U.S. patent application number 09/978101 was filed with the patent office on 2002-06-06 for transition metal complexes with polydentate ligands for enhancing the bleaching and delignifying effect of peroxo compounds.
Invention is credited to Jakob, Harald, Kunz, Ulrike.
Application Number | 20020066542 09/978101 |
Document ID | / |
Family ID | 7660017 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066542 |
Kind Code |
A1 |
Jakob, Harald ; et
al. |
June 6, 2002 |
Transition metal complexes with polydentate ligands for enhancing
the bleaching and delignifying effect of peroxo compounds
Abstract
Transition metal complex compounds of polydentate ligands with
improved delignifying and bleaching performance. These polydentate
ligands are organic ligands which, in aqueous solution and in the
presence of atmospheric oxygen, or hydrogen peroxide, form a
complex with a transition metal, in particular cobalt. The
complexes are mono- or polynuclear and they have, when peroxo
compounds are used, better delignifying and bleaching performances
than conventional transition metal complex compounds. A
delignifying and bleaching method, in which these transition metal
complex compounds with polydentate ligands having improved
delignifying and bleaching performance are used as catalysts, is
also described.
Inventors: |
Jakob, Harald; (Hasselroth,
DE) ; Kunz, Ulrike; (Gelnhausen, DE) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
Suite 800
1850 M Street, N.W.
Washington
DC
20036
US
|
Family ID: |
7660017 |
Appl. No.: |
09/978101 |
Filed: |
October 17, 2001 |
Current U.S.
Class: |
162/72 ; 162/78;
162/79 |
Current CPC
Class: |
D21C 9/163 20130101;
D21C 9/1042 20130101 |
Class at
Publication: |
162/72 ; 162/78;
162/79 |
International
Class: |
D21C 003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2000 |
DE |
100 51 317.4 |
Claims
We claim:
1. A method for the delignification and/or bleaching of fibrous
materials compromising contacting a) an aqueous suspension of
fibers, which have a consistency of from 3% to 40%; with b) a
peroxo compound, which is used at from 0.1% to 10%, based on the
bone-dry fibrous mass; and with c) a mononuclear transition metal
complex of the formula (1), (LMX.sub.p).sup.zY.sub.q Formula (1)
wherein L is a polydentate ligand of the formula (a), (b), (c) or
(d), 2in which R1, R2, and R3 independently of one another
represent hydrogen, linear of branched alkyl or alkenyl, or an
optionally substituted aryl or arylalkyl; R4 independently of one
another represents an optionally N-substituted linear, branched or
cyclic aminoalkyl, or an optionally substituted heteroaryl; M is a
transition metal ion, selected from the group consisting of iron in
oxidation states (II) to (V); manganese in oxidation states (II) to
(VII); and cobalt in oxidation states (II) to (IV); X is a
coordinate species which can be neutral or anionic; Y is a
counter-ion or counter-molecule. p is an integer from 0 to 4; z is
a complex charge (+/0/-); q is z/[charge of Y]; the transition
metal complex being present in an amount of from 10 ppm to 5000
ppm, based on the amount of bone-dry fibers.
2. The method according to claim 1 wherein R4 is: pyridyl,
pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, pyrimidyl, triazolyl or
quinolyl.
3. The method according to claim 1 wherein X is: CH.sub.3CN,
CH.sub.3COO.sup.-, Cl.sup.-, Br.sup.-, H.sub.2O, OH.sup.-,
HOO.sup.-, OCN.sup.-, SCN.sup.-, PO.sub.4.sup.3-, NH.sub.3,
NO.sub.3.sup.-, NO.sub.2.sup.-, NO, O.sup.2-, O.sub.2.sup.2-.
4. The method according claim 1 wherein Y is: ClO4-, Br-, Cl-,
PF.sub.6.sup.-, NO.sub.3.sup.-, BPh.sub.4.sup.-, SO.sub.4.sup.2-,
CH.sub.3COO.sup.-.
5. The method according to claim 1, wherein the transition metal
complex is present in an amount of from 50 ppm to 3000 ppm, based
on the amount of bone-dry (b.d.) fibers used.
6. The method according to claim 5, wherein the amount is from 200
ppm to 2000 ppm.
7. The method according to claim 5 wherein the amount is from 200
ppm to 1500 ppm.
8. The method according to claim 1, wherein the transition metal
complex is formula (1a).
9. The method according to claim 5, wherein the transition metal
complex is formula (1a).
10. The method according to claim 8, where M in the transition
metal complex of the formula (a), is cobalt(II) or (III).
11. The method according to claim 9, where M in the transition
metal complex of the formula (a), is cobalt(II) or (III).
12. The method according to claim 1, wherein the transition metal
complex is formula (1b).
13. The method according to claim 5, wherein the transition metal
complex is formula (1b).
14. The method according to claim 12, where M in the transition
metal complex of the formula (1b) is cobalt(II) or (III).
15. The method according to claim 13, where M in the transition
metal complex of the formula (1b) is cobalt(II) or (III).
16. The method according to claim 1, wherein the transition metal
complex is formula (1d).
17. The method according to claim 5, wherein the transition metal
complex is formula (1d).
18. The method according to claim 1, further comprising preparing
the transition metal complex "in situ".
19. The method according to claim 5, further comprising preparing
the transition metal complex "in situ".
20. The method according to claim 1, further comprising the peroxo
compound being present in an amount from 0.3 to 6%, based on the
bone-dry fibrous mass.
21. The method according to claim 1, further comprising contacting
at a reaction temperature of 20.degree. C. to 130.degree. C.
22. The method according to claim 21, where the temperature of
40.degree. C. and 100.degree. C.
23. The method according to claim 21, where the temperature of
50.degree. C. and 98.degree. C.
24. Transition metal complex having the formula (1b), namely
(LMX.sub.p).sup.zY.sub.q Formula (1) wherein L is a polydentate
ligand of the formula, 3
25. A method for the delignification of fibrous materials
comprising contacting a) an aqueous suspension of fibers, which
have a consistency of from 3% to 40%; with b) a peroxo compound,
which is used at from 0.1% to 10%, based on the bone-dry fibrous
mass; and with c) as a bleaching catalyst a mononuclear transition
metal complex of the general formula (2), (LMX.sub.p).sup.zY.sub.q;
Formula (1) wherein L is a polydentate ligand of the formula, 4in
which R1, R2, and R3 independently of one another represent
hydrogen, a linear of branched alkyl or alkenyl, or an optionally
substituted aryl or arylalkyl; R4 independently of one another
represents an optionally N-substituted linear, branched or cyclic
aminoalkyl, or an optionally substituted heteroaryl; M is a
transition metal ion, selected from the group consisting of iron in
oxidation states (II) to (V); manganese in oxidation states (II) to
(VII); or cobalt in oxidation states (II) to (IV); X is a
coordinate species which can be (neutral or anionic), Y is a
counter-ion or counter-molecule; p is an integer from 0 to 4; z is
a complex charge (+/0/-); q is z/[charge of Y]; the transition
metal complex being used in an amount of from 10 ppm to 5000 ppm,
based on the amount of bone-dry fibers.
26. A method for the delignification of fibrous materials with
comprising treating d) an aqueous suspension of fibers, which have
a consistency of from 3% to 40%; with e) a peroxo compound, which
is used at from 0.1% to 10%, based on the bone-dry fibrous mass;
and with a) a mononuclear transition metal complex of the formula
(2), (L.sub.mCo.sub.nX.sub.p).sup- .zY.sub.q; Formula (2) wherein L
is a ligand of the formula (a), (b), (c) or (d); Co stands for
cobalt in oxidation states (II) to (IV) or mixtures of these
oxidation states, the oxidation states (II) and (III) being
particularly preferred; X, Y, z and q are as described for formula
(1); m and n are integers from 2 to 4; and p is an integer from 0
to 12; the transition metal complex being present used in an amount
of from 10 ppm to 5000 ppm, based on the amount of bone-dry fibers
used.
27. The method according to claim 26, wherein the transition metal
complex is present in an amount of from 50 ppm to 3000 ppm based on
the amount of bone-dry (b.d.) fibers used.
28. The method according to claim 27 where the amount is 200 ppm to
2000 ppm.
29. The method according to claim 27 where the amount is 200 ppm to
1500 ppm.
30. The method according to claim 26, wherein the transition metal
is formula (2a)
31. The method according to claim 27, wherein the transition metal
is formula (2a).
32. The method according to claim 26, wherein the transition metal
complex is formula (2c).
33. The method according to claim 27, wherein the transition metal
complex is formula (2c).
34. The method according to claim 26, further compromising
preparing the transition metal complex "in situ".
35. The method according to claim 27, further compromising
preparing the transition metal complex "in situ".
36. The method according to claim 26, wherein the peroxo compound
is present from 0.3% to 6%, based on the bone-dry fibrous mass.
37. The method according to claim 26, wherein the reaction
temperature is between 20.degree. C. to 130.degree. C.
38. Transition metal complex having the formula (2a), where
X=O.sub.2.sup.2-.
39. Transition metal complex having the formula (2b) or (2c), where
X=O.sub.2.sup.2-.
40. Transition metal complex according to claim 38, where m and
n=2, and p=1.
41. Transition metal complex according to claim 39, where m and
n=2, and p=1.
42. A method for the delignification of fibrous materials with
comprising contacting d) aqueous suspension of fibers, which have a
consistency of from 3% to 40%; with e) a peroxo compound, which is
used at from 0.1% to 10%, based on the bone-dry fibrous mass; and
with a) a mononuclear transition metal complex of the formula (2),
(L.sub.mCo.sub.nX.sub.p).sup- .zY.sub.q; Formula (2) wherein L is a
ligand of the formula (a), Co stands for cobalt in oxidation states
(II) to (IV) or mixtures of these oxidation states, the oxidation
states (II) and (III) being particularly preferred; Y, z and q are
as described for formula (1); m and n are integers from 2 to 4; and
X in O.sub.2.sup.2-, and p is an integer from 0 to 12; the
transition metal complex being present used in an amount of from 10
ppm to 5000 ppm, based on the amount of bone-dry fibers used.
43. A method for the delignification of fibrous materials with
comprising contacting d) aqueous suspension of fibers, which have a
consistency of from 3% to 40%; with e) a peroxo compound, which is
used at from 0.1% to 10%, based on the bone-dry fibrous mass; and
with a) a mononuclear transition metal complex of the formula (2),
(L.sub.mCo.sub.nX.sub.p).sup- .zY.sub.q; Formula (2) wherein L is a
ligand of the formula (b) or (c); Co stands for cobalt in oxidation
states (II) to (IV) or mixtures of these oxidation states, the
oxidation states (II) and (III) being particularly preferred; Y, z
and q are as described for formula (1); m and n are integers from 2
to 4; and X in O.sub.2.sup.2-, and p is an integer from 0 to 12;
the transition metal complex being present used in an amount of
from 10 ppm to 5000 ppm, based on the amount of bone-dry fibers
used.
44. A method for the delignification of fibrous materials with
comprising contacting d) aqueous suspension of fibers, which have a
consistency of from 3% to 40%; with e) a peroxo compound, which is
used at from 0.1% to 10%, based on the bone-dry fibrous mass; and
with a) a mononuclear transition metal complex of the formula (2),
(L.sub.mCo.sub.nX.sub.p).sup- .zY.sub.q; Formula (2) wherein L is a
ligand of the formula (d); Co stands for cobalt in oxidation states
(II) to (IV) or mixtures of these oxidation states, the oxidation
states (II) and (III) being particularly preferred; Y, z and q are
as described for formula (1); m and n are integers from 2 to 4; and
X in O.sub.2.sup.2-, and p is an integer from 0 to 12; the
transition metal complex being present used in an amount of from 10
ppm to 5000 ppm, based on the amount of bone-dry fibers used.
Description
INTRODUCTION AND BACKGROUND
[0001] The present invention relates to transition metal complexes
with polydentate ligands for enhancing the bleaching and
delignifying effect of peroxo compounds. In a further aspect, the
present invention relates to the use of such complexes and to a
method for the delignification of fibrous materials.
[0002] The term "fibrous materials" will be used below to denote
all lignin-containing fibers, which have either been mechanically
and/or chemically pretreated by the process of lignin production or
pulp production or are subjected to this method as chemically or
mechanically untreated natural fibers. These fibers may also have
undergone several stages of chemical and/or mechanical processing,
for example chemical pulping and a first delignifying treatment
after pulping.
[0003] Lignin-containing fibers from wood or from annual plants
should, as far as possible, be freed from lignin for most
applications. The fibers should furthermore have high brightnesses,
advantageously 90% ISO. These high brightnesses will be achieved
only if lignin is substantially removed from the fiber or from the
fiber surface. Using elemental chlorine and other
chlorine-containing bleaching chemicals, it has been possible to
delignify lignin-containing fibers efficiently and highly
selectively in the past.
[0004] Since, when chlorine and/or chlorine-containing chemicals
such as e.g. chlorine dioxide are used, it is not possible to avoid
the formation of AOX ("adsorbable organically bound halogen") in
the waste water and OX ("organically bound halogen") in the pulp,
therefore, pulp manufacturers are making increased use of
chlorine-free bleaching agents, such as for example oxygen and
oxygen-containing chemicals, which are intended to brighten the
fibers to the highest possible brightness (elemental chlorine-free
bleaches (ECF bleaches) and totally chlorine-free bleaches (TCF
bleaches). In order to obtain approximately the same effect as with
chlorine-containing bleaching agents, it is necessary to select
more drastic conditions, such as for example higher reaction
temperatures and longer reaction times. A disadvantage with
oxygen-containing bleaching agents is that the reaction mechanisms
of these chemicals are far less selective than is the case with
chlorine or chlorine-containing chemicals, so that the
delignification or bleaching entails greater damage to the
cellulose. There is therefore a great need for methods, and also
therefore for chemicals, which selectively and mildly break down by
oxidation the residual lignin still present after pulping.
[0005] The chlorine-free bleaching agents, which are used for this
purpose in the pulp industry, also include hydrogen peroxide.
Hydrogen peroxide is used, above all, for environmental protection
reasons. It is more expensive than chlorine-containing bleaching
agents, and significantly less selective. For these reasons,
hydrogen peroxide has to date been used under the mildest possible
conditions wherever fibrous materials are to be brightened but not
delignified. Under more intense reaction conditions, for example
higher temperature, greater use of chemicals and/or longer reaction
time, although the residual lignin still present does become broken
down to some extent, this is accompanied by increased damage to the
fiber and yield losses. A particularly undesirable feature is that
the unselective reaction of hydrogen peroxide attacks the
cellulose, so that the strength of the fiber is significantly
reduced.
[0006] In order to make best use of the brightening effect of
hydrogen peroxide, attempts have for some time been made to find
catalysts which suppress the many unselective side reactions and
thereby make more hydrogen peroxide available for the removal of
chromophoric groups and/or activate hydrogen peroxide for the
delignification. To that end, substances which, for example, have
been described for bleaching or brightening use in detergents are
used time and time again. The results from the field of detergents,
however, are scarcely applicable to the pulp and paper industry,
since textile fibers are not comparable with lignin-containing
fibers. The reason for this is that the chemical structure of
stubborn stains in fabrics is very different from the structure of
the wood lignin to be oxidized. Furthermore, the dirt is located on
the textile fiber, whereas the majority of the lignin to be removed
is embedded in the cellulose fiber (middle lamella).
[0007] The previously known methods, for instance that described in
DE 19 620 241, WO 97/44520 and WO 99/64156, use manganese or iron
complexes as catalysts to activate peroxo compounds. These
compounds have the disadvantage that they are difficult to
synthesize. Furthermore, they significantly show an H.sub.2O.sub.2
degradation effect (catalase activity), the result of which is that
only certain amounts of the transition metal complex compounds can
be used.
[0008] An increase in the amount of catalyst hence does not lead to
an increase in the bleaching effect (see DE 19 620 241, Example 3),
but rather to degradation of the hydrogen peroxide, which is
thereby made unavailable for the bleaching. The consequences are
inferior brightness, or increased kappa numbers, and significant
damage to the fibrous mass. These compounds also have the
disadvantage that they are degraded under bleaching conditions (at
least pH 10. 80.degree. C.). This instability of the complexes
during bleaching makes it appropriate to add the catalyst
portionwise, as described explicitly in APPITA Annual Conference
1999, pp. 455 to 461. Although this procedure is possible at the
laboratory scale, it cannot be used industrially since additional
mixing machines cannot be integrated into the bleaching towers.
[0009] In view of the prior art described and discussed above, it
is an object of the invention to develop a method for the improved
and selective delignification and/or bleaching of lignin-containing
fibrous materials by using peroxo-containing and therefore
environmentally friendly chemicals.
SUMMARY OF THE INVENTION
[0010] It has now been surprisingly found that the above and other
objects of the present invention can be achieved by using certain
transition metal complex compounds with polydentate ligands which
considerably surpass the delignifying and bleaching performance of
hitherto known catalytic systems. In this case, increasing the
amount of catalyst leads to an increase in the bleaching effect and
not, as in the case of conventional catalytic systems, to
uncontrolled degradation of the hydrogen peroxide. The consequences
are better brightnesses, or decreased kappa numbers, and gentle
treatment of the fibrous mass.
[0011] This invention therefore provides a method for the
delignification and/or bleaching of fibrous materials by treating
or contacting
[0012] a) an aqueous suspension of fibers, which have a consistency
of from 3% to 40%; with
[0013] b) a peroxo compound, which is used at from 0.1% to 10%,
based on the bone-dry fibrous mass; and with
[0014] c) a mononuclear transition metal complex of the formula
(1),
(LMX.sub.p).sup.zY.sub.q Formula (1)
[0015] wherein
[0016] L is a polydentate ligand of the formula (a), (b), (c) or
(d), 1
[0017] in which
[0018] R1, R2, and R3 independently of one another represent
hydrogen, linear of branched alkyl or alkenyl, or an optionally
substituted aryl or arylalkyl;
[0019] R4 independently of one another represents an optionally
N-substituted linear, branched or cyclic aminoalkyl, or an
optionally substituted heteroaryl such as pyridyl, pyrazinyl,
pyrazolyl, pyrrolyl, imidazolyl, pyrimidyl, triazolyl or
quinolyl;
[0020] M is a transition metal ion, advantageously selected from
the group consisting of iron in oxidation states (II) to (V);
manganese in oxidation states (II) to (VII); and cobalt in
oxidation states (II) to (IV); cobalt preferably being in oxidation
states (II) or (III);
[0021] X is a coordinate species (neutral or anionic), such as for
example CH.sub.3CN, CH.sub.3COO.sup.-, Cl.sup.-, Br.sup.-,
H.sub.2O, OH.sup.-, HOO.sup.-, OCN.sup.-, SCN.sup.-,
PO.sub.4.sup.3-, NH.sub.3, NO.sub.3.sup.-, NO.sub.2.sup.-, NO,
O.sup.2-, O.sub.2.sup.2-;
[0022] Y is a counter-ion or counter-molecule, such as for example
ClO4-, Br-, Cl-, PF.sub.6.sup.-, NO.sub.3.sup.-, BPh.sub.4.sup.-,
SO.sub.4.sup.2-, CH.sub.3COO.sup.- or mixtures thereof;
[0023] p is an integer from 0 to 4;
[0024] z is a complex charge (+/0/-);
[0025] q is z/[charge of Y];
[0026] or with
[0027] d) instead of (c), a mononuclear transition metal complex of
the general formula (2),
(L.sub.mCo.sub.nX.sub.p).sup.zY.sub.q; Formula (2)
[0028] wherein
[0029] L is a ligand of the formula (a), (b), (c) or (d);
[0030] Co stands for cobalt in oxidation states (II) to (IV) or
mixtures of these oxidation states, the oxidation states (II) and
(III) being particularly preferred;
[0031] X, Y, z and q are as described for formula (1);
[0032] m and n are integers from 2 to 4; and
[0033] p is an integer from 0 to 12;
[0034] the transition metal complex (c) or (d) being used in an
amount of from 10 ppm to 5000 ppm, based on the amount of bone-dry
(b.d.) fibers used.
[0035] Complex compounds of the formula (2), in which
X=O.sub.2.sup.2- and m, n=2 and p=1, are particularly
preferred.
[0036] Examples of ligands of the formula (a) which can be used
according to the invention are:
[0037] N,N-bis(2-aminoethyl)propane-1,2,3-triamine;
[0038] N,N-bis(2-aminoethyl)-2-methylpropane-1,2,3-triamine;
[0039] N,N-bis(2-aminoethyl)-bis(pyridin-2-yl)methylamine;
[0040]
N,N-bis(2-aminoethyl)-1,1-bis(pyridin-2-yl)-1-aminoethane;
[0041]
N,N-bis[2-(N,N-dialkyl)aminoethyl]]-bis(pyridin-2-yl)methylamine;
[0042] N,N-bis[2-(N,N-dialkyl)amino
ethyl]]-1,1-bis(pyridin-2-yl)-1-aminoe- thane;
[0043] N,N-bis(pyridin-2-ylmethyl)-bis(pyridin-2-yl)methylamine
(N4Py);
[0044]
N,N-bis(pyridin-2-ylmethyl)-1,1-bis(pyridin-2-yl)-1-aminoethane
(MeN4Py); and
[0045]
N,N-bis(pyridin-2-ylmethyl)-1,1-bis(pyridin-2-yl)-2-phenyl-1-aminoe-
thane.
[0046] Examples of ligands of the formula (b) which can be used
according to the invention are:
[0047] N-[2-amino-1-(aminomethyl)ethyl]propane-1,2,3-triamine;
[0048] bis[di(pyridin-2-yl)methyl]amine;
[0049] bis[1,1-di(pyridin-2-yl)ethyl]amine;
[0050] N-methyl-bis[di(pyridin-2-yl)methyl]amine; and
[0051] N-methyl-bis[1,1-di(pridin-2-yl)ethyl]amine.
[0052] Examples of ligands of the formula (c) which can be used
according to the invention are:
[0053] 1,4-bis(2-aminoethyl)-1,4,7-triazacyclononane;
[0054]
1,4-bis[2-(N,N-dialkyl)aminoethyl]-1,4,7-triazacyclononane;
[0055] 1,4-bis(2-aminoethyl)-7-methyl-1,4,7-triazacyclononane;
[0056]
1,4-bis[2-(N,N-dialkyl)aminoethyl]-7-methyl-1,4,7-triazacyclononane-
;
[0057] 1,4-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane; and
[0058]
1-methyl-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane.
[0059] Examples of ligands of the formula (d) which can be used
according to the invention are:
[0060] N,N,N'-tris(2-aminoethyl)ethylene-1,2-diamine;
[0061]
N,N-bis(2-aminoethyl)-N'-(pyridin-2-ylmethyl)ethylene-1,2-diamine;
[0062] N,N,N'-tris(2-aminoethyl)-N'-methylethylene-1,2-diamine;
[0063]
N,N-bis(2-aminoethyl)-N'-methyl-N'-(pyridin-2-ylmethyl)ethylene-1,2-
-diamine;
[0064] N,N,N'-tris(pyridin-2-ylmethyl)ethylene-1,2-diamine;
[0065]
N,N,N'-tris(3-methylpyridin-2-ylmethyl)ethylene-1,2-diamine;
[0066]
N-methyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylene-1,2-diamine;
and
[0067]
N-methyl-N,N',N'-tris(3-methylpyridin-2-ylmethyl)ethylene-1,2-diami-
ne.
[0068] In a first aspect of the invention, transition metal complex
compounds of polydentate ligands with improved delignifying and
bleaching performance will be described. These polydentate ligands
are organic ligands which, in aqueous solution and in the presence
of atmospheric oxygen and/or hydrogen peroxide, form a complex with
a transition metal, in particular cobalt, characterized in that the
complexes are mono- or polynuclear and they have, when peroxo
compounds are used, better delignifying and bleaching performances
than conventional transition metal complex compounds.
[0069] The transition metal complex compounds with polydentate
ligands, which are described here, will also be referred to as
bleaching catalysts. In this context, the term "polydentate
ligands" means ligands which have at least 4 or more heteroatoms
(so-called donor atoms), preferably nitrogen, which can coordinate
with the transition metal ion. Pentadentate ligands are preferred.
Pentadentate N-donor ligands are particularly preferably used in
the present invention.
[0070] In a second aspect, a delignifying and bleaching method will
be described, in which these transition metal complex compounds
with polydentate ligands having improved delignifying and bleaching
performance are used as catalysts. In this context, it has been
demonstrated that mononuclear transition metal complex compounds of
the general formula (1), in particular the mononuclear complexes of
the formula (1a) with the pentadentate ligand N4Py and derivatives
thereof, which are described for the low-temperature bleaching of
textile fabrics in EP 0 909 809 and WO 00/12667, are useful as a
bleaching catalyst in the bleaching of fibrous material and can be
employed therein.
[0071] It has furthermore been found that polynuclear, in
particular binuclear, cobalt complexes with polydentate ligands of
the general formula (2) also activate peroxo compounds for the
delignification or oxidative bleaching of fibrous materials.
[0072] It has been found that, when using the known iron or
manganese complexes of the formula (1a), in particular with the
ligand N4Py and derivatives thereof, in pulp bleaching or
delignification with hydrogen peroxide, it is possible to achieve
an improved effect compared with the reference test without the
addition of catalyst.
[0073] It has furthermore been found that a cobalt complex of the
formula (1a) can be obtained when the ligand N4Py known from the
literature [M. Lubben, A. Meetsma et al., Angew. Chem. 1995, 107,
1610, EP 0 909809, WO 95/34628], as described in WO 00/12667, is
reacted with a corresponding cobalt(II) salt instead of the
iron(II) salt. This cobalt-containing complex shows a significantly
better effect in the bleaching test than the said iron or manganese
compound.
[0074] However, the introduction of cobalt as a transition metal
ion in the way described above would not have appeared expedient to
the person skilled in the art. When following literature methods
for the reaction of cobalt(II) salts with polydentate ligands [G.
A. Lawrance, T. M. Manning et al., J. Chem. Soc., Dalton Trans.,
1992, 1635; G. A. Lawrance, M. A. O'Leary et al. Aust. J. Chem.
1988, 41, 1533, D. A. Buckingham, P. J. Cresswell et al., Inorg.
Chem. 1975, 14, 1485], with the ligand N4Py or derivatives thereof,
a binuclear cobalt complex is obtained with a .mu.-peroxo
(.mu.-O.sub.2) bridge similar to formula (2a), wherein
X=O.sub.2.sup.2-. This compound class, which has not to date been
described, provides better results in pulp bleaching or
delignification compared with the mononuclear compounds of the
formula (1a) prepared according to WO 00/12667, in particular the
said cobalt complex of the formula (1a) (see Table 1).
[0075] Peroxo compounds with a structure according to formula (2),
in which X=O.sub.2.sup.2-, can generally be prepared by reacting
the polydentate ligand or its salt (in the "one-pot method", see
Example 2), dissolved in corresponding solvents such as methanol,
water or mixtures thereof, with cobalt(II) salts and subsequent air
oxidation. The results achieved with these compounds in pulp
bleaching or delignification surpass the prior art discussed in the
introduction.
[0076] The use, according to the invention, of the transition metal
complex compounds substantially consists in creating conditions
under which the peroxo compound and the bleaching catalyst can
react with one another, for the purpose of obtaining consecutive
products which have a more strongly oxidizing effect. Such
conditions exist, in particular, when the two reaction partners
encounter one another in aqueous solution. The aqueous fibrous mass
already contains the bleaching catalyst according to the invention.
The peroxo compound may preferably be added separately to the
aqueous fibrous mass, and in substance or as an advantageously
aqueous solution. The bleaching catalyst may advantageously be
kneaded into the aqueous fibrous mass, optionally with other
bleaching additives, such as for example sodium hydroxide.
[0077] The bleaching catalyst may alternatively be prepared "in
situ" by separate addition of the metal salt and the ligand, or its
salt, to the aqueous solution of the bleaching additives, which is
subsequently mixed into the fibrous mass. In the case of such an
"in situ" method, the bleaching catalyst need not be isolated.
[0078] With these transition metal complexes according to the
invention, which are used in concentrations of from 10 ppm to 5000
ppm, preferably from 50 ppm to 3000 ppm, advantageously from 200
ppm to 2000 ppm, and particularly preferably from 200 ppm to 1500
ppm, based on the amount of bone-dry (b.d.) fibers used, the
delignification of fibers with the method according to the
invention can, quite surprisingly, be increased significantly
compared with the known, merely brightening peroxide stage, with
the cellulose being broken down only slightly. What is particularly
astounding is that these increase factors are achieved with rather
low residual lignin contents, where, according to the invention,
there are lignin structures which are particularly difficult to
break down, strongly condensed and therefore relatively
unreactive.
[0079] This enormous delignification and/or bleaching is achieved
by employing the transition metal complexes and process conditions
according to the invention.
[0080] The method according to the invention can be used for a wide
variety of fiber types, for instance mechanically and/or chemically
pretreated fibers, including waste-paper fibers, but also untreated
natural fibers.
[0081] As the peroxo compound, it is possible to use hydrogen
peroxide or compounds which release hydrogen peroxide, but also
organic or inorganic per-acids or salts thereof, for example
peracetic acid, peroxymonosulfuric acid or percarboxylic acid and
salts thereof. Mixtures of different peroxo compounds can be used
in a delignifying stage. Adaptation to special process requirements
is therefore possible.
[0082] The method according to the invention can be employed in a
wide consistency range (the consistency is equal to the ratio of
the bone-dry (b.d) fibrous mass to the total weight). The
consistency may be between 3% and 40%, although it is
advantageously a consistency of between 10% and 15%.
[0083] In order to achieve an optimum delignifying or bleaching
effect, between 0.1% and 10%, although advantageously between 0.3%
and 6%, of a peroxo compound should be used, in each case based on
the bone-dry (b.d.) fibrous mass to be delignified.
[0084] The method according to the invention shows excellent
delignifying or bleaching results when from 10 ppm to 5000 ppm,
preferably from 50 ppm to 3000 ppm, advantageously from 200 ppm to
2000 ppm, and particularly preferably between 200 ppm and 1500 ppm,
of the transition metal complex according to the invention are
used, based on the bone-dry (b.d.) fibrous mass. The breakdown of
the residual lignin takes place very efficiently when the pH at the
start of the reaction is more than 10, preferably more than 11.
[0085] The reaction temperature can be selected in a wide range,
according to the raw fibrous material in question. Between
20.degree. C. and 130.degree. C., although advantageously between
40.degree. C. and 110.degree. C., most fibers can be delignified.
The temperature range between 50.degree. C. and 98.degree. C. is
particularly preferred, because in this case it is still possible
to delignify very selectively under mild conditions, and with
relatively short reaction times.
[0086] The reaction time, like the reaction temperature, can also
be selected in a wide range, between 5 and 240 minutes (min).
However, a reaction time of from 30 to 150 min is preferred. The
delignification is particularly extensive when the reaction is
employed over a time period of from 45 to 120 min. These reaction
times are shorter than in the case of customary peroxide
stages.
[0087] The transition metal complexes used according to the
invention for delignifying and/or bleaching not only improve the
effect of a simple peroxide stage, but they also increase the
delignification or bleaching of an oxygen stage, which is carried
out with the addition of peroxide. If bleaching is carried out with
the addition of oxygen, particularly good results are achieved when
an overpressure of between 0.15 MPa and 1.5 MPa is applied. A
reaction pressure of from 0.2 MPa to 0.9 MPa is preferably
applied.
[0088] The complexing of transition metal ions has an advantageous
effect. Diethylenetriamine pentaacetic acid (DTPA),
diethylenetriamine penta(methylene phosphonic acid) (DTPMPA) or
poly(.alpha.-hydroxyacrylic acid), which are even stable at quite
high pH values, are advantageously used. In addition, or as an
alternative, water glass and/or magnesium sulfate can be used.
DETAILED DESCRIPTION OF INVENTION
[0089] The method according to the invention will be described
below with some exemplary embodiments:
[0090] The studies of catalyzed delignification stages with
peroxide, and optionally also with oxygen-containing chemicals,
were carried out using a kraft pulp (softwood, spruce/pine, kappa
number 24.0), which was previously subjected to an acid wash (1.7%
H.sub.2SO.sub.4, 70.degree. C., 3% consistency, residence time 0.5
hours (h)) and was then characterized as follows:
[0091] kappa number: 23.5
[0092] brightness: 30.5% ISO
[0093] viscosity: 32.3 mPa*s
[0094] Unless otherwise indicated, all the tests were carried out
with a 10% consistency, a reaction temperature of 80.degree. C. and
a reaction time of 90 min. Data in "%" are based on the amount of
bone-dry (b.d.) fibers. The analyses were carried out according to
the following standards:
[0095] The kappa number was established according to Zellcheming
instruction sheet IV/37/80. The viscosity of the pulp was
determined according to TAPPI instruction T230 om-82. The
brightness was measured with an Elrepho 2000 (from Datacolor).
[0096] The invention will be explained by the following examples,
without implying any limitation.
EXAMPLE 1
[0097] Synthesis of
{[Co(N4Py)].sub.2O.sub.2}Cl.sub.2(ClO.sub.4).sub.2, referred to
below as (Co--N4Py).sub.2(.mu.-O.sub.2)
[0098] A solution of 1.43 g (3.89 mmol) of the ligand N4Py in a
small amount of methanol (approx. 5 ml) was added at room
temperature to a solution of 925 milligrams (mg) (3.89 mmol) of
CoCl.sub.2.times.6H.sub.2O and 1.09 grams (g) (7.78 mmol) of sodium
perchlorate monohydrate in 10 milliliters (ml) of water. Air in
moderation was then introduced into the reaction solution over 2 h.
A red-brown solid immediately precipitated. The product was
filtered off and dried in air. 2.07 g (92%) of
(Co--N4Py).sub.2(.mu.-O.sub.2) was obtained as a red-brown
powder.
[0099] C.sub.46H.sub.42N.sub.10Cl.sub.4Co.sub.2O.sub.10 (1154.6
g/mol)
1 Calculated C 47.85 H 3.67 N 12.13 Co 10.2 Found C 47.74 H 3.72 N
11.73 Co 9.9
EXAMPLE 2
[0100] Synthesis of (Co--N4Py).sub.2(.mu.-O.sub.2) by the "one-pot
method"
[0101] 2.5 M aqueous NaOH solution was added to a solution of 476
mg (2.00 mmol) of CoCl.sub.2.times.H.sub.2O and 1.54 g (2.00 mmol)
of N4Py-4HClO4 in 100 ml of methanol/water (1:1) until pH>7. Air
in moderation was then passed through the reaction solution over 2
h. The solution was then vacuum-evaporated to half volume, the
red-crystalline solid was filtered off and the latter was dried in
air (820 mg, 71%).
EXAMPLES 3-16
[0102] The chemicals were added to 30 g of b.d. pulp so that an
aqueous solution of the additives and the catalyst was first mixed
in. The pH needed for the reaction was then adjusted using NaOH.
The corresponding amount of hydrogen peroxide was subsequently
kneaded in and the pH was measured. The sample was then held at
temperature in a polyethylene bag (PE bag) in a water bath. The
results without (Comparative Example A) and with bleaching catalyst
((Co--N4Py).sub.2(.mu.-O.sub.2), (Co-MeN4Py).sub.2(.mu.-O.sub.2);
Co--N4Py(CH.sub.3CN) and Fe-MeN4Py(CH.sub.3CN)) can be found in
Table 1.
COMPARATIVE EXAMPLES A-G
[0103] The chemicals were added to 30 g of b.d. pulp so that an
aqueous solution of the additives and the catalyst was first mixed
in. The pH needed for the reaction was then adjusted using NaOH.
The corresponding amount of hydrogen peroxide was subsequently
kneaded in and the pH was measured. The sample was then held at
temperature in a PE bag in a water bath. The results with the
selected comparative catalysts (CC) can be found in Table 1.
Equipment used for purposes of the invention is well known in the
act.
2TABLE 1 Example/ Comparative Catalyst Residual Example Type [ppm]
H.sub.2O.sub.2 [%] NaOH [%] H.sub.2O.sub.2 [%] Kappa Number After
acid -- 23.5 wash A -- 4.0 2.0 2.04 14.7 3
(Co-N4Py).sub.2(.mu.-O.su- b.2) 70 4.0 2.0 1.94 13.6 4
(Co-N4Py).sub.2(.mu.-O.sub.2) 200 4.0 2.0 1.64 12.3 5
(Co-N4Py).sub.2(.mu.-O.sub.2) 600 4.0 2.0 1.04 10.3 6
(Co-N4Py).sub.2(.mu.-O.sub.2) 1000 4.0 2.0 0.52 9.5 7
(Co-N4Py).sub.2(.mu.-O.sub.2) 1000 4.0 2.5 0.07 8.4 8
(Co-N4Py).sub.2(.mu.-O.sub.2) 1000 4.0 3.0 <0.01 8.4 9
(Co-N4Py).sub.2(.mu.-O.sub.2) 1500 4.0 2.0 0.38 8.6 10
(Co-N4Py).sub.2(.mu.-O.sub.2) 2000 4.0 2.0 0.13 8.3 B CC 1 33 4.0
2.0 1.32 14.7 C CC 1 100 4.0 2.0 0.31 14.2 D CC 1 167 4.0 2.0 0
13.7 E CC 2 70 4.0 2.0 0.33 10.9 F CC 2 100 4.0 2.0 0.14 9.9 G CC 2
150 4.0 2.0 0 9.8 11 Co-N4Py(CH.sub.3CN) 200 4.0 2.0 1.45 13.0 12
Co-N4Py(CH.sub.3CN) 600 4.0 2.0 0.57 11.2 13 Fe-MeN4Py(CH.sub.3CN)
150 4.0 2.0 1.04 13.4 14 Fe-MeN4Py(CH.sub.3CN) 300 4.0 2.0 0.44
12.5 15 (Co-MeN4Py).sub.2(.mu.-O.sub.2) 150 4.0 2.0 1.39 12.5 16
(Co-MeN4Py).sub.2(.mu.-O.sub.2) 1200 4.0 2.0 0.64 8.8
Example/Comparative Brightness Example [% ISO] Viscosity [mPa*s]
.DELTA.kappa w.r.t. A Delignification [%] after acid 30.5 32.3 wash
A 51.8 26.2 -- 37.4 3 Nm Nm 1.1 42.1 4 Nm Nm 2.4 47.7 5 56.6 22 4.4
56.2 6 55.9 21.6 5.2 59.6 7 57.4 19.5 6.3 64.3 8 56.9 19.2 6.3 64.3
9 55.9 20.8 6.1 63.4 10 54.3 19.8 6.4 64.7 B Nm Nm 0.0 37.4 C Nm
23.4 0.5 39.6 D Nm Nm 1.0 41.7 E 23.9 23.9 3.8 53.6 F 18.1 18.1 4.8
57.9 G 16.1 16.1 4.9 58.3 11 Nm Nm 1.7 44.7 12 54.8 Nm 3.5 52.3 13
Nm Nm 1.3 43.0 14 Nm Nm 2.2 46.8 15 Nm Nm 2.2 46.8 16 Nm Nm 5.9
62.6 CC 1 = CoCl.sub.2*6H.sub.2O CC 2 = Catalyst K2 from WO
97/44520 (Mn-TMTACN(.mu.-O).sub.3) nm = not measured
[0104] Table 1 clearly shows that increase factors in the
delignification of up to 65% can be achieved by using the catalysts
(Co--N4Py).sub.2(.mu.-O.sub.2) and (Co-MeN4Py).sub.2(.mu.-O.sub.2),
which considerably surpasses the delignifying and bleaching
performance of the comparative catalyst Mn-TMTACN(.mu.-O).sub.3 (CC
2). With the mononuclear complexes Co--N4Py(CH.sub.3CN) and
Fe-MeN4Py(CH.sub.3CN) described in EP 0 909 809 and WO 00/12667 for
the low-temperature bleaching of textile fabrics, it was likewise
possible to increase the delignifying performance by up to 52%
compared with the reference test. In the catalytic systems
according to the invention, unlike the CC Mn-TMTACN(.mu.-O).sub.3,
increasing the amount of catalyst led to an increase in the
bleaching effect and not to uncontrolled degradation of the
hydrogen peroxide.
EXAMPLES 17-18
[0105] The ligand or its salt and the corresponding transition
metal salt were dissolved in water and added to an aqueous solution
of MgSO.sub.4, DTPA and NaOH. This solution was kneaded into 30 g
of b.d. pulp. The corresponding amount of hydrogen peroxide was
subsequently mixed in and the pH was measured. The pulp prepared in
this way was then held at temperature in a PE bag in a water bath.
The results without ligand addition (Comparative Example A) and
with the ligand N4Py, or its salt, are listed in Table 2.
COMPARATIVE EXAMPLE H
[0106] A further test was conducted similarly, but the ligand, or
its salt, was used alone, i.e. without addition of transition metal
salt. The results are also listed in Table 2.
3TABLE 2 Resid- Example/ NaO ual Comparative Catalyst
H.sub.2O.sub.2 H H.sub.2O.sub.2 Kappa Example [ppm] [%] [%] [%]
number After acid -- 23.5 Wash A -- 4.0 2.0 2.04 14.7 17 1147
(N4Py*4HclO.sub.4) + 4.0 2.0 0.46 9.3 353 (CoCl.sub.2*6H.sub.2O) 18
1995 (N4Py*4HclO.sub.4) + 4.0 2.0 0.11 8.2 615
(CoCl.sub.2*6H.sub.2O) H 1147 (N4Py*4HClO.sub.4) 4.0 2.0 2.39 15.4
Example/ Comparative Brightness Viscosity Delignification Example
[% ISO] [mPa*s] .DELTA.Kappa w.r.t. A [%] after acid 30.5 32.3 wash
A 51.8 26.2 -- 37.4 17 Nm 21.5 5.4 60.4 18 Nm 19.3 6.5 65.1 H Nm
27.6 -0.7 34.5 nm = not measured
[0107] Further variations and modifications of the foregoing will
be apparent to those skilled in the art and are intended to be
encompassed by the claims appended hereto.
[0108] German priority application 100 51 317.4 is relied on and
incorporated herein by reference.
* * * * *