A METHOD AND PLANT FOR THE CONTINUOUS EXTRACTION, FROM A WOODY MATERIAL, OF A TANNIC SUBSTANCE CONTAINED THEREIN AND FOR THE PRODUCTION OF A USABLE LIGNOCELLULOSIC MATERIAL

Abstract: A method for the extraction, from a highly tannic woody material, of a tannic substance contained therein, and/or for the production of a usable lignocellulose product in particle form, comprises the following successive steps: a first fragmentation consisting of a reduction of the woody material to chips, a second fragmentation consisting of a reduction of the chips to particles, dispersal of the particles in water thus producing an aqueous solution of the tannic substance as well as lignocellulose particles in suspension in the aqueous solution, and separation of the particles from the solution by filtration. Plant for implementing the method comprises at least, in succession: a shredder (2) of known type for reducing the woody material to chips, means (5, 7) for reducing the chips to particles, a series (6) of containers for dispersing the particles in water to produce an aqueous solution of the tannic substance as well as lignocellulose particles in suspension in the aqueous solution, and filtration means (10) for separating the particles from the solution.

Description: A METHOD AND PLANT FOR THE CONTINUOUS EXTRACTION, FROM A WOODY MATERIAL, OF A TANNIC SUBSTANCE CONTAINED THEREIN AND FOR THE PRODUCTION OF A USABLE LIGNOCELLULOSIC MATERIAL The present invention relates to a method according to the preamble to Claim 1 and to plant according to the preamble to Claim 21. The invention has been developed for application to the treatment of chestnut wood in order to extract the tannin therefrom and, at the same time, to produce a woody material, substantially free of tannin and usable, amongst other things, for the formation of sheet or board products. The invention may, however, be applied to other woody materials containing a high proportion of vegetable tannin, such as the bark of oak and of some acacias, including mimosas, and such as the wood of many conifers, red quebracho wood, algarobilla, cherry plum, divi-divi, as well as valonia fruits, mangrove roots, acorns, Sicilian sumac, and tara. With reference to the conventional method applied to chestnut wood, the raw wood is collected in heaps and is then reduced, by means of a chopper or shredder, to chips having average dimensions of 30 x 30 x 0.5 mm with a specific surface area of at least 400-600 mm 2 per cm 3 of chip. The chips are then treated in batches in a series of diffusers in which the tannin is extracted from the chips in aqueous solution by treatment with a counter-flow of water at high temperature (110- 120°C) . The tannin extracted is then sent to a multi-stage evaporator. The concentrate is sold, after various chemical treatments, mainly for the production of leather. The slightly polluting material evaporated from the evaporator may be used partially in the extraction process or may be discharged to the exterior. Examples of the known method are given by the documents SU-B- 924 104 and US-A-5 238 680. This known method has various disadvantages. A first disadvantage consists of the fact that the yield from the extraction of tannin in the diffusers is quite low (70- 80%) . Another disadvantage consists of the fact that, because of the use of the diffusers, the method is discontinuous, whereas it would be desirable to have a substantially continuous, and hence more economical, process. Yet another disadvantage consists of the fact that the chips discharged from the 'diffusers still contain a quantity of tannin such that their use as constituents, for example, of compressed boards, is undesirable, given the strong colouring capacity of tannin. Board manufacturers preferably use fibres produced from wood chips which do not contain a great amount tannin (which may be more expensive if they are not chestnut wood) . One example of a method and plant for obtaining such substantially tannin-free fibres and boards is given by the document FR-A-2 621 784. This document discloses a method and a plant in which a woody substance is reduced into fibres, and the fibres are suspended in a recycled aqueous liquor. From the suspension one obtains, by separation, on the one hand, a foodstuff for cattle and other animals, and, on the other hand, a wood pulp from which fibre panels are made. The foodstuff contains starches, sugars, and also tannins, the latter to give the foodstuff antidiarrheal properties. The document FR-A-2 621 784 teaches to prepare a fifty-fifty mixture of two kinds of wood pulp; one of the pulps is made of fibres of chestnut wood from which tannin has already been extracted as far as possible beforehand; the other pulp is made of fibres of wood naturally poor in tannin, such as beech, alder, oak (not oak bark) and hornbeam. This can be explained by the fact that the concern of FR-A- 2 621 784 is to obtain, on the one hand, fibre board as white as possible, i.e. as free as possible from tannin and, on the other hand, a foodstuff having medicinal properties due to the presence of a certain proportion of tannin, in addition to starch and sugar. Therefore, the method and plant according to FR-A-2 621 784 are not adapted for the extraction of a tannic substance from woods which contain high percentages of tannins, such as chestnut wood and oak bark (15%) and quebracho wood (40%), such woods containing low and uninteresting percentages of starches and sugars. Yet another disadvantage which makes, according to the prior art, chestnut wood chips not very suitable for the production of boards or the like is that, m the diffusers, the chips undergo an excessively intense heat treatment (at about 110- 120°C for several hours) as a result of which tne chemico- physical characteristics of the boards which can be produced from them are mediocre, because the intense heat treatment degrades the cellulose into hemicellulose and sugars. Further, the intense heat treatment to improve the extraction of tannin may also degrade the tannins contained m the wood, giving rise to tannic products of lower quality. The object of the invention is to provide a substantially continuous method and plant which eliminate these problems. According to the invention, this object is achieved by means of a method and plant as claimed. By virtue of this concept, the woody material s no longer treated discontmuously as m conventional diffusers. Instead of being sent into the diffusers, the chips are subjected to further fragmentation into very small particles which may advantageously be achieved by grinding. During the subsequent dispersal of the particles m water, since the exchange surface between the particles and the water is much larger than that between chips and water, much higher percentages, for example 90%, of the tannm can be dissolved m the water than m conventional methods. However, even if a yield equal to that of conventional methods (70-80%) is considered satisfactory, a plant according to the invention is more economical than a conventional plant, amongst other things, because it enables a continuous or substantially continuous method to be implemented. At the same time, the wood particles are no longer subject to the ill-treatment which they undergo in the diffusers and retain optimal chemico-physical properties which render them more suitable for the manufacture of sheet or board products or the like, as will be explained in the course of the description with reference to the drawing. The invention also relates to the products obtained by the method claimed, amongst which are the lignocellulose products in particle form produced by the method, and the sheet or board materials and the like produced with the products in particle form. The invention will be explained further by the following description relating to the appended drawing which shows schematically, by way of non-limiting example, plant for treating chestnut wood in order to derive therefrom both tannin and compressed boards. With reference to the drawing, the arrows A ... M indicate the movements of the materials from one treatment step to the next. A pile of pieces of chestnut wood is indicated 1. A chopper or shredder of known type to which the pieces from the pile 1 are supplied substantially continuously (arrow A) for reduction to chips, is indicated 2. By way of non-limiting example, the chips discharged from the shredder 2 preferably have an average size of the order of 30 x 30 x 0.5 mm with a specific surface area of the order of at least 400 mm 2 per cm 3 of chip. A conveyor system 3 removes the chips from the shredder 2 and piles them in a heap of chips 4 (arrow B) . A thermo-mechanical defibrator to which the chips 4 are supplied substantially continuously in accordance with the arrow C is indicated 5. The defibration preferably produces fibres or groups of fibres having a specific surface area of at least 2000 and preferably of at least 4000 mm 2 per cm 3 of fibre. For certain woody materials which cannot produce fibres usable for the manufacture of fibre boards, the defibrator 5 may be replaced by a mill, for example, a ball mill or a hammer mill, to produce particles in the form of granules which in any case have a specific surface area of at least 2000 and preferably of at least 4000 mm 2 per cm 3 of particle. A series of dispersal containers, which may be constituted by open tanks or by pressure vessels, is generally indicated 6. The fibres discharged from the defibrator 5 are sent substantially continuously, in accordance with the arrow D, to a first container of the series 6. The connections for the circulation of the water in the containers 6 can be switched so as to achieve a progressive dispersal of the fibres (or of other particles) in a counter- flow. Alternatively, this progressive dispersal may be performed with an equidirectional flow. If the defibration performed in the defibrator 5 does not split the fibres up sufficiently, a refiner 7 may be provided, the fibres or groups of fibres discharged from the defibrator 5 being transferred substantially continuously thereto, in accordance with the broken arrow E. Steam, preferably supersaturated and at a pressure of the order of a few bars, is advantageously admitted to the defibrator 5 to achieve, amongst other things, a partial extraction of the tannin from the fibres. Superheated water may be admitted to the defibrator 5 instead of steam. The refiner 7, which is similar to the defibrator 5, preferably increases the specific surface area of the fibres to more than 4000 mm 2 per cm 3 of fibre and, more preferably, to a value of the order of at least 7000 mm' per cm 3 of fibre . The refined fibres are then transferred substantially continuously, in accordance with the broken arrow F, from the refiner 7 to the series of containers 6. The temperature in the defibrator 5 is preferably of the order of 140°C, which is the highest possible temperature at which tannins do no undergo degradation and at which substances different from tannin are not substantially formed and therefore are not substantially extracted by thermal degradation of the wood. In this manner it is possible to obtain an aqueous solution in which the proportion by weight between tannic and non- tannic substances is of not less than 3.5. The solution of tannin resulting from the extraction with steam in the defibrator 5 and/or in the refiner 7 is transferred to the series of containers 6 together with the fibres. Both in the case of the fibres coming directly from the defibrator 5 and in the case of fibres coming from the refiner 7, the fibres are dispersed in water in the series of containers 6, thus producing an aqueous solution of tannin extracted from the fibres (or other particles) . A satisfactory extraction may be effected by a treatment in the containers 6 of a duration of 2 hours at a temperature of 70-80°C, which is not harmful to both the woody material and the tannic substances it contains. A machine such as a Fourdrinier machine or the like is indicated 9. The machine 9 comprises, amongst other things, a conveyor filter screen 10. The screen 10 is in the form of a continuous belt and circulates continuously clockwise, with reference to the drawing. The aqueous solution with the fibres or particles in suspension is transferred from the battery 6 to the screen 10 in accordance with the arrow G and is distributed uniformly on the screen 10. The aqueous solution transferred to the screen 10 preferably contains fibres, with a density of fibres of the order of 1- 2% by weight. The screen 10 acts as a filter and retains the fibres. The aqueous solution, however, descends through the screen 10 partly by dripping and partly owing to suction by means of suction boxes 11 of the type well known in paper-making machines . The web of fibres being formed or felted is also squeezed between pairs of rollers 12 which increase the amount of the aqueous solution removed from the fibres. All of the aqueous solution removed by dripping and/or by suction and/or by squeezing falls, in accordance with the arrow H, into an underlying collection container 13 from which the fibre-free solution is pumped into the series of evaporators 8. In the series of evaporators 8, the aqueous tannin solution is concentrated to the density prescribed for commercial uses . Concentration to produce a dry product in powder form, which is more convenient for long-distance transportation to places of use (for example for tanning) is not excluded. The method and plant according to the invention allow to obtain tannic products in the from of aqueous solution or in dry form which are totally useful, and do not give rise to unvaluable by-products whose disposal is difficult and expensive. A board-forming press is indicated 14. The web of fibres discharged from the machine 9 is transferred, in accordance with the arrow K, to the press 14 where the web is transformed into fibre boards. The press 16 is preferably of the wet type and, in this case, has a collection container 15 into which the residual aqueous solution drips in accordance with the arrow L in order to be sent to the evaporator 8 in accordance with the arrow M. The use of a dry press is not, however, excluded, if the dry press is preceded by a fibre-drier. For general information about the presses usable instead of the press 14 illustrated, and about the boards which can be manufactured, reference should be made to the "DIZIONARIO D' INGEGNERIA" (DICTIONARY OF ENGINEERING) , UTET, Turin, 1976, Vol. VIII, pages 192 and 193. The Fourdrinier machine 9 or the like could also be a paper- making machine and could produce a web of paper or cardboard, that is, a sheet material rather than a board material such as the aforementioned boards. Instead of the screen 10, the filtration means could be constituted by a normal separator filter. The foregoing description has referred basically to the reduction of chips to fibres but, with the use of a mill instead of the defibrator 5, a woody material in granule form can be obtained. Boards can also be formed with these granules, but they are not of excellent quality. In this case, the granules in the boards will be bound by a glue. The use of the granules as a fuel for use even in the same plant is not excluded. In this case, the advantage of the plant is in any case still that of producing the maximum possible quantity of tannin from the woody material by virtue of the high specific surface area of the particles in suspension in the water. Another great advantage of a plant according to the invention in which one obtains, on the one hand, tannin and, on the other hand, fibreboard or the like, is the following. Given that the heat treatment of wood is reduced with respect to the prior art, the thermal destruction of the wood is reduced with a spare of wood about 10%. Further, the method and plant according to the invention do not produce the so-called black liquor or sugar liquor which is usually produced in the fibreboard plants. A method according to the invention lends itself to the use of an existing plant in which diffusers, defibrators and/or refiners are already provided for other reasons. In this case it may be convenient to carry out a partial extraction of tannin from the chips in the diffusers and then submit the chips to the second fragmentation in an defibrator and/or a refiner at a temperature in the range of 120-140°C. This second fragmentation allows to obtain on the one hand a solution having the above-said proportion by weight of not less than 3.5 between tannic and non-tannic substances and, on the other hand, fibres suitable for the other uses mentioned above. If the existing plant only includes diffusers, the only expense to be made is the purchase of a defibrator for reducing the chips to particles or fibres.

Claims: CLAIMS 1. A method for the extraction, from a highly tannic woody material, of a tannic substance contained therein, and/or for the production of a usable lignocellulose product, in which the raw woody material is subjected to a fragmentation step and the fragmented material is subjected to a step for the extraction of the tannic substance in the form of an aqueous solution, characterized in that it comprises the following successive steps : - a first fragmentation consisting, in known manner, of a reduction of the woody material to chips, - a second fragmentation consisting of a reduction of the chips to particles having a specific surface area of at least 2000 mm 2 per cm 3 of particle, - dispersal of the particles in water, thus producing an aqueous solution of the tannic substance as well as lignocellulose particles in suspension in the aqueous solution, separation of the particles from the solution by filtration. 2. A method according to Claim 1, characterized in that the first fragmentation produces chips having an average size of the order of 30 x 30 x 0.5 mm with a specific surface area of the order of at least 400 mm 2 per cm 3 of chip and the second fragmentation produces particles having a specific surface area of at least 4000 mm 2 per cm 3 of particle. 3. A method according to Claim 1 or Claim 2, characterized in that the dispersal is effected with water in a series of containers . 4. A method according to Claim 3, characterized in that tanks are used as containers. 5. A method according to Claim 3, characterized in that pressure vessels are used as containers. 6. A method according to any one of Claims 3 to 5, characterized in that the dispersal is effected in a counter- flow. 7. A method according to any one of Claims 3 to 5, characterized in that the dispersal is effected with an equidirectional flow. 8. A method according to any one of the preceding claims, characterized in that the aqueous solution separated from the particles is subsequently concentrated until at least some of the water has been removed therefrom. 9. A method according to any one of the preceding claims, characterized in that the second fragmentation consists of mechanical milling and the particles obtained are granules. 10. A method according to any one of Claims 1 to 8, characterized in that the second fragmentation consists of thermo-mechanical defibration and the particles obtained are fibres or groups of fibres. 11. A method according to Claim 10, characterized in that the fibres coming from the thermo-mechanical defibration are subjected to a refining step to increase their specific surface area to more than 4000 mm 2 per cm 3 of fibre. 12. A method according to Claim 10 or Claim 11, characterized in that a partial extraction of the tannic substance is performed simultaneously with the defibration and/or with the refining. 13. A method according to Claim 11, characterized in that the refining step increases the specific surface area of the fibres to a value of at least 7000 mm 2 per cm 3 of fibre. 14. A method according to any of Claims 1 to 13, characterised in that between the first fragmentation and the second fragmentation a partial extraction of tannin is carried out in a battery of diffusers. 15. A method according to Claim 14, characterised in that the second fragmentation is carried out at a temperatures in the range of 120-140°C. 16. A method according to any one of Claims 10 to 15, characterized in that the aqueous solution containing the fibres is spread on a conveyor filter screen of a Fourdrinier machine or the like, from which the residual aqueous solution is removed by dripping and/or suction and/or squeezing, whilst the paste of fibres carried by the screen is sent to a section for the formation of a sheet or board material. 17. The use of a method according to any one of the preceding claims for the extraction of tannin from a woody material which contains it. 18. A product produced by a method according to Claim 8. 19. A lignocellulose product in particle form produced by a method according to any one of Claims 1 to 13. 20. A sheet, board or similar material produced from a product in particle form according to Claim 19. 21. A sheet, board or similar material produced by a method according to Claim 16. 22. Plant for the extraction, from a highly tannic woody material, of a tannic substance contained therein and/or for the production of a usable lignocellulose product in particle form, comprising means (2, 5, 7) for fragmenting the raw woody material and means (6) for extracting the vegetable substance in the form of an aqueous solution, characterized in that it comprises at least, in succession: a shredder (2) of known type for reducing the woody material to chips, - means (5, 7) for reducing the chips to particles having a specific surface area of at least 2000 mm 2 per cm 3 of particle, - a series (6) of containers for dispersing the particles in water to produce an aqueous solution of the tannic substance as well as lignocellulose particles in suspension in the aqueous solution, - filtration means (10) for separating the particles from the solution. 23. Plant according to Claim 22, characterized in that the shredder (2) is arranged to produce chips having an average size of the order of 30 x 30 x 0.5 mm with a specific surface area of the order of at least 400 mm 2 per cm 3 of chip and the means (5) for reducing the chips to particles are arranged to produce particles having a specific surface area of at least 4000 mm 2 per cm 3 of particle. 24. Plant according to Claim 22 or Claim 23, characterized in that the containers of the series are tanks (6) . 25. Plant according to Claim 22 or Claim 23, characterized in that the containers of the series are pressure vessels. 26. Plant according to any one of Claims 22 to 25, characterized in that the series of containers (6) is of the counter-flow type. 27. Plant according to any one of Claims 22 to 25, characterized in that the series of containers (6) is of the type with an equidirectional flow. 28. Plant according to any one of Claims 22 to 27, characterized in that it further comprises an evaporator (8) for at least partially removing the water from the solution separated from the particles. 29. Plant according to any one of Claims 22 to 28, characterized in that the means for reducing the chips to particles consist of a mechanical mill for milling the chips, reducing them to granules. 30. Plant according to any one of Claims 22 to 28, characterized in that the means for reducing the chips to particles comprise a thermo-mechanical defibrator (5) for reducing the chips to fibres or groups of fibres. 31. Plant according to Claim 30, characterized in that it further comprises a refiner (7) situated between the defibrator (5) and the series of dispersal containers (6) and arranged so as to increase the specific surface area of the fibres to more than 4000 mm 2 per cm 3 of fibre. 32. Plant according to Claim 30 or Claim 31, characterized m that the defibrator (5) and/or the refiner (7) are arranged so as to perform a partial extraction of the tannic substance. 33. Plant according to Claim 31, characterized m that the refiner (7) is arranged to increase tne specific surface area of the fibres to a value of at least 7000 mm" per cm 3 of fibre. 34. Plant according to any one of Claims 31 to 33, characterized m that it comprises a Fourdπnier machine (9) or the lικe with a conveyor filter screen (10) on which the aqueous solution containing the fibres is spread, the screen (10) constituting the filtration means and being provided with means (11) for the suction of the aqueous solution and/or means (12) for squeezing out the aqueous solution, and means (13) for collecting the aqueous solution which drips and/or is drawn and/or squeezed through the screen (10), and for sending the paste of fibres carried by the screen to a section (14) for the formation of a sheet or board material. 35. Plant according to Claim 34, characterized m that it comprises an evaporator (8) to which the solution separated from the fibres is sent from the collection means (13) m order to be concentrated.

Inventors: BATTAGLIA RICCARDO, CALLERI GIACOMO, BATTAGLIA, RICCARDO, CALLERI, GIACOMO
Applicants: BATTAGLIA RICCARDO, CALLERI GIACOMO, LUYKX THERESIA, BATTAGLIA, RICCARDO, CALLERI, GIACOMO, LUYKX, THERESIA
Application year: 1999
Main classification: D21C11
IPC codes: C08H5, D21C11