Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Gas – vapor or mist contact
Reexamination Certificate
2001-04-13
2002-01-29
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Gas, vapor or mist contact
C162S072000, C162S076000, C162S078000, C162S088000
Reexamination Certificate
active
06342124
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of bleaching cellulose pulp, and more particularly, to a method of bleaching an alkaline aqueous slurry of cellulose pulp with oxygen, or peroxide.
BACKGROUND ART
Cellulose pulp, which is used for many purposes, usually requires bleaching for the removal of any colored substance therefrom, except when used for purposes not calling for its whiteness, as when it is used for a packing material, such as the core of corrugated cardboard.
It has hitherto been usual to use chlorine-containing bleaching agents, such as chlorine, sodium hypochlorite, sodium chlorite, and a bleaching powder, for bleaching such pulp, simply because they are inexpensive and high in reactivity.
These chlorine-containing bleaching agents exhibit an excellent bleaching action, but their reaction with lignin produces harmful substances including organic chlorine compounds, such as dioxin, as by-products, and thereby presents the problem of environmental pollution. Under these circumstances, it has been a matter of great importance for mankind to have the pulp manufacturing industry decrease, or eventually end the use of chlorine.
It has been becoming common practice on a worldwide basis to employ oxygen gas, or hydrogen peroxide as a bleaching agent in a part of a process for bleaching pulp in order to decrease the use of chlorine. It has, however, been impossible to realize a satisfactory reduction in the use of chlorine, since it has generally been impossible to bleach pulp satisfactorily with oxygen, etc. Attempts have been made to employ high-pressure oxygen gas at a high temperature to obtain an improved bleach of pulp by bleaching with oxygen, while decreasing the use of chlorine even by a small amount, but have presented a new problem, since the depolymerization of cellulose is promoted, and results in pulp of lower strength.
In order to solve the above problem, the applicant of this application has previously proposed a method of realizing an improved bleach of pulp by adding a bleaching assistant during its bleaching with oxygen, hydrogen peroxide, etc. (Japanese Patent Application Laid-Open No. Hei 5-186987).
The above method has been able to realize an improved bleach of pulp as compared with any prior method of bleaching with oxygen, etc., but has still been unsatisfactory, and unable to realize a satisfactory reduction in the use of chlorine. Moreover, the heavy foaming of a bleached pulp slurry has presented a problem of operation during the step of dewatering, etc.
We, the inventors of this invention, have made a serious study of a problem as to how it will be possible to achieve an improved bleach of cellulose pulp and thereby a greater reduction in the use of any chlorine-containing bleaching agent by employing oxygen or peroxide, while having cellulose retain its strength, and without having any problem of operation caused by the foaming of a bleached pulp slurry, and as a result, we have made this invention by finding that the use of a specific compound as a bleaching assistant provides a very effective and economical solution to the above problems.
DISCLOSURE OF THE INVENTION
This invention relates to a method of bleaching cellulose pulp, and employs one or more compounds selected from a compound (U) represented by general formula (1), a compound (V) represented by general formula (2) and a compound (W) represented by general formula (3) as a bleaching assistant when bleaching an alkaline aqueous slurry of cellulose pulp (pulp slurry) with oxygen or peroxide:
R
1
—O—[(C
2
H
4
O)
m
/(AO)
n
]—H (1)
R
2
—O—[(C
2
H
4
O)
m
/(AO)
P
]—(AO)
q
—H (2)
(R
3
)
t
—X—[(C
2
H
4
O)
m
/(AO)
p
]—(AO)
r
—H (3)
where R
1
stands for a branched alkyl group having 6 to 12 carbon atoms, m stands for an average added mol number of 4 to 15, A stands for a propylene, butylene or phenylethylene group, n stands for an average added mol number of 0 to 4, the addition shown in [ ] is in a random or block form, R
2
stands for a linear or branched alkyl group having 6 to 12 carbon atoms, p stands for an average added mol number of 0 to 3.9, q stands for an average added mol number of 0.1 to 4, R
3
stands for a hydrogen atom, a methyl or ethyl group, or a branched alkyl group having 3 to 12 carbon atoms, t stands for an integer of 1 to 5, X stands for a residual phenol group, and r stands for an average added mol number of from 0, exclusive, to 4, inclusive.
It is possible that R
1
in general formula (1), R
2
in general formula (2) and R
3
in general formula (3) may be a branched alkyl group represented by general formula (4):
where R
4
stands for a methyl, ethyl, propyl or butyl group, R
5
stands for a linear or branched alkyl group having 1 to 9 carbon atoms, and R
6
stands for an alkyl group having 1 or 2 carbon atoms.
The compounds (U) to (W) preferably have a cloud point of 40° C. to 110° C. in a 2% aqueous solution.
Bleaching is usually performed with a chlorine-containing bleaching agent before bleaching with oxygen or peroxide, or thereafter. Bleaching with a chlorine-containing bleaching agent is preferably performed after bleaching with oxygen or peroxide.
The use of the bleaching assistant according to this invention makes it possible to realize an improved bleach of pulp and thereby a reduction in the use of a chlorine-containing bleaching agent, while having cellulose retain its strength. The use of the compound (V) as the bleaching assistant is particularly effective for restraining the foaming of a bleached pulp slurry and eliminating any problem of operation caused by its foaming.
[Compound (U)]
The compound (U) according to this invention is obtained by adding ethylene or propylene oxide, etc. to branched alcohol, and represented by general formula (1):
R
1—O—[(C
2
H
4
O)
m
/(AO)
n
]—H (1)
where R
1
stands for a branched alkyl group having 6 to 12 carbon atoms, A stands for a propylene, butylene or phenylethylene group, m stands for an average added mol number of 4 to 15, n stands for an average added mol number of 0 to 4, and the addition shown in [ ] is in a random or block form.
If the branched alkyl group is R
1
has less than 6, or more than 1 carbon atoms, no satisfactorily improved bleach of pulp can be obtained. The branched alkyl group R
1
is preferably represented by general formula (4):
where R
4
stands for a methyl, ethyl, propyl or butyl group, R
5
stands for a linear or branched alkyl group having 1 to 9 carbon atoms, and R
6
stands for an alkyl group having 1 or 2 carbon atoms.
Specific examples of the branched alkyl group R
1
represented by general formula (4) are isohexyl, isoheptyl, isooctyl, 2-ethylhexyl, an isobutylene dimer, isononyl, a propylene trimer, isodecyl, isoundecyl, isododecyl, a propylene tetramer, and a branched alkyl group synthesized by the oxo process. A 2-ethylhexyl or isodecyl group is, among others, preferred.
Referring to (C
2
H
4
O)
m
in general formula (1), C
2
H
4
O stands for ethylene oxide, and if its average added mol number m is less than 4, or more than 15, no satisfactorily improved bleach of pulp can be obtained. “C
2
H
4
O” is sometimes expressed as “CH
2
CH
2
O”.
Referring to (AO)
n
in general formula (1), AO stands for one or more of propylene, butylene and styrene oxides, n stands for the total of the average added mol numbers of those oxides, and if its average added mol number n is larger than 4, no satisfactorily improved bleach of pulp can be obtained.
Referring to (C
2
H
4
O)
m
and (AO)
n
in general formula (1), there is no rule concerning the order in which C
2
H
4
O and AO are added. The compound (U), however, excludes any compound having propylene, butylene or styrene oxide added in a block form to the end.
Specific examples of the compound (U) include the following:
Example 1: Isodecyl-O—(EO)
10
—H
Example 2: 2-Ethylhexyl-O—(EO)
12
—H
Example 3: 2,4-Dimethylheptyl-O—[(EO)
9
//(PO)
2
]—H
Example 4: Isononyl-O—[(EO)
10
//(PO)
1
//(BO)
0.5
]—H
Hisada Nobuo
Maeda Hiroaki
Nakamura Daisuke
Alvo Steve
Arent Fox Kintner Plotkin & Kahn
Sanyo Chemical Industries Ltd.
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