium.
[0008] Many of the compositions used in the prior art for binding
impurities are very expensive and not optimally suitable for
certain impurity compositions. There is therefore a constant need
for compositions for binding impurities in paper production.
[0009] An object of the present invention was therefore to provide
an improved process for binding impurities in paper production, in
which a composition which is easy and economical to prepare can be
used and which permits a high degree of binding of impurities,
including hydrophobic fractions.
[0010] According to one aspect of the invention, this object is
achieved by the method as claimed in claim 1.
[0011] Thus, in the present invention, it was surprisingly found
that surprisingly good binding of impurities in a method for
binding impurities in paper production can be provided by the use
of a bentonite which has a proportion of the monovalent cations,
based on the cation exchange capacity (referred to herein as CEC),
of at least about 0.7 (i.e. 70%), and a CEC (total) of at least 85
meq/100 g.
[0012] In the context of the present invention, impurities are
understood as meaning both tacky substances, referred to in the
literature as stickies, and so-called pitch, i.e. primarily tree
resin components. Reference may be made here to the statements made
in the introduction to the description with regard to the
impurities. A detailed list of the pitch and stickies constituents
is to be found, for example, in Wo01/71092 on pages 1 and 2, and
the disclosure there is hereby expressly incorporated by reference
into the present description.
[0013] As mentioned above, the impurities are thus primarily
anionic (negatively charged) or hydrophobic. Thus, it was all the
more surprising that the highly activated bentonites used according
to the invention and having a high CEC can very readily bind both
anionic and hydrophobic impurity fractions and can neutralize them
in their harmful effects. The bentonites used according to the
invention themselves have a relatively high negative layer charge
and subsequently make this high (negative) surface charge available
in delaminated form to the paper pulp. Thus, good binding of
impurities would not be expected for anionic or hydrophobic
impurities. It would also be expected that a calcium bentonite
binds such impurities better because a major part of the charges of
the bentonites is saturated by the calcium ions and these could
immobilize impurities, for example, via soap formation and fatty
acids in the tree resin. In particular, the stickies, such as tree
resin particles, contain many rather nonpolar (hydrophobic)
components, e.g. triglycerides. These should bind particularly well
to nonpolar surfaces, such as, for example, those of talc. Talc has
no surface charges and is therefore also described in the prior art
as being optimum for the binding of (hydrophobic) impurities.
[0014] The results in the context of the present invention,
according to which both nonpolar and anionic impurities can be
efficiently bound in the method according to the invention with
bentonites which make available a large surface having numerous
negative charges are therefore unexpected.
[0015] The method according to the invention with the use of the
special bentonite described herein can be used generally in all
methods for paper or cardboard production. Accordingly, the
expressions paper pulp and fiber suspension are intended generally
to include all impurity-containing compositions or streams which
are used in paper production. Otherwise, the expressions "pulp" and
"fiber suspension" are familiar to the person skilled in the art
and need not be explained in detail here.
[0016] In a preferred embodiment according to the invention, the
pulp or the fiber suspension is a (fine) groundwood-containing
suspension. Groundwood is in general finely digested (finely beaten
wood, generally without further chemical or thermal treatment). The
groundwood suspension is either used directly after comminution or
is subjected to a peroxide bleach, in which case so-called
peroxide-bleached groundwood forms. It has surprisingly been found
that the bentonite used according to the invention gives
particularly good results in the case of paper types containing
groundwood or peroxide-bleached groundwood. However, the method
according to the invention can also be advantageously used in the
case of other paper types. Thus, for example, the pulp or fiber
suspension (in addition to the groundwood) may also contain highly
purified fiber fractions, as is the case, for example, in so-called
newsprint paper. The invention furthermore gives very good results
in the case of so-called "deinked pulp" (DIP). This is a paper
stock which is produced from wastepaper. In particular, hydrophobic
stickies occur there, from the stickies of magazines and
newspapers. These too can be readily bound in the end product by
the bentonite used according to the invention. Further so-called
paper stocks in which the bentonite according to the invention can
be advantageously used comprise TMP (thermomechanical pulp) sulfate
pulp, sulfite pulp and mixtures of different chemical pulps.
Depending on the paper type and localization of the paper mill,
such chemical pulps are mixed in different ratios and adapted to
the material requirements of the end product.
[0017] In an advantageous embodiment according to the invention,
the preferred groundwood fraction in the paper pulp or fiber
suspension is at least 10% by weight, in particular at least 30% by
weight, based in each case on the dry weight of the total pulp or
suspension.
[0018] The bentonite in the method according to the invention
probably acts without the invention being limited to the
correctness of this assumption, in that it binds the impurities or
interacts with them and thus, counteracts the aggregation and
deposition on the parts of the paper machine, such as, for example,
the rolls.
[0019] According to the invention it is important that the
bentonite used has a cation exchange capacity (CEC) of at least 85
meq/100 g, preferably at least 90 meq/100 g, in particular at least
95 meq/100 g.
[0020] "Cation exchange capacity" (CEC) is understood as meaning
the sum of all exchangeable cations, stated in meq/100 g and
determined by the CEC analysis method as explained below before the
example section (determination of the cation exchange capacity).
The cation exchange capacity thus comprises, for example, the sum
of all exchangeable divalent and monovalent cations, such as
calcium, magnesium, sodium, lithium and potassium ions. For the
determination of the cation exchange capacity, the bentonite is
treated with an ammonium chloride solution. Owing to the high
affinity of the ammonium ions for the bentonite, virtually all
exchangeable cations are exchanged for ammonium ions. After
separation and washing, the nitrogen content of the bentonite is
determined and the content of ammonium ions is calculated
therefrom.
[0021] It is possible to use both natural bentonites and bentonites
obtained by activation, for example from calcium bentonites,
provided that the above conditions for the fraction of monovalent
cations, based on the CEC, and the minimum values for the CEC are
complied with. Processes for producing or activating bentonite are
known per se to the person skilled in the art and need not be
explained in detail here. For example, it is possible to start from
a calcium bentonite having a suitable CEC and to treat it with an
alkali metal carbonate, e.g. sodium carbonate. In the treatment or
activation of the phyllosilicate, contact can be established in any
desired manner familiar to the person skilled in the art, for
example by preparing a solids mixture, a suspension with the
phyllosilicate and the sodium carbonate or treatment or spraying of
the phyllosilicate with a solution of the sodium carbonate.
[0022] For example, according to the first method variant, a
calcium-containing crude bentonite having a water content of from
about 25 to 40% by weight is kneaded with solid sodium carbonate,
dried and milled. The crude bentonite is broken beforehand into
pieces of less than 3 cm diameter. If the crude bentonite does not
have the stated water content, this is established by spraying with
water.
[0023] The activation can also be effected, for example, as
follows: 350 g of crude bentonite having a water content of from
about 30 to 35% by weight are introduced into a mixing apparatus
(for example a Werner & Pfleiderer mixer (kneader)) and kneaded
for 1 minute. The amount of sodium carbonate (soda) which
corresponds to the difference between CEC and sodium content of the
bentonite is then added while the mixing apparatus continues to run
and further kneading is effected for 10 min. Here, the added
amounts are based on the anhydrous bentonite. If required a little
more distilled water is added so that the kneaded material "shears"
thoroughly. The kneaded material is then comminuted in to small
pieces and dried to a water content of 10.+-.2% in a
forced-circulation drying oven at about 75.degree. C. for from 2 to
4 hours. The dry material is then milled in a rotor beater mill
(e.g. in a Retsch mill) over a 0.12 mm sieve. The CEC and the
fraction thereof of sodium ions were determined as described
further below.
[0024] Overactivation of the bentonite, for example with soda, is
likewise possible, it being possible to use more soda than would be
stoichiometrically required for complete activation of the
bentonite.
[0025] In a particularly preferred embodiment according to the
invention, the stated fraction of monovalent cations is based on
the fraction of sodium, potassium and lithium ions, in particular
of sodium ions.
[0026] In a preferred embodiment according to the invention, the
bentonite used has a swellability of at least 25 ml/2 9, in
particular of at least 30 ml/2 g, more preferably at least 35 ml/2
g. Thus, it has surprisingly been found that bentonites having such
high swellability permit particularly advantageous binding of
impurities. The swelling volume is determined as follows: a
calibrated 100 ml measuring cylinder is filled with 100 ml of
distilled water. 2.0 g of the substance to be measured are
introduced slowly in portions of from 0.1 to 0.2 g onto the water
surface. After the material has sunk, the next portion is added.
After the end of the addition, a waiting time of 1 hour is allowed
and the volume of the swollen substance is then read in ml/2 g.
[0027] Furthermore, it has been found that the proportion of iron
ions, based on the CEC, should preferably be less than about 0.005
(0.5%). It has been found that such bentonites give better results
with regard to the whiteness of the paper pulp.
[0028] According to a further preferred aspect, the proportion of
the monovalent cations, based on the CEC of the bentonite, is more
than 0.7, in particular more than 0.8, preferably more than 0.81,
more preferably more than 0.85. It is furthermore preferable if the
proportion of calcium and/or magnesium ions, based on the CEC of
the bentonite, is less than 0.2, in particular less than 0.18,
preferably less than 0.15.
[0029] In a further preferred embodiment according to the
invention, the BET surface area (determined according to DIN 66131)
of the bentonites used is less than 100 m.sup.2/g, in particular
less than 90 m.sup.2/g. It is surprising that bentonites having a
relatively low specific BET surface area exhibit particularly
advantageous binding of impurities in comparison with bentonites
which can provide a higher specific surface area for adsorption of
impurities.
[0030] Typically, the demand for cationic charges in the headbox
decreases while the method according to the invention is being
carried out. This is demonstrated by the binding of the negatively
charged impurities by charge interactions.
[0031] The concentration of the impurities in paper production is
typically determined in the white water by the three customary
processes of cation demand (cationic charge demand), stability
measurement and chemical oxygen demand. In the case of cation
demand, it is assumed that the impurities are all negatively
charged and the white water filters in short-chain cationic
polyelectrolytes. The consumption is converted into the so-called
cation demand. In the turbidity measurement, it is assumed that the
impurities are partly present in colloidal form and their
concentration can be determined via the extinction caused by the
turbidity. In the case of the chemical oxygen demand, the
proportion of organic compounds present is tested by means of an
oxidizing agent. Although these methods are very widely used in the
paper world, more recent investigations have shown that they
average over the total ingredients in white water and only partly
detect particularly critical impurities. This arises, for example,
from the fact that the so-called tree resin colloids, some of which
are composed of hydrophobic compounds, may carry only small surface
charges and hence contribute little to the cation demand. On the
other hand, lignins have a high cationic demand; if they are
present in the white water, they interfere only very little in
paper production. More recent investigations furthermore show that
the correlation between the turbidity measurement and the
concentration of colloidal impurities is not always present. Owing
to this more recent experience with the customary impurity
determination methods, the additives according to the invention
were also characterized in their action by more recent methods.
These are, for example, a gas chromatographic analysis of the white
water by the method of F. Orsa and B. Holmbom "A Convenient Method
for the Determination of Wood Extractives in Papermaking Process
Waters and Effluents", Journal of Pulp and Paper Science, Vol. 20
No. 12 December 1994, pp J361. In the production of a
groundwood-containing paper, the individual tree resin components
are determined in their concentration by a gas chromatographic
method. This is a complete, quantitative analysis, whereas the
standard methods of determination, such as turbidity, cation demand
and chemical oxygen demand, are actually to be considered as only
being semi-quantitative at best. Furthermore, L. Vahasalo et al.
(loc. cit., cf. "Flowcytometrische Analyse des Siebwassers [Flow
cytometric analysis of white water]", further below, show that
so-called flow cytometry is very suitable for determining the
number of colloidal impurities in paper white waters. This new
method was therefore also used in the present invention in order to
show the impurity-reducing effect of the bentonites according to
the invention.
[0032] The addition of the bentonite used according to the
invention to the pulp or fiber suspension can be effected at any
desired point in the paper production which is suitable for the
person skilled in the art. In particular, the addition directly in
the pulper is also advisable because a long contact time with the
paper stock is possible there and there is the probability of a
high degree of binding of impurities. Further addition points are
in the entire so-called high-consistency stock region. Addition for
dissolved air-floatation for water purification is also
conceivable. In many cases, an already present addition point for
additives, for example in the form of a metering apparatus or
metering pump, will also be present in the apparatuses used in each
case for paper production, which apparatus or pump can be used for
the addition of the bentonite used according to the invention. The
bentonite can be used both in powder form and in the form of a
suspension or slurry. The suspension or slurry will in many cases
permit better meterability and is more easily automatable in
industrial, continuous processes.
[0033] It has furthermore been found that the effect of the
bentonite used according to the invention is particularly positive
if a certain particle size is maintained. Thus, according to a
particularly preferred embodiment of the invention, the particle
size of the bentonite is chosen so that in the wet sieve residue
less than 2% by weight, preferably less than 1% by weight, in
particular less than 0.5% by weight, is 45 .mu.m. The determination
of the wet sieve residue is explained in more detail before the
examples. The preferred particle size can also be determined by the
light scattering method (Malvern). In a particularly preferred
embodiment according to the invention, the median particle size
(D50) (based on the sample volume) is from 0.5 to 10 .mu.m, in
particular from 2 to 6 .mu.m, particularly preferably from 3 to 5
.mu.m.
[0034] In the present invention, it was also surprisingly found
that the use of the bentonite used according to the invention leads
to particularly good binding of impurities if talc is not used in
the method. The use of cationic polymers, such as, for example,
poly(dadmac) or polyacrylamide, according to the prior art can also
be reduced or even completely omitted with the aid of the bentonite
used according to the invention.
[0035] The amounts of bentonite used in the method according to the
invention can be determined by the person skilled in the art in a
routine manner using empirical experiments. In most cases, it is
advantageous to use amounts of from 0.5 to 12 kg/t of paper pulp or
fiber suspension, preferably from 1 to 8 kg/t, and in particular
from 1.5 to 7 kg/t, based in each case on the anhydrous
pulp/suspension (dry weight).
[0036] In the present invention, it was surprisingly also found
that the method according to the invention permits not only very
good binding of anionic impurity fractions, such as fatty acids,
but also outstanding binding or elimination of hydrophobic impurity
fractions, such as sterols, steryl esters and triglycerides. The
results achieved here surprisingly surpass both those which were
obtained with conventional bentonites and those of talc.
[0037] A further aspect of the present invention relates to the use
of a bentonite as described herein for binding impurities in paper
production. As mentioned above, the bentonite is preferably used in
a paper pulp or fiber suspension which contains groundwood
fractions. However, all paper types or pulps are covered by the use
according to the invention. The paper types mentioned further
above, such as paper types containing groundwood or
peroxide-treated groundwood, those which (in addition to the
groundwood) also contain highly purified fiber fractions, as is the
case, for example, in so-called newsprint paper, so-called deinked
pulp (DIP), TMP (thermomechanical pulp), sulfate pulp, sulfite pulp
and mixtures of different chemical pulps are particularly
preferred.
[0038] Method section: Unless stated otherwise, the analytical
methods stated below are used:
[0039] 1. Determination of the Cation Exchange Capacity (CEC
Analysis) and of the Cation Fractions
[0040] Principle: The clay is treated with a large excess of
aqueous NH.sub.4Cl solution and washed out, and the amount of
NH.sub.4.sup.+ remaining on the clay is determined according to
Kjeldahl.
Me.sup.+(clay).sup.-+NH.sub.4.sup.+--NH.sub.4.sup.+(clay).sup.-+Me.sup.+
(Me.sup.+.dbd.H.sup.+, K.sup.+, Na.sup.+, 1/2Ca.sup.2+,
1/2Mg.sup.2+. . . )
[0041] Apparatuses: Sieve, 63 .mu.m; conical flask with ground
glass joint, 300 ml; analytical balance; membrane suction filter,
400 ml; cellulose nitrate filter, 0.15 .mu.m (from Sartorius);
drying oven; reflux condenser; hotplate; distillation unit,
VAPODEST-5 (from Gerhardt, No. 6550); graduated flask, 250 ml;
flame AAS.
[0042] Chemicals: 2N NH.sub.4Cl solution, Nessler's reagent (from
Merck, Art. No. 9028); boric acid solution, 2% strength; sodium
hydroxide solution, 32% strength; 0.1 N hydrochloric acid; NaCl
solution, 0.1% strength; KCl solution, 0.1% strength.
[0043] Procedure: 5 g of clay are sieved through a 63 .mu.m sieve
and dried at 110.degree. C. Thereafter, exactly 2 g are weighed
into the conical flask having a ground glass joint on the
analytical balance by differential weighing, and 100 ml of 2N
NH.sub.4Cl solution are added. The suspension is boiled under
reflux for one hour. In the case of bentonites having a high
CaCo.sub.3 content, ammonia may be evolved. In these cases,
NH.sub.4Cl solution must be added until the odor of ammonia is no
longer perceptible. An additional check can be carried out with a
moist indicator paper. After a standing time of about 16 h, the
NH.sub.4.sup.+-bentonite is filtered off over a membrane suction
filter and washed with demineralized water (about 800 ml) until
substantially free of ions. The testing of the wash water for
freedom from ions is carried out for NH.sub.4.sup.+ ions with
Nessler's reagent which is sensitive to them. The washing time can
vary from 30 minutes to 3 days, depending on the type of clay. The
washed-out NH.sub.4.sup.+-bentonite is removed from the filter,
dried at 110.degree. C. for 2 h, milled, sieved (63 .mu.m sieve)
and dried again at 110.degree. C. for 2 h. Thereafter, the
NH.sub.4.sup.+ content of the bentonite is determined according to
Kjeldahl.
[0044] Calculation of the CEC: the CEC of the clay is the
NH.sub.4.sup.+ content of the NH.sub.4.sup.+ bentonite, determined
by means of Kjeldahl (for CEC of some clay minerals, cf. appendix).
The data are given in meq/100 g of clay.
[0045] Example: Nitrogen content=0.93%;
[0046] Molecular weight: N=14.0067 g/mol
C E C = 0.93 .times. 1000 14.0067 = 66.4 meq / 100 g
##EQU00001##
[0047] CEC=66.4 meq/100 g of NH.sub.4.sup.+-bentonite
[0048] Exchanged Cations and the Proportions Thereof:
[0049] The cations liberated by the exchange are present in the
wash water (filtrate). The proportion and the type of the
monovalent cations ("exchanged cations") are determined
spectroscopically in the filtrate according to DIN 38406, part 22.
For example, for the AAS determination, the wash water (filtrate)
is concentrated, transferred to a 250 ml graduated flask and made
up to the mark with demineralized water. Suitable measuring
conditions for FAAS are shown in the following tables.
TABLE-US-00001 Element Calcium Potassium Lithium Magnesium Sodium
Wavelength 422.7 766.5 670.8 285.2 589.0 (nm) (202.6) Gap width 0.2
0.5 0.5 0.5 0.2 (nm): Integration 3 3 3 3 3 time (sec): Flame
gasses: N.sub.2O/C.sub.2H.sub.2 Air/C.sub.2H.sub.2
Air/C.sub.2H.sub.2 N.sub.2O/C.sub.2H.sub.2 Air/C.sub.2H.sub.2
Background no no no yes no comp.: Measuring conc. conc. conc. conc.
conc. method: Ionization 0.1% KCI 0.1% NaCl 0.1% NaCl 0.1% KCI 0.1%
KCI buffer: Burner 15-20.degree. -- -- -- -- position Calibration
1-5 mg/l 1-5 mg/l 2-10 mg/l 0.5-3 mg/l 1-5 mg/l standard (5-40
mg/l) (mg/l):
TABLE-US-00002 Element Aluminum Iron Wavelength 309.3 248.3 (nm):
Gap width 0.5 0.2 (nm): Integration time (sec): 3 3 Flame gasses:
N.sub.2O/C.sub.2H.sub.2 Air/C.sub.2H.sub.2 Background comp.: yes no
Measuring method: conc. conc. Ionization buffer: 0.1% KCl -- Burner
position -- -- Calibration 10-50 mg/l 1-5 mg/l standard(mg/l):
[0050] Calculation of the Cations:
Me = Me - value ( mg / 1 ) .times. 100 .times. dilution 4 .times.
weight taken ( in g ) .times. molar mass ( g / mol ) = meq / 100 g
##EQU00002##
[0051] Molar mass (g/mol): Ca=20.040; K=39.096; Li=6.94; Mg=12.156;
Na=22.990; Al=8.994; Fe=18.616
[0052] In the case of so-called overactivated bentonites, i.e.
those which were activated with an amount of, for example, sodium
carbonate which is greater than the stoichiometric amount, the sum
of the amounts of monovalent cations determined may be greater than
the CEC determined as stated above. In such cases, the total
content of monovalent cations (Li, K, Na) is regarded as 100% of
the CEC.
[0053] The invention is now illustrated in more detail with
reference to the following, non-limiting examples.
[0054] 2. Determination of the BET Surface Area:
[0055] The determination was effected according to DIN 66131
(multipoint measurement).
[0056] 3. Determination of the Wet Sieve Residue:
[0057] With the use of pigments and fillers, it is of interest
whether the material to be investigated contains coarse fractions
which differ in their particle size from the normal particles and
how much of said coarse fractions said material contains. These
fractions are determined by sieving an aqueous suspension with
water as wash liquid. The wet sieve residue is considered to be the
residue determined under specified conditions.
[0058] Apparatuses: analytical balance, plastic beaker, Pendraulik
LD 50; sieve: 200 mm diameter, mesh size 0.025 (25 .mu.m), 0.045 mm
(45 .mu.m), 0.053 mm (53 .mu.m) or 0.063 mm (63 .mu.m); ultrasonic
bath.
[0059] First, a 5% strength suspension of the bentonite (oven dry,
i.e. after drying at 110.degree. C.) in 2000 g of water was
prepared. For this purpose, the bentonite is stirred in at 930 rpm
in about 5 min. After a stirring time of a further 15 min at 1865
rpm, the suspension is poured into the cleaned and dried sieve
(mesh size 45 .mu.m) and washed with flowing tap water while
tapping until the wash water runs out clear. After the washing of
the sieve residue with tap water, the sieve is placed for 5 min in
an ultrasonic bath in order to sieve off the remaining fine
fractions. When using the sieve in the ultrasonic bath, it should
be ensured that no air remains between water surface and sieve
bottom. After the ultrasonic treatment, rinse again briefly with
tap water. Thereafter, the sieve is removed and the water in the
ultrasonic bath is replaced. The procedure in the ultrasonic bath
is repeated until contamination of the water is no longer
detectable. The sieve with the remaining residue is dried to
constant weight (oven dry) in a forced-circulation drying oven.
After cooling, the residue is transferred by means of a brush into
a dish. Evaluation: wet sieve residue (WSR) in (%), based on the
amount weighed out.
[0060] 4. Particle Size Determination According to Malvern:
[0061] This is a customary method. A Mastersizer from Malvern
Instruments Ltd, UK, was used according to the manufacturer's
instructions. The measurements were carried out with the sample
chamber provided ("dry powder feeder") in air and the values based
on the sample volume were determined.
[0062] 5. Investigation of Binding of Impurities: in the
Investigation of the Binding of Impurities, the Following Procedure
was Adopted:
[0063] a) Preparation of Paper Stock and Filtration:
[0064] The chosen paper stock (e.g. 45% of chemical pulp and 55% of
peroxide-bleached groundwood) can either be obtained directly from
the paper mill or stored in a refrigerator before use. The paper
stock was then thoroughly shaken at 20 g absolutely dry and diluted
to 2% with warm demineralized water in a 2000 ml beaker. While
being stirred at 400 rpm, the paper stock batch warmed up to
40.degree. C. with the aid of a hotplate. When the temperature is
reached, the amount of adsorbent to be tested is added to the paper
stock batch with the aid of a Pasteur pipette. Thereafter, the
adsorption time in the stock batch is fixed at 30 min at 40.degree.
C. and the mixture is stirred for this time at 400 rpm. Thereafter,
the paper stock batch of the adsorbent is diluted to 1% solids
content with the aid of demineralized water (40.degree. C.).
[0065] For the white water preparation, 1000 g of this dilute stock
batch (1% by weight solids content) is drained in a drainage and
retention apparatus (Mutek DF3 03 from Mutek, Germany) for 420
seconds (170 .mu.m sieve, stirring speed 700 rpm). The white water
samples are investigated analytically.
[0066] b) Flow Cytometric Analysis of the White Water:
[0067] Here, so-called flow cytometry was used, as described in
Vahasalo et al., "Use of Flow Cytometry In Wet End Research", Paper
Technology, 44 (1), page 45, February 2003 and additionally in
"Effects Of pH and calcium chloride on pitch in peroxide-bleached
mechanical pulp suspensions", 7th European Workshop on
Lignocellulosics and Pulp, Aug. 26-29, 2002, .ANG.bo/Finland. In
brief, a light scattering method for counting the particles is
combined with fluorescence marking.
[0068] c) Gas Chromatographic Analysis of the White Water:
[0069] Here, the method of F. Orsa and B. Holmbom "A Convenient
Method for the Determination of Wood Extractives in Papermaking
Process Waters and Effluents", Journal of Pulp and Paper Science,
Vol. 20 No. 12, December 1994, pp J361, was used.
[0070] The following was found:
[0071] FIG. 1 shows a graph of the dependence of the concentration
of the impurity particles in the white water (filtrate water) on
the type and amount of the adsorbent used (bentonite or talc).
[0072] The invention is now illustrated further with reference to
the non-limiting examples below.
EXAMPLE 1
[0073] The following materials were investigated for the binding of
impurities.
[0074] 1. Calcium Bentonite (Bentonite 1)
[0075] The analytical data of the calcium bentonite used are
summarized in table 1. The proportions and the CEC are to be found
in table 2.
TABLE-US-00003 TABLE 1 Analytical data of the calcium bentonite
(bentonite 1) Water content 12.2% by weight pH (5% by weight of
suspension 9.0 in water) Montmorillonite content 100% by weight
(methylene blue method) Quartz 0.5% by weight Calcite <1% by
weight Specific surface area (BET) 86 m.sup.2/g
[0076] The wet sieve residue (45 .mu.m) was less than 0.5% by
weight.
TABLE-US-00004 TABLE 2 Proportion of the monovalent cations, based
on the cation exchange capacity (CEC) of the calcium bentonite
(bentonite 1); CEC (total) = 106 meg/100 g. Cation Proportion of
the CEC (%) Na 34 K 2 Li 0
[0077] 2. Cationized Talc (Product Malusil 75-7 K from Talc de
Luzenac)
[0078] 3. Bentonite According to the Invention (Bentonite 2)
[0079] Bentonite 2 was obtained from bentonite 1 by kneading
bentonite 1 with 5% by weight of sodium carbonate, based on the
anhydrous bentonite, according to the above method, drying to a
water content of 10% by weight and milling to a particle size
corresponding to that of bentonite 1 (comparison: table 2). By
means of these processing steps, the mineralogical data of the
bentonite are not changed, so that the montmorillonite content and
the content of impurity minerals remain unchanged. The BET surface
area was 85.+-.2 m.sup.2/g.
[0080] The analytical data for bentonite 2 are shown in table
3.
TABLE-US-00005 TABLE 3 Proportion of the monovalent cations, based
on the cation exchange capacity (CEC) of the bentonite according to
the invention (bentonite 2); CEC (total) = 102 meq/100 g of
bentonite. Cation Proportion of the CEC (%) Na 98 K 2 Li 0
[0081] Using the two bentonites 1 and 2, the binding of impurities
was investigated as described in the method section. For carrying
out the filtration experiments, a paper stock which was taken from
a paper machine and consisted of 45% of long fiber chemical pulp
and 55% of peroxide-bleached groundwood was used.
[0082] For comparison, in each case a "zero sample" was run, i.e.
no adsorbents were used for binding impurities.
[0083] For characterization of the filtrate waters (white waters)
with regard to a reduction of impurities, the abovementioned flow
cytometry was used. The results are shown in FIG. 1. The amount of
adsorbent used (bentonite or talc) is plotted against the
concentration of the impurity particles in the white water. It is
clearly found that the bentonite 2 according to the invention
exhibits substantially better binding of impurities than bentonite
1 or talc even when a small amount of three kilograms per tonne,
based on the paper pulp/suspension, is used in dry pulp.
[0084] The content of fatty acids, lignins, sterols, steryl esters
and triglycerides was determined for the above samples by means of
the gas chromatographic analysis (cf. method section). The
bentonites 1 and 2 were used in each case in an amount of 6 kg/t of
paper (dry weight); the cationized talc was used in an amount of
11.25 kg/t of paper, since 6 kg/t gives poor results. The values
obtained are shown in table 4.
TABLE-US-00006 TABLE 4 Concentrations of individual impurities
after the treatment with the impurity-binding agents in mg/l
according to gas chromatography Fatty Steryl Sample acids Lignins
Sterols esters Triglycerides "Zero 0.08 4.38 0.25 1.26 1.69 sample"
Cat. talc 0.04 4.23 0.20 1.07 1.77 Bentonite 1 0.05 4.16 0.07 0.46
0.96 Bentonite 2 0.04 4.07 0.06 0.31 0.67
[0085] As is evident in table 4, the sample treated with the
bentonite 2 according to the invention shows substantially better
binding/removal of fatty acids, lignins, styrenes, styryl esters
and triglycerides both compared with the sample treated with
cationized talc and with the sample treated with the calcium
bentonite (bentonite 1) not according to the invention.
[0086] In a further example, the bentonite according to the
invention was compared with conventional bentonites which have a
proportion of monovalent cations, based on the CEC, of at least 0.7
(70%) but a CEC of less than 85 meq/100 g.
[0087] Once again, substantially better binding of impurities by
the bentonite according to the invention was found in comparison
with the conventional bentonites, even when small amounts were
used.
* * * * *