EP3275610B1 - Method for producing enriched wood nodes powder - Google Patents

Description

The invention relates to a method for manufacturing enriched wood knot powder according to claim 1. The closest prior art is the document WO 02/098830 A1 .

Tree nodes do not have the same structure or chemical composition as the rest of the trunk. These knots form the base of the branches located inside the trunk. Generally, the nodes are more compact and denser than the rest of the trunk. The nodes of some trees contain molecules of interest for different industries, including the pharmaceutical and food industries. Thus, the nodes of conifers are known to contain between 6 and 29% of lignans while this family of products is practically absent from the parts of the trunk distant from the nodes. However, the knots contain less cellulose than the rest of the trunk, but more light-absorbing substances. In addition, their fibers are shorter. The presence of knots in the chips used to make paper pulp makes it more fragile and darker, making it difficult to obtain a high degree of whiteness. The paper industry therefore seeks as far as possible to remove from the beginning of the manufacturing process the wood chips containing knots.

The document WO 02/09893 A1 presents a process for manufacturing a wood knot powder from platelets used as a basis for the paper industry. Platelets containing knots are usually larger than the others. They are separated by passing through a screen and / or through an aeraulic separator. These “oversized” wafers are then crushed to be reduced to chips whose dimensions are between 5 and 30 mm long and 2 to 7 mm thick. The shavings are allowed to dry until a dry matter content of at least 85% is obtained. The dry shavings are then mixed with cold water contained in a tank and left to stand for about 1.5 minutes. The chips containing knots, of a density greater than 1, fall to the bottom of the tank, while the chips free from knots, less dense, remain on the surface. The sedimented fraction at the bottom of the tank is recovered, dried and subjected to a chemical extraction process for lignans. The results of the analyzes show that the total content of lignans in the sedimented fraction is approximately 9.7% and that the sedimented fraction contains between 80 and 100% of lignans.

The objective of the invention is to improve the quality of the wood extract to obtain an extract having a high content of lignans and the quality of which allows recovery in fields such as pharmacy or food.

1. a) Récupération de plaquettes de bois ;
2. b) Tri mécanique des plaquettes de bois et prélèvement de la fraction ayant une densité supérieure à une densité seuil (D1) et/ou une taille supérieure à une taille seuil (T1), la densité seuil (D1) correspondant à la densité moyenne des plaquettes de bois et se situant entre 0,7 et 0,9 g/cm³ et la taille seuil (T1) correspondant à la taille seuil définissant le refus de classage pour taille excessive dans l'étape de tri de plaquettes de bois dans un procédé de fabrication de pâte thermomécanique et/ou la taille seuil (T1) valant 35 à 45 mm ;
3. c) Tri optique de la fraction de plaquettes prélevée à l'étape b) et collecte des plaquettes présentant des nœuds ayant une taille supérieure à une taille seuil (T2) dans l'une des dimensions et/ou exemptes de contaminants ;
4. d) Broyage des plaquettes collectées à l'étape c) jusqu'à une granulométrie seuil (T3) comprise entre 6 à 8 mm ;
5. e) Séchage du broyat obtenu à l'étape d) jusqu'à ce que son taux d'humidité soit inférieur à un taux d'humidité seuil (H) ;
6. f) Tri par densité du broyat et séparation de la fraction ayant une densité supérieure à une densité seuil (D2) ;
7. g) Micronisation de la fraction séparée à l'étape f) pour obtenir une poudre ayant une taille de particules maximale inférieure à une granulométrie seuil (T4), la granulométrie seuil (T4) s'élevant à 1 mm ;

procédé dans lequel les autres variables peuvent prendre les valeurs suivantes :

• la taille seuil (T2) de l'étape c) vaut 1 cm ;
• la densité seuil (D2) de l'étape f) vaut 1 ;
• le taux d'humidité seuil (H) de l'étape e) est inférieur à 15 % ;
• les contaminants éliminés à l'étape c) comprennent notamment des morceaux d'écorce, des plaquettes attaquées par de la moisissure, des champignons, les plaquettes sans nœuds ou des éléments de douglas.

This objective is achieved by the method according to the invention which provides for the following steps:

1. a) Recovery of wood chips;
2. b) Mechanical sorting of wood chips and sampling of the fraction having a density greater than a threshold density (D1) and / or a size greater than a threshold size (T1), the threshold density (D1) corresponding to the average density of the wood chips and between 0.7 and 0.9 g / cm ³ and the threshold size (T1) corresponding to the threshold size defining the refusal of classification for excessive size in the step of sorting wood chips in a thermomechanical dough manufacturing process and / or threshold size (T1) worth 35 to 45 mm;
3. c) optical sorting of the fraction of platelets sampled in step b) and collection of platelets having nodes having a size greater than a threshold size (T2) in one of the dimensions and / or free of contaminants;
4. d) grinding of the platelets collected in step c) up to a threshold particle size (T3) of between 6 to 8 mm;
5. e) drying of the ground material obtained in step d) until its humidity level is lower than a threshold humidity level (H);
6. f) Sorting by density of the ground material and separation of the fraction having a density greater than a threshold density (D2);
7. g) micronization of the fraction separated in step f) to obtain a powder having a maximum particle size less than a threshold particle size (T4), the threshold particle size (T4) amounting to 1 mm;

process in which the other variables can take the following values:

• the threshold size (T2) of step c) is 1 cm;
• the threshold density (D2) of step f) is 1;
• the threshold humidity level (H) of step e) is less than 15%;
• the contaminants removed in step c) include, in particular, bark pieces, molds attacked by mold, fungi, knotless plates or Douglas fir elements.

Thanks to the wood powder obtained by this process, it is possible to obtain wood powder extracts of excellent quality which can be used in particular in the pharmaceutical, agrifood and food sector as well as in the cosmetic field. Legislation in these areas severely limits the type and percentage of solvents that can be used during the extraction phases. In addition, certain elements such as terpenes are only authorized in very small quantities in extracts from wooden knots. The same is true for fungi and bacteria. Another requirement of this sector is not to thermally degrade the extracted molecules. It is important that at no stage in the process does the temperature of the material exceed 40 ° C in order to avoid any chemical degradation of the molecules contained in the powder.

The threshold density (D1) for step b) is preferably between 0.75 and 0.85 g / cm ³ .

The threshold size (T1) of step b)
preferably about 40 mm.

With the threshold size (T2) of step c) being equal to 1 cm, the plates containing nodes not exceeding 1 cm in one of their dimensions are not retained.

The threshold particle size (T3) used for step d) is preferably less than 7 mm.

By retaining a threshold density (D2) for step f) equal to 1, we take into account the fact that the nodes have a density greater than 1, while the wood which surrounds the nodes has a density close to 0.9 on wood wet and 0.7 on dry wood.

The threshold humidity level (H) of step e) is preferably less than 12%.

It may happen that the wood chips recovered in step a) contain Douglas fir, which is undesirable. This dark orange wood is easy to detect and remove in step c).

Step c) of optical sorting can for example be carried out by means of an optical sensor and / or an X-ray sensor.

The X-ray sensor makes it possible to distinguish the plates containing nodes from the other plates, and the optical sorting makes it possible to remove the elements of douglas, the barks and the plates contaminated by the fungi. All these elements are discarded during sorting.

During step f), sorting by density can be carried out dry using a dry density sorting device, preferably with density sorting stages mounted in cascade with upstream recycling.

A gravimetric table that operates in air with density sorting stages mounted in cascade and upstream recycling is indeed preferred to density sorting in water.

The wood chips recovered in step a) consist for example of sawmill chips, debarked logs and then put into chips in a cutter or a mixture of the two. In particular, the chips can be rejects from the step of sorting wood chips in a process for manufacturing thermomechanical or chemical pulp. They can also be refusals from sawmills or come from the manufacture of molded fiber objects or from the wood paneling industry.

The wood chips of step a) can consist of a mixture of 65 to 85%, preferably 70 to 80%, of sawmill chips and 15 to 35%, preferably 20 to 30% of peeled and ground logs.

The wooden boards of step a) are preferably boards of one or more of the species chosen from the group comprising Abies alba, Picea abies, Betula pendula, Pinus sylvestris, Abies sibirica, Pinus sibirica, Abies balsamea, Thuja occidentalis , Northern white-cedar, Pinus cembra, Pseudotsuga menziesii (douglas), Larix decidua, Picea glauca, Picea mariana, Picea pingens, Abies pectinata, Abies lasiocarpa, Pinus banksiana, Pinus resinosa, Larix lariciana, Larix sibirica, Thuja plicata, Fagus Sylv , Populus tremula, Populus tremulus, Tsuga heterophylla, Pinus contorta, and Juniperus virginiana (red cedar), and preferably platelets of fir (Abies Alba) and spruce (Picea Abies).

The mechanical sorting in step b) can be carried out using a sieve with plates. The sorting by density of step f) can be carried out by means of a device which vibrates the ground material by blowing air from below, the air carrying away the fractions having a density below the threshold density (D2) .

The micronization of step g) can be carried out by means of an attrition mill putting the ground particles in suspension in the air and agitating them. In this case, it is preferable, during micronization, to maintain the ground material at a temperature less than or equal to 40 ° C., preferably using the air flow from the attrition mill. Micronization makes it possible to mechanically increase the specific surface of the material in order to increase the possibilities of exchange and extraction.

The micronized fraction in step g) can be filtered by passing through a 1 mm sieve, the refusal of filtration by sieve is preferably passed back to micronization.

The invention is described below in more detail by means of the figure 1 which shows a block diagram of the process.

The objective of the process of the invention is to manufacture enriched knot powder. Tree nodes contain bioactive phenolic compounds of interest different market segments including the pharmaceutical and food industries. These molecules can be easily extracted from the knot tissue and are therefore part of the “extractables” family. The molecules contained in the "extractables" depend on the nature of the wood. Lignans are found in particular in softwood knots or flavonoids in hardwood knots.

The molecules sought are mainly located in the dense part of the node. The process must therefore make it possible to sort the healthy nodes, then to separate the heart of the node from its periphery. The process uses the difference in density between the center of the knot (greater than 1) and the normal wood which surrounds it which is approximately 0.7 for dry wood and 0.9 for wet wood.

The first step, called step a), consists in obtaining the plates usually used for the manufacture of paper pulp. Paper can be manufactured by various methods, in particular by a process manufacturing thermomechanical pulp (TMP) from a mixture of wood chips. These plates are generally composed for 75% of sawmill plate (coproduct put in chips) and for 25% of thinning logs of fir, spruce, and can contain between 5 and 10% of Douglas fir. Once the logs have been peeled and blistered, they are mixed with the chips from sawmills.

In the next step, step b), the mixture is sorted mechanically in order to take the heaviest fraction and / or whose dimensions are larger than the general mass. Indeed, the knots being denser and harder than the rest of the wood, they are more difficult to grind. Inserts containing knots are generally larger than those containing normal wood. In practice, this step b) is part of a preliminary step in the manufacture of paper pulp. In this preliminary step, the stationer removes elements that are too large, too large, abnormally dense and too small which could degrade the quality of the pulp and therefore that of the paper. Only the elements whose dimensions are greater than a threshold size (T1) and / or whose density is greater than a threshold density (D1) are recovered for the manufacture of the powder according to the invention. Concretely, the threshold size (T1) is between 35 and 45 mm, and the threshold density (D1) between 0.7 and 0.9 g / cm ³ , preferably between 0.75 and 0.85 g / cm ³ and ideally 0.8 g / cm ³ . It is in this fraction that the nodes are found. The filing cabinet which allows this sorting is inclined and animated by a rotary rocking movement (sieve with plates). It is fitted with separation grids. Particles that are too dense like the nodes are separated from normal platelets and join the elements that are too large. The proportion of nodes in this classification refusal is around 30%.

This step b) makes it possible to multiply by 10 the concentration of the nodes.

In practice, the first two stages of the process are common to a process for manufacturing paper pulp. The platelets retained at the end of step b) consist of a portion of the platelets rejected by the stationer. This is shown schematically on the figure 1 by the frame surrounding the first two steps.

The third step, step c), consists of an optical sorting of the nodes. It allows to obtain at the end of the process a powder more concentrated in knots and the least polluted possible by other elements.

The plates previously removed in step b) are placed on a carpet and subjected to a sorting operation making it possible to select the plates containing correct knots. A correct knot is a fir or spruce knot having a minimum size (T2) in one of its dimensions and which is free from mold or attack by fungi. Generally, we retain the nodes having at least 1 cm long in one of their dimensions. Indeed, one finds among the plates leaving stage b) elements of Douglas fir, plates attacked by blue (fungus) or mold, pieces of bark and of course a significant quantity of plates without knot which do not contain very few interesting active ingredients.

Platelets not containing a knot lower the concentration of active products in the final powder. Blue chips, mold and bark affect the quality of the powder.

The fourth step, step d), consists in grinding the platelets collected in step c) until a threshold particle size (T3) is obtained, fixed between 6 and 8 mm, preferably about 7 mm. The knots are ground for example in a grinder equipped with a rotor fitted with knives and a calibrated grid. This step makes it possible to standardize the size of the raw material, to cut into knot core elements and other normal wood elements. It also makes it possible to dry the crushed knots more quickly.

It is provided in the context of the invention, in a step e), to dry the ground material obtained at the end of step d) until its humidity level is lower than a threshold humidity level. (H). By removing the moisture, the difference in density of the knot core particles by ratio to simple wood particles is increased. In fact, the density of the knots is in all cases greater than 1, while the density of simple wood is around 0.9 for wet wood and only 0.7 for dry wood. This greater density difference will facilitate the next step of sorting by density. Drying also facilitates subsequent powdering and it prevents degradation of the material by stabilizing it. The threshold humidity level is preferably set at 15%, or even 12% or less.

After the grinding of step d), and the drying of step e), the density of the core of knots is much greater than that of normal wood. Sorting by density makes it possible to separate heavy elements (core of knots) from light elements (wood or knot tower). The machine vibrates the mixture by blowing air from below which will cause separation. Components with a density greater than a threshold value (D2) are separated from the others. Generally, this threshold density (D2) is fixed at 1. The advantage of this pneumatic sorting process by density lies in the fact that the ground material is not humidified again as is the case during sorting by sedimentation in a tank of water. Steps d), e) and f) make it possible to enrich the final powder by multiplying by 5 the concentration of molecules of interest.

In order to facilitate the chemical extraction of the interesting molecules contained in the wood powder thus obtained, it is preferable to micronize the ground material in order to pass from a particle size (T3) to a particle size below a threshold value (T4). For this, the fraction of ground material separated in step f) is subjected to a micronization step in order to increase the specific extraction surface. The apparatus used can be an attrition mill which makes it possible to reduce the powdered material. The particles are suspended in the air and stirred so that they rub and fragment into powder. The large air flow makes it possible to maintain a maximum temperature at 40 ° C which preserves the quality of the molecules to be extracted. After separation of the air in a bag filter, the powder is filtered by passing through a 1 mm sieve, the rejects being recycled at the top of the micronization. The threshold particle size (T4) is 1 mm.

All these stages are accompanied by quality control and monitoring of the product throughout its transformation.

A study was carried out to show the importance of the different stages. This study is summarized in the table below:

These results show that the pre-sorting of the wafers and the drying before the gravimetric sorting are particularly important.

Claims (13)

1. Method for manufacturing enriched knotwood powder, comprising the following steps:

   a) recovery of wood chips;

   b) mechanical sorting of the wood chips and taking off of the fraction having a density greater than a threshold density (D1) and/or a size greater than a threshold size (T1), the threshold density (D1) corresponding to the mean density of the wood chips and being situated between 0.7 and 0.9 g/cm³ and the threshold size (T1) corresponding to the threshold size defining the residue of screening for excessive size in the wood chip sorting step in a method for manufacturing thermomechanical pulp and/or the threshold size (T1) being equal to 35 to 45 mm;

   c) optical sorting of the fraction of chips taken off at step b) with collection of the chips having knots with a size greater than a threshold size (T2) in one of the dimensions and free from contaminants;

   d) grinding of the chips collected at step c) to a threshold particle size (T3) of between 6 and 8 mm;

   e) drying of the ground material obtained at step d) until the moisture content thereof is below a threshold moisture content (H);

   f) sorting of the ground material by density and separation of the fraction having a density greater than a threshold density (D2);

   g) micronisation of the fraction separated at step f) in order to obtain a powder having a maximum particle size below a threshold particle size (T4), the threshold particle size (T4) being 1 mm;

   a method wherein the other variables may take the following values:

   - the threshold size (T2) of step c) is equal to 1 cm;

   - the threshold density (D2) of step f) is equal to 1;

   - the threshold degree of moisture (H) of step e) is less than 15%;

   - the contaminants eliminated at step c) comprise in particular pieces of bark, chips attacked by mould or fungi, chips without knots or elements of Douglas fir.
2. Method according to claim 1, characterised in that

   - the threshold density (D1) for step b) is situated between 0.75 and 0.85 g/cm³; and/or

   - the threshold size (T1) of step b) is equal to approximately 40 mm; and/or

   - the threshold degree of moisture (H) of step e) is less than 12%.
3. Method according to claim 1, characterised in that the optical sorting step c) is performed by means of an optical sensor and/or an X-ray sensor.
4. Method according to claim 1, characterised in that, in step f), the sorting by density is performed dry by means of a dry-density sorting device, preferably with density sorting stages mounted in cascade with upstream recycling.
5. Method according to any of the preceding claims, characterised in that the wood chips of step a) are sawmill chips, barked and ground billets or a mixture of the two, and in particular are oversize particles resulting from the wood chip sorting step in a thermomechanical paper manufacturing method.
6. Method according to claim 5, characterised in that the wood chips of step a) are a mixture of 65% to 85%, preferably 70% to 80%, sawmill chips and 15% to 35%, preferably 20% to 30%, barked and ground billets.
7. Method according to any of the preceding claims, characterised in that the wood chips of step a) are fir, Norway spruce and/or Douglas fir chips.
8. Method according to any of the preceding claims, characterised in that the mechanical sorting of step b) is performed by means of a chip sieve.
9. Method according to any of the preceding claims, characterised in that the density sorting of step f) is performed by means of a device that vibrates the ground material while blowing air from below, the air taking away the fractions having a density below the threshold density (D2).
10. Method according to any of the preceding claims, characterised in that the micronisation of step g) is performed by means of an attrition grinder putting the ground particles in suspension in air and agitating.
11. Method according to claim 10, characterised in that the ground material during micronisation is maintained at a temperature of less than or equal to 40°C, preferably by means of the flow of air from the attrition grinder.
12. Method according to any of the preceding claims, characterised in that, at step g), the micronised fraction is filtered by passing through a 1 mm sieve.
13. Method according to claim 12, characterised in that the oversize particles of the filtration by sieve in step g) are passed to micronisation again.

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