Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Gas – vapor or mist contact
Reexamination Certificate
1999-03-12
2001-05-22
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Gas, vapor or mist contact
C162S072000, C162S087000, C162S089000
Reexamination Certificate
active
06235154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for delignifying and/or bleaching a lignocellulosic material, and more particularly, to a method for improving the performance of chlorine dioxide in the process of bleaching lignocellulosic pulp.
2. Description of the Prior Art
Pulp mills are aggressively moving to elemental chlorine-free bleaching to address environmental and market issues. The move to chlorine dioxide virtually eliminates the formation of poly-chlorinated phenolic compounds, and substantially reduces the contributions of adsorbable organic halides (AOX), colour and chloroform in the effluent. Drawbacks of chlorine dioxide include the high cost of increased chlorine dioxide generation and the poorer bleaching performance of chlorine dioxide in the first stage (delignification) of the bleaching process when chlorine is replaced entirely by chlorine dioxide. The need for more oxidation equivalents increases the overall bleaching cost to reach a target kappa number and/or brightness.
Over the years various modifications and improvements to the basic chlorine dioxide process have been described in the technical literature. These efforts have addressed the optimization of the bleaching conditions and the optimization of the bleaching sequence configurations. However, little work has been done on enhancing chlorine dioxide bleaching through the use of additives. Dimethylsulfoxide, sulfamic acid and hydrogen peroxide have been tested as additives in chlorine dioxide bleaching to reduce the formation of AOX, but these additives also reduced the delignification efficiency of chlorine dioxide and increased bleaching cost to a varying degree [Y. Ni, G. J. Kubes, and A. R. P. van Heiningen, J. Pulp Paper Sci., 1994, 20(4): J103-106; M. J. Joncourt, P. Froment, D. Lachenal, and C. Chirat, International Pulping Conf., Chicago, Oct. 1-5, 1995, p 149-152; M. J. Joncourt, G. Mortha and D. Lachenal, International Symp. Wood Pulping Chemistry, Montreal, Jun. 9-12, 1997, p J6-1 to J6-5; B.-H. Yoon and L.-J. Wang, International Pulp Bleaching Conf., Helsinki, Jun. 1-5, 1998, p 407-412]. It is known that a certain proportion of chlorine dioxide is converted to chlorite during chlorine dioxide bleaching, which may represent a loss of oxidizing power of chlorine dioxide [W. H. Rapson and C. B. Anderson, CPPA Trans. Tech., Sect., 1977, 3(2):Tr52-55 and Tappi J., 1978, 61(10):97-99; I. Wartiovaara, Paperi ja Puu-Papper o. Trä, 1982, 64(9): 534-545 and 64(10): 581-584]. A two-step high-pH/low-pH method for chlorine dioxide bleaching has been proposed and tested as a means to improve the performance of the chlorine dioxide bleaching process [G. E. Seger, H. Jameel and H.-m. Chiang, Tappi J., 1992, 75(7):174-180]. The working hypothesis of the two-step method is that chlorate formation can be reduced at the higher pH conditions, and the chlorite formed in the first high-pH step can become reactive in the second low-pH step [G. E. Seger, H. Jameel and H.-m. Chiang, Tappi J., 1992, 75(7):174-180; B.-H. Yoon and L.-J. Wang, International Pulp Bleaching Conf., Helsinki, Jun. 1-5, 1998, p 407-412]. Iron has been tested as an additive in chlorine dioxide bleaching to regenerate chlorine dioxide from chlorite [M. J. Joncourt, G. Mortha and D. Lachenal, International Symp. Wood Pulping Chemistry, Montreal, Jun. 9-12, 1997, p J6-1 to J6-5]. It was found, however, that iron also reacted with chlorine dioxide and reduced its delignification efficiency. Moreover, a significant loss of pulp viscosity was observed.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide an improved chlorine dioxide bleaching process.
In a typical implementation of the present invention this object is accomplished by enhancing the effectiveness of chlorine dioxide in reaction with lignocellulosic material by carrying out the reaction in the presence of an aldehyde in the delignification and/or the bleaching stages of the bleaching process. In accordance with the method of the present invention the lignocellulosic pulp after reaction with chlorine dioxide in the presence of the aldehyde may be bleached in accordance with known bleaching and extraction methods.
Thus, in accordance with the invention, the chlorine dioxide delignification and/or bleaching performance is improved, compared to the performance obtained with conventional chlorine dioxide bleaching, as evidenced by a decrease in Kappa number, which is an indicator of the lignin content in pulp, an increase in brightness or both. Alternatively, one can practice the present invention by reducing the consumption of the chlorine dioxide required to reach a target kappa number and/or brightness.
Another object of the invention is to simplify conventional bleaching processes by using fewer bleaching stages. It has been found that a 3-stage D
0
EoD
1
bleaching sequence with the first D
0
stage carried out according to the present invention can replace a 5-stage D
0
EoD
1
ED
2
sequence.
Thus in accordance with the invention there is provided, a process for improving delignification and/or brightening during the bleaching of a lignocellulosic pulp comprising reacting the lignocellulosic pulp with chlorine dioxide in the presence of an aldehyde.
In another aspect of the invention there is provided, in a process of treating a lignocellulosic pulp with a chlorine dioxide solution to effect a reduction in Kappa number and an increase in brightness of the pulp, the improvement wherein the pulp is reacted with the chlorine dioxide solution in the presence of an aldehyde.
DETAILED DESCRIPTION OF THE INVENTION
A “chlorine dioxide stage” as contemplated by the present invention can be any of the stages in a bleaching process which use chlorine dioxide. At the beginning of the sequence, the chlorine dioxide stage is typically referred to as a delignification stage, whereas in the middle or towards the end of the sequence, it is referred to as a bleaching stage.
The lignocellulosic pulps used in the method of the present invention can be derived from wood and/or non-wood derived lignocellulosic material and. This material can be treated with other known delignification, extraction, or bleaching agents before being reacted with chlorine dioxide. For example, typical stages applied to a pulp before a chlorine dioxide stage can be another chlorine dioxide stage, an alkali extraction, oxygen delignification, ozone, peroxide, peracetic acid, chelation, acid hydrolysis, enzyme treatment, applied as a single stage or as multi-stages, with or without washing between the stages.
The chlorine dioxide solution used in the method of the present invention can be generated using known processes and may or may not contain chlorine or other chlorine species. The chlorine dioxide may be added to a stage where other delignification/bleaching agents such as chlorine or ozone are being added.
In a particular embodiment: in the chlorine dioxide stage, the lignocellulosic material is placed in a vessel or container, to which is added a solution containing chlorine dioxide and a solution containing an aldehyde compound.
The aldehyde suitably is of formula:
RCHO, where R=C
n
H
m
O
x
S
y
N
z
where n and x are each integers of from 0 to 12; m is an integer of from 1 to 24; and y and z are each integers of from 0 to 4.
In especially preferred embodiments R is H or lower alkyl of 1 to 5 carbon atoms.
This group of aldehydes includes formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde and benzaldehyde and such aldoses as glyoxal, arabinose, xylose, mannose, rhamnose, glucose, lactose, maltose and derivatives thereof which provide a source of the aldehyde or aldose, such derivatives may be added as such or formed in situ, for example, formaldehyde bisulfite.
The reaction with chlorine dioxide is suitably conducted at a temperature within the range from about 20° C. to about 100° C. (or if pressurized, from 20° C. to about 130° C.), at a consistency from 1 to 35%, an
Jiang Zhi-Hua
McK. Berry Richard
van Lierop Barbara
Alvo Steve
Pulp and Paper Research Institute of Canada
Swabey Ogilvy Renault
LandOfFree
Chlorine dioxide bleaching in the presence of an aldehyde does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chlorine dioxide bleaching in the presence of an aldehyde, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chlorine dioxide bleaching in the presence of an aldehyde will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2460213