Note: Descriptions are shown in the official language in which they were submitted.
21 ~6458
English Translation of Article 34 Amendment of
April 7, 1995
H 812 PCT/07.04.1995
A process for reducing the c~nt~nt of finely dispersed solids in
papel, k;ng process waters
Field of the Invention
This invention relates to a process for reducing the content
of finely dispersed solids in papermaking process waters.
Prior Art
Various water-soluble and colloidally dissolved inorganic and
organic substances are formed in the production and processing of
chemical pulp, mechanical pulp and wastepaper. Other water-soluble
substances enter the production circuit with the fresh water, the
fillers and chemical auxiliaries. With the growing reduction in the
size of the water circuits, the concentration of these substances is
undergoing a very considerable increase. This results in additional
pollution of the wastewater~ However, far more serious is the
disturbing effect on the papermaking process itself. These sub-
stances, which are known among experts as "impurities" (cf. for
example W. Auhorn, Wo~h~nhl~tt fur Papierfabrikation, 1984, 2, 37-
48), can have a serious effect on production, can reduce the
effectiveness of the chemical ~l]x;l;~ries and refining agents and can
impair paper quality. It is mainly the dissolved organic substances
which are an obstacle to any further reduction in the size of the
circuits.
In view of the adverse affect of the impurities, water
purification is generally necessary in the case of closed water
circuits and compact circuits. Flocculation, precipitation,
adsorption or flotation processes or combinations thereof are
normally used for this purpose (cf. for example J. Schurz, W-
orh~nhl~tt fur Papierfabr;~t;nn, 1990, 3, 109-118). Microflotation,
for example, is normally used in wash deinking systems. In this
process, the suspended solids and the dissolved and colloidal
substances are flocculated and then floated out from the water (cf.
for example K. Schnabel, W_~h~nhl~tt fur Papierfa-hrikation~ 1990, 6,
233-237).
Typical flocculants in the treatment of papermaking process
waters are inorganic and organic flocculants, such as milk of lime,
aluminium or iron salt solutions, cationic polymers, such as
polyethyl~n~;m;nP~ cationic starches, polyamidoamine/epichlorohydrin
resins and m~l; ' ne/formaldehyde resins (cf. the above-cited articles
by W. Auhorn and J. Schurz). A flocculant particularly preferred
among experts is polydiallyl dimethylammonium chloride (cf. for
example R. Nicke et al., W_ hl~tt fur Papierfabrikation, 1992, 14,
2 1 66458
H 812 PCT 2
559-564 and the above-cited article by J. Schurz). This compound,
which is normally known as poly-DADMAC, is a linear molecule which
carries a positive charge at the nitrogen atom in each of the
recurring structural units. Towards the outside, this positive
charge is neutralized by a negatively charged chloride ion. In
overall terms, a polyelectrolyte with a very high charge density is
thus formed.
In addition to the water-soluble and colloidally dissolved
impurities mentioned aboye, finely dispersed solids also enter
papermaking process waters and undesirably accumulate therein at
constrictions in the circuit. These solids are, above all, fillers,
fine fibers and printing inks. The removal of these unwanted finely
dispersed solids is difficult, above all in the presence of dissolved
or colloidally dissolved impurities.
Description of the Invention
The problem addressed by the present invention was to provide
a process for reducing the content of finely dispersed solids in
papermaking process waters. In particular, the process according to
the invention would not be affected by the presence of dissolved or
colloidally dissolved impurities.
It has now been found that special cationic polymers are
suitable for the treatment of papermaking circuit waters and
wastewaters and are superior in this regard to other cationic
polymers known from the prior art.
Accordingly, the present invention relates to a process for
reducing the content of finely dispersed solids in process waters of
the papermaking industry, a cationic polymer being added to the
process water and the flocculated solids being subsequently removed
by flotation and/or filtration, characterized in that
i) an at least partly water-soluble nitrogen-cont~;n-ng compound
with weight average molecular weights of 2,000 to 1,000,000
obt~n~hle by copolymerization of aminofunctional mt~nt ?rs cor-
responding to general formula I:
O Rs
Rl-CH=CR2-C-Z-(CnH2n)-N (I)
R4
in which Rl and R2 are each a hydrogen atom or a methyl group,
R3 and R4 are each a hydrogen atom or a Cl_~ alkyl group or a
piperazine, piperidine or morpholine group and Rs is a linear
or branched Cl_22 alkyl radical, with the proviso that the
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H 812 PCT 3
counterion to the ammonium function is a halogen, sulfate,
phosphate, borate or organic acid anion or an electron pair,
Z is oxygen or NH and n is a number of 2 to 5,
with
m~n~ -riC, unsaturated carboxylic acid esters corresponding to
general formula III:
R7-CH=CR8-C-o-(CmH2mo)p-R9 tIII)
in which R7 and R3 are each a hydrogen atom or a methyl group
and R9 is a linear or branched C1_22 alkyl group, m is a number
of 2 to 4 and p is a number of 0 to 18, with the proviso that,
where p = 0, the content of unsaturated carboxylic acid esters
in the copolymer does not exceed 90~ by weight,
is used as the cationic polymer and
ii) the cationic polymer mentioned in i) is used in a quantity of
1 to 500 mg of active substance per liter of process water.
"At least partly water-soluble" in the context of the present
invention means that more than 0.01~ by weight of the copolymers form
clear or cloudy solutions in water under in-use conditions.
Finely dispersed solids in the context of the present invention
are solids with particle sizes of around 0.1 to 1000 ~m. In the
narrower sense, finely dispersed solids are thus fine fibers, fillers
and printing inks.
The process according to the invention may be applied with
advantage even when the process water in which the content of the
finely dispersed solids is to be reduced additionally contains
dissolved or colloidally dissolved impurities.
The weight average molecular weights of the cationic polymers
to be used in accordance with the invention are preferably in the
range from 5,000 to 500,000. The range from 10,000 to 200,000 is
most particularly preferred.
In one preferred embodiment of the present invention, the
special cationic polymers mentioned are used in a quantity of 5 to
100 mg of active substance per liter of process water.
Suitable aminofunctional m~om~rs corresponding to general
formula I are in particular those in which R1 is hydrogen, R7 is
hydrogen or methyl, R3 and R4 are methyl or ethyl, Rs represents an
electron pair or a C1_4 alkyl group, with the proviso that the
counterion to the ammonium function is a halogen anion. Examples are
dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate,
dimethyl; nopropyl methacrylamide, dimethyl~mlnoneopentyl acrylate,
diethylaminoethyl acrylate, diethylaminoethyl methacrylate and/or
2 1 66458
H 812 PCT 4
methacrylamidopropyl dimethyl~ ;um chloride.
Monomeric unsaturated carboxylic acid esters corresponding to
general formula III, in which R9 is preferably a linear or branched
C18 alkyl group, include for example ethyl acrylate, methyl methacry-
late, butyl acrylate, butyl methacrylate, octyl acrylate and/or anadduct of 3 moles of ethylene oxide with butyl acrylate.
In addition, acrylamide, methacrylamide, N-ethyl acrylamide
and/or tert.butyl acrylamide are suitable for copolymerization with
aminofunctional m~nom~rs corresponding to general formula I.
The copolymerization of the aminofunctional m~nt ~rs corre-
sponding to general formula I is carried out by polymerization
processes known per se in aqueous media optionally cont~in;ng water-
miscible solvents, such as alcohols, for example isopropanol. The
initiator used is a radical-forming substance, for example potassium
or ammonium peroxodisulfate, tert.butyl hydroperoxide, azo-bis-
(isobutyronitrile), added in small quantities. The copolymerization
of the aminofunctional mont- -rs corresponding to general formula I
may be carried out for example by simultaneously adding the ,- om~rs
I and the mont_ -rs of general formula III dropwise to water con-
t~n;ng the initiator. The polymerization temperature is not criti-
cal per se and may vary within wide limits. Temperatures of 60 to
100C can be optimal, depending on the initiator used. Aqueous
copolymer solutions with polymer contents of, for example, 10 to 60
by weight are obtained.
sasically, there are no particular limits to either the nature
or the origin of the process waters in the process according to the
invention. Examples include circuit waters from wash deinking and
combined flotation/washing, waters from drainage units of paper ma-
chines (tray waters), deckering waters from presses.
In many cases, the extent to which the dispersed solid
impurities are removed can be increased by using the special cationic
polymers suitable for the purposes of the invention in combination
with flotation collectors and/or inorganic adsorbents or flocculants.
In another embodiment, therefore, the present invention relates to
combinations of the special cationic polymers mentioned with other
flotation collectors and/or inorganic flocculants.
Examples of flotation collectors are C10_22 fatty acids and
alkali metal and alkaline earth metal salts thereof, alkoxylated C6_22
alcohols, alkoxylated alkylphenols. The above-mentioned fatty acids
and fatty alcohol alkoxylates with a high percentage content of
alkylene oxide, more particularly ethylene oxide, are most particu-
larly suitable. Examples of flocculants are milk of lime, aluminium
or iron salt solutions.
In another preferred embodiment of the present invention, the
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H 812 PCT 5
flocculated solids are removed by flotation.
The present invention also relates to the use of the special
cationic polymers mentioned above for reducing the content of finely
dispersed solids in papermaking process waters. It has been found
in this regard that the percentage content of finely dispersed solids
is reduced to a distinctly greater extent by the use of the cationic
polymers according to the invention than by the use of conventional
cationic polymers known from the prior art.
The following Examples are intended to illustrate the invention
without limiting it in any way.
~ x a m p 1 e s
1. Substances used
Poly-DADMAC: Commercial polydiallyl dimethylammonium chloride;
approx. 40~; average molecular weight 200,000 (a product of Mutek).
Polymer A: The production of this cationic polymer according to the
invention was carried out in various batch sizes. The following
description of the production process relates to the 1.5 kg labora-
tory scale; the percentages by weight of the components in phases a),
b) and c) shown below are based on the batch as a whole and,
accordingly, add up to 100%.
a) Aqueous phase:
- 59.3 parts by weight of ~ml n~ralized water
- 6.5 parts by weight of 30% sulfuric acid
- 2.0 parts by weight of acrylic acid
b) Organic phase:
- 13.3 parts by weight of dimethylaminoethyl methac-
rylate
- 2.8 parts by weight of methyl methacrylate
- 6.0 parts by weight of isopropanol
~1 66458
H 812 PCT 6
c) Initiator solution:
- 10.0 parts by weight of isopropanol
- 0.1 part by weight of azo-bis-(isobutyronitrile).
The aqueous phase was introduced into a reactor (reaction
vessel equipped with a stirrer, heating system, external cooler,
reflux c~n~n~er, internal thermometer and feed mixing vessel). The
organic phase was homogenized in a feed mixing vessel and then slowly
introduced with stirring into the reactor. The reaction mixture
underwent a slight increase in temperature through the exothermic
nature of the reaction. The initiator solution was then added at
around 30C. The pH value of the mixture was 7.3. The reaction
mixture was then carefully heated to 65C by an external heating
system. The heat of reaction generated after the start of the
reaction was controlled by careful external cooling. After 30 min-
utes, the lnt~rn~l temperature of the reaction mixture was increased
to 70C and, after another hour, to 80C, the reaction mixture being
stirred for another hour at that temperature. A clear, pale
yellowish solution with an active substance content of around 20.5
by weight was obtained after cooling.
2. Origin of the impurity-c~nt~ining circuit water
A circuit water from a wastepaper recycling plant was used for
the tests described below. In addition to the usual stock prepara-
tion and the paper machines, the plant had a flotation deinkingsystem.
The circuit water sample required for the tests described below
was taken from the stock preparation part of the plant. It had a pH
value of around 8 and, in addition to the unwanted solids, also
contained dissolved and colloidally dissolved anionic impurities.
The percentage content of the last-mentioned impurities was deter-
mined by the method developed by L. Bley (cf. Wo~h~nhl~tt fur
Papierfabr;k~t;~n 1989, 3, page 114) and measured 510-3 mole/l.
3. Test procedure
3.1. net~ n~tinn of the solids c~nt~nt in the circuit water
A sample of the circuit water emanating from the wastepaper
recycling plant was filtered through a paper filter (medium-quick
filter rate, mean pore diameter 5.8 ~m), after which the filter was
dried for one hour at 90C. The increase in weight of the paper
filter is a measure of the finely dispersed solids present in the
circuit water. The solids content of the circuit water was found by
this method to amount to 0.79 g/l.
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H 812 PCT 7
3.2. Comparison test 1
A Denver 9 liter laboratory flotation cell was filled with the
circuit water sample emanating from the wastepaper recycling plant.
Flotation was carried out over a period of 2 minutes at an air
throughput of 200 l/h and at a rotational speed of the stirrer of
1200 min~1. The water from the flotation cell was then filtered
through a filter paper as described in 3.1. and the filter was
subsequently dried. The solids content of the circuit water was
found to be 0.57 g/l. Comparison with the value of 0.79 g/l
determined in 3.1. shows that the solids content was reduced by 28
without the addition of an auxiliary, i.e. solely by flotation.
3.3. Comparison test 2
A Denver 9 liter laboratory flotation cell was filled with the
circuit water sample emanating from the wastepaper recycling plant.
A dilute aqueous solution of the polymer poly-DADMAC known from the
prior art was added in a quantity of 10 mg of poly-DADMAC active sub-
stance per liter of circuit water. Flotation was carried out for 2
minutes at an air throughput of 1200 l/h and at a rotational speed
of the stirrer of 1200 min~l. The water from the flotation cell was
then filtered through a paper filter as described in 3.1. and the
filter was subsequently dried. The solids content of the circuit
water was found to be 0.31 g/l. Comparison with the value of 0.79
g/l determined under 3.1. shows that the solids content was reduced
by 61~ through the addition of poly-DADMAC.
3.4. ~xample 1 (Inv~nt;nn)
A Denver g liter laboratory flotation cell was filled with the
circuit water sample emanating from the wastepaper recycling plant.
A dilute aqueous solution of polymer A according to the invention was
added in a quantity of 10 mg of polymer A active substance per liter
of circuit water. Flotation was carried out for 2 minutes at an air
throughput of 200 l/h and at a rotational speed of the stirrer of
1200 min~1. The water from the flotation cell was then filtered
through a paper filter as described in 3.1. and the filter was subse-
quently dried. The solids content of the circuit water was found to
be 0.06 g/l. Comparison with the value of 0.79 g/l determined under
3.1. shows that the solids content was reduced by 92~ through
addition of polymer A according to the invention.
4. Discussion of the results
In the interests of clarity, the values obtained in 3.1. to
3.4. are set out in the following Table:
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H 812 PCT 8
PolymerSolids content (g/l) Reduction in the
added solids content
Before After
flotation flotation
- 0.79 0.57 28
Poly-DADMAC 0.79 0.31 61
Polymer A 0.79 0.06 92~
It can clearly be seen that better results are obtained with
the cationic polymers according to the invention than with the poly-
DADMAC known from the prior art.
