Patent Application
20240076831
The invention relates to methods for producing products based on wood, in particular methods for pretreatment of wood.
Wood as a raw material for the industrial processing to products based on wood (such as wood fiber boards or cardboard) contains—besides the main components cellulose, hemicelluloses and lignin—many different low- and high-molecular materials like fatty acids, resin acids, phenols and terpenes. These substances are subsumed as so-called extract materials (or extractives) since they can be extracted from wood with hot water and/or organic solvents (Koch, Raw Material for Pulp; in: Sixta (ed) Handbook of Pulp (2006), Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, p 21-68). Many of these extractives are “organoleptically relevant substances”, since they can result in olfactory and flavor interactions and impairments in products based on wood particles with the environment relevant to the respective final application (for example food in case of packaging cardboard or room air in case of wood fiber boards). Besides extractives, which inherently have characteristic odors as volatile hydrocarbons (e.g. terpenes), especially aldehydes (particularly hexanal) are responsible therefor, which are formed by an autocatalytic oxidation of fatty acids naturally occurring in the wood (Schreiner et al., Resolving the smell of wood-identification of odour-active compounds in Scots pine (Pinus sylvestris L.) (2018), Scientific Reports 8:8294).
Furthermore, wood particles contain resins, which can coagulate to sticky particles in processing the wood particles, which is augmented by the fats and waxes also naturally occurring in the wood. These resinous particles, also referred to as “pitch” or “stickies”, also cause disturbing effects on the paper/cardboard surface, which can entail problems in further processing the paper/cardboard (e.g. imprinting) in further consequence. These materials can also have a disruptive effect on the production process in that they cause deposit on machine parts, rollers and covering parts and the like (Sixta et al., Chemical Pulping Processes; in: Sixta (ed) Handbook of Pulp (2006), Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, p 109-509; Bjorklund Jansson et al., Wood Extractives; in: Ek et al. (eds) Wood Chemistry and Wood Biotechnology, 1 (2009), Walter de Gruyter GmbH & Co. KG, Berlin, pp 147-171).
At present, fatty acids are not removed from wood particles for products based on wood particles, such as for example cardboard or wood fiber boards. Instead, the autooxidation of these fatty acids is inhibited or delayed in that the heavy metal ions acting as a catalyst are bound in the wood particle products by the addition of chelating agents such as ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA). However, EDTA and its metal complexes are only poorly and slowly degradable in the wastewater purification and therefore are considered to be ecologically critical today, which in particular entails increasingly great problems for wastewater from production plants for products based on wood particles.
In further methods, which have been described for improving the organoleptic characteristics, bleaching (e.g. DE 10 2004 050 278 A1), delignifying (e.g. DE 28 18 320 A1), oxidizing or reducing (e.g. DE 33 44 239 C2, WO 2006/039914 A1, DE 10 2006 020 612 A1) chemicals are employed.
DE 10 2014 114 921 A1 relates to a method for producing an “emission-reduced” solid wood product or an “emission-reduced” wood containing basic material, in which it is treated with a “buffer solution” with a pH of ≥6 to precisely “reduce” the emissions (substantially of VOCs), however, wherein cellulose, hemicellulose and lignin are obviously not substantially maintained, and it is not disclosed, to which extent the content of fatty acids can be reduced with this method. According to WO 2006/032267 A1, solid wood or wood particles are treated such that the fatty acid esters contained therein are “inhibited, cleaved or oxidized”, but not extracted. WO 93/20279 A1 discloses the treatment of cellulose pulp (thus not wood particles) with organic solvents, which are to be again separated subsequent to this treatment. WO 2020/000008 A1 discloses the production of lignin particles. WO 00/34568 A1 relates to a method for producing chemical pulp from wood chips, wherein hemicellulose and lignin are separated. EP 2 138 528 A1 relates to a method for producing a cellulose material with reduced content of wood extractive. DE 10 2013 001 678 A1 discloses a method for treating wood with an oxidant. EP 2 356 977 A1 relates to the use of honey locust wood extracts for treating cellulite.
Therefore, it is the object of the present invention to reduce the content of releasable odor- and flavor-active aldehydes in products based on wood particles like cardboard or wood fiber boards by autooxidation of fatty acids naturally occurring in the wood. This is to be effected without the employment or addition of chelating agents.
A further object of the present invention is a significant improvement of the organoleptic characteristics of the wood particles as well as of aged wood particles, which are produced according to this method, such that the products produced therewith have no or only low odor loads also without the employment or addition of bleaching, delignifying, oxidating or reducing chemicals. With the method according to the invention, after aging of the wood particles (up to 6 months), undesired odor and flavor changes occurring in the course of this aging are in particular to be prevented in the food coming in contact therewith.
Finally, a preferred object of the present invention is in removing further ingredients from wood particles, which are undesired in the planned product, for example resin acids.
Accordingly, the present invention relates to a method for producing products based on wood as a raw material, in which wood in the form of wood particles is subjected to an extraction treatment with an extracting agent, which includes one or more organic solvents in an organic-aqueous mixture or the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as a hexanal content in wt % after accelerated aging for 72 h at 90° C., by the extraction treatment of the wood particles with the extracting agent, but the content of cellulose, hemicelluloses and lignin is substantially maintained in this extraction treatment.
As it has revealed in the course of the present invention, with the extraction of the organoleptically critical materials from the raw materials according to the invention, a significant improvement of the organoleptic characteristics of the wood particles can be achieved without addition of chelating agents, but by removal of potential aldehyde sources, especially fatty acids. However, it is known that fatty acids as aldehyde source and in further consequence source of organoleptic impairments of the wood particles can only be satisfactorily quantified by measurement techniques with great effort. Therefore, for the assessment of the extraction success, the hexanal content of the wood particles after aging was used according to the invention. This has proven to be a reliable parameter for the organoleptic characteristics of the products to be produced from the raw material, like paper, cardboard, wood fiber boards etc., which excellently correlates with the (very time-consuming) traditional aging attempts (hereto, see the studies and evidences in the example part below).
It has become apparent that a large part of the fatty acids and other disturbing materials (resin acids etc.) can be extracted with the method according to the invention, without the substance of wood material (cellulose, hemicelluloses and lignin) being significantly impaired thereby. Although any improvement in the removal of fatty acids from the wood raw material entails advantages, thus, a relevant reduction of at least 70% is readily possible for an economical use suitable in large scale with the present method. However, the treatment according to the invention is preferably selected such that the desired reduction is thereby achieved anyway, and a reduction by at least 70%, preferably by at least 90%, in particular by at least 95%, is thus achieved. Correspondingly, the conditions to be applied according to the invention can then be selected e.g. based on the character of the wood or the extracting agent such that the hexanal reduction according to the invention results anyway. Thereby, maximum values in absolute contents of hexanal can also be preferably adjusted. Although wood particles with a hexanal content of 2 mg/kg dry material (TM) can also be used for certain applications, absolute values below 1 mg/kg TM are preferred. With the particularly strict guidelines, which have been applied in the course of the examples of the present invention, a hexanal content of 0.5 mg/kg TM of hexanal (related to dry wood) was marked as an empirically ascertained value, below which organoleptic impairments are empirically no longer sensorially perceivable. Accordingly, a preferred embodiment of the method according to the invention relates to an extraction of the wood particles to a hexanal content of 0.5 mg/kg TM or below. For hexanal contents of the wood particles >0.5 mg/kg TM, it could be determined that the risk of an organoleptic impairment of the wood particles also increased here with increasing hexanal content.
For the purposes of the present invention, the determination of the hexanal content can be effected via a headspace gas chromatography (HS-GC) in case of doubt, in that ca. 0.2 g of air-dry wood particles (90-95 wt % (=% by wt.) dry substance content (TSG)) are filled in a headspace vial. The wood particles then have to be aged sealed in these vials at room temperature (ca. 20° C.) for six months to oxidize the fatty acids to hexanal. Since this takes very much time and thereby does not allow a soon assessment of the extraction success, the determination of the hexanal content is effected via the accelerated aging according to DIN ISO 5630-2 according to the present invention. Thereby, the hexanal content was performed in the experiments in the example part (unless explicitly otherwise indicated); this method is also relevant to the determination of the hexanal content for the purposes of the present invention in case of doubt. Therein, the wood particles are sealed in HS-GC vials, aged for 72 h at 90° C. and the hexanal content was subsequently ascertained by means of HS-GC.
Preferably, the wood particles are present in a size of less than 2 mm, preferably in the form of fibers, chips or mixtures thereof. This particle feature (as “particle size”) is defined according to the National Renewable Energy Laboratory (NREL) Laboratory Analytical Procedure (LAP) NREL/TP-510-42620 “Preparation of Samples for Compositional Analysis”, to which the NREL LAP NREL/TP-510-42619 “Determination of Extractives in Biomass” also relates. The particle feature of the particle size is accordingly formulated on the screen mesh (2 mm) of the cutting mill for sample preparation.
The wood particles are preferably present in the form of fibers, chips or mixtures thereof. This limitation of the particle size to 2 mm, as also preset in the NREL method NREL/TP-510-42620, entails the great advantage that besides the relatively well accessible resin channels, the comparatively difficultly accessible parenchyma cells, where the fatty acids are located, can also be extractively well reached (Lehr et al., Removal of wood extractives as pulp (pre-)treatment: a technological review (2021), SN Applied Sciences 3:886).
According to a preferred embodiment, the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion, in particular wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 μm. Therein, average fiber length as well as average fiber diameter relate to the length average, determined by means of optical measurement of the suspended fibers. This optical measurement usually results in uniform results (independently of chosen methodology and analysis apparatus), however, the apparatuses PulpEye (http://www.pulpeye.com/products/pulpeye/) and in particular MorFi Fiber Analyzer (http://www.techpap.com/fiber-and-shive-analyzer-morfi-neo,lab-device,31.html) have proven to be particularly suitable.
The amount of organic compounds, which can be extracted with the method according to the invention, is different according to wood type and constituent of the tree, from which the wood particles are obtained (heartwood/sapwood). For example, pines contain up to 9 wt % of extractable material in the heartwood, whereas fir sapwood usually only comprises up to 1% of extractable material (Bjorklund Jansson et al., Wood Extractives; in: Ek et al. (eds) Wood Chemistry and Wood Biotechnology, 1 (2009), Walter de Gruyter GmbH & Co. KG, Berlin, pp 147-171; Nisula Wood Extractives in Conifers: A Study of Stemwood and Knots of Industrially Important Species (2018), Abo Akademi University Press, Abo). Especially wood types like pine, birch, lime or poplar contain higher amounts of fatty acid ester (birch 2315 mg/kg, lime 7544 mg/kg or pine 5807 mg/kg of fatty acids; DE 10 2009 046 127 A1), which can be degraded to aldehydes and organic acids by the production of products from these woods without this being capable of being prevented by changing technological parameters. In addition, greater fluctuations of the contents of fatty acids and triglycerides appear depending on site, tree age, height section of the individual tree as well as between heart- and sapwood.
In DE 10 2009 046 127 A1, a method for producing wood fiber materials is described, in which volatile organic compounds (“VOC”), aliphatic and aromatic aldehydes, in particular hexanal and furfural, are reduced, wherein wood is treated with at least one compound for adjusting a neutral to alkaline pH value (like NaOH) and at least one chelating agent (like EDTA or DTPA). Therein, it is emphasized that bleaching, delignifying, oxidizing or reducing chemicals are not employed for such a production and squeezing of liquid formulation is not effected before the plastification of the wood or the wood chips. However, the employment of chelating agents like EDTA and DTPA, as above mentioned, entails a severe wastewater and environmental problem. Thus, the present invention brings crucial advantages also with respect to a pure chemical-thermal-mechanical digestion (CTMP) known per se, wherein wood chips are mixed with sodium sulfite and EDTA, namely both with respect to the environmental aspects and with respect to the effect according to the invention in the efficient depletion of fatty acids from the raw material.
U.S. Pat. No. 5,698,667 A discloses a pretreatment of a lignin containing cellulose containing material by extraction with an organic solvent (e.g. acetone) to remove wood extractives like volatile organic compounds (VOC) and higher-molecular pitch components without substantially impairing the integrity of the lignocellulose constituents of the material. However, industrially exploitable depletions with respect to the undesired ingredients therein could not be achieved (the maximum depletion of pitch and VOCs was 54.4 and 65% (after two-time extraction for acetone in water (80/20) and 100% acetone) and at most 78.2% with pure acetone, respectively, although the methodology used there cannot ensure that volatile components transition into the gas phase upon removing the solvent from the extract and thus the depletions are to be even lower estimated in determination by the evaporation residue of the extract.
In contrast, in the method according to the invention, with the aid of an extractive pretreatment of wood particles (like for example wood fibers) with organic solvents in an organic-aqueous mixture of the solvent or solvents with water, a major part of the fatty acids naturally occurring in the wood is already removed before further processing (for example to cardboard or wood fiber boards). Moreover, further extractives, like for example resin acids, phenols and terpenes, are highly reduced in the wood material by this pretreatment. According to the invention, the hexanal content has proven as an indicator for the autooxidation of fatty acids naturally occurring in the wood, especially if it is therein ascertained after accelerated aging of the wood particles (72 h at 90° C.). According to the invention, this hexanal content is reduced by at least 70% related to the potential of the basic raw material (as well as—in absolute contents) preferably down to below 0.5 mg/kg TM. Thereby, olfactory and flavor interactions of products based on wood particles with the environment relevant to the respective final application (for example food in case of packaging cardboard or room air in case of wood fiber boards) can be highly reduced with the present invention. At the same time, the wood particles are not substantially changed in their composition by the pretreatment, that is cellulose, hemicelluloses and lignin are not extracted and/or degraded to appreciable extent (in any case not by more than 10%, preferably by not more than 6%, in particular by not more than 4%), wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles. Besides the reduction of the portion of organoleptically relevant components in the wood particles, further important product and process advantages arise by the present invention in particular for the paper and cardboard production:
Pitch (stickies, resins and the like) are removed from the process and thereby cannot have a disturbing effect on the production process such that no or a reduced deposition on machine parts, rollers and covering parts and the like occurs.
Thereby, disturbing effects on the paper/cardboard surface can also be reduced by the present invention, whereby problems in further processing of the paper/cardboard (e.g. imprinting) are also considerably reduced in further consequence. By the considerably lower portion of these components on the surface and also in the interior of the paper/cardboard, an increased product quality like increase of the mechanical strength further results.
By the mentioned improved product characteristics of products, which are produced from the wood particles extracted according to the invention, new fields of application can also be exploited, which one can only cover with paper/cardboard today, the fiber components of which originate from pulp and/or treated BCTMP (bleached chemi-thermo-mechanical pulp) (for example high-quality packaging cardboards), or for particularly delicate applications, which can be met exclusively with pulp today.
In addition, by the extractive pretreatment according to the present invention, the CSB loads of the wastewater of the process are also highly reduced, whereby greater production capacities are allowed with consistent CSB load in the wastewater.
The release of odor- and flavor-active aldehydes in products based on wood particles like cardboard or wood fiber boards by autooxidation of fatty acids naturally occurring in the wood can be achieved according to the present invention also completely without the addition of chelating agents. Thus, the addition of a chelating agent like EDTA or DTPA in the production of products based on wood particles for reducing the olfactory and flavor load of these products becomes unnecessary, whereby the EDTA/DTPA load of the wastewater is eliminated, and thus the (ground) water-related environmental effects of the production of products based on wood particles are decreased as well as the EDTA/DTPA load of the products themselves is avoided. Furthermore, besides fatty acids, other extractives are also significantly reduced and thereby unloaded from the process, which decreases the extractive load of the process water in the production of the wood particles and thus entails lower requirements to the wastewater purification/processing. The reduced extractive load of the process water also has the advantage that problems in the production process of products based on wood particles can be reduced and the quality of the products can be increased (e.g. avoiding pitch/sticky problems in the cardboard production). Therefore, this variant is a particularly environment-friendly embodiment of the present invention.
The specific method conditions (like size, shape and dry substance content of the wood particles, choice of the extracting agent, water content, temperature, treatment duration, pH, amount of extracting agent (in proportion to wood), pressure, number of the extraction stages, variants of contacting between extracting agent and solid, operating mode etc.) required in practice for a certain wood type or for certain wood materials for an extraction of at least 70% of the fatty acids and for establishing a maximum absolute value of hexanal below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular below 0.5 mg/kg dry matter (respectively measured as a hexanal content in wt % of the extracted wood particles after accelerated aging for 72 h at 90° C.), respectively, can be immediately determined based on the teaching disclosed herein, in particular considering the results set forth in the example part, without further inventive assistance, in particular in view of the (usually known) amounts of organic materials (like fatty acids, resin acids, phenols, terpenes etc.) of the wood basic material, of the character of the wood (heartwood, sapwood, mixtures, etc.) and the requirements to the final product (cardboard, paper, wood fiber board, application in certain areas (food, drugs, animal feed, etc.)).
In particular, the present invention can be relatively easily integrated in existing production plants and be operated with existing plants, respectively.
According to the invention, one or more of the above set objects can be solved by a method with the features of claim 1. Advantageous configurations with convenient developments of the invention are specified in the respective dependent claims.
The choice of the liquid phase of the extract according to the invention (here referred to as extracting agent) is also dependent on the relevant wood type (and the natural content of extractives thereof). However, the solvent or solvent mixture in the extracting agent also has to be selected such that a significant loss of cellulose, hemicelluloses and lignin does not occur and the treatment duration nevertheless is not unduly long. Therein, mixtures according to the invention of ethanol, acetone and water with 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol and 0-99 wt % of acetone, preferably 30-90 wt % of acetone, as the organic-aqueous solvent in the extracting agent have proven to be particularly advantageous. Further organic solvents, which can be used in the extracting agent instead of (or for certain purposes optionally also together with) ethanol or acetone with regard to an industrial scale, are for example methanol, n-propanol and iso-propanol.
Preferred ratios of extracting agent to solid dry substance are 5:1-25:1 (w/w), preferably 8:1-17:1 (w/w), in the method according to the invention.
The following considerations apply to the ratios and concentrations in the extracting agent indicated herein: With 100% of extracting agent, the total amount of extracting agent, which is present after the extraction, is always meant, namely the extracting agent, including the materials extracted from the wood particles and the water contained in the wood basic material (in the wood particles). However, since the amounts of wood basic material are usually indicated as “wood dry matter” herein and the substances extracted from the wood are usually below 1% of the total mass of the extracting agent, the ratios before the extraction substantially (just +/−1%) also correspond to the ratios after the extraction (the optionally present water portion in the wood basic material, which mostly exists in the economical exploitation, is accordingly always already attributed to the extracting agent herein). Therefrom, in using 100 wt % of acetone concentration of the extracting agents at 1:10 (solid: extracting agent), thus, 1 kg of wood dry matter and 10 kg of acetone result. 70 wt % of acetone concentration of the extracting agents at 1:10 (solid: extracting agent) then would e.g. be 1 kg of wood dry matter, 7 kg of acetone and 3 kg of water. The extracted material would be added, as mentioned, but empirically is at concentrations far below 1 wt % in the extracting agent and thus is negligible. Due to the water content in the basic material, at least 10% of water, preferably at least 7.5% of water, in particular at least 5% of water, are preferably contained in the organic-aqueous mixture of the solvent or solvents according to the invention, preferably in any event in a method with a single extraction step or (e.g. in a method with at least two extraction steps) in the first extraction step.
The extraction temperatures can also be determined based on the remaining wood and process parameters, in particular also considering the energy input, which higher temperatures require. According to the invention preferred, the treatment is effected at an extraction temperature of 20-150° C., preferably 40-120° C., in particular 50-110° C.
According to a preferred embodiment, the method according to the invention is operated at normal pressure; in certain cases, an extraction under pressure can be advantageous (despite of the energetic overhead of the pressure application). Therefore, the treatment is effected according to a preferred embodiment at an absolute extraction pressure of 1-5 bar, preferably 1-1.49 bar, according to the invention.
Also with respect to the duration of the extraction method according to the invention, one can determine based on the remaining process parameters, which duration is required for the depletion of fatty acids to be achieved. Preferably, the treatment according to the invention is effected during an extraction time of 10 min-8 h, preferably 30 min-7 h, in particular 1-5 h.
The present method is principally suitable for all products based on wood, in which organoleptic characteristics play a role. The method according to the invention is particularly suitable for products, which are in use for longer time, are used for the packaging of food or in interior rooms. Therefore, the method according to the invention is particularly suitable for (large-scale) production of cardboard, paper, wood fiber boards, chipboards, objects of utility (for example (or in case of doubt) according to the definition of the Austrian food safety and consumer protection law (LMSV, BGB1. I No. 13/2006, in the version of 01.10.2020)), medical products (for example (or in case of doubt) according to the definition of the Austrian medical product law (MPG, BGB1. No. 657/1996, in the version of 01.10.2020)), in particular for producing cardboard.
Particularly advantageous method parameters for the extraction treatment according to the present invention are selected from:
Within the scope of the present invention, it has turned out that both batch and continuous and semi-continuous extractions are possible and can even advantageously act on the extraction result, in particular if the partial dwell time per extraction step is at most 1 h.
It is also essential in determining the method parameters that conditions are selected, on which substantial losses of the wood substance do not occur (thus in the content of cellulose, hemicelluloses and lignin). Therefore, one can also provide that the content of dry substance of the employed wood particles is reduced by less than 10%, preferably less than 5%, in particular less than 4%, in the treatment according to the invention, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, namely the wood particles.
As already above mentioned, various woods vary in their contents of VOCs. The specific method parameters according to the invention are also to be accordingly adjusted. However, since this is allowed for all of the industrially relevant wood types with the disclosure of the invention contained herein, the wood particles can preferably be selected from the industrially relevant wood types, thus e.g. from coniferous wood particles, spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
According to a preferred embodiment, the wood particles are mixed during the treatment with the extracting agent.
As already above mentioned, a preferred embodiment of the method according to the invention is in that the wood particles are squeezed after the treatment with the extracting agent to remove the extracting agent. Preferably, the wood particles can be cleaned once or multiple times with an extracting agent, even more preferably with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent after the (extraction) treatment with the extracting agent. The extracting agent used in the extraction and/or washing can be removed from the wood particles by multiple times of washing with water and/or water steam stripping and/or drying, wherein water steam stripping and/or drying are particularly preferred. Both extracting agents and washing waters are preferably regenerated subsequent to the method according to the invention for reuse. Therein, the extractives, particularly fatty acids and resin acids, can be separated from the extracting agent, as mentioned, and be used as byproducts.
With the method according to the invention, it is possible to prepare wood particles such that the content of fatty acids in the wood particles is reduced such that the product to be produced of the wood raw materials does not have organoleptically disadvantageous characteristics. Preferably, the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles respectively after accelerated aging for 72 h at 90° C., by extraction of the wood particles with the extracting agent according to the invention.
The wood particles thus obtained preferably have a content of fatty acids in the wood particles below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90° C.
In addition to the reduction of the hexanal content, it is also possible with the method according to the invention to increase the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, by at least 10%, preferably by at least 15%, in particular by at least 25%, wherein the degree of grinding, measured in ° SR, therein changes by less than 10%.
According to the invention, it has become apparent that besides the extraction of fatty acids with the method according to the invention, resin acids (besides other VOCs) can also be extracted. Within the scope of a preferred embodiment, the fatty acids, resin acids and/or optionally further extractives extracted into the extracting agent are supplied to a further purification method and can then be provided as byproducts of the production in extracted and optionally further purified form. In particular, this can be effected by mechanical separation technique after the thermal separation of the organic solvent from the organic-aqueous extracting agent to thus separate the precipitated lipophilic extractives (such as fatty acids and resin acids), and to obtain an aqueous phase enriched with the hydrophilic extractives (such as lignans), wherein the hydrophilic extractives can be still further concentrated by subsequent treatment with thermal separation technique (e.g. membrane separation methods and/or adsorption) (Lindemann et al., Selective recovery of polyphenols from MDF process waters by adsorption on a macroporous, cross-linked pyrrolidone-based resin (2019), Holzforschung volume 74 magazine 2). The achieved extractive enrichments can be still additionally increased by preceding membrane filtration of the extracting agent (Shi et al., Separation of vegetable oil compounds and solvent recovery using commercial organic solvent nanofiltration membranes (2019), Journal of Membrane Science 588; Weinwurm et al., Lignin Concentration by Nanofiltration and Precipitation in a Lignocellulose Biorefinery (2015), Chemical Engineering Transactions 45, pp. 901-906). The employment of the lipophilic extractive fraction obtained according to this method lends itself as animal feed supplement (WO 2015/071534 A1, U.S. Pat. No. 10,092,610 B2), since the resin acids contained in the lipophilic extractive fraction inhibit the growth of harmful bacteria in the animal digestive tract and thus prevent digestion disorders, which was in particular already shown for poultry by very different studies (Kettunen et al., Natural resin acid—enriched composition as a modulator of intestinal microbiota and performance enhancer in broiler chicken (2015), Journal of Applied Animal Nutrition Vol. 3; Kettunen et al., Dietary resin acid composition as a performance enhancer for broiler chickens (2017), Journal of Applied Animal Nutrition Vol. 5, pp. 349-355; Vienola et al., Tall oil fatty acid inclusion in the diet improves performance and increases ileal density of lactobacilli in broiler chickens (2018) British Poultry Science Vol. 59 No. 3). According to a preferred embodiment, chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers, are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles. In this embodiment, the method according to the invention represents an extremely advantageous and practice-oriented variant already for ecological reasons alone.
Further features of the invention are apparent from the claims, the figures and the description of figures. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of figures and/or shown in the figures alone are usable not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. Thus, implementations are also to be considered as encompassed and disclosed by the invention, which are not explicitly shown in the figures and explained, but arise from and can be generated by separated feature combinations from the explained implementations. Implementations and feature combinations are also to be considered as disclosed, which thus do not comprise all of the features of an originally formulated independent claim. Moreover, implementations and feature combinations are to be considered as disclosed, in particular by the implementations set out above, which extend beyond or deviate from the feature combinations set out in the relations of the claims. In particular, the present invention is explained in more detail based on the following examples and the figures, of course without being restricted thereto.
The goal of the developed method in this patent is a significant improvement of the organoleptic characteristics of the wood particles as well as of aged wood particles, which are produced according to this method. The undesired odor of them—in particular occurring after aging of the wood particles (up to 6 months)— and flavor of the food coming in contact therewith, especially comes about by aldehydes (particularly hexanal), which are formed by an autocatalytic oxidation of fatty acids naturally occurring in the wood. This autocatalytic oxidation is, as above mentioned, currently industrially prevented or greatly decelerated by the complexation of the metal ions present in the wood particles, which act as a catalyst, by means of addition of chelating agents like for example ethylenediaminetetraacetic acid (EDTA). The method of this patent achieves a significant improvement of the organoleptic characteristics of the wood particles without addition of chelating agents, but by removal of potential aldehyde sources, especially fatty acids.
Since fatty acids as an aldehyde source and in further consequence source of organoleptic impairments of the wood particles can be satisfactorily quantified by measurement technique only with great effort, the hexanal content of the wood particles after aging was used for assessing the extraction success of the experiments of this patent. It is to be noted at this point that 0.5 mg/kg TM of hexanal (related to dry wood) mark that empirically ascertained value, below which organoleptic impairments are empirically no longer sensorially perceivable. For hexanal contents of the wood particles >0.5 mg/kg TM, it applies: the higher the hexanal content, the higher the organoleptic impairment of the wood particles.
The determination of the hexanal content can be effected via headspace gas chromatography (HS-GC) in that ca. 0.2 g of air-dry wood particles (90-95 wt % TSG) are filled into a headspace vial. In these vials, the wood particles then have to be aged sealed at room temperature (ca. 20° C.) for six months to oxidize the fatty acids to hexanal. Since this takes very much time and therefore does not allow soon assessment of the extraction success, the accelerated aging according to DIN ISO 5630-2 was performed for the present experiments (unless explicitly otherwise indicated). The wood particles were sealed in HS-GC vials, aged for 72 h at 90° C. and subsequently the hexanal content was ascertained by means of HS-GC. Although this standard for accelerated aging was withdrawn, the performed extraction experiments in table 1 show that the method of the accelerated aging provides comparable values and the hexanal values with the accelerated aging are even higher on average, respectively, and thereby even offer safeties with respect to the extraction success.
For the extraction success of all of the experiments according to the present invention, the hexanal content was used since it empirically represents the main influencing factor of the organoleptic impairment of wood particles. The extractive content by means of Soxhlet extraction according to the TAPPI standard T204 is too inaccurate hereto, as table 2 shows. At this point, it is to be noted that for the determination of the extractive content of the wood particles of all of the experiments of this patent, not the TAPPI standard T204, but the NREL method NREL/TP-510-42619 very similar to the T204 was applied and groundwood or 2 mm sized wood particles were employed as the basic material instead of wood dust.
As is apparent in table 2, the Soxhlet extractions with ethanol significantly differ from those with acetone in the hexanal content, but not significantly in the extractive content. This means that two differently extracted wood particles can for example have different organoleptic characteristics despite of non-significantly different extractive content. The hexanal content of the wood particles after aging is thus a substantially stronger and more accurate indicator for the organoleptic impairment than the extractive content, and therefore was used for the extraction success according to the present invention. In addition, the hexanal content of the basic material and the reduction of the hexanal content resulting from it was indicated for all of the experiments, since the basic materials are snapshots and the hexanal content therefore can possibly very greatly fluctuate.
Nevertheless, the extracted extractive mass (ascertained as evaporation residue of the extract) is an important indicator for the solid mass loss of the extractions since it nearly includes the entire extractively removed solid mass—except for some few very volatile compounds. Thus, the evaporation residue of the extract together with the hexanal content of the extracted wood particles is an important measure of the assessment of the selectivity of the extractions.
For the solvent preselection, groundwood samples were extracted with three different solvents. 3 g of air-dry groundwood were respectively extracted for 24 h by means of Soxhlet method according to the NREL procedure NREL/TP-510-42619. The results are represented in table 3.
In table 3, it is apparent that even with higher hexanal contents of the basic material, ethanol extracts best, followed by acetone. Cyclohexane extracts worst by far, which means that completely nonpolar solvents are unsuitable for the extraction of fatty acids. According to Reichardt and Welton (Reichardt and Welton, Solvents and Solvent Effects in Organic Chemistry 4 (2011), Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, pp 550-552), the empirically determined polarity of cyclohexane is 0 (very nonpolar) compared to 0.355 of acetone and 0.654 of ethanol. Nevertheless, the extraction with cyclohexane also could reduce the hexanal content by 79%.
Based on the extraction of air-dry groundwood (consisting of ca. 95% of spruce and 5% of pine) with ethanol (EtOH), the influence of the parameters of solvent concentration, temperature and extraction duration was examined. Thereto, ca. 2 g of air-dry groundwood were extracted in an ethanol-water mixture with a solid: extracting agent ratio of 1:10 w/w and ethanol concentrations of 50, 70 and 90 wt % at temperatures of 70, 90 and 110° C. respectively for 0.5, 1, 2, 4 and 8 h in small autoclaves. After the extraction, the groundwood was squeezed, washed with ethanol, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. In
The
In table 4, it is visible that despite of the high hexanal content reductions achieved in this experimental series, the extracted solid mass is max. 7 wt % (related to the basic material)—but mostly considerably below. This means with an ascertained extractive content of the basic material of ca. 3 wt %, that neither hemicelluloses nor lignin are extracted to appreciable extent.
The extraction of wet groundwood represents real conditions much better than the extraction of dry groundwood, like experiment 1, in particular in the cardboard production. In addition, substantially more sample mass was taken for these experiments (factor 225) than for experiment 1, to obtain a more meaningful result. Ca. 450 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% of spruce and 5% of pine) were extracted in an ethanol-water mixture with a solid: solvent ratio of 1:10 w/w and ethanol concentrations of 60 wt % at temperatures of 70 and 90° C. for 2 and 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with ethanol, again squeezed and one again washed with demineralized water before it was dried, aged and analyzed. Table 5 shows the results of these extractions.
The experiments show that—compared to the extraction of lower and especially air-dry wood material mass—the experiments with mechanically dehydrated wood material and more sample mass have higher hexanal contents in the extracted wood material. Nevertheless, over 73% reduction of the hexanal content was achieved at each setting.
Experiment 3 was performed to test three different technically relevant solvents under real extraction conditions. Ca. 450 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% pine) were extracted in a solvent-water mixture with a solid: extracting agent ratio of 1:10 w/w and a solvent concentration of 70 wt % at a temperature of 70° C. for 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. Table 6 shows the results of these extractions.
As is visible in table 6, acetone extracts the unsaturated fatty acids, which are responsible for the hexanal formation, significantly better than non-denatured ethanol. However, the best extraction results could be achieved with ethanol, which was incompletely denatured with butanone. The hexanal content of 2.77 mg/kg TM achieved herein with 70 wt %, 70° C. and 4 h extraction time is still considerably above the 0.5 mg/kg TM limit, but corresponds to a reduction of 80%. In all extractions, the evaporation residue of the extract is only between 2.2 and 2.4 wt % related to the basic material dry matter, which means with an ascertained extractive portion of 3.6 wt % that the wood main constituents cellulose, hemicelluloses and lignin de facto were not attacked and the extractions were thus very selective. The abietinic acid content of the extractions of this experiment was reduced by 41-55% related to the basic material. Since abietinic acid was here selected as a lead substance for the content of resin acids, a reduction of the content by around 50% is an indication of the considerable reduction of resin by the method of this patent.
The influence of different solid—extracting agent ratios was examined in this experiment. Ca. 200-450 g TM (according to solid: extracting agent ratio) of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% pine) were extracted in an acetone-water mixture consisting of 70 wt % of acetone and 30 wt % of demineralized water with solid: extracting agent ratios of 1:10, 1:15 and 1:25 w/w at a temperature of 50° C. for 1, 2 and 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. The results of these extractions are listed in table 7.
As table 7 shows, the hexanal content is reduced by over 80% in all extractions (with the exception of the solid: extracting agent ratio of 1:10 (w/w) with a basic material—hexanal content of 14.07 mg/kg TM). With extracting agent—solid ratios above 10:1 (w/w), the reduction of the hexanal content under identical extraction conditions is comparably high and always far above 70% despite of different basic material—hexanal contents. Therein, the evaporation residue of the extract is less than 3%, which is an evidence for the quantitative preservation of the lignocellulose constituents in this method with ascertained extractive contents of the basic material of 3.4-3.7 wt %. This experiment too has shown that the method of this patent can significantly reduce resin by the reduction of the abietinic acid content by 31-54% related to the basic material.
In this experiment, multi-stage extractions were performed, wherein for each stage (=each one stage) fresh unloaded extracting agent was used. The groundwood (ca. 400-450 g TM; ca. 25 wt % TSG) was squeezed after each extraction stage (to ca. 30 wt % TSG) and mixed with acetone and demineralized water (both preheated to 50° C. extraction temperature) such that the solid: extracting agent ratio is 1:10 and the acetone concentration in the extracting agent is 70 wt %. The extractions were performed in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. The results of these extractions are listed in table 8.
As table 8 shows, the hexanal content is reduced by over 80% in all extractions already after the first stage, however, is still considerably over 0.50 mg/kg TM in particular with a basic material with higher hexanal contents. After stage three, however, the hexanal content is below 0.50 mg/kg TM, partially even below the determination limit of 0.20 mg/kg TM, with all extracted groundwoods of this experiment. Therein, the evaporation residue of the extract is less than 3-5%, which is an evidence for the quantitative preservation of the lignocellulose constituents in this method with ascertained extractive contents of the basic material of 2.5-3.7 wt %. This experiment too has shown that the method of this patent can significantly reduce resin, in particular with increasing extraction stage number, by the reduction of the abietinic acid content by 55-100% related to the basic material.
Experiment 6: Multi-Stage Extraction of Wet Wood Particles of Different Particle Sizes with Acetone
The influence of the particle size was examined with different extraction parameters in this experiment. Ca. 650 g TM of woodchips (ca. 20 mm; ca. 55 wt % TSG; spruce), ca. 450 g TM of chopped woodchips (2 mm mesh of the cutting mill screen; ca. 60 wt % TSG; spruce) and ca. 400 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% fir) were extracted respectively in two stages (each one hour) at 50° C. as well as respectively in two stages (each 30 min) at 21° C. in an autoclave. The multi-stage extractions were performed analogously to experiment 5 by squeezing the wood particles after each extraction stage and mixing with fresh unloaded extracting agent. Therein, the extraction parameters were 50° C., extraction durations of each 1 h per extraction stage and acetone concentrations of 70 wt % in the extracting agent (extraction parameter 1) as well as 21° C., extraction durations of each 30 min per extraction stage and pure acetone as admixed extracting agent, which results in acetone concentrations of 70-99 wt % according to extraction stage and particle size (extraction parameter 2). The solid: extracting agent ratios were selected such that the wood particles were just covered with extracting agent (1:6 with woodchips and ground woodchips and 1:10 with groundwood). After the extraction, the wood particles were squeezed (and washed with extracting agent with extraction parameter 1) and again squeezed before they were dried, aged and analyzed. The results of these results are listed in table 9.
As table 9 shows, the hexanal content of woodchips can only be decreased by ca. 20-30% with the method according to the invention. Upon grinding the woodchips to 2 mm particle size, as the NREL method NREL/TP-510-42620 also presets, in contrast, the hexanal content can be decreased to ca. 1 mg/kg TM, which corresponds to a reduction of ca. 95% with the starting hexanal content of 21.36 mg/kg TM, with the method according to the invention. With even lower particle size, such as for instance in groundwood, the reduction of the hexanal content with ca. 97% is even higher. The two extraction parameters provide comparable hexanal contents with larger particle size, whereas with smaller particle size, in particular groundwood, the extraction parameters 1 (higher temperature and longer extraction time) provide significantly better results. In the reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction, the extraction parameters provide better results with all particle sizes. In table 9, it is additionally apparent that the reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction cannot be used as an indicator for the extraction success of the intended method since for example with woodchips, even with high reduction of 73%, the hexanal content was only decreased by ca. 20, whereas with groundwood with a reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction by 75%, the hexanal content could be decreased by ca. 96%.
This experiment serves for examining the effects of the extractive treatment on the mechanical characteristics of the extracted wood particles. Thereto, ca. 300-450 g TM (according to solid: extracting agent ratio) of mechanically dehydrated groundwood (ca. 25 wt % TSG) were extracted in a solvent-water mixture with solid: extracting agent ratios of 1:10 and 1:15 w/w and a solvent concentration of 60 and 70 wt % at temperatures of 50° C., 70° C. and 90° C. As the solvent, ethanol 96 vol % non-denatured (EtOH pure), ethanol 96 vol % incompletely denatured with butanone (EtOH den.) and acetone were employed. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before sample sheets were formed therefrom, based on which the mechanical characteristics were examined. The mass loss results from the evaporation residue of the extract and is related to the basic material dry matter. In table 10, the results are listed.
As is visible in table 10, the degree of grinding and thus the dehydration of the groundwood hardly alters by the extraction, which entails the advantage with regard to a possible further processing (for example to cardboard) that existing production plants do not have to be retrofitted or converted. The stiffness index also only little alters by the extraction, whereas the tensile index as a measure of the breaking strength reproducibly highly increases. Compared to this high increase between 20 and 41% on average, the mass loss by the evaporation residue of the extract is very low with around 2%. This means that the wood particles over-proportionally highly gain strength by the extraction with low mass loss, which is in particular of great importance for the lightweighting trend in the packaging sector.
In this experiment, mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% fir) was extracted with a solid—extracting agent ratio of 1:10 w/w at 50° C. for 1 h in an autoclave, wherein the extracting agent was composed of 70 wt % of acetone and 30 wt % of demineralized water. After the extraction, the groundwood was squeezed (to ca. 30 wt %) and the extract thus obtained was processed as follows:
First, the acetone was separated by distillation in that the distillation flask was heated up to 108° C. and distilled under atmospheric pressure up to the equilibrium setting. The remaining residue was centrifugated with 7197 g for 10 min and the sediment was subsequently separated from the supernatant. The supernatant was weighed and the dry substance content thereof was ascertained by gently drying at room temperature, which substantially corresponds to the content of extracted extractives. The sediment was also weighed and dissolved in defined mass of pure acetone. Analogously to the supernatant, the dry substance content thereof was determined. The deposits already precipitated in the distillation were also dissolved in pure acetone. Thereof, the dry substance content was determined analogously to the sediment. From the extract, the supernatant, the sediment dissolved in acetone and the deposits dissolved in acetone, the content of free fatty acids (linolenic acid, linolic acid, oleic acid and stearic acid, each expressed in linolic acid equivalents), resin acids (isopimaric acid, palustric acid, dehydroabietinic acid and abietinic acid, each expressed in abietinic acid equivalents) and lignans (i solariciresinol, secoisolariciresinol, conidendrinic acid, hydroxymatairesinol and matairesinol, each expressed in hydroxymatairesinol equivalents) was ascertained by means of gas chromatography. The results of experiment 1 and experiment 2 (repetitions with ident parameters) are listed in tables 11 and 12.
As it is visible in tables 11 and 12, the predominant extractive mass arises as a centrifugated sediment. Despite of the reduction of the amount of liquid by ca. 80% (from extract to supernatant), by the selected separating methods, the dry substance content (which here substantially corresponds to the extractive mass) in the supernatant is only at a similarly low level as in the extract (<1 wt %). However, the portion of free fatty acids and resin acids could be decreased to a very low level in the supernatant, whereas the lignans were enriched. In contrast, in the sediment and the deposits, there are few to no lignans, but a high content of free fatty acids and resin acids. Although the extractives analyzed here (free fatty acids, resin acids and lignans) only represent a part of the extractives (and dry substance found here), thus, it is uniquely apparent that with the selected thermal and mechanical separating method (distillation and centrifugation), not only the liquid phase (extract and supernatant, respectively) can be most widely freed from fatty and resin acids, but also lipophilic extractives (e.g. fatty acids and resin acids) and hydrophilic extractives (e.g. lignans) can respectively be significantly concentrated and purified as byproducts.
Key:
In view of the above description of the present invention, the following preferred embodiments of the invention are herein disclosed:
1. A method for producing products based on wood as a raw material, characterized in that wood in the form of wood particles is subjected to an extraction treatment with an extracting agent, which includes one or more organic solvents in an organic-aqueous mixture of the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as the hexanal content in wt % after accelerated aging for 72 h at 90° C., by the extraction treatment of the wood particles with the extracting agent, but the content of cellulose, hemicelluloses and lignin is substantially maintained in this extraction treatment.
2. The method according to embodiment 1, characterized in that the wood particles are present in a size of at most 2 mm, wherein the particle size is preferably defined according to the National Renewable Energy Laboratory (NREL) Laboratory Analytical Procedure (LAP) NREL/TP-510-42620 “Preparation of Samples for Compositional Analysis” by the screen mesh of 2 mm of the cutting mill for sample preparation.
3. The method according to embodiment 1 or 2, characterized in that the wood particles are present in the form of fibers, chips or mixtures thereof.
4. The method according to any one or more of the embodiments 1 to 3, characterized in that the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion.
5. The method according to any one or more of the embodiments 1 to 4, characterized in that the wood particles are wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 μm, wherein the average fiber length as well as the average fiber diameter relate to the length average determined by means of optical measurement of the suspended fibers.
6. The method according to any one or more of the embodiments 1 to 5, characterized in that the solvent portion of the organic-aqueous solvent mixture in the extracting agent, determined as the concentration of the liquid phase of the extract, is composed of 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol, 0-99 wt % of acetone, preferably 30-90 wt % of acetone, 0-70 wt % of n-propanol, 0-85 wt % of iso-propanol and/or 0-99 wt % of methanol.
7. The method according to any one or more of the embodiments 1 to 6, characterized in that the ratio of extracting agent to solid dry substance is 5:1-25:1 (w/w), preferably 8:1-17:1 (w/w).
8. The method according to any one or more of the embodiments 1 to 7, characterized in that the extraction treatment is effected at an extraction temperature of 20-150° C., preferably 40-120° C., in particular 50-110° C.
9. The method according to any one or more of the embodiments 1 to 8, characterized in that the extraction treatment is effected at an absolute extraction pressure of 1-5 bar, preferably 1-1.49 bar.
10. The method according to any one or more of the embodiments 1 to 9, characterized in that the extraction treatment is effected during an extraction time of 10 min-8 h, preferably 30 min-7 h, in particular 1-5 h.
11. The method according to any one or more of the embodiments 1 to 10, characterized in that the method is used for producing cardboard, paper, wood fiber boards, chipboards, objects of utility, medical products, in particular for producing cardboard.
12. The method according to any one or more of the embodiments 1 to 11, characterized in that the extraction treatment is selected from:
13. The method according to any one or more of the embodiments 1 to 12, characterized in that the treatment with the extracting agent is performed as a batch, continuous or semi-continuous extraction, preferably with a partial dwell time of at most 1 h per extraction step.
14. The method according to any one or more of the embodiments 1 to 13, characterized in that the content of cellulose, hemicelluloses and lignin is reduced by less than 10%, preferably by less than 5%, in particular by less than 4%, in the extraction treatment, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles.
15. The method according to any one or more of the embodiments 1 to 14, characterized in that the wood particles are selected from coniferous wood particles, preferably spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
16. The method according to any one or more of the embodiments 1 to 15, characterized in that the wood particles are mixed during the treatment with the extracting agent.
17. The method according to any one or more of the embodiments 1 to 16, characterized in that the wood particles are squeezed after the treatment with the extracting agent to remove the extracting agent.
18. The method according to any one or more of the embodiments 1 to 17, characterized in that the wood particles are purified once or multiple times with an extracting agent after the treatment with the extracting agent, preferably purified with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent.
19. The method according to any one or more of the embodiments 1 to 18, characterized in that the extracting agent is removed from the wood particles by one-time or multi-time washing with water and/or water steam stripping and/or drying, preferably by water steam stripping and/or drying.
20. The method according to any one or more of the embodiments 1 to 19, characterized in that the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles after accelerated aging for 72 h at 90° C., by extraction of the wood particles with the extracting agent.
21. The method according to any one or more of the embodiments 1 to 20, characterized in that the content of fatty acids in the wood particles is reduced to a content below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular of below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90° C., by extraction of the wood particles with the extracting agent.
22. The method according to any one or more of the embodiments 1 to 21, characterized in that resin acids are also extracted with the extraction besides the fatty acids.
23. The method according to any one or more of the embodiments 1 to 22, characterized in that the fatty acids, resin acids and/or optionally further extractives extracted with the extracting agent are supplied to a further purification method, preferably by mechanical separating technique after the thermal separation of the organic solvent from the organic-aqueous extracting agent, wherein lipophilic extractives, in particular fatty acids and resin acids, are precipitated and separated, and a liquid phase enriched with hydrophilic extractives, in particular lignans, is obtained, wherein the hydrophilic extractives are preferably further concentrated by subsequent treatment with thermal separating technique, in particular by means of membrane separating methods and/or adsorption.
24. The method according to embodiment 23, characterized in that a preceding membrane filtration of the extracting agent is effected in the extractive enrichment.
25. The method according to any one or more of the embodiments 1 to 24, characterized in that chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles.
26. The method according to any one or more of the embodiments 1 to 25, characterized in that the extracting agent as well as optionally used washing liquids, in particular water, are regenerated for reuse.
27. The method according to any one or more of the embodiments 1 to 26, characterized in that in addition to the reduction of the hexanal content, the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, is also increased by at least 10%, preferably by at least 15%, in particular by at least 25%, by the extraction treatment, wherein the degree of grinding, measured in ° SR, therein changes by less than 10%.
28. The method according to any one or more of the embodiments 1 to 27, characterized in that at least 10% of water, preferably at least 7.5% of water, in particular at least 5% of water, are contained in the organic-aqueous mixture of the solvent or solvents.
Further preferred embodiments of the present invention are the following embodiments:
1. A method for producing products based on wood as a raw material, characterized in that wood in the form of wood particles is subjected to an extraction treatment with an extracting agent, which includes one or more organic solvents or an organic-aqueous mixture of the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as the hexanal content in wt % after accelerated aging for 72 h at 90° C., by the extraction treatment of the wood particles with the extracting agent, but the content of cellulose, hemicelluloses and lignin is substantially maintained in this extraction treatment.
2. The method according to embodiment 1, characterized in that the wood particles are present in a size below 5 cm, wherein the particle size is preferably ascertained by sieving by means of square mesh screen, in particular by means of square mesh screen with a mesh of 5 cm or less.
3. The method according to embodiment 1 or 2, characterized in that the wood particles are present in the form of fibers, chips, strands, woodchips or mixtures thereof.
4. The method according to any one or more of the embodiments 1 to 3, characterized in that the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion.
5. The method according to any one or more of the embodiments 1 to 4, characterized in that the wood particles are wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 μm, wherein the average fiber length as well as the average fiber diameter relate to the length average determined by means of optical measurement of the suspended fibers.
6. The method according to any one or more of the embodiments 1 to 5, characterized in that the solvent portion of the organic-aqueous solvent mixture in the extracting agent, determined as the concentration of the liquid phase of the extract, is composed of 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol, 0-99 wt % of acetone, preferably 30-90 wt % of acetone, 0-70 wt % of n-propanol, 0-85 wt % of iso-propanol and/or 0-99 wt % of methanol.
7. The method according to any one or more of the embodiments 1 to 6, characterized in that the ratio of extracting agent to solid dry substance is 5:1-25:1 (w/w), preferably 8:1-17:1 (w/w).
8. The method according to any one or more of the embodiments 1 to 7, characterized in that the extraction treatment is effected at an extraction temperature of 20-150° C., preferably 40-120° C., in particular 50-110° C.
9. The method according to any one or more of the embodiments 1 to 8, characterized in that the extraction treatment is effected at an absolute extraction pressure of 1-5 bar, preferably 1-1.49 bar.
10. The method according to any one or more of the embodiments 1 to 9, characterized in that the extraction treatment is effected during an extraction time of 10 min-8 h, preferably 30 min-7 h, in particular 1-5 h.
11. The method according to any one or more of the embodiments 1 to 10, characterized in that the method is used for producing cardboard, paper, wood fiber boards, chipboards, objects of utility, medical products, in particular for producing cardboard.
12. The method according to any one or more of the embodiments 1 to 11, characterized in that the extraction treatment is selected from:
13. The method according to any one or more of the embodiments 1 to 12, characterized in that the treatment with the extracting agent is performed as a batch, continuous or semi-continuous extraction, preferably with a partial dwell time of at most 1 h per extraction step.
14. The method according to any one or more of the embodiments 1 to 13, characterized in that the content of cellulose, hemicelluloses and lignin is reduced by less than 10%, preferably by less than 5%, in particular by less than 4%, in the extraction treatment, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles.
15. The method according to any one or more of the embodiments 1 to 14, characterized in that the wood particles are selected from coniferous wood particles, preferably spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
16. The method according to any one or more of the embodiments 1 to 15, characterized in that the wood particles are mixed during the treatment with the extracting agent.
17. The method according to any one or more of the embodiments 1 to 16, characterized in that the wood particles are squeezed after the treatment with the extracting agent to remove the extracting agent.
18. The method according to any one or more of the embodiments 1 to 17, characterized in that the wood particles are purified once or multiple times with an extracting agent after the treatment with the extracting agent, preferably purified with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent.
19. The method according to any one or more of the embodiments 1 to 18, characterized in that the extracting agent is removed from the wood particles by one-time or multi-time washing with water or drying, preferably by drying.
20. The method according to any one or more of the embodiments 1 to 19, characterized in that the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles after accelerated aging for 72 h at 90° C., by extraction of the wood particles with the extracting agent.
21. The method according to any one or more of the embodiments 1 to 20, characterized in that the content of fatty acids in the wood particles is reduced to a content below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular of below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90° C., by extraction of the wood particles with the extracting agent.
22. The method according to any one or more of the embodiments 1 to 21, characterized in that resin acids are also extracted with the extraction besides the fatty acids.
23. The method according to any one or more of the embodiments 1 to 22, characterized in that the fatty acids, resin acids and/or optionally further extractives extracted with the extracting agent are supplied to a further purification method.
24. The method according to any one or more of the embodiments 1 to 23, characterized in that chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles.
25. The method according to any one or more of the embodiments 1 to 24, characterized in that the extracting agent as well as optionally used washing liquids, in particular water, are regenerated for reuse.
26. The method according to any one or more of the embodiments 1 to 25, characterized in that in addition to the reduction of the hexanal content, the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, is also increased by at least 10%, preferably by at least 15%, in particular by at least 25%, by the extraction treatment, wherein the degree of grinding, measured in ° SR, therein changes by less than 10%.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20217520.4 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/087767 | 12/29/2021 | WO |
