Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Patent
1995-02-23
1997-05-20
Spear, Frank
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
162 78, D21C 914
Patent
active
056309066
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the delignification and bleaching of a lignocellulose material by an aqueous solution of an oxidizing agent and of an oxidation-reduction catalyst.
The invention therefore relates to the technical field of wood and of paper pulp and also to that of natural or synthetic oxidation-reduction catalysts.
2. Background Art
Many studies relate to processes for the degradation of wood lignin or paper pulp.
As restated by A. Paszcynski et al., Applied and Environmental Microbiology, 1988, 62-68, many of these studies are based on the study of natural wood degradation phenomena.
Thus a specific strain of basidiomycetes, known under the name of "Phanerochaete chryosporium" and leading to white rot of wood, was particularly studied as regards the biochemical mechanisms which are involved in delignification.
Two types of extracellular enzymes containing porphyrin groups are involved in the degradation of wood.
These enzymes have in common the ability to decompose peroxides, which ability is characteristic of peroxidases; their catalytic cycle comprises the oxidation of the iron porphyrin by the peroxide and then the return to the initial state by virtue of electrons withdrawn from the molecules present in the medium.
Ligninases capture an electron from the aromatic rings of lignin and thus form radical cation species which progress non-enzymatically and which lead to depolymerization of lignin.
Manganese peroxidases oxidize Mn.sup.2+ cations to Mn.sup.3+ cations. The Mn.sup.3+ cations diffuse into the structures of wood and capture an electron to restore Mn.sup.2+.
The above writers treated wood shavings or paper pulp with a number of natural or synthetic iron porphyrins in the presence of an oxidizing agent chosen from hydrogen peroxide or tert-butyl hydroperoxide (TBH), in an aqueous medium.
The experiments were carried out with a wood/water ratio by mass of 0.2% and a pulp/water ratio by mass of 0.1% at approximately 100.degree. C. (reflux temperature of water) for 24 to 48 h.
The chosen kraft pulp, treated with an iron hemin/TBH, sees its kappa number decrease from 36 to 2 with removal of 100% of the lignin and only 10% of the cellulose.
On the other hand, wood shavings treated under identical temperature and time conditions with hydrogen peroxide alone or with the H.sub.2 O.sub.2 /hemin combination lead to the same results, namely a degradation of the lignin and cellulose which is non-selective and of the same order of magnitude. Heroin does not seem to play any specific role in the presence of H.sub.2 O.sub.2.
On the other hand, in the presence of TBH, by refluxing for 48 h, 38% of the lignin is removed with concomitant removal of 9.5% of the cellulose.
In concluding their studies, these writers recognize that their process cannot be applied industrially.
For their part, P. S. Skerker et al., Biotechnology in Pulp and Paper Manufacture, Chap. 18, 203-210, Butterworth, Heinemann (1990), have studied the biomimetic bleaching of kraft pulps using synthetic porphyrins in the presence of TBH. The porphyrin which is soluble in water and which is resistant to oxidation is mesotetra -(2,6-dichloro-3-sulphonatophenyl)-.beta.-octachloroporphinatoiron(III).
It should be noted that this porphyrin comprises 16 chlorine atoms substituting the phenyl and pyrrole rings and 4 sulphonato groups and that its synthesis is very expensive. Replacement of iron by manganese in this porphyrin structure does not substantially change the results.
Having a pulp with a consistency of 2.5%, a delignification of better than 45% is obtained in 15 min at 80.degree. C. in water with the above Fe(III) porphyrin, the kappa number decreasing from 23.5 to 18.7. However, these conditions lead to a decrease in the viscosity of the pulp by a factor of approximately 2, which is a sign of severe depolymerization of the cellulose.
In their conclusion, these writers themselves recognize that their process cannot be operated industrially.
Forrester et al., B
REFERENCES:
patent: 5143580 (1992-09-01), Basta et al.
patent: 5244594 (1993-09-01), Favre et al.
Boe Jean-Fran.cedilla.ois
Girerd Jean-Jacques
Guignard Claude
Seris Jean-Louis
Verlhac Jean-Baptiste
Elf Aquitaine Production
Spear Frank
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