Chemistry: natural resins or derivatives; peptides or proteins; – Lignins or derivatives
Reexamination Certificate
2000-02-14
2001-04-10
Nutter, Nathan M. (Department: 1711)
Chemistry: natural resins or derivatives; peptides or proteins;
Lignins or derivatives
C530S506000
Reexamination Certificate
active
06214976
ABSTRACT:
DESCRIPTION
Technical Field
This invention relates to a new method for depolymerizing and/or modifying lignin or lignin related compounds by using copper, a copper coordination compound and peroxide in an aqueous solution. Lignin, a heterogeneous phenylpropanoid structural polymer of vascular plants, is the most abundant renewable material next to cellulose but it constitutes a barrier which must be broken down before utilization of cellulose. Lignin related, or lignin like, compounds include lignins that are synthetically produced. Over centuries, extensive studies have been made to degrade lignin by chemical, enzymatic and microbial treatments of woody materials.
The technology of delignification accumulated so far is mainly utilized for the production of paper or dissolving pulp. For that reason the present invention is mainly discussed in relation to methods used for delignification in pulp and paper production, although its field of application goes far beyond. It includes also processes like deinking of waste paper, effluent treatment, pretreatment of lignocellulosics as animal feed stock, wood saccharification and wood processing. It can also be used to depolymerize or modify lignin-related compounds like polyaromatic hydrocarbons (PAH) or coal.
Chemical pulp production includes mainly methods such as kraft pulping, sulfite pulping or soda pulping. The aim of these technologies is bulk delignification of wood or other lignocellulosic materials like straw. In mechanical pulping, chemical pretreatment of wood chips at elevated temperatures (CTMP) is usually practiced to reduce the refining energy and to improve pulp quality.
The second and more critical step in pulp production is pulp bleaching, aiming at the removal of lignin and chemical modification of the remaining lignin in the pulp. In classical bleaching technologies pulp is treated with chlorine, chlorine dioxide and hypochlorite. Because of the adverse effect of chlorine in nature, totally chlorine free bleaching sequences (TCF) based on oxygen, ozone, and alkaline peroxide or sodium peroxide were developed more recently. The modern oxygen-based bleaching sequences are environmentally benign but compared to chlorine bleaching, the chemical reactions are much less specific and lead to a bleached pulp of higher lignin content and reduced fibre strength. While in chlorine bleached pulps the kappa value for the lignin content was 1 or lower, commercial TCF bleached pulps may have kappa values of 4-6. The high lignin content of these pulps is a great disadvantage and leads to yellowing and accelerated aging of paper. Another drawback of TCF bleached pulps is the decrease in fiber strength due to less specific chemical reactions.
To overcome the low specificity of the TCF bleaching sequences biological agents like white rot fungi or the isolated ligninolytic enzymes of these fungi have been investigated for pulp bleaching recently. However, when living fungi are used for bleaching, an incubation time of at least 4 days has to be accepted, making this method only interesting for fundamental studies. The main enzymes known to be responsible for lignin degradation in nature are laccase, manganese peroxidase and lignin peroxidase. The latter two enzymes are out of scope for technical applications as they can only be produced on laboratory scale so far. Laccase is already produced by large-scale fermentation and a technical bleaching process including the use of the mediators like ABTS or HBT is described in the literature (R. Bourbonnais, M. G. Paice, Appl. Microbiol. Biotechnol. 36, 823-827, 1992; H. P. Call, I. Mücke, J. Biotech. 53,163-202, 1997) and in the patent PCT/EP94/01966. In combination with other bleaching sequences this process results in pulp of high brightness and viscosity but the lignin content is still high and comparable to that of TCF bleached pulp and not of chlorine bleached pulp. Furthermore, the known laccase/mediator process has some crucial drawbacks: due to their way of production, ligninolytic enzymes are relatively expensive and have to be used within stringent process conditions, usually at acidic pH. Their industrial use requires skilled personnel. Moreover, the mediator ABTS cannot be used industrially as it creates colored reaction products. The mediator HBT is not redox recycled and has to be applied in large amounts of about 5-10% of the dry weight of pulp (H. P. Call, I. Mücke, J. Biotech. 53,163-202, 1997). Moreover, its environmental impact is questionable. So far, no new mediators to overcome the drawbacks have been reported.
Chemical bleaching processes are mostly easier to handle, are usually cheaper and if the desired bleaching effect is reached and the environmental requirements are complied with, they are more advantageous than microbial and enzymatic treatments. However, the chemical reactions developed so far either lead to toxic degradation products like organochlorine or to a high lignin content and unspecific reactions depolymerizing the cellulose.
BACKGROUND ART
Various approaches to develop new and more specific chemical lignin depolymerizing processes for industrial purposes are reported in the literature. G. C. Hobbs and J. Abbot (J. Wood Chem. Technol., 14, 195-125, 1994) tried to use free copper ions as additive in peroxide bleaching without the application of a coordination compound to bleach Eucalyptus regnans SGW pulp. The addition of free copper ions did not improve the result: the brightness increase in a three-hour peroxide bleaching stage using copper was 17.6% compared to 18.4% without copper. No results are reported on the reduction of kappa or viscosity values.
In some cases the idea was to mimic the redox cycle of the lignin polymerizing/depolymerizing enzymes. Laccase is a copper containing enzyme which is oxidized by molecular oxygen while lignin peroxidase and manganese peroxidase are iron containing enzymes, oxidized by hydrogen peroxide. No copper containing enzyme, oxidized by hydrogen peroxide is known. Related to lignin degradation, copper is a transition metal constituting the catalytic site of laccase. Copper also constitutes the catalytic site of various other metal proteins such as galactose oxidase, tyrosinase, ascorbate oxidase, superoxide dismustase, nitrite reductase, hemocyanin and plastocyanin. In relation to this invention a system mimicking the catalytic function of laccase reported by S. Kawai and H. Ohashi (Holzforschung, 47, 97, 1993) has to be mentioned. Dimeric lignin model compounds were decomposed in the organic solvent dichloromethane by a copper-amine complex. This reaction does not include peroxide in the catalytic cycle and for that reason cannot be compared with the reaction described in this invention.
A reaction of copper with lignin including peroxide has been reported by M. M. Santos et al. (J. Braz. Chem. Soc., 6, 257, 1995). The so-called Gif system has been developed originally to achieve the oxygenation of hydrocarbons. The reaction medium of the Gif system is invariably a mixture of pyridine and carboxylic acid, in which carboxylic acid, as well as the organic solvent pyridine has to be present in large excess (80% solution). Santos et al. tried to use the Gif system to decompose isolated lignin from different pulps with Cu(II) plus Fe (II) in a pyridine/acetic acid solution under an inert atmosphere. Under these conditions, phenolic degradation products were analyzed, but concomitantly a high amount of toxic pyridine derivatives such as 2,2′-bipyridyl, 2,3′-bipyridyl, methyl pyridine and pyridinone are yielded. The high amount of pyridine per se as well as the creation of large amounts of toxic derivatives makes it impossible to utilize this process for industrial purposes, as stated by the authors.
Oxidation of lignin model compounds with copper and peroxide in a 83% acetic acid solution as solvent has been reported by Van-Ba Huynh (Biochem. Biophys. Res. Commun., 139, 1104, 1986). This reaction was carried out at refluxing temperature above 100° C.
Only the last two processes can be compared to some ex
Koller Karin
Messner Kurt
Watanabe Takashi
BakerBotts LLP
Nutter Nathan M.
Watababe T.
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