Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With agitation or forced circulation
Reexamination Certificate
1998-10-19
2002-04-30
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With agitation or forced circulation
C162S063000, C162S065000, C162S072000, C162S096000, C162S097000, C162S098000, C435S277000, C435S278000
Reexamination Certificate
active
06379495
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Applicants claim priority under 35 U.S.C. §119 of Italian Application No. MI96A000160 filed Jan. 31, 1996. Applicants also claim priority under 35 U.S.C. §120 of PCT/EP97/00424 filed Jan. 31, 1997. The international application under PCT article 21(2) was published in English.
1. Field of the Invention
The present invention relates to a process for the production of cellulose pulps starting from cultured vegetative biomasses (treespecies, textile plants, etc.), with special reference to kenaf (
Hibiscus cannabinus
) or residues from other agricultural-industrial productions such as cereal straws, maize stalks, and the like.
The present invention also relates to the apparatus suitable to realise said process, as well as the vegetative biomasses produced from kenaf and textile plants in general.
2. Prior Art
“Textile fibre plants” and more simply “textile plants”, even though they belong to different botanical genuses and species, have a stem formed by two main fractions, quite distinct and easily separable from one another: external cortical fibres (bast fibres) which constitute the real textile part characterised by aggregates of long and flexible fibres with a high content of cellulose and a low content of lignin, and the internal part (core or wood), constituted by aggregates of very short and rigid fibres.
Cortical fibres have good general characteristics, while the fibres of the internal part, on the contrary, have poor characteristics.
The ratio between cortical fibres and fibres of the wood part is generally 1:2, and they can be separated from one another by means of mechanical systems.
Among the plants that belong to the “textile fibre” group, the most common are: kenaf, hemp, flax, cotton (for the stem part), jute, ramie, roselle (
Hibiscus sabdarifa
), etc.
Kenaf, in particular, is an annual plant of Asian origin, that grows quickly (3-4 months), needs no particular cultivation practises and can grow in poor soils and with relatively low rainfall. At present it is cultivated in many regions of the world for the utilisation of the cortical part for textile purposes (sacks, ropes, etc.). Given its high productivity (up to 20 t/ha of dry matter), in the last years several attempts have been made at utilising kenaf also as a potential source of raw material for paper making.
The production of cellulose pulp for the paper industry is a process that utilises mainly arboreal species from specialised cultivations. Wood, reduced to dimensions of about 30-40 mm and a thickness of about 5-7 mm, is treated at high temperature and pressure with suitable mixes of chemical reagents that selectively attack lignin and hemicellulose macromolecules, rendering them soluble. Pulps coming from this first treatment, commonly called “cooking”, are called “raw pulps”; they still contain partly modified lignin and are more or less Havana-brown coloured.
Raw pulps may be directly used to produce papers for packing or other industrial uses. However, if pulps should be used for fine and very fine papers (culture-papers, white papers, writing and printing papers and the like), raw pulps must be submitted to further chemical-physical treatments suitable to eliminate almost entire lylignin molecules and coloured molecules in general; this second operation is commonly referred to as “bleaching”.
For this process, rapid growth ligneous plants are mainly used, which, with the help of chemical substances (alkali or acids), in condition of high pressure and temperature, are selectively delignified to obtain pulps containing cellulose and other components of lignocellulose. These pulps are then submitted to mechanical and chemical-physical treatments, in order to complete the removal of lignin and hemicellulose residual components, and utilised thereafter for paper production. Such paper making processes are characterised by a high consumption of thermal and mechanical energy and as much high use of chemical reagents that are found, at the end of the process, in the fabrication waters mixed with the organic substances dissolved by cooking (refluents).
Refluents must be treated in satellite plants comparable, for size and complexity, to the same paper mills; because of the absolute need of treating refluents, running production units with a production power of less than 150,000 t/year is uneconomic and prevents a cellulose production in countries, such as Italy, that do not have large areas to be assigned to these productions.
The same is true for countries whose internal paper consumptions are lower than the aforesaid quantities, as are generally emergent countries.
Fabrication yields, expressed as pulp quantity obtained compared to the starting material, vary within a wide range that depends especially on the quantity of chemical reagents used, from a minimum amount of 40-45% for bleached chemical pulps used in the fabrication of fine and very fine papers, to about 90% for pulps produced utilising only mechanical energy (however, such pulps have poor resistance and durability and are used especially for newspapers).
An approximate classification of pulps, based on the intrinsic qualities of pulps and fabrication yields, may be the following:
Bleached chemical pulps
40-50% yield
Raw chemical pulps
45-60% yield
Semi-chemical pulps
70-75% yield
Semi-mechanical pulps
75-85% yield
Mechanical and thermomechanical pulps
85-93% yield
Recently, many economic, ecological and market reasons have spurred an active interest for the setting up of new technologies for the production of cellulose pulps, which technologies, besides allowing to run small and little pollutant production units because of the use of lesser amounts of chemical products, may profitably use raw materials other than the traditional arboreal species, and in particular annual plants and vegetable residues coming from other agricultural-industrial workings. Among said technologies, the thermomechanical process used in the preparation of cellulose pulps is worth mentioning, as this process provides several non negligible advantages, among which the high yields and the production of effluents having a polluting charge markedly lower than that obtained by the use of conventional chemical processes.
In the beginning, the use of new technologies was on the colonisation of the material by fungi having a high ligninolythic activity Ander, P., Eriksson, K. E. L., Svensk Papperstid. 78:641 (1975), but such approach was not applicable because of many drawbacks due to the high weight losses of the material, ascribable to mycelium metabolism, and especially to the length of the treatment period, which seemed incompatible with paper production cycles [Samuelsson, L. Mjoberg, .J., Hartler, N., Vallander, L. and Eriksson, K. E. L., Svensk Papperstid. 83:221 (1980); Eriksson, K. E., Vallander, L. Svensk Papperstid., 85(6):33 (1982), even though said processes seemed to have good results for energy saving Myers, G. C., Leatham, G. F., Wegner, T. H., TAPPI J. 71(5):105 (1988]) and improvement in strength characteristics of paper layers.
Such difficulties have oriented research towards the development of applications based on the use of enzymes suitable for lignocellulose degradation. Said enzymes are produced by organisms that can utilise lignocellulose residues, in particular fungi responsible for wood butt rot, or more generically wood saprophyte mycelia, of which some thousands of species are known. In particular, the discovery of an enzyme, lignin peroxidase, involved in lignin degradation, has polarised the attention of many people on the development of applications based on its utilisation [Arbeloa, M., de Leseleuc, J., Goma, G., Pommier, J. C., TAPPI J. 75(3):215 (1992)]. Afterwards, also these applications have been downsized by several evidences; in particular, the extreme fragility of this enzyme, the necessity of adding hydrogen peroxide to ensure working, and the necessity of utilising it in combination with other enzymes, such as xylanase and beta-kylosidase, to obtain substantial results &lsq
Baldo Ruggero
Cappellletto Pier Luigi
D'Annibale Alessandro
Giovannozzi Sermanni Giovanni
Perani Claudio
Alvo Steve
Collard & Roe P.C.
Consiglio Nazionale Delle Ricerche
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