Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Gas – vapor or mist contact
Patent
1997-01-17
2000-02-01
Alvo, Steven
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Gas, vapor or mist contact
162 76, 162 78, 162 80, D21C 9147, D21C 916
Patent
active
060198702
DESCRIPTION:
BRIEF SUMMARY
The invention related to a process for the preparation of a delignified and bleached chemical paper pulp.
Chemical paper pulps or chemical pulps are those obtained by cooking lignocellulose materials, in particular wood. Thus it is that the following are distinguished among the chemical pulps: Organosolv process (Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, vol. A. 18, 1991, pages 568 and 569),
All types of wood are suitable:
Chemical pulps obtained by cooking are conventionally subjected to a number of dignifying and/or bleaching treatment stages.
The first stages consist in completing the delignification resulting from the cooking. The following stages are bleaching stages.
On conclusion of these dignifying and bleaching treatments, the pulps should usually have a whiteness of at least 88-90.degree. ISO and a very low kappa number while retaining good mechanical properties, that is to say without significant degradation of the cellulose. This degradation can be detected by measuring the viscosity of the pulp or else its degree of polymerization (DP). The DP should remain as high as possible.
The definitions of the terms used above and subsequently correspond to the following standards:
The first dignifying stages are usually carried out by treatments with chlorine gas or chlorine dioxide.
For the preparation of chlorine-free pulps, it has been proposed to replace the chlorinated reactants with other oxidizing agents. The article by C. L. Forber, "Chlorine and chlorine dioxide replacements in kraft pulp bleaching: Emerging technologies or Laboratory curiosities?, TAIPPI Press, Atlanta, Ga. 1993", concludes that a number of compounds exist which have a sufficient bleaching ability for replacing chlorine in delignification but that the replacement of chlorine dioxide in bleaching does not seem achievable as no reactant is as effective and as inexpensive as chlorine dioxide.
This article shows in particular the comparative dignifying and bleaching abilities of a series of reactants, such as chlorine, chlorine dioxide, oxygen, ozone and hydrogen peroxide, and also shows the results obtained, generally in terms of kappa number, whiteness and viscosity.
Thus, oxygen alone has a dignifying ability and no significant bleaching ability. Its chlorine replacement factor (CRF) is 5 and its use results in the kappa number decreasing by approximately a half (17 from 35), the viscosity obtained being 980 dm.sup.3 /kg (approximately 37 cps) and the whiteness 34.degree. ISO.
In comparison, the use of hydrogen peroxide is known both in delignification and bleaching.
In delignification, the kappa number decreases by a little less than half (20 from 35), the viscosity obtained being 900 and more dm.sup.3 /kg (approximately 30 cps) and the whiteness 45.degree. ISO; 91.degree. ISO is obtained for a viscosity of approximately 600 and more dm.sup.3 /kg.
In order to lower the kappa number below a value usually of between 7 and 14, it is necessary to resort to a second dignifying stage which can be carried-out with ozone (C. Chirat and Lachenal, TAPPI Proceedings, Pulping Conference, 1993, p. 717) or else with peracetic acid or alternatively with Caro's acid (F. Desprez, S. Devenyns, N. Troughton, TAPPI Proceedings, Pulping Conference, 1993, p. 443).
A treatment with hydrogen peroxide, as described in Patent Application EP 0,578,304 A1, only makes it possible to strongly bleach pulps in which the kappa number is less than 5, in which the manganese content is less than or equal to 3 ppm and in which the consistency is at least 25% by weight of dry matter with respect to the total weight of the pulp. This treatment with H.sub.2 O.sub.2 is carried out at a claimed temperature between 50 and 140.degree. C.
This manganese content less than or equal to 3 ppm is obtained by a pretreatment with a complexing or sequestering agent or acid in acid medium.
The temperatures given as examples are 80, 90 and 120.degree. C. No corresponding information is given at this temperature of 120.degree. C. on the pressure prevailing in th
REFERENCES:
patent: 4244778 (1981-01-01), Lindahl et al.
patent: 5310458 (1994-05-01), Lundgren et al.
Using Oxygen and Peroxide to Bleach Kraft Pulps, B. Van Lierop, N. Liebergott and M.G. Faubert, Journal of Pulp and Paper Science, vol. 20, No. 7, pp. J193-J198.
Chemicals, Dry Solids and Solid Waste in Low Effluent Bleach Mills, B. Dillner, Helsinki, Finland, Feb. 16, 1994, p. 9.
Chlorine and Chlorine Dioxide Replacements in Kraft Pulp Bleaching: Emerging Technologies or Laboratory Curiosities?, C.L. Forber, Bleaching: A TAPPI Press Anthology of Published Papers, Chapter 6, pp. 443-451 (1993).
P*: One-Stage Hydrogen Peroxide Full Bleaching of Previously Delignified Softwood Kraft Pulp, Application to TCF Sequences, by F. Desprez, J. Devenyns and N. Troughton, TAPPI Proceedings, 1993 Pulping Conference Book 2, Nov. 1-3, 1993, pp. 443-452.
TCF Bleaching Can Be Carried Out with Different Bleaching Systems, by P. Tibbling and B. Dillner, XXV. Eucepa Conference, Oct. 4-8, 1993, Vienna, Austria, pp. 65-83.
Optimization of Bleaching Sequences Using Peroxide as First Stage, by D. Lachenal, L. Soria, C. de Choudens, and P. Monzie, TAPPI Proceedings, 1982 International Pulp Bleaching Conference, pp. 145-151.
Non Degrading TCF Bleaching Sequences Including an Ozone Stage for Hardwood and Softwood Kraft Pulps, and Characterization of the Effluents, by C. Chirat and D. Lachenal, TAPPI Proceedings, 1993 Pulping Conference Book 2, Nov. 1-3, 1993, pp. 717-723.
Devic Michel
Schirmann Jean-Pierre
Alvo Steven
Elf Atochem S.A.
LandOfFree
Process for the preparation of delignified and bleached chemical does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the preparation of delignified and bleached chemical, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of delignified and bleached chemical will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-934667